Analysis of Archimedean Spiral Slot Antennas in Infinite Ground Planes Using the Theory of Characteristic Modes

Abstract

The analysis of Archimedean spiral slots using the theory of characteristic modes is presented in this article. Purely magnetic characteristic modes are used to study the behavior of a spiral slot etched in an infinite ground plane. The effect of the spiral geometry parameters (slot width, separation between spiral slot arms, number of spiral turns, and inner spiral spacing) on the characteristic modes are investigated using the theory of characteristic modes. Based on the results of the characteristic mode analysis, guidelines are presented for selecting the appropriate slot dimensions for realizing a compact spiral slot assembly (miniaturization), multimode behavior and for improving the bandwidth of the purely magnetic characteristic modes. Additionally, analytical equations are presented for accurately predicting the resonant frequencies of the purely magnetic characteristic mode of the spiral slot antenna.

Keywords

• Characteristic modes
• magnetic modes
• modal analysis
• planar antenna
• slot antenna
• spiral antenna