THE NORMAL MODES OF CAVITY ANTENNAS
Abstract
The resonance properties of small cavity antennas were investigated by studying their normal modes. The concept of q is discussed and defined in terms of the complex frequency. An equivalence theorem is developed which states that the field in a source-free region is equivalent to that produced by a double layer of surface currents, electric currents J = H x n, and magnetic currents K = n x E, where n is the outward normal. In addition to the boundary values, the inclusion of initial values is necessary if the boundary values are not known for all past times. The behavior of waves with a complex exponential time dependence is analyzed. A theoretical treatment is presented of the normal modes of radiating cavities. An arbitrary cavity opening into a half-space is considered, and by a variational method a stationary formula for the complex frequencies (eigen-values) is obtained. In the cavity modes. The first normal mode of a square wave-guide cavity was calculated. The results are given of measurements on 3 square wave-guide cavity antennas. The antennas had 1/a values of 7.7, 2.0, and 0.4, with corresponding epsilon sub r (dielectric constant) values of 3.80, 3.88, and 8.41. The first 6 modes of the first antenna were measured, 4 modes of the second were measured, and only the first mode of the last was measured. The measured resonance frequencies agreed with those calculated within a few per cent. The values of Q did not agree as closely, but the agreement was generally within 30%.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1952
- Accession Number
- AD0001246
Entities
People
- Marshall H. Cohen
Organizations
- Ohio State University