US 6,636,128 B2Granted

Frequency-tunable notch filter

AssigneeThe United States of America as represented by the Secretary of the Navy

InventorChristen Rauscher

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Abstract

A new type of frequency-tunable active notch filter achieves frequency selectivity through interaction among input derived signal components that are passed through parallel signal channels in a forward-only direction. The notch filter differs from earlier channelized notch filters by using multiple, instead of just one, bandpass channels that maintain required forward signal flow in the main, passband-determining signal path without signal distortion at passband frequencies. The new approach has been experimentally verified with a hybrid-integrated three-channel filter whose 40-dB-deep band-reject notch can be continuously tuned, with the help of voltage-controlled variable-capacitance elements, from 9.5 to 10.5 GHz. A single-pole bandpass filter tunes in frequency with the help of only one variable capacitance element, yet still maintains constant passband width across the tuning span. One feature of the bandpass filter is the achievement of constant notch bandwidth across the entire frequency-tuning span of the notch filter.

Claims18

Dependent claims

A notch filter comprising:

a reciprocal passive phase-shift network having a first port and a second port,
a frequency-selective directional coupling network having a third port, a fourth port, a fifth port, and a sixth port,
the third port of the frequency-selective coupling network being receptive to an input signal,
the fourth port of the frequency-selective coupling network being capable of producing an output signal,
the fifth port of the frequency-selective coupling network being connected to the first port of the reciprocal passive phase-shift network,
the sixth port of the frequency-selective coupling network being connected to the second port of the reciprocal passive phase-shift network,
the frequency-selective directional coupling network allowing essentially no signal to flow from the third port of the frequency-selective directional coupling network to the sixth port of the frequency-selective directional coupling network through the frequency-selective directional coupling network,
wherein upon receiving a first input signal having a frequency within a predetermined frequency band, a first portion of the first input signal passes from the third port of the frequency-selective directional coupling network to the fifth port of the frequency-selective directional coupling network, from the fifth port of the frequency-selective directional coupling network to the sixth port of the frequency-selective directional coupling network through the reciprocal passive phase-shift network, and from the sixth port of the frequency-selective directional coupling network to the fourth port of the frequency-selective directional coupling network;
and
a second portion of the first input signal passes from the third port of the frequency-selective directional coupling network to the fourth port of the frequency-selective directional coupling network through the frequency-selective directional coupling network, resulting in cancellation of the first portion of the first input signal with the second portion of the first input signal at the fourth port of the frequency-selective directional coupling network, and
wherein upon receiving a second input signal having a frequency outside the predetermined frequency band, essentially all of the second input signal passes from the third port to the fifth port, from the fifth port to the sixth port through the reciprocal passive phase-shift network, and from the sixth port to the fourth port.

8 more elements

A channelized notch filter comprising:

a main input port;
a main output port;
a first branch channel;
a second branch channel;
a third branch channel;
the first branch channel comprising a first input port, a first bandpass filter, a first phase-shift network, a second bandpass filter, and a first output port electrically connected sequentially in cascade,
the second branch channel comprising a second input port, a third bandpass filter, and a second output port electrically connected sequentially in cascade,
the third branch channel comprising a third input port, a second phase-shift network and a third output port electrically connected sequentially in cascade,
wherein the main input port, the first input port, the second input port and the third input port are electrically connected;
and
a third phase-shift network having a fourth input port and a fourth output port,
wherein the first output port of the first branch channel is electrically connected to the main output port and to the fourth output port of the third phase-shift network, and
wherein the second output port of the second branch channel is electrically connected to the fourth input port of the third phase-shift network and to the third output port of the third branch channel.

10 more elements

A channelized notch filter comprising:

