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Prior Artificial Magnetic Conductor (AMC) designs using Genetic Programming (GP) showed that GP-based designs are competitive and often exceed those based on human expertise. However, the resultant...

In this paper, we report the results of a field measurement campaign carried out inside a pedestrian tunnel at 24 GHz in two conditions, namely, empty tunnel scenario and busy tunnel scenario with pedestrian movement. The experiment measures the fading effects of various groups of pedestrian crowds using directional antennas at the transmitter and receiver for millimeter-wave radio communications. Having presented and analyzed the measurement data in several diverse scenarios, we have further investigated human scattering effects in the crowded pedestrian tunnel and performed ray-tracing simulation for an empty pedestrian tunnel condition. Because tunnel is an enveloped scenario that is not bound by any geographic areas, the results of this study can be applied to a wider scenario like other pedestrian tunnels across the globe. Above all, these findings contribute towards ensuring wireless connectivity for everyone even in a remote scenario like underground passages.

We study the problem of finding the minimum energy beamforming that satisfies the users' signal-to-noise ratio requirements. Traditional transform based beamforming uses heuristics to determine the radiation pattern first, and then calculates the beamforming vector. Recent optimization based beamforming optimizes the beamforming vector directly and greatly outperforms the transform based beamforming. However, optimization based beamforming has prohibitively high complexity due to the semidefinite programming to be solved. In this paper, we propose to solve the optimal beamforming problem by the alternating direction method of multipliers (ADMM). We can achieve near optimal performance while greatly reducing the computational complexity. Simulations demonstrate the advantages of our proposed algorithm over transform based beamforming in terms of performance (e.g., 4 dB reduction in transmit power), and over optimization based beamforming in terms of computation time (e.g., 10 times reduction in computation time).

In this paper, we discuss an advanced base station system with smart algorithms operating on its multiple directional antenna arrays to provide seamless full-directional wireless connectivity and present its simulation result for 5G using Matlab. The system has six-sectors for communication and a scanning array for user discovery. Based on angle-of-arrival (AoA) estimation, optimized beamforming algorithm is employed to establish communication link between respective sector with optimized beams and the identified users. This system modifies the physical layer without affecting other layers and can be installed on the existing infrastructure. All the standards for WiFi, LTE and 5G radios are kept intact. The initial results of simulation show that continued connectivity and tracking with high data rate in multiuser LTE and 5G environment can be achieved.

This paper investigates the impacts that open-trench drains make on the accuracy of radio propagation prediction in an urban city environment. Compared with conventional prediction styles that assume the ground to be flat, in this paper, we have considered for the first time the real scenario in many Asian cities to make open-trench drains inclusive in radio propagation modeling. The aims of this paper are twofold. First, to scrutinize one narrow L-shaped structure, modeled after an open-trench drain, by means of comparing ray-tracing simulation results with the actual field measurement results at 2.4 and 5.8 GHz. Second, to compare one city model built without and with the inclusion of open-trench drains for running ray-tracing simulation in yielding radio propagation prediction results. The findings from this paper are especially beneficial to the improvement of mobile communications in extraordinary environments such as open-trench drains, caves, coal mines, underground passageway, and others. Besides, they provide a unique insight into how the presence of the open-trench drains may affect radio wave propagation in an urban city environment.

We study the problem of estimating angle-of-arrival (AoA) using practical antenna arrays. In practical antenna arrays, the antenna elements have nonuniform radiation patterns. However, most existing AoA estimation algorithms are developed based on the assumption that antenna elements are isotropic sources with uniform radiation patterns. Hence, the performance of existing algorithms can be significantly degraded when they are deployed on practical antenna arrays. To overcome the difficulty from nonuniform radiation patterns, we propose a fundamentally different approach of AoA estimation, where we train a neural network to learn the mapping from received signals to AoAs. Since we can generate a large amount of training data from propagation models of electromagnetic waves, our neural network can achieve high estimation accuracy (e.g., 10% estimation errors), which greatly improves the performance of state-of-the- art algorithms (e.g., up to 30% estimation errors). Moreover, by training with data generated from different radiation patterns, our neural network is agnostic of the specific radiation patterns of antenna elements. Since most computation is done in the training phrase, our trained neural network can perform AoA estimation in real time and can be used for tracking AoAs of mobile targets.

