Circulant PLL LO Distribution for Phase-Coherent Microwave Arrays
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Solution Overview
Problem
Conventional LO signal distribution systems for MIMO and phased array applications face challenges in maintaining coherence due to significant losses and distortion, especially at microwave and higher frequencies, leading to noise and increased power consumption.
Innovation Solution
A system utilizing a one-way, circulant coupling topology of PLL modules, where each module receives a reference clock signal and outputs a frequency-divided LO signal, ensuring phase coherence through feedback loops and reduced frequency division, thereby minimizing noise and distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If metallic transmission lines are used to distribute LO signals, then the system structure is simple and easy to implement, but signal loss increases significantly at microwave and higher frequencies
Solution Approach 1:
The patent replaces metallic transmission lines (mechanical/electrical system) with optical fibers (optical system) for LO signal distribution. This substitution eliminates the high signal loss characteristic of metallic lines at microwave frequencies while maintaining system implementability through optical coupling techniques between the laser and antenna elements.
2Loss of energy
If lower-loss waveguides or optical fibers are used to distribute LO signals, then signal loss is reduced, but manufacturing cost increases and phase matching becomes difficult
Solution Approach 1:
The patent employs feedback control mechanisms to maintain phase coherence among multiple optical channels. By continuously monitoring and adjusting phase differences between channels, the system achieves accurate phase matching despite variations in optical path lengths, thereby reducing manufacturing complexity and cost while maintaining low signal loss.
Solution Approach 2:
The patent utilizes parameter changes in the optical domain (wavelength, phase, frequency) to achieve precise control over signal distribution characteristics. By adjusting optical parameters dynamically, the system compensates for manufacturing tolerances and achieves accurate phase matching without requiring expensive precision manufacturing.
3Power
If signal amplification is increased to compensate for transmission line losses, then signal strength is maintained, but noise and distortion increase
Solution Approach 1:
The patent replaces electrical signal amplification with optical signal transmission. By using optical fibers to distribute LO signals, the system maintains signal strength over long distances without requiring intermediate amplification, thereby avoiding the noise and distortion that would be introduced by amplifiers.
4Device complexity
If conventional LO distribution systems are used, then system complexity is low, but phase coherence is lost due to noise and distortion
Solution Approach 1:
The patent substitutes optical transmission for electrical transmission to preserve phase coherence. The optical domain inherently provides better immunity to noise and distortion, maintaining phase coherence among distributed LO signals while adding manageable complexity through optical coupling and phase control mechanisms.
Data Source
AI summary
A local oscillator (LO) distribution system is described. The LO system includes a plurality of phase-locked loop (PLL) modules coupled to each other in a one-way, circulant coupling topology. Each PLL module receives a reference clock signal and outputs an output LO signal. Each PLL module provides a local LO signal to an adjacent downstream PLL module, where the local LO signal is a frequency divided version of the output LO signal. Each PLL module receives an adjacent LO signal from the adjacent upstream PLL module. The phase of the output LO signal is made to be coherent with the phase of the reference clock signal and the phase of the adjacent LO signal, using a feedback loop.