Undersampling Radar Receiver Eliminates I-Q Calibration
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Solution Overview
Problem
Conventional Doppler radar receivers face challenges in distinguishing between approaching and receding targets due to gain and phase mismatches in I & Q channels, requiring complex calibration and numerous components, and are cumbersome in monopulse systems.
Innovation Solution
A Doppler radar receiver employing undersampling according to the Nyquist criterion to produce aliased digital signals, which are then processed to generate in-phase and quadrature components, reducing the need for analogue matching and eliminating the requirement for a large microwave comparator unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional I & Q demodulation with two mixers is used, then Doppler frequency detection is achieved, but gain and phase mismatch between channels causes spurious images and requires complex calibration
Solution Approach 1:
The patent replaces the conventional analogue mixer-based I & Q demodulation system with a digital signal processing approach. The received RF signal is mixed with a digital local oscillator signal in the digital domain, and the in-phase and quadrature components are separated through digital filtering and processing. This substitution eliminates the need for precise analogue matching between separate receiver channels, thereby removing the calibration complexity while maintaining Doppler frequency detection accuracy.
2Measurement precision
If conventional I & Q demodulation arrangement is used, then carrier frequency translation to baseband is achieved, but a significant number of components are required
Solution Approach 1:
The patent merges the functions of multiple separate components into a unified digital signal processing system. Instead of using two separate mixers, multiple local oscillators, and separate filtering stages as in conventional I & Q demodulation, the invention combines these functions into a single digital processing architecture where the RF signal is mixed with a digital local oscillator and the I & Q components are extracted through digital filtering. This merging significantly reduces the number of components while maintaining accurate carrier frequency translation to baseband.
3Measurement precision
If gain and phase matching is enforced between receiver channels, then spurious images are reduced, but the system requires calibration that becomes invalid with temperature changes
Solution Approach 1:
The patent replaces the analogue mixer system with digital signal processing, where the local oscillator is a digital signal generated with high precision. The mixing and separation of I & Q components occur in the digital domain, eliminating sensitivity to temperature-induced gain and phase drift that plagues analogue systems. This substitution ensures that the frequency measurement accuracy remains stable without requiring recalibration under varying temperature conditions.
4Measurement precision
If a large microwave comparator unit is used in monopulse systems, then sum and difference channels are provided, but the system becomes large, heavy and expensive
Solution Approach 1:
The patent replaces the heavy microwave comparator unit with a digital signal processing system. The sum and difference channel formation, which traditionally required large waveguide-based microwave comparators, is achieved through digital beam forming and signal processing. This substitution dramatically reduces the weight and size of the receiver while maintaining angle-of-arrival measurement accuracy through precise digital computation of the sum and difference signals from multiple antenna elements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution simplifies the receiver design by eliminating the need for precise analogue matching and reduces component count, enabling smaller, lighter, and cheaper radar systems while maintaining accurate target differentiation.
Implementation Method 1
the sampling by the analogue-to-digital converter is undersampling according to the Nyquist criterion, so that a plurality of IF digital signals are produced, in different Nyquist zones, including one or more aliased IF digital signals
Implementation Method 2
a digital demodulator arranged to convert the selected IF digital signal to a baseband digital signal having in-phase (I) and quadrature (Q) components, the I and Q components being produced by multiplying the selected IF digital signal by a cosine signal and by a sine signal
Implementation Method 3
In a Doppler radar system, pulses are transmitted and echoes are received from radar-reflecting objects within range of the radar system. The I & Q signals form a complex-number phasor that is processed using a Fourier transform to obtain a Doppler spectrum of the echo signal. In the Doppler spectrum, closing and receding targets correspond to positive and negative Doppler frequencies, respectively.
Data Source
Figure 1~3
Figure 2a~2c
Figure 4
AI summary
A radar receiver (200) comprises an analogue receiver (230) for receiving a radar echo signal and a digital receiver (240). The digital receiver (240) includes an analogue-to-digital converter (300A-D) arranged to receive and sample an IF analogue signal from the analogue receiver (230). The sampling is undersampling according to the Nyquist criterion, so that a plurality of IF digital signals are produced, in different Nyquist zones, including one or more aliased IF digital signal. The digital receiver (240) is arranged to select an IF digital signal from the one or more aliased digital signals.