UWB-Bandpass Filters with Improved Stopband Performance

In wireless communication systems, microwave planar bandpass filters are employed in most applications. The broadband and multiband applications are renewing the interest in the design of planar broadband filters with low loss, compact size, high suppression of spurious responses, and improved stopband performances. However, since the ultrawideband (UWB) system covers very wide frequency range of 3.1 to 10.6 GHz and then may be interfered with the existing undesired narrow band from the 5.2 GHz or 5.8 GHz wireless local area network (WLAN) radio signals. Moreover, the WiMAX (3.5 GHz) and RFID (6.8 GHz) communications may interfere with the UWB system within the range defined by the FCC. Therefore, UWB bandpass filters with singleand multi-narrow notched bands are needed to avoid being interfered by the exiting RF signals. In order to obtain operations, several techniques have been reported in literatures based on UWB-bandpass filters with slotted resonators (Meeloon et al., 2007, 2008, 2009), UWB-bandpass filters with slotted resonators and embedded slotted feed (Meeloon et al., 2009, 2011), and UWB-bandpass filters with slotted resonators and embedded fold-slot feed (Meeloon et al., 2010, 2011).