HIGH-SELECTIVITY UWB FILTERS WITH ADJUSTABLE TRANSMISSION ZEROS

This letter proposes a novel ultra-wideband (UWB) bandpass filter with compact size and high-selectivity performance. The filter has been studied and implemented through multiple-mode resonator (MMR) using new coupling schemes such as capacitive source-load (S-L) coupling/inductive source-load (S-L) coupling. By properly adjusting the length and width of these stubs, its first four resonant modes can be allocated within the 3.1-10.6 GHz passband, whereas its fifth resonant mode is placed above 16.0 GHz. Two transmission zeros (an inherent transmission zero and an additional transmission zero) can be produced. Moreover, the position of the additional zero can be controlled by adjusting the direct coupling inductance/capacitance. Simulated and measured results are in good agreement indicating that the proposed BPF has a passband (3.0-11.0 GHz)/(2.92-10.6 GHz) and a wide stopband width with 23 dB/25 dB attenuation up to 27.0 GHz. The group delay of the filter is relatively constant and less than 0.65 ns/0.52 ns over the operating pass band.