Set Of Antennas Research Articles

Wideband and Ultra Wideband Radio Propagation in Heavy Multipath Environments

The authors have focused on wideband, including ultra-wideband (UWB, 3.1 to 10.6GHz) radio propagation in various environments, such as a small space-craft and a passenger car, moreover on-body radio propagation measurements have been conducted. Many studies have been reported about indoor propagation for narrowband and wideband. However previous study has not been examined characteristics between 10-MHz and 1-GHz frequencies. In our previous study, UWB and narrowband propagation were measured in a UWB frequency band within closed/semi-closed spaces (e.g. a spacecraft, a passenger car, and a metal desk equipped with a metal partition). While narrowband propagation resulted in considerable spatial variations in propagation gain due to interferences caused by multipath environments, UWB yielded none. This implies that the UWB systems have an advantage over narrowband from a viewpoint of reducing fading margins. Thus, a use of UWB technology within spacecrafts has been proposed with a view to partially replacing wired interface buses with wireless connections. Adoption of wireless technologies within the spacecrafts could contribute to reduction in cable weight (and launching cost as a result), reduction in the cost of manufacture, more flexibility in layout of spacecraft subsystems, and reliable connections at rotary, moving, and sliding joints. Path gains and throughputs were also measured for various antenna settings and polarizations in the small spacecraft. Polarization configurations were found to produce almost no effect on average power delay profiles and substantially small effects on the throughputs. Furthermore, statistical channel models were proposed. Also UWB technologies have been considered for use in wireless body area networks (WBAN) because of their possible low power consumption and anti-multipath capabilities. A series of propagation measurements were carried out between on-body antennas in five different rooms. A new path loss and statistical models considering room volume had been proposed. In this paper, we evaluated propagation characteristics in heavy multipath environments, especially examined the channels at 10-MHz to 1-GHz frequencies.

Design of Near-Field Synthesis Arrays Through Global Optimization

We provide a study of the relation between the near- and far-fields in antenna systems by working with a concrete design problem. The task of finding an antenna array capable of synthesizing a desired near-field distribution is tackled within the general framework of near-field theories recently proposed in literature. We use a genetic algorithm to search for a set of small antennas by working only with far-field data. It is shown, as predicted theoretically, that such information in the far zone are sufficient for reconstructing the entire near-field in the exterior region. We provide a set of examples demonstrating the procedure and validating the proposals. The methodology can be applied to arbitrary antennas and any desired near-field pattern, and we hope it will help automating design methods in the emerging research area of near-field array synthesis.

Multiple Sector ID Capture (MIDC): A Novel Beamforming Technique for 60-GHz Band Multi-Gbps WLAN/PAN Systems

A novel beamforming (BF) technique (MIDC: Multiple sector-ID Capture) is proposed for 60-GHz band WLAN/PAN systems. In contrast to conventional BF techniques adopted in 60-GHz band standards, where quasi-omni (Q-omni) antenna radiation patterns are utilized, MIDC precisely detects the best link even when the Q-omni pattern is imperfect. Furthermore, it can reserve multiple antenna settings corresponding to existing communication links in the initial training by making use of the quasi-optical nature of millimeter-waves. This enables fast beam switching when link blockage occurs. The training is executed in short durations by putting together DoA/DoD-estimation and “beam-combining” techniques. The basic function of MIDC is verified experimentally in a simple multipath propagation environment by using our 60-GHz CMOS transceiver LSIs integrated with planar phased-array antennas. MIDC has been adopted in the MAC/PHY specification of the primary 60-GHz band standards: WiGig (Wireless Gigabit Alliance) and IEEE 802.11ad.

