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- Advancements in Filter Design: Wideband, Dual-Band, and Terahertz Applications
Advancements in Filter Design: Wideband, Dual-Band, and Terahertz Applications
Here’s what you need to know about RF filters today:
A method for designing wideband filtering switches with improved performance and validation through both simulation and practical fabrication.
The development and validation of an adjustable Ka-band bandpass filter using spoof surface plasmon polariton in a groove gap waveguide.
A dual-band filtering differential phase shifter design using a cascaded approach that maintains phase characteristics while splitting the passband, offering controlled responses and consistent dual-phase shifts, with validated results.
A miniaturized terahertz bandpass filter utilizing through-silicon via technology, highlighting its design, simulation methods, and integration potential with 3D IC manufacturing, along with its performance metrics.
A terahertz bandpass multilayer frequency-selective surface (FSS) filter with mechanical tunability and high spectral selectivity, demonstrating superior performance in tunable range and insertion loss compared to existing reconfigurable filters.
A Wideband Filtering Switch: Its Synthesis and Design
This article presents a method for designing a wideband filtering switch using p-i-n diodes incorporated into each resonator. The p-i-n diodes contain parasitic parameters, so an ideal transformer is introduced in each resonator to allow for the proper designation of inductances and capacitances. The synthesis process involves creating an Nth order bandpass filter (BPF) network with N transmission zeros (TZs) based on the rejection specification in the ON state. A new circuit model extraction procedure is then used to extract lumped circuits within the BPF network. To simplify the network topology, two ideal transformers remain at the input-output port after absorbing the ideal transformers between resonators. The lumped circuit model is then converted into a distributed circuit model while maintaining the filtering response over a wide frequency range in the ON state. Additionally, the N TZs of the filtering switch in the OFF state can be strategically positioned to achieve high isolation within the stopband. Two filtering switches with fractional bandwidths (FBWs) of 30% and 50% were fabricated and measured to demonstrate the feasibility of the proposed method. The simulated and measured results show good agreement, validating the effectiveness of the method.
Authors: Kai-Da Xu; et al.
Published in: IEEE Transactions on Microwave Theory and Techniques
Groove Gap Waveguide Bandpass Filter Based on Spoof Surface Plasmon Polariton for Ka-Band Applications
In this article, a spoof surface plasmon polariton (SSPP) is developed in a groove gap waveguide (GGW) to create an adjustable bandpass filter for Ka-band applications. The proposed SSPP structure consists of a single row of corrugated metallic blocks embedded into the groove of the GGW. The lower cut-off frequency of the passband can be adjusted by changing the groove width or pin height, while the upper cut-off frequency of the passband is determined by the period or height of the SSPP unit cell through dispersion and S-parameter analysis. To demonstrate this, a GGW-SSPP bandpass filter is fabricated and measured using the proposed method. The measured bandwidth ranges from 29.8 to 35.8 GHz, which aligns with the simulated results. The proposed GGW-SSPP filter achieves adjustable bandpass characteristics with a low insertion loss of 0.22 dB, thanks to the application of GGW.
Authors: Qinlong Li; et al.
Published in: IEEE Transactions on Microwave Theory and Techniques
Dual-Band Filtering Differential Phase Shifter Using Cascaded Wideband Phase Shifter and Bandstop Network With Two Same Phase Shifts
This letter presents a novel design approach for a dual-band filtering differential phase shifter. The proposed method involves cascading a wideband phase shifter and a bandstop network. By cascading the bandstop network, the phase shift characteristic of the initial wideband filtering differential phase shifter remains unchanged, but its wide passband is divided into two subpassbands. In comparison to traditional dual-band-filter-based topologies, the proposed cascaded approach offers the advantage of independently controlling phase and amplitude responses. Additionally, it can achieve the same phase shifts in two passbands that conventional methods cannot. To validate the approach, a dual-band differential phase shifter with two identical phase shifts of 90° is designed, fabricated, and measured. The simulated and measured results demonstrate good agreement.
Authors: Lei-Lei Qiu; et al.
Published in: IEEE Microwave and Wireless Components Letters
Miniaturized SIW Bandpass Filter Based on TSV Technology for THz Applications
A miniaturized substrate-integrated waveguide bandpass filter, measuring 0.682 × 0.210 mm², is proposed for terahertz (THz) applications using through-silicon via (TSV) technology. The design method of the THz cavity filter, based on rectangular TSV, is introduced and the filtering characteristics are investigated using the finite element method and the mode matching method. To explore the possibility of integration with typical three-dimensional integrated circuit manufacturing processes, the rectangular TSV is replaced with cylindrical structures and the THz cavity filter is fabricated and measured. The cavity filter, utilizing cylindrical TSV, exhibits a bandwidth of 0.051 THz centered at 0.331 THz, an insertion loss of 1.5 dB, and a reflection higher than 15 dB in the passband.
Authors: Fengjuan Wang; et al.
Published in: IEEE Transactions on Terahertz Science and Technology
Frequency-Selective-Surface-Based Mechanically Reconfigurable Terahertz Bandpass Filter
Frequency-tunable filters are in high demand for applications that require high spectral selectivity. In order to achieve this, frequency-selective surfaces (FSSs) have been widely used for spatial filtering. Varactors are commonly used for electronic reconfiguration at microwave frequencies, but they become unavoidably lossy in terahertz applications due to their small cross section, which is necessary to achieve small capacitance values. In this study, we propose a terahertz bandpass multilayer FSS with a finesse of approximately 20 and 80% power transmission. The operating frequency of this filter can be mechanically tuned within a 40% frequency range by adjusting the thickness of an interlayer spacer. The experimentally validated bandwidth is 31%, limited by the measurement apparatus, and the power transmission is above 75%. This filter is not affected by misalignment and can maintain tunability even under oblique angles of incidence. Compared to other reconfigurable filters discussed in the literature, our proposed filter outperforms them in terms of tunable range and insertion loss. This design is one of the first few reconfigurable terahertz filters, and the design methodology can be easily applied to other FSS-based structures.
Authors: Xiaojing Lv; et al.
Published in: IEEE Transactions on Terahertz Science and Technology
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