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This paper introduces a methodology to design a scheme enabling simultaneous near-field focusing and far-field radiation by using multiple lenses. A large-size lens is designed to convert the spherical wave emanating from the feed source to a quasi-plane wave. A small-size lens is located at a parallel plane away from the large-size lens. By imposing proper phase shifts on the small-size lens, it can capture part of the electromagnetic waves from the large-size lens to achieve a focal spot in the near-field region of the small-size lens. The gain of the radiation beam and the intensity of the focal spot can be controlled by either adjusting the area ratio of, or the separation between the large- and small-size lenses. The simulations validate the effectiveness of the proposed methodology. The proposed scheme offers an alternative solution to achieve simultaneous near-field focusing and far-field radiation.

This paper proposes a solution that allows reducing the obstruction from the mobile phone frame to electromagnetic waves in two bands of the mm-wave spectrum. This response is obtained by etching longitudinal corrugations of two different lengths in the metal frame. The corrugations are inspired on the hard surfaces principle, which supports the propagation of electromagnetic waves on metal. The proposed structure is matched to a 50-Ohm source in the following bands: 25.4-27.7 GHz, 28.7-29.9 GHz, and 36.4-40.3 GHz. The realized gain of the mm-wave array with the corrugated frame is higher than the one of the array in free space in the majority of the operating bandwidth. The proposed solution can increase the gain of the array with a normal frame up to 10 dB.

In principle, both scalar and tensor holographic artificial impedance surfaces (HAISs) can generate circularly-polarized waves. It is found, however, the previously-reported works on circularly-polarized holographic antennas are based on tensor impedance surfaces. This paper studies the generations of circularly-polarized waves by using scalar and tensor HAISs, and compare their performance in terms of design complexity, impedance bandwidth, 3dB axial ratio (AR) bandwidth, realized gains, etc. The mechanisms of producing circularly-polarized waves using scalar and tensor HAISs are first formulated and presented. Two right-hand circularly-polarized holographic antennas are then implemented with the scalar and tensor HAISs, respectively, and simulated. The simulations conclude that the tensor HAIS indeed outperforms the scalar HAIS in generation of circularly-polarized waves. In particular, the peak gain of the tensor HAIS is much higher than that of the scalar HAIS. The conclusions obtained in this paper give a clear answer on designing circularly-polarized HAISs with good performance.

In this paper, we demonstrate how a deep neural network (DNN) can be used to compensate for nonlinearities and distortion effects introduced by the latest technology of 5G transmitters. A linearization approach based on neural networks can successfully cope with the challenges introduced not only by the high nonlinearity, wide bandwidth, and high frequency but also with challenges due to inter-PA crosstalk and load modulation. The device-under-test used in this experiment, is a state-of-the-art 5G 4x4 active phased array (APA) operating in very highly nonlinear regions at 28 GHz with a 100 MHz wide 3GPPbasestationsignalandwithOTAmeasuredsignalsusedfor training. Using the proposed DNN based linearization technique, an improvement of 11 % in error vector magnitude (EVM) and 10 dB adjacent channel leakage ratio (ACLR) are achieved which demonstrates the promising potential of this technique for emerging broadband communication systems such as 5G/6G and low earth orbit (LEO) satellite networks

With the utilization of massive multiple-inputmultiple-output (MIMO) and millimeter-wave (mmWave) technologiesin 5G communications, over-the-air (OTA) testing for 5Gantenna systems has become a strong need because conductedtesting is no longer applicable. New OTA testing metrics arerequired to evaluate new performance of 5G antenna systems.This paper investigates whether the recently proposed metric,e.g. beam probability is suitable to evaluate channel emulationaccuracy for adaptive antenna systems in multi-probe anechoicchamber (MPAC) OTA setups. Well-known 2D spatial channelmodels are selected as examples in simulation results to discussthe relationship between device under test (DUT) size andnumber of OTA antennas for beam probability metric.

