Size Reduction of a MMIC Direct Up-Converter at 44 GHz in Multilayer CPW Technology Using Thin-Film Microstrip Stubs Loading

This paper proposes a novel compact multilayer 44.5-GHz coplanar waveguide (CPW) single-sideband (SSB) subharmonically pumped (SHP) mixer for direct up-conversion GaAs monolithic microwave integrated circuit. It uses previously developed thin-film microstrip (TFMS) and CPW structures for capacitive and inductive loading techniques to drastically reduce its size. The SSB SHP mixer uses 50-MHz in-phase and quadrature signals to directly modulate the second harmonic of a 22.25-GHz carrier to produce the required 44.55-GHz RF output. Two pairs of antiparallel diodes reduce feedthrough of the fundamental 22.25-GHz signal to the RF output while novel CPW/TFMS-based structures provide matching. This 1.2times1.5 mm2 chip uses a lumped Wilkinson divider as a local-oscillator divider and a previously developed reduced size 90deg coupler. The SSB SHP mixer acts as an up-converter with a measured conversion gain of -10plusmn1 dB and the lower sideband suppression is greater than 23 dB across the RF bandwidth of 43.5-45.5 GHz. Additionally, it is shown that the RF port return loss is better than 20 dB, and 2timesfLO was suppressed by 21 dB over the same band. The circuit also does not require any dc bias. Compared to the conventional SSB SHP mixer, a 70% reduction in circuit area was achieved with better performances