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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.


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.


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.


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.


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.


Heng 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: 2013

This paper presents a simple and efficient method for the design of a microstrip contiguous diplexer comprising doubly terminated filters. The equivalent circuit for the channel filters is presented, which can accurately represent both the in-band and out-of-band characteristics of the channel filters. By analyzing and properly adjusting the input impedance of the channel filters, the equivalent circuit of the diplexer can be easily optimized. A high-temperature superconducting diplexer at S-band is successfully designed with this method and fabricated on a MgO substrate with a compact size of 32.6 mm× 18 mm. The measured results show high performance and agree well with the simulations. © 2002-2011 IEEE.


Heng Y.,Tsinghua University | Guo X.,Tsinghua University | Cao B.,Tsinghua University | Wei B.,Tsinghua University | And 3 more authors.
Electronics Letters | Year: 2013

A superconducting dual-band bandpass filter with a mixture of bandpass and bandstop sub-filters is presented. The bandpass sub-filter is designed with λ/2 double spiral resonators mid-tapped by λ/4 connecting lines which act as admittance inverters. The tap position of each resonator is adjusted to meet the required susceptance slope parameter. The bandstop sub-filter is designed with λ/2 folded resonators embedded in and coupled with the centres of the λ/4 connecting lines. The dual-band filter is designed and fabricated on an LaAlO3 substrate with a compact size of 30.4 × 10.3 mm. The measurements show good dual-band response and match well with the simulations. © The Institution of Engineering and Technology 2013.


Heng Y.,Tsinghua University | Guo X.,Tsinghua University | Cao B.,Tsinghua University | Ying Z.,Tsinghua University | And 5 more authors.
Electronics Letters | Year: 2013

A dual-band superconducting microstrip filter with two passbands of 2.985-3.015 GHz and 3.045-3.075 GHz, respectively, is synthesised by a frequency transformation method. Open-loop resonators with embedded single spiral resonators are proposed to realise the synthesised resonator frequencies and coupling coefficients. This structure has the advantages of compact size and weak parasitic couplings, which benefit the implementation of the dual-band planar filter. The filter is successfully designed and fabricated on an MgO substrate. The measured results show high performance and match well with the simulations. © The Institution of Engineering and Technology 2013.


Ying Z.,Tsinghua University | Wei B.,Tsinghua University | Cao B.,Tsinghua University | Guo X.,Tsinghua University | And 4 more authors.
IEEE Microwave and Wireless Components Letters | Year: 2013

A superconducting resonator, consisting of a microstrip spiral and a 2 b interdigital capacitor array, is proposed. The resonator has a measured unloaded Q over 51 000 in all four states. A two-pole reconfigurable superconducting filter at P-band with a fractional bandwidth of 1% is designed with this resonator and fabricated. The measurements show that the tuning range of the center frequency is from 499.4 to 484.9 MHz with insertion losses of less than 0.1 dB in all four states, and are in good agreement with the simulations. © 2001-2012 IEEE.


Heng Y.,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: 2013

A four-pole dual-band bandpass filter is designed with stub-loaded resonators and dual-feeding structure. The stub-loaded resonator generates two resonant modes, and the interstage couplings between the resonators at the two modes can be controlled independently. A dual-feeding structure is proposed to meet the required external couplings of the two passbands simultaneously. The filter is successfully designed and fabricated on a MgO substrate with a compact size of 29.2 mm×, 13.8 mm. The measured results show high performance and agree well with the simulations. © 2001-2012 IEEE.

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