Improved planar Marchand balun using a patterned ground plane
In this article, a novel planar Marchand balun using a patterned ground plane is presented. This new design has a slot under the coupled lines cut on the ground plane so that the even-mode impedance can be increased substantially. Meanwhile, we propose that two additional separated rectangular conductors be placed under the coupled lines in order to act as two capacitors, so that the odd-mode impedance will be decreased. The design theory and procedure for optimizing the Marchand balun are presented. As an example, one Marchand balun on a double-sided PCB is designed, simulated, fabricated, and measured. The measured return loss is found to be better than -10 dB over the frequency band from 1.2 to 3.3 GHz, or around 100% bandwidth. The measured amplitude and phase imbalance between the two balanced output ports are within 1 dB and 4 degrees, respectively, over the operating frequency band. (c) 2005 Wiley Periodicals, Inc.
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