RF notch filter having multiple notch and variable notch frequency characteristics
First Claim
1. A notch filter for attenuating an undesired frequency spectrum in an input signal having desired frequency spectra, said notch filter comprising:
- A) a passive bandpass filter means having a center frequency corresponding to the undesired frequency spectrum for receiving the input signal,B) an inverter that generates an inverted output from said bandpass filter, andC) a signal combiner for combining the input signal and the inverted output to produce an output signal in which that portion of the input signal in the undesired frequency spectrum is attenuated.
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Abstract
A filter network having the capability of establishing multiple, tunable notch frequencies. A notch filter path is established for each notch frequency and includes a bandpass filter and inverter. An input RF signal covering a wide frequency range is applied to all the notch filter paths. Each notch filter path produces an output spectrum that is equal in magnitude and 180° out of phase with respect to an undesired frequency spectrum. A combiner circuit combines the outputs of each notch filter path in parallel with the RF input signal to produce an RF output signal with all desired spectra unchanged and all undesired spectra attenuated.
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Citations
20 Claims
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1. A notch filter for attenuating an undesired frequency spectrum in an input signal having desired frequency spectra, said notch filter comprising:
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A) a passive bandpass filter means having a center frequency corresponding to the undesired frequency spectrum for receiving the input signal, B) an inverter that generates an inverted output from said bandpass filter, and C) a signal combiner for combining the input signal and the inverted output to produce an output signal in which that portion of the input signal in the undesired frequency spectrum is attenuated. - View Dependent Claims (2, 3, 4, 5)
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6. A multiple frequency notch filter network for attenuating portions of a plurality of undesired frequency spectra centered at different frequencies, from an input signal having desired frequency spectra, said notch filter comprising:
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A) a notch filter path for each undesired frequency spectrum, each said notch filter path including; i) a passive bandpass filter means for receiving the input signal having a passband at a center frequency that corresponds to the center frequency of and a width corresponding to each undesired frequency spectrum, and ii) an inverter that generates an inverted output in response to the output from said bandpass filter, B) a signal divider for coupling the input signal to each of said notch filter paths in parallel, and C) a signal combiner for combining the input signal and the inverter outputs from said notch filter paths thereby to produce a filtered output signal in which each of the portions of the input signal corresponding to the undesired frequency spectra are attenuated without change to the input signal at the desired frequency spectra. - View Dependent Claims (7, 8, 9, 10, 11, 12)
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13. A multiple frequency notch filter circuit for attenuating the magnitudes of signals in undesired RF spectra in an incoming RF signal including signals at desired and the undesired RF spectra, said notch filter circuit comprising:
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A) input terminal means for receiving the incoming RF signal and output terminal means for generating a filtered RF signal, B) a notch filter path for signals in each undesired RF spectrum, each said notch filter path being connected to said input terminal means and including; i) a passive RF bandpass filter means connected to said input terminal means for receiving the incoming RF signal, each bandpass filter means having a passband corresponding to the width of the undesired RF spectrum and a center frequency corresponding to the center frequency of the undesired RF spectrum, ii) an inverter for shifting the phase of the output of said bandpass filter means substantially 180°
, andC) a combiner connected to the output terminal means for receiving signals from said input terminal means and each of said notch filter paths in parallel thereby to produce the filtered signal at said output terminal means. - View Dependent Claims (14, 15, 16, 17)
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18. A notch filter for attenuating at least one undesired frequency spectrum in an input signal including desired and undesired frequency spectra, said notch filter comprising:
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A) a bandpass filter having a fixed center frequency and a passband that corresponds to the width of the undesired frequency spectrum, B) a local oscillator, C) a first mixer for combining the input signal and the local oscillator frequency thereby to translate the frequency of signals in the undesired frequency spectrum to the passband of said bandpass filter, D) an inverter that generates an inverted output or response to the output from said bandpass filter, E) a second mixer for combining the signals from said inverter and the local oscillator thereby to translate the inverted output to the original frequency of the undesired frequency spectrum, and F) a signal combiner for combining the input signal and the output from said second mixer to produce an output signal in which signals at the undesired frequency spectra are attenuated. - View Dependent Claims (19, 20)
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Specification