High figure-of-merit compact phase shifters based on liquid crystal material for 1–10 GHz applications

International Journal of Antennas and Propagation

2017

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A wave interference filtering section that consists of three stubs of different lengths, each with an individual stopband of its own central frequency, is reported here for the design of band-stop filters (BSFs) with ultra-wide and sharp stopbands as well as large attenuation characteristics. The superposition of the individual stopbands provides the coverage over an ultra-wide frequency range. Equations and guidelines are presented for the application of a new wave interference technique to adjust the rejection level and width of its stopband. Based on that, an electrically tunable ultra-wide stopband BSF using a liquid crystal (LC) material for ultra-wideband (UWB) applications is designed. Careful treatment of the bent stubs, including impedance matching of the main microstrip line and bent stubs together with that of the SMA connectors and impedance adaptors, was carried out for the compactness and minimum insertion and reflection losses. The experimental results of the fabricated device agree very well with that of the simulation. The centre rejection frequency as measured can be tuned between 4.434 and 4.814 GHz when a biased voltage of 0–20 Vrms is used. The 3 dB and 25 dB stopband bandwidths were 4.86 GHz and 2.51 GHz, respectively, which are larger than that of other recently reported LC based tunable BSFs.

Section: Design Of the Liquid Crystal Based Band-stop Filtermentioning

confidence: 99%

Compact Liquid Crystal Based Tunable Band-Stop Filter with an Ultra-Wide Stopband by Using Wave Interference Technique

Cai

International Journal of Antennas and Propagation

2017

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“…The ground plane is etched to insert the SMA contact and for ease of fabrication. Due to the liquid-like state of the LC, the SMA contact doesn't touch the LC layer directly, hence the impedance adaptors at both ends with width W 3 shown in Figure 1 are designed to eliminate the impedance mismatch caused by the change in substrate between the air and the LC material [19]. The best impedance match that could be obtained by simulation has a width of W 3 = 2.5mm, and W 1 = 0.245mm.…”

Section: Filter Structure and Design Proceduresmentioning

confidence: 99%

Highly anisotropic LC material with low dielectric loss for the application of tunable notch filters

Cai

Journal of Electromagnetic Waves and Applications

2019

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We present here a compact liquid crystal (LC) based tunable notch filter with a narrow 3 dB bandwidth and a high quality factor. The structure of the proposed filter consists of two embedded resonators in serial, with an impedance adaptor and linear taper at each port. The notch filter combines tunable dielectric material LC with inverted microstrip technology, and was designed, fabricated and characterized to deliver a continuously tuned rejection frequency range from 3.545 GHz to 3.731 GHz, together with a narrow 3 dB bandwidth of ∼ 0.8 GHz and a high quality factor of ∼ 4.6. Such a notch filter is both compact (41 mm × 13 mm) and light weight (18.08 grams, including SMA connectors). It is suitable for working in the S band to suppress WiMAX signals that may cause interference in UWB communication systems. The narrow stopband and high quality factor of the device can be further improved at the expense of a certain extent of tuning efficiency, by using a thicker LC layer, and this is verified in experiment. The measured results of the proposed devices confirm the feasibility of using the current LC technology to manufacture tunable notch filters with a narrow bandwidth and a high quality factor. ARTICLE HISTORY

“…more stringent requirement regarding phase shifting range and resolution, insertion loss, operating bandwidth, linearity, signal-to-noise figure, power consumption, response time, robustness, size, large-scale integration, manufacturing tolerance, and cost, etc. We have explored the use of LC as low-loss tunable media for passive microwave analog components [11,12] and extended our phase shifter design into 60-90 GHz [3]. Different approaches of electrically-tunable device configurations combining with LC were studied for the millimeter-wavelength range, among which coplanar waveguide (CPW) was desirable as compared with other transmission lines [5,13,14] or waveguide structures [15][16][17][18] in terms of overall performance, ease of control, and circuit size.…”

Section: Introductionmentioning

confidence: 99%

Liquid Crystal-Based Enclosed Coplanar Waveguide Phase Shifter for 54–66 GHz Applications

2019

Crystals

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A 0–10 V bias voltage-driven liquid crystal (LC) based 0°–180° continuously variable phase shifter was designed, fabricated, and measured with insertion loss less than −4 dB across the spectrum from 54 GHz to 66 GHz. The phase shifter was structured in an enclosed coplanar waveguide (ECPW) with LC as tunable dielectrics encapsulated by a unified ground plate in the design, which significantly reduced the instability due to floating effects and losses due to stray modes. By competing for spatial volume distribution of the millimeter-wave signal occupying lossy tunable dielectrics versus low-loss but non-tunable dielectrics, the ECPW’s geometry and materials are optimized to minimize the total of dielectric volumetric loss and metallic surface loss for a fixed phase-tuning range. The optimized LC-based ECPW was impedance matched with 1.85 mm connectors by the time domain reflectometry (TDR) method. Device fabrication featured the use of rolled annealed copper foil of lowest surface roughness with nickel-free gold-plating of optimal thickness. Measured from 54 GHz to 66 GHz, the phase shifter prototype presented a tangible improvement in phase shift effectiveness and signal-to-noise ratio, while exhibiting lower insertion and return losses, more ease of control, and high linearity as well as lower-cost fabrication as compared with up-to-date documentations targeting 60 GHz applications.