JP2006121463A - Band-pass filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a band-pass filter which can dispense with external circuit for impressing a magnetic field, and is capable of varying its center frequency without changing the passband width, can be miniaturized as a filter for high frequencies, and is capable of compensating the temperature characteristics of a waveguide. <P>SOLUTION: A dielectric 14 is loaded on at least one location on rectangular waveguides 11, 12 in parallel to their H planes, and the length of the waveguide 11, 12 in the direction of the H planes is made to change electrically to realize a band-pass filter whose pass band width is fixed and the center frequency is variable. As the center frequency, an arbitrary frequency can be selected by selecting a thickness tFreq and a dielectric constant εr of the dielectric 14. Moreover, temperature compensation of the band-pass filter can be performed, by loading a dielectric having a dielectric constant temperature characteristics that is reverse to that of the waveguide 11, 12 in parallel with the H planes, on at least one place. Variations in temperature can be made very small, and its center frequency can also be made variable, without changing the pass-band width by combination of the two dielectrics. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a band-pass filter, and more particularly to a high-frequency band-pass filter in which a rectangular waveguide and a dielectric are combined.

  In general, in a waveguide bandpass filter using an E-plane parallel metal plate that is not loaded with a dielectric material, in order to change the center frequency, the metal plate constituting the filter must be replaced with another metal plate. The reason is that the shape of the metal plates arranged in a ladder shape (plate thickness, metal fin width / interval) constitutes a coupling coefficient necessary for the band-pass filter. Therefore, in order to change the center frequency and the pass bandwidth, it is necessary to design a new metal plate.

  In addition, as a bandpass filter capable of changing the center frequency, for example, Patent Document 1 proposes a filter that can quickly switch the center frequency by disposing a magnetic circuit outside and providing ferrite in the waveguide. Has been.

  As shown in FIG. 7, this band-pass filter is an azil-type band-pass filter 3 having a ferrite resonator 18, and changes a center frequency by changing an applied magnetic field by a magnetic circuit arranged outside. ing. This magnetic field is generated by an external magnetic circuit. A magnetic field is generated coaxially with the ferrite bar 18 between the two magnetic pole members 22 and 23 of the electromagnet 21 including the soft iron magnetic circuit 19 and the excitation coil 20 through which the adjustable DC current flows. By changing the excitation current flowing through the coil 20, the value of the magnetic field H changes. As a result, the resonance frequency of the ferrite bar 18 changes, and the center frequency of the bandpass filter 3 changes.

JP-A-5-37202

  However, the band-pass filter 3 described in Patent Document 1 has an advantage that the center frequency can be changed with the filter connected, but an external circuit needs to be provided to apply a magnetic field. For this reason, there is a problem that the entire circuit becomes large and it is difficult to reduce the size when handling the high-frequency filter.

  Therefore, the present invention has been made in view of the problems in the conventional bandpass filter described above, and does not require an external circuit for applying a magnetic field, and changes the center frequency without changing the passband width. An object of the present invention is to provide a band-pass filter that can be miniaturized for high frequency use.

  In general, a waveguide formed of a metal such as aluminum or brass expands when the temperature decreases and expands when the temperature increases. That is, when the temperature decreases, the resonator constituting the band pass filter becomes smaller and the resonance frequency shifts to a higher side. Conversely, when the temperature is lowered, the resonator becomes larger and the resonance frequency shifts to a lower side. As described above, there is a problem that the center frequency (passband) changes when the temperature changes.

  Accordingly, an object of the present invention is to provide a bandpass filter capable of compensating for the temperature characteristics of a waveguide in addition to the above object.

  In order to achieve the above object, the present invention is a bandpass filter, which is parallel to at least one side of a metal plate provided in parallel to the E-plane of the waveguide and an H-plane located on the top, bottom, left and right of the metal plate And a plate-like dielectric having a relative dielectric constant of 1.0 or more.

  According to the present invention, by changing the thickness, height, and relative dielectric constant of the plate-like dielectric, the center frequency can be made variable without changing the passband width. It is possible to provide a band-pass filter that does not require an external circuit for application and can be miniaturized for high frequency use.

  In the band pass filter, the dielectric may be configured to have a negative temperature characteristic with respect to a relative dielectric constant. Here, the negative relative dielectric constant temperature characteristic means a characteristic that the relative dielectric constant increases as the temperature decreases. For example, PTFE or the like is a dielectric having negative dielectric constant temperature characteristics. Aluminum and copper used for the waveguide and these dielectrics have temperature characteristics opposite to each other in configuring the waveguide filter. This makes it possible to compensate for frequency fluctuations due to changes in the temperature of the material constituting the waveguide filter.

