Source: http://patents.com/us-10018716.html
Timestamp: 2018-12-10 17:27:08
Document Index: 656540925

Matched Legal Cases: ['Application No. 13176560', 'Application No. 13176560', 'Application No. 131551160', 'Application No. 15170178', 'Application No. 15168777', 'application No. 13176560', 'Application No. 201310476753', 'Application No. 13176560', 'Application No. 201310128132', 'Application No. 16198451', 'Application No. 201310128132', 'Application No. 1516877', 'Application No. 201310128132', 'Application No. 201310476753', 'Application No. 2007', 'Application No. 2007', 'Application No. 2012', 'Application No. 13155116', 'Application No. 13154997', 'Application No. 13154997']

US Patent # 1,001,8716. Systems and methods for calibration and optimization of frequency modulated continuous wave radar altimeters using adjustable self-interference cancellation - Patents.com
United States Patent 10,018,716
Ferguson , et al. July 10, 2018
Ferguson; Paul David (Redmond, WA), Pos; Marc (Duvall, WA), Tinsley; Robert Jason (Norcross, GA)
Family ID: 53269398
14/316,176
US 20150378017 A1 Dec 31, 2015
Current CPC Class: G01S 13/882 (20130101); G01S 7/034 (20130101); G01S 7/038 (20130101); G01S 7/4008 (20130101); G01S 7/4017 (20130101); G01S 13/343 (20130101); G01S 7/023 (20130101)
Current International Class: G01S 7/34 (20060101); G01S 13/88 (20060101); G01S 7/03 (20060101); G01S 7/40 (20060101); G01S 13/34 (20060101)
Field of Search: ;342/120
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1. A radar altimeter system comprising: a transmitter configured to output a transmitter signal; a local oscillator delay line coupled to the transmitter and including a variable time delay circuit comprising at least one analog radio frequency component, the local oscillator delay line configured to receive at least a portion of the transmitter signal and to add a time delay to the at least the portion of the transmitter signal using the at least one analog radio frequency component and resulting in a delayed signal, the variable time delay circuit configured to be adjustable so as to adjust the time delay used in creating the delayed signal, wherein the variable time delay circuit includes a filter comprising a variable shunt capacitor coupled to ground, a shunt inductor coupled to ground, a variable series capacitor, and a series inductor coupled to the variable series capacitor; a transceiver circulator coupled to the transmitter; an antenna coupled to the transceiver circulator; a frequency mixer coupled to the local oscillator delay line and coupled to the transceiver circulator; wherein the transceiver circulator directs the at least the portion of the transmitter signal to the antenna; wherein the antenna is configured to transmit the at least the portion of the transmitter signal and receive a target reflected signal from a target, wherein the target reflected signal includes at least a portion of the transmitter signal reflected from the target; wherein the transmitted signal, the delayed signal, and the target reflected signal are analog radio frequency signals; and wherein the frequency mixer is configured to receive the delayed signal and the target reflected signal from the transceiver circulator.
6. A method comprising: outputting a transmitter signal from a transmitter in a radar altimeter system; delaying at least a portion of the transmitter signal using at least one analog radio frequency component of a variable time delay circuit of a local oscillator delay line of the radar altimeter system resulting in a delayed signal, the local oscillator delay line including a variable time delay circuit adjustable to adjust the time delay added to the delayed signal, wherein the variable time delay circuit includes a filter comprising a variable shunt capacitor coupled to ground, a shunt inductor coupled to ground, a variable series capacitor, and a series inductor coupled to the variable series capacitor; transmitting at least a portion of the transmitter signal using a transceiver circulator and an antenna; receiving a target reflected signal from a target at the antenna and passing it through the transceiver circulator to a frequency mixer, the target reflected signal including at least a portion of the transmitter signal reflected from the target; wherein the transmitted signal, the delayed signal, and the target reflected signal are analog radio frequency signals; and receiving the delayed signal and the target reflected signal at the frequency mixer.
7. The method of claim 6, wherein a phase of the delayed signal at the frequency mixer is configured to maintain a quadrature relationship between the phase of the delayed signal and a phase of a composite-leakage signal; wherein the composite-leakage signal comprises a circulator-leakage signal and an antenna-reflection-leakage signal.
8. An apparatus comprising: a local oscillator delay line including a variable time delay circuit for use in an altimeter, wherein the variable time delay circuit includes at least one analog radio frequency component, wherein the variable time delay circuit includes a filter comprising a variable shunt capacitor coupled to ground, a shunt inductor coupled to ground, a variable series capacitor, and a series inductor coupled to the variable series capacitor; wherein the local oscillator delay line delays a signal travelling through the local oscillator delay line by a quantity of time using the at least one analog radio frequency component to maintain a quadrature relationship with a composite-leakage signal in the altimeter, wherein the local oscillator delay line is configured to be adjustable so as to adjust the quantity of time, and wherein the composite-leakage signal is comprised of a circulator-leakage signal and an antenna-reflection-leakage signal, wherein the composite-leakage signal, the circulator-leakage signal, and the antenna-reflection-leakage signal are analog radio frequency signals.
