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Suo G.,Tsinghua University | Zhang G.,Sino Superconductor Technology Ltd. | Cao B.,Tsinghua University | Guo X.,Tsinghua University | And 5 more authors.
Microwave and Optical Technology Letters | Year: 2014

This article presents a four-pole continuously tunable high-temperature superconducting combline filter at L band on MgO substrate. Gallium Arsenide varactors are used as tuning elements in the filter. Additional varactors are used to tune the external quality factor of the input and output couplings. A shorted U-shape secondary coupling line is introduced to match the desired couplings so as to maintain a good return loss in the entire tuning range. The four-pole filter achieves a tuning range of 11.5% from 983.85 to 1103.6 MHz. The insertion loss is 0.46 dB at 1103.6 MHz with the bias of 9 V. The unloaded quality factor of the resonators in the four-pole filter is estimated to be 710 at 1077.6 MHz. © 2014 Wiley Periodicals, Inc. Source


Ying Z.,Tsinghua University | Guo X.,Tsinghua University | Cao B.,Tsinghua University | Zhang X.,Tsinghua University | And 7 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2013

This paper proposes a modified spiral resonator with a tight three-turn spiral and inner/outer tails. The resonator has good spurious response because the mutual inductances between the three turns at the fundamental mode are positive and thus reduce the fundamental resonant frequency f0, whereas those at the first spurious mode are negative and increase the first spurious resonant frequency fS. By further optimizing the lengths of the spiral and inner/outer tails of the proposed resonator, a spurious resonant frequency fS up to 3.4 f0 is obtained. Moreover, the couplings between such resonators at spurious modes are much weaker than that at the fundamental mode, which is helpful to suppress the spurious response of bandpass filters consisting of such resonators. Furthermore, three dissimilar types of resonators with the same fundamental frequency but with different spurious resonant frequencies are used to compose a bandpass filter and further suppress the spurious response in the stopband. With these methods, a ten-pole superconducting filter at 360 MHz with a 15-MHz bandwidth is successfully designed and fabricated on a LaAlO3 substrate. The overall measurements show a high performance and agree very well with the simulations. The maximum insertion loss is 0.15 dB, the return loss is greater than 19 dB, and the rectangle coefficient (the ratio between the 40-dB bandwidth and the 3-dB bandwidth) is 1.35. Moreover, the out-of-band rejection is higher than 76 dB up to 2030 MHz, which is 5.64 f0. The ten-pole filter occupies a compact area of 33 mm × 15 mm, which amounts to only 0.15 λ g0 × 0.07 λg0, where λg0 is the guided wavelength of the 50-Ω line on the substrate at f0. © 2013 IEEE. Source


Suo G.,Tsinghua University | Guo X.,Tsinghua University | Cao B.,Tsinghua University | Wei B.,Tsinghua University | And 3 more authors.
IEEE Microwave and Wireless Components Letters | Year: 2014

This letter presents a superconducting continuously tunable bandpass filter with dual-mode resonator and Gallium arsenide (GaAs) varactors. The even- and odd-modes of the dual-mode resonator can be tuned simultaneously using a single bias voltage. The interstage and external couplings are realized with interdigital coupling structure to enhance the coupling strength. A four-pole dual-mode superconducting filter at L-band with a fractional bandwidth of approximately 20% is successfully designed. Two transmission zeors are generated in the upper stopband to increase the stopband rejection. The tuning range of the filter is 16% from 784.92 to 918.23 MHz. The insertion loss at 918.23 MHz is 0.69 dB with a reverse bias voltage of 9 V. The measurements of the filter match well with the simulated ones. © 2014 IEEE. Source


Suo G.,Tsinghua University | Guo X.,Tsinghua University | Cao B.,Tsinghua University | Wei B.,Tsinghua University | And 3 more authors.
IEEE Microwave and Wireless Components Letters | Year: 2014

This letter presents a superconducting tunable filter with a constant bandwidth using semiconductor varactors. A coupling line is introduced to adjust the inter-resonator coupling to meet the requirement of constant bandwidth. The external couplings are designed to remain a good passband shape with the tunable frequency. With the proposed method, a superconducting tunable filter with constant bandwidth is successfully implemented. The measured results of the filter agree well with the simulated ones. It shows a frequency tuning range of 11% from 924.5 MHz to 1030.8 MHz, a 1 dB bandwidth of 23.8 ± 0.3 MHz, and an insertion loss of 0.16 to 1.41 dB. © 2014 IEEE. Source


Zhang Y.,Tsinghua University | Guo X.,Tsinghua University | Cao B.,Tsinghua University | Wei B.,Tsinghua University | And 4 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2012

This paper presents a superconducting filter with a bandwidth of 0.5 MHz at 40 MHz on a LaAlO 3 substrate. It has a compact size of 40 mm × 19 mm, which amounts to only 0.02 λ g0 × 0.01 λ g0, where λ g0 is the guided wavelength of the 50-Ω line on the substrate at the midband frequency. The effect of the resonator structure on the unwound length and, hence, the size of the resonator is analyzed. A spiral resonator with positive mutual inductances between adjacent microstrip turns can greatly reduce the resonator's unwound length and is used to miniaturize the filter size. A feedline structure spiraled inside the spiral resonator is proposed to realize a strong external coupling. Furthermore, a cross-coupling line is added to the six-pole filter to improve the band-edge steepness. The filter is successfully designed and fabricated. The measured results demonstrate a 0.3-dB insertion loss, a -19.2 dB return loss, an 80-dB out-of-band rejection, and steep band edges, which are in good agreement with electromagnetic simulations. © 2012 IEEE. Source

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