Broadband Microstrip Leaky Wave Antenna With Inhomogeneous Materials

Analytical solutions for the fields and propagation constant in an open microstrip line above an inhomogeneous substrate are derived and the finite element method (FEM) is used as a tool to validate the theory. Excellent agreement between theoretical and simulated results is obtained and the theory is used to determine the driving point impedances. The complex propagation constant corresponding to the leaky mode is derived from the fields computed using the FEM technique and compared to the values obtained using the transverse resonance method (TRM). It is demonstrated that by periodically loading the microstrip line with air gaps and keeping the period much less than a wavelength, it is possible to realize a leaky wave antenna with lower dielectric constant whose bandwidth is increased by a factor of approximately 50% or so. The proposed inhomogeneous LWA has been fabricated, and measured with results corroborating the theory shown here.