Anthony K. Brown

High Resolution 3-D Angle of Arrival Determination for Indoor UWB Multipath Propagation

Propagation measurements using a large array are used to study the angle of arrival (AOA) across the ultrawideband (UWB) frequency range of 3.1 to 10.6 GHz. A two-dimensional Unitary ESPRIT algorithm is employed to give a high resolution estimation of AOA including both the azimuth and elevation angles of multipath components. The frequency dependence of AOA is investigated over the UWB frequency band. The multipath rays form clusters in both angular and temporal domains. Within a cluster the azimuth and elevation AOAs are determined to follow Laplacian and Gaussian distributions respectively. In the indoor environment considered, a typical cluster extends over an angular sector of approximately 14 degrees in azimuth and 9 degrees in elevation, with up to 5 clusters observed. We note that these propagation characteristics will allow UWB systems to utilise smart antennas or MIMO structures to improve overall throughput.

Octagonal Ring Antenna for a Compact Dual-Polarized Aperture Array

A wideband dual-polarized aperture array design is presented based on elements formed by a triangular configuration of octagonal rings. The octagonal ring elements are linked by capacitors and placed a defined distance from a groundplane. A broader frequency bandwidth has been achieved by placing a further layer of conductive rings above the element rings forming a metamaterial superstrate layer. Low dielectric constant material can be used to fill the space between the array rings and the groundplane, and between the elements and the superstrate layer. A dual-polarized finite ORA array has been fabricated and measured. The octagonal ring antenna array inherently exhibits a broad scan range with a stable cross polarization performance, however in practice the cross polarization depends on the feeding arrangements. Two feeding methods are discussed with a stripline feed showing best performance.

EMPIRICAL MINIATURIZATION ANALYSIS OF INVERSE PARABOLIC STEP SEQUENCE BASED UWB ANTENNAS

In this paper we develop an empirical approach to the design of Ultra Wideband (UWB) antennas employing the Inverse Parabolic Step Sequence (IPSS). The relationships developed can be used to miniaturize the antenna and achieve a good impedance match over the UWB bandwidth. The overall aim of this process is to give a good starting point for detailed numerical optimizations. We will illustrate the use of these formulae in three difierent designs of IPSS- based antennas. A low loss duroid substrate of loss tangent, tan-, 0.0009, low relative permittivity 2.2 and thickness 1.575mm is used to simulate these planar monopole antennas in Ansoft High Frequency Structure Simulator (HFSS).

Comparison of FDTD Hard Source With FDTD Soft Source and Accuracy Assessment in Debye Media

To radiate electromagnetic energy from a single point of a finite difference time domain (FDTD) grid, there are typically two general classes of electromagnetic wave sources; the soft source which consists of impressing a current, and the hard source which consists of impressing an electric field. The physical meaning of the soft source is well understood and its analytical solution is known, whereas there is no analytical solution for the hard source excitation. Nevertheless, many FDTD works utilize the hard source for its practicality. A novel aspect is that the derivation of a field radiated from the hard source towards the free space is identical to the field radiated from the soft source, provided that a certain relationship holds between the source excitations. This provides us with an analytical solution for the field radiated from the hard source. The assessment of accuracy is then considered for a wide band field radiated from a punctual source into frequency-dependent FDTD Debye media. The quantification of the deviation of the waveform observed in the FDTD space from the analytical solution is demonstrated. The numerical experiments with this quantification show that the waveform observed with the soft source excitation matches the one with the hard source excitation when the minimum wavelength to the spatial discretization ratio is greater than 10. It turns out that the soft source outperforms the hard source when the minimum wavelength relative to the spatial discretization is less than 10 in the case of lossless media. Equivalent accuracy is achievable for both lossless and lossy media even when the minimum wavelength to the spatial discretization ratio is lower than 10 due to the loss tangent which absorbs the spurious frequencies related to the numerical noise.

