Planar Multiband FSS with Stable Filter Response
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Solution Overview
Problem
Conventional Frequency Selective Surfaces (FSS) are limited by large size due to unit cell dimensions being λ/2, poor roll-off at sidebands, and unsuitability for multifunctional applications requiring multiple resonances, especially in 5G applications where spatial filtering in Ka and Ku bands with high angular stability and polarization insensitivity is needed.
Innovation Solution
A Frequency Selective Surface (FSS) with periodicity between one eighth and one quarter of an operational wavelength, featuring multiple pattern elements that produce multiple transmission poles and zeros, including modified Jerusalem crosses and spiral resonators, arranged in a grid pattern to achieve low profile and high angular stability, suitable for 5G applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If conventional FSS unit cells with size λ/2 are used, then the FSS can achieve basic bandstop or bandpass filtering, but the FSS becomes relatively large in size and can only accommodate a few elements within limited area
Solution Approach 1:
The patent changes the fundamental parameter of unit cell size from conventional λ/2 to much smaller dimensions (e.g., λ/8 × λ/8 or λ/10 × λ/10), enabling dense packing of multiple elements within the same area while maintaining filtering functionality through modified geometric patterns
2Device complexity
If first order FSS elements are used, then the FSS structure remains simple, but the roll-off at lower and higher sidebands is poor
Solution Approach 1:
The patent divides the filtering function into multiple independent pattern elements (first, second, third, and fourth elements) within each unit cell, where each element contributes to different aspects of the filter response, achieving sharp roll-off through their combined effect rather than requiring complex cascaded structures
Solution Approach 2:
The patent merges multiple pattern elements into a single integrated unit cell design, combining the functions of multiple first-order elements to achieve second-order or higher filter response characteristics with improved roll-off while maintaining a compact planar structure
3Reliability
If cascaded elements with λ/4 spacing are used to sharpen roll-off, then the filter response improves, but the total profile height of the FSS increases
Solution Approach 1:
The patent transitions from a vertical stacking approach (cascaded elements in multiple layers with spacing) to a planar integration approach, achieving enhanced roll-off through in-plane arrangement of multiple pattern elements within a single low-profile unit cell structure
4Device complexity
If conventional FSS with single resonance is used, then the design is simple, but it is unsuitable for multifunctional applications requiring multiple resonance spatial filters
Solution Approach 1:
The patent designs a universal unit cell structure containing multiple independently tunable pattern elements, each capable of being configured to produce different resonant frequencies, enabling a single FSS to perform multiple filtering functions simultaneously for multifunctional applications
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 FSS design achieves high angular stability and polarization insensitivity, with frequency shifts less than 3% at 60° incident angles, and provides efficient spatial filtering with low insertion loss and high reflection magnitude, suitable for 5G applications in Ka and Ku bands.
Implementation Method 1
a first pattern element positioned at a center of the unit cell and configured to produce a first transmission pole at a first frequency
Implementation Method 2
a second pattern element positioned around a border of the unit cell and configured to produce a second transmission pole at a second frequency different from the first frequency
Implementation Method 3
the first pattern element is further configured to produce a transmission zero between the first frequency and the second frequency
Data Source
AI summary
A frequency selective surface (FSS) having periodicity between one eighth and one quarter of an operational wavelength of the FSS and a low profile. The FSS has multiple pattern elements which are used to produce multiple transmission poles, and in some embodiments multiple transmission zeros. The transmission poles and transmission zeros are in the Ka and Ku bands, making the FSS applicable to 5G application. The transmission poles and transmission zeros also have high angular stability an oblique incident angle as high as 60°, as well as polarization insensitivity.