The fabrication and measurement of previously proposed artificial magnetic conductor (AMC) designs are presented in this paper. The AMC ground planes were synthesized by a hybrid genetic program (HGP) and were compared with AMC designs found in the literature. The HGP designed AMCs outperformed those in the literature. The performance was determined from full-wave electromagnetic simulations. We also validate the performance of the HGP designed AMCs through fabrication and measurement.

Measuring lung water change is invaluable for monitoring patients with heart failure and pulmonary diseases and assessing their responses to the treatment. Sensors for such measurement have been developed in Hawaii Advanced Wireless Technologies Institute (HAWTI) and clinical trials have been carried out. In this paper, we use numerical simulations to obtain the signals received by the sensors as a function of lung water content and sensor locations on the human torso. The data are interpolated to obtain a finer distribution of signals on the chest. The higher resolution data are used to train the support vector regression (SVR) machine to establish a prediction model for lung water content as a function of received signal and location of the sensors. The interpolation and SVR methods can save significant simulation time and will be used for building a database for lung water prediction for various human torsos.

Radio propagation modeling and prediction play an important role in the understanding of electromagnetic (EM) wave propagation in complex environments, as well as in the design of wireless communications and radar systems.

This paper reviews the basic concepts of rays, ray tracing algorithms, and radio propagation modeling using ray tracing methods. We focus on the fundamental concepts and the development of practical ray tracing algorithms. The most recent progress and a future perspective of ray tracing are also discussed. We envision propagation modeling in the near future as an intelligent, accurate, and real-time system in which ray tracing plays an important role. This review is especially useful for experts who are developing new ray tracing algorithms to enhance modeling accuracy and improve computational speed.

Techniques of radio propagation modeling and simulation are briefly reviewed, and the advantages of ray tracing methods are discussed. Spatial division methods are employed to accelerate the ray tracing algorithms and achieve computational efficiency and accuracy for propagation modeling. Algorithms extracting 3D models from geospatial resources are developed to establish realistic models for propagation environments. Terrain features such as ridges in mountainous regions are important elements characterizing the propagation of electromagnetic waves. Simple methods are introduced to extract these features. Different levels of detail of propagation environment are examined to gain insight of their effect on the efficiency and accuracy of propagation simulation. Computer hardware acceleration using graphics processing units (GPUs) is applied to the propagation simulation over terrains and a significant speedup is achieved. For source localization applications using ray tracing simulations, two methods (time reversal and machine learning) are discussed and their performances are investigated. A perspective of propagation modeling in the near future is given, and it points out that ray tracing methods will play a more significant role in providing accurate simulation results in real time for dynamic environments.

A fundamental approach in the optimal design of wireless communication systems is a proper comprehension of radio wave propagation through wireless channels. As wireless communications become more ubiquitous, new propagation environments emerge and the propagation mechanisms therein are being constantly investigated. The objectives of this chapter are twofold: firstly, to give a succinct review of new and emerging complex environments that require fine-tuning of the propagation models since traditional propagation models that simplify the propagation environment by ignoring the small and fine structures are no longer valid for such complex environments and, secondly, to recount the fundamental concepts of radio propagation modeling and its significance, as well as the basic propagation mechanisms and ray-tracing image method. These fundamental working principles of ray-tracing image method can be utilized both for indoor and outdoor environments because these two settings are governed in essence by the same propagation mechanisms.

In this paper, a smart physical layer based directional communication networking approach is described. It consists of “smart nodes,” equipped with multiple directional antennas and propagation modeling capabilities. This approach brings more “intelligence” (digital logic) in the physical layer to enable full directional communication networking operation without requiring changes in the upper OSI layers. Smart nodes consist of six-sectors, each having a scanning array for user discovery and a dynamic beamforming array for maintaining communication with users. Procedures are developed to enable seamless full-directional link between mobile users and smart nodes, within WiFi and LTE set standards. Simulations are performed using Matlab, and obtained results show successful tracking and continued maintenance of high data rate communication with mobile users.

