Two new microstrip triple-mode resonators loaded with T-shaped open stubs using axially and centrally symmetric spiral structures, respectively, are presented. Spiraled for circuit size reduction, these two halfwavelength resonators can both generate three resonant modes over a wide frequency band by loading two T-stubs with different lengths. Due to the structural symmetry, they can be analyzed by odd-and even-mode method. To validate the design concept, two compact bandpass filters (BPFs) using these two novel resonators with center frequencies of 1.76 GHz and 2.44 GHz for the GSM1800 and WLAN/Zigbee applications, respectively, have been designed, fabricated and tested. The center frequencies and bandwidths can be tunable through the analysis of resonant frequency responses, fractional bandwidths and external quality factor versus the resonator parameters. The final measured results have achieved good consistence with the simulations of these two BPFs. where he is now a Professor. He has authored and co-authored over 80 papers in peer-reviewed journals and conference proceedings. He received the UESTC Outstanding Graduate Award in 2004, and the Excellent Doctoral Dissertation Award of Sichuan Province of China in 2012. His research interests include antenna array design, array signal processing, and microwave imaging methods.Jing AI was born in Sichuan, China. He received the B.respectively, where he is currently working toward the Ph.D. degree in Electromagnetic Field and Microwave Technology. His recent research interests include microwave and millimeter-wave circuits and systems.
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