JP2007088545A - Tunable filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive tunable filter which can regulate the central frequency electrically through a simple arrangement and can be mounted on an apparatus easily. <P>SOLUTION: The tunable filter comprises rectangular waveguides 11 and 12 divided into two, a three layer substrate 13 held between the rectangular waveguides divided into two and provided with resonators 203-205, and active elements 304-306 mounted in the resonators wherein the central frequency and/or the bandwidth is regulated by applying a bias voltage to the active elements from the outside of the three layer substrate through the line pattern of the inner layer of the three layer substrate. The line pattern of the inner layer of the three layer substrate can be utilized as a line for applying a bias voltage and a varactor diode can be employed as the active element. A low-pass filter for attenuating a high frequency signal and preventing leak of a signal to the outside can be provided in the line for applying a bias voltage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a tunable filter, and more particularly to a filter that electrically adjusts a center frequency and a bandwidth using an active element.

  As a method for adjusting the center frequency and bandwidth of the rectangular waveguide filter, manual adjustment methods such as inserting an adjustment screw in the cavity resonator or physically changing the size of the cavity resonator are generally used. Is. On the other hand, a method of adjusting a filter mechanically or electrically is known.

  As a mechanical adjustment method, there is a method of controlling the insertion amount of the adjustment screw using a motor. As an electrical adjustment method, there is a method of adjusting by external voltage control using a variable capacitor such as a varactor diode. For example, Patent Document 1 proposes a tunable filter configured by mounting a plurality of voltage-controlled ferroelectric varactors on a fin line waveguide.

  The tunable filter is grounded by contact with the waveguide and is insulated from the waveguide between the two plates, a foil-like copper plate having two short-circuited fin-line resonators, and a bias voltage. A foil-like copper plate for applying a voltage is arranged in the center of the waveguide in parallel with the E plane, and a ferroelectric varactor is mounted between the insulating plate and the ground plate arranged on both sides thereof. .

JP 2002-528899 A (FIGS. 9 and 10)

  However, in order to manually adjust the filter, such as by inserting an adjustment screw into the cavity resonator, advanced know-how is required, and the work time and labor cost required for the adjustment increase, and in response to the demand for cost reduction. There was a limit.

  Further, when mechanical adjustment using a motor is performed, the scale of the apparatus becomes large and the configuration of the apparatus becomes complicated. Moreover, in order to perform machine control, electrical control from the outside is required, which is not a realistic method.

  From the above, an electrical adjustment method using an active element is most desired. However, the tunable filter described in the patent publication has the following problems. That is, in order to construct a ferroelectric varactor, materials having a high dielectric constant in the range of about 20 to 2000 are required. These materials are not easily available, are expensive, and development of ferroelectric varactors. Cost problems arise. In addition, when making the frequency variable, a high bias voltage of 300 volts is required, so that there is a problem that it cannot be easily mounted on the apparatus.

  Therefore, the present invention has been made in view of the problems in the above-described conventional tunable filter, and is easily mounted in an apparatus with a simple configuration and at a low cost when the filter is electrically adjusted. An object of the present invention is to provide a tunable filter.

  In order to achieve the above object, the present invention provides a tunable filter, a rectangular waveguide divided into two, and a three-layer substrate sandwiched between the two divided rectangular waveguides and provided with a resonator. An active element mounted in the resonator, and applying a bias voltage to the active element from the outside of the three-layer substrate through a line pattern on the inner layer of the three-layer substrate, And adjusting the bandwidth.

  According to the present invention, since a bias voltage is applied to the active element mounted in the resonator of the rectangular waveguide through the line pattern on the inner layer of the substrate from the outside, the device is simple and inexpensive. It is possible to provide a tunable filter that can be easily mounted on the vehicle.

  In the tunable filter, the line pattern of the inner layer of the three-layer substrate can be used as the line for applying the bias voltage.

  In the tunable filter, a varactor diode can be used as the active element. By using a commercially available varactor diode, it is possible to provide a filter that is excellent in mass productivity and cheaper, and uses a bias voltage as low as about 30 V, so that it can be easily mounted on the apparatus.

  The tunable filter may be configured to include a plurality of the resonators and to have an independent bias voltage application line for each of the plurality of resonators. By increasing the number of resonators, the transition bandwidth can be further narrowed, and a filter having sharp characteristics can be provided.

  Further, a low pass filter is provided by providing a pattern for forming a capacitor for the purpose of attenuating a high frequency signal flowing from the waveguide into the bias line and preventing leakage of the signal to the outside in the line pattern for applying the bias voltage. Can be configured. The size of the capacitor forming pattern is determined based on the filter frequency.

  As described above, according to the present invention, in a tunable filter that electrically adjusts a filter, it is possible to provide a filter that can be easily mounted on a device with a simple configuration and at a low cost.

  FIG. 1 shows an embodiment of a tunable filter (hereinafter abbreviated as “filter”) according to the present invention. This filter is roughly divided into a case 11, a cover 12, and a three-layer substrate 13. This is a so-called bilateral finline filter. The case 11 and the cover 12 have rectangular waveguides divided at the center of the H plane, and the three-layer substrate 13 is sandwiched between them in parallel with the E plane.

