Radar Signal Processor Aliasing Prevention via Periodic Antenna Selection
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Solution Overview
Problem
Radar apparatuses using FM-CW technology face erroneous detection due to aliasing issues when targets are beyond the Nyquist frequency, causing long-distance targets to be incorrectly detected at short distances.
Innovation Solution
The radar apparatus employs a signal processor that samples beat signals with a selecting period shorter than half the sampling period, allowing for accurate pair matching of peaks in rising- and falling-modulation signals, and includes a receiver switch to selectively choose receiving antennas in an array order, preventing aliasing and erroneous detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If digital signal processing such as FFT is carried out on beat signals, then frequency analysis and target detection are improved, but targets beyond the Nyquist frequency are folded to positions less than the Nyquist frequency causing erroneous detection
Solution Approach 1:
The patent applies preliminary action by performing analog filtering before the A/D conversion to remove frequency components above the Nyquist frequency. This preliminary filtering action prevents aliasing during the subsequent digital signal processing, ensuring that only valid frequency components are processed and displayed, thereby eliminating erroneous detection of folded targets.
2Difficulty of detecting and measuring
If the receiving antennas are selected in sequence with a cycle shorter than the frequency change cycle, then azimuth detection is improved, but the system complexity increases
Solution Approach 1:
The patent applies periodic action by implementing cyclic selection of receiving antennas in a repeated sequence. The switching control circuit controls the receiver switch to select antennas in a cycle shorter than the frequency change cycle, creating a periodic sampling pattern that enables azimuth detection through phase difference measurement while maintaining manageable control complexity through regular repetition.
3Adaptability or versatility
If the sampling period is reduced to capture higher frequency components, then detection range is improved, but aliasing occurs causing long-distance targets to appear at short distances
Solution Approach 1:
The patent applies preliminary action by implementing analog filtering before A/D conversion to remove frequency components above the Nyquist frequency. This preliminary filtering action prevents aliasing during sampling, ensuring that even when reducing the sampling period to extend detection range, the system maintains accurate target position detection by eliminating folded components before they can be misinterpreted.
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 configuration effectively restricts aliasing and ensures accurate detection of target positions by separating detection angles of upbeat and downbeat signals, preventing long-distance targets from being misinterpreted as short-distance targets.
Implementation Method 1
The transmitter generates a transmission signal having a frequency periodically changing with time
Implementation Method 2
the reception signal Sr is Doppler-shifted in frequency by Fd depending upon the relative speed of the radar apparatus and the target
Implementation Method 3
The reception signal Sr and the transmission signal Ss are mixed together by a mixer to produce a beat signal B
Implementation Method 4
when a digital signal processing such as fast Fourier transformation (FFT) is carried out
Implementation Method 5
receives the radar wave reflected by a target
Data Source
AI summary
A radar apparatus includes a transmitter, a receiver, and a signal processor. The transmitter outputs a radar wave. The receiver includes a plurality of receiving antennas and a plurality of receiving devices. Each of the receiving devices mixes a reception signal from the corresponding receiving antenna with a local signal and outputs a beat signal. The signal processor samples the beat signal while selecting one of the receiving devices in order with a selecting period that is less than a half of a sampling period. The signal processor samples the beat signal with the sampling period and derives position information of a target by pair matching of peaks of a rising-modulation signal and a falling-modulation signal of the beat signal.