Microwave hairpin-comb filters for narrow-band applications
First Claim
1. A narrow band bandpass microwave hairpin-comb filter having a microstrip configuration comprising:
- a plurality of microstrip side coupled resonators, each resonator being nominally a half wavelength long at the resonant frequency in a medium of the microstrip line and each resonator comprising a hairpin configuration having an open end and a closed end,an input coupling to a first one of said plurality of resonators,an output coupling to a last one of said plurality of resonators, andwherein said filter is characterized in that the plurality of microstrip resonators are oriented with the open ends thereof in a common direction thereby providing a comb configuration and defining a respective side coupling region between neighboring resonators, and the respective side coupling region having a length from between substantially 1/8 wavelength to a value approaching 1/4 wavelength at the resonance frequency of the resonators.
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Abstract
Microwave hairpin-comb filters utilize a plurality of hairpin (i.e., folded) half-wavelength microstrip or stripline resonators arranged side-by-side and all with the same orientation. The coupling regions between resonators extend parallel to the sides of the resonators for substantially 1/8 to 1/4 wavelength at the frequency of resonance of the resonators. This length of coupling region between resonators, along with all resonators being oriented in the same direction, result in resonance effects in the coupling regions between the resonators. These effects greatly reduce the couplings between the resonators so that the resonators can be very closely spaced so as to produce a compact filter structure yet still have a narrow passband. The structure can also be made to produce poles of attenuation adjacent to the passband in order to enhance the filter cutoff characteristic. The filter structure can be conveniently tuned using asymmetric dielectric pieces which rotate above an interdigital conductor pattern placed between the open ends of each resonator, the axis of rotation being normal to the substrate. This manner of tuning is particularly attractive for narrow-band, very low loss, high temperature superconductor (HTS) filters since these tuners can be made to give smooth tuning with no normal metal parts in the circuit and with no ground connections required. Such normal metal parts or ground connections would introduce considerable loss and degrade the HTS filter performance.
56 Citations
15 Claims
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1. A narrow band bandpass microwave hairpin-comb filter having a microstrip configuration comprising:
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a plurality of microstrip side coupled resonators, each resonator being nominally a half wavelength long at the resonant frequency in a medium of the microstrip line and each resonator comprising a hairpin configuration having an open end and a closed end, an input coupling to a first one of said plurality of resonators, an output coupling to a last one of said plurality of resonators, and wherein said filter is characterized in that the plurality of microstrip resonators are oriented with the open ends thereof in a common direction thereby providing a comb configuration and defining a respective side coupling region between neighboring resonators, and the respective side coupling region having a length from between substantially 1/8 wavelength to a value approaching 1/4 wavelength at the resonance frequency of the resonators. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A narrow band bandpass microwave hairpin-comb filter having a stripline configuration comprising:
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a plurality of stripline side coupled resonators, each resonator being nominally a half wavelength long at the resonant frequency in a medium of the stripline and each resonator comprising a hairpin configuration having an open end and a closed end, an input coupling to a first one of said plurality of resonators, an output coupling to a last one of said plurality of resonators, and wherein said filter is characterized in that the plurality of stripline resonators are oriented with the open ends thereof in a common direction thereby providing a comb configuration and defining a respective side coupling region between neighboring resonators, and the respective side coupling region having a length from between substantially 1/8 wavelength to a value approaching 1/4 wavelength at the resonance frequency of the resonators. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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Specification