Rectangular Waveguide Filter with Transversal Slot Coupling
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Solution Overview
Problem
Current microwave filters in satellite transponders face challenges in achieving high frequency selectivity and compact structure, particularly at high frequencies and narrow pass-bands, due to difficulties in manufacturing small coupling coefficients and maintaining frequency selectivity.
Innovation Solution
A single-mode microwave filter design using rectangular waveguide technology with a symmetric folded circuit structure, where rectangular waveguide resonators are transversally coupled through slots or pairs of slots, allowing for positive and negative coupling coefficients with a single type of iris, facilitating easier manufacturability and alignment of resonator fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional waveguide filters are used for frequency separation, then frequency selectivity can be achieved, but the structure becomes complex and manufacturing precision requirements increase
Solution Approach 1:
The filter is divided into multiple resonant cavities (first, second, third cavities) that are coupled together through irises. Each cavity acts as an independent resonator that contributes to the overall frequency selectivity, allowing the complex filtering function to be achieved through simpler modular components rather than a single complex structure
Solution Approach 2:
Multiple resonant cavities are combined in a folded configuration within a single waveguide body. The cavities are coupled through shared irises, merging their individual resonant responses to create the desired band-pass filtering characteristic with multiple transmission zeros, thereby achieving complex frequency selectivity without requiring separate filter assemblies
2Manufacturing precision
If the pass-band is narrowed for high frequency selectivity, then adjacent channel interference is reduced, but the filter becomes more sensitive to manufacturing tolerances
Solution Approach 1:
Different regions of the filter (different cavities and irises) are designed with specific local characteristics optimized for their function. The irises are positioned at specific locations within the cavities to create localized coupling effects that generate transmission zeros. This local optimization allows the narrow pass-band to be achieved while distributing the tolerance requirements across multiple localized features rather than requiring uniform high precision throughout
Solution Approach 2:
The filter employs asymmetric iris positioning and cavity dimensions to create the desired non-uniform frequency response with sharp roll-off characteristics. The asymmetric design allows transmission zeros to be placed at specific frequencies to enhance selectivity, while the asymmetry itself provides robustness against certain types of manufacturing variations by making the response less sensitive to symmetric dimensional deviations
3Manufacturing precision
If multiple transmission zeros are allocated for high selectivity, then frequency separation improves, but the coupling coefficient requirements become more stringent and difficult to manufacture
Solution Approach 1:
The irises serve multiple functions simultaneously: they act as coupling elements between adjacent cavities, define the resonant frequencies of the cavities, and create the transmission zeros through their positioning. This multi-functionality means that a single manufacturing feature (the iris) achieves multiple objectives, eliminating the need for separate components or adjustments to create transmission zeros, thereby simplifying manufacturing while maintaining high frequency selectivity
Solution Approach 2:
The filter structure is designed so that the natural resonant modes of the cavities and the coupling through the irises automatically produce the desired transmission zeros without requiring additional active control or adjustment mechanisms. The geometry and positioning of the irises self-determine the coupling coefficients and transmission zero locations, making the filter self-configuring and reducing manufacturing complexity
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 design achieves enhanced frequency selectivity and a compact structure with improved manufacturability, maintaining a good agreement with ideal frequency responses over a wide frequency range, suitable for high-frequency applications with narrow pass-bands.
Implementation Method 1
rectangular waveguide resonators are transversally coupled through slots or pairs of slots
Implementation Method 2
a first folded circuit including a plurality of first rectangular waveguide resonators... and a second folded circuit including a plurality of second rectangular waveguide resonators
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The invention concerns a microwave filter (2), that comprises: a first folded circuit (21) including a plurality of first rectangular waveguide resonators (211,212,213) connected in cascade by means of first line couplings (214,215) in rectangular waveguide technology; and a second folded circuit (22) including a plurality of second rectangular waveguide resonators (221,222,223) connected in cascade by means of second line couplings (224,225) in rectangular waveguide technology. The first and second folded circuits (21,22) are designed for operating with a TE10N resonant mode and are transversally coupled on a coupling plane (PC) that is perpendicular to a transversal plane (PT) crossing all the first and second rectangular waveguide resonators (211,212,213,221,222,223). Each first rectangular waveguide resonator (211,212,213) is separated from a respective second rectangular waveguide resonator (221,222,223) by means of a respective metal or metallized wall lying on the coupling plane (PC). Moreover, each first rectangular waveguide resonator (211,212,213) is transversally coupled to said respective second rectangular waveguide resonator (221,222,223) by means of: a respective positive transversal coupling including a respective single slot (23,25) made through said respective metal/metallized wall and centered with respect to the transversal plane (PT); or a respective negative transversal coupling including a respective pair of slots (24) made through said respective wall and symmetrically spaced apart from the transversal plane (PT) by a predefined distance. For each positive transversal coupling, each of the first (211,213) and second (221,223) rectangular waveguide resonators transversally coupled by means of the respective single slot (23,25) is crossed by the transversal plane (PT) at a respective resonator section where magnetic field component coupled by said respective single slot (23,25) is maximum. For each negative transversal coupling, each of the first (212) and second (222) rectangular waveguide resonators transversally coupled by means of the respective pair of slots (24) is crossed by the transversal plane (PT) at a respective resonator section where magnetic field component coupled by said respective pair of slots (24) is null.