Analysis and design of low-frequency microstrip antennas

The use of printed microstrip antennas is generally limited to the high frequency range. However, their versatility has solicited investigation on their suitability for low-frequency applications. We investigate the considerable reduction in the working frequency attainable by means of a double-layer substrate of ferroelectric and ferrimagnetic materials. High values of permittivity and permeability allow the use of the proposed antenna down to the MHz range. The possibility of varying the permeability of the ferrite through a simple DC bias represents a versatile feature in terms of tunability (and selectivity). The design of the proposed antenna calls for a careful simulation of both substrates with regard to their frequency-dependent behavior and the anisotropy of the ferrite. A Debye model is adopted for the ferroelectric material, while a classical Polder tensor form is considered for the permeability of the ferrite. The problem is solved by an analysis method based on a 3D finite-element method (FEM), with a nodal-based approach in terms of magnetic vector and electric scalar potentials. In the frequency range of interest, the magnetic field is the quantity of major interest. The results, validated through a commercial code, demonstrate the feasibility of the antenna as source or receiver of low-frequency EM fields.