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Abstract-In this research, a compact printed antenna design operating on ultra-wideband (UWB) and three extra wireless communication bands is proposed. An ellipse-shaped monopole is utilized to realize UWB application (3.1-10.6 GHz). The modified ground employs three folded Capacitive Loaded Line Resonators (CLLRs) to obtain triple relatively lower communication bands, including parts of global System for Mobile Communications (GSM) band at the centre frequency of 1.78 GHz, Wideband Code Division Multiple Access (WCDMA) band at the centre frequency of 2.15 GHz, and Wireless Local Area Networks (WLAN) band at the centre frequency of 2.4 GHz.The CLLRs are designed with quarterwavelength to control the corresponding frequencies independently. Good agreement is achieved between the simulation and measurement to verify our presented design. The basic, dual-, triple-band UWB antennas are also simulated and good results are obtained. Small group delay variations across UWB frequencies are obtained for the presented antenna and reference antennas, with some level of distortion observed.

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A compact semi‐elliptical patch antenna fed by a tapered coplanar waveguide is introduced for super‐wideband (SWB) applications. The simulated and experimental results demonstrate that the antenna possesses the desirable SWB characteristics, achieving a ratio bandwidth of 19.7:1 for VSWR ≤ 2, and exhibits a nearly omni‐directional radiation pattern, while its area is only about 0.15λl × 0.21λl, where λl is the wavelength of the lowest operating frequency. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2061–2063, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22644

In this study, we report the ultrafast excitation and dynamics of the carrier and photocurrent in a 3D typical topological insulator Sb2Te3. We utilize time-resolved optical pump-THz probe spectroscopy to explore the nonequilibrium carrier dynamics of Sb2Te3. The electron system undergoes an ultrafast relaxation and releases through intra-band and inter-band scattering. Additionally, THz emission spectroscopy is employed to investigate the different ultrafast photocurrents in Sb2Te3 through tuning the polarization of excitation pulses and rotating the sample's azimuthal angle. We distinguish the different ultrafast photocurrents driven by the linear photogalvanic effect, circular photogalvanic effect, and thermoelectric effect. Our results potentially enable an all-optical modulation of THz emission without any external bias field, which could play an important role in the development of topological insulator-based high-speed THz optoelectronic and opto-spintronic devices.

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