Farshad Keshmiri

Design of Compact Dual Band High Directive Electromagnetic Bandgap (EBG) Resonator Antenna Using Artificial Magnetic Conductor

A compact high directive EBG resonator antenna operating in two frequency bands is described. Two major contributions to this compact design are using single layer superstrate and using artificial surface as ground plane. To obtain only the lower operating frequency band using superstrate layer is enough, but to extract the upper operating frequency band both superstrate layer and artificial surface as ground plane are necessary. Therefore, design of a superstrate to work in two frequency bands is very important. Initially, using appropriate frequency selective surface (FSS) structure with square loop elements, we design an optimum superstrate layer for each frequency band separately to achieve maximum directivity. Also, to design an artificial surface to work in the upper frequency band we use a suitable FSS structure over dielectric layer backed by PEC. Next, by using the idea of FSS structure with double square loop elements we propose FSS structure with modified double square loop elements, so that it operates in both of the desired operating frequency bands simultaneously. Finally, the simulation results for two operating frequency bands are shown to have good agreement with measurements.

A Body Area Propagation Model Derived From Fundamental Principles: Analytical Analysis and Comparison With Measurements

Using wireless sensors worn on the body to monitor health information is a promising new application. To realize transceivers targeted for these applications, it is essential to understand the body area propagation channel. Several numerical, simulated, and measured body area propagation studies have recently been conducted. While many of these studies are useful for evaluating communication systems, they are not compared against or justified by more fundamental physical models derived from basic principles. This type of comparison is necessary to provide better physical insights into expected propagation trends and to justify modeling choices. To address this problem, we have developed a simple and generic body area propagation model derived directly from Maxwells equations revealing basic propagation trends away, inside, around, and along the body. We have verified the resulting analytical model by comparing it with measurements in an anechoic chamber. This paper develops an analytical model of the body, describes the expected body area pathloss trends predicted by Maxwells equations, and compares it with measurements of the electric field close to the body.

An Analytical Modeling of Polarized Time-Variant On-Body Propagation Channels with Dynamic Body Scattering

On-body propagation is one of the dominant propagation mechanisms in wireless body area networks (WBANs). It is characterized by near-field body-coupling and strong body-scattering effects. The temporal and spatial properties of on-body channels are jointly affected by the antenna polarization, the body posture, and the body motion. Analysis on the time variant properties of on-body channels relies on a good understanding of the dynamic body scattering, which is highly dependent on specific scenarios. In this paper, we develop an analytical model to provide a canonical description of on-body channels in both time and space domains to investigate the on-body propagation over the trunk surface of a walking human. The scattering from the arms and the trunk in different dimensions is considered with a simplified geometrical description of the body and of the body movements during the walk. A general full-wave solution of a polarized point source with multiple cylinder scattering is derived and extended by considering time evolution. The model is finally validated by deterministic and statistical comparisons to different measurements in anechoic environments.

Design of dual-band low profile high directive EBG resonator antenna, using single layer frequency selective surface (FSS) superstrate

In this paper, we present a novel design of a dual-band high directive EBG resonator antenna that utilizes a single layer frequency selective surfaces (FSS) as a superstrate. In this study we use a special configuration of square loop-array to design the FSS superstrate layer. We obtain the different operating frequencies by adjusting the distance of FSS from printed patch antenna and also the perimeter of square loops. The proposed structure presents more than 18 dBi directivity enhancement at 11.25 GHz and 13.15 GHz as compared to those of a patch antenna with 6 dBi directivity

Moment-Method Analysis of Normal-to-Body Antennas Using a Green's Function Approach

The cylindrical wave decomposition of fields from a normal-to-cylinder point source is derived using a modified addition theorem. The fields scattered from a lossy cylinder, as an approximation of the human body, are also calculated and tabulated for use in an integral equation study of dipoles. The transmittance between two optimized radially polarized dipoles is evaluated on the body trunk surface, using the method of moments (MoM) in the 2.45 GHz ISM band. An anechoic chamber measurement is performed and the measured transmittance between two dipoles on the human body has been compared to the simulated one on the lossy cylinder. Although the abdominal cross section of the body does not have exactly a circular shape, strong similarities have been observed in their path-loss trends around the body. A very good agreement has been obtained between the dipoles transmittances provided by the analytical/MoM model, CST Microwave Studio simulations, and experiments, including interference effects attributed to the body-attached radiating waves.

Design of a UWB antenna with stabilized radiation pattern

The UWB circular disc monopole (CDM) antenna has been previously used for positioning applications. But at higher frequencies, its pattern does not remain omnidirectional in azimuth and it tends to shift upward. We propose new structures for both monopole radiator and ground plane to yield an antenna with a stabilized radiation pattern. Comparing the main lobe characteristics of the proposed and CDM antenna shows that the proposed one radiates in the horizon plane with enhanced electric field at higher frequencies. All root-mean-square differences for S11 and S21 for MOM simulation and measured results are around 3 dB between 1 to 10 GHz, which is a reasonable value.

Amplitude Distribution Synthesize of Unequally Spaced Arrays

In this paper, we study two different methods, called Legendre and LMS, to find the current distribution of an unequally spaced array structure. In both methods, we aim to find the most similar radiation pattern to a desired one toward an arbitrary angle and then show the ability of LMS method to provide the low SLL (Side Lobe Level) comparing to Legendre method due to its better performance for minimizing error.

Testbed for IR-UWB based ranging and positioning: Experimental performance and comparison to CRLBs

In this paper we describe a testbed for impulse radio ultra wideband based ranging and positioning. We show the characteristics of the generated, transmitted and received pulses. We consider both the maximum likelihood estimator and a threshold-based estimator for the estimation of the time of arrival. We measure the variances for ranging and positioning and compare them to the Cramer-Rao lower bounds for range and position estimation. We discuss the impact of both false multipath component detection and false sidelobe detection on the estimation accuracy. The obtained variances are close to the Cramer-Rao lower bounds when the mainlobe of the first multi-path component is detected. In realistic multipath environments we can use a threshold-based time of arrival estimator in order to detect the first multipath component which may be missed by the maximum likelihood estimator. We show also that the errors on positioning due to false multipath component and sidelobe detection can be highly mitigated by increasing the number of receivers. For a radiated energy of 8.1 pJ and a distance of 5 meters between the transmit and receive antennas, the obtained accuracy is in the order of one centimeter.

A Green's function approach for analysis of body-area-network antennas

In this paper we develop a Method of Moment (MOM) formulation in order to find the current distribution and also total radiated electric fields due to a half-wavelength dipole antenna, oriented parallel to a lossy cylinder. We insert the Greens function of the lossy cylinder in the MOM code to consider its effects in the calculation of total current and fields.

3-D body scattering interference to vertically polarized on-body propagation

In this paper, we developed an analytical model of vertically polarized on-body propagation to describe the body scattering interference to the on-body channels. The 3-D dimension scattering from the trunk and arms by a point source are considered. Measurements results in an anechoic chamber at 2.45 GHz are also presented to validate the model.