Design of Compact Planar Ultra-Wideband Bandpass Filters

Abstract

Since the Federal Communication Commission (FCC) adopted a First Report and Order in 2002, a wide frequency range from 3.1 GHz to 10.6 GHz has been released for the marketing and operation of new types of wireless communication systems incorporating ultrawideband (UWB) technology. Because of the high-speed data handling capability, the UWB system is expected to be used for delivering real-time HDTV video streaming, transmitting of non-compressible audio/visual signals, and replacing USB cables with wireless connections. In addition, due to the low-power consumption, new short-range wireless applications have attracted considerable attentions in the fields of home electronics, home entertainment, security sensors, and health care devices. To meet today's huge demands, the research on UWB devices has been greatly accelerated. One of the difficulties in developing the UWB system is the bandwidth utilized for communication. Since the system uses very short impulse signals to transmit bit-data trains, it inherently requires an extremely wide frequency range. This unique feature always presses us to develop new technologies. In an RF front-end design, for instance, highperformance bandpass filters and antennas have been too large when we engaged in the conventional design methodology. An initial UWB filter was realized by a combination of low-pass and high-pass filters. Since then, tremendous efforts have been devoted to this subject, and a way to use a multi-mode resonator (MMR) was proposed in 2005. In this design, the first three resonant frequencies of the MMR are placed equally within the UWB band so as to create the huge passband response. By applying this technology, overall filter dimension was drastically reduced to less than 10 mm x 15 mm. After that, a variety of UWB filters have been proposed based on the MMR configuration. For example, some had a ground defected structure (DGS) or a periodic band gap (PBG) structure, and some used plural stages of MMRs to obtain the high selectivity performance. However, such approaches can sometimes cause an increase of the filter dimensions, leading to fabrication difficulties in a practical system design. Again, it should be noted that the short-range UWB systems are extremely low-power consumption and need to be pocket-sized or smaller. My goal is to develop a super-compact planar UWB filter based on the microstrip line configuration. For this purpose, the following requirements are assumed; (1) For frequency response 15