Modern microwave systems require high performance, compact size and low cost. To avail these requirements, many new technologies are available such as Low-Temperature co-fire ceramic technology (LTCC), low-temperature co-fire ferrite (LTCF) and some new structures such as Photonic band gap (PBG), Defected Ground Structure (DGS), Substrate Integrate Waveguide (SIW). John (1987) and Yablonovitch (1987) proposed a 3D PBG, which implodes and utilizes metallic ground plane and breaks traditional microwave circuit confined design to surface components and distributions of the medium circuit plane. Based on the dimensional periodicity of the crystal structure, the bandgaps can be in one, two, or three-dimensional planes, with the level of complexity increasing as the dimensions increase. In most communication applications, however, the use of Yablonovitch method is not practical. Instead, in a 2-D photonic crystal, the band gap exists only within a plane, thereby allowing propagation along one axis of the crystal (Agi and Malloy, 1999; and Gonzalo and Martinez, 1999). This is the ideal scenario for microstrip antenna designs, since the ‘rejection plane’ could be in the plane of the patch to prevent surface wave formation. Consequently, there has been an increasing interest in microwave and millimeter-wave applications of Electromagnetic Band Gap (EBG) (Tarot et al., 2003;
Zheng and Zhang, 2003a and 2003b; Yuan et al., 2008). Similarly, another method to size reduction is DGS, which suppresses spurious response. DGS adds an extra degree of freedom in microwave circuit design and opens the door to a wide range of applications. In the following years, quite a lot of novel DGSs were proposed and they had become one of the most interesting areas of research owing to their extensive applicability in microwave circuits. The parameters of equivalent circuit models of DGSs were also researched and utilized to design planar circuit easily. Many passive and active microwave and millimeter devices have been developed to suppress the harmonics and realize the compact physical dimensions of circuits for the design flow of circuits with DGS comparatively simple (Li et al., 2005; Chen et al., 2006; and Niruth et al., 2009). In this paper, the performance of square notch patch antenna using DGS with two different substrates is compared.
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