An ultra-wideband coupled-line balun using patterned ground shielding structures

In this paper a new planar balun for UWB- applications has been developed using a two-stage Wilkinson divider for power splitting followed by two coupled line sections for plusmn90 phase shifting. Patterned ground shielding (PGS) is used to increase the even-mode and decrease the odd mode impedances. The compact balun structure covers an area of less than 5 mm² and has been fabricated on a conventional double-layer printed circuit board to validate simulation results by measurement. The measured input and output return loss is below -10 dB from 3.5 to 10.5 GHz, so that a relative bandwidth of 100% is achieved. The measured insertion loss is about 0.5 dB by an acceptable phase imbalance over the operating frequency range. Measurements show a good agreement with the corresponding simulations.