Millimeter-Wave Ultra-Wideband (UWB) Bandpass Filter (BPF) Using Microstrip Parallel Coupled Lines

A compact millimeter-wave bandpass filter for automotive radar systems is developed and proposed in this paper. The filter is designed to select the UWB spectrum (2229GHz) to meet the FCC specifications. The filter consists of two of parallel-coupled line sections that are quarter-wavelength long at a center frequency of about 25.5 GHz. In order to improve the filter performance and to allow the filter to exhibit a new transmission zero at each side of the passband, a shunt ring resonator and a shunt stepped-impedance open-circuited stub are loaded at the center between the coupled line sections. As a result, the filter can exhibit a high selectivity filtering characteristic. The filter design is realized using RT/duroid 6002 substrate and the design is verified by the EM simulation and the experiment. The filter design is successfully fabricated and measured and a very good agreement between the simulated and measured results is attained. The fabricated filter is compact in size and has low insertion loss, high selectivity and excellent out-of-band performance.