Tunable RF Notch Filters for Low-Cost Avionics Interference Rejection
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Solution Overview
Problem
Existing avionics communication and navigation radios face high costs due to the use of high-end processors and crystal filters in FFT-based techniques and narrowband IF filters, necessitating a low-cost solution for interference rejection.
Innovation Solution
A system utilizing tunable RF notch filters, a low-noise amplifier, a splitter, and a processor with a surface acoustic wave filter and analog-to-digital converter to detect and reject interference signals without requiring FFT implementation or narrowband IF crystal filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If FFT-based techniques are used for interference rejection, then interference rejection capability is improved, but processor cost and complexity increase
Solution Approach 1:
The system segments the interference rejection function into multiple independent tunable RF notch filters, each targeting specific interference frequencies. This replaces the need for complex FFT processing while maintaining effective interference rejection through parallel filter operation.
Solution Approach 2:
The patent employs dynamically tunable RF notch filters that can adjust their center frequencies and bandwidths in real-time to track and reject varying interference signals. This dynamic adaptability provides effective interference rejection without requiring high-speed FFT processing.
2Reliability
If narrowband IF filter is used for interference rejection, then interference rejection capability is improved, but device versatility decreases
Solution Approach 1:
The system implements multiple tunable RF notch filters that can operate across different frequency bands and bandwidth configurations. This multi-functional approach allows the same filter architecture to provide narrowband interference rejection while maintaining compatibility with wideband receiver operations, eliminating the need for separate narrowband IF filters.
3Reliability
If crystal filters are used for narrowband IF filter, then filter performance is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive crystal filters with cheaper tunable RF notch filters that achieve comparable narrowband filtering performance. These alternative filters provide sufficient filter performance for interference rejection at a significantly reduced manufacturing cost, making the solution economically viable for cost-sensitive applications.
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
Enables low-cost interference rejection in avionics radios by avoiding high-cost processors and crystal filters, improving accuracy and resolution of interference frequency detection.
Implementation Method 1
a surface acoustic wave (SAW) filter in signal communication with an output of the mixer, wherein the SAW filter is configured to reject any IF signal generated due to a desired received RF signal and to improve an accuracy and resolution of a detected interference frequency
Data Source
AI summary
A system comprises a radio receiver including an antenna, tunable RF notch filters that receive a desired RF signal and reject an interference signal, a LNA, a splitter, and a processor. A received RF signal is divided by the splitter and directed along a main signal path and an interference detection path. The interference detection path comprises a mixer that converts the received RF signal to an IF band, a synthesizer, and a SAW filter in communication with the mixer. The SAW filter rejects any IF signal generated due to a desired received RF signal and improves an accuracy/resolution of a detected interference frequency. The processor estimates the interference frequency based on a detected amplitude of signal samples and a synthesizer tuned frequency for that amplitude. If the detected amplitude is more than a threshold, then a control signal is sent to configure the notch filters at the interference frequency.