JPS6327450Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to an improvement of a resonant frequency fine adjuster of a cavity resonator used mainly in the microwave band. A cavity resonator is a tuning circuit mainly used in the microwave band, and usually consists of a cylindrical or hexagonal cubic metal outer shell 1 with both ends covered, as shown in FIG. It consists of a resonant rod 2 in the center with one end 21 fixed and supported on the bottom surface 3 of the outer circumferential case, and an extremely high Q value can be obtained as a resonant circuit. Since it is determined from the outer diameter dimension, it is practically used in the microwave band where the volume size can be small. In order to finely adjust the resonant frequency of the completed cavity resonator to the desired value, it is best to make the resonant rod longer than the calculated value in advance, and then cut the length until it matches the desired frequency. Since this requires a lot of time and effort and is difficult to adjust after completion, a movable capacitor electrode 5 is provided facing the resonant rod tip surface 22 from the top surface 4 of the outer circumferential device for fine frequency adjustment, and the opposing spacing between 5 and 22 is adjusted. Measures are being taken to change the However, recently, in connection with automobile control operations, it is necessary to electronically change the resonant frequency according to changes in control voltage, and in LC tuning circuits used for frequencies below the VHF band, part of the tuning capacitance is controlled by voltage. If you replace it with a variable capacitance diode (hereinafter referred to as a varactor diode) and apply a bias voltage opposite to the conduction direction of the diode, you can control the frequency by voltage by utilizing the fact that the capacitance between the electrodes of the diode changes depending on the applied voltage value. Therefore, it is theoretically possible to control the resonant frequency of the cavity resonator shown in Fig. 1 by inserting a varactor diode between the upper surface 4 of the outer circumferential element and the resonant rod end surface 22. For a varactor diode suitable for this purpose, the capacitance and amount of change may be extremely small, but it is necessary to have an extremely high Q in the microwave band, and even if such a diode could be made, its uses would be limited. Naturally, it is extremely expensive. As illustrated in FIG.
A cylinder trimmer 50 is held by a mounting bracket 51 inside the center of the outer upper surface 4 toward the other end surface 22 of the resonance rod 2 that is fixedly supported. One end of the insulator 52 is fixed to a metal fitting 51, and a metal piston 53 is movably held in its internal cavity by screwing a rod screw 54 supporting it into a threaded hole provided in the center of the metal fitting 51. . A metal external electrode 55 is provided in a ring shape on the outer surface of the cylinder 52 facing the piston 53, a small capacitor is formed between the piston and the external electrode, and a rod screw 54 supporting the piston is rotated. Accordingly, the piston 53 can move back and forth to change the area facing the external electrode 55, thereby changing the capacitance between the two electrodes. The above structure is called a piston trimmer capacitor and is often used in tuners of television receivers, etc., but in the frequency fine adjuster of the present invention, as shown in detail in Fig. 3, the above structure is The length of the cylindrical insulator 52 is extended, an independent electrode 56 is provided at the end, and a varactor is connected between the electrode 55 and the cylindrical insulator 52.
A diode is installed, and a bias voltage for capacitance control is applied to the electrodes 55 and 56 from the outside of the cavity resonator through high-frequency choke coils 7A and 7B. The electrode 56 is the connection part of the varactor diode 6 and the end face 2 of the resonant rod 2.
In order to form a capacitance between the cylinder 52 and the cylinder 52, the electrode 56 not only covers the end face of the cylinder 52, but also has an electrode shape larger than the outer diameter of the cylinder 52 if necessary. Next, the features of the present invention will be explained in comparison with other cavity resonator frequency fine adjustment methods. FIG. 4A is a simplified electrical equivalent circuit of the structure shown in _FIG . Since a resonant circuit is formed with the inductance of the outer circumference, the frequency can be changed by changing the capacitance of C _V. Since this C _V is an air capacitor with air as an insulator, Q is large. Electrode 5
A sufficient fine adjustment range can be obtained by increasing the movable range of . Figure 4B shows a configuration in which a varactor diode C _V is used instead of C _V , and the resonant frequency is finely adjusted electronically by changing the bias voltage applied to it. Generally, it is difficult to obtain, and even if it is available, it is expensive. Furthermore, since variations in the characteristics of the individual varactors and diodes used have a large effect on the resonant frequency, it cannot be applied to the current situation where large quantities of microwave band equipment are produced in factories. In the frequency fine adjustment of the present invention, in FIG. 4C, the capacitance C ₁ between the piston 53 and the external electrode 55 and the capacitance C ₂ of the varactor diode 6
and the capacitance C ₃ between the electrode 56 and the resonant rod tip surface 22 are connected in series, and the resonance frequency can be determined electronically by changing the bias voltage applied to the varactor diode 55. Furthermore, by mechanically changing the stopping position of the piston, C ₁
Since it operates as a semi-fixed capacitor, it has the effect that it is extremely easy to correct variations in the varactor diode and to make the fine adjustment range of the resonant frequency of the cavity resonator the same. Also, C ₁ and C ₂ are connected in series to the varactor diode forming C ₂ , so in order to have the same variable range as C _V in Figure 4B, C ₂ naturally has a minimum capacitance compared to C _V.・
Both capacitance change ranges must be large. In a practical cavity resonator structure, C ₁ is 1 to several pF,
Since C ₂ is 1 to several tens of pF and C ₃ is about 1 pF or less,
As C ₂ , varactor diodes for VHF and UHF bands, which are widely used in tuners of television receivers, etc., can be used, and these have the advantage of being extremely inexpensive and easily available. Q because the frequency used becomes higher
The problem with the decrease in Q is a small capacitance with a high Q (especially
Another advantage of the fine adjuster of the present invention is that the effective Q of the circuit is several tens _to hundreds of times as large as the Q value of _C2 . The cylindrical insulator 52 forming C ₁ is made of high-insulating, low-loss materials such as high-frequency porcelain, glass, and Teflon, but some porcelain and glass have different temperature coefficients of dielectric constant depending on their composition. Therefore, the selection has the effect of improving the temperature characteristics of the resonance frequency of the cavity resonator. In the above, the present invention was explained exclusively as a frequency fine tuner for a cavity resonator in the microwave band, but the structure in which the resonant rod 2 in Fig. 2 is replaced with a helical coil is a helical resonance device used in the VHF/UHF band. Since the frequency fine adjuster shown in FIG. 3 exhibits exactly the same functions and effects, the present invention is similarly applicable to helical resonators.

