Gain Enhancement in Microstrip Patch Antennas Using Hybrid Substrates

A substrate design that uses a ferrite ring to enhance the gain of a microstrip patch antenna without compromising the bandwidth is proposed. This design forces constructive interference between the incident and reflected fields inside the substrate. The interference is created by introducing a ferrite ring at a distance d₁ from the circumference of the patch with a ring width d₂. Initial values of d₁ and d₂ of one-quarter of the free-space wavelength ( d₁ = d₂ = λ₀/4) are selected. An unbiased ferrite, with relative permeability of μ_r2 = 14, relative permittivity of ε_r2 = 10, dielectric loss tangent tan δ_e = 0.0017, and magnetic loss tangent tan δ_m = 0.0391, is used. Using HFSS, the results of the patch antenna above a conventional substrate (i.e., no ferrite ring) and above the hybrid substrate (which includes the ferrite ring) are compared. Enhancements of about 4 dB in gain and nearly 1% in impedance bandwidth are obtained by using the hybrid substrate instead of the conventional one.