A geostationary satellite must be at a radius of 4.2 x 107 m . Its period will then be 24 hours. Other conditions include : 1 same axis of rotation (rotate in the plane of the equator ) 2. rotate West to east.
Advantages of geostationary orbit:
1. It always remain at the same height above a fixed point from the Earth.No tracking is required.
2. Continuous communication between satellite and earth station is possible throughout 24 hours.
Advantages of polar orbit:
1. It is very much closer to Earth and therefore cost involved is lower
2. The satellite is much faster and orbit many times in one day thus enables the monitoring of data over all longititudes and latitudes.More data can be obtained due to greater coverage.