Antenna Array Calibration Using External Probe Antennas
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Solution Overview
Problem
Current antenna array calibration methods in RF systems only correct routing electronic errors without accounting for antenna reflections, limiting the accuracy of high-frequency measurements and failing to provide full 2-port characterization.
Innovation Solution
The method involves using external probe antennas to perform initial and secondary measurements, allowing for the calculation and calibration of S-parameters for the antenna array, including the VNA, without disconnecting or disabling the system, thereby enabling full 2-port characterization and correction of return-loss and transmission-loss coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional calibration methods are used that only correct routing electronic errors, then the calibration process is simple and quick, but measurement accuracy deteriorates because antenna reflections are not accounted for
Solution Approach 1:
The calibration process is performed in advance before actual measurements, establishing correction coefficients that account for antenna reflections and routing errors. This preliminary characterization of the measurement system eliminates the need for complex real-time corrections during subsequent measurements.
Solution Approach 2:
Probe antennas are introduced as intermediary elements to facilitate the calibration process. These probe antennas enable the measurement of S-parameters between array elements through a controlled coupling mechanism, allowing the extraction of correction coefficients without requiring direct access to the antenna array ports.
2Measurement precision
If full 2-port characterization including antenna reflections is implemented, then measurement accuracy improves, but the calibration process becomes more complex and time-consuming
Solution Approach 1:
The calibration process is divided into two distinct phases: Phase 1 measures S-parameters between probe antennas to characterize the probe array, and Phase 2 measures S-parameters between probes and array elements to extract correction coefficients. This segmentation allows systematic handling of the complex calibration task.
Solution Approach 2:
The calibration methodology transforms the problem from measuring direct antenna parameters to measuring S-parameters of probe-array combinations. By changing the measurement parameters and using mathematical transformations (S-parameter to correction coefficients), the complex antenna characterization is achieved through more manageable measurements.
3Measurement precision
If traditional calibration methods requiring disconnection of antennas are used, then complete calibration is possible, but system availability deteriorates due to required disassembly
Solution Approach 1:
Probe antennas serve as intermediary coupling elements that enable calibration measurements without requiring disconnection of the antenna array from the VNA. The probes are temporarily attached to array element ports, allowing in-situ calibration while maintaining system connectivity and minimizing disruption to system operation.
4Device complexity
If only routing electronic correction is performed, then calibration simplicity is maintained, but return-loss and transmission-loss coefficient accuracy deteriorates
Solution Approach 1:
The methodology changes the measurement parameters from simple routing corrections to full S-parameter measurements of probe-array combinations. This parameter transformation enables the extraction of both routing error corrections and antenna reflection characteristics, providing accurate return-loss and transmission-loss coefficients through mathematical processing of the extended measurement data.
Data Source
AI summary
A method and a system for calibrating an antenna array. The method may include the following steps: attaching successively pairs of a plurality of probe antennas to each other; performing an initial measurement of a multiport formed by the ports of said pair of probe antennas, the initial measurement yielding initial coefficients of said probe antennas; attaching successively one of said probe antennas to one of the antennas in said antenna array; performing a second measurement of multiports formed by the ports of said probe antennas and said antenna array, the second measurement yielding coefficients of the combination of said antenna array and said probe antennas; and using the initial coefficients and the second measurement coefficients to calibrate said antenna array.