The propagation characteristics of indoor multi-floor environments have been studied extensively and empirical models for many scenarios are available. These studies usually do not concern about stair structures. In this paper we study radio propagation in four typical stairwells through measurement at two frequencies (2.4 GHz and 5.8 GHz). Values of path loss exponent n have been derived for vertical and horizontal polarizations. These n-values for stairwells are found to be higher than the n-values for multi-floor environments. We also propose a new path loss model based on the so-called “accumulative distance” the receiver has traveled, in addition to the conventional separation distance between transmitting and receiving antennas. The new path loss model has lower n values and, most importantly, smaller standard deviation and can thus be considered a better model fitting the measurement data. The results in this study can be useful for designers of small cell wireless communications system such as pico- and femto-cells.

In this paper, the performance of an existing Multiuser Wireless Communication System is analyzed using accurate site specific propagation modelling data (such as path gain, angle of arrival/departure and delay spread) of a typical urban environment. For optimal utilization of realistic temporal, spectral and spatial data, obtained from the available ray-tracing tools, a novel multiple detail-level adaptive cognitive communication system is proposed. Desirable system performance in terms of bit-error rate and capacity is shown to be achievable using only AoA and path gain information of as little as 5 paths in generating the channel matrix. As a result, significant savings (85%) in computational cost are achieved, thus emphasizing the potential practical implementation of the proposed approach in cognitive communication applications.

Emerging homeland security applications require low-cost and fast, deployable, high-frequency (HF) radar systems and the ability to operate in challenging terrain environments. With the need to cover as many border and coastal areas as possible, taking advantages of available transmitter resources to track targets using passive radar technologies is yet another area of research of considerable interest. In this paper, we describe the development of an HF radar system that meets these operational challenges, and we also highlight some recent implementation of the passive radar technology for homeland security applications. Specifically, we describe the design of a novel, electrically small HF antenna system consisting of three helical elements, one connected to the feed port while the other two are folded arms terminated with switchable loads. The antenna is 0.90-m (ka range from 0.44 at 30 MHz down to 0.08 at 5.7 MHz. The achieved bandwidths range from 1.4% up to 12% and associated efficiencies range from 66.2% to 76% within the HF band (3‐30 MHz). As for the operational requirement in challenging terrain environments, a setup in a hilltop-type environment with a slope terrain and surface roughness was considered. A propagation modeling and ray-tracing approach was used to evaluate the impact of such terrain conditions on the effective interelement spacing of an HF radar antenna array and the subsequent impact on its beamforming and beam steering performance. It is shown that while the effect of the slope on the effective interelement spacing of the array could be very significant, diffraction effects from surface roughness resulted in a much smaller, but significant, error of about 18°. Results from some initial work on the implementation of passive radar technology, with focus on addressing the bandwidth requirement to ensure practical resolution values, are also described. It is shown that signals from wide-band transmitters (e.g., High Definition Television [HDTV] signals) rather than those from radio stations are required to provide acceptable range resolution. These as well as simulation and experimental results of the antenna design, and results from beamforming simulations illustrating the effect of a rough hilltop terrain on the HF radar performance are described.

In this paper, a low complexity hybrid smart antenna system with directional elements and reduced-size digital beamformer is proposed to combat the inter-symbol interference (ISI) problem over frequency-selective fading channels. The conventional smart antenna systems with omni-directional elements utilize the full-size digital beamformer to suppress interference and obtain the optimum performance. However, the proposed hybrid smart antenna system with directional elements can split the linear receive array into two subarrays. One subarray contains the elements with no ISI, which can be processed with a simple maximum ratio combiner (MRC). The second subarray includes the elements with the ISI interference, which require the use of a reduced-size optimum beamformer for interference suppression. Finally, the outputs of the two subarrays are combined for optimal detection of the transmitted signals. Simulation results confirm that the proposed low complexity hybrid smart antenna system can provide robust performance under the multipath fading channel with ISI, and outperform the conventional smart antenna systems due to the use of directional antennas and utilization of multipath diversity gain.

