A COMPACT BALUN BASED ON MICROSTRIP EBG CELL AND INTERDIGITAL CAPACITOR

A novel compact balun (balanced-to-unbalanced) that consists of a low-pass network served by a microstrip electromagnetic bandgap (EBG) cell and a high-pass …-network formed with an interdigital capacitor is presented. This proposed approach can efiectively operate the compact balun without the use of ‚=4 microstrip lines to reduce the circuit area over 50% compared to the conventional Marchand balun. The core dimension of the compact balun is 0:74cm£0:7cm. The planar structure enables an e-cient circuit design in printed circuit boards (PCB) without using any bonding wires, defected ground structures (DGS), or surface mounted devices (SMD). A compact balun operating in the 3GHz band has been implemented in a FR-4 PCB. From the measured results, the return loss of the input port is better than 15dB over the band from 2.6 to 4GHz. The amplitude and phase imbalances are less than 1.4dB and 3 - with the 20% operational bandwidth ranging from 2.7 to 3.3GHz, respectively.