Active Tunable Notch Filter for Wideband RF Interference Cancellation
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Solution Overview
Problem
Existing active cancellation schemes in RF and microwave receivers face limitations in power handling due to the incorporation of low-noise amplifiers in the primary signal path and are inadequate for high-power, wideband interference cancellation, especially for modulated signals and continuous wave interferers.
Innovation Solution
The proposed interfering signal canceller employs a voltage sensor, a Hartley image-reject down-converting element, a phase slope compensator, and an inverse Hartley image-reject up-converting element in the auxiliary path, along with amplifiers and bandpass filters, to accurately phase and amplitude align the interfering signal for cancellation, reducing noise figure and enhancing power handling capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low-noise amplifier is incorporated in the primary signal path to achieve active cancellation, then the cancellation accuracy is improved, but the power handling capability is limited
Solution Approach 1:
The patent introduces an intermediary frequency conversion stage that transforms the RF interfering signal to baseband, processes it through low-noise amplifiers in the baseband domain, and then transforms it back to RF for cancellation. This mediator (frequency conversion) allows the use of low-power baseband amplifiers instead of requiring high-power RF amplifiers directly in the cancellation path, resolving the contradiction between cancellation accuracy and power handling capability
Solution Approach 2:
The patent changes the operating frequency parameter of the signal processing chain by down-converting the RF interfering signal to baseband frequency. This parameter change enables the use of low-noise amplifiers optimized for baseband operation rather than RF operation, achieving both high cancellation accuracy through low-noise amplification and adequate power handling since baseband circuits can handle the required power levels without the limitations of RF LNA design
2Adaptability or versatility
If conventional feed-forward cancellation is used with baseband filtering, then continuous wave interferers are cancelled, but modulated and encoded signals cannot be effectively mitigated
Solution Approach 1:
The patent employs dynamic adaptive filtering in the baseband domain that can adjust its transfer function in real-time to match the characteristics of the interfering signal. This dynamic adaptation allows the system to effectively cancel various types of interferers including continuous wave, modulated, and encoded signals by learning and replicating their temporal and spectral characteristics, thereby achieving both broad interferer type coverage and high cancellation effectiveness
Solution Approach 2:
The patent implements feedback mechanisms where the baseband filtered interfering signal is continuously monitored and used to adjust the cancellation parameters. This feedback loop enables the system to adapt to different interferer types by analyzing their characteristics and optimizing the cancellation signal accordingly, ensuring reliable cancellation across diverse signal types while maintaining versatility
3Quantity of substance
If the auxiliary path processes the full spectrum signal, then all signals are available for cancellation, but the desired signal cannot be filtered out for precise interferer extraction
Solution Approach 1:
The patent segments the signal processing into distinct functional blocks: a wideband RF front-end that preserves the full spectrum, a baseband conversion stage that separates signal components in the frequency domain, and selective filtering stages that extract only the interferer components. This segmentation allows the system to maintain full spectrum availability at the input while achieving precise interferer extraction through frequency-domain separation and selective filtering in subsequent stages
Solution Approach 2:
The patent introduces frequency conversion as an intermediary transformation that maps the RF spectrum to the baseband spectrum. This intermediary frequency domain representation acts as a mediator that enables precise identification and extraction of interferer signals through baseband filtering, while the original full-spectrum RF signal remains available for further processing or alternative cancellation approaches
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
This configuration enables effective cancellation of interfering signals with high accuracy and reduced noise figure, improving the power handling and interference mitigation capabilities in RF and microwave receivers.
Implementation Method 1
The desired signal and the interfering signal in the auxiliary path are down-converted in frequency with in-phase (I) and quadrature (Q) local oscillator signals (LOI, LOQ) and a pair of mixers, as shown; with the interfering signal being converted to a known intermediate frequency (IF) or baseband frequency
Implementation Method 2
a phase slope compensator disposed in the auxiliary path after the Hartley image-reject element to phase adjust an interfering signal component of a converted input signal
Implementation Method 3
an inverse Hartley image-reject up-converting element disposed in the auxiliary path after the phase slope compensator to convert the passed interfering signal component to the predetermined band of frequencies
Implementation Method 4
a coupler disposed in the primary path and fed by the voltage sensor element; having a second input receiving the output of the inverse Hartley image-reject up-converting element and having an output providing an output signal
Data Source
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AI summary
An interfering signal canceller for cancelling an interfering signal component of an input signal includes a voltage sensor element disposed in a primary path and fed by the input signal, a coupler disposed in the primary path and fed by the voltage sensor element, a Hartley image-reject element disposed in an auxiliary path and fed by the input signal for converting the input signal to an intermediate or baseband frequency signal, a phase slope compensator disposed in the auxiliary path after the Hartley image-reject element to allow broadband phase adjustment of the interfering signal component of a converted input signal, and an inverse Hartley image-reject element disposed in the auxiliary path after the phase slope compensator to convert the passed the interfering signal component to the predetermined band of frequencies and having an output fed to the coupler.