A Compact MultiBand and Dual-Polarized Mobile Base-Station Antenna Using Optimal Array Structure

This paper introduces a multiband base-station antenna to provide multiple communications services. There is growing need for multiband base-station antennas for mobile communications to serve existing 2nd and 3rd generation systems and to provide emerging 4th generation communication service as well as WiFi. For example, cellular, PCS, and especially WCDMA service are currently widely used in Korea, and 4th generation service (WiBro and LTE), introduced in 2011, will have to operate in parallel with existing services. The proposed multiband base-station antenna can provide a single/dual/triple or more multiple services using dual-polarization (±45° linear polarizations) according to the requirements of the service provider. This antenna has a shared aperture, having several array antenna sets for multiple services (Band 1: cellular service in 0.824~0.894 GHz, Band 2: PCS, WCDMA, and WiFi in 1.920~2.170 GHz, Band 3: WiBro and WiMAX in 2.300~2.400 GHz, and Band 4: WiMAX in 5.150~5.850 GHz). This antenna can be helpful for reducing base-station operating expenses and to create a clean urban landscape by minimizing the number of base-station antennas, which are increasing rapidly.

Molecular Structure and Chirality Detection by Fourier Transform Microwave Spectroscopy.

We describe a three-wave mixing experiment using time-separated microwave pulses to detect the enantiomer-specific emission signal of the chiral molecule using Fourier transform microwave (FTMW) spectroscopy. A chirped-pulse FTMW spectrometer operating in the 2-8 GHz frequency range is used to determine the heavy-atom substitution structure of solketal (2,2-dimethyl-1,3-dioxolan-4-yl-methanol) through analysis of the singly substituted (13)C and (18)O isotopologue rotational spectra in natural abundance. A second set of microwave horn antennas is added to the instrument design to permit three-wave mixing experiments where an enantiomer-specific phase of the signal is observed. Using samples of R-, S-, and racemic solketal, the properties of the three-wave mixing experiment are presented, including the measurement of the corresponding nutation curves to demonstrate the optimal pulse sequence.

On Energy Efficiency Maximization in Downlink MIMO Systems Exploiting Multiuser Diversity

Energy efficiency (EE) maximization in MIMO systems has received much attention in next generation wireless communications. Within recent years, a lot of great works have been proposed to improve EE dramatically by power allocation and/or antenna selection. However, the systems significantly exploiting multiuser diversity were not considered in these works. With rapid popularization of wireless communication devices, the increasing density of user equipments (UEs) brings more multiuser diversity gain to be exploited. In this letter, we study the joint EE maximization over power allocation, UE and antenna selection. It will be shown that the maximum EE can be achieved by switching on all the antennas and selecting as many UEs as possible in a time slot with significant multiuser diversity. Simulation results demonstrate that with over tens of UEs, the proposed strategy can achieve less than 2% loss of EE compared to exhaustive antenna set selection.

Joint Power Splitting and Antenna Selection in Energy Harvesting Relay Channels

The simultaneous wireless transfer of information and power with the help of a relay equipped with multiple antennas is considered in this letter, where a “harvest-and-forward” strategy is proposed. In particular, the relay harvests energy and obtains information from the source with the radio-frequent signals by jointly using the antenna selection (AS) and power splitting (PS) techniques, and then the processed information is amplified and forwarded to the destination relying on the harvested energy. This letter jointly optimizes AS and PS to maximize the achievable rate for the proposed strategy. Considering that the joint optimization is according to the non-convex problem, a two-stage procedure is proposed to determine the optimal ratio of received signal power split for energy harvesting, and the optimized antenna set engaged in information forwarding. Simulation results confirm the accuracy of the two-stage procedure, and demonstrate that the proposed “harvest-and-forward” strategy outperforms the conventional amplify-and-forward (AF) relaying and the direct transmission.

The DoF of the 3-User <inline-formula> <tex-math notation="TeX">$(p,p+1)$</tex-math></inline-formula> MIMO Interference Channel

The degrees of freedom (DoF) of the 3-user multiple-input multiple-output (MIMO) interference channel (IC) with full channel state information and constant channel coefficients are investigated when (p,p+1) antennas are deployed at the transmitters and receivers, respectively. The point of departure of this paper is the work of Wang et al., which conjectured but did not prove the DoF for the antenna settings with p>1. Here the achievability of the DoF outer bound is formally proved using linear methods, thereby avoiding the use of the rational dimensions framework. The proposed transmission scheme exploits asymmetric complex signaling together with symbol extensions in time and space interference alignment concepts. While the paper deals with the p=2,3,\ldots,6 cases, providing the specific transmit and receive filters, there are also provided the tools needed for proving the achievability of the optimal DoF for p>6, whose DoF characterization is conjectured.

