Low Profile Spiral on a Thin Ferrite Ground Plane for 220–500 MHz Operation

A small size, low profile spiral antenna (2" thick and 14" in aperture) is described that is backed by a thin ferrite ground plane. The antenna is intended to cover Satellite (UHF TacSat earth to LEO: 243-318 MHz) and enhance Radio (PRC-148, PRC-117F, PSC-5D: 243-512 MHz) communications. We carry out a step-by-step design to achieve the challenging goals of RHCP gain >0 dBi at θ = 0°; Bandwidth 220-500 MHz; VSWR <;2:1; Low LHCP (cross-pol) gain (<; -10 dBi); Low profile (2") and desired aperture size 14". Ground plane ferrite treatment, inductive loading, resistive termination and impedance matching techniques are adopted to raise the gain between 200-300 MHz and achieve the stated goals. As the aperture size is about λ/3.5 at 220 MHz and only λ/30 in height, achieving 0 dBi (from 220-500 MHZ) is quite challenging. Measured and simulated data are presented in the last section leading to impressive conclusions about the capability of the magnetic material coating to overcome the perennial issue associated with the ground plane's negative effects.