Development of a fractional loop antenna in front of a 60o corner reflector

Abstract

The level of shielding of the enclosure in preventing EMI is usually determined through the Shielding Effectiveness (SE) measurements of the material used for the enclosure. Standard field simulation is the starting point of any SE measurement technique. Thus, it is necessary for an antenna which could simulate standard EM waves. In this research work, a Hexad-Loop (H-Loop) antenna has been proposed to simulate standard EM wave for magnetic-field shielding effectiveness measurement of the planar sheet. In making the H-loop antenna, one sixth of the loop is mounted on a 60° corner reflector to produce the effect of magnetic dipole in a confined region. The imaging of the reflector transforms the H-loop virtually into a complete loop which means the H-loop acts as a magnetic dipole isolated from the complete loop. This is a magnetic dipole located in a quasi-shielded test environment which produces typical low impedance field. This is particularly important in the measurement of magnetic field SE against EMI. The mathematical model of the H-loop antenna has been developed by using the image theory and the theory of pattern multiplication. Analytically, the field due to the arc (one sixth of the loop) is to be calculated first and then applying image theory considering the images of the arc. The effect of these images on the field of the original H-loop are then superimposed by a method similar to pattern multiplication. The radiation patterns of the H-loop antenna in the horizontal plane is measured by using the two H-Loop antenna (one acts as a transmitting antenna while the other acts as a receiving antenna). Measured radiation pattern is found identical with the theoretical pattern. The antenna parameters such as, directivity, gain, and radiation efficiency of the H-Loop antenna are compared with those of the Q-Loop and complete loop antenna. Comparison shows that, both the directivity and gain of the H-Loop antenna are much higher than those of the existing antenna. It is also found that the gain and radiation efficiency of the H-Loop antenna become constant at a frequency above 100MHz. This means that the developed antenna can be treated as a frequency independent antenna above 100MHz.