Speed is the major killer in traffic. The typical approach to enforce speed limits is by having the police monitor drivers and issue tickets when they are speeding. In this paper, we introduce a new platform where speeding is reduced by nudging. The three major approaches are to warn drivers if they are speeding, praise the drivers if they are driving within the speed limit, and grade each trip. The latter is used to rank drivers, e.g., drivers within a company are ranked according to their trip scores. We present the DriveLaB smartphone app that provides real-time feedback to the drivers. All computations are done at the server-side and we show how to compute real-time feedback and store trip data. In addition, we report on two field trials in the Copenhagen and Aalborg Areas where the platform is tested in collaboration with a major Danish insurance company.

In this paper, the feasibility of an antenna isolation technique based on null-steer beamforming, polarization diversity and spatial diversity is investigated. The proposed system consists of six patch antennas which are fed by a feeding network to obtain a null-steer beamformer. To achieve spatial diversity, antenna elements are located on two layers, facing in a different direction. Moreover, the antenna elements in two layers use different polarization. The measured results of the antenna system present a high TX-RX isolation in the order of 70 dB which shows the feasibility of such a system for Full-duplex transmission.

In this paper, a Full-duplex (FD) antenna system is presented with a high isolation between the TX and RX antennas. The isolation method is based on utilizing balanced antennas to localize the current on the ground plane and single mode excitation of the ground plane with capacitive coupling elements. The simulation results show a promising isolation level of 75 dB. User impact investigation on the antenna isolation, antenna matching and efficiency is presented. The isolation level varies from 60 dB to 30 dB in the worst user scenarios. The proposed antenna system can be used in a MISO/SIMO FD system.

The broadcast television spectrum around 600 MHz has been freed in the united states and will be put for auction to wireless carriers in 2015. The newest generation of mobile communication standards will be deployed on these newly available bands, to provide mobile device users with an enhanced connectivity. This paper proposes a novel antenna design that overcomes the bandwidth challenge of such low operating frequencies on handsets.

Number of frequency bands that have to be covered by smart phones, are ever increasing. This broadband coverage can be obtained either by using a low-Q antenna or a high-Q tunable antenna. This study investigates high-Q antennas performance when placed in proximity of the user. This study is carried out through measurements, using Cellular Telecommunications Industry Association (CTIA) specified head and hand phantoms. The results of the high-Q antenna are, at low as well as high frequencies, compared to the results for a low-Q antenna. The results show that detuning of low-Q antennas is more severe compared to high-Q antennas. However, the drop in efficiency is comparable for both antennas in proximity of the user. Number of frequency bands that have to be covered by smart phones, are ever increasing. This broadband coverage can be obtained either by using a low-Q antenna or a high-Q tunable antenna. This study investigates high-Q antennas performance when placed in proximity of the user. This study is carried out through measurements, using Cellular Telecommunications Industry Association (CTIA) specified head and hand phantoms. The results of the high-Q antenna are, at low as well as high frequencies, compared to the results for a low-Q antenna. The results show that detuning of low-Q antennas is more severe compared to high-Q antennas. However, the drop in efficiency is comparable for both antennas in proximity of the user.

MIMO OTA testing methodologies are being intensively investigated by CTIA and 3GPP, where a multi-probe anechoic chamber based solution is an important candidate for future standardized testing. In this paper, the probes located on an OTA ring are used to reproduce the channel spatial information. This paper investigates the extent to which we can emulate the channel spatial characteristics inside the test zone where the device under test is located. The focus is on performance deterioration introduced by system non-idealities on spatial correlation emulation in practical MIMO OTA test systems.

