A highly selective tri‐band bandpass‐to‐bandstop filter with the third band independently tunable

Abstract

A highly selective tri-band bandpass (BP)-to-bandstop (BS) filter with the third tunable band and the other two fixed ones is proposed in this article. This filter is based on a novel crossed resonator that is composed of a two-end-open UIR with an open stub and a short stub connected in parallel on both sides of the resonator center. A PIN diode is utilized to achieve BP-to-BS switchable characteristics. Then, varactor diodes loaded at the open stub are employed to obtain the independently tunable third band. In addition, due to the symmetry of the resonator structure, the even-and odd-mode analysis method is used to derive the resonant frequencies. For validation, a tri-band BP-to-BS filter operating at 2.4 GHz (WLAN), 3.3 GHz (WiMAX), and 4.9 GHz (LAA/LTE-U) is designed, manufactured, and measured that achieves the continuous frequency tuning range (FTR) of the third band from 4.52 to 4.90 GHz with return loss (RL) better than 10.05 dB under the BP characteristic, from 4.55 to 4.90 GHz with the rejection level (RL) higher than 15.53 dB under the BS characteristic. The measured results agree well with the simulated ones.

Design of Multi-Band Bandstop Filters Based on Mixed Electric and Magnetic Coupling Resonators

“…Therefore, the stopbands of the current multi-band bandstop filters are mainly concentrated in the dual bands. In [4][5][6][7][8][9][10][11][12][13][14], different techniques are presented to achieve the multi-band bandstop frequency response. For example, in [4][5][6][7][8][9], various researchers used different methods to implement dual-band BSFs.…”

“…Similarly, in [10][11][12][13], tri-band bandstop filters were implemented in different ways. In [10], Yang H investigated tri-band bandpass (BP)-to-bandstop (BS) filters.…”

“…Similarly, in [10][11][12][13], tri-band bandstop filters were implemented in different ways. In [10], Yang H investigated tri-band bandpass (BP)-to-bandstop (BS) filters. In [11], Chen W Y developed a tri-band bandpass filter designed based on a stub-loaded stepped-impedance resonator (SIR).…”

A novel miniaturized sext‐band bandstop filter based on tree‐shaped branches loaded asymmetric multimode resonators

“…Chen and Cai realized tunable dual-band BSFs in [6,7]. In addition, other tri-band BSFs were obtained using complex configurations in [8][9][10][11]. In [8,] Jankovic employed the Hilbert-fork ring resonator to realize a tri-band BSF, in [9], Yang developed a highly selective quadra bandgap filter with the third band individually adjustable, in [10,11], Mahmud used parametric analysis on a defective ground structure (DGS).…”