Monostatic LFMCW Radar Leakage Cancellation Using DDS Calibration
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Solution Overview
Problem
Monostatic radars with linearly frequency modulated continuous waves (LFMCW) face signal leakage from the transmitter to the receiver due to the presence of a circulator, leading to signal degradation and potential receiver saturation, which prevents the use of low-noise amplifiers and complicates digital processing.
Innovation Solution
A cancellation signal is injected at the receiver input, controlled for delay, phase, and amplitude to cancel the leakage signal, using a direct digital synthesis component and a calibration process to determine optimal parameters for the cancellation signal, allowing the use of low-noise amplifiers and improving the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a circulator is used to enable simultaneous transmission and reception in a monostatic radar, then the radar can transmit and receive signals through the same antenna, but signal leakage from the transmitter to the receiver occurs (at least twenty decibels coupling)
Solution Approach 1:
The patent introduces a cancellation signal as an intermediary element that mediates between the transmitter and receiver. This cancellation signal is generated by a signal generator and injected into the receiver input to counteract the harmful leakage signal, allowing the circulator to remain in place while eliminating its harmful effect.
Solution Approach 2:
The patent converts the harmful leakage signal into a beneficial cancellation mechanism. By analyzing the leakage signal characteristics and generating an opposite-phase cancellation signal, the system transforms the harmful coupling effect into a useful tool for eliminating the leakage, thereby protecting the receiver while maintaining the monostatic architecture.
2Object-generated harmful factors
If digital processing is used to eliminate the leakage signal, then the leakage can be reduced, but the useful signal is already degraded by spurious lines and intermodulation lines from the moment it enters the receiver
Solution Approach 1:
The patent applies preliminary action by canceling the leakage signal before it can degrade the useful signal. The cancellation signal is injected at the receiver input to preemptively neutralize the leakage, preventing the formation of spurious lines and intermodulation products that would otherwise corrupt the received signal and limit digital processing effectiveness.
3Object-generated harmful factors
If an analog approach is used to cancel the leakage signal by reinjecting a modified transmission signal, then some cancellation is achieved, but the leakage cannot be completely canceled over the entire frequency range, especially when frequency dispersions are introduced by the circulator
Solution Approach 1:
The patent implements feedback by analyzing the actual leakage signal present at the receiver input and using this information to generate an accurate cancellation signal. The system measures the leakage characteristics including amplitude and phase, then feeds this information back to the signal generator to create a precisely matched cancellation signal that compensates for frequency dispersions introduced by the circulator.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the amplitude and phase parameters of the cancellation signal to match the leakage signal characteristics. The signal generator modifies these parameters based on the measured leakage, enabling complete cancellation across the entire frequency range despite circulator-induced frequency dispersions.
Data Source
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AI summary
Said radar system (10) comprises a transmitter (20) capable of outputting a transmission signal, and a receiver (30) capable of receiving a reception signal, the transmitter and receiver being coupled by a circulator (12) with an antenna (14). The transmitter includes a direct digital synthesis component (22), which can be configured in terms of amplitude, frequency, phase and/or delay, for generating the transmission signal. The system further comprises a cancellation channel (50) for cancelling an escaped transmission signal heading to the receiver, the cancellation channel reusing the direct digital synthesis component (22) to generate a cancellation signal, and comprising a coupler (56) which is arranged between the circulator (12) and the receiver (30) and is capable, on the basis of the cancellation signal, of emitting a replica of the cancellation signal to the receiver in order to cancel the escaped transmission signal.