a main input port;
a main output port;
a first branch channel;
a second branch channel;
a third branch channel,
the first branch channel comprising a first input port, a first bandpass filter, a first phase-shift network, an amplifier, a second phase-shift network, a second bandpass filter, and a first output port electrically connected in cascade,
the second branch channel comprising a second input port, a third bandpass filter, a third phase-shift network, an amplifier, a fourth phase-shift network, a fourth bandpass filter, and a second output port electrically connected in cascade,
the third branch channel comprising a third input port, a fifth phase-shift network, and a third output port electrically connected in cascade;
a sixth phase-shift network;
a seventh phase-shift network;
a first three-port compensated junction network connecting the main input port, the first input port of the first branch channel, and the sixth phase-shift network;
a second three-port compensated junction network connecting the sixth phase-shift network, the second input port of the second branch channel, and the third input port of the third branch channel;
a third three-port compensated junction network connecting the main output port, the first output port of the first branch channel, and the seventh phase-shift network;
and
a fourth three-port compensated junction network connecting the seventh phase-shift network, the second output port of the second branch channel, and the third output port of the third branch channel,
wherein the first and second branch channels, the sixth and seventh phase-shift networks, and the first, second, third and fourth compensated junction networks together form a frequency-selective directional four-port coupling network,
whereby upon receiving a first signal having a frequency with a predetermined frequency band, the coupling network directs a first portion of the first input signal through the first and second branch channels that are a part of the selective directional four-port coupling network and a second portion of the first input signal to the third branch channel, causing the second portion of the first input signal passing through the third branch channel to cancel the first portion of the first input signal passing through the first and second branch channels, and
whereby upon receiving a second signal having a frequency outside the predetermined frequency band, the frequency-selective directional four-port coupling network directs essentially all of the second signal through the third branch channel.

15 more elements

A single-pole bandpass filter comprising:

an input port having a first terminal and a second terminal;
an output port having a first terminal and a second terminal, wherein the second terminal of the input port and the second terminal of the output port are grounded;
a first capacitor having a first terminal and a second terminal, wherein the first terminal of the first capacitor is electrically connected with the first terminal of the input port and the second terminal of the first capacitor is grounded;
a second capacitor having a first terminal and a second terminal, wherein the first terminal of the second capacitor is electrically connected to the first terminal of the input port;
a third capacitor having a first terminal and a second terminal, wherein the first terminal of the third capacitor is electrically connected to the second terminal of the second capacitor and the second terminal of the third capacitor is grounded;
a first transmission-line segment having a first terminal, a second terminal, a third terminal, and a fourth terminal, wherein the first terminal of the first transmission-line segment is electrically connected to the second terminal of the second capacitor, and wherein the third and fourth terminals of the first transmission-line segment is grounded;
a fourth capacitor having a first terminal and a second terminal, wherein the first terminal of the fourth capacitor is electrically connected to the second terminal of the first transmission line segment, and wherein the second terminal of the fourth capacitor is grounded;
a variable-reactance element having a first terminal and a second terminal, wherein the first terminal of the variable-reactance element is electrically connected to the second terminal of the first transmission-line segment;
a fifth capacitor having a first terminal and a second terminal, wherein the first terminal of the fifth capacitor is electrically connected to the second terminal of the variable-reactance element and the second terminal of the fifth capacitor is grounded;
a second transmission-line segment having a first terminal, a second terminal, a third terminal and a fourth terminal, wherein the first terminal of the second transmission-line segment is electrically connected to the second terminal of variable-reactance element, and wherein the third and fourth terminals of the second transmission-line segment are grounded;
a sixth capacitor having a first terminal and a second terminal, wherein the first terminal of the sixth capacitor is electrically connected to the second terminal of the second transmission-line segment and the second terminal of the sixth capacitor is grounded;
a seventh capacitor having a first terminal and a second terminal, wherein the first terminal of the seventh capacitor is electrically connected to the second terminal of the second transmission-line segment and the second terminal of the seventh capacitor is electrically connected to the first terminal of the output port;
and
an eighth capacitor having a first terminal and a second terminal, wherein the first terminal of the eighth capacitor is electrically connected to the second terminal of the seventh capacitor and the first terminal of the output port and the second terminal of the eighth capacitor is grounded.

11 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/874,429Filed 7 Jun 2001
Published: US 2003/0169128 A111 Sep 2003
Granted: 21 Oct 2003
Term ends: Not estimatedThe source records don’t support an estimate.

Classification6 codes

H03H 7/0123
Frequency selective two-port networks: comprising distributed impedance elements together with lumped impedance elements
H03H 1/02
Constructional details of impedance networks whose electrical mode of operation is not specified or applicable to more than one type of network:…
H03H 2007/013
Frequency selective two-port networks: notch or bandstop filters
H03H 2210/015
Tuned parameter of filter characteristics: quality factor or bandwidth