Electronic image cancellation for doppler receivers

Claim 2

An electronic image cancellation circuit for a doppler receiver for cancelling the image noise introduced into the receiver through the mixing of the first IF signal returns toward the offset audio signal, including in combination: oscillator means for producing first and second coherent oscillator signals which are phase shifted from each other in a predetermined phase relationship; mixer means adaptable to receive first IF signal returns and being coupled to said oscillator means for mixing the first IF signal returns with each of the first and second coherent oscillator signals from said oscillator means to produce first and second coherent offset audio signals; each of the first and second coherent offset audio signals having signal and image noise components that are respectively phase shifted from each other and respectively phase shifted from the corresponding signal and image noise components of the other; and summing means coupled to said mixer means and being responsive to the first and second coherent offset audio signals therefrom for summing the signal components and cancelling the image noise components thereof.

Claim 3

The electronic image cancellation circuit of claim 1 used in conjunction with a CW doppler radar receiver.

Claim 4

The electronic image cancellation circuit of claim 1 used in conjunction with a pulsed doppler radar receiver.

Claim 5

A doppler receiver including in combination, channel means having means for receiving transmitted signal return information, oscillator means for producing a plurality of output signals at preselected frequencies, phase shifting means coupled between said oscillator means and said channel means for incrementally phase-shifting selected ones of the output signals of said oscillator means and selectively applying them to said channel means, said channel means selectively mixing the signal return information and the phase shifted output signals of said oscillator means to audio frequencies, and summing means coupled to said channel means for summing the mixed signal return information and cancelling the signals at the image frequencies produced by the mixing of the signal return information with the oscillator signals.

Claim 6

A doppler receiver including in combination, channel means having means for receiving transmitted signal return information, oscillator means for producing a plurality of output signals at preselected frequencies, phase shifting means coupled between said oscillator means and said channel means for incrementally phase-shifting selected ones of the output signals of said oscillator means and selectively applying them to said channel means, said channel means selectively mixing the signal return information and the phase shifted output signals of said oscillator means to audio frequencies, and summing means coupled to said channel means for summing the mixed signal return information and cancelling the signals at the image frequencies produced by the mixing of the signal return information with the oscillator signals.

Claim 7

A doppler receiver system including in combination: first and second channels for translating signal returns to baseband frequencies, each of said channels having input and output terminals and including a plurality of mixers in sequential alignment, a plurality of oscillator means selectively coupled to said mixer means, each of said oscillator means having quadrature voltage outputs and selectively applying same to said mixer means, each of said input terminals coupled together for reception of the signal return, summing means coupled between said output terminals and responsive to the heterodyning of the signal returns with the quadrature outputs to produce output Offset frequencies devoid of image noise.

Claim 8

A doppler receiver system including in combination: first and second channels for translating signal returns to baseband frequencies, each of said channels having input and output terminals and including a plurality of mixers in sequential alignment, a plurality of oscillator means selectively coupled to said mixer means, each of said oscillator means having quadrature voltage outputs and selectively applying same to said mixer means, each of said input terminals coupled together for reception of the signal return, summing means coupled between said output terminals and responsive to the heterodyning of the signal returns with the quadrature outputs to produce output Offset frequencies devoid of image noise.

Claim 9

The apparatus of claim 5 further including filter means coupled between adjacent ones of said mixers for passing a desired band of frequencies and filtering out undesired frequencies.

Claim 10

An electronic image frequency cancellation circuit for the receiver portion of a pulsed doppler radar system including in ombination: first, second, third and fourth mixer circuits, each of said mixer circuits having signal, oscillator and output terminals, said signal terminals of said first and third mixer circuits connected together for receiving signal return information applied thereto, and said signal terminals of said second and fourth mixer circuits respectively coupled to said output terminals of said first and third mixer circuits for reception of output signals therefrom, first and second oscillator means having different respective output frequencies, each of said oscillator means having outputs of first and second phases, said first oscillator means coupled between said oscillator terminals of said first and third mixer circuits in order to supply its first and second phases to said first and third mixer circuits respectively, said second oscillator means coupled between said oscillator terminals of said second and third mixer circuits in order to apply its first and second phases to said fourth and second mixer circuits respectively, summing means having first and second input terminals coupled between said output terminals of said second and fouth mixer means for reception of signals therefrom, said first and third mixer circuits responsive to the application of the signal return information and the outputs of said first oscillator means to produce mixed signal return information containing both signal and image noise components at a first frequency and at different phases for respective application to said second and fourth mixer circuits, said second and fourth mixer circuits responsive to the application of said mixed signal return information and the outputs of said second oscillator means to produce phase shifted mixed signals containing both signal and image noise components at a second frequency for respective application to said summing means, said summing means responsive to the reception of the second mixed signals to add the in-phase signal components and cancel the out-of-phase image noise components.