  A band-pass filter including a plate-like dielectric having negative temperature characteristics with respect to the dielectric constant, and a plate-like second dielectric having a dielectric constant of 1.0 or more parallel to at least one side of the H surface. It can be configured to include a body. As a result, it is possible to provide a bandpass filter having a very small temperature variation and a variable center frequency without changing the passband width.

  The bandpass filter can be configured by dividing the waveguide into two at the center of the H plane and sandwiching the metal plate by the divided waveguide.

  The band pass filter may be a plate-like dielectric having a relative dielectric constant of 1.0 or more or a relative dielectric constant of 1.0 or more parallel to one side of one H surface of the two-divided waveguide. And it can comprise so that the plate-shaped dielectric material which has a negative temperature characteristic regarding a relative dielectric constant may be provided.

  Further, the bandpass filter is formed in a plate-like shape having a relative dielectric constant of 1.0 or more and a negative temperature characteristic with respect to the relative dielectric constant in parallel with one side of the H surface of the two-divided waveguide. And a plate-like dielectric having a relative dielectric constant of 1.0 or more parallel to one side of the other H surface of the two-divided waveguide.

  As described above, according to the present invention, there is no need for an external circuit for applying a magnetic field, the center frequency can be changed with almost no change in the pass bandwidth, and the size can be reduced for high frequency use. A bandpass filter capable of compensating for the temperature characteristics of the wave tube can be provided.

  1 to 3 show a first embodiment of a band-pass filter according to the present invention. This band-pass filter 1 divides a waveguide 11 and 12 into two at the center of the H plane and at a predetermined frequency. A metal plate 13 designed to have a pass band is sandwiched, and a dielectric 14 parallel to the H plane is disposed in the waveguide 11.

  As for the dimensions of the waveguides 11 and 12, the lengths of the wide surface (H surface) and the narrow surface (E surface) are a and b, respectively, and the dielectric 14 has a width h as a length parallel to the H surface. The thickness tFreq and the length in the propagation direction may be the length from the first stage to the last stage of the metal plate 13 constituting the filter (see FIG. 3) or more.

  Next, the operation of the bandpass filter 1 having the above configuration will be described with reference to FIGS.

  First, an example of the frequency shift operation is shown. Since the bandpass filter 1 uses the TE10s mode (s = 1, 2, 3,...), The resonance frequency is determined by the length of the H plane and the propagation direction. Therefore, by loading a plate-like dielectric 14 parallel to the H plane, the electrical length in the H plane direction can be varied, and the resonance frequency is controlled.

  Specific examples are shown below. Consider a 5-stage E-plane filter using a 13 GHz waveguide. As shown in FIGS. 1 and 2, a dielectric 14 (relative dielectric constant 2.6) is loaded parallel to the H plane. Since the dielectric 14 is for frequency shift, the relative permittivity εr may be 1.0 or more. By making the thickness tFreq of the dielectric 14 variable, it is possible to change the center frequency while keeping the width of the pass band constant as shown in FIG. In the figure, there are shown a case where there is no dielectric and a case where the thickness of the dielectric is changed to 10% and 30%.

  Loading the dielectric 14 has an effect of equivalently increasing the length of the wide surface (H surface) of the waveguide. By increasing the thickness of the dielectric 14, as described above, the filter The resonance frequency of shifts to the lower side. Here, since the relationship between the length of the wide surface and the coupling coefficient of the filter when the resonance frequency changes is almost unchanged, the center frequency can be changed while the passband width is kept constant.

  The effect of loading the dielectric 14 is to increase the wide surface equivalently. Therefore, only a transition to a lower frequency is possible. In order to design a bandpass filter that can be adjusted to a higher frequency side, a bandpass filter whose center frequency is designed in advance with the dielectric 14 loaded is used, and the thickness tFreq and length h of the loaded dielectric 14 are set. Should be reduced.

  Next, the installation place of the dielectric 14 for changing the center frequency will be described. When the dielectric 14 is placed at the end of the E plane, there is almost no TE10s mode at the end of the E plane, so there is no effect. In addition, when installed parallel to the E plane and close to the metal plate 13, the electric field concentrates, so that the amount of change in the center frequency increases, but the dimension (thickness, etc.) Since it becomes very sensitive to the dielectric constant, it is difficult to reproduce from the viewpoint of dimensional accuracy and is not realistic.

  In view of the above points, loading the dielectric 14 parallel to the H-plane is convenient from the viewpoint of frequency adjustment sensitivity. Specifically, in FIG. 5, the amount of change is about 26 MHz per 1.0% of the normalized thickness of the dielectric 14, and realistic dimensional accuracy is obtained.

  Next, as a second embodiment of the bandpass filter according to the present invention, a case where frequency shift and temperature compensation are performed simultaneously will be described with reference to FIG.

