UWB Gilbert downconverter with lumped-distributed phase-inverter rat-race coupler based on Chebyshev band-broadening technique

A broadband Gilbert downconverter with a miniature phase-inverter rat-race coupler is demonstrated using 0.35m SiGe BiCMOS technology. By lumped-distributed and band-broadening techniques, a large shrinkage ratio with wide bandwidth of Chebyshev response can be simultaneously attained in the spiral-shape coplanar-stripline phase-inverter rat-race coupler. The area of the demonstrated lumped-distributed phase-inverter rat-race coupler is 0.65×0.65mm² and the experimental bandwidth ranging from 2.5 to 12.5GHz is large enough to cover the UWB bandwidth. As a result, a broadband Gilbert downconverter with the proposed coupler achieves a conversion gain of 11-12dB, IP_1dB of -11dBm, IIP₃ of -1dBm and noise figure of 16dB from 3 to 11GHz.