# US 9,519,050 B2 · Method of system compensation to reduce the effects of self interference in frequency modulated continuous wave altimeter systems

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- Number: US 9,519,050 B2
- Document ID: US9519050B2
- Status: Granted
- Kind: B2
- Application number: 15/006,766
- Filed: 2016-01-26
- Published: 2016-05-19
- Granted: 2016-12-13
- Earliest claimed: 2012-07-27
- Assignees: Honeywell International Inc.
- Applicants: Honeywell International Inc.
- Inventors: Paul David Ferguson
- Web page: https://patentgrep.com/patent/US9519050B2

## CPC

- G01S 7/023: {Interference mitigation, e.g. reducing or avoiding non-intentional interference with other HF-transmitters, base station transmitters for mobile communication or other radar systems, e.g. using electro-magnetic interference [EMI] reduction techniques (auxiliary means for detecting or identifying radar signals or the like G01S7/021; means for anti-jamming G01S7/36)}
- G01S 7/038: {Feedthrough nulling circuits}
- G01S 13/343: {using sawtooth modulation}
- G01S 13/882: {for altimeters (measuring height using barometric means G01C5/06)}
- G01S 13/32: using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES

## Abstract

An altimeter system is provided. The altimeter system includes a receiver mixer including an antenna-input and a local-oscillator-input; a transceiver circulator communicatively coupled to an antenna via a transmission line having a selected length and communicatively coupled to the antenna-input of the receiver mixer; and a transmitter configured to output a transmitter signal to the antenna via the transceiver circulator. The transmitter signal is frequency modulated with a linear ramp. The transmitter is communicatively coupled to the receiver mixer to input a local oscillator signal at the local-oscillator-input of the receiver mixer. The receiver mixer is communicatively coupled to input a target-reflected signal from the antenna at the antenna-input of the receiver mixer. The selected length of the transmission line is set so that a composite-leakage signal at the antenna-input of the receiver mixer has a linear phase across a sweep bandwidth.

## Claims

### Claim 1

An altimeter system, comprising:
a receiver mixer including an antenna-input and a local-oscillator-input;
a transceiver circulator communicatively coupled to an antenna via a transmission line having a selected length and communicatively coupled to the antenna-input of the receiver mixer;
a transmitter configured to output a transmitter signal to the antenna via the transceiver circulator, wherein the transmitter signal is frequency modulated with a linear ramp; and
a local oscillator delay line configured to input the transmitter signal from the transmitter and to output a local oscillator signal derived from the transmitter signal to the local-oscillator-input of the receiver mixer,
wherein the transmitter is communicatively coupled to the receiver mixer to input the local oscillator signal at the local-oscillator-input of the receiver mixer,
wherein the receiver mixer is communicatively coupled to input a target-reflected signal from the antenna at the antenna-input of the receiver mixer,
wherein the target-reflected signal is reflected from a target to the antenna, and
wherein the selected length of the transmission line is set so that a composite-leakage signal at the antenna-input of the receiver mixer has a linear phase across a sweep frequency range and composite-leakage-amplitude nulls are outside an operating bandwidth of the altimeter system, wherein the composite-leakage signal is a coherent superposition of an antenna-reflection-leakage signal and a circulator-leakage signal at the antenna input of receiver mixer,
wherein an input impedance of the antenna is tuned so: an amplitude response of an antenna-return signal reflected from the antenna is relatively flat a phase response of the composite leakage signal input at the antenna-input of the receiver mixer is linear across the sweep-frequency range of the altimeter system; and an output voltage of a receiver mixer is a direct current (DC) voltage with reduced alternating current (AC) voltage across the operating bandwidth; and
wherein a phase of the local oscillator signal input to the local-oscillator-input of the receiver mixer is adjusted by adjusting a phase length of a local oscillator (LO) delay line to maintain a quadrature relationship to a phase of the composite-leakage signal input to the antenna-input of the receiver mixer across the operating bandwidth.

### Claim 2 (depends on 1)

The altimeter system of claim 1, wherein an antenna-reflection-leakage signal of the transmitter signal is reflected by the antenna to the antenna-input of the receiver mixer via the transceiver circulator,
wherein the circulator-leakage signal of the transmitter signal is transmitted from the transmitter via the transceiver circulator to the antenna-input of the receiver mixer, and
wherein, based on the selected length of the transmission line, 180 degree phase differences between the antenna-reflection-leakage signal and the circulator-leakage signal occur at frequencies outside of the sweep frequency range.

### Claim 3 (depends on 1)

The altimeter system of claim 1, further comprising the antenna, wherein the antenna is configured to transmit the transmitter signal toward the target and configured to receive the target-reflected signal.

### Claim 4 (depends on 1)

The altimeter system of claim 1, further comprising a receiver intermediate frequency module communicatively coupled to input an intermediate frequency (IF) signal output from the receiver mixer.