A microwave oscillation circuit and a down converter using the same

Abstract: An object of the invention is to eliminate a special pre-treatment for adhering a dielectric resonator to a dielectric substrate and to heighten the production efficiency, to lower the cost, to enable the setting of the degree of coupling defined by the distance between a micro strip line and the dielectric resonator free, and to provide a microwave oscillation circuit which is economical in cost and high in reliability and a down converter containing the microwave oscillation circuit. One end of a micro strip line is connected to the gate terminal of FET for microwave oscillation mounted on a dielectric substrate which is surely contacting with a metal plate and the other end of the micro strip line is grounded to said metal plate via a terminal resistor. A dielectric resonator is secured on the inner wall of a shield case covering upper portion of the said dielectric substrate by using an ordinary adhesive to couple it with the micro strip line in order to obtain a desired oscillation frequency output from the source terminal of FET.

Description: FIELD OF THE INVENTION The present invention relates to microwave oscillation circuits used in down converters of satellite broadcast and satellite communication and to down converters using the circuit. BACKGROUND OF THE INVENTION Recently, satellite broadcasts have become widespread and CS broadcasts utilizing a communication satellite have started. So chances receiving a plurality of satellites directly at a home are increasing. Accordingly, compactness and low cost of receiving antennas incorporating a down converter have been demanded. Hereafter, a conventional microwave oscillation circuit used in a down converter of satellite broadcast and satellite communication will be illustrated referring to drawings. Fig. 1(a) is an exploded perspective view showing the structure of a conventional microwave oscillation circuit, Fig. 1(b) is the A-B section thereof. In Fig. 1(a) and Fig. 1(b), on metal plate 8, dielectric substrate 2 made of fluoride resin such as poly fluoride ethylene is disposed with its back surface securely contacted with metal plate 8. On the upper surface of dielectric substrate 2, field effect transistor (hereafter FET) 3 for microwave oscillation such as a metal semiconductor field effect transistor (hereafter MESFET) or a high electron mobility transistor (hereafter HEMT) is mounted. Also open stub 4, micro strip line 5, and the gate terminal 3g, drain terminal 3d, and source terminal 12 of FET 3 are formed on dielectric substrate 2. Open stub 4 is connected with drain terminal 3d of FET 3. One end of micro strip line 5 is connected with gate terminal 3g of FET 3, the other end of micro strip line 5 is grounded via terminal resistor 6 and through hole 7 to metal plate 8. Oscillation output of FET 3 is output from source terminal 12. Dielectric resonator 11 having a band rejection characteristic is secured by an adhesive via spacer 10 made of insulating material such as ceramics at the position escaping micro strip line 5 on dielectric substrate 2. The space above dielectric substrate 2 is covered with shield case 1 made of metal such as aluminum die casting and shield case 1 is grounded to metal plate 8. Said circuit portion is electrostatically shielded by shield case 1 and metal plate 8. A female screw thread, in the following also designated "female screw" is provided in shield case 1, and screw 9 for fine adjusting of oscillation frequency is screwed therein, screw 9 is closely opposing to dielectric resonator 11. The operation of the microwave oscillation circuit constituted as described above will be illustrated referring to Fig. 1(a) and Fig.1(b). Drain terminal 3d of FET 3 for microwave oscillation mounted on dielectric substrate 2 is grounded in terms of high frequency by open stub 4. By connecting micro strip line 3 whose one end is connected with gate terminal 3g and the other end is grounded to metal plate 8 via terminal resistor 6 and through hole 7 and dielectric resonator 11 having a band rejection characteristic, FET 5 oscillates and a stable oscillation frequency output is obtained from source terminal 12 of FET 3 for microwave oscillation. By rotating screw 9 provided at shield case 1 to change the distance to dielectric resonator 11, the oscillation frequency can be finely adjusted. However, as for the conventional structure, fluoride resin such as poly fluoride ethylene showing a small high frequency loss is often used as a material of dielectric substrate 2 of an oscillation circuit used in a microwave band especially 10 GHz band. Special pre-treatment of adhering surface of the fluoride resin such as poly fluoride ethylene by using a chemical such as metal sodium is needed to adhere ceramic spacer 10 onto dielectric substrate 2, and ordinary adhesives can't give sufficient adhesive strength, so, good production efficiency and low cost cannot be obtained. Also, due to the limit of physical dimension between micro strip line 5 and spacer 10, that is, spacer 10 has to be kept away from micro strip line 5, so that the center of dielectric resonator 11 is kept away by the radius of spacer 10 from micro strip line 5. Accordingly, degree of coupling which is an important factor defining stability of the oscillation and the oscillation output and defined by the distance between micro strip line 5 and dielectric resonator 11 cannot be set freely. US-A-4,435,688 discloses a microwave oscillator circuit with an FET, a dielectric resonator and a micro-strip line which has a capacitive reactance element connected between the source terminal of the FET and either its drain terminal or ground. Fluctuation in the oscillation frequency due to external conditions are reduced. In US-A-4,618,836 a microwave dielectric oscillator module is provided with a removable temperature compensated dielectric resonator channel element. The removable element cooperates with an electrically shielded housing and