OAM Antenna Calibration via Propagation Path Estimation
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Solution Overview
Problem
Array antennas used for OAM mode multiplex transmission systems face challenges in calibration accuracy due to low electromagnetic coupling between high-gain antenna elements separated by several wavelengths, making it difficult to estimate propagation paths accurately for calibration.
Innovation Solution
A calibration control apparatus and method that calculates receiving-side and transmitting-side correction coefficients based on propagation path estimation matrices to calibrate characteristic differences between reception and transmission units, ensuring uniform features across antenna elements arranged rotationally symmetrically and at equal distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If antenna elements are arranged with large separation distances to achieve high gain (20 dBi or higher), then transmission performance is improved, but electromagnetic coupling between elements becomes extremely weak (about −60 dB or lower), making propagation path estimation inaccurate
Solution Approach 1:
The patent introduces a calibration signal transmission mechanism where a calibration signal is sent from each transmission antenna element to all reception antenna elements. This calibration signal serves as an intermediary that enables accurate propagation path estimation even when electromagnetic coupling between elements is extremely weak (−60 dB or lower). The calibration signal provides a known reference that allows the system to measure and compensate for channel characteristics despite the weak coupling caused by large antenna separations required for high gain (20 dBi or higher).
Solution Approach 2:
The patent changes the approach from relying on natural electromagnetic coupling to using controlled calibration signals with specific parameters. By transmitting calibration signals at known powers and frequencies from each transmission element, the system can measure propagation paths accurately regardless of the weak coupling conditions. The correction coefficients calculated from these calibrated measurements then adjust the transmission signals to compensate for channel variations, effectively changing the system's operational parameters to overcome the gain-accuracy tradeoff.
2Adaptability or versatility
If antenna elements are arranged in rotationally symmetric pattern at equal distances for OAM mode multiplex transmission, then spatial multiplexing capability is improved, but characteristic differences between reception units become more pronounced, requiring more complex calibration
Solution Approach 1:
The patent segments the calibration process into individual transmission antenna element tests. Each transmission antenna element transmits a calibration signal separately, and the reception units measure the propagation paths from each element independently. This segmentation allows the system to handle the rotationally symmetric array configuration systematically, where N transmission elements each perform calibration with M reception elements. The correction coefficients are calculated and stored for each transmission-reception pair, enabling the complex OAM mode multiplex system to be calibrated through repeated application of the same basic calibration procedure.
3Power
If electromagnetic coupling between antenna elements is reduced to achieve high gain, then transmission power is improved, but the ability to perform calibration using natural coupling is lost
Solution Approach 1:
The patent performs calibration as a preliminary action before normal OAM mode multiplex transmission begins. During this preliminary calibration phase, each transmission antenna element transmits calibration signals while the reception units measure and store the propagation path characteristics. These measurements are used to calculate correction coefficients that are then applied during actual transmission operations. This preliminary calibration action captures the channel characteristics when the system is in a known state, enabling accurate compensation during high-power transmission where natural coupling is too weak for real-time calibration.
Data Source
AI summary
A calibration control apparatus (30) includes a receiving-side correction coefficient calculation unit (31) that calculates a receiving-side correction coefficient for calibrating a characteristic difference between reception units (23) based on a propagation path estimation matrix which has, as a matrix element, a propagation path estimation value of each propagation path from transmission units to reception units (23) in a plurality of transmission units of an OAM mode multiplex transmission apparatus and a plurality of reception units (23) of an OAM mode multiplex reception apparatus (20).