An HTS 20-Pole Microstrip Filter for GSM-1800 Base Stations

Abstract

In order to resolve the problems that the Chinese mobile communication was facing (high dropped call rate, not so good voice quality, etc.), we developed a 20-pole high-temperature superconductor thin-film microstrip filter with steep band edges. This filter which had a quasi-elliptic type frequency response was designed for GSM-1800 base station receiver system. Its frequency ranged from 1711 MHz to 1789 MHz. It was fabricated using double-sided YBCO thin films on LaAlO3 substrate. The substrate size was 0.52 mm × 21 mm × 40 mm. Experiments were performed on a Stirling cooler at a temperature of 60 K. The measured insertion loss in the passband is below 0.35 dB, return loss is bigger than 13.5 dB, and the steepness of the band-edge is up to 18 dB/MHz. Then we assembled it with an LNA (low noise amplifier) into a vacuum chamber to get a base station receiver front end and measured it. Its measured gain is 22.5 dB, and noise figure is below 0.6 dB in the passband which is very important to improve the sensitivity of the base station system.