A method for extracting the three-dimensional (3D) building structures using their single-view images available on the Internet/cyberspace is described. Height measurement technique is combined with two-dimensional (2D) projective transformation to obtain the 3D building information. It is shown that the reconstruction method is accurate for path-loss calculations using ray-tracing algorithms. Simulated path losses/gains are compared to results in literature, and good agreement is observed. The effect of building footprint and height inaccuracies on path-loss calculations is also examined and is found to result in errors within the common error range between experimental measurements and ray-tracing predictions.

This letter presents a method for determining the required number and locations of transmit antennas to optimize wireless propagation coverage in a given indoor environment. The ray-tracing method is employed to calculate the field distribution due to one or more transmitting antennas and the genetic algorithm (GA) is used to determine the required number and the locations of these antennas to achieve optimized wireless coverage in a given area. In the ray-tracing method, detailed parameters such as thickness, dielectric constant, and the conductivity of individual walls are assigned for realistic field calculations. Obtained simulation results illustrate the feasibility of using the integrated ray-tracing/GA method in determining the optimized coverage of a wireless network.

Phased array antennas have and will continue to be a critically important component in the development of future wireless systems with applications in communications, radar, and satellite technologies. In spite of the significant advances in the design of modern phased array antennas, there continue to be significant and growing need for developing high performance systems that are also low cost and with beam steering capabilities. In this paper we describe some of the antenna array designs that focus on achieving this goal. We will start with one approach that is based on an analog phase-shifting approach and involves an integrated use of ferroelectric materials and the Continuous Transverse Stub (CTS) antenna array technologies. A complementary design which is based on digital beamforming and the utilization of the Hybrid Smart Antenna technique recently developed by our group will then be described. This will be followed with comments regarding the trade-off between the analog and digital phase shifting techniques. We will conclude the chapter with a description of a novel ultra-wideband and low profile ground plane which is based on a hybrid ferrite and Electromagnetic Band Gap (EBG) materials design. In all cases simulation results and experimental validation, whenever available, will be presented and aspects of the required future work to fully enable these technologies will be discussed.

Continuous transverse stub (CTS) technology has been adapted to use with coaxial lines to produce effective microwave antenna structures that radiate omnidirectionally, with high efficiency, low reflection, and useful radiation patterns. In this paper, we describe the design, construction, and testing of a new type of antenna array, that is, a six-element multiband (4.2 and 19.4 GHz) CTS antenna array. The design of the CTS array was optimized through simulation using finite-difference time-domain and then built and tested using both S-parameters and radiation pattern measurements. Simulation results agreed very well with measured data. These simple and low cost coaxial CTS structures could be adapted for base station applications in wireless communication, for satellite communication systems, and Identification Friend-or-Foe systems for the military.

This paper presents a fast ray-tracing procedure based on triangular division of the propagation environments. Unlike other accelerating methods that are mostly based on pre-establishment of visibility, this method does not require knowledge of the position information of the base station and/or receiving antennas and is thus more general. Although the triangulation is done in a two-dimensional (2-D) plane, this method is suitable for three-dimensional (3-D) simulations when a proper data structure for buildings is constructed. Validation results show good agreement between calculated and measured data from the European COST 231 project. The improvement in the computational efficiency is clearly demonstrated in examples.

A ray-tracing approach for indoor/outdoor propagation through windows is proposed. Using both the finite-difference time-domain (FDTD) method and a ray-tracing algorithm, several cases of indoor/outdoor propagation through windows were investigated. It is shown that wave transmission through windows cannot generally be accounted for through a single transmission coefficient parameter. Instead, a full diffraction pattern needs to be accounted for and multiple-ray representation is therefore required. It is also shown that a single window model may be used to calculate transmission through set of windows in a typical building structure as a building block. Results from the implementation of a multiple-ray representation and FDTD simulations showed good agreement. Results were validated for both normal and oblique incident cases. The developed ray-tracing approach, therefore, facilitates the use of the developed window model in available ray-tracing algorithms often used for propagation characterization of urban environments. Simulation results were further validated by conducting measurements on scaled models at 30 GHz. The experimental results agreed well with the simulation data, thus validating the accuracy of the developed ray-tracing model for transmission through windows.

