Frequency translating circuit with multiple stages using common local oscillator

Claim 1

A multi-stage frequency translator for receiving an input signal (RF) of a first frequency at a first stage and producing an output signal (IF) of a lower frequency at a last stage, wherein the improvement comprises: a local oscillator, in each stage except the last, a mixer element and a filter means, the first stage mixer element (28) being connected directly to receive the input signal and connected to the local oscillator to receive a local oscillator signal (LO) from the local oscillator, the filter means in the first stage and in each other stage except the last stage connecting the mixer element of the associated stage to supply to the mixer element (29) of a next stage a signal that contains a difference frequency and the local oscillator signal, a last stage mixer element (29) connected to receive an output signal of a preceding stage (28) to form a chain of two or more mixer stages, and filter means (Mckt 4) in the last stage connecting the mixer element of the last stage to form the frequency translator output signal containing the difference frequency of the last stage mixer element but not the local oscillator signal, whereby the local oscillator signal is propagated from the first stage to each subsequent stage and each stage except the first mixes the difference frequency from the preceding stage and the local oscillator signal from the preceding stage.