**1. Introduction**

Electromagnetic band gaps (EBGs) are generally periodic structures that exhibit different bandgaps over specific frequency ranges that prohibit electromagnetic wave propagation [1]. Due to its frequency selective characteristics, EBG structures naturally find applications in microwave filters. The main limitation of EBG structures is their large overall sizes and complex structures, which are not easy to analyse, and in most cases, not feasible to fabricate [2]. Defected Ground Structure (DGS) can overcome large size problems, and the complexity of EBG structures can be overcome by Defected Ground Structure (DGS). DGS structures can produce band rejection in specific frequency bands, and hence, is also known as a kind of EBG structure [3]. A DGS is a non-periodic EBG structure. It is an etched structure in the metallic ground plane of a microstrip structure. D. Ahn et al. first introduced the dumbbell-shaped DGS structure [4]. A variety of geometry etched in the microstrip line ground plane has been implemented to serve as defected ground structure. These structures usually add an extra lumped inductance and capacitance to the microstrip line connected as a parallel resonant circuit in series with transmission lines at both ends. The main features of the DGS structures are as follows in [5–12].

#### **1.1 Some attractive features of DGS structure**

Photonic Band Gap (PBG) Structures or Electromagnetic Band Gap (EBG) Structures could be:

