Single-Layer and Bilayer Four-Arm Mode 1 Spiral Antennas and Their Feed Structures

摘要

Single-layer and bilayer four-arm spiral antennas and their feeding methods for Mode 1 operation are discussed in this article. Important design parameters such as metal-to-slot ratio and growth rate for better impedance matching and reduced far-field contamination are studied. Three feeding methods for Mode 1 operation are compared: a bundle of four coaxial cables for a single-layer spiral and vertical and horizontal feeds by two coaxial cables for bilayer spirals. It is shown that the single-layer spiral maintains beam symmetry with Wobble on Wave better than 1 dB at 6 = 30° over 10:1 bandwidth. However, the required beamformer is complex and expensive. Proposed, horizontally and vertically fed bilayer spirals need simpler beamformer while maintaining similar far-field performance over narrower 6:1 and 2:1 band widths, respectively, thus making them useful for many wideband applications. Modeling is conducted by a method of moments and validated with a finite element method and measurements.