A 2.4-GHz bandpass filter for flexible RF applications

A 2.4-GHz bandpass filter is implemented on a flexible printed circuit board with a thickness of 127 mu m for wearable RF applications. The bandpass filter is realized in a double-sided structure, of which the top side provides the main filtering characteristics using two coupled resonators and the bottom side provides efficient signal feeding and coupling using mixed coupling scheme. The mixed coupling scheme combining the broadside- and cross-coupling structures is advantageous to improve the insertion loss. The filter characteristics when bended by up to 90 degrees are simulated using a three-dimensional electromagnetic simulation tool and experimentally verified. Measurement results show that the insertion loss is less than 1 dB and the return loss is less than 26 dB across the total passband from 2.4 to 2.5 GHz. (C) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:384387, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26588