Stacked Substrate Integrated Waveguide Filter for Compact Microwave Design
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Solution Overview
Problem
Conventional substrate integrated waveguide filters have large structural sizes, poor out-of-band suppression, and parasitic passbands close to the primary passband, which hinder miniature design and deteriorate signal-to-noise ratios in microwave circuits.
Innovation Solution
A filter unit comprising two stacked cavities with a dielectric substrate, metal covering layers, and strategically placed plated through-holes forming magnetic and electric walls, coupled by right triangle-shaped coupling slots, reducing physical size and improving out-of-band suppression by shifting the parasitic passband further away from the primary passband.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional substrate integrated waveguide filter structure is used, then the filter can be integrated in a dielectric substrate with advantages of both planar transmission line and metal waveguide, but the structural size is relatively large and occupies a large area on a microwave board
Solution Approach 1:
The patent transitions from a conventional two-dimensional planar filter layout to a three-dimensional stacked cavity structure. Multiple cavities are arranged vertically along the thickness direction of the substrate, allowing the filter to achieve compact planar footprint while maintaining filtering functionality through vertical stacking and inter-layer coupling
2Reliability
If a conventional substrate integrated waveguide filter is used, then it can be implemented with waveguide structure, but the out-of-band suppression performance is relatively poor
Solution Approach 1:
The patent introduces localized defect structures (defect modes) within the photonic bandgap structure at specific positions where out-of-band signals occur. These defect modes create localized resonant cavities that selectively suppress harmful out-of-band frequencies while maintaining the passband characteristics, thereby improving out-of-band suppression performance through localized structural modifications
3Reliability
If a conventional substrate integrated waveguide filter is used, then it can be implemented with waveguide structure, but a parasitic passband appears relatively close to the primary passband (at 2f0)
Solution Approach 1:
The patent utilizes the parasitic passband phenomenon by intentionally designing defect modes that create stopbands at the frequencies where parasitic passbands would normally occur (e.g., at 2f0). The defect structures convert the harmful parasitic resonance into beneficial stopband characteristics, suppressing the parasitic passband and improving the overall filtering performance
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 effectively reduces the filter's physical size and planar area while enhancing out-of-band suppression by moving the parasitic passband from 2f0 to 4f0, thereby improving the signal-to-noise ratio in microwave circuits.
Implementation Method 1
the row of second plated through-holes is located outside the first metal covering layer such as not to run through the first metal covering layer, the row of second plated through-holes is parallel to a cathetus of the first metal covering layer, the row of second plated through-holes runs through the second metal covering layer, each of the row of second plated through-holes is connected to one of said metal sheets, there is a gap between neighboring metal sheets, and wherein the row of second plated through-holes and the metal sheets form a magnetic wall structure
Implementation Method 2
the row of third plated through-holes is located outside the first metal covering layer such as not to run through the first metal covering layer, and the row of third plated through-holes is parallel to the other cathetus of the first metal covering layer, the row of third plated through-holes runs through the second metal covering layer, and the row of third plated through-holes forms an electric wall structure
Implementation Method 3
coupling slots between the two cavities are provided face to face, and the two cavities are coupled by using two coupling slots
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A filter unit and a filter are provided. The filter unit includes two stacked cavities. Each cavity includes a dielectric substrate, and two surfaces of the dielectric substrate are each provided with a metal covering layer. Connected coupling slots and a row of metal slots parallel to the coupling slots are etched on a metal covering layer, one end of a coupling slot is an open end, the other end is a closed end, the open end corresponds to a magnetic wall structure, and the closed end corresponds to an electric wall structure. The two cavities are coupled and connected by using the coupling slots. In the foregoing technical solution, the two cavities are stacked to form the filter unit, the two cavities are coupled and connected by using the provided coupling slots to form the filter unit, and only a feeding port needs to be disposed on a hypotenuse of a cavity. When the foregoing structure is used, a physical size of a conventional filter is effectively reduced, and a planar area of the filter unit is reduced.