A Wideband, Sharp Roll-Off U-Band Diplexer in Suspended Stripline Technology

Abstract

This paper presents a low-loss, sharp roll-off, and wideband millimeter-wave contiguous diplexer implemented on 0.127 mm-thick TLY5 dielectric material to separate U-band frequency range into two jointed frequency ranges of 40-50 GHz and 50-60 GHz using two low-pass and high-pass filter channels. In order to integrate the diplexer in the front end of a wideband millimeter-wave down-converter and evaluate the frequency response, the proposed diplexer is supported by three add-on waveguide-to-suspended-stripline transitions. The final design of diplexer consisting of a low-pass filter with cut-off frequency of 50 GHz, a pseudo-high-pass filter with crossover at 50 GHz, and a T-junction is analyzed and optimized together with a 3D full-wave simulator. The realized diplexer features a VSWR of 2.5 : 1 across the entire operation frequency band of 40-60 GHz, low passband insertion loss of less than 2 dB in both channels, stopband rejection higher than 45 dB, and compact size with dimensions of $27\times 13$  mm2 due to its intelligent and guided design and technology selection.