60-GHz Microstrip pHEMT Subharmonic Down-/Up-Converters with an Extended CPWG RF Section for Flip-Chip Optimization

Two 60-GHz flip-chip pHEMT subharmonic down-/up-converters based on the anti-parallel diode pair (APDP) with an identical circuit topology for harmonics terminations are demonstrated with RF sections using microstrip (MS) and coplanar waveguide with backside ground (CPWG). The experimental results show that the degradation of conversion gain around 60-GHz frequencies before and after flip chip is less than 2 dB for the down-/up-converter with an extend CPWG RF section and can reach 5 dB for the one with a MS RF section. For chip size and performance optimization of 60-GHz pHEMT down-/up-converters using flip-chip technique, the experiments demonstrate that only an extend CPWG RF section is needed for the high-frequency RF flip-chip connection while simple CPW-to-MS transitions are sufficient for the low-frequency LO and IF flip-chip connections.