Space wave propagation at MF band and implications of the radiation pattern of monopoles in the reception of EMF levels

This paper shows the importance of characterizing exactly how the radiation pattern of any antenna in a real environment is, above all when we want to make predictions of field strength with guarantees. In particular we focus on the analysis of monopole antennas at Medium Wave, located in places where other set of antennas and metallic structures are usually located. We get differences in the H-plane up to 3dB for the worst case due to the coupling between structures, and variations of 1.6dB for typical soil conductivities, using MoM techniques.We create the RP-SPACEW tool, based on geometrical optics, to analyze the variation of electric field levels with the distance when considering different reception heights and elevation angles or tilts. Specifically, we have concentrated on areas close to the transmitters. For our scenarios, we obtain variations of electric field values up to 140dB, at 10km from the transmitter, for reception heights between 1.5m and 2km. We also calculate the electric field component due to the surface wave for contrasting the results between the space and surface components, and thus justifying in which situations the space wave can be essential for the signal reception and the exposure to electromagnetic fields.

Further Complexity Reduction Using Rotational Symmetry for EDAS in Spatial Modulation

Euclidean distance antenna selection (EDAS) is an effective transmit antenna selection technique for spatial modulation (SM). However, since an exhaustive search over both the antenna set and the set of conventional constellation points is executed, the computational complexity required to find the optimal solution of EDAS is too high for practical applications. In general, digital modulation constellations have rotational symmetry. In this letter, it is shown that the symmetric constellation points have the same value as EDAS. Hence, only one search is enough for the symmetrical constellation set. Using this proposition, we propose a fast algorithm to find the optimal EDAS solution, which exhibits lower computational complexity than the conventional EDAS solution.

Comparative Investigation of Half-mode SIW Cavity and Microstrip Hybrid Antenna Using Different Patch Shapes

A set of hybrid microstrip patch and semi-circular cavity antennas is introduced. The semi-circular cavity is implemented using Half-mode Substrate Integrated Waveguide (HMSIW) technique. Different shapes of the patch including rectangular, semi-circular and equilateral triangular are excited using proximity effect by the semi-circular SIW cavity at its TM010 mode. The proposed antenna structures have been excited using an inset 50 Ω microstrip line that leads to a facility of planar circuit integration. The inherent limited bandwidth of the conventional microstrip patch antenna and SIW cavity-backed slot antenna is improved about 6 to 10% depending on the type of the patch using the proposed structure. Additionally, the proposed hybrid antenna enhanced the antenna gain by about 1.5 dB in comparison with the half-mode cavity without patch. Meanwhile, the proposed hybrid antennas made on a single-layer substrate has a low fabrication cost using printed circuit board (PCB) process. Three hybrid antennas are numerically and experimentally investigated. A comparative study between the three different structures contains gain, bandwidth, Cross Polarization Level (CPL ) and Front to Back Ratio (FBR ) is presented.

The Spatial Effects of Antenna Configuration in a Large Area Inductively Coupled Plasma System for Flat Panel Displays

Spatial distributions of plasma parameters such as electron density, electron temperature and electric potential were investigated using a commercial simulation software (COMSOLTM) to predict the effects of antenna configuration in a large area inductively coupled plasma (ICP) system for flat panel displays. Nine planar antenna sets were evenly placed above a ceramic window. While the electron density was influenced by both the input current and gas pressure, the electron temperature and electric potential were dominantly affected by the gas pressure.

