Development of UWB Bandpass Filter with Two NotchBands to Reject IEEE 802.11a/b Services

Abstract

This paper presents an Ultra-Wideband (UWB) bandpass filter with two notched bands for avoiding interference between the UWB radio system and the existing radio systems. This novel UWB dual notch filter is based on microstrip structure which consists of ring resonator and interdigital coupling. The dual notched bands operation is implemented by integrating folded stubs in the inter-digital coupled microstrip conductors. The structure generates two distinct resonant frequencies to stop 2.4 GHz and 5 GHz Wireless Local Area Network (WLAN) services. The resonance of each stub introduces a narrow rejection band in the UWB passband which then results in dual notched bands. The notched band can be shifted to any other desired frequency by tuning the length of the stub. Simulation, design, fabrication and measurement of the proposed UWB bandpass filter with notched bands are carried out strictly following the FCC's spectrum mask. The filter demonstrated both excellent ultra-wide bandwidth (from 1.8 GHz to 7.8 GHz) and rejection performance of -41 dB at 2.6 GHz and -24 dB at 5.3 GHz. The designed filter is successfully simulated using electromagnetic simulator, IE3D. The overall size of the developed filter with the above features is 6 mm (length) x 39.2 mm (height) x 1.6 mm (height). The measured insertion loss and group delay of the developed filter over the desired passband is at acceptable level.