Electronically tunable magnetic patch antennas with metal magnetic films

Introduction: Patch antennas on ferrites substrates showed tunable radiation frequency, polarisation diversity, and beam steering [1]. In addition, it was recently demonstrated that patch antennas on a selfbiased ferrite-dielectric composite substrate showed a miniaturisation factor of > 5, a 600% enhanced bandwidth and a high efficiency at a resonance frequency of 277 MHz [2]. The introduction of magnetic materials into dielectric patch antenna substrates leads to enhanced substrate permeability, and an improved intrinsic impedance of the medium (Z 1⁄4 ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi m0mr=e0er p ) that better matches that of free space. The better impedance match results in enhanced bandwidth and efficiency of the patch antennas. Traditionally ferrites have been the default magnetic materials for antenna applications [1, 2]. However, the large loss tangents of the available self-biased ferrite materials (without applied magnetic bias field) severely limited their application frequencies to 500 MHz or less. Metal magnetic films have high saturation magnetisation values of up to 24 kG and self-biased ferromagnetic resonances at several GHz [3, 4]. In addition, metal magnetic films with narrow ferromagnetic resonance linewidth comparable to those of ferrites, and high squareness (remnance ratio Mr=Ms) of 100% [3, 4] were reported, making it possible to achieve self-biased magnetic patch antennas up to several GHz. Further, metal magnetic films and the associated fabrication technologies are low temperature processes compatible to MMIC technologies. In this Letter, we report a new type of electronically tunable magnetic patch antennas with metal magnetic films being designed, fabricated, and tested at 2.1 GHz, exhibiting enhanced performances.