Design and Measurement of a Low-Loss Bandpass Filter for Ku-Band in 45 nm SOI CMOS

This paper presents a preselector bandpass filter (BPF) designed for a high-power front-end module (FEM) targeting backhaul applications at Ku-Band frequencies 12-16 GHz. The proposed filter is intended for future integration into a high-power TX-RX switch module by combining it with an external 90° hybrid coupler. We implement an implicit filter capacitance in the RX mode by using a shunt NMOS transistors stack, which presents the C<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</inf> of the switches to the filter. Yet, in the TX mode the same NMOS stack provides a low-ohmic "short" path to ground by R<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</inf> and improves the switch module isolation. The presented circuit achieves in measurement a low insertion loss of 1.3 dB and a return loss better than 10 dB over the bandwidth. The chip is implemented in a 45 nm RFSOI CMOS technology and occupies an area of 0.31 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, including pads.