Meander-Shaped Cavity Filter for Image Frequency Rejection
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Solution Overview
Problem
Superheterodyne receivers face issues with image frequency interference due to the inefficiency of existing image reject filters, such as hairpin band pass filters and micro-strip line open stub structures, which occupy large circuit areas, are costly, and have limited noise rejection capabilities around the RF band.
Innovation Solution
A filtering device with a meander-shaped resonating cavity formed in the ground metal layer of an isolation substrate, which generates a rejection band on the micro-strip line, allowing for adjustable bandwidth and center frequency, effectively filtering out image frequency signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If hairpin band pass filter or micro-strip line open stub structure is used as image reject filter, then image frequency rejection effect is achieved, but circuit board area occupied is large and cost increases
Solution Approach 1:
The patent transitions from planar resonator structures (hairpin, open stub) to a three-dimensional cavity resonator structure. The cavity is formed by bending and folding a conductive sheet to create vertical walls enclosing a volumetric resonating space, utilizing the third dimension (height/depth) to achieve filtering functionality with reduced planar footprint.
Solution Approach 2:
The patent employs a thin conductive sheet that is bent and folded to form the cavity walls. This flexible conductive material serves both as the structural element defining the cavity shape and as the electromagnetic resonating element, eliminating the need for separate planar resonator traces on the circuit board.
2Object-affected harmful factors
If multiple resonators are used to improve filtering performance, then filtering effectiveness increases, but device complexity and circuit layout area increase
Solution Approach 1:
The patent combines multiple resonating functions into a single integrated cavity structure. The folded conductive sheet creates multiple reflective surfaces and resonating paths within one compact unit, achieving the filtering effectiveness of multiple separate resonators while maintaining device simplicity and reducing layout area.
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 filtering device reduces circuit layout area, lowers costs, and enhances noise rejection, providing improved adjustability and performance by effectively filtering out image frequency interference, thus improving the efficiency of wireless communication receivers.
Implementation Method 1
A meander-shaped resonating cavity is formed in an area of the ground metal layer corresponding to an area of the micro-strip line, for generating a rejection band on the micro-strip line
Data Source
AI summary
A filtering device includes an isolation substrate including a first plane and a second plane, a micro-strip line deposited on the first plane of the isolation substrate for transmitting signals, and a ground metal layer deposited on the second plane of the isolation substrate for providing grounding. A meander-shaped resonating cavity is formed in an area of the ground metal layer corresponding to an area of the micro-strip line, for generating a rejection band on the micro-strip line.