Tunable compact microstrip dual‐band bandpass filter with tapered resonators

Adjustable compact dual‐band microstrip bandpass filter using T‐shaped resonators

Abstract In this paper, a microstrip dual-band bandpass filter (DBBPF) based on an octagonal loop resonator (OLR), tapered resonators and open bended stubs (OBSs) is designed and analysed. The proposed structure produces two passbands with the centre frequencies of 3.65 and 5.67 GHz. The marked advantages of the proposed filter are as follows: Two centre frequencies can be individually tuned. The bandwidth of the upper passband can also be controlled. Furthermore, the DBBPF benefits from an ultra-wide upper stopband from 5.9 up to 21 GHz with an attenuation level of higher than 20 dB and a small size of 0.21 λg × 0.26 λg, where λg is the guided wavelength at 3.65 GHz. The designed filter is horizontally and vertically symmetrical leading to a reciprocal S matrix. Other remarkable specifications of the proposed filter are the insertion loss < 0.62 dB, the return loss > 20.2 dB and sharp response. To provide an analytical description, the LC equivalent circuits of initial and main resonators are presented. Acceptable similarity between simulated and measured results verifies the design process.

Compact Ultra-Wide Upper Stopband Microstrip Dual-Band BPF Using Tapered and Octagonal Loop Resonators

Fractal geometries are found attractive to designers seeking for compact size microwave circuits and antennas. In this paper, Peano fractal based open-loop resonators are adopted to design dual-band microstrip band-stop filters (PSFs). The suggested filter structure is essentially based on that of the conventional open-loop rectangular microstrip resonators. The resonators of the proposed PSF structure are made in the form of Peano fractal geometry with different iteration levels. Many filters have been modeled, and their performances have been evaluated using a commercially available full-wave electromagnetic simulator. Each of the modeled filter structures contains two pairs of open loop fractal based resonators with different iteration levels. The lower frequency band-stop performance is attributed to the resonators with higher iteration level while the higher frequency band-stop performance is due to the resonators with lower iteration level. Simulation results for the proposed microstrip filters have confirmed the validity to realize compact dual-band narrow-stopband microstrip filters. A comparative study implies that higher size reduction of the realized filter has taken place as the iteration level of the fractal microstrip open-loop resonators becomes higher. The results presented show that the fractal-based resonators can be used to construct compact narrow-stopband filters suitable for a wide variety of the recently available communication applications.

A Compact Dual-band Bandstop Filter Based on Fractal Microstrip Resonators

In this paper, Minkowski fractal based open-loop resonators are adopted to design triple band microstrip bandstop filters (BSFs). The suggested filter structures are primarily based on that of the conventional open-loop rectangular microstrip resonators. The resonators of the proposed BSF structure are made in the form of Minkowski fractal geometry with different iteration levels. Many filter structures have been modeled, and their performances have been evaluated using the commercially available EM simulator, Sonnet. Each of the modeled filter structures contains two pairs of open loop fractal based resonators with different iteration levels. The lower frequency bandstop performance is attributed to the resonators with higher iteration level while the higher frequency bandstop performance is due to the resonators with lower iteration levels. Simulation results for the proposed microstrip filters have confirmed the validity to realize compact multiband narrow-stopband microstrip filters. Measured results of a fabricated filter prototype are found to be in reasonable agreement with those predicted by numerical computation. The results presented show that the proposed fractal based resonators can be used to construct compact multiband filters with narrow stopbands.

A compact triple band BSF design based on Minkowski fractal geometry

In this paper, a fractal-based complementary split-ring resonator (CSRR) has been introduced as a defected ground structure (DGS) in the ground plane of a dual-mode microstrip bandpass filter to produce a new compact filter with dual-band response. The conventional double square ring resonator structure is modified such that its inner ring is made with a fractal shape instead of a square. Measured and simulation results show that the resulting filter offers a dual passband response; the higher passband is attributed to the dual-mode microstrip ring structure, whereas the lower passband is as a result of the embedded CSRR DGS structure. In addition, the results show that the position of the lower passband could be varied, to a certain extent, without affecting the position of the higher passband by applying higher fractal iteration levels to the inner split ring. These features, together with the compact size the proposed filter offers, make it suitable for use in a wide variety of dual-band communication applications. Measured results, carried out on filter prototypes, have been found in agreement with those theoretically predicted.

