Auto-tuned apparatus for band-pass filter

Abstract: An auto-tuned apparatus for a band-pass filter (30), wherein, the generated reference signals having a frequency to be set are mixed in a mixer (60) with the output of the band-pass filter (30). These reference signals are also input to the band-pass filter. The direct current component of the output signal of mixer (60) are filtered in a low pass filter (61) and via A/D converter applied to the controll circuit (50). This control circuit (50) controls via a motor driver (32) the motor (33) for tuning the band pass filter (30) in such a way that the center frequencies of the band-pass filter (30) agrees with the frequency of the reference signal in accordance with the said direct current component. The center frequency of the band-pass filter (30) can thus be adjusted automatically to the desired set value using a simple circuit construction and with a better precision than in the conventional embodiment.

Description: BACKGROUND OF THE INVENTION The present invention generally relates to an auto-tuned apparatus for a band-pass filter which is adapted to automatically set the center frequency of a band-pass filter to a given frequency. Fig. 15 is a block diagram of an automatic tuning type band-pass filter in a first conventional embodiment proposed in Japanese Laid-Open Patent Application Tokaihei No. 1-105601. In Fig. 15, the automatic tuning type band-pass filter in the first conventional embodiment comprises an isolator 101 which is adapted to pass in one direction high frequency signals to be inputted and is provided with a reflected wave coupling terminal 111, a resonator 102 operating as a band-pass filter for band pass-filtering high frequency signals passing through the isolator 101, a driving mechanism 103 for changing the resonance frequency of the resonator 102 by the movement of a resonance frequency adjusting element (not shown) within the above described resonator 102, a control circuit 104 for detecting with a diode D1 the high frequency signals outputted from the reflected wave coupling terminal 111 of the isolator 101 so as to control the driving mechanism 103 in accordance with the detected signals. In the automatic tuning type band-pass filter, the level of the high frequency signals (hereinafter referred to as reflection signals) of the reflection power detected by the above described diode D1 becomes minimum at the resonance frequency of the above described resonator when a high frequency signal has been passed into the band-pass filter. By the use of the minimum level caused thereby, the above described control circuit 104 controls the driving mechanism 103 so that the level of the above described reflection signals may become minimum in accordance with the above described reflection signals. The center frequency of the band-pass filter being approximately equal to the resonance frequency of the resonator 102 is tuned to the frequency of the high frequency signal passing through the isolator 101. The above described tuning operation is effected by use of the fact that the level of the reflection signal becomes minimum at the resonance frequency of the resonator 102 in the automatic tuning type band-pass filter in the first conventional embodiment. Therefore, there is a problem in that the above described tuning operation cannot be correctly effected when signals interfering from the other channel are inputted into the automatic tuning type band-pass filter or when interference wave signals coming closer to the high frequency signals passing through the above described isolator 101 are inputted into the automatic tuning type band-pass filter if, for example, the automatic tuning type band-pass filter of Fig. 15 is used for a transmitter multiplexer. The above described automatic tuning type band-pass filter is provided with one resonator 102. A multi-pole parallel connected band pass filter (hereinafter referred to a second conventional embodiment) is disclosed in Japanese Laid-Open Patent Application Tokaihei No. 3-72701. In the multi-poles parallel connected band-pass filter, a plurality of resonators which are different respectively from each other, and have adjacent resonance frequencies are electrically connected in parallel between the input terminal of the signal and the output terminal thereof. When the center frequency and the band width of the multi-poles parallel connected band-pass filter in the second conventional embodiment are adjusted, the network analyzer is connected with the input, output terminals of the multi-poles parallel connected band-pass filter. After sweep signals which sweep in frequency the signal passing band of the band-pass filter are inputted into the input terminal, the center frequency of the individual band-pass filter is adjusted while the spectrum of the signals of the output terminal is being observed. The center frequency and the band width of the multi-poles parallel connected band-pass filter cannot be automatically adjusted, with a problem that the adjustment is required to be manually effected. US-A-4,726,071 relates a microprocessor controlled self-tuning resonant cavity wherein an external motor is coupled to a tuning rod extending into a resonant cavity of a transmitter combiner. A microprocessor tuning control system generates motor control signals that cause the motor to rotate the tuning rod, varying the resonant frequency of the cavity so as to minimize the reflected power from the cavity. Incident and reflected power are detected by diodes in the transmitter cable connector of the cavity. The standing wave ratio is computed and compared with a threshold value to determine if the cavity needs to be retuned. The microprocessor effectuates reading of digital numbers representing the incident and reflected power and makes a "best effort" attempt to tune the resonant frequency of the cavity to the transmitter frequency using the motor to rotate the tuning rod. JP-A-2029112 relates to a channel selection device which is used to adjust a desired channel automatically by fixing an air-core coil and controlling separately the applied voltage of a vary cap diode of a band-pass filter of each stage for each stage. While the coil of the band-pass filters of each stage is fixed, the application voltage of the vary cap diode is controlled depending on each stage by a CPU. Therefore, the automatic adjustment of the tuner is attained and it is not required to use a pair of vary cap diodes to improve the tracking. SUMMARY OF THE INVENTION Accordingly, a first object of the present invention is to provide an auto-tuned apparatus, for a band-pass filter, which is capable of automatically adjusting the center frequency of the band-filter pass filter to a desired set value with better precision than in the conventional embodiment. A second object of the present invention is to provide an automatic tuning type band-pass filter which is capable of automatically adjusting the center frequency of the band-pass filter to a given set value with better precision than in the conventional embodiment. A third object of the present invention is to provide a transmitter multiplexer or an antenna combiner coupling a plurality of RF transmitters to a single antenna, provided with a plurality of auto-tuned type band-pass filters, which are capable of correctly effecting the above described tuning operation if the signal interfering from the other channel has been inputted into the automatic tuning type band-pass filter when, for example, the automatic tuning type band-pass filter has been used for the transmitter multiplexer. A fourth object of the present invention is to provide an auto-tuned apparatus, for a multi-poles parallel connected band-pass filter, which is capable of automatically adjusting the center frequency and the band width of the multi-poles parallel connected band-pass filter to the respective desired set values. A fifth object of the present invention is to provide a multi-poles auto-tuned parallel connected band-pass filter which is capable of automatically adjusting the center frequency and the band width of the multi-poles parallel connected band-pass filter to the respective desired set values with precision better than in the conventional embodiment. A sixth object of the present invention is to provide a transmitter multiplexer, provided with a plurality of multi-poles auto-tuned parallel connected band-pass filters, which are capable of correctly effecting the above described tuning operation even when the signal from the other channel has been inputted into the automatic tuning type band-pass filter when, for example, the multi-poles auto-tuned parallel connected band-pass filter has been used for the transmitter multiplexer. The above objects are achieved by the invention as defined by the independent claim, with advantageous embodiments of the invention being characterized by the appended dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which; Fig. 1 is a block diagram of an auto tuned type band-pass filter in a first embodiment of the present invention; Fig. 2 is a circuit diagram showing an equivalent circuit of a band-pass filter constructed from a dielectric resonator of Fig. 1; Fig. 3 is a sectional view of a band-pass filter of Fig. 2; Fig. 4 is a graph showing the relationship between the position of a dielectric tuning element of and a center frequency of the band-pass filter of Fig. 3; Fig. 5 is a graph showing the frequency characteristics with respect to the insertion loss of the band-pass filter of Fig. 3; Fig. 6 is a flow chart showing a main routine of the control flow of the control circuit of the automatic tuning type band-pass filter of Fig. 1; Fig. 7 is a flow chart showing a subroutine of the fine tuning processing of Fig. 6; Fig. 8 is a flow chart showing a first portion of a subroutine in a modified embodiment of the fine tuning processing of Fig. 6; Fig. 9 is a flow chart showing a second portion of a subroutine in a modified embodiment of the fine tuning processing of Fig. 6; Fig. 10 is a flow chart of a third portion of a subroutine in the modified embodiment of the fine tuning processing of Fig. 6; Fig. 11 is a flow chart showing a fourth portion of a subroutine in the modified embodiment of the fine tuning processing of Fig. 6; Fig. 12 is a block diagram of a two-stage auto-tuned parallel connected band-pass filter in a second embodiment of the present invention; Fig. 13 is a block diagram of a transmitter multiplexer provided with three two-stage auto-tuned parallel connected band-pass filters of Fig. 12; Fig. 14 is a flow chart showing a main routine of a control flow of the control circuit of the two-stage auto-tuned parallel connected band-pass filter of Fig. 12; and Fig. 15 is a block diagram of an automatic tuning type band-pass filter in the conventional embodiment; DETAILED DESCRIPTION OF THE INVENTION Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. (First Embodiment) Fig. 1 is a block diagram of an automatic tuning type band-pass filter 2d in a first embodiment of the present invention. The automatic tuning type band-pass filter 2d in a first embodiment is provided with a band-pass filter 30 including one dielectric resonator 31, the reference signals of the setting frequency fd being generated in the built-in signal generator 71 in accordance with the data of the center frequency (hereinafter referred to as set frequency) fd to be set of the band-pass filter 30, the data being input by the use of the keyboard 81, and the center frequency fc of the band-pass filter 30 can be tuned to roughly correspond to the above described center frequency fd by use of the reference signal. In the tuning operation of the band-pass filter 30 in the automatic tuning type band-pass filter 2d, the reference signal generated by the above described signal generator 71 passes through the band-pass filter 30. The signal, after passing the above described band-pass filter 30 is converted into a direct current component by a frequency converting circuit consisting of a mixer 60 and a low-pass filter 61 through which only the DC-component of the mixer output can pass, with the reference signal generated by the above described signal generator 71 being used as a local oscillation signal which is mixed in the mixer with the output signal from the band-pass filter. The stepping motor 33 for varying the variable capacitance VC of the dielectric resonator 31 within the band-pass filter 30 is driven so that the level of the signal of the above described direct current component becomes substantially 0 in accordance with the converted direct current component, namely, the center frequency fc of the band-pass filter 30 roughly corresponds to the frequency of the above described reference signal. As shown in Fig. 1, for example, a transmission signal of a frequency fl of a UHF