Search

A theoretical and an experimental study of the electromagnetic scattering from a perfectly conducting thin wire of V shape illuminated by a plane wave at an arbitrary incidence is presented. The distribution of current on the wire is first determined by a method of moments with the aid of a computer program WIRANT (developed by Walter L. Curtis of The Boeing Company). The scattered field and backscattering cross section are then obtained by standard techniques. Numerical calculations include the backscattering cross sections for the case of h = \lambda/2 and \lambda (where h is arm length and \lambda is wavelength) as a function of incidence angle \phi with enclosed angle \theta as a parameter. To check the accuracy of the theory, an experiment is conducted inside an anechoic chamber, using the conventional method of cancellation. The frequency used in the experiment is 9.8 GHz. A number of experimental models were constructed of a copper wire of a circular cross section with a diameter d = 0.025". The agreement between theory and experiment is, in general, very good. The results of this investigation provide an insight into the coupling effect between the halves of wire when viewed as two-coupled wires.

A study of the field distribution in a square aperture on a plane conducting screen illuminated by a plane electromagnetic wave at normal incidence is presented. In solving the problem, the square aperture is first formulated into a complementary square plate scattering problem. The distribution of current on the plate is then found by solving the corresponding wire mesh model with the aid of a computer program for linear wire antennas. A simple averaging process is then introduced in a straightforward manner to convert the currents flowing along the wires into continuously distributed equivalent surface currents on the square plate. The surface current density is, in turn, equal to the value of magnetic field intensity by the boundary condition for a perfect conductor. Finally, a direct application of the electromagnetic form of Babinet's principle gives the electric field distribution of the aperture. The far zone field in terms of a radar cross section of a square plate compares well with an experiment. A discussion is also included comparing the electric field distribution of a square aperture and circular apertures.

A study on the backscattering from two identical perfectly conducting thin circular loops illuminated by a plane electromagnetic wave with vertical polarization at normal incidence is presented. The theory is developed based on differential equations for the loop current rather than on an integral equation method. The induced current on the loops and the backscattering cross sections of the loops are determined, and comparisons are made between the calculated and measured values of the echo area. The experimental results are in good agreement with theory.