Delay Line Oscillator Circuit for Spurious Mode Suppression
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Solution Overview
Problem
Delay line oscillators, particularly optoelectronic oscillators, suffer from unwanted adjacent modes that generate spurious signals, reducing system performance in telecommunications, RADAR, and electromagnetic sensor systems.
Innovation Solution
A spurious suppression circuit using a frequency discriminator, phase shifters, and mixers to discriminate and cancel unwanted modes by applying phase modulation, utilizing a resonator to identify and suppress spurious signals without additional fiber loops or optical components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a delay line oscillator is used to achieve low phase noise and wide tuning bandwidth, then oscillator performance is improved, but unwanted adjacent modes generate spurious signals that reduce system performance
Solution Approach 1:
The patent extracts and removes the harmful spurious modes from the oscillator output by using a frequency discriminator to identify modes away from the center frequency and a phase modulator to cancel them, effectively taking out the harmful factors while preserving the desired oscillation
Solution Approach 2:
The patent implements a feedback mechanism where the oscillator output is fed through a frequency discriminator, and the detected mode information is used to control a phase modulator that adjusts the oscillation to suppress spurious modes, creating a closed-loop system that continuously eliminates harmful signals
2Object-generated harmful factors
If additional fiber loops or optical components are added to suppress spurious modes, then spurious signal suppression is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex optical components and additional fiber loops with electronic circuit elements including a frequency discriminator, phase shifters, and a phase modulator, substituting a simpler electronic system for what would have been a more complex optical system
Solution Approach 2:
The patent uses a phase modulator that serves multiple functions: it acts as the frequency discriminator's output element, the spurious mode suppression mechanism, and the oscillator control element, allowing one component to perform multiple roles and reducing overall system complexity
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
Effectively suppresses spurious signals by 45 dB, improving system performance in terms of sub-clutter visibility and bit error rate in RADAR and communication systems.
Implementation Method 1
a frequency discriminator having an insertion phase error proportional to an offset from a center frequency
Implementation Method 2
a first phase shifter configured to receive the discriminator output and apply a phase shift compensating for a mixer port phase differential; a second phase shifter configured to receive the mixer output and to output a phase modulated signal
Implementation Method 3
a mixer configured to provide a mixer output having a DC component proportional to a phase difference between inputs received at first and second mixer ports
Data Source
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AI summary
A circuit and method for suppressing, in a delay line oscillator, modes spaced by the reciprocal of the oscillator delay that are not located at the center frequency of the mode selection filter that sets the oscillatory mode. The circuit may include: a frequency discriminator configured to receive a delay line output and provide a discriminator output having a plurality of oscillatory modes; a first phase shifter configured to receive the discriminator output and apply a phase shift compensating for a mixer port phase differential; a mixer configured to provide a mixer output having a DC component proportional to a phase difference between inputs received at first and second mixer ports; a second phase shifter configured to receive the mixer output and to output a phase modulated signal; and a circuit coupler configured to provide a first circuit coupler output as an RF output of the circuit, and to provide a second circuit coupler output as an input to the delay line.