band is outputted from a transmitter 1 and has a constant predetermined level. The transmission signal is outputted to an antenna 4 through an automatic tuning type band-pass filter 2d of the present embodiment to be used as a transmission band-pass filter so as to radiate the above described transmission signals from the antenna 4. In the automatic tuning type band-pass filter 2d, the signal to be outputted from the transmitter 1 is inputted to the input terminal 20a of the directional coupler 20 through an isolator 10. The directional coupler 20 is provided with a transmission line and a coupling line so that the transmission signal coupled electromagnetically to the transmission line and the reference signal inputted into an input terminal 20r of the coupling line are combined. The signal to be outputted from the output terminal 20b of the transmission line of the directional coupler 20 is inputted to the input terminal T1 of the band-pass filer 30. The signal to be outputted from the output terminal T2 after passing through the band-pass filter 30 is outputted to an antenna 4 through the input terminal 21a and the output terminal 21b of the transmission line of the directional coupler 21. The directional coupler 21 is provided with a transmission line and a coupling line so that a part of the power of the transmission signal transmission coupled electromagnetically to the transmission line is branched and drawn out. The coupling line for detecting the transmission signal is provided with an output terminal 21p. The signal outputted from the output terminal 21p of the coupling line is inputted to the main signal input terminal of the mixer 60 as a main signal. The band-pass filter 30 is provided with a dielectric resonator 31 and has a variable center frequency fc. The dielectric resonator 31 within the band-pass filter 30 is, as shown in an equivalent circuit of Fig. 2, combined of two inductances L11, L12 and a variable capacitance VC and a loss resistance Ro connected in parallel. The inductance L11 is electromagnetically coupled to an output side coil L1 of the band-pass filter 30 with a induction coupling + M. The inductance L12 is electromagnetically coupled to an output side coil L2 of band-pass filter 30 with an induction coupling + M. One end of the input side coil L1 is connected with the input terminal T1. The other terminal is connected with an earth line. One end of the output side coil L2 is connected with the output terminal T2, the other end thereof is connected with the earth line. Further, electrostatic capacity of the capacitance VC is varied by a stepping motor 33 to be controlled through a motor driving circuit 32 by a control circuit 50 as described later in detail. Fig. 3 shows a sectional view of the band-pass filter 30 provided with a dielectric resonator 31. As shown in Fig. 3, a cylindrically shaped dielectric resonator 211 is placed on a support stand having the same coefficient of linear expansion as that of the dielectric resonator 211 in the center portion within the cylindrically shaped shield case 210. The dielectric resonator 211 is a ceramic dielectric resonator mixed with ZrSn with, for example, Ti02 being provided as principal component. The dielectric resonator 31 in the present embodiment has a resonance frequency fo of approximately 886.4MHz in a TEo1δ-mode as a dominant mode. A cylinder shaped dielectric tuning element 212 is supported, provided on a shaft 215 within the cylinder of the dielectric resonator 211. The shaft 215 is moved by a stepping motor 33 in - direction as indicated by arrow A1 and + direction as indicated by arrow A2 of the opposite direction. The above described dielectric tuning element 212 is moved in the grade of the electric field of the dielectric resonator 211 so that the resonance frequency of the dielectric resonator 211 is finely adjusted. Fig. 4 shows a graph illustrating the relationship between the position of the dielectric tuning element 212 of the band-pass filter 30 of Fig. 3 and the center frequency fc of the band-pass filter 30 being approximately equal to the resonance frequency fo of the dielectric resonator 31. Reference sign g indicates an interval from the top face of the dielectric tuning element 212 to the top face inner side of the shield case 210. As shown clearly from Fig. 4, the dielectric tuning element 212 is separated from the top face of the shield case 210, namely, the interval g is increased so that the resonance frequency of the above described dielectric resonator 31 changes in approximately inverse proportion relation to the interval g. In Fig. 3, the above described shield case 210 has a silver electrode baked for electromagnetic shielding operation on the external surfaces of a cylindrically shaped housing made of ceramics having the same coefficient of linear expansion as that of the dielectric resonator 211. For example, the input side coil L1 and the output side coil L2 are respectively provided so as to couple the magnetic field of the dielectric resonator 211, as shown in Fig. 3 respectively in two positions away from each other around the center of the cylinder on the under face of the shield case 210 and immediately under the cylindrically external side edge end portion of the above described dielectric resonator 211. Fig. 5 is a graph showing the frequency characteristics of the insertion loss of the band-pass filter 30 when the signal has been inputted to the input terminal T1 of the band-pass filter 30 in a case where the output terminal T2 of the band-pass filter 30 of Fig. 3 has been terminated by a terminal resistor having a given impedance. Here unloaded Q (Qo) of the dielectric resonator 31 within the band-pass filter 30 is 20,000 and the loaded Q (Q L ) is 1,800. As it is clear from Fig. 5, the insertion loss of the band-pass filter 30 becomes minimum at the resonance frequency of of the dielectric resonator 31. Generally in the band-pass filter 30 having a loaded Q (Q L ), consisting of a resonator, the transmission phase Q R of the band-pass filter 30 at the frequency fn shifted by frequency Δf from the resonance frequency fo and adjacent to the resonance frequency fo is expressed by the following equation 1, wherein the condition is Δf << fo.  R =tan -1 {Q L ( fn f 0 - f 0 fn )} The difference between the insertion loss ILo [dB] of the band-pass filter 30 at the resonance frequency fo and the insertion loss IL1 [dB] of the band-pass filter 30 at a frequency fn is expressed by the following equation 2. IL 1 -IL 0 =10·log {1+Q L ( fn f 0 - f 0 fn )} Therefore, the following equation 3 is obtained from the equation 1 and the equation 2. IL 1 - IL 0 = 10 · log (1 + tan 2  R ) The resonance frequency fo from the equation 1 is expressed by the following equation 4. f 0 = -F 1 + F 1 2 +4 2 · fn Here the constant F1 of no-dimension is expressed by the following equation 5. F 1 = tan R Q L The circuit of the signal processing system and the control system within the automatic tuning type band-pass filter 2d will be described with reference to Fig. 1. As shown in Fig. 1, a signal generator 71 which includes a PLL circuit and can change the frequency of the reference signal to be generated, generates the reference signal of the above described setting frequency fs so as to output it to the input terminal 25a of the directional coupler 25 as defined by the data of the setting frequency fs inputted through the interface circuit 54 from the CPU51 of the control circuit 50. The directional coupler 25 is provided with a transmission line to input transmission reference signals into the input terminal 25a through an amplifier 72 from the signal generator 71, and a coupling line for detecting the reference signals so that a part of the power of the transmittion reference signals coupled electromagnetically to the transmission line may be branched and drawn out so as to detect the above described reference signal, the coupling line for detecting the reference signals being provided with an output terminal 25p. The reference signal outputted from the output terminal 25b of the transmission line of the directional coupler 25 is inputted into the input terminal T1 of the band-pass filter 30a through the input terminal 20r of the coupling line of the directional coupler 20 and the output terminal 20b of the transmission line. The reference signal to be outputted from the output terminal 25p of the coupling line of the directional coupler 25 is inputted to the local oscillation signal input terminal of the mixer 60 as a first local oscillating signal. A mixer consisting of a multiplier mixes signals inputted into the main signal input terminal with signals inputted into the local oscillation signal input terminal to multiply them and outputs the signals mixed to the low-pass filter (LPF) 61. When the outputs of the transmission signals from the transmitter 1 have been stopped, the mixed signals outputted from the mixer 60 and mixed contain the frequency component of fs + fs and fs - fs (direct current component). The low-pass filter 61 passed only the direct current component from the mixed signals inputted. Thereafter, the signals of the direct current component is outputted to the analog/digital converting (hereinafter referred to as A/D converting) circuit 63 through an amplifier 62. Then, the A /D converting circuit 63 converts the analog signal of the above described direct current component into the digital signal Vd and outputs it to a CPU 51 through an interface circuit 57 within the control circuit 50. A voltage Vo of the direct current component outputted from the low-pass filter 61 is expressed by the following equation 6, where the voltage of a main signal inputted into the mixer 60 from the directional coupler 21 is V M , a voltage of the local oscillating signal inputted into the mixer 60 from the directional coupler 25 is V L , and a phase difference of each signal inputted into the mixer 60 is Δ. Vo=a 60 V M V L ·sinΔ Here, a60 is an apparatus constant dependent on a multiplication coefficient of the mixer 60 and on the insertion loss in the direct current of the low-pass filter 61. A transmission line for main signal use to the main signal input terminal of the mixer 60, passing the directional coupler 25 and the output terminal 25b of the transmission line with the input terminal 25a of the directional coupler 25 being a reference point, the input terminal 20r of the coupling line of the directional coupler 20 and the output terminal 20b of the transmission line, the band-pass filter 30, and the input terminal 21a of the directional coupler 21 and the output terminal 21p of the coupling line consitutes a first transmission line. The transmission line for local oscillation signal use to the local oscillation signal input terminal of the mixer 60a through the coupling line of the directional coupler 25 and the output terminal 25p from the above described reference point consitutes a second transmission line. The transmission phase 1a (but except for the transmission phase  R of the band-pass filter 30) of the above described first transmission line and the transmission phase 2a in the second transmission line at an frequency fa near the resonance frequency fo of the dielectric resonator 31, desirably within the band-pass filter 30, are measured in advance. When the resonance frequency fo of the dielectric resonator 31 within the above described band-pass filter 30 is set at a certain set frequency fss, the transmission phase of the above described first transmission line except for the transmission phase  R of the band-pass filter 30 is made 1, and the transmission phase of the above described second transmission line is made 2 in the set frequency fss, the phase difference Δ of each signal to be inputted to the mixer 60a is expressed in the following equation 7. Δ= ( 1 + R )- 2 = ( 1 a- 2 a) f ss f a + R In the present embodiment, at the set frequency fss set to be the resonance frequency fo of the dielectric resonator 31 within the above described band-pass filter 30, a delay circuit (not shown) is inserted in advance into the above described first or second transmission line so that the phase difference Δ of each signal inputted into the mixer 60 becomes 2nπ + π/2 [rad] (wherein n is an integer), desirably π /2 [rad]. Assume that the signal level of the reference signal inputted into the input terminal 25a of the directional coupler 25 is Sr [dBm] at a certain frequency fss, and that the signal level S M [dBm] of the main signal inputted respectively into the mixer 60 and the signal level S L [dBm] of the local oscillation signal become respectively the next equation 8 and equation 9. In the equation 8 and the equation 9, the loss of each transmission line for connecting each element is neglected. S M =S r -L 25 t-L 20 r-IL 1 -L 21 p=a 601 ·log V M S L =S r -L 25 p=a 602 ·log V L Here L25t is an