Hi Sherestha Ranjit, there are some techiniques used in cooling active antenna arrays. The most common are: Natural convection air cooling, forced air cooling, forced liquid cooling(cold plates), Peltier coolers etc.
In your project you have to take into account the enviromental condictions, the constraints involved and the kind of application for the array.
It is also important to study the aspects related to the heat transfer theory.
Thank you very much for your answer and the link you share. It was helpful. Considering the size and weight of the antenna, we are planning to design the liquid cooling technology. If you have idea about this, please do share with us. We also hope for some more links.