A compact L-band high temperature superconducting (HTS) microstrip input duplexer for satellite communication application has been developed. The duplexer has two output channels with center frequencies at 1200 and 1250 MHz, respectively. It was fabricated on a single piece of 2-in double-sided YBCO thin film on LaAlO 3 substrate with a dimension of 26 × 42 mm. The duplexer consists of a T-junction and two bandpass filters, i.e., a ten-pole filter and an eight-pole filter for the two transmission channels, respectively. Both of the two HTS bandpass filters were specially designed to suppress the second-harmonic spurious passband. Moreover, an HTS bandstop filter is added to the duplexer to improve the out-of-band rejection at a special frequency band. As a result of the preceding special designs, in addition to a very low insertion loss (0.2 dB), considerably sharp band edge (21 dB/MHz), and good voltage standing wave ratio (better than 1.4:1), much deeper out-of-band rejection (more than 75 dB) can be realized in a much wider frequency range, i.e., up to 3 GHz, which is almost three times above the center frequency of the passbands. Although all the elements of the duplexer are integrated within a single-piece YBCO film and the layout is compact, excellent isolation (higher than 80 dB) between the two channels has still been achieved.Index Terms-Bandpass filter, bandstop filter, high temperature superconducting (HTS) duplexer. His current research interests are HTS microwave devices and microwave tunable filters.

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Recent development of a high-performance narrowband high-temperature superconducting (HTS) filter is presented. A 10-pole quasi-elliptic function response filter with two pairs of transmission zeros (for high selectivity), which has a center frequency of 2.185 GHz and a 3 dB bandwidth of 10 MHz (a fractional bandwidth of 0.45%), is introduced. The filter was fabricated on a 40 mm×16 mm×0.5 mm MgO wafer with double-sided YBCO films. The measured results show that the filter has 0.15 dB insertion loss at the center of the passband and a return loss better than −22.5 dB at a temperature of 67 K. Band edge steepness reaches over 28.3 dB/MHz at both the low and high frequency edges. The out-of-band rejection is over 78 dB at 8 MHz away from the center frequency and close to 100 dB in a wideband range. high-performance, narrowband, HTS, filterCitation: Cui B, Zhang X Q, Sun L, et al. A high-performance narrowband high temperature superconducting filter. Recently, superconducting devices have been developed steadily in China. Superconducting materials have been widely used in the development of kinds of devices, such as filters [1-4], single photon detector [5] and hot electron bolometer (HEB) mixer [6]. Among these, an important aspect is the development of high-performance narrowband microwave filters. Generally speaking, the insertion loss of a filter is inversely proportional to its fractional bandwidth (FBW), and thus it is difficult to realize narrowband filters (for example FBW<0.5%) using normal metals. The hightemperature superconducting (HTS) films have a thousand times smaller microwave surface resistance than normal metal films. Therefore they are suitable for use in fabricating such narrowband filters and many works on narrowband HTS filters have been reported since early 1990s [7][8][9][10][11][12].In most cases, to realize high selectivity, HTS filters are constructed by numbers of resonators which are arranged within a testing house. The compact size of HTS filters will introduce some unwanted parasitic couplings between nonadjacent resonators, which makes it hard to realize a high out-of-band rejection. Besides, it is not easy to achieve better return loss (such as, better than −20 dB) due to the complexity of tuning at low temperature and in vacuum. There are, to our knowledge, only a couple of reports in the literature of HTS filters with high-performance specification of return loss (< −20 dB) and/or out-of-band rejection (> 95 dB) [13][14][15].In this work, we present a 10-pole high-performance narrowband HTS filter with a cascaded quadruplet coupling structure. The filter has an excellent return loss (−22.5 dB in the passband) and a high out-of-band rejection (close to 100 dB in a wideband range). A double-folded resonator structure [16], which has been developed in our laboratory for a filter with a center frequency of 8 GHz, is used in our design to realize the high out-of-band rejection level. A novel asymmetrical cross coupling structure is introduced to implement the filter with two pairs of t...

Different type HTS filters for the applications in satellite microwave receivers have been developed, aiming for space communications and astronomy observations. The HTS filters have been integrated with cryogenic low noise amplifiers and Stirling cryocoolers forming receiver front-end subsystems, which have passed all space qualification environmental tests. The first Chinese space HTS subsystem was taken into space with a civilian experimental satellite for new technology on October 14, 2012. Data received from this satellite show that the HTS filter is working on orbit perfectly. Moreover, an ultra-wide band HTS filter with a notch has been developed for the applications of deep space exploration. A novel K-band receiver with both HTS passive and active devices is under development and is expected to work in the planned space VLBI system by 2020.

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