AEU - INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATIONS, vol.170, no.2023, pp.1-10, 2023 (SCI-Expanded)
In this study, two low-profile wideband spiral antennas that are backed by
Circular Artificial Magnetic Conductors (C-AMC) are proposed for V/UHF
bands. Rather than using a C-AMC design that has single resonance frequency,
different C-AMC structures that have different resonance frequencies are used
beneath corresponding active regions of spiral antenna, such that frequency
independent radiation characteristics are achieved. The C-AMC surface is designed to aim of covering the entire frequency band of antenna so that frequency
regions where reflection phase of C-AMC rings are between +90◦ and -90◦ will
follow each other. It is observed that using frequency-independent C-AMC and
a thin absorber between C-AMC and outer region of spiral antenna element
provides wideband antenna characteristics and improves axial ratio of antennas.
Proposed Antenna 1 in this paper has low-profile (0.47λ0 × 0.47λ0 × 0.055λ0)
at 300 MHz and high gain at frequencies between 300 MHz and 950 MHz. An
absorbing material is used at the inner wall of the closed cavity to improve
performance of Proposed Antenna 2 at lower frequencies. In this manner, 0 dBi
realized gain transition point is achieved at 235 MHz. Proposed Antenna 2 has
also low-profile (0.37λ0 × 0.37λ0 × 0.043λ0) at 235 MHz.