A smart antenna with capability of beam steeringin azimuth over a wide frequency band using only spatial sig-nal processing is presented. Filters and tapped-delay networksemployed in conventional wideband linear arrays are avoidedby using a two-dimensional rectangular array structure. Inthis array, only constant real-valued weighting coefficients, re-alized with amplifiers or attenuators, are used to form a de-sired radiation pattern. In order to estimate direction of ar-rival of a wideband signal, the MUSIC algorithm in conjunc-tion with an interpolated array technique is applied. In theinterpolated array technique, a composite covariance matrixis generated, which is a simple addition of covariance matricesof narrowband virtual arrays, being stretched or compressedversions of a nominal array. A working prototype of this wide-band array is presented. Its operation is assessed via full EMsimulations and measurements.

This chapter discusses the use of smart antennas in Code Division Multiple Access (CDMA) systems. First, we give a brief overview of smart antenna classification and techniques and describe the issues that are important to consider when applying these techniques in CDMA systems. These include system architecture, array antennas, channel models, transmitter and receiver strategies, beamforming algorithms, and hybrid (beamforming and diversity) approach. Next, we discuss modeling of smart antennas systems. We present an analytical model providing rapid and accurate assessment of the performance of CDMA systems employing a smart antenna. Next, we discuss a simulation strategy for an adaptive beamforming system. A comparison between the analytical results and the simulation results is performed followed by a suitable discussion.

Generalized channel inversion (GCI) is a precoding technique for multiuser multiple-input multiple-output system. While producing each user’s precoding matrix, GCI takes into account noise and thus it is more robust compared with alternative techniques such as block diagonalization technique in terms of sum rate capacity and frame error rate. In this paper, two suboptimal multiuser scheduling schemes for GCI are proposed that by scheduling a subset of mobile users nearly maximize the sum rate capacity. They employ an iterative approach involving a number of search steps. At each step, unselected mobile users are evaluated one by one, and only one of them is chosen according to given criteria. It is shown via computer simulations that the proposed schemes are capable of achieving a large portion of the sum rate capacity that is offered by an exhaustive search. The performance of the proposed multiuser scheduling schemes is evaluated when the antenna mutual coupling effects are taken into account at the mobile users’ sides. Numerical results reveal that the presence of antenna mutual coupling can result in an increased sum rate capacity when the array inter-element spacing is in the range of 0.3–0.4 wavelength.

This article reports on the design of a wideband compact microstrip-fed tapered slot antenna aimed at microwave imaging of a brain stroke. The antenna is immersed in a carefully designed coupling liquid that is used to facilitate higher signal penetration in the brain and thus increased dynamic range of the imaging system. A parametric analysis is used to find out the required properties of the coupling liquid. A suitable mixture of materials is then used to implement those properties. In order to protect the antenna from the adverse effects of the coupling medium, dielectric sheets are used to cover the radiator and the ground plane. To verify the proposed design in brain imaging, the antenna is tested using a suitable head model. It is shown that the antenna with a compact size (24 mm × 24 mm) on RT6010 substrate (dielectric constant = 10.2) operates efficiently over the band from 1 GHz to more than 4 GHz with more than 10 dB return loss. The time domain performance of the antenna supports its capability to transmit a distortion-less pulse with a high fidelity factor inside the head tissues.

The design of a novel wideband six-port network on a single layer microstrip substrate is presented.Two different configurations of the single-layer six-port networks, one conventional and the other nonconventional, are designed, fabricated, and measured. The six-port network based on the conventional configuration is formed by one Wilkinson divider and three couplers, with one unused port terminated with a coaxial match termination. The nonconventional six-port network, proposed here, is constructed using a similar configuration except one of the couplers is replaced by a quadrature power divider eliminating the need for match termination. To obtain fully planar device with wideband operation, the six-port networks use double-stage Wilkinson dividers, disk type couplers, and a wireless via 90 degrees phase shifter. Their performances are assessed via full-wave electromagnetic simulations and measurements. Both the simulated and the measured results show a wide bandwidth of the two six-port configurations in terms of amplitude and phase characteristics across the frequency band of 4.58.5 GHz. (C) 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:17961803, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26976

The paper presents the design of a compact penta-band antenna for portable and embedded devices. The bands covered include GSM-900/1800/1900, UMTS-2100 and 2.4 GHz WLAN. A folded planar inverted-F antenna with a relocated shorting-stub and a secondary arm introduced on the bottom layer of the substrate provides resonances at the 900, 1800 and 2400 MHz bands. The inclusion of a narrow slot in the ground plane offers an additional resonance at 2300 MHz, resulting in more than 800 MHz bandwidth centered at 2100 MHz. The final design is confirmed by measurement showing the 6 dB return loss from 890-960 and 1650-2550 MHz with better than 10 dB return loss at the centers of the GSM-900/1800 and 2.4 GHz WLAN bands.

