Sergey N. Makarov

A Low-Multipath Wideband GPS Antenna With Cutoff or Non-Cutoff Corrugated Ground Plane

We compare the performance of the classic global positioning system (GPS) choke ring ground plane with a new shallower design. Both the choke ring and the new ground plane are here designed to operate uniformly between 1.15 GHz and 1.60 GHz while maintaining the required low-multipath performance in the whole bandwidth. To achieve reception in this wide range of frequencies, the radiating element chosen is a droopy bowtie turnstile. A classic choke ring is composed of deep concentric rings on a flat circular metal ground plane. We have modeled the choke ring as a metal corrugated surface of depth d such that lambda/4lesdleslambda/2 , operating at cutoff: the multipath suppression (i.e., the proper RHCP/LHCP pattern shaping) is obtained by eliminating the surface wave on the ground plane in a certain frequency band. When shallower concentric rings of depth dleslambda/4 are used, the corrugated surface operates at non-cutoff: the required multipath rejection can be achieved by cancellation (destructive interference) rather than suppression of surface waves. The comparisons performed in this study include theory, numerical simulations, and hardware tests. Our results show that both configurations, when properly optimized, are good candidates for reception of modernized GPS, GLONASS, and GALILEO satellite signals from GPS permanent stations.

Method of moments solution for a printed patch/slot antenna on a thin finite dielectric substrate using the volume Integral equation

In this paper, a volume integral equation (VIE)-based modeling method suitable for a patch or slot antenna on a thin finite dielectric substrate is developed and tested. Two new key features of the method are the use of proper dielectric basis functions and proper VIE conditioning, close to the metal surface, where the surface boundary condition of the zero tangential E -component must be extended into adjacent tetrahedra. The extended boundary condition is the exact result for the piecewise-constant dielectric basis functions. The latter operation allows one to achieve a good accuracy with one layer of tetrahedra for a thin dielectric substrate and thereby greatly reduces computational cost. The use of low-order basis functions also implies the use of low-order integration schemes and faster filling of the impedance matrix. For some common patch/slot antennas, the VIE-based modeling approach is found to give an error of about 1% or less in the resonant frequency for one-layer tetrahedral meshes with a relatively small number of unknowns. This error is obtained by comparison with fine finite-element method (FEM) simulations, or with measurements, or with the analytical mode matching approach. Hence it is competitive with both the method of moments surface integral equation approach and with the FEM approach for the printed antennas on thin dielectric substrates.

Comparison of TOA and RSS based techniques for RF localization inside human tissue

Localization inside the human body using radio frequency (RF) transmission is gaining importance in a number of applications such as Capsule Endoscopy. The accuracy of RF localization depends on the technology adopted for this purpose. The two most common RF localization technologies use received signal strength (RSS) and time-of-arrival (TOA). This paper presents a comparison of the accuracy of TOA and RSS based localization inside human tissue. Analysis of the propagation of radio waves inside the human body is extremely challenging and computationally intensive. We use our proprietary finite difference time domain (FDTD) technique algorithm reported in [1] to simulate waveform transmissions inside the human body, which is almost 60 times faster than commercially available solvers used for similar purposes. The RSS and TOA of the waveforms are extracted for localization and the accuracies of the two methods are compared. The accuracy of each technique is compared with traditional CRLB commonly used for calculation of bounds for the performance of localization techniques.

Electromagnetic visualization technique for non-metallic inclusions in a melt

The detection of inclusions in hot melts is of great importance to the manufacturing process as every aspect of quality is affected by the presence of second phases. However, the major dilemma is how to quantitatively determine the level of inclusions. In this paper, we present a theoretical model and preliminary experimental results of a Lorentz-force-based detection system to monitor small inclusions of micron size. The developed technique potentially has a better resolution performance than other on-line methods. The application area includes hot melts of metals and other highly conductive non-transparent fluids. Low-temperature modelling with liquid gallium was used to prove the measurement concept.

