Path-loss Modelling and Scalloping Aspects in Intelligent Reflecting Surface Assisted Communication: A Method-of-Moment Analysis

In this paper, we critically examine the frequency dependent path-loss characteristics and impacts of multiple additional side-lobes in the radiated beams (i.e. scalloping) in an IRS (intelligent reflecting surface) assisted SISO (single-input single-output) communication link. Using Method-of-Moment based MATLAB Antenna Toolbox, we analyze a system of two half-wavelength thin-wire dipoles placed near a planar IRS comprising of circular thin-wire loops. We showcase that, besides the IRS aperture size, the IRS unit-cell dimensions also play a crucial role in shaping the frequency dependent path-loss features. Considering the transmitter and IRS as a unified radiator, we further highlight the importance of properly accounting for multiple additional lobes appearing in the radiating beam due to presence of large reflector, which can cause ripple like variation in the path-loss characteristics. Finally, we demonstrate the significant impact of IRS positioning with respect to the transmit-receive system in altering the frequency dependent path-loss behaviour.