insertion loss [dB] of the directional coupler 25 to be measured in advance. L20r is a composite loss [dB] of the directional coupler 20 to be measured in advance, L21p is a branch loss [dB] of a directional coupler 21 to be measured in advance, L25p is a branch loss [dB] of the directional coupler 25 to be measured in advance. a601 and a602 are respectively constants to be determined in advance. As it is clear from the equation 8 and the equation 9, the signal level S M of the main signal is determined depending upon the insertion loss IL1 of the band-pass filter 30 at the set frequency fss with respect to the signal level Sr of the reference signal, while the signal level s L of the local oscillation signal is determined in advance with respect to the signal level Sr of the reference signal. As it is clear from the equation 6, the equation 8 and the equation 9, the voltage Vo of the direct current component outputted from the low-pass filter 61 is determined depending upon the insertion loss IL1 of the band-pass filer 30 at the set frequency fss, the phase difference Δ of each signal inputted into the mixer 60. Namely, as shown by the next equation 10, the voltage Vo of the direct current component is expressed by the insertion loss IL1 of the band-pass filter 30 at the set frequency fss and is a function of the phase difference Δ of each signal inputted into the mixer 60. Vo=f (IL 1 , Δ) In the present embodiment, the transmission signal outputted from the transmitter 1 is not inputted into the automatic tuning type band-pass filter 2d. The reference signal of, for example, the set frequency fss is generated in the signal generator 71 with the input terminal of the isolator 10 being terminated with the terminal resistor having the given impedance. At this time, the voltage Vo of the direct current component outputted from the low-pass filter 61 is measured and the voltage Vo measured is substituted into the equation 10. Thereafter, the ternary simultaneous equations of the above described equation 3, the equation 7 and the equation 10 are solved. Thus, the transmission phase  R , the insertion loss IL1, the phase difference Δ of the band-pass filter 30 at the set frequency fss set to be the center frequency of the band-pass filter 30 are calculated. Then, the calculated transmission phase  R is substituted in the equation 5 so as to compute a constant F1, further the calculated constant F1 is substituted in the equation 4 so as to calculate the resonance fo. The moving distance 1m for moving the dielectric tuning element 212 is calculated by use of the next equation 11 in accordance with the calculated resonance frequency fo and the set frequency fss. 1m=k (f 0 -fss) Here k is a constant to be determined from the graph of the above described Fig. 4. The pulse driving signal of the pulse number corresponding to the moving distance 1m calculated is inputted into the stepping motor 33 so as to move the dielectric tuning element 212 within the band-pass filter 30. The tuning process of the band-pass filter 30 can be effected so that the center frequency fc of the band-pass filer 30 roughly corresponds to the above described set frequency fss. As shown in Fig. 1, the control circuit 50 within the automatic tuning type band-pass filter 2d is provided with a CPU51 for effecting the above described tuning process of the band-pass filter 30 to control the dielectric resonator 31 within the band-pass filter 30, a ROM52 for accommodating in advance the data (for example, the loaded Q (Q L ) or the like of the dielectric resonator 31 within the band-pass filer 30) for carrying out the control program of each of the above described tuning process and the control program, a RAM53 to be used as the working area of the CPU51 for accommodating the data to be inputted through each of the interface circuits 57, 80. The control circuit 50 is further provided with an interface circuit 54 connected with the signal generator 71, an interface circuit 56 connected with the stepping motor 33 respectively through the motor driving circuit 32, an interface circuit 57 connected with the A/D converting circuit 63, and an interface circuit 80 to be connected with a keyboard 81. The CPU51, the ROM52, the RAM53, the respective interface circuits 54, 56, 57, 80 are connected with a bus 58 within the control circuit 50. When the CPU51 effects the tuning process of the band-pass filter 30, the data of the set frequncy fd are inputted by an operator by use of the keyboard 81 in the automatic tuning type band-pass filter 2d as described later in detail. In the present embodiment, the process for entering into the RAM53 through the interface circuit 80 from the keyboard 81 the data of the set frequency fd in the automatic tuning type band-pass filter 2d is effected by the CPU51. The CPU51 generates the reference signals of the frequency fs equal to the set frequency fd in the signal generator 71, thereafter the tuning process is effected for roughly making the resonance frequency fo of the dielectric resonator 31 within the band-pass filter 30 to correspond to the frequency fs of the above described reference signal. Namely, in the tuning process, the motor driving signal for driving the stepping motor 33 is outputted to the stepping motor 33 through the interface circuit 56 and the motor driving circuit 32 so as to effect the driving operation so that the level of the signal of the above described direct current component inputted into the CPU51 through the interface circuit 57 from the A/D converting circuit 63 may become roughly 0. When the motor driving signal of the pulse of + polarity is inputted to the stepping motor 33, the dielectric tuning element 212 within the band-pass filter 30 is moved in the direction of the arrow A2 as shown in Fig. 3. When the motor driving signal of the pulse of the - polarity is inputted into the stepping motor 33, the dielectric tuning element 212 within the band-pass filter 30 is moved in the direction an arrow Al. The electrostatic capacity of the variable capacitance VC in the equivalent circuit of Fig. 2 changes to vary the resonance frequency fo of the dielectric resonance 31, so that the center frequency fc of the band-pass filter 30 roughly equal to the resonance frequency fo can be changed. In the present embodiment, the control circuit 50 drives the stepping motor 33 so that the level of the direct current component outputted from the low-pass filter 61 can become 0 so as to vary the resonance frequency of the dielectric resonator 31 within the band-pass filter 30. The center frequency fc of the band-pass filter 30 roughly equal to the resonance frequency fo can roughly correspond to the frequency fs of the reference signal generated by the signal generator 71. The tuning process is carried out so that the center frequency of the automatic tuning type band-pass filter 2d can be automatically set to the above described set frequency inputted by use of the keyboard 81. Fig. 6 is a flow chart showing the main routine of the tuning process of the control circuit 50 of the automatic tuning type band-pass filter 2d of Fig. 1. The main routine processes the above described tuning process , and is a process operation for automatically setting the center frequency fc of the band-pass filter 30, to the set frequency fd inputted by use of the keyboard 81. In the initial condition before the start of the main routine, the dielectric tuning element 212 of the dielectric resonator 31 within the band-pass filter 30 is positioned in the optional distance g. In the main routine, the process of the step S103 and the step S104 is a rough tuning process operation for respectively changing the center frequency fc of the band-pass filter 30 built in to the frequency near the set frequency fd. The process operation from the step S105 to the step S107 is a fine tuning processing which changes the center frequency fc of the band-pass filter 30 built in from the frequency near the above described frequency fd after the above described rough tuning processing operation so as to roughly correspond to the above described set frequency fd. When the power switch (not shown) of the control circuit 50 is turned on, the main routine of the tuning process of Fig. 6 is started. In the step S101, the dielectric tuning element 212 within the band-pass filter 30 is moved to a position (hereinafter referred to as a home position) of g=4 [mm] by driving of the stepping motor 33. In the present embodiment, a stopper (not shown) for the dielectric tuning element use is provided within each band-pass filter 30 so that the dielectric tuning element 212 within the band-pass filter 30 can not be moved in the direction of an arrow A1 from the above described home position. In the step S101, when the motor driving signal of the - polarity is inputted continuously to the stepping motor 33 and each dielectric tuning element 212 is stopped at the home position by the above described stopper, a microswitch (not shown) provided at the home position is turned on and at this time, the driving operation of each stepping motor 33 is stopped. Each resonance frequency fo of each dielectric resonator 31 within the band-pass filter 30 at the home position is 897 [MHz] as shown in Fig. 4 measured in advance, with the data being accommodated in the RAM53. In the step S102, it is judged whether or not the data of the set frequency fd has been inputted into the automatic tuning type band-pass filter 2d by use of the keyboard 81. When the data has not been inputted (NO in the step S102), the loop processing of the step S102 is repeated into a waiting condition. When the data has been inputted (YES in the step S102), the routine moves to a step S103. In the step S103, as the rough tuning process is effected, the moving distance 1m to move the dielectric tuning element 212 within the band-pass filter 30 is calculated by the use of the equation 11 in accordance with the data of the resonance frequency fo accommodated in the RAM53 and the data of the set frequency fd (=fss) to be set. In the step S104, the pulse driving signals of the pulse number corresponding to the calculated moving distance 1m are respectively inputted to the stepping motor 33 so as to move the dielectric tuning element 212 within the band-pass filter 30. When the moving distance lm is positive, the pulse driving signal of + polarity is respectively inputted to the stepping motor 33. The dielectric tuning element 212 is moved in the direction of arrow A2 by the moving distance 1m. When the moving distance 1m is negative, the pulse driving signal of - polarity is respectively inputted to the stepping motor 33. The dielectric tuning element 212 is moved in the direction of an arrow A1 by the moving distance 1m. The rough adjusting is completed. In order to effect the fine tuning process, the data of the set frequency fd in the step S105 is outputted as the set frequency fs to the signal generator 71 so as to generate the reference signal of the set frequency fs . Thereafter, in the step S106, the data of the set frequency fd is accommodated in the RAM53 as the set frequency fss. In the step S107, the center frequency fc of the band-pass filter 30 to be built in is changed from the frequency near the above described frequency fd after the above described rough tuning process operation so as to execute the fine tuning process operation (see Fig. 7 and Fig. 8 through Fig. 11) to tune the center frequency to roughly correspond to the above described set frequency fd, and thereafter, the routine returns to the step S102. Hereinafter, the above described rough tuning process and the above described fine tuning process are repeated, by the use of the keyboard 81, every time the set frequency of the automatic tuning type band-pass filter 2d is newly inputted. In Fig. 7, the float chart of the subroutine of the fine tuning process (step S107, the steps S10, S14 to be described later) of Fig. 6 is shown. As shown in Fig. 7, in the step S121 the output voltage data Vd inputted into the control circuit 50 from the A/D converting circuit 63 is derived , assigned to the output voltage Vo of the low-pass filter 61, and stored in the RAM53. Thereafter, in the step S122, the resonance frequency fo is calculated by use of the equation 3, the equation 7, the equation 10, the equation 4, and the equation 5 as described hereinabove in accordance with the above-described converted output voltage Vo. The moving distance 1m for moving the dielectric tuning element 212 by use of the equation 11 has been calculated in accordance with the above-described calculated resonance frequency fo an with the set frequency fss established in the previous step in the step 123. Thereafter, in the step S124, the pulse driving signal of the pulse number corresponding to the above-described calculated moving distance 1m is inputted into the