Conical Mode Helix Antenna for GPS Side-Lobe Tracking
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Solution Overview
Problem
Current GPS systems for geosynchronous earth orbit (GEO) spacecraft struggle to achieve precise navigation accuracy due to limitations in tracking weak side-lobe signals, which are essential for position determination amidst orbit adjust maneuver uncertainties, as existing antennas have highest gain at Nadir and lower gain in side-lobe regions.
Innovation Solution
A conical mode helix antenna design with a single conductor wound into a helical shape, featuring a larger bottom diameter than top diameter and winding circumference greater than one operating wavelength, providing higher gain in side-lobe signals than main-beam signals, especially outside the Nadir direction, enabling improved tracking of GPS side-lobe signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional antenna with highest gain at Nadir is used, then main-beam signal reception is improved, but side-lobe signal tracking capability deteriorates
Solution Approach 1:
The antenna gain pattern is optimized to provide different gain characteristics in different spatial regions: higher gain in side-lobe signal regions (out to about 33 degrees from Nadir) and zero gain at Nadir. This local differentiation of gain quality enables the antenna to selectively enhance side-lobe signal reception while maintaining overall navigation accuracy.
Solution Approach 2:
Instead of concentrating gain at Nadir as in conventional antennas, this invention inverts the approach by placing zero gain at Nadir and distributing higher gain to side-lobe regions. This inversion of the traditional gain pattern strategy enables reliable tracking of side-lobe signals which are essential for achieving 100-meter position accuracy in GEO navigation.
2Power
If antenna gain is concentrated at Nadir, then main-beam signal strength is improved, but signal availability in side-lobe regions deteriorates
Solution Approach 1:
The antenna provides locally optimized gain characteristics: zero gain at Nadir and higher gain in side-lobe regions out to about 33 degrees from Nadir. This spatial differentiation of gain quality ensures signal availability across multiple regions, enabling the GPS-at-GEO system to adapt to varying orbital conditions and maintain navigation capability.
Solution Approach 2:
The antenna gain pattern is designed to dynamically support signal reception from GPS satellites in various positions relative to the GEO spacecraft. By providing higher gain in side-lobe regions, the antenna adapts to the changing geometric relationships between the spacecraft, GPS satellites, and Earth, ensuring continuous signal availability for navigation.
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 conical mode helix antenna design enhances navigation accuracy by increasing signal availability and signal-to-noise ratio, allowing GPS systems to achieve position accuracy within 100 meters even in the presence of Delta-V uncertainties, by providing higher gain in side-lobe regions and reduced noise temperature.
Implementation Method 1
The conical mode helix antenna is configured to receive GPS signals including side-lobe signals and main-beam signals
Data Source
Figure 1
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Figure 4~5A
AI summary
A GPS-at-GEO system is provided that includes a receive antenna design that enables improved tracking of GPS space vehicle side-lobe signals. The receive antenna design is a conical mode helix antenna configured to produce a conical mode radiation pattern, which has zero gain at Nadir and higher gain in the side-lobe signal regions. The conical mode radiation pattern provides several advantages for GPS-at-GEO navigation applications. For example, this mode provides higher gain in the GPS space vehicle side-lobe signal regions for improved acquisition and tracking performance and lower gain at Nadir, providing reduced noise temperature and higher signal to noise ratio.