ANTENNA SHARING DEVICE

Abstract: Antenna sharing device narrows transmission and reception bands and increases isolation by using combinations of pass filters and associated filters in the transmission and reception circuits. A transmission terminal (11) is connectable by a first switch (18) to a transmission side lowpass filter (14) or a transmission side highpass filter (15) which are selectively connectable to an antenna (13) by a second switch (19).S On the receiving side, a reception terminal (12) is connectable by a third switch (20) to a reception side lowpass filter (16) in series with the transmission side lowpass filter (14) or to a reception side highpass filter (16) in series with the transmission side highpass filter (15).

Description: TECHNICAL FIELD The present invention relates to an antenna sharing apparatus for use in a communication system, for example, an automobile telephone or the like in which the transmitting frequency and receiving frequency are different and which uses an antenna in common with the transmission and the reception. BACKGROUND ART As shown in Fig. 1, a conventional antenna sharing apparatus comprises a combination of two band pass filters. That is, a transmitting filter 3 for passing a transmission band is provided between a transmitting terminal 1 and an antenna terminal 2. A receiving filter 5 for passing a reception band is provided between a receiving terminal 4 and the antenna terminal 2. Fig. 2 shows transmitting characteristics of the conventional antenna sharing apparatus. A transmission band 6 and a reception band 7 are provided. The isolation in the reception band 7 of the transmission band 6 is indicated by a point 8. The isolation in the transmission band 6 of the reception band 7 is indicated by a point 9. Such a conventional apparatus is shown in the article "Mobile Radio Equipment, Type SRR 178" on page 58 of the December 1951 edition of Communication News. In the conventional antenna sharing apparatus, in the case where the transmission band 6 and reception band 7 are wide or where the transmission band 6 and reception band 7 are close to each other, it is difficult to set the transmission and reception isolation with large isolation points 8 and 9. An, when the transmission and reception bands are adjacent to each other, the transmission and reception isolations cannot be obtained. According to the present invention there is provided an antenna sharing apparatus having a transmission side filter operable over a transmission band and a reception side filter operable over a reception band for connection to an antenna, wherein each of said transmission side filter and reception side filter comprises a combination of at least two filter elements and characterised by: switching means for switching each combination of filter elements between frequency bands; the frequency bands being of a narrower bandwidth than the wider reception and transmission bands and forming a section of those wider bands; the combination being such that at any instant of time the isolation of the narrow frequency bands being higher than the isolation of the wider reception and transmission bands. The invention will be described now by way of example only, with particular reference to the accompanying drawings. In the drawings: Fig. 1 is a block diagram of a conventional antenna sharing apparatus, Fig. 2 is a transmission characteristic diagram of the conventional antenna sharing apparatus, Fig. 3 is a block diagram of an antenna sharing apparatus in an embodiment of the present invention, Figs. 4a and 4b are transmission characteristic diagrams of the antenna sharing apparatus, Fig. 5 is an electric circuit diagram showing a practical example of the antenna sharing apparatus, Fig. 6 is an exploded perspective view showing a practical structure, Fig. 7 is a perspective view showing a dielectric coaxial resonator used in the antenna sharing apparatus, Fig. 8 is an equivalent circuit diagram of the dielectric coaxial resonator, Fig. 9 is a circuit diagram showing an embodiment of a circuit using a varactor diode as a filter for use in the antenna sharing apparatus, and Fig. 10 is a circuit diagram of an embodiment of the circuit using a PIN diode as a filter. BEST MODE FOR CARRYING OUT THE INVENTION A block diagram of an antenna sharing apparatus in an embodiment of the present invention is shown in Fig. 3. A transmitting terminal 11 is connected to a transmission side low band filter 14 and to a transmission side high band filter 15 through a transmission side switch 18. The other terminals of the filters 14 and 15 are connected to an antenna side switch 19. Similarly, a receiving terminal 12 is connected to a reception side low band filter 16 and to a reception side high band filter 17 through a reception side switch 20. The other terminals of the filters 16 and 17 are connected to the antenna side switch 19. The antenna side switch 19 is connected to an antenna 13. In such an arrangement, the high band and low band filters 14, 15, 16, and 17 for transmission and reception are switched by the switches 18, 19, and 20. As the switches, it is possible to use either electrical switches using PIN diodes or the mechanical switches using relays. In general, when a high output is transmitted, the mechanical switches using the relays are advantageous. Since the PIN diodes are saturated by a high output, they are improper for use in the high output switches. The transmitting characteristics of the respective low and high bands of the antenna sharing apparatus in this embodiment are shown in Figs. 4a and 4b. As shown in Fig. 4, transmission band 21 and reception band 22 are divided into halves of the high band and low band, thereby obtaining large isolations for transmission and reception. Namely, the transmission and reception isolation points are set to transmission and reception isolation points 23 and 24 in the case of the low band and to transmission and reception isolation points 