stepping motor 33 so as to move the dielectric tuning element 212. In the step S125, the output voltage data Vd inputted from the A/D converting circuit 63 is derived, assigned to the output voltage Vo of the low-pass filter 61, and stored in the RAM53 as the data Vd. Thereafter, in the step S126, it is judged whether or not an absolute value |Vd| is less than a threshold value voltage Vth, which is a positive number considerably near 0 for judgment of having approximately tuned. When the absolute value |Vd| of the output voltage data is smaller than the threshold value voltage Vth (YES in the step S126), the fine tuning process is considered to be complete and returns to the original main routine. When the absolute value of the output voltage data is larger (NO in the step 126), the fine tuning process operation is further is effected. In the step S127, the resonance frequency fo is calculated as in the above described step S122 in accordance with the output voltage data Vo measured and converted in the previous step S125. Thereafter, the routine returns to the step S123. While the absolute value |Vd| of the output voltage data becomes smaller than the threshold value voltage Vth, namely, until the center frequency fc of the band-pass filter 30 approximately corresponds to the set frequency fd, the process operation of the loop is executed. In the automatic tuning type band-pass filter 2d constructed as in Fig. 1, the directional couplers 21, 25 are provided even when the interference wave signal adjacent to the frequency f1 from another radio system and so on through the antenna 4 is inputted, so that the frequency component interfering from the interference other channel is not inputted to the mixers 60a, 60b as the directional couplers 21, 25 are provided. Therefore, the above described tuning processing operation can be effected without influences upon the frequency component of the interference wave signal as in the conventional embodiment. Even where a divider or the like is provided, instead of the directional couplers 21, 25, to which reflection signals are outputted, when the frequency of the above described interference wave signal is sufficiently shifted with respect to the frequency f1 of the transmission signal to be outputted from the transmitter 1, the above described interference wave signal is inputted into the local oscillation signal input terminal of the mixer 60 after the interference wave signal has passed through the band-pass filter 30 having an attenuation amount sufficiently large with respect to the frequency component. The level of the direct component of the frequency component of the above described interference wave signal, appearing at the output of the low-pass filter 61, is considerably small, thus hardly giving influences upon the above described tuning process. The above described tuning process can be effected without influences on the frequency component of the interference wave signal as in the conventional embodiment. A flow chart of a modified embodiment of a subroutine of the fine tuning process (step S107, steps S10, S14 to be described later) of Fig. 6 is shown, in Fig. 8 through Fig. 11. As shown in Fig. 8, in a step S131, the set frequency fss is stored as an initial set frequency fp in the RAM53, thereafter in a step S132, the output voltage data Vd inputted from the A/D converting circuit 63, is assigned to the output voltage VO of the low-pass filer 61 in a step S133, and stored in the RAM53. In a step S134, the initial value Δfpo of the frequency change amount stored in the predetermined ROM52 is stored as the frequency change amount Δfp in the RAM53. Thereafter, in a step S135, the data of the frequency fs is outputted to the signal generator 71 with frequency (fp + Δfpo) being provided as the frequency fs so as to generate the reference signal of the frequency fs. In the step S136, the output voltage data Vd inputted from the A/D converting circuit 63 is derived, assigned to the output voltage V1 of the low-pass filter 61 in the step S137, and stored in the RAM53. Then, in a step S138, the absolute value |V1| of the output voltage V1 is subtracted from the absolute value |VO| of the output voltage VO, and it is judged whether or not the difference of the subtracted results is larger or not in value than 0. If |VO| - |V1|> 0 (YES in the step S138), the frequency change flag FF showing the change direction of the frequency fs of the reference signal of the signal generator 71 is set, thereafter the routine advances to the step S141 of Fig. 9. If |VO|-|V1|≤0 (NO in the step S138), the frequency change flag FF is reset to 0 in a step S140, thereafter the routine moves to a step S141 of Fig. 9. As shown in Fig. 9, in the step S141 the processing parameter J is reset to 0, thereafter it is judged in a step S142 whether or not the frequency change flag FF is 1. If the frequency change flag FF is 1, (YES in the step S142), in a step S143, the frequency (fs + Δfp) is set as a frequency fs so as to output the data of the frequency fs to the signal generator 71. After the reference signal of the frequency fs has been generated, the routine moves to a step S145. When the frequency change flag FF is 0 (NO in the step S142), in the step S144, the frequency (fs-Δfp) is set to a frequency fs so as to output to the signal generator 71 the data of the frequency fs. After the reference signal of the frequency fs has been generated, the routine moves to a step S145. In the step S145, the output voltage data Vd inputted from the A/D converting circuit 63 is derived. In the step S146, it is converted to the output voltage V2 of the low-pass filter 61, and is stored in the RAM53. In the step S147, it is judged whether or not the value of the product of the V2 · V1 is smaller than 0. If V2 · V1≥0 (NO in the step S147), the frequency of the reference signal of the signal generator 71 is changed in the same frequency changing direction again. In a step S148, the output voltage V2 stored in the RAM53 is stored in the RAM53 as the output voltage V1, thereafter the routine returns to the step S142 to continue the processing of the step S142 and its subsequent steps. If V2 · V1 < 0 (YES in the step S147), in a step S149, it is judged whether or not the processing parameter J is 2 or more. If the processing parameter J is 2 or less (NO in the step S149), it is judged that the process from the above described step S142 to the step S146 is not effected in the two frequency changing directions (hereinafter referred to as two frequency changing directions) for raising and lowering the frequency fs of the reference signal of the signal generator 71, and the routine moves to the step S151 of Fig. 10. When the processing parameter J is 2 or more, it is judged that the processing from the above described step S142 to the step S146 has been processed in the above described two frequency changing directions and the routine moves to the step S150. In the step S150, it is judged whether or not the absolute value |fs-fss| of the difference between the frequency fs of the reference signal corresponding substantially to the resonance frequency fo and the set frequency fss is smaller than a threshold value ε of the predetermined frequency error. If |fs-fss|<ε (YES in the step S150), it is assumed that the fine tuning processing has been completed with the desired precision within the given error range and the routine returns to the original main routine. If |fs-fss| ≥ε (NO in the step S150), the frequency fs of the reference signal of the signal generator 71 is not within the given error range, the routine moves to the step S161 of Fig. 11. In the step S151 of Fig. 10 branched from the step S149, it is judged whether or not the frequency change flag FF is 1. If the frequency change flag is 1 (YES in the step S151), in the step S152, the frequency change flag FF is reset to 0, thereafter the routine moves to a step S154. If the frequency change flag is 0 (NO in the step S151), in the step S153, the frequency change flag FF is set to 1. Thereafter, the routine moves to the step S154. In the steps S151 through S153, the changing direction of the frequency is changed. Thereafter, in the step S154, the frequency change amount Δfp is divided by 2 and is stored in the RAM53 as the frequency change amount Δfp so as to reduce the frequency change amount Δfp. Thereafter in the step S155, 1 is added to the processing parameter J. The added value is stored in the RAM53 as the processing parameter J. The routine returns to the step S142 of Fig. 9 so as to repeat the processing of the step S142 and its subsequent steps. The frequency fs of the reference signal of the signal generator 71 is changed in the process so far as the step S150 so that the resonance frequency fo of the dielectric resonator 31 within the band-pass filter 30 may be obtained by the change in the frequency fs of the reference signal of the signal generator 71. The frequency fs of the reference signal before the processing of the step S161 of Fig. 11 branched from the step S150 is approximately equal to the resonance frequency fo of the dielectric resonator 31 within the band-pass filter 30. In the step S161, the moving distance 1m for moving the dielectric tuning element 212 has been calculated by use of a computing formula similar to the above described equation 11, namely, a computing formula of 1m=k (fs-fss) in accordance with the difference (fs-fss) between the frequence fs and the set frequency fss of the reference signal generated by the signal generator 71. Thereafter, in the step S162, the pulse driving signal of the pulse number corresponding to the moving distance 1m calculated is inputted to the stepping motor 33 so as to move the dielectric tuning element 212. In the steps S163 through S165, a process for changing the changing direction of the frequency fs of the reference signal is carried out. In the step S163, it is judged whether or not the frequency change flag FF is 1. If the frequency change flag is 1 (YES in the step S163), in a step S164, the frequency change flag FF is reset to O. Thereafter, the routine advances to a step S166. If the frequency change flag is 0 (NO in the step S163), in the step S165, the frequency change flag FF is set to 1, thereafter, the routine moves to the step S166. In the step S166, the frequency change amount Δfp is divided by 2 is stored in the RAM53 as the frequency change amount Δfp so as to reduce the frequency change amount. Thereafter, the routine returns to the step S141 of Fig. 9. In the modified embodiment of the fine tuning process shown in Fig. 8 through Fig. 11, the frequency fs of the reference signal of the signal generator 71 is changed so that the above described frequency fs can be tuned to become close to the resonance frequency fo by use of the characteristics that the insertion loss of the band-pass filter 30 shown in Fig. 5 may become minimum at the resonance frequency fo of the dielectric resonator 31. The resonance frequency fo is obtained by the approached frequency fs being approximately equal to the resonance frequency fo. Thereafter, in accordance with the obtained resonance frequency fo and the set frequency fss, the moving distance 1m for moving the dielectric tuning element 212 is calculated. By the movement of the moving distance 1m only, the fine tuning process is effected so that the center frequency fc of the band-pass filter 30 is automatically set to the set frequency fss. In the fine tuning process illustrated in the above described in Fig. 7, the fine tuning process is effected only by the driving operation of the stepping motor 33. In the fine tuning process illustrated in the Fig. 8 through Fig. 11, the frequency fs of the reference signal of the signal generator 71 is changed so as to obtain the resonance frequency fo of the dielectric resonator 31 and to drive the stepping motor 33 at the same time. Generally the processing speed of moving the dielectric tuning element 212 by the driving operation of the stepping motor 33 is slower than the processing speed for setting the frequency of the reference signal, for example, generated by the signal generator 71 including the PLL circuit to the given frequency so that the fine tuning process of the modified embodiment of the latter can carry out the processing with higher speed. In the step S155, S166, 2 is used as a divisor for reducing the change amount Δfp of the frequency. The initial value Δfpo of the predetermined frequency change amount to be used in the above described step S134 is desirably about 30kHz. The threshold value ε of the frequency error to be used in the above described step S150 is desirably 5kHz through 10kHz. According to the simulation of the present inventor, the frequency lag between the set frequency fss and the center frequency fc of the actual band-pass filter 30 is approximately 50kHz