Non-Cutoff FSS Ground Plane Antenna Multipath Rejection
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Solution Overview
Problem
Current high-accuracy GPS antennas have a narrow axial-ratio bandwidth, unable to effectively cover the 1.15 to 1.60 GHz frequency range and fail to adequately reject multipath signal reflections at low elevation angles, which interferes with positioning and navigation system accuracy.
Innovation Solution
A wideband antenna with a Non-Cutoff Frequency Selective Surface ground plane featuring corrugations with a depth less than λ/4, combined with a droopy turnstile bowtie feeding element, which cancels multipath signals by controlling the phase of surface waves relative to line-of-sight signals, eliminating edge diffraction and reducing back and side lobe radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a choke ring ground plane with corrugation depth d≥λ/4 is used to eliminate surface wave propagation, then multipath signal rejection is improved, but the axial-ratio bandwidth becomes too narrow to cover frequencies between 1.15 and 1.60 GHz
Solution Approach 1:
The patent changes the corrugation depth parameter from the conventional d≥λ/4 to d<λ/4, specifically using d=λ/8. This parameter change allows surface wave propagation to occur while still achieving multipath rejection through a different mechanism (phase cancellation rather than complete suppression), thereby enabling wideband operation from 1.15 to 1.60 GHz while maintaining reliability
Solution Approach 2:
Instead of using deep corrugations to block surface waves entirely, the patent inverts the approach by using shallow corrugations that allow surface waves to propagate but control their phase to achieve destructive interference with multipath signals. This inverted strategy resolves the contradiction by achieving multipath rejection without the bandwidth limitations of deep choke rings
2Device complexity
If a non-corrugated metal ground plane is used, then the antenna structure is simpler, but edge diffraction increases causing increased back lobe and side lobe radiation
Solution Approach 1:
The patent applies local quality by adding shallow corrugations only at the edges of the ground plane rather than making the entire structure complex. These localized edge corrugations with depth d<λ/4 specifically address edge diffraction and back lobe radiation while maintaining overall structural simplicity and wideband operation capability
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 enables accurate signal reception across the 1.15 to 1.60 GHz bandwidth with improved multipath signal rejection and reduced edge diffraction, enhancing the accuracy and performance of GPS antennas by ensuring only the information-bearing signal is received.
Implementation Method 1
a Non-Cutoff Frequency Selective Surface ground plane having a metal plate with a plurality of corrugations, such as concentric rings, each corrugation having a predetermined height and a predetermined spacing from adjacent corrugations to cause a line-of-sight signal and a surface wave signal to cancel
Data Source
AI summary
Described is an apparatus and method for reducing noise in an information bearing signal is provided. A feeding element receives dual-polarized wideband electromagnetic signals. The feeding element is coupled to a Non-Cutoff Frequency Selective Surface ground plane. The Non-Cutoff Frequency Selective Surface ground plane allows for a line-of-sight signal and a surface wave to cancel. The Non-Cutoff Frequency Selective Surface ground plane can be a metal plate with a plurality of corrugations. The corrugations can be concentric rings, each corrugation having a predetermined height and a predetermined spacing from adjacent corrugations.