The article reports the design of an ultrawideband quadrature power divider in uniplanar microstrip technology. The proposed device uses the conventional Wilkinson power divider with one of its output arms equipped with a double wireless via acting as a phase adjusting circuit. The device is manufactured showing a wide bandwidth in terms of return loss, isolation, power division, and a differential phase shift of 90 degrees across the frequency band of 38 GHz. Its compact size and good performance makes it suitable for use in wideband-balanced amplifiers. (C) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 54:300305 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26519

SUMMARYThis paper describes an analytical model and an associated algorithm for assessing the throughputs of each host in wireless mesh networks (WMNs). It provides a framework for studying WMNs, particularly when the performance and parameters in multiple protocol layers have to be jointly evaluated and optimized. From the point of the implementation, a simple recursive formula with N − 1 iterations is used to obtain the throughput performance of N node WMNs. The produced expressions offer insights into understanding the performance of the individual nodes without referring to a specific medium access control layer or physical layer technology. The model serves as a general tool for capturing the characteristics of the WMNs. Using the model, the complexity of cross‐layer studies is reduced, thus allowing researchers to focus on the modelling of other associated layers. The paper explains the rationale behind the model and provides examples of scenarios for which it is suitable. It is validated using discrete event simulations in the OPNET network simulator. Copyright © 2012 John Wiley & Sons, Ltd.

This article describes an ultra wideband (UWB) microwave system that uses the frequency‐domain reflection coefficient data acquired by a UWB antenna to form a microwave image of a homogenous cylindrical dielectric body containing cylindrical targets. Both hardware and signal processing aspects of the system are described. The system uses a frequency‐domain image reconstruction algorithm using the different data obtained for adjacent positions of the scanning antenna so that the effect of air‐image body interface is removed. The algorithm is tested in examples of a cylindrical dielectric container including a vegetable oil and targets in the form of small‐diameter plastic straws filled with water. Both simulated and measured results are presented. The successful detection and location of the targets is achieved by visual inspection of the formed microwave images. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:13–18, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26465

The letter describes double microstrip-slot transitions for use in planar ± 90° phase shifters. The described devices exhibit broadband performance and offer compatibility with ordinary microstrip circuits. Full-wave EM simulation results show a phase shift of ± 90° ± 7° over the frequency band of 3.1-12.0 GHz when compared with a suitably chosen section of microstripline. The observed differential phase shift is accompanied by return losses of not less than 14 dB and insertion losses between 0.7 to 1.5 dB in the band 3.1-11.0 GHz. The simulated performance is confirmed by experimental results of ± 90° ± 8° phase shift, return loss not less than 14 dB and insertion loss between 0.5 and 1.8 dB in the frequency band of 3.1-11.0 GHz.

The design of a single-layer reflectarray, which employs a new phasing element in the form of a fixed-size circular ring and a variable-length open-circuited stub, is presented. The array is developed on a thin substrate supported by a thick foam material. Investigations are performed to obtain a linear reflection phase as a function of the stub's length when the element operates in a unit cell. This goal is achieved by a suitable choice of the ring's radius and width and the stub's width. In order to validate the simulated element's reflection phase behavior, a waveguide simulator is manufactured to perform experimental tests. The phasing element offering best linear phase characteristics is used to design an -band offset fed 13×13 element reflectarray pointing at 20° from the broadside direction. Full-wave simulations performed using CST Microwave Studio show desired radiation characteristics of the designed array antenna. The simulated performance is confirmed by experimental tests performed on the fabricated reflectarray prototype showing a 17.8% 3-dB gain drop bandwidth.

