Panayiotis A. Tirkas

Finite-difference time-domain method for antenna radiation

The finite-difference time-domain (FDTD) method is used to model and predict the radiation patterns of wire and aperture antennas of three basic configurations. A critical step in each is the modeling of the feed. Alternate suggestions are made and some are implemented. The first antenna is a quarter-wavelength monopole and the second is a waveguide aperture antenna. In both bases the antenna is mounted on ground planes, either perfectly conducting or of composite material. The results obtained using the FDTD technique are compared with results obtained using the geometrical theory of diffraction (GTD) and measurements. The third configuration of interest is a pyramidal horn antenna. To model the flared parts of the horn, a staircase approximation was applied to the antenna surface. The computed radiation patterns compared well with measurements. >

Folded loop antenna for mobile hand-held units

The vertical folded loop antenna, modeled as wire and printed radiating element mounted on a conducting box, simulating a cellular telephone with and without dielectric coating, is analyzed. The finite-difference time-domain (FDTD) method is used to calculate radiation patterns and input impedance. The results are compared with measurements and with NEC data. Very good agreement is obtained in all cases. Parasitic loading is used to enhance the bandwidth of the printed element. The antenna meets the design requirements for existing and future mobile communication systems.

Higher order absorbing boundary conditions for the finite-difference time-domain method

Higher-order absorbing boundary conditions are introduced and implemented in a finite-difference time-domain (FDTD) computer code. Reflections caused by the absorbing boundary conditions are examined. For the case of a point source radiating in a finite computational domain, it is shown that the error decreases as the order of approximation of the absorbing boundary condition increases. Fifth-order approximation reduces the normalized reflections to less than 0.2%, whereas the widely used second-order approximation produces about 3% reflections. A method for easy implementation of any order approximation is also presented. >

The finite-element method for modeling circuits and interconnects for electronic packaging

A full-wave finite-element method (FEM) is formulated and applied in the analysis of practical electronic packaging circuits and interconnects. The method is used to calculate S-parameters of unshielded microwave components such as patch antennas, filters, spiral inductors, bridges, bond wires, and microstrip transitions through a via. Although only representative microwave passive circuits and interconnects are analyzed in this paper, the underlined formulation is applicable to structures of arbitrary geometrical complexities including microstrip and coplanar-waveguide transitions, multiple conducting vias and solder bumps, multiple striplines, and multilayer substrates. The accuracy of the finite-element formulation is extensively verified by calculating the respective S-parameters and comparing them with results obtained using the finite-difference time-domain (FDTD) method. Computational statistics for both methods are also discussed.

Finite-difference time-domain method for electromagnetic radiation, interference, and interaction with complex structures

The finite-difference-time-domain (FDTD) method is reviewed and then used to model and predict the radiation patterns of a monopole antenna mounted on the bottom of a perfectly conducting helicopter structure. The computed radiation patterns are compared with measurements to demonstrate the accuracy of the FDTD method. To study the effect of antenna interference, a second monopole antenna is mounted on the structure and the patterns are recalculated. The perfectly conducting helicopter model is then replaced by a partially composite/partially conducting material structure and the electromagnetic fields penetrating the structure from an incident plane wave are analyzed. A preprocessing geometry program, GEOM, is used to generate an FDTD geometry model, assuming solid surface helicopter structure. >

A comparison of the Berenger perfectly matched layer and the Lindman higher-order ABC's for the FDTD method

Higher-order absorbing boundary conditions are compared to the recently introduced Berenger perfectly matched layer (PML) absorbing boundary conditions (ABC). Reflections caused by the ABCs are examined in both the time and frequency domains for the case of a line source radiating in a finite computational domain. It is shown that the PML ABC significantly reduces reflections from the truncation of the computational grid when compared to 7th order Lindman ABCs. Also, except for at low frequencies, higher-order absorbing boundary conditions are no better than 2nd order Mur absorbing boundaries. >

Propagation model for building blockage in satellite mobile communication systems

A propagation model for building blockage in satellite mobile communication systems is developed. This model characterizes the signal transmitted from a low-Earth orbiting (LEO) satellite when there is an obstruction in the path of the signal. The obstruction is assumed to be a man-made structure. The analysis is performed using the uniform theory of diffraction (UTD). Using this method, both single and double diffractions from the structure edges were included. Direct and reflected rays from the ground and building were also included, whenever the satellite signal was not completely obstructed. The satellite is assumed to be moving along a circular orbit while the receiver is stationary. The normalized signal level (in decibels) and the signal attenuation rate (in decibels per second) are computed. Such information is considered very useful in developing the mobile systems hand-off algorithm.

Folded loop antenna for mobile communication systems

There has been tremendous world-wide activity aimed at developing mobile communication systems. The growing market demand generates interest in the performance of compact antenna structures mounted on portable devices. Some of the desired features for these antennas include low profile geometry, ease of construction, low cost, attractive appearance, and omnidirectional radiation pattern on the azimuthal plane. This paper presents the radiation characteristics of a new antenna, the folded loop mounted vertically on a conducting box with and without a dielectric coating, to simulate a handheld portable telephone. The radiation patterns and input impedance are determined by computer simulations based upon the FDTD and verified with measurements and computations performed using NEC.

Finite-difference time-domain analysis of HF antennas on helicopter airframes

In this paper, the finite-difference time-domain (FDTD) method with the Berenger perfectly matched layer (PML) absorbing boundary condition (ABC) is used to model the radiation characteristics of high frequency (HF) antennas operating in the 2-30 MHz range on a full-scale helicopter. The computed input impedance of both antennas is compared with actual measurements from an operational full-scale helicopter and also with measurements on a scale model NASA generic advanced attack helicopter (GAAH). To study the coupling effects of the helicopter fuselage on the antenna systems, the S-parameters are computed and compared with measurements on the NASA GAAH scale model. Finally, computed gain patterns are compared with actual in-flight measurements of the antenna systems on an operational full-scale helicopter.

Contour path FDTD method for analysis of pyramidal horns with composite inner E-plane walls

The contour path finite-difference time-domain (FDTD) method is used for modeling pyramidal horn antennas with or without composite E-plane inner walls. To model the pyramidal horn surface, a locally distorted grid is used. Modified equations are obtained based on the locally distorted grid and the assumptions of the contour path method. The developed algorithm is validated by comparing computed antenna gain patterns, with and without the presence of composite material, with available measurements. >