An L-band HTS duplexer with improved performance

Abstract

An L-band HTS duplexer with improved performance for communication applications has been developed. This is an improved version of the duplexer previously developed by our group. The duplexer was composed of a T-junction and two channels. Each channel has a 10-pole quasi-elliptic function bandpass HTS filter with a bandwidth of 27 MHz, and center frequencies at 1200 MHz and 1260 MHz. To achieve higher performance, especially a good balance between selectivity and flat group delay, the two pairs of transmission zeros from the two filters were reassigned so that one pair is used for high selectivity and the other for flat group delay. To reduce the influence of parasitical coupling, new coupling structures were developed in the simulation process. The duplexer was fabricated on a 2 inch diameter, 0.5 mm thick LaAlO 3 wafer with a double-sided YBCO film. The measured results showed a very high performance: a mid-band insertion loss of 0.2 dB, a return loss better than -14 dB, a shape factor better than 1.4 : 1, an out-of-band rejection of better than 70 dB in a wide frequency range up to 3 GHz and excellent isolation (higher than 80 dB) between the two channels. In addition, the frequency band 5 ns group delay variation is over 10.5 MHz (38.7% of 1 dB bandwidth).Since the discovery of high temperature superconductors in 1987, many kinds of HTS microwave devices and systems have been developed [1-10]. The duplexer is an important development among these devices. A duplexer is usually used to split the input frequencies into two separate bands, or combine two separate bands into one. So far, a number of HTS duplexers have been reported [11][12][13][14][15][16][17][18]. However, few of them have high performance in all of their operating parameters, including the insertion loss (<0.2 dB), return loss (<-14 dB), out-of-band rejection (>70 dB) and channel isolation (>80 dB). In particular, none were designed with consideration of the group delay, which is as important as high selectivity since high capacity digital signals are transmitted on many communication systems.In a recent work, we reported on a compact L-band microstrip HTS manifold-coupled input duplexer with high *Corresponding author (email: yshe@aphy.iphy.ac.cn) selectivity performance for satellite communication application [19]. In this paper, we present an improved HTS duplexer that not only has high selectivity but also takes group delay flatness into consideration. The duplexer has two channels with center frequencies in the L-band.

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