Polarization Cross-Coupling Calibration for Phased Arrays
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Solution Overview
Problem
Existing calibration methods for wireless communications devices, particularly phased arrays, face challenges in accurately measuring relative phase shifts and non-linearities in signal chains due to tight area constraints and the absence of a Local Oscillator, leading to incomplete calibration that does not account for antenna feed lines and elements.
Innovation Solution
The method employs polarization cross-coupling between horizontal and vertical polarization TX/RX front ends to calibrate signal processing chains, using one polarization mode to transmit test signals and the other to receive and measure errors, thereby including antenna feed line and antenna element imperfections in the calibration process without the need for additional hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a complete TX RX chain with downconverter is used for calibration, then measurement precision is improved, but device complexity and area increase due to additional hardware requirements
Solution Approach 1:
The existing RX chain is made multi-functional by using it both for its primary receive function and for calibration measurements of the TX chain. The RX chain processes signals from both external sources and internal TX elements, eliminating the need for separate calibration hardware.
Solution Approach 2:
The system performs self-calibration by using its own RX chain to measure the TX chain's output. The device calibrates itself without external equipment by having the RX chain detect and measure signals from the TX chain through the antenna system.
2Area of stationary object
If signal sensing is performed on-chip, then device area is reduced, but measurement precision deteriorates due to exclusion of antenna feed line and element imperfections
Solution Approach 1:
The antenna system serves as an intermediary that connects the on-chip TX and RX chains to the external environment. By routing test signals through the antenna feed lines and elements to the RX chain, the calibration process includes these components without requiring external sensing equipment.
Solution Approach 2:
The calibration approach moves from purely on-chip sensing to a hybrid approach that utilizes the spatial dimension of the antenna system. Test signals are transmitted through the antenna feed lines and elements into free space, then captured by the RX chain, thereby including off-chip components in the calibration loop.
3Measurement precision
If additional test hardware is added for calibration, then measurement precision is improved, but device area and cost increase
Solution Approach 1:
The RX chain is designed to perform dual functions: receiving external signals during normal operation and measuring internal TX chain signals during calibration. This eliminates the need for dedicated calibration hardware while maintaining measurement precision.
Solution Approach 2:
The calibration function is merged with the existing RX chain functionality. The same hardware components (antenna, feed lines, RX chain) used for signal reception are also used for calibration measurements, consolidating functions into existing infrastructure.
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 approach enhances calibration accuracy by accounting for off-chip components like antenna feed lines and elements, reducing the need for extra hardware and improving beam formation precision.
Implementation Method 1
Test signals transmitted via the horizontal polarization antenna element are received by the vertical polarization antenna element
Data Source
AI summary
Methods and apparatus for calibrating signal processing chains using cross coupling between polarizations are described. Various exemplary methods and apparatus, in accordance with the present invention, are well suited for use in communications devices using beamforming and including arrays of TX/RX front ends, e.g., a first plurality of horizontal polarization front ends and a second plurality of vertical polarization front ends.