In this article, impedance transformers and branch line hybrids are selected to demonstrate the impact of defected ground structures on the operational bandwidth of microwave circuits. Three different branch line hybrids are studied with simulations and laboratory measurements, these are; a standard branch line hybrid, one using tapered lines and another one using both tapered lines and DGS. Based on these results, an optimum design in terms of location, size and number of DGS was proposed to achieve the widest operational bandwidth. Simulation and measured results demonstrate that correct usage of DGS and tapered lines can enhance the bandwidth of a narrowband microwave circuit. (c) 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:311-316, 2016.