Toward Online Adaptive Hyperthermia Treatment Planning: Correlation Between Measured and Simulated Specific Absorption Rate Changes Caused by Phase Steering in Patients

Hyperthermia is the clinical application of heat, in which tumor temperatures are raised to 40°C to 45°C. This proven radiation and chemosensitizer significantly improves clinical outcome for several tumor sites. Earlier studies of the use of pre-treatment planning for hyperthermia showed good qualitative but disappointing quantitative reliability. The purpose of this study was to investigate whether hyperthermia treatment planning (HTP) can be used more reliably for online adaptive treatment planning during locoregional hyperthermia treatments. This study included 78 treatment sessions for 15 patients with non-muscle-invasive bladder cancer. At the start of treatments, temperature rise measurements were performed with 3 different antenna settings optimized for each patient, from which the absorbed power (specific absorption rate [SAR]) was derived. HTP was performed based on a computed tomography (CT) scan in treatment position with the bladder catheter in situ. The SAR along the thermocouple tracks was extracted from the simulated SAR distributions. Correlations between measured and simulated (average) SAR values were determined. To evaluate phase steering, correlations between the changes in simulated and measured SAR values averaged over the thermocouple probe were determined for all 3 combinations of antenna settings. For 42% of the individual treatment sessions, the correlation coefficient between measured and simulated SAR profiles was higher than 0.5, whereas 58% showed a weak correlation (R of <0.5). The overall correlation coefficient between measured and simulated average SAR was weak (R=0.31; P<.001). The measured and simulated changes in average SAR after adapting antenna settings correlated much better (R=0.70; P<.001). The ratio between the measured and simulated quotients of maximum and average SARs was 1.03 ± 0.26 (mean ± SD), indicating that HTP can also correctly predict the relative amplitude of SAR peaks. HTP can correctly predict SAR changes after adapting antenna settings during hyperthermia treatments. This allows online adaptive treatment planning, assisting the operator in determining antenna settings resulting in increased tumor temperatures.

Antenna Selection and Placement Analysis of MIMO Radar Networks for Target Localization

A distributed MIMO radar network consists of a large number of transmitters/receivers to cover a sensing area of interest but under the constraint that the number of antennas is limited. The problem of selecting a subset of antennas at a sampling time to maximize the diversity capability of the MIMO radar in terms of target resolvability is addressed from the information geometric viewpoint in this paper. Fisher information matrix of distributed MIMO radar which takes both radar waveform and SNR into account is derived as a function of individual antenna locations. The Fisher information distance (FID) between the measurement distribution based on all antennas and that based on only the selected set of antennas is calculated and is adopted as the criterion of selecting a subset of antennas. The underlying antenna selection problem is then to select a subset of antennas from all antennas which can result in the “shortest” FID with respect to a given target location. Since an NP hard search process is involved, an exhaustive search method is considered for efficient antenna subset selection. Simulation examples are presented to demonstrate the effectiveness of the proposed algorithm compared with other criteria in different antenna configurations.

Dealing With Interference in Distributed Large-Scale MIMO Systems: A Statistical Approach

This paper considers the problem of interference control through the use of second-order statistics in massive MIMO multi-cell networks. We consider both the cases of co-located massive arrays and large-scale distributed antenna settings. We are interested in characterizing the low-rankness of users' channel covariance matrices, as such a property can be exploited towards improved channel estimation (so-called pilot decontamination) as well as interference rejection via spatial filtering. In previous work, it was shown that massive MIMO channel covariance matrices exhibit a useful finite rank property that can be modeled via the angular spread of multipath at a MIMO uniform linear array. This paper extends this result to more general settings including certain non-uniform arrays, and more surprisingly, to two dimensional distributed large scale arrays. In particular our model exhibits the dependence of the signal subspace's richness on the scattering radius around the user terminal, through a closed form expression. The applications of the low-rankness covariance property to channel estimation's denoising and low-complexity interference filtering are highlighted.

Design of a stacked loops antenna array to produce dual circularly polarized and multibeam radiations

This paper presents the design of an antenna array utilizing stacked multiloop structures to produce the electromagnetic radiations with dual circular polarizations and multiple directional beams. In particular, with a proper design of isolations, each combination of these polarizations and beams can be operated in a relatively independent fashion to increase the system capacity by using a single antenna set. The antenna structure was validated by numerical simulations and experimental measurements, which are presented to exhibit the characteristics of radiation.