25 and 26 in the case of the high band. The isolation points are shifted so as to go away from the band edges of the bands depending on the low band and high band. Therefore, even in the case of wide bands or where the transmission and reception bands are adjacent to each other, the transmission and reception isolations can be assured. Fig. 5 is a circuit diagram showing a practical example of the antenna sharing apparatus according to the embodiment. Each of the filters 14 to 17 is constituted such that a plurality of dielectric coaxial resonators 27 of 1/4 λ type having a variable capacitor 28 are connected through a coupling capacitor 29. In such an arrangement, the characteristics of the dielectric coaxial resonators 27 are set and adjusted by the variable capacitor 28 so as to satisfy the characteristics of the filters 14 to 17. A practical structure of the antenna sharing apparatus of the circuit shown in Fig. 5 is shown in Fig. 6. In Fig. 6, reference numeral 30 denotes dielectric coaxial resonators of the 1/4 λ type. Every five dielectric coaxial resonators 30 constitute one section and are arranged, thereby constituting a transmission side high band filter section 31, a transmission side low band filter section 32, a reception side high pass filter section 33, and a reception side low band filter section 34. Reference numeral 35 denotes a filter casing to enclose the filter sections 31 to 34 comprising the dielectric coaxial resonators 30. For the filter sections 31 to 34, the transmission side high band filter section 31 and transmission side low band filter section 32 constitute one block. And, the reception side high band filter section 33 and reception side low band filter section 34 constitute one block and are arranged adjacent to the block on the transmission side. A relay 36 serving as a switch on the antenna side is arranged between the transmission and reception side blocks. In this state, those filter sections are attached on a printed board 39. And, on the printed board 39, a relay 37 serving as a switch on the transmission side is attached to the edge portion adjacent to the transmission side block. Further, a relay 38 serving as a reception side switch is attached to the edge portion adjacent to the reception side block. And, the printed board 39 is provided with a transmitting terminal 40, a receiving terminal 41, an antenna terminal 42 serving as a connecting portion to the antenna, and a relay power source terminal 43 to apply a voltage to drive the relays 36, 37, and 38. The resepctive parts attached on the printed board 39 are enclosed in a casing 44 made of metal. The casing 44 has an earth terminal 45. Fig. 7 shows an external shape of the dielectric coaxial resonator 30 and Fig. 8 shows its equivalent circuit. In Fig. 7, there is shown a structure such that an electrode 46 is continuously formed on the inner peripheral surface, outer peripheral surface, and one end surface of a cylindrical resonator main unit 47 and a rotor 50 which is rotatably supported by a shaft 48 and a spring 49 is arranged to the remaining end surface of the resonator main unit 47. The rotor 50 has a rotor electrode 51. A variable capacitor is constituted by the rotor electrode 51 which faces through the rotor 50 and an electrode 46a of the end surface of the resonator main unit 47. In this embodiment, the filters themselves have been switched by the switch. However, the resonant frequencies of the resonant elements constituting the filters may be also changed by tuning of the elements so that the high and low bands can be switched. An embodiment in the case will now be described hereinbelow. Fig. 9 is a circuit diagram of an embodiment of a voltage controlled filter using a varactor diode. Reference numeral 52 denotes a varactor diode; 53 is a by-pass capacitor; 54 a voltage control terminal; 55 a capacitor which is arranged serially with the varactor diode 52; 56 a coupling capacitor; 57 an input/output terminal; 58 a dielectric coaxial resonator of the 1/4 λ type; and 59 a voltage controlling bias resistor. A voltage is applied to the voltage control terminal 54. A reverse voltage is applied to the varactor diode 52 through the voltage controlling bias resistor 59 to cause change in capacitance of the varactor diode 52. The resonant frequency of the resonator is changed. In this manner, the center frequency of the filter is changed. In this circuit, the deterioration due to insertion loss is small because the resonator having a high Q (quality factor) is used in the resonant system. Fig. 10 shows a circuit diagram of an embodiment of a voltage controlled filter using a PIN diode. Reference numeral 60 denotes a by-pass capacitor; 61 a PIN diode; 62 a switching capacitor; 63 a coupling capacitor; 64 a PIN diode biassing power source terminal; 65 a 3-terminal switch; 66 a dielectric coaxial resonator; 67 an input/output terminal; 68 a switch OFF terminal; and 69 a switch ON terminal. In the 3-terminal switch 65, when the switch OFF terminal 68 is set to ON, the switch ON terminal 69 is grounded and at this time, a reverse bias is applied to the PIN diode 61 and the switching capacitor 62 is not grounded. On the contrary, when the switch ON terminal 69 is set to ON, the switch OFF terminal 68 is grounded and at this time, the switching capacitor 62 is grounded through the bias resistor 60 and PIN diode 61. In this case, the resonant frequency of the dielectric coaxial resonator 66 changes (to a lower frequency) and the center frequency of the filter changes. In this circuit, the filter frequency can be switched to the center frequency of only either one of the high band side and the low band side. However, since the resonator can be constituted so as to have a higher Q as compared with the circuit using the varactor diode, the filter insertion loss is reduced. On the other hand, since the capacitance change in the diode is not used, the embodiment can be also used with a high electric power. In