Steerable Antenna Offset Axis Eliminates Key-Hole Singularity
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Solution Overview
Problem
Steerable antennas for wide scan angles face challenges with singularities, particularly the 'key-hole effect' at nadir, leading to high actuator speeds and complex drive electronics, and existing solutions either eliminate rotary joints or suffer from singularities, affecting reliability and cost.
Innovation Solution
A steerable antenna configuration with a dual reflector system and a single RF rotary mechanism, where the beam is steered using two rotation axes, one perpendicular to the coverage area and the other aligned with the feed axis, eliminating singularities and optimizing mass, size, and signal gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a nadir-pointing azimuth rotation axis is used for wide scan steering, then the antenna can cover large angular ranges, but a key-hole singularity occurs at nadir requiring high actuator speed and complex drive electronics
Solution Approach 1:
The patent applies asymmetry by deliberately offsetting the rotation axis from the nadir point. Instead of using a symmetric nadir-pointing configuration, the rotation axis is positioned at a specific offset distance, which eliminates the key-hole singularity while maintaining wide scan capability. This asymmetric positioning changes the geometric relationship between the antenna beam and rotation axis, preventing the singularity condition from occurring.
Solution Approach 2:
The patent changes the geometric parameter of the rotation axis position from nadir (zero offset) to an offset position. By modifying this critical geometric parameter, the system eliminates the singularity issue while preserving the wide scan angle capability. The offset distance becomes a design parameter that can be optimized to balance scan range and singularity avoidance.
2Adaptability or versatility
If multiple RF rotary joints are used to enable wide scan steering, then the antenna can track moving targets over large angles, but signal loss and reliability decrease
Solution Approach 1:
The patent extracts and eliminates unnecessary RF rotary joints from the system. By using an offset rotation axis configuration, the system achieves wide scan capability without requiring multiple rotary joints in the signal path. This reduction in the number of RF rotary joints directly decreases signal loss and improves reliability, as each rotary joint represents a potential failure point and source of insertion loss.
3Reliability
If larger rotary actuators are used to overcome the key-hole singularity, then the antenna can maintain adequate link during nadir alignment, but mass and cost increase
Solution Approach 1:
The asymmetric offset rotation axis configuration eliminates the key-hole singularity condition that would otherwise require oversized actuators. By changing the geometric relationship through offset positioning, the system avoids the extreme actuator speed demands that occur during nadir alignment in symmetric configurations, allowing for smaller, lighter actuators to be used.
Solution Approach 2:
The patent changes the rotation axis position parameter to eliminate the singularity condition. This parameter change removes the need for high-speed actuation during nadir alignment, thereby reducing the power and mass requirements for the rotary actuators while maintaining reliable tracking throughout the scan range.
Data Source
AI summary
A steerable antenna architecture, or configuration, for optimal steering of transmitting and/or receiving beam over wide scan angles, is capable of steering the beam on a full hemisphere (2π steradians), with no singularity or key-hole within a coverage area and with only one RF rotary joint. The architecture includes a dual-reflector assembly defining an antenna focal point located close to a main reflector surface and a signal feed chain having a signal source located adjacent to the antenna focal point and defining a feed axis substantially pointing towards a sub-reflector intersection point. A first actuator rotates the feed chain and the dual-reflector assembly about a first rotation axis generally perpendicular to the feed axis and not intersecting with the coverage area. A second actuator rotates one of the main reflector and the dual-reflector assembly about a second rotation axis aligned with the feed axis.