Learn More
A reconfigurable aperture (RECAP) antenna is described in which a planar array of electrically small, metallic patches are interconnected by switches. The antenna can be reconfigured to meet different performance goals by changing the switches that are open and closed. The switch configuration for a particular goal is determined using an optimizer, such as(More)
The analysis of a group of three simple antennas is used to illustrate the accuracy of the FDTD (finite-difference time-domain) method and to show that various geometrical features are handled correctly by the method. Each antenna is a well-posed electromagnetic boundary value problem that corresponds to a realizable experimental model. The three antennas(More)
The basic TEM horn antenna consists of two identical triangular plates meeting at an apex of each. The angular width of each plate is /spl alpha/, and the angular separation between the plates is /spl beta/. The length of each plate (as measured along the side) is s. A key parameter is the characteristic impedance, Z/sub c/, of the spherical TEM wave on the(More)
Some time ago, Carrel presented an analytical formula, based on conformal mapping, for the characteristic impedance of the transverse electromagnetic horn antenna . Later, results from this formula were shown to be in error, and Lambert et al. offered a new analytical formula, also based on conformal mapping . This formula also contains an error that is(More)
  • G Smith
  • IEEE Transactions on Antennas and Propagation
  • 2004
In this paper, a single-antenna reciprocity relation is derived for the time domain. First, the antenna is considered on transmission; next, the same antenna is considered when it is receiving an incident plane wave. The two states, transmission and reception, are related by the application of a modified form of the reciprocity theorem for electromagnetic(More)
A total-field/scattered-field (TF/SF) plane-wave source is developed for the finite-difference time-domain analysis of general (possibly lossy) planar layered media. A 1-D auxiliary grid is created to generate the incident field in the presence of the layered medium. Inhomogeneous plane waves are also allowed for lossless layers and narrowband excitation.
A well-known problem with convergence that detracts from the theory for the thin-wire circular-loop antenna is eliminated by using a more realistic model for the excitation, one that corresponds more closely to an actual method of excitation for the loop than does the delta-function. The input admittances of several half-loop antennas were measured as a(More)
Ground penetrating radar (GPR) systems are electromagnetic systems used in detecting objects buried in the Earth. The U.S. Army is investigating a particular GPR, a separated aperture sensor, as a method for detecting buried land mines. The sensor consists of transmitting and receiving dipole antennas housed in corner reflectors and separated by a metallic(More)
A Fresnel zone plate is designed to perform the function of a doubly-hyperbolic lens. The focusing characteristics of the zone plate and the lens are compared using both measured data and body-of-revolution finite-difference time-domain simulations. The results from this comparison are used to evaluate the use of zone plates as focusing elements in a(More)
The authors demonstrate an approach that is an effective, noninvasive means of measuring surface current distributions. Some guidelines for making the measurements are given, and results from an actual measurement are presented. For example, it is shown that the magnetic field components have better measurement characteristics than the electric field(More)