An mm-Wave Wilkinson Combiner with Stacked Coupling and Capacitive Loading Technique

Abstract

This paper introduces a small Wilkinson power combiner (WPC) created in a 0.18 μm CMOS process for use in millimeter-wave systems. The suggested combiner substitutes typical λ/4 microstrip arms with stacked coupled transmission line segments, which are made on the uppermost metal pair (M5/M6). This allows for significant vertical coupling and field confinement, which raises the effective phase constant and decreases the physical arm length. Furthermore, distributed capacitive loading is added along the arms to create a slow wave effect and adjust the arm susceptance for better input matching. A small trim capacitor at the combining node also corrects for any remaining pad/transition reactance. Measurements taken around 60 GHz show an insertion loss of 0.6 dB, a return loss of -19 dB, and an isolation of -36 dB within a small area of 0.28 mm2. In comparison to current CMOS combiners, the presented method strikes a good balance between size reduction and electrical performance, delivering a CMOS-compatible, low loss, and high isolation option ideal for compact millimeter-wave phased-array and highly integrated front-end systems.