The Huygens' box (HB) method of replacing an arbitrary module inside an electronic apparatus with a set of current sources on a closed surface is discussed. A numerical study is performed, with a typical printed circuit board (PCB) representing the module placed inside a tight metallic enclosure. It is observed that the accuracy of the HB method is generally good except at a few resonant frequencies. Even previously proposed correction to the method that consists of including the main features of the module inside HB is not found to be very effective. The traces on the PCB and especially the parallel plate resonator formed by the ground plane of the PCB and the enclosure are identified as causing the resonances. We estimate that it is most likely the narrowband character of the resonances that considerably increases the sensitivity of the HB method toward small differences in the structure. The Huygens' box (HB) method of replacing an arbitrary module inside an electronic apparatus with a set of current sources on a closed surface is discussed. A numerical study is performed, with a typical printed circuit board (PCB) representing the module placed inside a tight metallic enclosure. It is observed that the accuracy of the HB method is generally good except at a few resonant frequencies. Even previously proposed correction to the method that consists of including the main features of the module inside HB is not found to be very effective. The traces on the PCB and especially the parallel plate resonator formed by the ground plane of the PCB and the enclosure are identified as causing the resonances. We estimate that it is most likely the narrowband character of the resonances that considerably increases the sensitivity of the HB method toward small differences in the structure.

The trend in wireless communication is to provide high-speed services utilizing MIMO antenna systems. Moreover, cognitive radio (CR) technology targets to exploit the so-called TV white space (TVWS) utilizing tunable antennas operating over vacant TV bands. The joint requirements for cognition and spatial multiplexing expressed by sufficient antenna matching and decoupling bandwidth, frequency agility over the TVWS as well as minimum occupying space and complexity impose significant challenges to antenna engineers. The paper discusses the major design considerations for compact TVWS terminals and presents a promising approach that empowers the TVWS device with CR-MIMO capabilities under modern smartphone size constraints. The idea is to aggregate a pair of antennas per communication port for a) providing attractive bandwidth properties across the desired TV bands and b) isolating the communication ports within a local interference cancellation setup.

This paper investigates the problem of spectrally efficient operation of a multi-user uplink cognitive radio system in the presence of a single primary link. The secondary system applies opportunistic interference cancelation (OIC) and decode the primary signal when such an opportunity is created. We derive the achievable rate in the secondary system when OIC is used. This scheme has a practical significance, since it enables rate adaptation without requiring any action from the primary system. The approximated formulas and tight lower and upper bounds for the ergodic sum-rate capacity of the secondary network are found. Next, the power allocation is investigated in the secondary system for maximizing the sumrate under an interference constraint at the primary system and it is shown that the optimal solution leads to a opportunistic user selection strategy. We propose a simple user selection strategy combined with OIC which achieves the optimal capacity given an interference constraint at the primary system. Finally, the analytical results are confirmed by simulations, indicating the fact that the low-complexity, spectral-efficient, flexible, and high-performing cognitive radio can be designed based on the proposed scheme.

In this paper, a novel paradigm is proposed to overcome the limitations posed by conventional small antenna design, exploiting the high isolation potential of narrow-band antenna systems. Several planar inverted-F antennas (PIFAs) operating in different Universal Mobile Telecommunications System (UMTS) bands are investigated, showing also the influence of different hand phantoms in average use trough Finite-Difference TimeDomain (FDTD) simulations. It is confirmed that the way a mobile phone is held is very important in determining the amount of absorption loss, detuning and antenna isolation. Narrow-band antennas are found to be more robust against mutual coupling, having therefore a better isolation.

This paper deals with the challenges related toevaluating the performance of multiple, small terminal antennaswithin a natural MIMO environment. The focus is on theantenna measurement accuracy. First a method is presented formeasuring small phone mock-ups, with the use of optical fibers.The problem using coaxial cable is explained and a solutionsuitable for long distance channel sounding is presented. A largescale measurement campaign is then described. Special attentionis paid to bring the measurement setup as close as possible to arealistic LTE network of the future, with attention to base stationlocation, number of base station antennas, antenna prototypesdesign, user interaction, etc.

