Triangular Patch UWB Filter with a Band-Notched Characteristic Ravi Dutt Gupta, Mahesh P. Abegaonkar, Ananjan Basu, Shiban K. Koul Centre for Applied Research in Electronics, Indian Institute of Technology Delhi, Hauz-Khas, New Delhi-110016, INDIA E-mail: mpjosh@care.iitd.ac.in , ravi_dutt81@yahoo.com Introduction Since the US Federal Communications Commission (FCC) released the unlicensed use of the ultra-wideband (3.1-10.6 GHz) spectrum for indoor and hand-held systems in Feb-2002[1]. Recently, the development of new UWB filters has increased via different methods and structures [2]–[5]. In [2] an initial UWB filter is presented by mounting a microstrip line in a lossy composite substrate to attenuate the signal at high frequencies, and the reported insertion loss is higher than 6.0 dB. In [3] a novel microstrip UWB BPF has been constructed by using a circular ring resonator structure in cascade and the reported insertion loss is 0.58dB in the passband, integration of multiple-mode resonator (MMR) with two coupled- lines for the UWB passband [4]. In [5] the authors utilized circular and triangular resonators integrated with capacitive-ended interdigital coupled line to improve the out-band performance. For the indoor and hand held UWB systems one general problem is a possible interference with relatively strong narrowband signals within the allocated UWB spectrum like those from WLAN applications. Most of the WLAN systems are designed to operate in the 2.4 GHz and 5.0 GHz frequency bands, e.g., 5.15 to 5.35 GHz (IEEE 802.11a lower bands) and 5.725 to 5.825 GHz (IEEE 802.11a upper bands). Therefore it has become an issue to develop such filters which can reject such unwanted or disturbing radio signals. Some researchers have proposed some new structures to realize the UWB BPF with notched band characteristics [6]-[7]. To obtain a notched band in defined UWB passband, open-ended stubs are placed in the first and last connecting lines of a UWB BPF [6] while modified coupled line sections have been used to create a notch band at a specific frequency in [7]. In this work a novel UWB Bandpass notched filter has been demonstrated and implemented by using a triangular patch resonator structure [5]. A notch in filter’s response is introduced by using a set of open-ended stubs. The insertion loss and group delay characteristics are excellent over the full passband. Filter Design An isosceles triangular patch has a dual mode operation and a property to produce a single finite frequency transmission zero with a single resonant frequency [9]. This property has been used for the bandpass filtering operation in which two transmission zeros are required. First of all an isosceles triangular patch has been designed to give the lower frequency transmission zero, for this length L is taken to 13 mm. A slot has been made in the patch to reallocate the transmission pole and also for miniaturizing the filter size. An open circuited stub is placed; with length (A) 3.6 mm and width (B) is 0.9 mm, at the center of the base of the triangular patch to produce the upper frequency transmission pole and to achieve an ultra- wide bandwidth. The length of the stub is chosen to quarter-wavelength at the upper transmission zero frequency. In this way two transmission zeros are realized necessary for bandpass characteristics. To increase the bandwidth of the filter a slot has been made in the ground plane. This slot has been optimized for the width (M) as 1.2 mm and length (N) is 978-1-4244-2642-3/08/$25.00 ©2008 IEEE