This Application is related to U.S. patent application Ser. No. 13/662,755 entitled, "HIGH SENSITIVITY SINGLE ANTENNA FMCW RADAR", and U.S. patent application Ser. No. 13/559,834 entitled, "METHOD OF SYSTEM COMPENSATION TO REDUCE THE EFFECTS OF SELF INTERFERENCE IN FREQUENCY MODULATED CONTINUOUS WAVE ALTIMETER SYSTEMS", both of which are incorporated herein by reference in their entirety.
In conventional implementations, separate transmit and receive antennas (bistatic radar) have been used to address many of the coupling and reflection problems discussed above. In systems that use a single antenna (monostatic radar) to transmit and receive signals, the approximate time delay matching of the local oscillator (LO) signal path has been used to address the loss of receiver sensitivity due to the transmitter phase noise raising the noise floor of the receiver. Recent improvements in system modeling and explicit control of leakage signals both in amplitude and group delay disclosed in U.S. patent application Ser. No. 13/559,834, and incorporated herein by reference, have shown that a monostatic FMCW radar can be designed to have near optimal performance along with range capability down to nearly zero range. The techniques discussed in U.S. patent application Ser. No. 13/559,834 have been successfully proven on the Single Antenna Radar Altimeter (SARA) prototypes built and tested in 2013. However, the compensation technique requires delay lines that are well matched to the characteristics of each individual radar system. Variations in the manufactured systems require each system to have a slightly different compensation delay. In conventional implementations, the different compensation delays that the systems require were solved by varying the physical lengths of transmission lines in the LO paths. Tests show that the physical lengths of the LO transmission lines have to be manually trimmed to the optimal value for the particular system with a tolerance of +/-0.005'' or about +/-0.57 ps group delay. Total overall variation in LO transmission line length (also referred to herein as "delay line") for 10 prototype units was approximately 0.050''.
As stated above, the frequency mixer 106 receives the target reflected signal 122, the combined-leakage signal 121 and the delayed signal 124. However, in order to obtain accurate ultra-short range (1-4 feet) performance, the frequency difference output 126 must have little or no alternating current (AC) content, due to combined-leakage signal 121, which could interfere with the very low frequency baseband signals produced by an ultra-short range target reflection 122. Embodiments of altimeter system 100A compensate for the self-interference due to the combined-leakage signal 121 Specifically, the phase of the delayed signal 124 maintains a quadrature phase relationship (i.e., 90.degree. or 270.degree.) with the phase of the combined-leakage signal 121 by setting the phase delay in the LO delay line 108 and the variable delay circuit 110. By maintaining a quadrature phase relationship between the delayed signal 124 and the combined-leakage signal 121, the energy in the combined-leakage signal 121 is converted to a zero volt baseband signal by the phase detector properties of the frequency mixer 120. As a result, altimeter system 100A is able to determine an ultra-short distance to a target 118 that is less than 4 feet from the altimeter system 100A.
As mentioned above, however, there may be slight manufacturing differences between altimeter systems 100A, which can lead to phase relationships between the delayed signal 124 and the combined-leakage signal 121 that are not exactly 90.degree. or 270.degree. if the same LO delay line length is chosen for each LO delay line 108. In these embodiments, the variable delay circuit 110 can be adjusted to further change the delay in the LO delay line 108. Different examples of variable delay circuits 110 include, but are not limited to, switched line techniques and continuously variable delay filter structures. The variable delay circuit 110 can also be implemented using any of the same media as the fixed LO delay line 108 including, but not limited to, microstrip, coaxial cable, stripline, and coplanar waveguide.
FIG. 1C is a block diagram of an example altimeter system 100C that includes a variable filter 110C as the variable delay circuit 110. The term "variable filter" and "filter" will be used interchangeably throughout this disclosure. The filter 110C can be any type of filter including a bandpass filter, an all-pass filter, a low-pass filter or a high-pass filter. The filter 110C includes at least one first variable capacitor 132. Further, in some embodiments, the filter 110C can also include at least one second variable capacitor 136. For example, in some embodiments, the first variable capacitor 132 can be a variable shunt capacitor 132 and the second variable capacitor 136 can be a variable series capacitor 136. In other embodiments, the first variable capacitor 132 can be a variable series capacitor and the second variable capacitor 136 can be a variable shunt capacitor. In some embodiments, the filter 110C can include at least one first inductor 134, 138. Further, in some embodiments, the filter 110C can also include a second inductor 134, 138. In exemplary embodiments, the filter 110C is a second-order bandpass filter comprising a variable shunt capacitor 132, a shunt inductor 134, a variable series capacitor 136 and a series inductor 138, as shown in FIG. 1C. In other embodiments, other quantities of inductors and capacitors can be included. The at least one first inductor 134, 138 and the at least one second inductor 134, 138 can have fixed values and be implemented in any transmission line media, such as microstrip, or by discrete components.