Study of K band Bandpass Filters Using Dual-Mode Loop of Tian Ma Telescope

This paper presents a low insertion-loss, sharp-rejection, and wide-band dual-mode microstrip bandpass filter using meander square loop with two tuning stubs,which applies to integrated down converter modules for Tian Ma K-band focal plane array. The designed filter is based on a bandstop filter, which uses a meander ring resonator with direct-connected orthogonal feed lines, and uses two tuning stubs to construct a wide-band passband with two sharp stopbands. Single-ring filter and cascaded dual-ring filter are presented. The measured results show that 3dB bandwidth of the single-ring filter is 42.8%, with return loss larger than 20dB within 17.4GHz-26.9GHz, insertion loss of -1.05dB, and rejections are greater than 35dB within 15.1GHz-16GHz and 28.1GHz-28.9GHz. The 3dB bandwidth of the cascaded dual-ring filter is 39.8%, with return loss larger than 14dB within 17.7GHz-26.5GHz, insertion loss of -1.27dB, and rejections are greater than 35dB within 12.8GHz-15.3GHz and 27.9GHz-30.6GHz. The measured results of the two filters are highly consistent with the simulation results.