JP5100578B2 - High frequency resonator and high frequency filter - Google Patents

Description

  The present invention relates to a microwave band and a millimeter wave band high-frequency resonator and a high-frequency filter constituted by coaxial lines or microstrip lines.

  A conventional distributed constant low-pass filter or band rejection filter is configured by connecting an open-ended stub to a transmission line connecting input and output terminals. For example, there is a band rejection filter in which a signal input terminal and a signal output terminal are connected by a strip line, and four open-ended stubs having a length of about ¼ wavelength at the attenuation frequency of the filter are connected to the strip line ( For example, refer nonpatent literature 1).

  In the same filter, when the length of the four open stubs becomes a quarter wavelength or an odd multiple thereof, the stub is in a series resonance state, and the connection point with the strip line is electrically grounded. The same frequency component passing between the signal input / output terminals is blocked. Note that a frequency at which the length of the stub is ¼ wavelength is generally referred to as a fundamental order resonance frequency.

  In addition, this filter has a low-pass characteristic, and in order to suppress the reflection amount to a certain amount or less in the pass band, a low-pass filter can be configured by appropriately giving each stub length and the distance between stubs. It has been known.

G. Matthaei et al., "Microwave Filters, Impedance-Matching Networks, and Coupling Structures" (Artech House, 1980), p727

  A typical application of the above-described band rejection filter and low-pass filter is to suppress spurious radiation in a high frequency band that occurs in various wireless transmitters. The open-ended stub included in the filter is in a series resonance state at a fundamental order resonance frequency having a length of ¼ wavelength and an odd multiple of the higher order resonance frequency, and the filter exhibits a band rejection characteristic. Since the stub is in an anti-resonant state at a frequency where the length of the filter is an even multiple of the quarter wavelength, the filter cannot prevent the frequency component.

In particular, the spurious radiation of the radio transmitter has a component power corresponding to an integral multiple of the transmission frequency f ₀ , which is relatively large. For example, the above-mentioned frequency band is used to suppress the second harmonic 2f ₀ of the transmission wave with the band rejection filter described above. Is designed to be the fundamental resonance frequency of the stub, the frequency component of 2 × 2f ₀ = 4f ₀ where the stub length is ½ wavelength, that is, the fourth harmonic component of the transmitted wave cannot be blocked by the filter. Will be leaked.

  The present invention has been made to solve the above-described problems. By providing a cavity at the tip of the open-ended stub included in the filter and electromagnetically coupling the two, the stub alone becomes an anti-resonant state. An object of the present invention is to obtain a high-frequency resonator capable of obtaining a desired attenuation amount in a frequency band in which the attenuation amount cannot be secured, and a high-frequency filter configured using the resonator.

  A high frequency resonator and a high frequency filter according to the present invention form a cavity resonator at a tip portion of an open stub formed of a coaxial line or a microstrip line, and the resonance frequency of the cavity resonator is the same as that of the coaxial line resonator. A high-frequency resonator in which the dimensions of the cavity resonator are set so as to be higher than a fundamental order resonance frequency, and a high-frequency filter configured using the resonator.

  According to the present invention, by providing a cavity at the tip of the open-ended stub included in the filter and electromagnetically coupling them together, the stub alone is in an anti-resonant state, and the desired attenuation is not obtained in the frequency band. Can be obtained.

Embodiment 1 FIG.
1 is a diagram showing a high-frequency resonator and a high-frequency filter according to Embodiment 1 of the present invention. The high-frequency resonator shown in FIG. 1 has a length of an inner conductor 3 of a coaxial line resonator including a coaxial line inner conductor 3 having an open end and a metal housing 1 as an outer conductor that functions as a coaxial line outer conductor. The desired fundamental order resonance frequency is obtained by setting the thickness to about ¼ wavelength, and the cavity resonator 4 is formed in the metal casing 1 surrounding the tip portion of the inner conductor 3, and the resonance frequency of the cavity resonator 4 is The dimensions of the cavity resonator 4 are set so as to be higher than the fundamental order resonance frequency of the coaxial line resonator. The signal input terminal 5 a and the signal output terminal 5 b are connected by the coaxial line 2, and the high frequency resonator is connected to the coaxial line 2 to constitute a high frequency filter.

  Next, the operation of the filter according to Embodiment 1 of the present invention will be described. In FIG. 1, the resonator includes an open-ended stub composed of a metal housing 1 that functions as a coaxial line inner conductor 3 and a coaxial line outer conductor, and a cavity resonator 4 provided inside the metal housing 1. The band rejection filter is configured by connecting the cavity resonator 4 to the coaxial line 2 connecting the input / output terminals 5a and 5b.

  The cavity resonator 4 is in a fundamental resonance state at a frequency fc at which the length (L + Lp) of the tip open stub is approximately ¼ wavelength, and at this time, the point C shown in FIG. The filter having the configuration shown in FIG. 1 exhibits band rejection characteristics. In the same frequency band, the dimensions A and H of the cavity resonator 4 are less than ½ wavelength, and the cavity is cut off. Therefore, in the same frequency band, the portion operates as a slightly high impedance coaxial line in which the distance between the inner and outer conductors is slightly larger than the other portions. FIG. 2A shows an equivalent circuit of the resonator in the same state.

  On the other hand, at a frequency of about 2fc where the length of the stub (L + Lp) is approximately ½ wavelength, the cavity resonator is in a resonance state and the cavity resonator and the coaxial line are electromagnetically coupled. The point D shown in FIG. At this time, assuming that the length L of the coaxial line portion is about ¼ wavelength, the point C shown in FIG. 1 is almost in an electrical short-circuit state due to the impedance transformation function that the ¼ wavelength line generally has. Accordingly, the filter of FIG. 1 exhibits a band rejection characteristic. FIG. 2B shows an equivalent circuit of the resonator in the same state.

