Operating Band Shifting of Resistor-Loaded Antenna-Based Absorber by Using Parasitic Element Concept

The size of an electromagnetic (EM) absorber is a critical design parameter since it determines the operating frequency band. The realization of lower starting frequency requires enlargement of the absorber which often is not desired. In this communication, a technique for overcoming this problem in the case of an absorber, constructed of a resistor-loaded wideband bowtie antenna, is studied. The method is about placing parasitic elements around the antenna in order to change its input impedance and thus to realize large shifting of the operating band of both single- and dual-polarized absorbers. Without using parasitic elements large move of the operating band can only be achieved by a considerable increase in the absorber's size. However, the used method for absorption band shifting leads to shrinking of the bandwidth which means a compromise is to be made between these two parameters. For validation purposes, prototypes are fabricated and tested, and a good agreement between the simulation and measurement results is obtained.