A balanced even harmonic quadrature mixer using anti parallel diode pairs

An even harmonic quadrature mixer (EH-QMIX) with a balanced configuration is proposed for a direct conversion receiver. The unit even harmonic mixer (EHMIX) used for I/Q paths consists of two anti parallel diode pairs (APDPs) and a pair of diplexers. When the second harmonic of LO (2LO) from the LO section is applied to the LO port as a spurious component, a conventional single-ended EHMIX using APDP converts the 2LO leakage from the LO section into the baseband and the d.c. offset and the self-detected LO noise arise at the baseband degrade the sensitivity. This proposed balanced EHMIX configuration can cancel out the 2LO leakage in itself. Therefore, the d.c. offset and the LO noise are significantly suppressed and the degradation of the sensitivity can be avoided. The suppression characteristic of the d.c. offset and the LO noise are verified by the simulation and the measurements. By using this balanced configuration, the fabricated EH-QMIX achieves wider frequency band characteristic than that of the single-ended EH-QMIX, and it shows 20 relative bandwidth at L-band.