Notch filter

Claim 1

An improved notch filter for rejecting a predetermined band of signal frequencies comprising: a. a first circuit having a signal input terminal and a signal output terminal for providing an output signal at said output terminal, 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 band width at the center of the notch frequency, said first circuit having primarily reactive characteristics at signal frequencies higher or lower than the notch frequency band width and primarily resistive characteristics at the center of said notch frequency, and b. a second circuit having a signal input terminal and a signal output terminal in electrical parallel with said first circuit and being resistive at all frequencies and having a second output signal at its output terminal 180° out-of-phase with said first circuit output signal whereby at the center of said notch frequency said first and second circuit output signals are substantially equal and cancelling thereby providing no output and rejecting a predetermined band width of frequencies.

Claim 18

A method of forming an improved notch filter comprising the steps of: a. forming an impedance device with input and output terminals and having a susceptance versus frequency response with a substantially flat portion over a finite bandwidth on both sides of a predetermined frequency, b. placing an inductor means in parallel with said impedance element to form a first parallel resonant circuit which is substantially resistive at resonance and a low impedance at all other frequencies, c. coupling a resistor means having input and output terminals in parallel with said first parallel circuit to form a second parallel circuit having first and second parallel legs, said resistor passing all frequencies applied thereto, and d. coupling means to one but not both legs of said second parallel circuit to reverse signal polarity only through said one leg whereby at resonance said signal through said legs are equal and opposite and thereby cancelled to form a notch filter.

Claim 19

A method of forming an improved notch filter comprising the steps of: a. forming an impedance device with input and output terminals and having a susceptance versus frequency response with a substantially flat portion over a finite bandwidth on both sides of a predetermined frequency, b. placing an inductor means in parallel with said impedance element to form a first parallel resonant circuit which is substantially resistive at resonance and a low impedance at all other frequencies, c. coupling a resistor means having input and output terminals in parallel with said first parallel circuit to form a second parallel circuit having first and second parallel legs, said resistor passing all frequencies applied thereto, and d. coupling means to one but not both legs of said second parallel circuit to reverse signal polarity only through said one leg whereby at resonance said signal through said legs are equal and opposite and thereby cancelled to form a notch filter.

Claim 21

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° 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.

Claim 22

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° 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.

Claim 29

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.

Claim 30

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.

Claim 35

A method of forming an improved notch filter circuit comprising the steps of: a. providing an impedance element with input and output terminals and having an input admittance substantially constant in both phase and magnitude over a predetermined frequency bandwidth, b. forming a first parallel resonant circuit having input and output terminals and which is primarily resistive at the center of said predetermined bandwidth by placing an inductor in parallel with said impedance element, c. forming a second parallel circuit by placing a bridging resistor in parallel with said impedance element and said inductor, said resistor having a value substantially equal to the resistive value of said first parallel circuit at resonance, d. coupling a phase reversal transformer to one but not the other of said first and second parallel circuits to cause the outputs of said first and second parallel circuits to cancel at resonance thereby forming a notch filter having a bandwidth equal to said predetermined bandwidth, e. coupling a signal source impedance to the input of said first and second parallel circuits, and f. coupling a load impedance to the output of said first and second parallel circuits, said source and load impedance each having a value substantially equal to one-half of the value of said bridging resistor.

Claim 36

A method of forming an improved notch filter circuit comprising the steps of: a. providing an impedance element with input and output terminals and having an input admittance substantially constant in both phase and magnitude over a predetermined frequency bandwidth, b. forming a first parallel resonant circuit having input and output terminals and which is primarily resistive at the center of said predetermined bandwidth by placing an inductor in parallel with said impedance element, c. forming a second parallel circuit by placing a bridging resistor in parallel with said impedance element and said inductor, said resistor having a value substantially equal to the resistive value of said first parallel circuit at resonance, d. coupling a phase reversal transformer to one but not the other of said first and second parallel circuits to cause the outputs of said first and second parallel circuits to cancel at resonance thereby forming a notch filter having a bandwidth equal to said predetermined bandwidth, e. coupling a signal source impedance to the input of said first and second parallel circuits, and f. coupling a load impedance to the output of said first and second parallel circuits, said source and load impedance each having a value substantially equal to one-half of the value of said bridging resistor.

Claim 37

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° 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.

Claim 38

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° 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.

Claim 39

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° 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.

Claim 40

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° 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.