Design of Dual-Band Bandpass Filters Using Stub-Loaded Open-Loop Resonators

In this paper, open-loop resonators loaded by shunt open stubs are proposed to design compact dual-band bandpass filters with improved out-of-band rejection characteristics. The second passband of the dual-band filter is obtained by tuning higher resonant modes of the open-loop resonator by the stub length and position. A tapped-line input/output feed structure is used for external coupling. Required external coupling is obtained by adjusting the tapping position and dimension of the stub-loaded resonator. A lossless transmission line model is used to determine the resonance properties of the resonator and the external quality factor. Theoretical predictions are verified by the experimental results of three dual-band filters.

[1]  Chih-Ming Tsai,et al.  Planar filter design with fully controllable second passband , 2005, IEEE Transactions on Microwave Theory and Techniques.

[2]  Min-Hua Ho,et al.  A Parallel Doubly Coupled Dual-Band Bandpass Filter , 2006, 2006 IEEE MTT-S International Microwave Symposium Digest.

[3]  M. Makimoto,et al.  Bandpass Filters Using Parallel Coupled Strip-Line Stepped Impedance Resonators , 1980 .

[4]  T. Ishizaki,et al.  A miniaturized monolithic dual band filter using ceramic lamination technique for dual mode portable telephones , 1997, 1997 IEEE MTT-S International Microwave Symposium Digest.

[5]  Chu-Yu Chen,et al.  A simple and effective method for microstrip dual-band filters design , 2006, IEEE Microwave and Wireless Components Letters.

[6]  Cheng-Ying Hsu,et al.  Design of Miniature Planar Dual-Band Filter Using Dual-Feeding Structures and Embedded Resonators , 2006, IEEE Microwave and Wireless Components Letters.

[7]  Sheng-Fuh Chang,et al.  Dual-band step-impedance bandpass filter for multimode wireless LANs , 2004 .

[8]  Lei Zhu,et al.  Coupling dispersion of parallel-coupled microstrip lines for dual-band filters with controllable fractional pass bandwidths , 2005, IEEE MTT-S International Microwave Symposium Digest, 2005..

[9]  J. Kuo,et al.  Design of microstrip bandpass filters with a dual-passband response , 2005, IEEE Transactions on Microwave Theory and Techniques.

[10]  Hong-Ming Lee,et al.  Dual-Band Filter Design With Flexible Passband Frequency and Bandwidth Selections , 2007, IEEE Transactions on Microwave Theory and Techniques.

[11]  Min-Hang Weng,et al.  Compact and Low Loss Dual-Band Bandpass Filter Using Pseudo-Interdigital Stepped Impedance Resonators for WLANs , 2007, IEEE Microwave and Wireless Components Letters.

[12]  Jen-Tsai Kuo,et al.  Microstrip stepped impedance resonator bandpass filter with an extended optimal rejection bandwidth , 2003 .

[13]  Kai Chang,et al.  Tunable microstrip bandpass filters with two transmission zeros , 2003 .

[14]  Yue Ping Zhang,et al.  Dual-Band Microstrip Bandpass Filter Using Stepped-Impedance Resonators With New Coupling Schemes , 2006, IEEE Transactions on Microwave Theory and Techniques.

[15]  C. Quendo,et al.  An original topology of dual-band filter with transmission zeros , 2003, IEEE MTT-S International Microwave Symposium Digest, 2003.

[16]  Jia-Sheng Hong,et al.  Microstrip filters for RF/microwave applications , 2001 .