Code-modulated embedded test for phased arrays

Millimeter wave (mm-wave) design has become the forefront for enabling multi-Gb/s wireless communications due to the abundance of available bandwidth at frequencies above 24 GHz. At these frequencies, phased arrays are used to meet link budgets by combining phase-adjusted responses of multiple antennas to form a high-gain, directive beam which is electrically steerable. Current requirements point to array sizes ranging from 8-32 elements, each of which must be measured and calibrated in terms of RF output power and phase to obtain the desired array performance. This paper will first review phased-array topologies and calibration requirements. We will then present a code modulated technique for manufacturing test of the array which uses only digital code modulators per element and a single global mm-wave squaring circuit in the form of a power detector. This approach allows measurement of full array performance with a single detector using minimum additional built-in-test hardware. Behavioral models indicate that this method can estimate the phase response within 1 degree and an output power within 0.2 dB for each individual element using global array measurements.