microstrip of stripline technology couples energy from the oscillator to the rest of the circuitry. EP-A-0638818 describes dielectric-based oscillators in which the oscillator output is down-converted to an intermediate frequency. SUMMARY OF THE INVENTION The present invention provides a microwave oscillation circuit comprising: a metal plate; a dielectric substrate whose back surface is surely contacting with said metal plate; a shield case for shielding the circuit on the said dielectric substrate; and a dielectric resonator secured by an adhesive on the inner wall of said shield case; characterized by further comprising: a FET for microwave oscillation mounted on said dielectric substrate whose drain terminal is grounded in terms of high frequency by an open stub; and a micro strip line provided on said dielectric substrate whose one end is connected with gate terminal of said FET for microwave oscillation and the other end is grounded to said metal plate via a terminal resistor; wherein said dielectric resonator has a band rejection characteristic and said micro strip line on said dielectric substrate and said dielectric resonator are coupled and an oscillation frequency output is obtained from the source terminal of said FET for microwave oscillation; the circuit further comprising a screw engaging with a female screw thread of said metal plate and penetrating said dielectric substrate for finely adjusting the oscillation frequency by changing the distance between said screw and said dielectric resonator. Preferably, the dielectric resonator is secured on the inner wall opposing against said dielectric substrate via a spacer by an adhesive. The invention thus is able to eliminate the special pre-treatment for adhering a spacer for supporting a dielectric resonator onto a dielectric substrate to enhance the production efficiency and reduce the cost. Also, the degree of coupling may be freely set by the distance between micro strip line 5 and dielectric resonator 11. And a microwave oscillation circuit and a down converter incorporating the microwave oscillation circuit which are low in the cost and high in the reliability will be offered. A down converter of the invention employs a microwave oscillation circuit constituted as described above, and the oscillation frequency output from the source terminal of the FET for microwave oscillation in said microwave oscillation circuit is passed through a band pass filter to output as a local oscillation frequency output. The local oscillation frequency output is mixed with an input signal at a diode for converting frequency so that the input signal is converted to an intermediate frequency. As for the present invention, a dielectric resonator to be coupled with a micro strip line is secured on a shield case through a spacer through the above structure. Therefore, a special pre-treatment is not needed different from the conventional method in which a spacer is fixed on a dielectric substrate such as polyfluoride etylene. The spacer can be fixed using an ordinary adhesive (such as an epoxy adhesive). Accordingly a microwave oscillation circuit and a down converter for receiving satellite waves of high productivity, low cost, and high reliability can be realized. Moreover, as the dielectric resonator can be set at an arbitrary position above the micro strip line, a desired degree of coupling can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1(a) is an exploded perspective view showing the structure of a conventional microwave oscillation circuit. Fig. 1(b) is the A - B section thereof. Fig. 2(a) is a plane view showing the structure of a microwave oscillation circuit of an embodiment of the invention. Fig. 2(b) is the A - B section thereof. Fig. 3 is a block diagram of a down converter employing a microwave oscillation circuit of the invention. EMBODIMENTS OF THE INVENTION Fig. 2(a) is a plane view showing the structure of a microwave oscillation circuit of an embodiment of the invention. Fig. 2(b) is the A - B section thereof. The same members as in the conventional example in Fig. 1 are attached with the same numbers. In Fig. 2(a) and Fig. 2(b), on metal plate 8, dielectric substrate 2 made of fluoride resin such as poly fluoride ethylene is disposed with its back surface securely contacted with metal plate 8. On the upper surface of dielectric substrate 2, FET 3 for microwave oscillation such as MESFET or HEMT is mounted. Also open stub 4, micro strip line 5, and the gate terminal 3g, drain terminal 3d, and source terminal 12 of FET 3 are formed on the upper surface of dielectric substrate 2. Open stub 4 is connected to drain terminal 3d of FET 3. One end of micro strip line 5 is connected with gate terminal 3g of FET 3, the other end of micro strip line 5 is grounded via terminal resistor 6 and through hole 7 to metal plate 8. Oscillation output of FET 3 is output from source terminal 12. The space above dielectric substrate 2 is covered with shield case 1 made of metal such as aluminum die casting and shield case 1 is grounded to metal plate 8. Said circuit portion is electrostatically shielded by shield case 1 and metal plate 8. The portions different from the conventional example in Fig. 1 are as follows. Dielectric resonator 11 having a band rejection characteristic is secured by an ordinary adhesive which needs no special pre-treatment (for example an epoxy system resin material) via spacer 10 at the position on the inner wall opposing dielectric substrate 2. Screw 9 for fine adjusting of oscillation frequency is disposed metal plate 8 side. Screw 9 engages with a female screw provided at metal plate 8 penetrating dielectric substrate 2 and opposing against dielectric resonator 11. Screw 9 can thus vary the distance to dielectric resonator 11. The operation of a microwave oscillation circuit constituted as described above will be illustrated referring to Fig. 2. Coupling dielectric resonator 11 and micro strip line 5 and rotating screw 9 to vary the distance between the screw and dielectric resonator 