The absorption and coupling of an electromagnetic wave incident on a microstrip circuit with superstrate

The absorption of an electromagnetic wave incident on a microstrip circuit covered with a dielectric layer is studied. The exact analytical expression for the plane-wave reflection coefficient at the air-superstrate interface of a four-layer model for a superstrate-loaded microstrip circuit is given. Numerical results illustrating the power absorption by the microstrip circuit and the electric and magnetic fields on the surface of the circuit as a function of wave frequency, superstrate thickness, superstrate permittivity, and incident angle are presented. It is found that the power absorption by the circuit at resonant frequencies increases with increasing superstrate permittivity. Higher superstrate thickness and permittivity can both cause more resonant power absorption peaks in the frequency spectrum. Significant intensities of electric or magnetic fields can also exist on the surface of the circuit for almost all the frequencies, which may couple to the circuit and cause malfunctions or interference. Details of the numerical results are presented