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 wavelength (
d
₁
=
d
₂
= λ
₀
/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.