Board-level Code-Modulated Embedded Test and Calibration of an X-band Phased-Array Transceiver

TL;DR

This paper introduces a novel code-modulated embedded test (CoMET) method for board-level calibration of X-band phased-array transceivers, achieving high accuracy and improved gain and phase uniformity.

Contribution

The paper presents a new CoMET technique for embedded testing and calibration of phased arrays, demonstrating high accuracy and effective calibration outside the array's designed frequency band.

Findings

CoMET achieves gain accuracy within 0.2 dB and phase accuracy within 3 degrees.

Calibration improves gain and phase errors from 0.8 dB and 8 degrees to 0.1 dB and 1.7 degrees.

Method demonstrated on an 8-element 8-16 GHz phased array with ADAR1000 chips.

Abstract

We present methods for built-in test and calibration of phased arrays using code-modulated embedded test (CoMET). Our approach employs Cartesian modulation of test signals within each element using existing phase shifters, combining of these signals into an aggregate code-multiplexed response, downconversion and creation of code-modulated element-to-element "interference products" using a built-in power detector, demodulation of correlations from the digitized interference response, and extraction of amplitude and phase per element using an equation solver. Rotated-axis methodology is discussed for accurate extraction of phase near the original 0/90/180/270 degree axes. Our techniques are demonstrated at board level for both receive and transmit modes using an eight-element 8-16 GHz phased array constructed using ADAR1000 chips from ADI. At 6 GHz, CoMET-extracted gain and phase are accurate to within 0.2 dB and 3 degree compared to network-analyzer measurements. We then employ CoMET in a calibration loop to determinate optimum control settings at 6 GHz, outside the 8-16 GHz band for which the array was designed. We achieve seven-bit phase resolution with equalized gain. The root-mean squared gain and phase errors are improved from 0.8 dB and 8 degree before calibration to 0.1 dB and 1.7 degree after calibration.