  In this band pass filter 2, the dielectrics 15 and 16 may be loaded on any of the upper, lower, left and right surfaces as long as they are parallel to the H surface. The dielectric 15 used for frequency shift and the dielectric 16 used for temperature compensation are used in the same configuration, but their design and effects can be separated.

  The frequency shift dielectric 15 functions to shift the center frequency to the lower side by loading a filter designed at a predetermined frequency. As described above, the amount of change in the frequency is as follows. The thickness tFreq can be adjusted. The bandpass filter having a temperature compensation function functions to compensate for temperature fluctuations at a predetermined center frequency by designing a filter loaded with a temperature compensation dielectric 16 having a thickness tTemp in advance. . The temperature compensating dielectric 16 must have a negative relative dielectric constant temperature characteristic.

  Even if the frequency shift dielectric 15 has a negative dielectric constant temperature characteristic, it functions in a direction to compensate for frequency fluctuations due to temperature at that time.

  For example, since the aluminum contracts when cooled, the diameter of the waveguide becomes small. That is, the resonator constituting the band pass filter becomes smaller, and the resonance frequency shifts to a higher side. On the other hand, when the loaded dielectric 15 is cooled, the relative permittivity increases, so that the electrical length in the H-plane direction of the waveguide can suppress temperature fluctuations small by adding the effects of aluminum and the dielectric. it can. Therefore, by selecting a combination of a material used for the waveguide and a material used for the dielectric, frequency fluctuation due to temperature can be suppressed to a small level. The effect of the dielectric 15 can be adjusted by adjusting the thickness tFreq and the length h in the H-plane direction.

  For example, as shown in FIG. 6, the temperature characteristic when a dielectric with a normalized thickness of 30% shown in FIG. 5 is loaded is the same as the frequency fluctuation when the normalized thickness of the loaded dielectric is 30%. Become. That is, by loading a dielectric with a standardized thickness of 30%, a temperature compensation of about 14 MHz (38%) is realized with a frequency shift of 820 MHz.

It is a disassembled perspective view which shows 1st Embodiment of the bandpass filter concerning this invention. It is sectional drawing which looked at the bandpass filter of FIG. 1 from the front. It is sectional drawing which looked at the bandpass filter of FIG. 1 from the side surface (upper side). It is sectional drawing which looked at 2nd Embodiment of the bandpass filter concerning this invention from the front. It is an actual measurement graph which shows the pass characteristic at the time of loading the dielectric material of the band pass filter similar to the structure of 1st Embodiment of the band pass filter concerning this invention. It is the measurement graph which showed the frequency fluctuation characteristic with respect to the temperature change at the time of loading the dielectric material ((epsilon) r = 2.6) of the bandpass filter similar to the structure of 2nd Embodiment of the bandpass filter concerning this invention. It is a schematic external view which shows an example of the conventional band pass filter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bandpass filter 2 Bandpass filter 3 Bandpass filter 11 Waveguide 12 Waveguide 13 Metal plate 14 Dielectric 15 Frequency shift dielectric 16 Temperature compensation dielectric 17 Coaxial cable 18 Ferrite bar 19 Soft iron magnetism Circuit 20 Coil 21 Electromagnet 22 Magnetic pole member 23 Magnetic pole member 24 Waveguide 25 Coaxial antenna 26 Metal end plate 27 Coaxial cable 28 Coaxial antenna 29 Metal end plate

Claims (6)

A metal plate provided parallel to the E-plane of the waveguide;
A band-pass filter comprising: a plate-like dielectric having a relative dielectric constant of 1.0 or more, provided in parallel to at least one side of an H surface located on the top, bottom, left, and right of the metal plate.   The bandpass filter according to claim 1, wherein the dielectric has a negative temperature characteristic with respect to a relative dielectric constant.   The band pass filter according to claim 2, further comprising a plate-like second dielectric material having a relative dielectric constant of 1.0 or more provided in parallel with at least one side of the H-plane.   4. The bandpass filter according to claim 1, wherein the waveguide is divided into two at the center of the H plane, and the metal plate is sandwiched between the divided waveguides. 5.   The plate-like dielectric having a relative dielectric constant of 1.0 or more or the relative dielectric constant of 1.0 or more and a negative relative dielectric constant in parallel with one side of one H surface of the two-divided waveguide. The band-pass filter according to claim 4, further comprising a plate-like dielectric having a temperature characteristic of: A plate-like dielectric having a relative dielectric constant of 1.0 or more and having a negative temperature characteristic with respect to the relative dielectric constant, parallel to one side of one H surface of the two-divided waveguide,
5. The bandpass filter according to claim 4, further comprising a plate-like dielectric having a relative dielectric constant of 1.0 or more parallel to one side of the other H-plane of the two divided waveguides.

Images