Intersymbol Interference and Equalization for Large 5G Phased Arrays With Wide Scan Angles

Intersymbol interference (ISI) is introduced in a phased array when the beam is scanned. The cause of the ISI is demonstrated and its dependence on the phased array dimensions, scan angle, and symbol rate is derived. A mathematical model is created to simulate the ISI effects on transmitted (or received) symbols, and an equalizer model is introduced and achieves near-perfect equalization of the ISI. Also, for wideband signals, it is shown that large phased arrays result in amplitude modulation versus frequency. The effect of ISI on the error vector magnitude (EVM) is simulated using complex modulated signals, and the EVM before and after equalization is compared, using an adaptive 17-tap linear equalizer implemented in MATLAB. The results show that ISI in large phased arrays can be equalized regardless of the modulation, bandwidth, scan angle, and symbol rate. The EVM of 16-, 64-, and 256-quadrature amplitude modulation (QAM) signals is measured for a 256-element array in the transmit mode. The measurements verify the derivations, eliminating ISI and resulting in low EVM values after equalization. The effect of array tapering on EVM is also presented, and the results show no difference in the EVM for uniform and tapered excitations.