[Brief explanation of drawings]

Fig. 1 is an example of a structure of a conventional cavity resonator, Fig. 2 is an example of a structure of a cavity resonator with a frequency fine adjuster of the present invention, and Fig. 3 is an example of a structure of a cavity resonator of the present invention with a frequency fine adjuster. FIG. 4 is a simplified electrical equivalent circuit diagram. 1 ...Cavity resonator outer casing, 2...Resonance rod, 3...
...Bottom surface of the circumferential device, 4...Top surface of the circumferential device, 5...Moveable capacitance electrode, 6...Varactor diode, 7A, 7
B...High frequency chiyoke, 50 ...Frequency fine adjuster, 51...Mounting bracket, 52...External electrode, 53
...Metal piston, 54...Bar screw, 55...
Cylindrical insulator, 56...electrode.

Claims (1)

[Scope of utility model registration request] A type of cavity that finely adjusts the resonance wave number by changing the capacitance between the upper end surface of a resonant rod supported at the center of a metal outer shell with one end fixed to the bottom of the outer shell and the upper surface of the outer shell. In the resonator, a cylindrical trimmer capacitor is attached to the upper surface of the outer circumference as a fine adjustment capacitor, an electrode is provided on the end face of the trimmer capacitor opposite to the resonance rod, and a varactor is connected between the electrode and the original external electrode of the trimmer capacitor. A frequency fine tuner for a cavity resonator that can finely adjust the resonant frequency by connecting a diode and changing the bias voltage applied to it.