Within the field of high frequency ultrasound there has been a call for a new technology for fabrication of devices working at higher frequencies and suitable for production in large numbers at a low cost. The technique of screen-printed PZT thick film (TF) has been widely studied as a means to produce miniaturised, integrated devices at a low cost. Nevertheless, the technology has not yet taken the leap from the academic to the industrial world. Since essential properties favoured in high frequency applications are inherent features of the PZT thick film, it is a natural development in high frequency ultrasound to adopt this technology. However, the process of screen printing PZT thick films involves potential problems of thermal matching and chemical compatibility at the processing temperatures between the functional film, the substrate and the electrodes. We present InSensor TF2100 as a PZT TF using the relative permittivity as a quality parameter verifying the performance of this material. The results are compared with the density of the film indicating that the reduction of the properties in the PZT TF is due to porosity. The comparison indicates good performance of the thick film and good compatibility between the PZT TF, the electrode and substrate material

The SLC damping rings function to provide low emittance, short bunches for injection into the linac. As the beam intensity in the rings was raised, as part of the SLC luminosity improvement program, we observed a threshold above which beam jitter would occur in the linac. Frequent machine trios, caused by beam loss on some bunches, were associated with the jitter. These erratic "flier" pulses were traced to extraction phase errors from the damping rings. This paper covers the diagnosis of this condition and the observations of the transient bunch length instability phenomena. The evidence of this turbulent (microwave) bunch length instability is seen in both time domain and in frequency domain measurements. The instability has been dubbed the "sawtooth" because of the characteristic time dependent nature of the phase and bunch length signals. It is present in both the SLC electron and positron damping rings at about the same threshold of 3/spl times/10/sup 10/ particles per bunch. There is also some evidence in numerical simulations of transient bunch lengthening phenomena, which is discussed later in this paper. >

An RF feedback around the cavities and klystron has been added to the SLC Damping Rings to provide stability under changing beam loading conditions. The beam loading changes in the cavity as a result of programming the RF voltage during the beam store time. The RF voltage is lowered to control the onset of bunch length instabilities, but without RF feedback the beam becomes unstable in the Robinson zero frequency mode. The steady state analysis of the beam loading with and without feedback is presented together with a description of the hardware implementation. Operational experience with the system during SLC running is described. >

The hybrid pixel detector has recently been introduced in digital radiography. A Monte Carlo simulation was performed with the purpose of comparing the photon counting and energy integration registration strategies, using the detective quantum efficiency DQE. The results were compared with the input screen of an image intensifier. A cascaded model of the hybrid pixel detector is outlined.

At the CERN Low Energy Antiproton Ring (LEAR), high-density beams are obtained with electron and stochastic cooling. The authors have tried to determine the characteristics of the beam and its environment in a regime where the cooling force is present and where the impedance is space-charge-dominated. Methods used include beam-transfer function (BTF) measurements and Schottky scans. It is shown that, when the beam is strongly cooled, Landau damping is lost. A powerful active feedback is necessary to recover beam stability and increase the possible circulating current. It is noted that transverse BTFs are a convenient tool for adjusting and monitoring the action of the damper. By a combination of longitudinal BTF and Schottky measurements, the momentum distribution of very cold beams can be determined despite the strong signal distortion, and the beam coupling impedance can be estimated. >

The new, low-energy antiproton physics facility at CERN has been successfully commissioned and has been delivering decelerated antiprotons at 100 MeV/c since July 2000. The AD consists of one ring where the 3.5 GeV/c antiprotons produced from a production target are injected, rf manipulated, stochastically cooled, decelerated (with further stages involving additional stochastic and electron cooling and rf manipulation) and extracted at 100 MeV/c. While proton test beams of sufficient intensity could be used for certain procedures in AD commissioning, this was not possible for setting-up and routine operation. Hence, special diagnostics systems had to be developed to obtain the beam and accelerator characteristics using the weak antiproton beams of a few 10/sup 7/ particles at all momenta from 3.5 GeV/c down to 100 MeV/c. These include systems for position measurement, intensity, beam size measurements using transverse aperture limiters and scintillators and Schottky-based tools. This paper gives an overall view of these systems and their usage.