A comprehensive review of the propagation prediction models for terrestrial wireless communication systems is presented in this paper. The classic empirical models are briefly described and the focus is placed on the application of ray-tracing techniques to the development of deterministic propagation models. Schemes to increase the computational efficiency and accuracy are discussed. Traditional statistical models are also briefly reviewed for completeness. New challenges to the propagation prediction are described and some new approaches for meeting these challenges are presented.

The finite-difference time-domain (FDTD) technique has become increasingly popular and is being used to model extremely complex and electrically large structures. These simulations are computationally demanding and often exceed available limits on computer resources. In this paper, we present an FDTD sub-gridding technique that allows for increased resolution in regions of interest without increasing the overall computational requirements beyond the available resources. Furthermore, the formulation presented here allows for traversing dielectric boundaries using any integer refinement factor and the maximum Courant number. By allowing the coarse-/fine-grid boundary to traverse dielectric boundaries, numerical simulations that were previously either extremely difficult or impossible to perform are now possible. The technique presented here uses a weighted current value from the coarse region at the boundary between the fine- and coarse-grid regions to update the fine-region tangential fields on that boundary. The weighting function depends on the material properties and the relative position of the fine-region electric field within the current contour at the boundary. The complete formulation of this new technique is described and some results of simulation cases are presented to validate the accuracy and stability of the newly developed FDTD code. Simulations include simple cases where the analytical solution exists and more complex cases, which were impossible to model using a uniform-grid FDTD code. In some simulation examples, computer memory savings as high as 70 times what would have been necessary with a uniform-grid code were achieved. It is shown that errors of less than 2% are achievable with ratios of coarse-to-fine grid sizes exceeding ten. The new technique is expected to be used in simulating many electrically large and complex structures in the biomedical microwave processing of materials and the wireless communications areas.

A new method is proposed for the extraction of three-dimensional (3-D) building structures for simulating radio waves propagation in urban environments. The procedure is based on obtaining readily available high-resolution 2-D images (satellite and/or aerial photos) and images on the Internet (e.g., the google earth); and building accurate 3-D models of structures through a process of coordinates and dimensions matching. The new method provides an efficient and economic way for 3-D structure extraction. Combined with the computationally efficient ray-tracing algorithms recently developed by our group and reported in the literature, it is now possible to carry out radio wave propagation predictions for many outdoor urban areas efficiently and accurately.

The wide spread of geospatial data in cyberspace provides a great opportunity for establishing more accurate three-dimensional (3D) propagation environments which are crucial for propagation modeling using ray-tracing methods. Many government agencies such as NASA and USGS (U. S. Geological Survey), and military and commercial companies have developed their own databases for housing the geospatial information which are accruing exponentially. Some of these data are free and others are not and may be very expensive.

A comparative study of neural networks and genetic programming was conducted on six character classification problems. Based on the obtained results of the six problems, genetic programming showed better performance than neural networks in the various levels of problem difficulty. Genetic programming also showed robustness to untrained data, which caused difficulties for the neural networks. The optimization of the neural network structure was observed to be integral in obtaining both convergence and acceptable performance. A clear trend for structure optimization is not evident in the case of neural networks, and a global optimal solution may not be practical. On the other hand, because of the global searching nature of genetic programming, these problems with neural networks could be solved by using genetic programming.

A new method is introduced for the reconstruction of 3D building structures using single-view 2D image with controlling objects setup in Google Earth. The method is based on the theory of projective geometry and the aid of GE which provides means that make it possible to set controlling objects possible. Two types of building structures and their variations and combinations could be reconstructed. It is shown that the accuracy of the reconstruction is satisfactory based on observations of some test cases. The ray tracing method is used to calculate the received power in five routes in Rosslyn, VA. Comparison with the path gain obtained using a more accurate city model shows that the new model provides good results. More details and examples will be provided in the presentation.

