Radar Transceiver Frequency Shifting for IQ Imbalance Control
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Solution Overview
Problem
Conventional radar units face challenges in achieving high dynamic range and angular resolution due to IQ imbalance and hardware imperfections, particularly at mm-wave frequencies, limiting the ability to distinguish target direction and range accurately.
Innovation Solution
A radar unit and circuit design that utilizes 'I' and 'Q' branches to support different Tx antennas with simultaneous transmission, employing frequency shifts and additional mixers to separate and process signals in each branch, effectively moving IQ imbalance limitations to the angular domain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If quadrature (IQ) receivers are used to double the acquired frequency interval, then the measurement range of beat frequencies is improved from fb∈[0, fs/2] to fb∈[0, fs], but hardware imperfections (IQ imbalance/non-orthogonality) cause image rejection ratio to deteriorate to only 30-40 dB
Solution Approach 1:
The patent divides the signal processing into separate I and Q branches, each handling specific frequency intervals. By segmenting the receiver paths and applying different processing to each branch, the system can utilize the full ADC bandwidth while managing IQ imbalance effects through separate channel processing and combination strategies.
Solution Approach 2:
The patent applies frequency shifting to the received signal before processing in the I and Q branches. This parameter change in the frequency domain allows the system to move signals away from the problematic DC region where IQ imbalance has maximum impact, thereby improving image rejection while maintaining full bandwidth utilization.
2Measurement precision
If the full complex ADC bandwidth is utilized for distance measurements, then the dynamic range is improved, but hardware imperfections and coupling at RF for compact size cause the image rejection ratio to deteriorate to unacceptable levels
Solution Approach 1:
The patent applies frequency shifting parameters to move the beat frequency signals away from DC and into regions where IQ imbalance has less impact. This parameter change allows full ADC bandwidth utilization for distance measurements while maintaining acceptable image rejection ratios by avoiding the most problematic frequency regions.
Solution Approach 2:
The patent introduces frequency shifting as an intermediary processing step between the IQ mixer and the ADC. This intermediary operation transforms the signal spectrum to a form that can be fully utilized by the ADC while mitigating the effects of hardware imperfections, thereby achieving both high dynamic range and acceptable image rejection.
3Device complexity
If a single static transmit antenna and single static receive antenna are used, then the device complexity is reduced, but the ability to obtain angular information deteriorates
Solution Approach 1:
The patent transitions from spatial dimension (multiple physical antennas) to frequency dimension (multiple frequencies from single antenna). By transmitting at different frequencies and processing the received signals accordingly, the system obtains angular information through frequency-based differentiation rather than spatial array processing, reducing device complexity while preserving measurement capabilities.
4Measurement precision
If mechanical rotation of directive antennas is used to obtain angular information, then the angular resolution is improved, but the speed of measurement deteriorates due to mechanical movement requirements
Solution Approach 1:
The patent replaces mechanical antenna rotation with electronic frequency switching and signal processing. Instead of physically moving antennas to scan different angles, the system uses frequency-modulated signals and digital signal processing to extract angular information, achieving both high angular resolution and fast measurement speeds without mechanical limitations.
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 approach allows for full utilization of the complex ADC bandwidth, maintaining range and Doppler dynamic range without signal loss, and enhances angular resolution by creating a virtual array, improving target detection capabilities.
Implementation Method 1
a phase rotator configured to receive the reference signal and the clock signal, wherein the clock signal rotates a phase of the reference signal in at least one transmitter path
Implementation Method 2
a down-conversion circuit coupled to the Ref LO is configured to down-convert the reflected FMCW radar signal in each receiver path to a baseband signal
Implementation Method 3
A down-conversion circuit coupled to the Ref LO is configured to down-convert the reflected FMCW radar signal in each receiver path to a baseband signal, wherein a frequency shifter circuit located in a first receiver path is configured to apply a frequency shift to either the received reflection of the FMCW radar signal or one path of the reference signal
Data Source
AI summary
A radar unit includes a radar transceiver with a reference local oscillator (LO) and at least two transmitter paths arranged to transmit the reference LO. One transmitter path transmits the reference LO with a frequency shift of at least the ADC sampling frequency. A receiver coupled to two receiver paths includes a down-conversion circuit configured to receive a reflected radar signal and the reference signal and provide a down-converted baseband signal to a band-pass filter and an ADC. A DSP is configured to process the digital form of the down-converted, filtered, baseband signal. A frequency shifter circuit applies a frequency shift to the reference signal that shifts the transmit signals an amount where a first down-converted baseband signal is passed by a first bandpass filter in the first receiver path, and a second down-converted baseband signal is passed by a second bandpass filter in a second receiver path.