Poly-Frequency CW Doppler Radar System With Leakage Cancellation and Method

1. A Continuous Wave (CW) Doppler radar system with leakage cancellation comprising: a) an antenna for transmitting and receiving signals; b) an antenna interface in electrical communication with the antenna, the antenna interface having an input for receiving a plurality of transmit signals, each transmit signal having a different frequency, and an output for outputting a plurality of return signals, each return signal having a received signal component from the antenna and a leakage signal component leaked through the interface from the transmit signal associated with the received signal; c) an intermediate frequency (IF) mixer for mixing each of the plurality of return signals with a common reference signal to generate a plurality of IF return signals; d) an adder for receiving the plurality of IF return signals and a plurality of leakage cancellation signals and for generating an adder output signal therefrom; e) a plurality of cancellation loops in electrical communication with the adder for generating a plurality of associated leakage cancellation signals for each individual transmit signal, each of the plurality of cancellation loops comprising: 1) a reference signal mixer for mixing the common reference signal with one of the transmit signals to generate an associated mixed reference signal therefrom, 2) a first cancellation mixer for mixing one of the IF return signals with the associated mixed reference signal to generate an associated mixed IF return signal therefrom; 3) a linear feedback cancellation circuit for generating an associated mixed leakage cancellation signal from the associated mixed IF return signal, the feedback cancellation circuit being operative to generate a filtering notch with a notch bandwidth of less than 1 Hertz and a notch depth of over 40 dB at the frequency of the associated mixed IF return signal; 4) a second cancellation mixer for mixing the associated mixed leakage cancellation signal with the associated mixed reference signal to generate an unmixed leakage cancellation signal therefrom; and f) the adder being operative to sum the plurality of IF return signals with a plurality of leakage cancellation signals and to output a plurality of filtered return signals, each filtered return signal being characterized by the absence of an associated leakage component.

2. The CW Doppler radar system of claim 1, further comprising a local oscillator to generate a local oscillator signal, and a single sideband generator being operative to mix the reference signal with the local oscillator signal.

3. The CW Doppler radar system of claim 2 further comprising an up-converter to mix the local oscillator signal with the plurality of transmit signals.

4. The CW Doppler radar system of claim 3 further comprising an amplifier disposed between the adder and the first cancellation mixer.

5. The CW Doppler radar system of claim 4, wherein for each transmit signal, a pair of cancellation loops are coupled with a first loop having an in-phase cancellation circuit, and a second loop having a quadrature-phase cancellation circuit.

6. The CW Doppler radar system of claim 5 wherein each loop of the paired cancellation loops includes a phase compensation circuit coupled the first cancellation mixer.

7. A method of canceling leakage in a CW Doppler radar system comprising the steps of: (a) transmitting a plurality of transmit signals; (b) receiving a plurality of return signals each having a received signal component from the antenna and a leakage signal component from an associated transmit signal; (c) mixing the plurality of return signals with a reference signal, to generate a plurality of IF return signals; (d) mixing the reference signal with a plurality of associated transmit signals to form a plurality of mixed reference signals; (e) mixing the plurality of IF return signals with the plurality of associated mixed reference signals to generate a plurality of mixed IF return signals; (f) correlating the plurality of mixed IF return signals to generate a plurality of associated mixed leakage cancellation signals; (g) mixing the plurality of mixed leakage cancellation signals with the plurality of associated mixed reference signals to generate a plurality of unmixed leakage cancellation signals; (h) summing the plurality of leakage cancellation signals to generate a feed-back signal representative of the plurality of leakage cancellation signals; and (i) subtracting the feed-back signal from the plurality of IF return signals to generate a received signal.

8. The method of claim 7, wherein step (c) further includes the step of amplifying the IF signal.

9. The method of claim 8 wherein step (c) includes the step of splitting the plurality of IF return signals into an in-phase IF return signal and a quadrature-phase IF return signal for each transmit signal; step (e) further includes the step of mixing the in-phase IF return signal with an associated in-phase reference signal and mixing the quadrature-phase IF return signal with an associated quadrature-phase reference signal; step (f) further includes the step of correlating the mixed in-phase IF return signal to form an associated mixed in-phase leakage cancellation signal and correlating the mixed quadrature-phase IF return signal to form an associated mixed quadrature-phase leakage cancellation signal; and step (g) further incudes the step of mixing the in-phase leakage cancellation signal and mixing the quadrature-phase leakage cancellation signal.

10. The method of claim 9 wherein the plurality of transmit signals are mixed with a signal from a local oscillator.

11. The method of claim 10 wherein step (c) further includes mixing the reference signal with the local oscillator signal.