The development of advanced phased array antennas and new propagation models that address wireless applications in challenging propagation environments have and will continue to be a critically important component in the development of future wireless systems with applications in communications, radar, and Satellite technologies. In spite of the significant advances in these technologies, challenges continue to preclude their low cost, reliable, and high speed application in tough propagation environments including urban areas, UAVs, and other DoD applications. In this paper we describe some of the ongoing research activities at the University of Hawaii in the area of advanced wireless systems. In the antenna array design technology, two complementary antenna arrays designs will be described and the development of an ultra-wideband ground plane for foliage penetrating radars will be discussed. For the propagation modeling area, new models for characterizing indoor/outdoor transmission and for evaluating wireless coverage in urban areas taking into account the radiation patterns of the transmitting and receiving antennas will be presented. In all cases simulation results will be presented and validation with experimental observations will be included whenever available.

This paper presents a new method of incorporating propagation models into wireless systems simulations. The multipath data for each transmitter-receiver pair in a realistic environment is calculated using the site-specific propagation modeling software developed at the University of Hawaii. Instead of fitting the multipath data into a statistical model, we directly use the data for the calculation of discrete channel impulse responses for each transmitter-receiver pair. The Doppler effects and the effects of pulse shaping filters on the calculation of discrete channel impulse responses are investigated. Finally, these channel impulse responses are employed in a CDMA system simulator to evaluate the output signal-to-noise ratio (SNR) and the corresponding bit error rate (BER).

This research focuses on the characterization of time reversal (TR) technique in indoor multipath environments which have typical propagation features such as the waveguide effect of hallways, multiple reflection and transmission of slab walls, diffraction from edges (especially metal edges), and scattering from various small structures. The two-dimensional FDTD method is employed for the simulation of the wave propagation. An indoor environment is simulated and the effect of furniture and other scattering objects in the region of interest is examined. To quantitatively characterize the spatial focusing and time compressing, the spatial energy focusing factor (SEF) and the time compressing factor (TCF) are defined. It is found that energy focusing and time compressing can be achieved in the indoor environment and scatterers such as metal door frames can significantly improve the focusing and compression effects.

The ultra-wide hand (UWB) communications systems have been evolving quickly due to the recent FCC approval of the use of 7.5 GHz band of the unlicensed spectrum. To help with the effective implementation of impulse radio it is necessary to carefully characterize propagation in complex environments. This paper reports on the numerical simulation of UWB pulse reflections and transmissions through complex wall structures that are often encountered in indoor propagation environments. The finite-difference time-domain method is employed to accurately and efficiently calculate the field responses. Simulation results show that different structures of the walls have significant effect on the propagation characteristics. It is shown that the scattering due to the complex wall structures leads to complicated reflected and transmitted signals that could result in serious challenges in the design and effective implementation of an UWB communications system.

This paper reports on simulation results for the MIMO capacity and fading characteristics for indoor/outdoor propagation environments. The finite-difference time-domain (FDTD) method is used for the calculation of the reflection and transmission characteristics through windows and metal-framed structures and the obtained diffraction-type effects were then represented by an equivalent ray-tracing model. An integrated ray tracing code that accounts for these effects is then used to calculate MIMO capacity and Rician K-factor. The obtained results are then compared with those based on available data for Gaussian channels. In related preliminary results, it is shown that for an indoor environment with realistic walls of complex structures, the MIMO capacity and the K values are very different from those calculated based on simplified wall structures.

In a network with several transmitting nodes, array antennas at both ends of MIMO links can be exploited to have multiple links operate in the same channel. Depending on the network topology, each interfering link can transmit fewer modes than it would in an isolated environment, and use the remaining degrees of freedom to avoid or suppress interference. With interference, channel state information (CSI) must be fed back to the transmitter to reach the highest level of performance. We show that the difference between closed- and open-loop capacities when links interfere is usually much larger than with isolated links. This implies that less frequent CSI updates are sufficient to keep closed-loop MIMO performance above open-loop MIMO. We analyze the effect of CSI aging for MIMO links. To understand the effect of fading and study the feasibility of closed-loop operation in MIMO links, we utilize two models for the MIMO channels. First, we use a Rayleigh fading model, and a filtered Gaussian noise method to simulate a fading channel. Then, we consider a more realistic scenario, where we simulate propagation in a typical indoor environment using the finite-difference time-domain (FDTD) method. The results, especially with the realistic channels, indicate that, even with the overhead of CSI updates multiplied by the number of iterations, spatial multiplexing may be attractive for static and low-mobility networks, such as in indoor environments.