Modeling Methodology for Computing the Radar Cross Section and Doppler Signature of Wind Farms

Detailed modeling of radar scattering from wind turbines using commercial computational electromagnetic (CEM) tools requires large computing resources and extended run times. This paper will present a dynamic model specifically designed to model the radar cross-section (RCS) of wind turbines and the Doppler signature generated by the rotating blades in a rapid manner. The paper will elaborate on the methodology used for the meshing and the RCS computation of blades, tower and nacelle. Verification of the developed model against measured RCS of canonical shapes is provided. Finally, RCS and Doppler signature results of a generic turbine and a wind farm are presented.

A Hybrid Model for Radio Wave Propagation Through Frequency Selective Structures (FSS)

A novel hybrid model is presented to study the radio wave propagation through frequency selective structures (FSS) used to control propagation in an outdoor to indoor building environment. This hybrid model is based on combining ray-tracing with a commercial tool, Computer Simulation Technology (CST) Microwave Studio. Numerical results of the hybrid model have been compared with those of a full wave rigorous solver for FSS small in wavelength terms. Good agreement has been achieved with substantially increased computation efficiency, which validates the recommended hybrid method for this class of applications.

Ultra-wide bandwidth communication channel analysis using 3-D ray tracing

A true 3-D ray tracing model has been developed for UWB propagation in a typical modern office. A time domain approach is used to determine all dominant paths by which radiation radiates from a transmitter to a receiving site. The number of rays that have to be considered can then be dramatically reduced for subsequent analyses. The properties of received power and delay spread as well as angle of arrival are presented. Each dominant path could then be represented by a function with these properties. Predictions of received waveform are produced by convolving a typical input UWB pulse with these functions. Hence, different input pulse characteristics can be applied to the transmit antenna and the receiver characteristics rapidly evaluated. The model also gives the transmission direction for each successful ray, which is difficult to measure in reality but essential to build the smart antenna.

The discone antenna in a BPSK direct-sequence indoor UWB communication system

The current ultra-wideband (UWB) channel models proposed by different research groups are generally based on measurements in which the effect of the antennas used are inevitably embedded. There is potentially significant waveform distortion by UWB antennas, and it is difficult to distinguish between antenna and real propagation path effects in many of the reported channel measurements. However, understanding these effects is important for overall system performance prediction. The discone antenna is known for its broadband characteristics and has been widely used for channel measurements. In this paper, we address the importance of the antenna and indoor propagation effects as applied to a UWB system analysis. This is achieved by use of a true time-domain three-dimensional ray-tracing propagation model coupled with accurate simulation of the time-domain performance of the discone antenna. A DS-UWB system approach was adopted for detailed study and its performance is evaluated under the channel model with and without considering the antenna pattern effect. Both line-of-sight and non-line-of-sight cases are considered. The antenna effect can be seen to be significant, leading to the conclusion that interpretation of practical system measurements must allow for the antennas being used in the measurement system.

Bunny Ear Combline Antennas for Compact Wide-Band Dual-Polarized Aperture Array

A bunny ear shaped combline element for dual-polarized compact aperture arrays is presented which provides relatively low noise temperature and low level cross polarization over a wide bandwidth and wide scanning angles. The element is corrugated along the outer edges between the elements to control the complex mutual coupling at high scan angles. This produces nearly linear polarized waves in the principle planes and lower than -10 dB cross polarization in the intercardinal plane. To achieve a low noise temperature, only metal conductors are used, which also results in a low cost of manufacture. Dual linear polarization or circular polarization can be realized by adopting two different arrangements of the orthogonal elements. The performances for both mechanical arrangements are investigated. The robustness of the new design over the conventional Vivaldi-type antennas is highlighted.

RCS and radar propagation near offshore wind farms

The wind farm impact on marine radars has not been widely reported. Some past publications have touched on the subject but there has been no accurate model in place to readily examine the effects of different farm geometries, tower shapes and turbine sizes. This paper discusses the radar propagation modeling near offshore wind farms including the methods used to model individual turbine mono and bi-static RCS, and the multiple reflections of radar signals within the wind farm. An initial qualitative comparison between the results of the model and measured data is provided.