A Sideband-Mixing Superheterodyne Receiver

Microwave receivers having bandwidths as much as 22 times greater than the intermediate-frequency amplifier bandwidth have been constructed by generating sidebands on a local oscillator signal and utilizing these sidebands as virtual local oscillators. Both a microwave and a vhf local oscillator signal are injected on a crystal to generate an infinite set of sideband signals separated by the frequency of the vhf oscillator and centered about the microwave oscillator. The low-level received signal mixes with one of these generated virtual local oscillator signals to produce the desired IF signal. The two mixing operations can take place in one crystal or two separate crystals. Measurements have been made of tangential sensitivity and conversion loss and indicate that sensitivities greater than -70 dbm and a continuous bandwidth of 700 mc can be achieved with an intermediate-frequency amplifier having 50 mc bandwidth.