Smart antenna and associated technologies are expected to play a significant role in enabling broadband wireless communication systems. Smart antennas exploit space diversity to help provide high data rates, increased channel capacity, and improved quality of service at an affordable cost. In this paper we present a new procedure for implementing smart antenna algorithms. It is a hybrid approach that integrates the features of the switched beam method and the adaptive beam forming approach. Specifically it is shown that by using high gain antenna elements and combining the switched beam process with the adaptive beam forming procedure on a limited number of elements (as low as two in an eight-element array), a performance close to that of a more complex eight-element adaptive array may be achieved. The proposed hybrid method, therefore, is fast, is computationally efficient, and provides a cost effective approach for exploiting space diversity. Even with the inclusion of interference signals, the proposed hybrid approach out-performed the switched beam method, and provided performance similar to that of an adaptive array with less number of elements (three in an eight-element array). Implementation of an adaptive array also includes estimations; hence, reducing the number of elements in an array may lead to improved accuracy, in addition to fast convergence and reduced complexity.

As the search continues for low-cost and high-performance components for the front-end devices for wireless communications systems, the focus has been on the use of MEMS technology; but some attention has recently been given to exploring new and innovative designs based on the Ferroelectric and the Continuous Transverse Stubs (CTS) technologies. In this paper we present new phase shifter designs and an integrated phased array antenna system based on the use of multilayer ferroelectric materials. Simulation results show that with the appropriate selection of the materials properties and the dimensions of the multilayer dielectric system, insertion losses may be reduced by as much as a factor of 100. These results also show that while only a slight reduction (15%) in the maximum achievable tunability was observed, it was possible to achieve significant improvement in the impedance matching characteristics. A procedure to enhance the radiation efficiency from an integrated ferroelectric/CTS phased antenna array design will be described and specific array designs discussed.

This paper presents the development of 2.5D and 3D extensions of a 2D procedure that is described in an earlier paper (see Zhang, Z. et al., Electronics Letters, vol.36, no.5, p.464-5, 2000) for modeling propagation environments. These methods are based on dividing the propagation region into cells whereby the number of cells is decided by the number of vertices of structures instead of their dimensions. Results from the 2.5D and 3D methods show significant improvement in computational efficiency. Specifically, the CPU time for the 2.5D method is less than 5% of that of the visibility ray tracing method. Accuracy, on the other hand, is related to that of a traditional ray tracing method and includes accounting for reflected, transmitted and diffracted rays.

A fast ray tracing procedure using space division is presented for two-dimensional propagation predictions. The space containing the propagation region is divided into a uniform rectangular grid. It is assumed that the reflection/transmission surfaces are exactly coincide with the grid lines. Cleary's algorithm is used for fast space traversing of a ray. CPU time comparisons between the proposed method and the traditional method utilizing visibility are presented. It is shown that CPU time for the proposed rectangular grid method is approximately 14% of that of the visibility procedure. Furthermore the method is especially useful for some indoor and outdoor-to-indoor propagation predictions, since the scenarios in these cases may fit the employed assumptions. Some results for delay spread, angle of arrivals are given.

A new triangular-grid ray tracing (TGRT) method is proposed in this paper. It is based on dividing the propagation region into triangles. The number of triangles is decided by the number of structures' vertices, instead of their dimensions. For the 2D case, it can reduce the visible decision calculation to 2 edges for each triangle. It is shown that this method unifies the indoor and/or outdoor propagation problems and provides savings in computational time.

A fast ray tracing procedure using space division is presented with the assumption that the reflection/transmission surfaces exactly coincide with the grid lines. Cleary's algorithm is used for the fast space traversing of a ray. The CPU time for the proposed method is approximately 14% of that of the visibility procedures.