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A miniature fractal-based dual-mode dual-band microstrip bandpass filter design

Four square ring resonators together with an L-shaped uniform open tuning stub is the base of an ultra-wide bandpass filter. Based on the bandpass-coupled edge, a small gap was created in the feed lines of the proposed bandpass filter to obtain a second lower band. This study introduces a dual-band bandpass filter. The main advantage of this bandpass filter is its capability to reconfigure bandwidth and tune the center frequency of a dual-band bandpass filter function. The microstrip bandpass filter is reconfigured into a dual band when varactor diodes are fixed on the head of each uniform stub. The roll-off is characterized by sharp edges of 81.325 and 80.165 GHz/dB, which provided this filter with high selectivity in the transmission band, a wide stopband of more than 2 GHz in both sides, and a rejection band of up to 32 dB. Results show better performance of S21, which fluctuated from 4 to 1.5 dB within the transmission band from 8.327 to 13.942 GHz. All the reported filters were modeled, and t...

Reconfigurable Bandwidth and Tunable Dual-Band Bandpass Filter Design for Ultra-Wideband (UWB) Applications

In this manuscript, serial-shunt of square ring resonators with step-impedance open circuited stub resonators to produce a new on-off switchable bandpass to bandstop response in the same ultra-wideband microstrip filter structure is proposed. The closed ring of series-shunt square ring resonators with a combine stubs are introduced to excite the bandpass response while bandstop characteristic excited when gaps are embedded in the corners of the square ring resonators. The main advantage of this microstrip filter is its capability to switch from bandpass-to-bandstop operation using open-short gap, respectively. A microwave simulator is utilized to show the switchable case by replacing Skyworks radio frequency diodes (RF-PIN) instead of those gaps. The entire filter models have been simulated using the computer simulation technology (CST) Microwave Studio. The computed results for the proposed filters were compared with the measured results of the both prototype structures (bandpass- and bandstop-filter). The codes also showed good agreement between them. Other advantages include being small in size, and low in effective cost.

Switchable square ring bandpass to bandstop filter for ultra-wideband applications

Four square ring resonators together with an L-shaped uniform open tuning stub is the base of an ultra-wide bandpass filter (BPF). Based on the bandpass-coupled edge, a small gap was created in the feed lines of the proposed BPF to obtain a second lower band. This study introduces a dual-band BPF. The main advantage of this BPF is its capability to reconfigure bandwidth and tune the center frequency of a dual-band BPF function. The microstrip BPF is reconfigured into a dual band when varactor diodes are fixed on the head of each uniform stub. The roll-off is characterized by sharp edges of 81.325 and 80.165 GHz/dB, which provided this filter with high selectivity in the transmission band, a wide stopband of more than 2 GHz in both sides, and a rejection band of up to 32 dB. Results show better performance of S21, which fluctuated from 4 dB to 1.5 dB within the transmission band from 8.327 GHz to 13.942 GHz. All the reported filters were modeled, and their corresponding responses were assessed by using CST Microwave Studio. Measured and simulated results of the proposed BPF filters were compared, and the results indicate good agreement.

Chandan Chakrabraty

Papers

A miniature fractal-based dual-mode dual-band microstrip bandpass filter design

Reconfigurable Bandwidth and Tunable Dual-Band Bandpass Filter Design for Ultra-Wideband (UWB) Applications

Switchable square ring bandpass to bandstop filter for ultra-wideband applications

Reconfi gurable Bandwidth and Tunable Dual- Band BPF Design for UWB Applications