Triple-Band Frequency-Selective Surfaces to Enhance Gain of X-Band Triangle Slot Antenna

A new modified microstrip triangle slot antenna is first investigated and designed at X-band. By adding two rectangular slits in the edge of the radiating aperture and adjusting the dimension of the feeding stub, a very good impedance matching within the X-band is obtained. Afterwards, by using microstrip transmission line (suspended line) and unit-cell box analyses, a new triple-band frequency selective surface (FSS) is designed that is compoed of three conductor-based split-ring resonators, connected together. The effect of the unit-cells periodicity in the finite FSS alone and the antenna with FSS behaviors is discussed. Moreover, the different distances between the antenna and FSS surfaces are experimentally analyzed. For this purpose, two foam-based holders along with a compound prototype of the antenna and FSS are manufactured. Return loss, radiation pattern, and gain of the antenna with an increment of about 2.5 dB without disturbing the matching and bandwidth are presented.