the radio communication or the like having a wide band, many stages of resonators are arranged to obtain attenuation amounts out of bands. However, according to this filter, since the band width of the filter can be reduced into half, a desired attenuation amount out of the band can be obtained without arranging many stages of resonators. The small-sized and cheap wide-band filter can be realized without deteriorating the performance so large. In addition, a temperature drift can be also made small. INDUSTRIAL FIELD OF UTILIZATION As described above, according to the present invention, the antenna sharing apparatus for adjacent transmission and reception bands which could not be accomplished so far can be realized. The invention is industrially advantageous. List of reference numerals in the drawings: 1, 11, 40 transmitting terminals, 2, 42 antenna terminals, 3 filter for transmission, 4, 12, 41 receiving terminals, 5 filter for reception, 6, 21 transmission bands, 7, 22 reception bands, 8, 9 points, 13 antenna, 14 transmission side low pass filter, 15 transmission side high pass filter, 16 reception side low pass filter, 17 reception side high pass filter, 18 transmission side switch, 19 antenna side switch, 20 reception side switch, 23, 24, 25, 26 isolation points, 27, 30, 58, 66 dielectric coaxial resonators, 28 variable capacitor, 29, 56, 63 coupling capacitors, 31 transmission side high pass filter section, 32 transmission side low pass filter section, 33 reception side high pass filter section, 34 reception side low pass filter section, 35 filter casing, 36, 37, 38 relay, 39 printed board, 43 relay power source terminal, 44 casing, 45 earth terminal, 46, 46a electrodes, 47 resonator main unit, 48 shaft, 49 spring, 50 rotor, 51 rotor electrode, 52 varactor diode, 53, 60 by-pass capacitors, 54 voltage control terminal 55 capacitor, 57, 67 input/output terminals, 59 voltage controlling varactor registor 61 PIN diode, 62 switching capacitor, 64 PIN diode bias power source terminal, 65 3-terminal switch, 68 switch OFF terminal, 69 switch ON terminal.

Claims: An antenna sharing apparatus having a transmission side filter (14, 15) operable over a transmission band (6) and a reception side filter (16, 17) operable over a reception band (7) for connection to an antenna (13), wherein each of said transmission side filter (14, 15) and reception side filter (16, 17) comprises a combination of at least two filter elements (14, 15, 16, 17) and characterised by: switching means (18, 19, 20) for switching each combination of filter elements (14, 15; 16, 17) between frequency bands; the frequency bands being of a narrower bandwidth than the wider reception and transmission bands and forming a section of those wider bands; the combination being such that at any instant of time the isolation of the narrow frequency bands being higher than the isolation of the wider reception and transmission bands. An apparatus according to claim 1, wherein each combination of filter elements (14, 15; 16, 17) includes at least a first (14, 16) and second (15, 17) filter element, and said switching means (18, 19, 20) switches between a first filter element (14, 16) operable in a first frequency band and a second filter element (15, 17) operable in a second frequency band. An apparatus according to claim 1, wherein said switching means (52, 54, 59, 64) switches each filter element in each combination of filter elements (14, 15; 16, 17) from a state in which it is operable in a first frequency band to a state in which it is operable is a second frequency band. An apparatus according to claim 1, wherein the transmission side filter (14, 15) comprises a transmission side low band filter (14) and transmission side high band filter (15); the receiption side filter (16, 17) comprises a reception side low band filter (16) and a reception side high band filter (17); the switch means (18, 19, 20) comprises transmission side switching means (18) which selectively connects the transmission side low and high band filter (14, 15) to a transmitting terminal (11); reception side switching means (20) which selectively connects the reception side low and high band filters (16, 17) to a receiving terminal (12); and antenna side switching means (19) which selectively connects the transmission side low and high band filters (14, 15) and the reception side low and high band filters (16, 17) to the antenna (13). An apparatus according to claim 4, wherein each combination of filter elements (33, 34) is provided by a block of filter elements; each block of filter elements thus comprises the high band filter section (32, 33) and the low band filter section (32, 34); and the blocks (31, 32; 33, 34) and the antenna side switching means (36) are enclosed in a casing (44). An antenna sharing apparatus according to claim 1, wherein each of said filters comprises a connection of a plurality of dielectric coaxial resonators of 1/4 λ type having variable capacitors. An antenna sharing apparatus according to claim 1, wherein each of said switching means comprises relays. An antenna sharing apparatus according to claim 3, wherein each said filter comprises a connection of a plurality of dielectric coaxial resonators of 1/4 λ type, said resonators respectively connected to a capacitor and a varactor diode, thereby changing resonant frequency of said filter by a change in capacitance of said diode. An antenna sharing apparatus according to claim 3, wherein each said filter comprises a connection of a plurality of dielectric coaxial resonators of 1/4 λ type, said resonators respectively connected to a capacitor and a PIN diode, thereby changing resonant frequency of said filter by switching of said diode.

Inventors: MIYAKE HIDEYUKI, NAGATA TAKASHI, NAKAMURA TOSHIAKI, TAKIMOTO NOBUHIRO, MIYAKE, HIDEYUKI, NAGATA, TAKASHI, NAKAMURA, TOSHIAKI, TAKIMOTO, NOBUHIRO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1987
Main classification: H01P1
IPC codes: H04B1, H01P1