Wideband , Multiband , Tunable , and Smart Antenna Systems for Mobile and UWB Wireless Applications 2014

With the advent of high data rate 3G and 4G wireless communication systems and the app-based use paradigm, wireless connectivity through multiple air interfaces has become a common requirement in the RF architecture of mobile communication devices. Modern wireless handsets frequently incorporate three or more antennas to enable cellular voice and data,Wi-Fi, andGPS connectivity, acrossmultiple bands.Multiple antenna systems are frequently designed to implement diversity or spatial multiplexing schemes, as in the case of WCDMA and LTE, to increase resiliency and capacity of wireless links and to operate multiple voice/data links simultaneously. Concurrently, ultrawideband (UWB) systems used in short range communications, remote sensing, and through-the-wall radar imaging have introduced a new paradigm in the antenna design where the mitigation of pulse distortion is of the essence, thus requiring a shift in antenna design approach and the introduction of novel radiating systems. This special issue is intended to reflect current R&D trends and novel approaches in the analysis and synthesis of antenna systems and associated RF front-ends for next generation mobile communication devices, applicable to various device form factors such as smartphones, tablets, laptops and wearable computers as well as for UWB communication systems and radars. A particular emphasis has been paid to the analysis anddesign of broadband,multiband, and reconfigurable antennas for wireless and UWB applications, as well as to the identification of special materials and integration techniques with the host platform. Important efforts have been devoted to the characterization of the radio channel as well as to the most innovative near-field-farfield transformation techniques employed to determine the radiation properties of the antennas employed in the modern wireless communication systems. The special issue is composed of 19 contributions that can be divided into the following 9 clusters.


Introduction
With the advent of high data rate 3G and 4G wireless communication systems and the app-based use paradigm, wireless connectivity through multiple air interfaces has become a common requirement in the RF architecture of new generation mobile communication devices.The modern wireless handset easily incorporates three or more antennas to enable cellular, Wi-Fi, and GPS connectivity, frequently over multiple bands.Multiple antenna systems are frequently designed to implement diversity or spatial multiplexing schemes, as in the case of WCDMA and LTE, to increase the resiliency and capacity of wireless links, and even to operate multiple voice/data links simultaneously.Concurrently, ultrawideband (UWB) systems used in short range communications, remote sensing, and through-the-wall radar imaging have introduced a new paradigm in antenna design where the mitigation of pulse distortion is of the essence, thus requiring a shift in antenna design approach and the introduction of novel radiating systems.
This special issue is intended to reflect current R&D trends and novel approaches in the analysis and synthesis of antenna systems for the new generation of mobile communication devices, such as smartphones, tablets, and laptop computers as well as for UWB communication systems and radars.A particular emphasis has been paid to the analysis and design of broadband, multiband, and reconfigurable antennas for wireless and UWB applications, as well as to the identification of integration techniques with the host platform.Important efforts have been devoted to the characterization of the radio channel for MIMO systems.
The special issue is composed of 18 contributions that can be divided into the following 8 clusters.

Contributions to Reconfigurable and Multiband Antenna Technology
In "Recent developments in reconfigurable and multiband antenna technology" by N. Haider et al., the authors present a comparative analysis of various reconfigurable and multiband antenna concepts.In particular, three basic approaches, tunable/switchable antenna integration with radiofrequency switching devices, wideband or multiband antenna integration with tunable filters, and array architectures with the same aperture utilized for different operational modes, have been analyzed in detail showing inherent benefits and challenges.
In "A reconfigurable triple-Notch-Band antenna integrated with defected microstrip structure band-stop filter for ultrawideband cognitive radio applications" by Y. Li et al., the authors describe a reconfigurable UWB monopole antenna for cognitive radio applications.Three narrow band-notched frequencies are obtained using a defected microstrip structure (DMS), a stop band filter (BSF) embedded in the microstrip feed line, and an inverted -shaped slot etched in the rectangular radiant patch, respectively.Reconfigurable International Journal of Antennas and Propagation characteristics of the proposed cognitive radio antenna are achieved by means of four ideal switches integrated on the DMS-BSF and the inverted -shaped slot.
In "Planar ultrawideband antenna with photonically controlled notched bands" by D. Draskovic et al., the authors describe a planar microstrip-fed UWB printed circular monopole antenna with optically controlled notched bands.The proposed antenna is composed of a circular UWB patch, with an etched T-shaped slot controlled by an integrated optical switch.The slot modifies the frequency response of the antenna suppressing the 3.5-5 GHz band when the switch is in an open state.The optical switch is controlled by a lowpower laser diode rendering the antenna remotely controlled by means of an optical fiber.
In "Compact, frequency reconfigurable, printed monopole antenna" by R. Gonc ¸alves et al., the authors propose, a compact reconfigurable printed monopole antenna, useful to operate in the UMTS and WLAN bands.To this purpose a chip inductor and PIN diode are employed to modify the electrical length of the monopole making the antenna able to operate in the mentioned frequency bands.

