Transposed Delay Line Oscillator for RF Phase Noise Suppression
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Solution Overview
Problem
Conventional RADAR systems employing optical delay lines face challenges with large physical size, susceptibility to thermal and mechanical perturbations, and reduced mode spacing due to increased fiber length, which affects phase noise reduction and oscillator performance.
Innovation Solution
A transposed delay line oscillator with a mode selection filter and phase noise suppression loop, which eliminates the need for an optical delay line, allowing for a fully electrical implementation and improved mechanical resilience, while maintaining wide broadband input and high Q-factor components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fiber length is increased to achieve higher quality factors and lower phase noise, then the phase noise is reduced, but the physical size increases and susceptibility to thermal and mechanical perturbations increases
Solution Approach 1:
The patent replaces the mechanical/optical delay line system with an electrical transposed delay line system. Instead of using physical optical fiber (1-15 km length) to achieve delay and quality factor, the invention uses electrical circuits (delay filter, frequency mixers, phase detectors) to synthesize the same functionality. This substitution eliminates the need for long physical fiber while maintaining the quality factor and phase noise performance through electrical means.
Solution Approach 2:
The invention changes the fundamental parameter from optical domain to electrical domain. By using frequency transposition techniques and electrical delay lines instead of optical fiber, the system achieves the same delay and quality factor characteristics without the physical constraints of long fiber lengths. The parameter transformation allows maintaining high Q-factor while reducing physical dimensions.
2Reliability
If the fiber length is increased to achieve higher quality factors, then the quality factor increases, but the spacing between electro-optical modes decreases making mode selection more problematic
Solution Approach 1:
The patent replaces the optical delay line with an electrical transposed delay line system comprising frequency mixers, delay filters, and phase detectors. This substitution eliminates the electro-optical modes issue entirely by operating in the electrical domain. The mode selection problem is resolved by using electrical frequency synthesis and filtering techniques instead of optical mode management.
Solution Approach 2:
The invention introduces frequency transposition as an intermediary process. By converting signals to intermediate frequencies, applying delay, and then transposing back, the system achieves the desired quality factor without directly manipulating optical modes. This intermediary frequency domain approach simplifies the selection and management of oscillation modes.
3Reliability
If conventional optical delay lines are used to reduce phase noise, then phase noise is reduced, but the system becomes susceptible to thermal and mechanical perturbations
Solution Approach 1:
The patent replaces the vulnerable optical fiber system with a robust electrical circuit system. The transposed delay line using frequency mixers, electrical delay filters, and phase detectors is inherently more resistant to thermal and mechanical perturbations. Electrical components can be stabilized using standard techniques without the susceptibility of optical fiber to environmental factors.
Solution Approach 2:
The invention implements feedback mechanisms through phase detectors that continuously monitor and correct phase variations. This active feedback system compensates for any perturbations in real-time, providing enhanced stability against thermal and mechanical effects compared to passive optical fiber systems.
Data Source
AI summary
A transposed delay line oscillator including a mode selection filter and a transposed delay line is provided. An output of the transposed delay line is coupled to an input of the mode selection filter to establish an oscillator loop. Based on the transposed delay line output, the mode selection filter generates a mode selection signal including an isolated oscillatory mode, in a Radio Frequency (RF) band. The transposed delay line receives the mode selection signal for transposition to an intermediate frequency of an intermediate frequency (IF) delay line. The IF delay line includes a delay filter and a phase noise suppression loop configured to suppress de-correlated transposition phase noise resulting from a delay of the delay filter. Suppression of phase noise in the IF delay line enables cancellation of transposition phase noise when transposing the IF delay line output to the RF band.