11, fine adjusting of an oscillation frequency is performed and a stable oscillation frequency output can be obtained from the source terminal 12 of FET 3 for microwave oscillation. As for the embodiment, a dielectric resonator to be coupled with a microwave strip line provided on a dielectric substrate in the prior art is provided on a shield case side. Therefor, when it is secured via a spacer, there is no need for a special pre-treatment as seen in the conventional example in which the dielectric resonator is secured on a dielectric substrate made of fluoride resin such as poly fluoride ethylene. Accordingly, very high productivity, low cost, and high reliability of the microwave oscillation circuit can be realized. Moreover, as the dielectric resonator is secured to a shield case, there is no need for escaping it from the micro strip line as seen in the conventional example, and it can be set at an arbitrary position above the micro strip line, so that a desired degree of coupling can be obtained. Here, in the embodiment, spacer 10 and dielectric resonator 11 are described as they are provided on a inner wall of shield case 1 opposing against dielectric substrate 2 though, it is needless to say that the similar effect can be obtained by providing them on the side wall of the shield case. Fig. 3 shows a circuit configuration of a down converter in an embodiment of the invention. Marks of the members of said microwave oscillation circuit surrounded by the broken line (a) in Fig. 3 are corresponding to those of said Fig. 2(a). The down converter surrounded by the broken line (b) in Fig. 3 is, for example, a down converter for receiving satellite waves. In Fig. 3, 13 is a microwave signal input circuit, 14 and 15 are low noise amplifiers, 16 is a band pass filter, 17 is diode for frequency conversion, 18 is a low pass filter, 19 and 20 are intermediate frequency amplifiers, 21 is an intermediate frequency signal output terminal. The operation of a down converter for receiving a satellite wave of the invention will be illustrated referring to Fig. 3. The operation of microwave oscillation circuit (a) is the same as illustrated in Fig. 2, and a stable local oscillation frequency output (for example 11.2 GHz) is obtained. The local oscillation frequency output is applied to diode 17 for frequency conversion through band pass filter 16. On the other hand, a signal of 12 GHz band (for example 11.75 GHz - 12.75 GHz) input to microwave signal input circuit 13 is amplified by low noise amplifiers 14 and 15 and mixed with the local oscillation frequency output at diode 17 for frequency conversion to be converted to an intermediate frequency of 1 GHz band. The signal converted to the intermediate frequency of 1 GHz band is passed through low pass filter 18 and amplified to a desired level by intermediate frequency amplifiers 19 and 20 and output from intermediate frequency signal output terminal 21. These numerics used in the embodiments are examples, and are not intended limits of the invention. As illustrated above, according to the invention, a dielectric resonator to be coupled with a micro strip line connected to the gate terminal of FET for microwave oscillation provided on a dielectric substrate is secured on a shield case opposing against the dielectric substrate through a spacer by adhering. Therefore, there is no need for a special pre-treatment for adhering a dielectric resonator to a dielectric substrate through a spacer as in the prior art, and ordinary adhesives can be used for that. Thus the problems of the productivity and the cost can be solved, and the degree of coupling defined by the distance between the micro strip line and the dielectric resonator can be set freely. A microwave oscillation circuit which is low in cost and high in reliability and a down converter equipped with this microwave resonator can be realized.

Claims: A microwave oscillation circuit comprising: a metal plate (8); a dielectric substrate (2) whose back surface is surely contacting with said metal plate; a shield case (1) for shielding the circuit on the said dielectric substrate; and a dielectric resonator (11) secured by an adhesive on the inner wall of said shield case; characterized by further comprising: a FET (3) for microwave oscillation mounted on said dielectric substrate whose drain terminal (3d) is grounded in terms of high frequency by an open stub (4); and a micro strip line (5) provided on said dielectric substrate whose one end is connected with gate terminal (3g) of said FET for microwave oscillation and the other end is grounded to said metal plate via a terminal resistor; wherein said dielectric resonator has a band rejection characteristic and said micro strip line on said dielectric substrate and said dielectric resonator are coupled and an oscillation frequency output is obtained from the source terminal (12) of said FET (3) for microwave oscillation; the circuit further comprising a screw (9) engaging with a female screw thread of said metal plate (18) and penetrating said dielectric substrate (2) for finely adjusting the oscillation frequency by changing the distance between said screw and said dielectric resonator (11). The microwave oscillation circuit of claim 1, wherein said dielectric resonator is secured on the inner wall opposing against said dielectric substrate via a spacer (10) by an adhesive. A down converter wherein an oscillation frequency output from the source terminal (12) of FET (3) for microwave oscillation of the microwave oscillation circuit of claim 1 or 2 is output through a band pass filter (16) as a local oscillation frequency output and the output is mixed with an input signal at a diode (17) for frequency conversion to convert the input signal to an intermediate frequency.

Inventors: KASHIMA YUKIRO, MORINO TAKAYOSHI, KASHIMA, YUKIRO, MORINO, TAKAYOSHI, Morino, Takayoshi, 411 Goody Tsunashima,
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1996
Main classification: H03B5
IPC codes: H01P7, H03B5, H03B1, H03D9