Microstrip Dual-narrowband Bandpass Filter with Independent Passbands

In this letter, a novel tri-band bandpass filter (BPF) with high selectivity is presented. The proposed tri-band BPF employs a symmetrical π-type structure loaded with λ/4 open stubs and hybrid stepped impedance resonator (SIR). The hybrid SIR consists of two-section cascaded SIR and a pair of parallel-coupled lines. Using λ/4frequency-selected open stubs, the complete π-type structure is restructured into a basic π-type structure with three microstrip lines. The filtering responses of the second passband are controlled only by the basic π-type structure. The filtering responses of the first and third passbands are influenced by the complete π-type structure. By embedding coupled-lines into the two-section cascaded SIR, four extra transmission zeros (TZs) are obtained. For validation, a tri-band BPF with 3-dB fractional bandwidths of 14.3%, 9.4%, and 6.6%, respectively, operating at 1.77 GHz (GSM), 2.37 GHz (WLAN), and 3.43 GHz (WiMAX) is simulated, fabricated, and measured. The measured insertion losses are less than 1.5 dB and return losses are better than 24.5 dB within three passbands. In total, seven TZs are generated and the maximum roll-off rate of three passbands is up to 173 dB/GHz. The good agreement between simulations and measurements verifies the proposed design.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A high selectivity tri‐band BPF using π‐type structure loaded with λ/4 open stub and hybrid SIR

Zhu

Guan

Zheng

et al. 2022

“…Compared to the waveguide type, parallel-coupled microstrip line type bandpass filters have some natural advantages in circuit integration. However, most of the reported microstrip line bandpass filters were designed for low-frequency applications, [9][10][11][12][13][14][15][16][17][18][19][20] and so far, there are only few reports for MMW applications. In MMW frequency range, the circuit structures need to be shielded inside the rectangular cavity to prevent electromagnetic energy leakage and external electromagnetic interference.…”

Section: Introductionmentioning

confidence: 99%

Design of millimeter‐wave bandpass filters based on improved asymmetric parallel‐coupled microstrip line structure for direct detection system of CubeSat radiometer

Chen

Zhang

2021

In this paper, two improved asymmetric parallel-coupled microstrip bandpass filters with center frequencies of 89 GHz and 150 GHz were designed and implemented. The improvement of the circuit structure is based on the rotation of several asymmetric parallel-coupled microstrip line segments, which achieves a great area reduction compared to the conventional structure. The improved bandpass filters were designed and optimized based on the conventional structure. The measured results show that the return loss of the W-band bandpass filter is better than 16 dB and that of the D-band bandpass filter is better than 15 dB within the passband. The insertion loss is less than 2.3 dB and 2.5 dB within the passband for W-band and D-band bandpass filters, respectively. These results verify the feasibility of the improved asymmetric parallel-coupled microstrip line bandpass filter as a broadband pre-filter for the direct detection system of a CubeSat radiometer.

“…Bandpass filters (BPFs) with good performance play an important role in modern wireless communication systems. A plurality of BPFs with low insertion loss, good return loss and broad stopband have been reported 1–7 . One of the shortcomings of these conventional BPFs is that unwanted energy within stopband will be reflected at the input port, which may cause performance degradation of the adjacent components such as high gain amplifiers and mixers.…”

Section: Introductionmentioning

confidence: 99%

An X‐band centrosymmetric microstrip bandpass filter with reflectionless range over 3.9–18.6 GHz and stopband up to 40 GHz

Zhang

Liu

2021

In this letter, the design of a centrosymmetric absorptive bandpass filter (ABPF) with ultra‐wide reflectionless band at both input and output port and wide stopband is reported. It is based on a balanced‐circuit structure, consisting of a pair of 3‐dB couplers and two channels of conventional reflective bandpass filters (BPFs). The bandwidth of the 3‐dB couplers is maximized, which covers from C‐band up to beyond Ku‐band, to extend the reflectionless band of the ABPF. It is realized by introducing a cross‐fingered defected ground structure (DGS) into the classical coupled‐line coupler to strongly enhance the coupling effect while maintaining a compact size. To suppress the harmonics outside the passband, two C‐shaped DGSs are employed at the input and output ends of the coupled‐line‐based BPF which introduces extra transmission zeros in the stopband. A prototype of the proposed ABPF is fabricated and tested. Measured input/output return loss are better than 10 dB over 3.94–18.63 GHz, which is commonly viewed as the reflectionless band. Moreover, the upper stopband is extended up to 40 GHz with suppression higher than 23 dB. The presented ABPF features advantages in convenient integration, dual‐port ultra‐wide reflectionless band and broad stopband.