Notch filter

An improved notch filter for rejecting a predetermined bandwidth of signal frequencies comprising:

• a. a first impedance element having a signal input terminal and a signal output terminal and having an input admittance substantially constant in both phase and magnitude over a predetermined notch frequency bandwidth and having a primarily reactive impedance characteristic at all other frequencies,
• b. a second conventional impedance element having an input terminal and an output terminal in electrical parallel with said first impedance element, and
• c. a phase reversal transformer in series with one but not the other of said first and second impedance elements to cause said signal frequency output from said one impedance element to be substantially equal to and cancelled by an opposite phase output signal from said other impedance element at said notch frequency bandwidth.

An improved notch filter comprising:

• a. a first circuit including an impedance element having an input admittance substantially constant in both phase and magnitude over a predetermined notch frequency bandwidth, said circuit having primarily reactive characteristics at frequencies higher or lower than said notch frequency, and primarily resistive characteristics at the center of said notch frequency,
• b. a second circuit in parallel with said first circuit and comprising a resistance and being resistive at all frequencies, and
• c. a series coupled, phase reversing transformer in series with one but not the other of said first and second circuits to cause an output 180.degree. out-of-phase with said other circuit output whereby at said notch frequency said first and second circuit outputs are substantially equal and cancelling thereby providing no output and rejecting a predetermined bandwidth of frequencies.

A method of constructing an improved notch filter for rejecting a predetermined band of signal frequencies comprising the steps of:

• a. providing a first circuit with input and output terminals and having an output signal, said first circuit having an inductor in parallel with an impedance element having an input admittance substantially constant in both magnitude and phase over a predetermined bandwidth at the center of the notch frequency, said circuit having primarily reactive characteristics at signal frequencies higher or lower than the notch frequency bandwidth and primarily resistive characteristics at the center of said notch frequency, and
• b. placing a second circuit with input and output terminals in parallel with said first circuit, said second circuit being resistive at all frequencies and having an output signal 180.degree. out-of-phase with said first circuit output to cause said first and second circuit outputs to be substantially equal and cancelling at the center of said notch frequency thereby providing no output and rejecting a predetermined bandwidth of frequencies.

A method of forming an improved notch filter for rejecting a predetermined bandwidth of signal frequencies comprising the steps of:

• a. forming a first impedance element having an input admittance substantially constant in both phase and magnitude over a predetermined notch frequency bandwidth and having a primarily reactive impedance characteristic at all frequencies,
• b. placing a second conventional impedance element in parallel with said first impedance element, and
• c. placing a phase reversal transformer in series with one but not the other of said first and second impedance elements to cause said signal frequency output from said one impedance element to be substantially equal and cancelled by an opposite phase output signal from said other impedance element at said notch frequency bandwidth.

A method of forming an improved notch filter having a predetermined notch frequency bandwidth and comprising the steps of:

• a. forming a first circuit with a single port, single phase, unidirectional transducer having an input and an output, said circuit having primarily reactive characteristics at higher or lower frequencies than said notch frequency bandwidth and primarily resistive characteristics at the center of said notch frequency bandwidth,
• b. placing a second circuit in parallel with said first circuit, said second circuit comprising a resistance and being resistive at all frequencies, and
• c. placing a series coupled, phase reversing transformer in series with one but not the other of said first and second circuits to cause an output 180.degree. out-of-phase with said other circuit output whereby at said notch frequency bandwidth said first and second circuit outputs are substantially equal and cancelling thereby providing no output and rejecting a predetermined bandwidth of frequencies.

A method of forming an improved notch filter having a predetermined notch frequency bandwidth and comprising the steps of:

• a. providing a first circuit having an input and an output and that has primarily reactive characteristics at frequencies higher or lower than said notch frequency bandwidth and primarily resistive characteristics at the center of said notch frequency bandwidth,
• b. providing a second circuit having an input and an output in parallel with said first circuit, said second circuit comprising a resistance and being resistive at all frequencies, and
• c. placing a series coupled, phase reversal means in series with one but not the other of said first or second circuits to cause an output 180.degree. out-of-phase with said output of said other circuit whereby at said notch frequency said first and second outputs are substantially equal and cancelling thereby providing no output and rejecting a predetermined bandwidth of frequencies.