An Uplink Capacity Analysis of the Distributed Antenna System (DAS): From Cellular DAS to DAS with Virtual Cells

Performance of cellular networks is severely limited by intense inter-cell interference due to aggressive frequency reuse among cells. How to characterize the dependency of inter-cell interference on positions of BS antennas and users is a key question for the capacity analysis of cellular systems, which unfortunately remains elusive. In this paper, a comparative study on the uplink ergodic sum capacity of cellular systems is presented, where L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> BS antennas are either co-located at the cell center or uniformly distributed within each cell. With a large number of users, the inter-cell interference density is shown to be inversely proportional to L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> if the co-located antenna (CA) layout is adopted. With the distributed antenna (DA) layout, it scales in the order of L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-α/2</sup> , where α is the path-loss factor, and is much lower than that in the CA case when L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> is large. Substantial gains on the uplink sum capacity are achieved by the DA layout thanks to the reduction of inter-cell interference level. The analysis also reveals that the inter-cell interference density of each BS antenna is sensitive to its position. With the DA layout, BS antennas at cell boundary areas suffer from much higher inter-cell interference than those at the cell center, which may exacerbate the performance disparity of users in cellular systems. To tackle the cell-edge problem, a distributed antenna system (DAS) is further considered, where L BS antennas are distributed over a wide area, and each user chooses V ≪ L surrounding BS antennas as its virtual cell, i.e., its own serving BS antenna set. A uniform inter-cell interference density is shown to be achieved thanks to the adaptive formation of virtual cells. More importantly, by the use of virtual cell, the number of users served by each BS antenna decreases with an increasing L, implying that much of the signal processing and information exchange can be performed in a local and distributed way. The uplink ergodic sum capacity and the ergodic rate with orthogonal access of DASs with V=1 are further derived, and shown to be close to each other even with a large L. It is in sharp contrast to cellular systems where a significant tradeoff between performance and complexity has to be made when the number of BS antennas is large.

Narrowband Short Range Directive Channel Propagation Loss in Indoor Environment at Three Frequency Bands

Propagation loss models for indoor environment are presented. The narrowband directive channel propagation loss in indoor environment at three frequency bands namely (2.4, 3.3 and 5.5) GHz is measured. Sets of directive panel antennas are used in the measurements. RF signal generator and a spectrum analyzer are used in the measurement campaign. It is found that propagation loss is sensitive to the scenario configuration. It is noticed that the propagation loss can be modelled by a single slope propagation model or two slopes propagation model.

Ultrawideband Time-Reversal Imaging With Frequency Domain Sampling

A new ultrawideband (UWB) time-reversal imaging method based on the unconventional utilization of UWB frequency data is introduced. First, a set of monostatic antennas is used to acquire the scattering data for a given scenario. Then, a corresponding multistatic data matrix is formed by casting the fine and coarse frequency samples of the scattering information into matrix form. The resulting frequency-frequency monostatic matrix is later fed into the adapted DORT (French acronym for decomposition of the time-reversal operator) and MUSIC (Multiple-Signal Classification) algorithms. The performance of the proposed method is investigated numerically by applying it to discrete scatterers embedded in homogeneous and continuously random inhomogeneous media. The effect of frequency bandwidth on image resolution is studied. It is observed that wider frequency bandwidths yield to better focusing resolutions.

Designs of Double whip Antenna for Mobile Phone

Whip type antennas are probably the most commonly used antennas in portable RF systems, such as cordless and cellular phones, RF enabled laptop computers, , and handheld computers. Whip antennas are almost always mounted on the chassis which contains the radio and other electronics. Normally in mobile phone two set of antenna used for receiving different application such as GSM and GPS. In this paper models and measurements are used to discuss choice of using single Double whip antennas and the impact of the chassis on radiation characteristics. Ansoft HFSS tool which has been has been successfully used to predict radiated field patterns is used for simulations, and measured and modeled results are shown.