TABLE OF CONTENTS Glenn S. Smith
Georgia Institute of Technology
The single-turn loop antenna is a metallic conductor bent into the shape of a closed curve, such as a circle or a square, with a gap in the conductor to form the terminals. A multiturn loop or coil is a series connection of overlaying turns. The loop is one of the primary antenna structures; its use as a receiving antenna dates back to the early experiments of Hertz on the propagation of electromagnetic waves.1
The discussion of loop antennas is conveniently divided according to electrical size. Electrically small loops, those whose total conductor length is small compared with the wavelength in free space, are the most frequently encountered in practice. For example, they are commonly used as receiving antennas with portable radios, as directional antennas for radio-wave navigation, and as probes with field-strength meters. Electrically larger loops, particularly those near resonant size (circumference of loop/wavelength ? 1), are used mainly as elements in directional arrays.
The following symbols are used throughout the chapter:
| ? = | wavelength in free space at the frequency f = ?/2 ?, when the complex harmonic time-dependence exp ( j ?t) is assumed |
| ? = | 2 ?/ ? = propagation constant in free space |
| ? = | |
| b = | mean radius of a circular loop or mean side length of a square loop |
| a |
