Miniaturised tri-band lowpass–bandpass filter using lumped-element structure

• Published in: Electronics letters 2019-03, Vol.55 (5), p.272-274
• Main Authors: Xu, Jin, Wan, Hao, Ding, Jiang-Qiao, Zhu, Yin-Xia
• Format: Article
• Language: English
• Subjects: band‐pass filters; dual‐band LP‐BP filter; frequency 1.0 GHz; frequency 2.4 GHz; frequency 5.2 GHz; frequency response; loss 0.08 dB; loss 0.69 dB; loss 1.38 dB; low passband insertion losses; lowpass passband; low‐pass filtering response; low‐pass filters; lumped‐element circuit; lumped‐element structure; microstrip filters; Microwave technology; miniaturised tri‐band lowpass–bandpass filter; transmission zeros; UHF filters; wireless LAN; WLAN applications
• ISSN: 0013-5194; 1350-911X; 1350-911X
• DOI: 10.1049/el.2018.8054

In this Letter, a miniaturised tri-band lowpass–bandpass (LP-BP) filter is proposed by using lumped-element structure. The lowpass passband (LP) and the first bandpass passband (1-BP) are produced by using the transmission zeros to divide a lowpass filtering response into a dual-band LP-BP filtering response. The second bandpass passband (2-BP) is produced by further loading a lumped-element circuit. As an example, an LP with 3 dB cut-off frequency of 1 GHz, and two BPs centred at 2.45/5.2 GHz for the WLAN applications are designed. The fabricated tri-band LP-BP filter has low passband insertion losses of 0.08/0.69/1.38 dB, and occupies a compact circuit area of 0.055λgc × 0.063λgc.