Studies On Miniaturized Microwave Dual-band Filters

Modern wireless communication systems demand that radio frequency (RF) devices can operate in multiple bands. As a key component in mutiband communication system, such as Wireless Local Area Network (WLAN), Global System for Mobile Communications (GSM) and Global Position System (GPS), microwave dual-band bandpass filter is essential to the performance of the system. This thesis gives a detail study on the design technique and theory of miniature dual-band filters. The proposed theories are verified by design examples.The author's main contribution includes three parts as follows:Firstly, two microstrip dual-band bandpass filters based on novel dual-band admittance inverters are presented. The filters consist of a pair of dual-band resonator and a dual-band admittance inverter. The dual-band resonator is realized by shunting a uniform impedance stub with a stepped-impedance stub. Two kinds of novel dual-band admittance inverters are proposed. One is realized by using three-section microstrip transmission line; another is realized by using an open-stub loaded transmission. All the theoretical analysis and design procedures are discussed in detail. Two 2.4GHz/5.2GHz dual-band bandpass filters for wireless local area network are designed. The design procedure is verified by experimental results.Secondly, a dual-wideband bandpass filter for Ultra-Wideband Bandpass (UWB) system is proposed. The filter consists of a multimode stepped-impedance resonator (SIR) and two pseudo-interdigital coupling lines. Two symmetrical spur-lines are embedded in the SIR to create a notch band in the UWB. Thus dual-wideband is achieved. The 3dB-bandwidth of the dual-wideband are 3.1~5.15GHz and 5.8~10.2GHz respectively. A -15dB suppression between 5.15-5.8GHz is obtained, which can eliminate the WLAN signals effectively. The filter is very compact and suitable for UWB system.Finally, two kinds of dual-band bandpass filters are designed using low temperature co-fired ceramic (LTCC) technique. First filter is realized by using dual-mode resonator and two different resonators. The second one is implemented by using combined resonators. The central frequencies and bandwidths of both filters can be controlled. Two microwave filters operating at 2.4GHz and 5.2GHz with different bandwith are designed based on the proposed theory. Experimental results verify the proposed design scheme.