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 d(1) from the circumference of the patch with a ring width d(2). Initial values of d(1) and d(2) of one-quarter of the free-space wave-length (d(1) = d(2) = lambda(0)/4) are selected. An unbiased ferrite, with relative permeability of mu(r2) = 14, relative permittivity of epsilon(r2) = 10, dielectric loss tangent tan delta(e) = 0.0017, and magnetic loss tangent tan delta(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.