through 100kHz at the completion of the rough tuning processing in Fig. 6. By the fine tuning process shown in Fig. 7 or Fig. 8 through Fig. 11, the above described frequency lag becomes approximately 5kHz or 10kHz or lower. The setting process of the center frequency of the band-pass filter 30 can be effected with more precision than in the conventional embodiment. In the above described embodiment, the data of the center frequency fd to be set is inputted by use of the keyboard 81. Without the restriction to it, the present invention may be provided with a receiving circuit for receiving the data of the center frequency fd from an external apparatus such as another control circuit or the like or an interface circuit of a control circuit 50. The control circuit 50 effects the above described tuning process in accordance with the data of the received center frequency fd. In the above described embodiment, the band-pass filter 30 is combined with the use of the dielectric resonator 31. Without restriction, the present invention may use other various band-pass filters capable of varying the center frequency. In the above described embodiment, the resonance frequency fo of each dielectric resonator 31 of the band-pass filter 30 is calculated in accordance with the output voltage Vd of the A/D converting circuit 63. The moving distance 1m for moving the dielectric tuning element 212 is calculated in accordance with the calculated resonance frequency fo. The dielectric tuning element 212 is respectively moved by the calculated moving distance 1m so as to effect the above described tuning process. Without restriction, the present invention moves each dielectric tuning element 212 to effect the tuning process operation so that the output voltage Vd may become 0 in accordance with the output voltage Vd of the A/D converting circuit 63 without the calculation of the above described resonance frequency fo. In the above described embodiment, in the set of the frequency fss to be set by the resonance frequency fo of the dielectric resonator 31 within the above described band-pass filter 30, a delay circuit is inserted, adjusted in advance so that the phase difference Δ of each signal inputted to the mixer 60 becomes 2nπ + π/2 [rad] (wherein n is an integer), desirably, π/2 [rad]. The center frequency fc of the band-pass filter 30 is changed so that the output voltage Vo of the low-pass filter 61 becomes 0 so as to effect the above described tuning process operation. Without restriction in the set of the frequency fss to be set by the resonance frequency fo of the dielectric resonator 31 within the above described band-pass filter 30, the delay circuit is inserted, adjusted in advance so that the phase difference Δ of each signal to be inputted to the mixer 60 becomes 2nπ [rad], desirably, 0 [rad]. The center frequency fc of the band-pass filter 30 is changed so that the output voltage Vo of the low-pass filer 61 becomes maximum. The tuning process operation may be effected. In the set of the frequency fss to be set by the resonance frequency fo of the dielectric resonator 31 within the above described band-pass filter 30, the delay circuit is inserted, adjusted in advance so that the phase difference Δ of each signal to be inputted to the mixer 60 becomes 2nπ+π [rad], desirably, π or or -π [rad]. The center frequency fc of the band-pass filter 30 is changed so that the output voltage Vo of the low-pass pass filter 61 becomes a minimum. The above described tuning process operation may be effected. In the above described embodiment, the tuning process operation is effected digitally with the use of the stepping motor 33. Without restriction, the controlling, tuning process operations may be effected so that the output voltage Vo of the low-pass filter 61 becomes 0 by the use of the driving motor with analog signals. (Second Embodiment) Fig. 13 is a block diagram of a transmitter multiplexer 2 provided with two-stage auto-tuned parallel connected band-pass filters 2a, 2b, 2c in a second embodiment of the present invention. Fig. 12 is a block diagram of a two-stage auto-tuned parallel connected band-pass filter 2a of Fig. 13. In Fig. 12 and Fig. 13, the same reference characters are given to those similar in Fig. 1. Each of the two-stage auto-tuned parallel connected band-pass filters 2a, 2b, 2c in the present invention is connected electrically in parallel by use of a combiner 12 and a divider 11 is provided with two band-pass filters 30a, 30b including one dielectric resonator 31 as compared with the automatic tuning type band-pass filter 2d in a first embodiment illustrated in Fig. 1. Each of the two-stage auto-tuned parallel connected band-pass filters 2a, 2b, 2c calculates the center frequencies flc, f2c to be set in each band-pass filter 30a, 30b in accordance with the data of the center frequency fd and band width ΔF of the each two-stage auto-tuned parallel connected band-pass filters 2a, 2b, 2c. The signal of the above described center frequency flc is generated in the signal generator 71 to be built in in accordance with the above-described calculated center frequency flc. With the use of the signal as the reference signal, the center frequency fc of the band-pass filter 30a is tuned to approximately correspond to the above described center frequency flc. Thereafter, the signal of the above described center frequency f2c is generated in the signal generator 71 built in in accordance with the above-described calculated center frequency f2c. By use of the signal as the reference signal, the center frequency fc of the band-pass filter 30b is tuned to roughly correspond to the above described center frequency f2c. The center frequency and band width of each two-stage auto-tuned parallel connected band-pass filter 2a, 2b, 2c is automatically adjusted to the above-described inputted data value. As shown in Fig. 13, each transmission signal of mutually different frequencies f1, f2, f3 (f1<f2<f3), for example, in the UHF band, which is respectively outputted from each transmitter 1a, 1b 1c and has a predetermined constant level is composited after passing through the two-stage auto-tuned parallel connected band-pass filters 2a, 2b, 2c in the present embodiment. Here, each output terminal of each two-stage auto-tuned parallel connected band-pass filter 2a, 2b, 2c are alike electrically connected with each other. Each of the above described transmission signals, which are outputted to the antenna 4 through the band-pass filter 3 to be passed through the frequency band including the above described frequencies f1, f2, f3 and which have been combined by frequency multiplex, is radiated from the antenna 4. The two-stage auto-tuned parallel connected band-pass filters 2a, 2b, 2c are similar in construction. Description will be effected hereinafter in detail with reference to Fig. 12 by way of the two-stage auto-tuned parallel connected band-pass filter 2a. As shown in Fig. 12, the signal outputted from the transmitter 1a is inputted into the input terminal of the divider 11 through the isolator 10. The divider 11 divides the inputted transmission signal into two signals so as to direct the output to the input terminal 20a of the directional coupler 20 and to the input terminal 22a of the directional coupler 22. The directional couplers 20, 21, 25 are similar to those in the first embodiment. The signal outputted from the output terminal 20b of the transmission line of the directional coupler 20 is inputted to the input terminal Tla of the band-pass filter 30a. The signal outputted from the output terminal T2a after passing the band-pass filter 30a is inputted into the first input terminal of the combiner 12 through the input terminal 21a and the output terminal 21b of the transmission line of the directional coupler 21. Also, the signal outputted from the output terminal 21p of the coupling line of the directional coupler 21 is connected with the major signal input terminal of the mixer 60a as the first main signal. The directional coupler 22 is provided with a transmission line for transmitting the above described divided transmission signal, and a coupling line so that the transmission signal transmission coupled electromagnetically to the transmission line and the reference signal inputted to the input terminal 22r of the coupling line is combined. The signal outputted from the output terminal 22b of the transmission line of the directional coupler 22 is inputted into the input terminal T1b of the band-pass filter 30b. The signal which is outputted from the output terminal T2b after passing through the band-pass filter 30b is inputted into the second input terminal of the combiner 12 through the input terminal 23a and the output terminal 23b of the transmission line of the directional coupler 23. The directional coupler 23 is provided with a transmission line for transmitting the signal after passing through the band-pass filter 30b, and a coupling line for detecting the transmission signal so that a part of the power of the transmission signal transmission coupled electromagnetically to the transmission line may be branched and drawn out. The coupling line for transmission signal detection use is provided with an output terminal 23p. The signal to be outputted from the output terminal 23p of the coupling line is connected to the main signal input terminal of the mixer 60b as the second main signal. The combiner 12 combines the signal inputted into the first, second input terminals. The combined signal is outputted to the band-pass filter 3. Each band-pass filter 30a, 30b is combined as the band-pass filter 30 in the first embodiment. The signal processing system and the control system circuit within the two-stage auto-tuned parallel connected band-pass filter 2a will be hereinafter described with reference to Fig. 12. As in Fig. 12, the signal generator 71 is similar to the one of the first embodiment. In accordance with the data of the set frequency fs inputted through the interface circuit 54 from the CPU51 of the control circuit 50a, the reference signal of the above-described set frequency fs is generated so as to output the reference signal to the common terminal of the switch SW3 through the amplifier 72. The reference signal outputted from the a terminal of the switch SW3 is inputted to the input terminal 25a of the directional coupler 25 through the b side of the switch SW1. The reference signal inputted from the b terminal of the switch SW3 is inputted to the input terminal 26a of the directional coupler 26 through the b side of the switch SW2. The a side of the switch SW1 is connected with an earth line through a terminal resistor R L1 having a given impedance, the a side of the switch SW2 is connected with an earth line through the terminal resistor R L2 having a given impedance. Here each switch SW1, SW2, SW3 is respectively switched onto the a side or b side selectively through the interface circuit 55 by the CPU51 within the control circuit 50a. The reference signal outputted from the output terminal 25b of the transmission line of the directional coupler 25 is inputted into the input terminal T1a of the band-pass filer 30a through the output terminal 20r of the coupling line of the directional coupler 20 and the output terminal 20b of the transmission line. The reference signal outputted from the output terminal 25p of the coupling line of the directional coupler 25 is inputted, as a first local oscillation signal, to the local oscillation signal input terminal of the mixer 60a. The mixer 60a consisting of a multiplier mixes the signals inputted into the main signal input terminal with the signals inputted into the local oscillation signal input terminal, multiplies them, and outputs the signal mixed to the low-pass filter (LPF) 61a. The signal after the mixing thereof outputted from the mixer 60a includes the frequency component of fs + fs and fs - fs (direct current component) . The low-pass filter 61a lets only pass the direct current component of the mixed signal inputted, and thereafter outputs the signal of the direct current component to the A/D converting circuit 63a through the amplifier 62a. The A/D converting circuit 63a converts the analog signal of the above described direct current component into the digital signal Vd so as to output it to the CPU51 through the interface circuit 57 within the control circuit 50a. A transmission line for main signal use to the main signal input terminal of the mixer 60, passes the directional coupler 25 and the output terminal 25b of the transmission line with the input terminal 25a of the directional coupler 25 as a reference point, the input terminal 20r of the coupling line of the directional coupler 20 and the output terminal 20b of the transmission line, the band-pass filter 30a, and the input terminal 21a of the directional coupler 21 and the output terminal 