DGPS Antenna Near-Spherical Coverage Multipath Suppression
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Solution Overview
Problem
Current antennas for Differential GPS (DGPS) applications face challenges in providing a near-spherical antenna pattern of circular polarization, which is essential for accurate signal reception, as existing designs fail to adequately discriminate against multipath signals reflected from various surfaces and objects, especially in space-limited environments like ships, leading to phase discrepancies and reduced accuracy.
Innovation Solution
The design incorporates a cylindrical first assembly with a conductive top and bottom portion, dielectric cylindrical portion, and signal divider/combiner to produce a near-spherical right-hand circular polarization pattern, excluding a downward cone, using four exciter members and a signal absorbent base assembly to suppress left-hand circular polarization signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional antenna designs are used, then the antenna can be constructed with simple structure, but the antenna cannot adequately discriminate against multipath signals reflected from various surfaces and objects
Solution Approach 1:
The antenna is divided into multiple functional segments: a radiating element assembly with specific geometric configuration, a signal absorbent base assembly, and a signal divider/combiner. Each segment performs a specific function in achieving near-spherical circular polarization coverage while suppressing multipath signals.
Solution Approach 2:
A signal absorbent material is introduced as an intermediary between the radiating elements and the environment. This material absorbs reflected multipath signals within the base assembly, preventing them from re-radiating and interfering with the received GPS signals.
2Measurement precision
If an ideal spherical polarization pattern is implemented, then accurate phase center location can be maintained, but such a pattern is theoretically not realizable with known antenna designs
Solution Approach 1:
Instead of attempting to achieve a perfect spherical polarization pattern in all directions (which is theoretically impossible), the design achieves near-spherical coverage for all directions except within a downward cone having an acute internal angle. This partial achievement provides sufficient accuracy for DGPS applications while being physically realizable.
Solution Approach 2:
The antenna design accepts that polarization performance will be degraded in specific local regions (the downward cone), while maintaining excellent near-spherical circular polarization characteristics in all other directions. This localized compromise enables practical implementation with adequate overall performance.
3Ease of operation
If the antenna is positioned on a ship in a crowded and space-limited environment, then the antenna can be installed in constrained spaces, but adequate discrimination against multipath signals reflected from nearby objects and surfaces becomes difficult
Solution Approach 1:
The signal absorbent base assembly converts the harmful reflected multipath signals into absorbed energy. By placing the absorbing material in the base assembly beneath the radiating elements, the design actively counteracts multipath interference from nearby ship structures, converting a problematic environmental factor into a controlled condition.
4Measurement precision
If GPS signals are received without adequate multipath suppression, then the antenna can be simple in construction, but phase discrepancies and reduced accuracy occur in DGPS applications
Solution Approach 1:
The signal absorbent base assembly is positioned in advance beneath the radiating elements to preemptively absorb multipath signals before they can reflect off nearby surfaces and interfere with the received GPS signals. This preliminary suppression action prevents phase discrepancies from occurring in the first place.
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
This configuration provides effective suppression of multipath signals, maintaining accurate phase center location and minimizing phase errors, ensuring reliable GPS signal reception with a phase center stability of 6.3 to 9.5 mm and a 15 dB gain advantage for right-hand circular polarization signals over left-hand polarization signals, reducing system errors in DGPS applications.
Implementation Method 1
a cylindrical base assembly including a cylindrical side wall portion having a signal absorbent property
Implementation Method 2
a cylindrical portion extending around the space between the top and bottom portions and having a dielectric property
Data Source
AI summary
Accuracy of derivation of local corrections to GPS signals for use for aircraft landing guidance is subject to effects of reflected multipath signals. Antennas with a near-spherical antenna pattern of right-hand circular polarization, except within a downward cone, provide suppression of reflected multipath GPS signals incident from all azimuth angles and all relevant elevation angles. For such an antenna a cylindrical top assembly may include spaced conductive disks with intermediate exciter members excited at increments of 90 degree phase and surrounded by a dielectric ring. A cylindrical base assembly may include signal absorbent top and side wall portions and a bottom conductive disk and may alternatively include a signal absorbent inner wall portion.