Johnson J. H. Wang

An examination of the theory and practices of planar near-field measurement

Using computer simulation, several fundamental issues in planar near-field measurement are examined. The results indicate that some of the prevailing views of practices regarding the evanescent modes, the sampling and filtering of data, and the selection of the location and directivity of the probe are incomplete or misleading. In particular, the merits of using smaller low-directivity probes in conjunction with a closer probe-to-antenna distance have been found to be unduly overlooked. >

Design of multioctave spiral-mode microstrip antennas

The design of spiral-mode microstrip antennas with a bandwidth of 6:1 is demonstrated. The antenna has a small dissipative loss due to a resistive loading outside its active region. As a specific measure of bandwidth at microwave frequencies, the spiral-mode microstrip antenna gain is higher than that of the conventional loaded-cavity spiral over a 5:1 and if the spacing d between the microstrip and the ground plane is 0.25 in. or larger over the 2-12 GHz range. Cursory efficiency calculations show consistent improvement over a loaded-cavity spiral. A study of ground plane spacing showed that the antenna gain remains above the conventional spiral gain as d is reduced until it is as small as 0.1 in. >

The magnetically coated conducting surface as a dual conductor and its application to antennas and microwaves

An electric conducting surface coated with a thin, lossy magnetic layer has been both theoretically and experimentally observed to be equivalent to a surface that is conducting to both electric and magnetic fields of plane waves at near-grazing incidence angles. This dual conductivity phenomenon has been utilized to design horn antennas for desired performance characteristics such as symmetric beams, low sidelobes, and low cross polarization. The effects of this surface are in many ways similar to those of the corrugated conducting surface. However, this coated surface appears to have a broader spectrum of applications in other antennas and microwave devices because of its apparent dual (electric and magnetic) conductivity. >

Design and performance of the magnetic hybrid-mode horn

Design techniques are presented for a class of circular magnetic hybrid-mode (MHM) horns together with experimental results. In comparison with earlier techniques, this design method is simpler and more amenable to physical interpretation. The horns designed exhibit performance comparable to that of the corrugated horn except that they have an ohmic loss of 0.8 to 2.7 dB. However, it appears feasible to reduce the gain loss to less than 1 dB. >

Computation of electromagnetic fields in large biological bodies by an iterative moment method with a restart technique

The computation of electromagnetic (EM) fields in a large, three-dimensional arbitrarily shaped dielectric or biological body is made practical by a conjugate gradient algorithm with a restart technique. This algorithm allows the operator to run the program for large bodies in a measured and controlled manner, minimizing the computing cost and avoiding the crashes inherent in an extended computer run. It is shown that in achieving convergence, a good initial guess plays only a very minor role while the G/sup (n)/ and A/sup (n)/ functions are crucial to the convergence in the conjugate gradient algorithm and must be included in the restart. >