21p of the coupling line. The transmission line for local oscillation signal use to the local oscillation signal input terminal of the mixer 60a through the coupling line of the directional coupler 25 and the output terminal 25p from the above described reference point forms a second transmission line. The transmission phase 1a (except for the transmission phase  R of the band-pass filter 30a) of the above described first transmission line and the transmission phase 2a of the above described second transmission line at an optional frequency fa near the resonance frequency fo of the dielectric resonator 31 desirably within the band-pass filter 30a are measured in advance. When the resonance frequency fo of the dielectric resonator 31 within the above described band-pass filter 30a is set to a certain set frequency fss, the transmission phase of the above described first transmission line except for the transmission phase  R of the band-pass filter 30a is made 1, and the transmission phase of the above described second transmission line is made 2 at the set frequency fss, the phase difference Δ of each signal inputted to the mixer 60a is expressed by equation 7 as in the first embodiment. In the present embodiment, at the set frequency fss to be set of the resonance frequency fo of the dielectric resonator 31 within the above described band-pass filter 30a, a delay circuit (not shown) is inserted in advance into the above described first or second transmission line so that the phase difference Δ of each signal inputted into the mixer 60a becomes 2nπ + π/2 [rad] (wherein n is an integer), desirably, π/2 [rad]. In the present embodiment, the transmission signal outputted from the transmitter la is not inputted to the two-stage auto-tuned parallel connected band-pass filter 2a. The reference signal of, for example, the set frequency fs is generated in the signal generator 71 with the input terminal of the isolator 10 being terminated with the terminal resistor having the given impedance, the switch SW3 is switched to the a side, and the switch SW1 is switched to the b side. At this time, the voltage Vo of the direct current component outputted from the low-pass filter 61a is measured and the voltage Vo measured is substituted in equation 10. Thereafter, the ternary simultaneous equations of the above described equation 3, the equation 7 and the equation 10 are solved. Thus, the transmission phase  R , the insertion loss IL1, the phase difference Δ of the band-pass filter 30a at the set frequency fss to be set by the center frequency of the band-pass filter 30 are calculated. Then, the calculated transmission phase  R is substituted in equation 5 so as to calculate a constant F1, further the calculated constant F1 is substituted in equation 4 so as to calculate the resonance frequency fo. The moving distance 1m for moving the dielectric tuning element 212 is calculated by use of the equation 11 in accordance with the calculated resonance frequency fo and the set frequency fss. The directional coupler 26 is provided with a transmission line for transmitting a reference signal inputted into the input terminal 26a through the amplifier 72 and the switches SW3, SW2 from the signal generator 71, and a coupling line for detecting the above described reference signal so that a part of the current of the reference signal transmission coupled electromagnetically to the transmission line is branched, drawn out, the coupling line for reference signal detection use is provided with an output terminal 26p. The reference signal outputted from the output terminal 26b of the transmission line of the directional coupler 26 is inputted to the input terminal Tlb of the band-pass filter 30a through the input terminal 22r of the coupling line of the directional coupler 22 and the output terminal 22b of the transmission line. The reference signal outputted from the output terminal 26p of the coupling line of the directional coupler 26 is inputted, as a second local oscillation signal, to the local oscillation signal input terminal of the mixer 60b. The mixer 60b consisting of a multiplier mixes the signals inputted into the main signal input terminal with the signals inputted into the local oscillation signal input terminal, multiplies them, and outputs the signal mixed to the low-pass filter (LPF) 61b. The signal after the mixing thereof outputted from the mixer 60b includes the frequency component of fs + fs and fs - fs (direct current component). The low-pass filter 61b lets only pass the voltage Vo of the direct current component of the mixed signal inputted, thereafter outputs the signal of the direct current component to the A/D converting circuit 63b through the amplifier 62b. The A/D converting circuit 63b converts the analog signal of the above described direct current component into the digital signal Vd to output it to the CPU51 through the interface circuit 57 within the control circuit 50a. In a processing circuit system for the reference signal for generating the voltage Vo of the direct current component by use of the second main signal and the second local oscillation signal, each formula from the equation 6 to the equation 11 is established as in the processing circuit system for the reference signal for generating the voltage Vo of the direct current component by use of the above described first main signal and the first local oscillation signal, so that the tuning operation of the band-pass filter 30b can be effected as described hereinafter. In the present embodiment, at a set frequency fss to be set by the resonance frequency fo of the dielectric resonator 31 within the above described band-pass filter 30b, the phase difference Δ of each signal inputted to the mixer 60b may become 2nπ + π/2 [rad] (n is an integer) and desirably may become π/2 [rad]. The delay circuit (not shown) is inserted in advance, as in the processing circuit system for the reference signal for generating the voltage Vo of the direct current component by use of the above described first main signal and the first local oscillation signal. In the present embodiment, the transmission signal outputted from the transmitter 1a is not inputted to the two-stage auto-tuned parallel connected band-pass filter 2a. The reference signal of, for example, the set frequency fss is generated in the signal generator 71 with the input terminal of the isolator 10 being terminated with the terminal resistor having the given impedance, the switch SW3 is switched onto the b side, and the switch SW2 is switched onto the b side. At this time, the voltage Vo of the direct current component outputted from the low-pass filter 61b is measured and the voltage Vo measured is substituted in equation 10. Thereafter, the ternary simultaneous equation of the above described equation 3, the equation 7 and the equation 10 is solved. Thus, the transmission phase  R , the insertion loss IL1, the phase difference Δ of the band-pass filter 30b at the set frequency fss to be set of the center frequency of the band-pass filter 30 are calculated. Then, the calculated transmission phase  R is substituted in equation 5 so as to calculate a constant F1, further the calculated constant F1 is substituted in equation 4 so as to calculate the resonance frequency fo. The moving distance for moving the dielectric tuning element 212 is calculated by use of equation 11 in accordance with the calculated resonance frequency fo and the set frequency fss. The pulse driving signal of the pulse number corresponding to the above described calculated moving distance 1m is inputted into the stepping motor 33b to move the dielectric tuning element 212 within the band-pass filter 30b. The tuning process for the band-pass filter 30b can be effected so that the center frequency fc of the band-pass filer 30b roughly corresponds to the above described set frequency fss. As shown in Fig. 12, the control circuit 50a within the two-stage auto-tuned parallel connected band-pass filter 2a is provided with an interface circuit 55 to be connected with switches SW1, SW2, SW3 when compared with the control circuit 50 in the first embodiment. The CPU51 executes each of the above described tuning processes of each of the band-pass filter 30a, 30b and controls the dielectric resonator 31 within the band-pass filters 30a, 30b. Also, the motor driving circuits 32a, 32b are connected to the interface circuit 56, and the A/D converting circuits 63a, 63b are connected to the interface circuit 57. When each tuning process of each tuning processing of each band-pass filter 30a, 30b is executed, the CPU51 calculates the center frequencies f1c, f2c to be set respectively in each band-pass filter 30a, 30b by use of the following equation 12, the equation 13 in accordance with the center frequency fd and the band width ΔF to be set in the two-stage auto-tuned parallel connected band-pass filter 2a inputted by use of the keyboard 81 as described later in detail. In the present embodiment, the process of storing the center frequency fd and the band width ΔF to be set in the two-stage auto-tuned parallel connected band-pass filter 2a in the RAM53 through the interface circuit 80 from the keyboard 81 is effected by the interruption processing of the CPU51. f1c=fd-2a 2 ΔF f2c=fd+2a 2 ΔF Here, a2 being within the range of desirably 0.8 <a2<2.0, is a constant to be predetermined depending upon the loaded Q(Q L ) of the dielectric resonator 31 within each band-pass filter 30a, 30b, and is stored previously in the ROM52. The CPU51 effects the tuning process (hereinafter referred to as first tuning process) for the band-pass filter 30a for making the resonance frequency fo of the dielectric resonator 31 within the band-pass filter 30a to roughly correspond to the frequency f1c of the above described reference signal after generating the reference signal of the frequency f1c in the signal generator 71. Thereafter, the tuning process (hereinafter referred to as second tuning process) for the band-pass filter 30b for tuning the resonance frequence fo of the dielectric resonator 31 within the band-pass filter 30b to roughly correspond to the frequency f2c of the above described reference signal after generating the reference signal of the frequency f2c in the signal generator 71. In the first tuning process, the motor driving signal for driving the stepping motor 33a is outputted, directed to the stepping motor 33a through the interface circuit 56 and the motor driving circuit 32a, as the level of the signal of the above described direction current component inputted into the CPU51 through the interface circuit 57 from the A/D converting circuit 63a so as to move the dielectric tuning element 212 within the band-pass filter 30a. At this time, the electrostatic capacity of the variable capacitance VC in the equivalent circuit of Fig. 2 changes to change the resonance frequency fo of the dielectric resonator 31, so that the center frequency fc of the band-pass filter 30a approximately equal to the resonance frequency fo can be changed. In the present embodiment, the control circuit 50a drives the stepping motor 33a so that the level of the direct current component outputted from the low-pass filter 61a becomes 0 so as to change the resonance frequency of the dielectric resonator 31 within the band-pass filter 30a. Therefore, the center frequency fc of the band-pass filter 3 approximately equal to the resonance frequency fo can be approximately tuned to correspond to the frequency of the reference signal to be generated by the signal generator 71. In a second tuning process, as in the first tuning processing, the motor driving signal for driving the stepping motor 33b is outputted to the stepping motor 33b through the interface circuit 56 and the motor driving circuit 32b to effect the driving operation so that the level of the signal of the above described direct current component inputted to the CPU51 through the interface circuit 57 from the A/D converting circuit 63b. Here, the control circuit 50a drives the stepping motor 33b so that the level of the direct current component outputted from the low-pass passing filter 61 may become 0 so as to change the resonance frequency of the dielectric resonator 31 within the band-pass filter 30b. Therefore, the center frequency fc of the band-pass filter 30b approximately equal to the resonance frequency fo can be tuned to approximately correspond to the frequency f2c of the reference signal to be generated by the signal generator 71. By the execution of the above described first and second tuning process, the center frequency and the band width of the two-stage auto-tuned parallel connected band-pass filter 2a may be respectively set automatically to each data value fd, ΔF inputted by use of the keyboard 81. Fig. 14 is a flow chart showing the main routine of the tuning process of the control circuit 50 of the