Dual-band filters for WLAN applications on liquid crystal polymer technology

This paper presents the development and performance of several dual-band filters for wireless local area network (WLAN) applications. Three dual-band filters meeting the specifications of 802.11 bg (2.412-2.484 GHz) for the lower band and the specifications of 802.11 a-L (5.180-5.320 GHz), 802.11 a-H (5.745-5.805 GHz) and 802.11 a-L&H (5.180-5.805 GHz) for the upper band are presented. These filters are developed based on dual behavior resonator (DBR) topology in combination with a new stepped impedance approach and are implemented for the first time on liquid crystal polymer (LCP) technology. LCP has been chosen because of its low cost, good RF performance and its ability to act both as a substrate and a package. Measurements show a very low insertion loss of -1.25 dB for the lower band and an insertion loss of -2.4 dB and -1.1 dB for the narrow and broad upper bands respectively. This work demonstrates that the proposed design methodology is simple, efficient and allows easy tuning of the filter parameters to suit different specifications.