This paper investigates the impact of defected ground structures (DGS) on the operational bandwidth of microwave circuits. Branch line hybrids were selected to investigate DGS. Three types of branch line hybrids were studied with both hardware and simulation results; a standard branch line hybrid, one using tapered lines and another one using DGS. An optimum model in terms of location, size and number of DGS has been proposed to achieve the widest operational bandwidth. Not only by simulation results, but also with measurements, it has been observed that correct usage of DGS and tapered lines can enhance the bandwidth of a narrowband microwave circuit.