A Q-band doubly balanced mixer in 0.15um GaAs pHEMT technology

In this paper, the development of a Q-band doubly balanced mixer in 0.15um GaAs pHEMT process is presented. Five-conductor coupled line Marchand balun is designed and utilized for the LO and RF signal input. Instead of using conventional input port matching method, the complex impedance of the diode ring is directly matched with differential single-stub networks between the balun and diode ring, which realized a compact layout for the matching network, and greatly improved the return loss of the LO port, thus enhanced the mixer operation bandwidth. Measured results coincide well with the simulations: the conversion gain is -9.2dB ~ -11.9dB for RF and LO frequency from 40GHz ~ 50GHz, and IF frequency is DC ~ 10GHz, with the LO power level of +15dBm. The typical LO-RF isolation is 33 dB with minimum value of 19.3dB for LO between 35GHz to 50 GHz, and the IIP3 is above +12.6dBm for 40GHz ~ 50GHz, which is suitable for the China millimeter wave communication standard “Q-LINKPAN”.