Bi-static Radar Coherent Operation via Distributed Reference Clock
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Solution Overview
Problem
Bi-static radar systems face challenges in maintaining coherence among multiple physically separated radar-transceivers at millimeter wave-length frequencies, particularly due to the impracticality of distributing Local Oscillator signals and the need for consistent timing synchronization for coherent operation.
Innovation Solution
A bi-static radar system is configured with a controller communicating a common reference clock and frame-sync signal to each radar-transceiver via a communications device, ensuring coherent operation by using separate Fractional N PLLs with a common reference clock and Frame Sync signal for timing synchronization, allowing for consistent waveform initiation across all transceivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Local Oscillator signals are distributed to each receiver, then coherent operation is achieved, but cost and practicality deteriorate at millimeter wave-length frequencies with significant separation
Solution Approach 1:
The system divides the coherent operation function into two parts: (1) a centralized reference clock source that generates the master clock signal, and (2) distributed Fractional-N PLLs at each receiver that locally generate LO signals locked to the reference clock. This segmentation avoids the need to physically distribute high-frequency LO signals while maintaining coherence through phase-locked synchronization.
Solution Approach 2:
The reference clock signal acts as an intermediary that mediates between the centralized clock source and the distributed LO generators. Each receiver's Fractional-N PLL uses this common reference clock to synchronize its LO signal, ensuring coherent operation without requiring direct LO signal distribution between receivers.
2Device complexity
If independent VCOs are used in each radar-transceiver, then device complexity is reduced, but phase coherence deteriorates
Solution Approach 1:
The Fractional-N PLL implements feedback control where the divided VCO output is compared with the reference clock signal, and the phase error is fed back to adjust the VCO frequency. This feedback mechanism ensures that independent VCOs maintain phase coherence with the reference clock despite being physically separated.
Solution Approach 2:
The system changes the control parameter from direct LO signal distribution to reference clock frequency distribution. By distributing the lower-frequency reference clock and using Fractional-N PLLs to generate the required LO frequencies, the system maintains phase coherence while allowing independent VCO operation and reducing device complexity.
3Device complexity
If timing synchronization is not implemented, then device complexity is reduced, but range measurement accuracy deteriorates due to range delays
Solution Approach 1:
The system performs preliminary timing synchronization by distributing the Frame Sync signal to all receivers before radar signal acquisition begins. This preliminary action ensures that all receivers start their integration periods and range measurements at the same reference time, eliminating range delays caused by timing offsets.
Solution Approach 2:
The Frame Sync signal provides periodic timing references at a defined rate, creating regular synchronization intervals. This periodic synchronization ensures that timing alignment is maintained throughout the radar operation, with each Frame Sync pulse resetting and coordinating the timing of all receivers.
Data Source
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AI summary
A bi-static radar system (10) configured for coherent detection of a radar-signal (44) includes a plurality of radar-transceivers (30A, 30B, 30K), a controller (34), and a communications device (32). The plurality of radar-transceivers (30A, 30B, 30K) is characterized as physically spaced apart with respect to each other. The controller (34) is in communication with the each of the radar-transceivers (30A, 30B, 30K) and is configured to coherently operate each of the radar-transceivers (30A, 30B, 30K). The communications device (32) communicates both a reference-clock signal and a frame-sync signal (38) from the controller (34) to each of the plurality of radar-transceivers (30A, 30B, 30K) whereby the plurality of radar-transceivers (30A, 30B, 30K) operate coherently. Alternatively, the system (10) may include a reference-signal generator (40), a transmitter (46), and a plurality of receivers (48). The reference-signal generator (40) generates a reference-signal (36) characterized by a reference-frequency proportional to a fraction of a radar-frequency of a radar-signal (44) transmitted. The transmitter (46) generates the radar-signal (44) at the radar-frequency based on the reference-signal (36). The plurality of receivers (48) operates coherently to detect the radar-signal (44) based on the reference-signal (36).