how do Microstrip Antenna radiate Energy? | applied electronics engineering


how do Microstrip Antenna radiate Energy?

By Applied Electronics - Tuesday, September 6, 2016 No Comments
To understand the mechanism of electromagnetic radiation from microstrip antenna the structure has to be first understood. Microstrip antenna has the structure of parallel plate capacitor. The difference is that high dielectric material is in between the two conductors. One conductor is the radiating conductor also called patch and the other is the ground conductor. The shape of the radiating conductor can be of any shape. Figure below shows an illustration of microstrip antenna.

The structure is same as that of microstrip lines but in case of microstrip antenna the shape is not a long conductor. Microstrip lines are designed to carry current but not to radiate. Whereas microstrip antenna are designed to radiate. In order not to radiate the dielectric substrate thickness is thin while in case of microstrip antenna, the dielectric substrate is thick(in comparison) to radiate energy.

Now we know the basics of the structure of microstrip antenna we explain the radiation mechanics. The radiation field or pattern from microstrip antenna is determined by the field distribution between the upper radiation patch conductor and the ground conductor.

When an alternating energy source is connected to the antenna, there will be charge or current distribution in the two conductors.

In the figure above, there are positive and negative charges both in the upper patch conductor and the ground conductor. The like charges for example +ve charges are repelled from the lower part of the patch to the upper part of the patch. What we eventually have are two current densities at the top and bottom of the patch- Jt and Jb which are also shown in the figure above.

Most of the charge circulation or current remains underneath the patch conductor because of the h/W ratio and attractive forces between charges is large. Only small current flows at the edges and produce weak tangential magnetic field. There will also be lines of forces between the patch and the ground. This lines of forces of can be considered vertical as the wavelength of energy is much larger than the height h.

This process of charge distribution in the microstrip antenna structure and the charge distribution at the top of the patch conductor creates the electromagnetic field. There charge distribution will always be changing because of the alternating signal source that is feed to the structure.

Read more on this in microstrip antenna design handbook and also see Patch antenna design tutorial with CST microwave.


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