two-stage auto-tuned parallel connected band-pass filter 2a of Fig. 12. The main routine executes the above described first and second tuning process, and is a process operation for automatically setting by each data value fd, ΔF inputted by use of the keyboard 81, the center frequency and the band width of the band-pass filter 2a. In the initial condition before the start of the main routine, the dielectric tuning element 212 of the dielectric resonator 31 within each band-pass filter 30a, 30b is positioned in the optional distance g. In the main routine, the processing of the step 5 and the step S6 is a rough tuning process operation for respectively changing the center frequency fc of each band-pass filter 30a, 30b built in to the frequency near the set frequency flc, f2c to be set. The processing operation from the step S7 to the step S10 is a first fine tuning process operation which changes the center frequency fc of the band-pass filter 30a built in from the frequency near the above described frequency flc after the above described rough tuning process operation so as to roughly correspond to the above described frequency flc. The processing from the step S11 to the step S14 is a second fine tuning process operation which changes the center frequency fc of the built-in band-pass filter 30b from the frequency near the above described frequency f2c after the above described rough tuning processing operation so as to tune it to approximately correspond to the above described frequency f2c. When the power switch (not shown) of the control circuit 50a is turned on, the main routine of the tuning process of Fig. 14 is started. In the step S1, the respective dielectric tuning elements 212 within the respective band-pass filters 30a, 30b are moved to a home position respectively by the driving of the stepping motors 33a, 33b. In the present embodiment, a stopper (not shown) for the dielectric tuning element is provided within each band-pass filter 30a, 30b so that the dielectric tuning element 212 within each band-pass filter 30a, 30b may not be moved in the direction of an arrow Al from the above described home position. In the step S1, when the motor driving signal of the - polarity is inputted continuously to the stepping motors 33a, 33b and each dielectric tuning element 212 is stopped at the home position by the above described stopper, a microswitch (not shown) provided at the home position is turned on, thus stopping the driving operation of each stepping motor 33a, 33b. In the step S2, 897 [MHz] is set as the data of the resonance frequency fol of the dielectric resonator 31 within the present band-pass filter 30a, and is stored in the RAM53. The 897 [MHz] is set as the data of the resonance frequency fo2 of the dielectric resonator 31 within the present band-pass filter 30b, and is stored in the RAM53. In the step S3, it is judged whether or not the data of the center frequency fd and the band width ΔF to be set in the two-stage auto-tuned parallel connected band-pass filter 2a have been inputted by use of the keyboard 81. When the data have not been inputted (NO in the step S3), the loop processing of the step S3 is repeated into a waiting condition. When the data have been inputted (YES in the step S3), the routine moves to the step S4. In the step S4, in accordance with the data of the inputted center frequency fd and the band width ΔF, the center frequencies (hereinafter referred to as to set frequencies) flc, f2c to be set in each band-pass filter 30a, 30b are calculated with by use of the above described equation 12 and the equation 13, and thereafter these data are stored in the RAM53. In the step S5, in order to effect the rough tuning processing, the moving distances 1ma, 1mb to move the dielectric tuning element 212 within each band-pass filter 30a, 30b are calculated by use of the next equation 14 and equation 15 which are similar to the computing formula of the equation 11 in accordance with the data of the resonance frequencies fo1, fo2 stored in the RAM53 and the data of the set frequencies f1c, f2c. 1ma=k(f 0 -f1c) 1mb=k(f 0 -f2c) In the step S6, the pulse driving signals of the pulse number corresponding to the calculated moving distances 1ma, 1mb are respectively inputted to the stepping motors 33a, 33b so as to move the dielectric tuning elements 212 within the band-pass filters 30a, 30b. When the moving distances 1ma, 1mb are positive, the pulse driving signals of + polarity are inputted to the stepping motors 33a, 33b. The dielectric tuning elements 212 are moved in the direction of an arrow A2 by the moving distances 1ma, 1mb. When the moving distances 1ma, 1mb are negative, the pulse driving signals of - polarity are inputted to the stepping motors 33a, 33b. The dielectric tuning elements 212 are moved in the direction of an arrow Al by the moving distances 1ma, 1mb. The rough tuning process operation is completed. In order to effect the first fine tuning process, the data of the set frequency flc in the step S7 is outputted as the set frequency fs to the signal generator 71 so as to generate the reference signal of the set frequency flc in the signal generator 71. Thereafter, in the step S8, the switch SW1 is switched onto the b side, the switch SW2 is switched onto the a side, and the switch SW3 is switched onto the a side. In the step S9, the set frequency f1c is stored in the RAM53 as the set frequency fss. Thereafter, in the step S10, the center frequency fc of the band-pass filter 30a to be built in is changed from the frequency near the above described set frequency flc after the above described rough tuning processing, and the fine tuning process operation (see Fig. 7 or Fig. 8 through Fig. 11) for tuning the center frequency to correspond approximately to the above described set frequency f1c is effected. Thereafter, the routine moves to the step S11. In order to effect the second fine tuning process , the data of the set frequency f2c in the step S11 is outputted as the set frequency f2c to the signal generator 71 so as to generate the reference signal of the set frequency f2c in the signal generator 71. Thereafter, in the step S12, the switch SW1 is switched onto the a side, the switch SW2 is switched onto the b side, and the switch SW3 is switched onto the b side. In the step S13, the set frequency f2c is accommodated in the RAM53 as the set frequency fss. Thereafter, in the step S14, the center frequency fc of the band-pass filter 30b to be built in is changed from the frequency near the above described set frequency f2c after the above described rough tuning process operation so as to execute the fine tuning process operation (see Fig. 7 and Fig. 8 through Fig. 11) for tuning the center frequency to roughly correspond to the above described set frequency f2c, and thereafter, in the step S15, the switch SW1 is switched onto the a side, the switch SW2 is switched on the a side so as to return to the step S3. Hereafter, the above described rough tuning process and the above described first, second fine tuning process are repeated, by the use of the keyboard 81, every time the center frequency and the band width of the parallel two-stage automatic tuning type band-pass filter 2a are newly inputted. In the two-stage auto-tuned parallel connected band-pass filter 2a constructed as shown in Fig. 12, the directional couplers 21, 23, 25, 26 are provided even when, for example, the components of the transmission signals of the frequencies f2, f3 interfer, inputted to the band-pass filter 2a through the two-stage auto-tuned parallel connected band-pass filters 2b, 2c from the transmitters 1b, 1c of the other channel, so that the frequency component to turn round from the other channel are not inputted to the mixers 60a, 60b. Accordingly, the above described tuning processing can be effected without influences upon the frequency component interfering from the other channel as in the conventional embodiment. Even where a divider or the like, instead of the directional couplers 21, 23, 25, 26 is provided to which reflection signals are outputted, when the frequencies f2, f3 of the other channel are sufficiently shifted with respect to the frequency f1 of the transmission signal to be outputted from the transmitter 1a, the above described interference signals of the other channel are inputted to the local oscillation signal input terminals of the mixers 60a, 60b after the interference signals of the other channel have passed through the band-pass filters 30a, 30b having an attenuation amount sufficiently large with respect to the frequencies f2, f3. The level of the direct component about the frequency f2, f3 of the above described other channel, appearing in the output of the low-pass filters 61a, 61b is considerably small, thus hardly giving influences upon the above described tuning process. Therefore, the above described tuning process operation can be effected without receiving the influences of the frequency component interfering from the other channel as in the conventional embodiment. The two-stage auto-tuned parallel connected band-pass filters 2b and 2c are similar in construction to the above described two-stage auto-tuned parallel connected band-pass filter 2a. In the respective parallel two-stage automatic tuning type band-pass filters 2b, 2c, the above described tuning process operation is effected so that the center frequencies of the built-in band-pass filters 30a, 30b may roughly correspond to the respective set frequencies f1c, f2c calculated in accordance with the center frequencies and the band widths of the band-pass filters 2b, 2c inputted by use of the keyboard 81. In the above described embodiment, the data of the center frequency fd and the band width ΔF to be set by use of the keyboard 81 are inputted. Without restriction in the present invention, a receiving circuit for receiving each data of the center frequency fd and the band width ΔF from an external apparatus such as another control circuit or the like or an interface circuit of the control circuit 50a are provided. The control circuit 50a may calculate the set frequencies flc, f2c in accordance with each data of the center frequency fd and the band width ΔF received. In the above described embodiment, a first circuit system of a mixer 60a necessary for effecting the first tuning process, a low-pass filter 61a, an amplifier 62a, an A/D converting circuit 63a, a motor driving circuit 32a, a stepping motor 33a and so on, and a second circuit system of a mixer 60b necessary for effecting the second tuning process, a low-pass filter 61b, an amplifier 62b, an A/D converting circuit 63b, a motor driving circuit 32b, a stepping motor 33b and so on are provided separately. One circuit system and a change-over switch may be provided without separate provision thereof, without restriction to it. The present invention may be constructed so that the selective use may be effected with respect to the first and second tuning process. In the above described embodiment, a transmitter multiplexer 2 shown in Fig. 13 is provided with three two-stage auto-tuned parallel connected band-pass filters 2a, 2b, 2c with two band-pass filters 30a, 30b being connected in parallel. The present invention may be adapted to be connected with the respective output terminals with a plurality of automatic tuning type band-pass filters 2d in the first embodiment shown in Fig. 1 without restriction to it. In the above described embodiment, the two-stage auto-tuned parallel connected band-pass filters 2a, 2b, 2c connected in parallel to two band-pass filters 30a, 30b have been described. The present invention may be applied to the multi-poles auto-tuned parallel connected band-pass filter having a plurality of band-pass filters 30 being connected in parallel, without restriction to it. In a case where the three-poles auto-tuned parallel connected band-pass filter provided with four band-pass filters 30, the center frequencies flc, f2c, f3c to be set respectively can be calculated in each band-pass filter 30 with the use of the next equation 16, the equation 17, the equation 18 in accordance with the center frequency fd and the band width ΔF to be set by use of the keyboard 81. f1c=fd-2a 3 ΔF f2c=fd+2b 3 ΔF f3c=fd+2c 3 ΔF Here each positive constant a3, b3, c3 is desirably within the range of 0.8 <a3 = c3 <2.0, and of |b3| «a3 and is predetermined constants depending upon the loaded Q (Q L ) of the dielectric resonator 31 within each band-pass filter. In a case where the parallel four-poles auto-tuned parallel connected band-pass filter provided with four band-pass filters 30, the center frequencies f1c, f2c, f3c, f4c to be set respectively can be calculated in each band-pass filter 30 with the use of the next equation 19 through the equation 22 in accordance with the center frequency fd and the band width ΔF to be set inputted by use of