Contributions to Broad-and Multibanding Techniques
In "Analysis and design of a novel compact multiband printed monopole antenna" by J. Wang and X. He, the authors present a compact T-shaped multiband printed monopole antenna integrating some U-shaped band-notch structures.The proposed antenna operates at 2.25-2.7 GHz, 3.25-3.6GHz, 4.95-6.2GHz, and 7-8 GHz, covering the operation bands of Bluetooth, WiMAX, and WLAN and the downlink of the Xband satellite communication systems.
In "Dual-band integrated antennas for DVB-T receivers" by A. D'alessandro et al., the authors present an overview on compact Planar Inverted-F Antennas (PIFAs) that are suitable for monitor-equipped devices.High efficiency PIFAs with a percentage bandwidth greater than 59% (470-862 MHz DVB-T band) are shown.Finally, to show the extreme flexibility of the previous two configurations, a novel dualband L-shape PIFA has been proposed.The L-shape PIFA prototype is obtained by properly cutting and folding a single metal sheet, thus resulting in a relatively low-cost and mechanically robust antenna configuration.
In "Planar printed shorted monopole antenna with coupled feed for LTE/WWAN mobile handset applications" by D. Kang and Y. Sung, the authors present a shorted monopole antenna with coupled feed for LTE/WWAN mobile handset applications.The basic resonance of the shorted monopole combines with the resonance caused by the interaction between the coupling strip and the feeding pad to cover the LTE700, GSM850, and GSM900 bands.Both the feeding pad and the coupling strip operate with the shorting strip as a loop antenna.The resonance of the loop antenna and the harmonics of the shorted monopole combine to cover the GSM1800, GSM1900, UMTS, and LTE2300 bands.A stable and omnidirectional radiation pattern with reasonable gain has been observed over the operating bandwidth.
In "Parasitic-element-loaded UWB antenna with bandstop function for mobile handset wireless USB" by Y. Lim et al., the authors present an antenna loaded by parasitic elements for the wireless USB of mobile handsets useful for UWB service in which a band-stop function of 5.725-5.825GHz WLAN band is required.To this end, two kinds of parasitic elements are incorporated into a rectangular radiator to obtain enhanced impedance bandwidth and bandstop function.In this way, bandwidths of 3.15-4.75GHz and of 7.2-10.2GHz are achieved, while the frequency band 5.725-5.825GHz is suppressed.

Contributions to Antennas for UWB Applications
In "A compact UWB antenna with a quarter-wavelength Strip in a Rectangular slot for 5.5 GHz band notch" by P. Moeikham et al., the authors present a monopole UWB antenna integrating a notch filter to reduce the electromagnetic interferences (EMIs) with WLAN/WiMAX communication systems operating in the frequency band located around 5.5 GHz.Consisting in a rectangular slot including a quarter-wavelength strip integrated on the lower inner edge of the UWB radiating patch, the filter proposed by the authors is capable of reducing the energy emission in the frequency range between 5.1 and 5.75 GHz resulting in lower EMIs with sensible electronic equipment working in this frequency band.
In "A modified vivaldi antenna for improved angulardependent fidelity property" by Z. Zeng et al., the authors present a modified Vivaldi antenna optimized to radiate impulsive signals.To this end, a spatial filter consisting of two suitable dielectric slabs parallel to the antenna substrate is introduced.As a result, the fidelity factor indicating the quality of the radiated field is significantly improved.In fact, the experimental measurements show that the ranges with the fidelity factor better than the value of 0.9 are improved by 95% in H-plane and by 14% in E-plane, respectively, with respect to a conventional Vivaldi antenna.
In "High gain compact strip and slot UWB sinuous antennas" by E. Agastra et al., the authors analyze three groundbacked compact strip and slot sinuous antennas.The proposed configuration allows for a single lobe, polarizationversatile, high efficiency, and ultrawideband antenna not needing a cumbersome lossy back cavity typical of conventional single-lobe sinuous antennas.

Contributions to Special Materials, and Fabrication Techniques
In "Innovative radiating systems for train localization in interference conditions" by C. Vegni et al., the authors, firstly, propose an innovative radiating systems based on the metamaterial technology for global navigation satellite system (GNSS) applications in radio frequency interference conditions.Secondly, fixed radiation pattern antenna (FRPA), and controlled radiation pattern antenna (CRPA) phased array configurations of miniaturized patch antennas are studied.