Intermediate-Frequency Receiver Filtering for Flatness and Signal Suppression
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Solution Overview
Problem
Prior intermediate frequency receiving circuits in microwave systems suffer from suboptimal in-band unflatness, low reflection factor, low receiving sensitivity, inadequate suppression of transmitted signals and control signals, and significant in-band loss, making them unsuitable for large capacity microwave systems.
Innovation Solution
An intermediate frequency receiving circuit comprising an LC resonance circuit, band-pass filter, automatic gain control circuit, and analog-to-digital converter, which suppresses transmitted signals, compensates for cable attenuation, and adjusts in-band flatness to enhance sensitivity and reflection factor, while providing a variable gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a band-pass filter with steep transition band is used to reduce interference between transmitting and receiving channels, then the suppression of transmitted signals is improved, but the in-band flatness deteriorates
Solution Approach 1:
The filtering function is divided into multiple stages: a first band-pass filter for initial filtering, followed by a second band-pass filter with steeper transition characteristics for enhanced suppression. This segmentation allows each filter to operate at optimized points, achieving both high suppression and good in-band flatness that would be difficult to achieve with a single filter stage.
Solution Approach 2:
Different filtering characteristics are applied at different stages of the signal processing chain. The first filter uses gentler characteristics to preserve in-band flatness, while the second filter applies steeper characteristics for enhanced suppression of out-of-band signals. This local differentiation of filtering quality resolves the contradiction between suppression and flatness.
2Manufacturing precision
If the bandwidth of the band-pass filter is increased to accommodate 28 MHz transmission, then the in-band flatness is improved, but the suppression of transmitted signals deteriorates
Solution Approach 1:
The filtering function is divided into multiple stages: a first band-pass filter for initial filtering, followed by a second band-pass filter with steeper transition characteristics for enhanced suppression. This segmentation allows each filter to operate at optimized points, achieving both high suppression and good in-band flatness that would be difficult to achieve with a single filter stage.
Solution Approach 2:
The filtering system uses a composite structure combining two different filter types with complementary characteristics. The first filter provides wide bandwidth with good flatness, while the second filter adds steep roll-off characteristics. Together they form a composite filtering system that achieves both wide bandwidth and high suppression.
3Measurement precision
If the receiving sensitivity is increased to improve system performance, then the detection capability is improved, but the suppression of low frequency control signals deteriorates
Solution Approach 1:
The signal processing is segmented into multiple filtering stages with different characteristics. The first band-pass filter allows wide bandwidth signals to pass with high sensitivity, while the second band-pass filter with steeper characteristics provides enhanced suppression of out-of-band signals including low frequency control signals, thus resolving the contradiction between sensitivity and suppression.
4Reliability
If a band-pass filter is used to separate receiving channel from other circuits, then the isolation is improved, but the in-band loss increases
Solution Approach 1:
The filtering function is divided into multiple stages: a first band-pass filter for initial filtering, followed by a second band-pass filter with steeper transition characteristics for enhanced suppression. This segmentation allows each filter to operate at optimized points, achieving both high suppression and good in-band flatness that would be difficult to achieve with a single filter stage.
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 significantly improves in-band unflatness, reflection factor, and receiving sensitivity, while reducing in-band loss and enhancing signal suppression, achieving desired performance indexes for intermediate frequency receiving channels in microwave systems.
Implementation Method 1
an inductor-capacitor (LC) resonance circuit whose primary resonance frequency is substantially equal to a central frequency of received signals, adapted to receive intermediate frequency signals and suppress transmitted signals and control signals
Data Source
AI summary
An intermediate frequency receiving circuit and an intermediate frequency receiving method are provided. The intermediate frequency receiving circuit includes an inductor-capacitor (LC) resonance circuit whose primary resonance frequency is a central frequency of received signals. The LC resonance circuit receives intermediate frequency signals and suppresses transmitted signals and control signals. A band-pass filter connected to the LC resonance circuit filters the transmitted signals and control signals. An automatic gain control circuit connected to the band-pass filter compensates the attenuation of an intermediate frequency cable. A low-pass filter connected to the automatic gain control circuit compensates an in-band flatness. An analog-to-digital converter connected to the low-pass filter performs a sampling and digital demodulation on the received signals.