Radar Frequency Synthesizer Mode Switching for Spectral Spike Reduction
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Solution Overview
Problem
Radar systems face limitations in spectral occupation due to non-uniform usage of the frequency spectrum, particularly with chirp-based sequences and digital RF architectures, which restrict the output power of radar chirps and lead to suboptimum spectral usage and compliance issues with regulations.
Innovation Solution
A radar apparatus and method that utilizes a transceiver circuit with a frequency synthesizer and control circuit to operate in different modes, adjusting the frequency synthesizer to be within or outside the transmit frequency band, thereby reducing spectral spikes and increasing the maximum allowed emitted power density, and widening the spectral density to relax Out of Band emissions requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If chirp-based sequences with constant frequencies during PLL settling and calibration are used, then the radar system can operate with simple frequency control, but the spectral occupation becomes non-uniform and suboptimum with spectral spikes in the transmit frequency band
Solution Approach 1:
The patent applies dynamics by making the frequency synthesizer adjustable between different operational modes. During detection mode, the synthesizer operates within the transmit frequency band, while during calibration and settling modes, it dynamically shifts to frequencies outside the transmit band, eliminating spectral spikes while maintaining operational simplicity
Solution Approach 2:
The patent changes the frequency parameter of the synthesizer based on operational mode. By adjusting the synthesizer frequency to be outside the transmit band during calibration and settling, the system modifies spectral distribution to eliminate harmful spikes while preserving ease of operation during detection
2Productivity
If digital RF architectures with all-digital PLLs are used, then the system benefits from digital speed and signal processing power, but unwanted signals appear at well-defined frequency offsets determined by clock frequencies
Solution Approach 1:
The patent extracts the unwanted digital clock signals from the transmit frequency band by operating the all-digital PLL at frequencies outside the transmit band during calibration and settling modes. This separates the harmful digital artifacts from the useful radar transmission band, allowing digital RF architecture benefits to be retained without the harmful frequency offset signals
3Reliability
If the spectral power density of unwanted emissions is limited by regulations, then compliance with spectral regulations is achieved, but the output power of radar chirps is restricted
Solution Approach 1:
The patent segments the operational spectrum into detection mode (within transmit band) and calibration/settling mode (outside transmit band). By separating these operations in frequency space, the system can maintain high output power during detection while directing unwanted emissions to different frequency regions where regulatory limits are more relaxed, thus achieving both compliance and high power
Data Source
AI summary
The present disclosure relates to a radar apparatus. The radar apparatus includes a transceiver circuit with a frequency synthesizer. The radar apparatus further includes a control circuit configured to set different operational modes of the transceiver circuit. The control circuit is configured to control the transceiver circuit to, in a detection mode, emit a sequence of subsequent FMCW radar chirps in a transmit frequency band between a minimum frequency and a maximum frequency, and, in another operational mode different from the detection mode, perform one or more other operations of the transceiver circuit by adjusting the frequency synthesizer to a frequency outside the transmit frequency band.