Question

Please elaborate on how to obtain circular polarization using rectangular microstrip antenna and explain why circular polarization can be achieved by doing so.

Answer 1

Since a circular polarized antenna transmit in all planes, it can create successful link. So in this case we need to obtain circular polarization in rectangular microstrip antenna.

Normally we use a double layer substrate of FR-4 epoxy (permittivity =4.3) to design circular polarization microstrip antenna.Thickness would be approximately 1.6 mm with a loss tangent of 0.026. But here first we are making a rectangular microstrip suitable for circular polarization.

So first design a rectangular microstrip antenna by finding out W and L.Following equations can be used for it.

After the design to obtain circular polarization, we should make a truncated corner in microstrip antenna with cutting angle equal to 45 degree. This should be at diagonal position. So the reason why we decided to cut the corner is to get circular polarization with an axial ratio of 3 dB.Dimensions of width of the cut can be find out from the equation,

Through this method we can achieve circular polarization because circular polarization occurs when current flowing through the patch interacts with its polarization. So making a truncated corner would help us to achieve it.

So this is one of the method to obtain circular polarization in rectangular microstrip antenna.