A Lumped Circuit for Wideband Impedance Matching of a Non-Resonant, Short Dipole or Monopole Antenna

A new technique is proposed for wideband impedance matching of short dipole- or monopole-like antennas in the VHF-UHF bands. Instead of constructing the network topology for every particular antenna, we propose a simple network of one fixed topology. This network is an inductive L-section cascaded with a high-pass T-section. The network includes five discrete components-three inductors and two capacitors. Although the approach is not general, the paper proves that matching with the present network is close to the theoretical limit impedance matching confirmed by Bode-Fano theory. The matching performance also approaches the performance of the Carlins equalizer for short dipoles and monopoles. The dipoles and monopoles may have different shape and different matching bandwidths. By using the matching circuit of fixed topology we avoid greater difficulties related to the practical realization of the Carlins equalizer. The key point is to minimize the antennas matching network complexity (and loss) so that the circuit can be designed and constructed in a straightforward manner.

New VHP-Female v. 2.0 full-body computational phantom and its performance metrics using FEM simulator ANSYS HFSS

Simulation of the electromagnetic response of the human body relies heavily upon efficient computational models or phantoms. The first objective of this paper is to present a new platform-independent full-body electromagnetic computational model (computational phantom), the Visible Human Project® (VHP)-Female v. 2.0 and to describe its distinct features. The second objective is to report phantom simulation performance metrics using the commercial FEM electromagnetic solver ANSYS HFSS.

Suspended Ring Resonator for Dielectric Constant Measurement of Foams

The present study introduces a microstrip-based resonant device that is specifically intended for measurements of polymer foam permittivity at frequencies of 1 to 10 GHz. The device utilizes the standard microstrip ring resonator. However, the ring and the ground plane/feed network are physically located in separate planes, enabling the placement of an arbitrary sample of material to be measured in the substrate of the ring resonator. A transmission line model is developed and tested in order to predict the frequency response of the circuit. Experimental data is reported and compared with theory. The measurements indicate a high potential resolution of the method

Continuous Wave Simulations on the Propagation of Electromagnetic Fields Through the Human Head

Characterizing the human head as a propagation medium is vital for the design of both on-body and implanted antennas and radio-frequency sensors. The following problem has been addressed: find the best radio-frequency path through the brain for a given receiver position - on the top of the sinus cavity. Two parameters, transmitter position and radiating frequency, should be optimized simultaneously such that 1) the propagation path through the brain is the longest; and 2) the received power is maximized. To solve this problem, we have performed a systematic and comprehensive study of the electromagnetic fields excited in the head by small on-body magnetic dipoles (small coil antennas). An anatomically accurate high-fidelity head mesh has been generated from the Visible Human Project data. The base radiator was constructed of two orthogonal magnetic dipoles in quadrature, which enables us to create a directive beam into the head. We have found at least one optimum solution. This solution implies that a distinct RF channel may be established in the brain at a certain frequency and transmitter location.

Analytical Model of the Split-Coaxial Balun and Its Application to a Linearly-Polarized Dipole or a CP Turnstile

A simple analytical transmission line model of a split-coaxial balun is proposed and tested. It is based on the coupled symmetric transmission line approach. The model leads to a closed-form analytical expression for the termination impedance/transfer function of the complete antenna system that includes antenna, balun, and a non-splitted coaxial line of certain length. It accepts the impedance of a center-fed symmetric antenna as input parameter. The model is in excellent agreement with full wave simulations and is confirmed by a series of prototype measurements. It can be applied to a linearly-polarized radiator or to a broadband circularly-polarized turnstile, where the phase quadrature is created by two complex-conjugate impedances. The present model only describes the impedance matching properties of the balun but is not capable of predicting the balance quality of baluns.

Electric Voltage Predictions and Correlation with Density Measurements in Green-State Powder Metallurgy Compacts

In this research we discuss an electrostatic measurement approach whereby electric current is injected into green-state compacts and the resulting surface voltages are recorded in an effort to determine density distributions. We present results for pure iron powder with and without lubricants compacted to various densities and their corresponding measured conductivity values, thereby clearly establishing correlation between these two entities. The electric conductivity recordings will ultimately be utilized to infer density distributions throughout the green-state P/M compact. The constant current is injected through point and aperture electrodes, and voltages are recorded along the surface of the compact. To gain confidence in the underlying physical concepts, the recorded voltages of the controlled cylindrical samples are compared with a mathematical Greens function model involving an analytical electrostatic solution of Poissons equation.