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Abstract
This paper presents a new balanced wideband band-pass filter (BPF) that is designed using a multi-mode slot-line resonator (MMSLR) with microstrip feed-lines. To obtain good differential operation and meanwhile reject unwanted common-mode (CM) noises, the balanced BPF is arranged in a symmetric fashion. For differential-mode (DM) operation, by locating the first three resonant modes of the MMSLR in the desired passband and feeding the MMSLR with tightly coupled microstrip feed-lines, we obtained a wideband response that meets the requirement of the OFDM group-B bandwidth specification (4.752–6.336 GHz). For CM operation, an open-circuited stub is effectively added to the feeding lines at the output port so that the transmitted CM signals can be attenuated. The measurement agrees well with the simulation. For the designed balanced wideband BPF, the measured minimum DM insertion loss is 0.63 dB in the DM passband, in which the CM suppression is larger than 17.6 dB.
Acknowledgements
This work was supported by the National Science Council of the Republic of China (in Taiwan) under Grant NSC 100-2221-E-018-030-MY2.