Design of a Balun Bandpass Filter with Asymmetrical Coupled Microstrip Lines

作者：Wang, Xuedao^*; Wang, Jianpeng; Zhang, Gang; Huang, Feng

来源：Frequenz, 2017, 71(7-8): 299-303.

DOI：10.1515/freq-2016-0230

• asymmetrical coupled-line
• balun bandpass filter
• triple-mode resonator

A new microstrip coupled-line balun topology and its application to the balun bandpass filter (BPF) with a triple mode response are proposed in this paper. The involved balun structure is composed of two back-to-back quarter-wavelength (lambda/4) asymmetrical coupled-line sections. Detailed design formulas based on the asymmetrical coupled-line theory are given to validate the feasibility of the balun. Besides, to obtain filtering performance simultaneously, the balun is then effectively integrated with a pair of triple mode resonators. To demonstrate the design concept of the balun BPF, a prototype operating at 2.4GHz with the fractional bandwidth (FBW) of about 19.2% is designed, fabricated, and measured. Results indicate that between the two balanced outputs, the amplitude imbalance is less than 0.3 dB and the phase difference is within 180 degrees +/- 5 degrees inside the whole passband. Both simulated and experimental results are in good agreement.

• 出版日期2017-7
• 单位南京理工大学