Inverse Transfer Function Filtering for RF Coupler Distortion
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Solution Overview
Problem
Typical HF wireless communications devices suffer from limited bandwidth and distortion due to non-linear components, particularly the coupler, which introduces impedance mismatches and affects the frequency spectrum of wideband signals.
Innovation Solution
A RF communications device with a tunable coupler and a processor that sets the coupler for impedance matching, generates an inverse transfer function to compensate for distortion, and performs digital filtering to maximize power transfer and minimize signal distortion, enabling broadband HF signal transmission with minimal distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the bandwidth of the HF wireless communications device is expanded beyond the typical operation bandwidth, then the bandwidth is improved, but the coupler introduces distortion into the frequency spectrum due to non-linear behavior
Solution Approach 1:
The patent applies inverse transfer function filtering to compensate for the distortion introduced by the coupler. By inverting the transfer function of the coupler and applying it as a filter in the signal path, the system cancels out the non-linear distortion effects, enabling broadband operation without the harmful distortion that would normally result from expanding beyond the typical 3-5 KHz bandwidth.
Solution Approach 2:
The system dynamically adjusts the filter parameters based on the actual transfer function of the coupler. By measuring or characterizing the coupler's frequency response and using that information to configure the inverse filter, the system adapts to the specific non-linear behavior of the coupler, allowing broadband signal transmission while compensating for distortion through parameter optimization.
2Device complexity
If a fixed coupler is used for impedance transformation, then the device complexity is reduced, but the bandwidth is limited to 3-5 KHz
Solution Approach 1:
The patent employs a tunable coupler with variable capacitance or inductance that can be dynamically adjusted to match different impedance conditions across a broader frequency range. This dynamic adjustment capability allows the coupler to maintain effective impedance transformation for broadband signals, overcoming the bandwidth limitation of fixed couplers while keeping the overall device complexity manageable through controlled tuning mechanisms.
Solution Approach 2:
The system replaces potential mechanical tuning mechanisms with electronic control of the tunable coupler parameters. By using electronic variable capacitors or inductors controlled by the processor, the system achieves broadband adaptability without complex mechanical adjustment mechanisms, maintaining device simplicity while expanding bandwidth capability.
3Reliability
If inverse transfer function filtering is applied to compensate for distortion, then the signal-to-noise ratio is improved, but the processing resources increase
Solution Approach 1:
The system performs preliminary characterization of the coupler's transfer function and pre-computes the inverse filter parameters before actual signal transmission. By measuring the coupler's frequency response in advance and storing the inverse filter coefficients, the system avoids real-time complex calculations during signal processing, thereby improving signal-to-noise ratio through distortion compensation while minimizing the processing resource requirements during operation.
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
The solution achieves significant signal-to-noise ratio (SNR) gain and expanded bandwidth up to 100 KHz, effectively compensating for distortion without additional hardware or excessive processing resources, enhancing communication reliability and efficiency.
Implementation Method 1
the coupler, which couples the antenna to the power amplifier by way of impedance transformation
Implementation Method 2
perform digital filtering upstream of the power amplifier based upon the inverse transfer function
Data Source
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AI summary
A radio frequency (RF) communications device may include a power amplifier, an antenna, a tunable coupler between the power amplifier and the antenna, a processor, and an exciter module coupled between the processor and the power amplifier and generating an RF signal based upon a baseband signal. The processor may be configured to set the tunable coupler to a desired tuning and thereby defining a transfer function for the tunable coupler, and to generate an inverse transfer function of the transfer function of the tunable coupler. The processor may be configured to perform digital filtering upstream of the power amplifier based upon the inverse transfer function.