On the Design of Radar Absorbing Materials Using Left-Handed Transmission Line

A novel radar absorbing material is designed by combining a high impedance surface and a transitional structure. The high impedance surface consists of a two-dimensional periodic array of unit cells that are implemented using a left-handed transmission line printed on a dielectric substrate with lumped elements. A transition between free space and the vertically placed microstrip line is designed using a horizontal strip to ensure that the incident electromagnetic energy can be strongly coupled to the guided wave in the microstrip line. A chip resistor is added in the printed microstrip line of each unit cell to absorb the electromagnetic energy. Both simulated and measured radar cross section results of a conducting plate with 4 times 8 cells show that the absorber has a reduction of 10 dB over a bandwidth 50% at the center frequency of 2 GHz. The thickness of the designed absorber is only 0.13 free-space wavelength at the center frequency. Simulation results of another designed absorber show that it has a wider bandwidth about 92% using a double-substrate structure.