the keyboard 81. f1c=fd-2a 4 ΔF f2c=fd-2b 4 ΔF f3c=fd+2c 4 ΔF f4c=fd+2d 4 ΔF Here each positive constant a4, b4, c4, d4 is desirably within the range of 0.2 < b4 = c4 < a4 = d4 < 2.0, and is predetermined depending upon the loaded Q (Q L ) of the dielectric resonator 31 within each band-pass filter. Likewise, even in a case of the multi-poles auto-tuned parallel connected band-pass filter provided with five band-pass filters 30 or more, the respective center frequencies to be set in the respective band-pass filters 30 can be calculated. In the above described embodiment, the band-pass filters 30a, 30b are connected in parallel through the divider 11 and the combiner 12. Here when the adjusting operation of the set processing of the center frequency of the band-pass filter 30a or 30b receives the influence of the load connected to the band pass filter to be processed, a change-over switch is provided for cutting off the load during the set process of the above described center frequency. A change-over switch for cutting off the band-pass filter 30a from the loaded may be provided, for example, between the divider 11 and the input terminal 20a of the directional coupler 20, and between the output terminal 21b of the directional coupler 21 and the combiner 12 for the set processing of the center frequency of the band-pass filter 30a. A change-over switch for cutting off the band-pass filter 30b from the loaded may be provided, for example, between the divider 11 and the input terminal 22a of the directional coupler 22, and between the output terminal 23b of the directional coupler 23 and the combiner 12 for the set processing of the center frequency of the band-pass filter 30b. As is clear from the foregoing description, in an auto-tuned apparatus for a band-pass filter in the first embodiment as described hereinabove, the reference signals having the given frequency to be set are generated, the above described reference signals generated are mixed with signals outputted from the above described band-pass filter when the above described reference signals have been inputted to the above described band-pass filter so as to multiply them for outputting the signals of the multiplied results. The signals of the direct current component from the signals of the multiplied results outputted are filtered. The above described band-pass filter is controlled so that the center frequencies of the above described band-pass filter may correspond the frequencies of the above described reference signal in accordance with the signal of the direct current component outputted. Even when interference wave signals having the frequency component sufficiently shifted with respect to the frequency of the above described reference signal are inputted to the output terminal of the above described band-pass filter, the level of the direct current component of the frequency component of the above described interference wave signal appearing at the output of the above described low-pass filtering means is considerably small, thus hardly giving influences upon the above described auto-tuned operation. Therefore, the center frequency of the above described band-pass filter can be adjusted automatically to the desired set value with simple circuit construction and precision better than in the conventional embodiment. An automatic tuning type band-pass filter according to a further embodiment comprises a band-pass filter capable of changing the center frequency, an auto-tuned apparatus described by the above embodiments so as to construct an automatic tuning type band-pass filter. An transmitter multiplexer described by the above embodiment comprises a plurality of automatic tuning type band-pass filters described above, an electric connection together with the output terminals of the described automatic tuning type band-pass filters, outputting each signal outputted from each band-pass filter within each of the above described automatic tuning type band-pass filters. The above described auto-tuned operation can be effected without the influences of the signals to turn round from the other channel being applied upon the above described respective automatic tuning type band-pass filters. In an auto-tuned apparatus for the multi-poles parallel connected band-pass filter in accordance with the present invention, each center frequency to be set in each of the above described band-pass filters is calculated in accordance with the center frequency and the band width to be set in a multi-poles parallel connected band-pass filter where a plurality of band-pass filters have been connected in parallel, each reference signal having each center frequency calculated is generated, the respective reference signals to be generated are mixed with, are multiplied by the respective signals outputted from the respective band-pass filters when each of the reference signals has been inputted respectively into each of the band-pass filters, each signal of the direct current component from each signal of the multiplied results is filtered, the respective band-pass filters are controlled so that the center frequencies of each of the band-pass filters may agree with the frequencies of each of the reference signals in accordance with each signal of the direct current component filtered. Even when interference wave signals having the frequency component sufficiently shifted with respect to the frequency of the above described reference signal are inputted to the output terminal of the above described band-pass filter, the level of the direct current component about the frequency component of the above described interference wave signal to appear in the output of the above described low-pass filtering means is considerably small, thus hardly giving influences upon the above described auto-tuned operation. Therefore, the center frequency and band width of the above described multi-poles parallel connected band-pass filter can be adjusted automatically to the desired set value with simple circuit construction and precision better than in the conventional embodiment. A multi-poles auto-tuned parallel connected bandpass filter according to a further embodiment is provided with a multi-poles parallel connected band-pass filter where a plurality of band-pass filters capable of changing the center frequencies are electrically connected in parallel, and an auto-tuned apparatus described above so as to construct a multi-poles auto-tuned parallel connected band-pass filter. An transmitter multiplexer according to yet another embodiment is provided with a plurality of multi-poles auto-tuned parallel connected band-pass filters described above, each output terminal of each of the above described multi-poles auto-tuned parallel connected band-pass filters for outputting each signal to be outputted from each band-pass filter within each of the above described multi-poles auto-tuned parallel connected band-pass filters is electrically connected, the above described auto-tuned operation can be effected without influences of the signal to turn round from the other channel being applied upon each of the multi-poles auto-tuned parallel connected band-pass filters. Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to whose skilled in the art without departing from the invention as defined in the appended claims.

Claims: An auto-tuned apparatus for a band-pass filter (30) which is adapted to automatically set the center frequency (f c ) of the band-pass filter (30) to a given frequency (f d ), comprising a control means (50) to control the band-pass filter (30) so that the center frequency (f c ) of the band-pass filter (30) corresponds to the given frequency (f d ); characterized by a signal generating means (71) for generating a reference signal having the given frequency (f d ); a mixing means (60) for mixing the reference signal generated by the signal generating means (71) with a signal outputted from the band-pass filter (30) when applying the reference signal to the band-pass filter (30) to produce a mixer output signal corresponding to the signal outputted from the band-pass filter (30) multiplied by the reference signal; a low-pass filtering means (61) for filtering the signal of a direct current component from the mixer output signal; wherein the control means (50) controls the band-pass filter (30) so that the center frequency (f c ) of the band-pass filter (30) corresponds to the frequency (f d ) of the reference signal such that the level of the signal of the direct current component outputted from the low-pass filtering means (61) becomes substantially zero. The auto-tuned apparatus as defined in claim 1, further comprising a first coupling means (25) which is provided between the signal generating means (71) and the input terminal (T1) of the band-pass filter (30), and between the signal generating means (71) and the mixing means (60), outputs to the input terminal of the band-pass filter (30) the reference signal generated by the signal generating means (71), and draws out a portion of the reference signal for outputting it to the mixing means (60), and a second coupling means (21) which is provided between the output terminal (T2) of the band-pass filter (30) and the output terminal of the auto-tuned apparatus, and between the output terminal (T2) of the band-pass filter (30) and the mixing means (60), outputs to the output terminal of the auto-tuned apparatus the signal outputted from the output terminal (T2) of the band-pass filter (30), and draws out a portion of the signal outputted from the output terminal (T2) of the band-pass filter (30) for outputting it to the mixing means (60). The auto-tuned apparatus as defined in claim 1 or 2, further provided with an input means (81) for inputting the center frequency to be set in the band-pass filter (30). The auto-tuned apparatus as defined in claim 1 or 2, further provided with a receiving means for receiving information concerning the center frequency to be set in the band-pass filter (30). The auto-tuned apparatus as defined in any of claims 1, 2, 3 or 4, wherein the band-pass filter (30) is provided with a resonator (31), the control means (50) is adapted to calculate the resonance frequency of the resonator (31) by controlling the level of the signal of the direct current component outputted from the low-pass filtering means (61) to become substantially zero, so as to control the band-pass filter (30) so that the center frequency of the band-pass filter (30) corresponds to the frequency of the reference signal. The auto-tuned apparatus as defined in any of claims 1, 2, 3 or 4, wherein the band-pass filter (30) is provided with a resonator (31), the control means (50) controls the signal generating means (71) so that the frequency of the reference signal corresponds to the center frequency of the band-pass filter (30) such that the level of the signal of the direct current component outputted from the low-pass filtering means (61) becomes substantially zero, so as to change the frequency of the reference signal, the control means (50) controls the band-pass filter (30) so that the center frequency of the band-pass filter (30) corresponds to the frequency of the reference signal according to the frequency of the changed reference signal. An automatic tuning type band-pass filter capable of changing the center frequency, comprising the auto-tuned apparatus described in any of claims 1, 2, 3, 4, 5 or 6. A transmitter multiplexer, comprising a plurality of automatic tuning type band-pass filters according to claim 7, wherein the output terminals of the automatic tuning type band-pass filters (30) are electrically connected to each other. An auto-tuned apparatus as defined in any of claims 1 to 8 for a multi-poles parallel connected band-pass filter, comprising a computing means for calculating each center frequency to be set in each of the band-pass filters in accordance with the center frequency and the band width to be set in a multi-pole parallel connecting band-pass filter where a plurality of band-pass filters capable of changing the center frequencies have been electrically connected in parallel, wherein the signal generating means generates reference signals having the center frequency computed by the computing means, wherein the mixing means mixes the respective reference signals generated by the signal generating means with the reference signals outputted from the respective band-pass filters when appyling each of the reference signals to the band-pass filters, wherein the low-pass filtering means filters each signal of the direct current component from each mixer output signal.

Inventors: ISHIKAWA YOUHEI, KUBO HIROYUKI, WADA HIDEKAZU, YAMASHITA SADAO, ISHIKAWA, YOUHEI, KUBO, HIROYUKI, WADA, HIDEKAZU, YAMASHITA, SADAO
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1992
Main classification: H03J7
IPC codes: H03J7