Greetings.
Can anyone explain the mechanism behind gain and directivity enhancement by placing a dielectric layer (superstrate) at a certain height above antenna.
Thanks
I prefer to think of it 1)from positions of ray optics, so it should be far enough to correct the phase and field distribution as a lens, or prism 2)as a brightening layer, an impedance matching layer. Though, at a distance it will make more trouble with local reflections. 3)from positions similar to magnetic cores which attract magnetic field, the layer collects electric field, which may improve its distribution. the same way the finite thickness may create as a resonant cavity... it is also a capacitive load in the equivalent circuit... well, a lot of minor effects that may improve or degrade the performance. But in the product there will be a cover anyway, so you have to consider it.
Antenna gain is directly related to directivity and efficiency. Therefore, to achieve high gain, the antenna should be made highly directional. Further, efficiency can be improved by enhancing the matching profile and reducing various losses. As shown in the figure an infinite ground plane (PEC) is used at the back of the substrate to direct the electric field in the vertical direction, and the magnetic field will be on its surface. When the antenna is excited, the current due to the magnetic field in the active antenna induces an electric field in the parasitic dielectric (Superstrate), which causes the creation of a magnetic field in the superstrate. The magnitude of the coupled field is a function of the spacing between the antenna and the superstrate. The accurate phasing of the electromagnetic field and constructive interference between the field constitutes the enhancement of gain and directivity.
Thank you Andrey Porokhnyuk Sir and Sovan Mohanty Sir for your reply.
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