The design of a novel wideband six-port network constituted by in-phase and quadrature Wilkinson power dividers is presented. To achieve wideband operation of the quadrature divider, the device uses a 90 degrees phase shifter in the form of a double vertical wireless interconnect that utilises microstrip to coplanar waveguide transitions. The performance of the designed in-phase and quadrature dividers and the entire six-port network is assessed via full-wave electromagnetic simulations and measurements. The obtained results show that the designed six-port network offers good performance in terms of amplitude and phase characteristics across the frequency band of 3.5-9 GHz.

In this article, the design of a dual-band slim inverted-F antenna with an enhanced operational bandwidth is presented. Initially, a slim inverted-F antenna for operation in 850 and 1900 MHz bands supported by a large ground plane of 120 x 40 mm is introduced. This antenna offers dual band operation but with narrow bandwidth around each desired frequency. To reduce its ground plane length to 90 mm as well as to improve its operational bandwidth, a ground slot and a strip are introduced. By the proper placing of the slot and the strip, the lower frequency bandwidth is improved, while the good performance at the upper band is maintained. The designed antenna is fabricated and experimentally tested showing operational bandwidths covering GSM850 and PCS1900, with reference to the 6 dB return loss (VSWR 3:1). Its radiation patterns are omnidirectional at the lower band and become directional at higher frequencies, with the gain varying between -1 and 3 dBi. (C) 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:684-689, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26643

The paper presents the design of a linearly polarized single-layer reflectarray which employs a fixed-size circular ring with a variable-length open-circuited stub run around it as a phasing element. To achieve a slow phase slope, a thick foam material is used to support this element developed on a thin substrate. Investigations are performed to achieve a linear reflection phase as function of the stub's length. This goal is achieved by a suitable choice of the ring's radius and width and the stub's width. The phasing element offering best linear phase characteristics is used to design an X-band 13 × 13 element reflectarray. The full-wave simulation performed using CST Microwave Studio shows an increased 1dB gain drop bandwidth of the designed array antenna.

In this letter, the design of a super slim multiband wrapped inverted-F antenna that covers the frequency bands allocated for GSM, DCS, and PCS wireless services is described. In the first step, the quarter-wavelength (at 850 MHz) open-end arm of an inverted-F radiator is folded and meandered. Then, the antenna is wrapped using a fourth-order folding technique to reduce its projection area to only 40 mm x 10 mm x 3 mm. Full wave electromagnetic (EM) simulations show that the antenna excites a lower mode resonance at similar to 850 MHz and a higher one at about 1900 MHz.Its radiation pattern is nearly omni-directional with a gain of about 2.5 dBi at the lower band and 4.6 dBi at the upper band. A prototype of the proposed antenna is fabricated and tested. A close agreement between the simulated and measured results is achieved. The measured 6-dB return loss or voltage standing wave ratio (VSWR) 3:1 bandwidths for the lower and upper resonances is 200 MHz (770-970 MHz) and 280 MHz (1710-1990 MHz), respectively. These bandwidths are sufficient to cover GSM 850/900/1800/1900 MHz, DCS 1800 MHz, and PCS 1900 MHz bands. Because of its small volume, the proposed antenna is a very attractive candidate for modern slim portable transceivers. (c) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:900-904, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25887

A novel industrial application of radar sensing technology as an aiding source for navigation systems in autonomous mining equipment is described. This paper proposes a radar-based solution to provide a stable external reference for an existing inertial-technology mining navigation system. It documents trials of a 26 GHz radar unit in an underground coal mine, using only the existing mine infrastructure in the form of reinforcing wall and roof bolts as targets. The presented pilot trial attempts to identify the bolt plates by their RCS back-scatter. An improvement to this approach, using complex natural resonance (CNR) for target characterisation based on broad bandwidth excitation, is investigated and a theoretical simulation of the target identification process is described.

This study reports investigations into phase characteristics of a unit cell of a single-layer microstrip reflectarray exploiting fractal geometries. The aim is to have the phase range larger than 3608 accompanied by a smaller slope of the reflected wave phase as a function of the elements' size. These are required to achieve a wide operational bandwidth and a smaller sensitivity to manufacturing errors. To achieve this goal, multi-resonance fractal elements are investigated. It is shown that sliced patches of square and circular shapes as well as multiple rings printed on a thick substrate can offer slower phase slopes while maintaining phase ranges exceeding 360 degrees. The achieved ranges and slopes of these elements are comparable with those of double-stacked patches printed on the equivalent low permittivity dielectric substrate. Choosing suitable dimensions and scaling factors of these elements, the phase characteristic can be made approximately a linear function of their size.