  Here, if there is no cavity resonator, the equivalent circuit is as shown in FIG. 2A, and the length of the stub (L + Lp) is approximately ½ wavelength, so that the point C is in an electrically open state, The filter does not have a band rejection characteristic. FIG. 3 shows filter pass characteristics when a cavity resonator is used (the present invention) and when not used (conventional).

  In this manner, a cavity resonator is provided at the tip of the open-ended stub made of a coaxial line, and the cavity dimensions are given so that the cavity resonator is cut off at the fundamental resonance frequency fc of the open-ended stub. By constructing a filter using a resonator designed so that the open-ended stub and the cavity resonator are electromagnetically coupled at a frequency 2 fc that is twice that of the open-ended stub, the open-ended stub is originally in an anti-resonant state and the filter The band rejection characteristic can be formed in the vicinity of the frequency 2fc that does not exhibit the rejection characteristic.

Embodiment 2. FIG.
FIG. 4 is a diagram showing a high-frequency resonator and a high-frequency filter according to Embodiment 2 of the present invention. The high-frequency resonator shown in FIG. 4 has a microstrip line formed of signal lines 12 and 13 and a ground conductor 16 formed on a dielectric substrate 17 and having an open end, and a microstrip line installed therein. A desired fundamental order resonance frequency is obtained by setting the length of the microstrip line of the microstrip line resonator composed of the metal casing 11 to be sealed to approximately ¼ wavelength, and the metal corresponding to the tip of the microstrip line is obtained. A cavity resonator 14 is formed in the casing 11, and the dimensions of the cavity resonator are set so that the resonance frequency of the cavity resonator is higher than the fundamental order resonance frequency of the microstrip line resonator. The signal input terminal 15a and the signal output terminal 15b are connected by a microstrip line, and a high frequency resonator is connected to the microstrip line to constitute a high frequency filter. The signal line 13 constitutes an open stub.

  Next, the operation of the filter according to the second embodiment of the present invention will be described. The second embodiment uses a microstrip line composed of the dielectric substrate 17, the signal lines 12 and 13, and the ground conductor 16 instead of the coaxial line in the first embodiment. Exhibits the same behavior as.

  In this way, a cavity resonator is provided at the tip of the open-ended stub made of a microstrip line, and at the basic resonance frequency fc of the open-ended stub, a cavity dimension is given so that the cavity resonator is cut off, By constructing a filter using a resonator designed so that the open-ended stub and the cavity resonator are electromagnetically coupled at a frequency 2fc that is approximately twice that frequency, the open-ended stub originally becomes anti-resonant and the filter The band rejection characteristic can be formed in the vicinity of the frequency 2fc that does not exhibit the band rejection characteristic.

It is a figure which shows the high frequency resonator and high frequency filter by Embodiment 1 of this invention. It is an equivalent circuit schematic of the resonator contained in the filter by Embodiment 1 of this invention. It is a figure which shows the pass characteristic of the filter by Embodiment 1 of this invention. It is a figure which shows the high frequency resonator and high frequency filter by Embodiment 2 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,11 Metal housing, 2, 3 Coaxial line inner conductor, 4, 14 Cavity resonator, 5a, 15a, 101a Signal input terminal, 5b, 15b, 101b Signal output terminal, 12, 13 Signal line, 16 Ground conductor, 17 Dielectric substrate, 102 Strip line.

Claims (4)

Tip Ri is opened near the inner conductors is a length (L + Lp), the length of the inner conductor of the coaxial line resonator comprising a metal housing serving as the outer conductor (L + Lp) approximately 1/4 wavelength Thus, a desired fundamental resonance frequency is obtained, and a cavity resonator is formed in the metal casing surrounding a portion having a length Lp corresponding to the tip portion of the inner conductor, and the resonance frequency of the cavity resonator is Set the cavity resonator dimensions to be higher than the fundamental resonance frequency of the coaxial line resonator ,
At a frequency fc where the length of the inner conductor (L + Lp) is approximately ¼ wavelength, the cavity resonator exhibits a band rejection characteristic by being in a cutoff state,
At a frequency 2fc where the length (L + Lp) of the inner conductor is approximately ½ wavelength, the cavity resonator exhibits a band rejection characteristic by electromagnetically coupling with the inner conductor. vessel.   A high frequency filter comprising: a signal input terminal and a signal output terminal connected by a coaxial line; and the high frequency resonator according to claim 1 connected to the coaxial line. Is formed on the dielectric substrate Ri is open near the tip, a microstrip line resonator composed of the microstrip line is a length (L + Lp), a metal housing for installing sealing the microstrip line inside A desired fundamental order resonance frequency is obtained by setting the length (L + Lp) of the microstrip line of the filter to about ¼ wavelength, and the length Lp corresponding to the tip part of the microstrip line is enclosed. Forming a cavity resonator in a metal housing, and setting the dimension of the cavity resonator so that the resonance frequency of the cavity resonator is higher than the fundamental resonance frequency of the microstrip line resonator ;
At a frequency fc where the length of the microstrip line (L + Lp) is approximately ¼ wavelength, the cavity resonator exhibits a band rejection characteristic by being cut off,
At a frequency 2fc where the length (L + Lp) of the microstrip line is approximately ½ wavelength, the cavity resonator exhibits a band rejection characteristic by electromagnetically coupling with the microstrip line. High frequency resonator.   A high frequency filter comprising: a signal input terminal and a signal output terminal connected by a microstrip line; and the high frequency resonator according to claim 3 connected to the microstrip line.

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