Investigation of the Influence of LO Leakage in an E-Band Quadrature Transmitter

This paper discusses the influence of local-oscillator leakage on signal quality based on a homodyne double-balanced quadrature E-band transmitter designed for broadband wireless communication. The varying severeness of the leakage over the local oscillator frequency tuning range from 72 to 88 GHz as well as with changing intermediate frequency input power is measured and evaluated using continuous wave as well as complex modulated signals. With power levels between -22 and 0 dBm at the RF port of the transmitter module, the leaked carrier exceeds the data signal power at some LO frequencies and is also traced back to lead to inherent saturation of the output amplifier. This is identified by evaluation of measured transmitter output spectra and constellation diagrams of the demodulated QPSK signals with baudrates up to 5 GBd.