Rectangular Microstrip Antenna (RMA) with square notch at its center is designed with an infinite ground and studied for its dual frequency characteristics. A microstrip antenna in its simplest configuration consists of a radiating patch on one side of a dielectric substrate (r) and a ground plane on the other side. In this paper, substrate (FR4) of permittivity of 4.4 and thickness of 1.6 mm and rectangular patch having dimension of 25.5 33.2 mm are used to fabricate microstrip antenna. However, this configuration has a disadvantage—surface waves are formed which reduces the efficiency and gain of RMA. An Electromagnetic Band Gap (EBG) structure is introduced on the other side of substrate which acts as ground plane to suppress the surface wave excited by radiating patch, resulting in the enhancement of gain and efficiency of antenna, named as EBGRMA. For making EBG structure, RMA is modified by etching five columns of holes of dimension 4 4 mm on the bottom ground side of patch which has dimension 63.75 83 mm. The five columns of square hole have center-to-center distance of 8 mm making up an equivalent EBG structure. Later, a metallic reflector is placed at a distance of 8.5 mm below the bottom side of substrate so that power is reflected and thereby increases the gain and directivity of EBGRMA. Patch is fed by a probe at a coordinate of 4.5 and 5.2 mm. The resonant frequency selected for this research is 2.4 GHz.

Dual frequency (Nakano and Vichien, 1989) characteristics are exhibited by rectangular patch (Derneryd, 1978; and Amol et al., 2008), having square notch at its center. Compactness of antenna is also achieved by having square notch at center as it reduces the size of antenna by 17% of the conventional antenna without slot. But these types of antennae suffer from the drawback of excitation of surface waves (Pozar, 1992; and Amol et al., 2008) which leads to lower gain and antenna efficiency Introduction of an Electromagnetic Band Gap (EBG) (Raghava and Asok De, 2006; Kliros et al., 2007; and Amol et al., 2008) structure in the ground plane reduces the excitation of surface waves. The EBG structure consists of a uniformly distributed periodic metallic pattern on one side of a dielectric slab which is capable of prohibiting the propagation of all the electromagnetic waves of certain band of frequencies. EBG materials are periodic structures designed to impede the propagation of electromagnetic waves at certain frequency bands, which are determined by the periodicities of the materials and their dielectric constants. These materials provide the ability to guide and control the electromagnetic waves by setting the period of the lattices around half of the wavelength. Normally, their arrangement is plane or cylindrical. The operating mode of the EBG (Tayebi et al., 2014) structure can be seen as an LC circuit with certain resonant frequencies. The electromagnetic properties of the EBG material can thus be described using capacitors and inductors. The LC circuit performs (Tayebi et al., 2014) as a filter to block the flow of the waves in the frequency range where the surface impedance is very high. In other words, when an electromagnetic wave impinges onto the EBG structure, the reflected wave is in phase, and the EBG surface acts as a perfect magnetic conductor. EBG materials have the ability to improve the radiation efficiency while reducing the size of the antennae, due to the fact the EBG structure forms a resonant cavity when it is placed above a metallic ground plane. This is why the gain, polarization properties and bandwidth (Elsheakh et al., 2009) of the antennae are enhanced.

Telecommunications Journal, Rectangular Microstrip Antenna (RMA), Electromagnetic Band Gap (EBG), EBGRMA.