Low-Leakage Constellation Formation Exploiting Combination Redundancy in a Digitally Modulated mmW Phased Array

Abstract

This paper introduces a new method to suppress the undesired spatial leakage of a 76-GHz phased array. In this system, $8 \times 1$ antenna elements on board are driven by digitally modulated quadrature phase shift keying (QPSK) and on–off keying (OOK) elements fabricated in 28-nm bulk CMOS. The total number of the eight-element output combinations is as large as 5&8hat;, and QPSK and 16 quadrature amplitude modulation (QAM) constellation can be formed at the broadside direction ( $\theta = 0^{\circ }$ ) by numerous qualified combinations. The peak array effective isotropic radiated power (EIRP) is measured at 31.6 dBm, and the EIRP for the redundancy-rich spatially synthesized QPSK (with eight elements) and 16QAM (with six elements) constellations are 28.5 and 23.3 dBm, respectively. The redundancy is utilized to alleviate the array spatial leakage: For a given zenith angle requiring a low leakage, the qualified combinations corresponding to the lowest leakage is adopted, and the broadside performance is not affected. Unlike conventional approaches, fine-grain magnitude and phase control for the elements are not required in synthesizing the low leakage. Simulation shows that the leakage power can be suppressed to −25 dBc for most zenith angles between 10° and 50°, supported by the measured results.