A study of the loop as a compact antenna

This thesis examines the suitability of the loop antenna for use as a compact radiating element. The current distribution, as derived from the loop equation by previous authors, is used to derive a theoretical radiation efficiency of the electrically large loop antenna. The theoretical input impedance is used to calculate the quality factor and bandwidth of the tuned loop antenna and a suitable impedance matching technique is presented to attain this bandwidth. Several loop antennas were constructed, and a Wheeler cap was used to measure the radiation efficiency of these antennas. This measured radiation efficiency is shown to agree reasonably well with the theoretically predicted values. Finally, the detailed design of a loop antenna for use in a compact wireless tag operating at 915MHz is presented. A prototype version of the antenna was build and tested, and the measurements are shown to agree well with numerical simulations.