  As shown in FIG. 2, the three-layer substrate 13 includes septa 206, 207, 208, and 209 in front and back layers in a direction orthogonal to the waveguide 202 to form resonators 203, 204, and 205.

  FIG. 3 is an enlarged view of a portion 218 for mounting the varactor diode on the three-layer substrate 13. Round patterns 301, 302, and 303 are provided near the septum in the resonator. The varactor diodes 304, 305, and 306 are mounted in the opposite direction with respect to the bias circuit, and the anode side is soldered on a septum (reference numeral 206 in FIG. 2) and the cathode side is soldered to the round patterns 301, 302, and 303, respectively. Is done. In place of the varactor diode, another active element having a variable capacitance can be used.

  FIG. 4 shows a line pattern for applying a bias voltage using the inner layer of the three-layer substrate 13. The inner layer round patterns 403, 404, and 405 are electrically connected to the substrate front and back layer round patterns 301, 302, and 303 in FIG. 3 through through holes, respectively. Further, the round pattern 406 on the inner layer at the substrate end is electrically connected to the round patterns 214, 215, 216, and 217 on the front and back layers at the substrate end in FIG. The case 11 and the cover 12 in FIG. 1 are not in contact with the round patterns 214, 215, 216, and 217 on the front and back layers of the three-layer substrate 13.

  When the bias line 401 is formed in the inner layer of the three-layer substrate 13, a high-frequency signal propagating from the waveguide leaks outside the filter through the bias line. As a general method for preventing this leakage, the line length from the mounting position of the varactor diode to the end of the substrate is set to 1/4 wavelength, and when the mounting position is viewed from the waveguide side, Configure the input impedance to be infinite. However, the length of the line may be larger than the length of the quarter wavelength depending on the dimensional shape of the waveguide or mechanical factors such as screwing. Therefore, the line of the bias line 401 is provided with a line pattern 402 that forms a capacitor for attenuating a high-frequency signal propagating from the waveguide, and a low-pass filter is formed in the three-layer substrate 13 to thereby prevent leakage of the high-frequency signal. It is set to prevent.

  With the above configuration, a bias voltage can be applied to the varactor diodes 304 to 306 in the resonators 203 to 205 of the filter from the outside through independent bias ports 210, 211, 212, and 213. And the center frequency and bandwidth of the filter can be easily adjusted electrically by changing the capacitances of the varactor diodes 304 to 306.

  FIG. 5 is a graph showing an example of characteristics of an embodiment of the present invention. Curves 51 and 53 represent insertion loss and reflection loss when the bias voltage is 0 volt, respectively. Curves 52 and 54 represent insertion loss and reflection loss when the bias voltage is 25 volts, respectively. Here, the left vertical scale is applied to the curves 51 and 52, and the right vertical scale is applied to the curves 53 and 54. As shown in the figure, the center frequency can be made variable by a bias voltage as low as about 30V.

1 is an exploded perspective view showing an embodiment of a tunable filter according to the present invention. It is a front view which shows the front and back layers of the 3 layer board | substrate of the tunable filter of FIG. It is an expanded sectional view which shows the varactor diode mounting part of the three-layer board | substrate of FIG. FIG. 3 is a cross-sectional view showing an inner layer line pattern for applying a bias voltage on the three-layer substrate of FIG. 2. 3 is a graph illustrating an example of characteristics of the tunable filter in FIG. 1.

Explanation of symbols

11 Case 12 Cover 13 Three-layer substrate 202 Waveguide 203, 204, 205 Resonator 206, 207, 208, 209 Septum 210, 211, 212, 213 Bias port 214, 215, 216, 217 Round pattern (Bias at substrate surface edge) Voltage application line pattern)
218 Part for mounting varactor diode 301, 302, 303 Round pattern 304 (for mounting varactor diode) 304, 305, 306 Varactor diode 401 Bias line 402 Capacitor forming pattern 403, 404, 405 Round pattern (for mounting varactor diode) Through-hole connection pattern)
406 Round pattern (Pattern for through-hole connection with bias line on substrate surface edge)
520 Insertion loss for 0 volt bias voltage 52 Insertion loss for 25 volt bias voltage 53 Reflection loss for 0 volt bias voltage 54 Reflection loss for 25 volt bias voltage

Claims (5)

A rectangular waveguide divided into two;
A three-layer substrate sandwiched between the two divided rectangular waveguides and provided with a resonator;
An active element mounted in the resonator,
A tunable filter characterized by adjusting a center frequency or / and a bandwidth by applying a bias voltage to the active element from the outside of the three-layer substrate through a line pattern of an inner layer of the three-layer substrate.   2. The tunable filter according to claim 1, wherein a line pattern in an inner layer of the three-layer substrate is used as the bias voltage application line.   The tunable filter according to claim 1, wherein a varactor diode is used as the active element.   4. The tunable filter according to claim 1, wherein a plurality of the resonators are provided, and an independent bias voltage applying line is provided for each of the plurality of resonators. 5.   5. The tunable according to claim 1, further comprising a low-pass filter for attenuating a high-frequency signal in the line pattern for applying the bias voltage and preventing leakage of the signal to the outside. filter.

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