A high-performance integrated K-band diplexer

This paper describes the design and measurement of a planar diplexer integrated on a single silicon substrate, The diplexer channels are 5% and 6.5% relative bandwidth at 28 and 31 GHz, respectively. The diplexer is based on a micropackaged membrane supported capacitively coupled microstrip structure and is 1.5 cm x 1.6 cm and only 1.4-mm thick. The measured insertion loss is 1.4 dB (5%) and 0.9 dB (6.5%) for the two channels with better than 35-dB isolation in the 28-GHz band and better than 50-dB isolation in the 31-GHz band. The measured results include all transition and packaging effects, The diplexer has coplanar-waveguide ports and can easily be integrated with other elements such as planar antennas, low-noise amplifier, and power amplifiers.