In this article a millimetre-wave (mm-wave) down-converter based on a six-port correlator and zero bias Schottky diode is presented over 10 GHz bandwidth, from 72 to 82 GHz. The six-port is designed in such a way to have excellent phase resolution at four output ports witch leads to very accurate symbol position for QPSK demodulator. A prototype circuit has been manufactured with miniaturized hybrid microwave integrated-circuit (MHMIC) technology on a 127μm ceramic substrate. The results are validated using a computer model of the circuit based on S-parameter measurements for QPSK demodulator for center frequency of 77 GHz.