Claim 11

An electronic image frequency cancellation circuit for the receiver portion of a pulsed doppler radar system including in ombination: first, second, third and fourth mixer circuits, each of said mixer circuits having signal, oscillator and output terminals, said signal terminals of said first and third mixer circuits connected together for receiving signal return information applied thereto, and said signal terminals of said second and fourth mixer circuits respectively coupled to said output terminals of said first and third mixer circuits for reception of output signals therefrom, first and second oscillator means having different respective output frequencies, each of said oscillator means having outputs of first and second phases, said first oscillator means coupled between said oscillator terminals of said first and third mixer circuits in order to supply its first and second phases to said first and third mixer circuits respectively, said second oscillator means coupled between said oscillator terminals of said second and third mixer circuits in order to apply its first and second phases to said fourth and second mixer circuits respectively, summing means having first and second input terminals coupled between said output terminals of said second and fouth mixer means for reception of signals therefrom, said first and third mixer circuits responsive to the application of the signal return information and the outputs of said first oscillator means to produce mixed signal return information containing both signal and image noise components at a first frequency and at different phases for respective application to said second and fourth mixer circuits, said second and fourth mixer circuits responsive to the application of said mixed signal return information and the outputs of said second oscillator means to produce phase shifted mixed signals containing both signal and image noise components at a second frequency for respective application to said summing means, said summing means responsive to the reception of the second mixed signals to add the in-phase signal components and cancel the out-of-phase image noise components.

Claim 12

The apparatus of claim 7 further including a first filter circuit coupled between said output terminal of said first mixer circuit and said signal terminal of said second mixer circuit, and a second filter circuit coupled between said output terminal of said third mixer circuit and said signal terminal of said fourth mixer circuit, and said first and second filter circuits passing a predetermined band of frequencies and rejecting all other frequencies.

Claim 13

An electronic image cancellation circuit for a doppler receiver including in combination: first and second mixer means having means for receiving a radio frequency input signal, means for providing output quadrature signals being coupled between said first and second mixer means, each of said first and second mixer means being responsive to the reception of the input signal and one of the quadrature signals to produce an intermediate frequency signal having phase-shifted signal and image noise components, phase shifting means connected to said second mixing means for shifting the phase of the signal and image noise components from said second mixing means, and summation means coupled between said first mixing means and said phase shifting means in order to cancel the image noise components and add the signal components.

Claim 14

An electronic image cancellation circuit for a doppler receiver including in combination: first and second mixer means having means for receiving a radio frequency input signal, means for providing output quadrature signals being coupled between said first and second mixer means, each of said first and second mixer means being responsive to the reception of the input signal and one of the quadrature signals to produce an intermediate frequency signal having phase-shifted signal and image noise components, phase shifting means connected to said second mixing means for shifting the phase of the signal and image noise components from said second mixing means, and summation means coupled between said first mixing means and said phase shifting means in order to cancel the image noise components and add the signal components.

Claim 15

The means for providing output quadrature signals of the apparatus of claim 9 including: oscillator means coupled to said first mixer means for providing a first signal thereto, and a further phase shifting means coupled between said oscillator means and said second mixer meanS for shifting the phase of a second signal from said oscillator means before applying same to said second mixer.

Claim 16

The apparatus of claim 10 further including filter means coupled to said summation means for rejecting all frequencies except the added signal components at the intermediate frequency.

Claim 17

The apparatus of claim 1 further including filter means coupled to said summing means for rejecting all frequencies except the summed signal components of the first and second coherent output signals.