In track while scan mode of radar operation what are the methods to predict next position of target?
Standard approach for radar tracking is as follows:


Prediction of next position using one Interacting Multiple Model per aircraft. The basic model is made from two Kalman Filters, one of which predicts constant velocity (in 3D), the other predicts a constant-rate turn (also in 3D). The model selects the prediction from the filter that performed better during the last few updates.
Data from the scan arrives. Positions of the blips are compared to the predicted positions and the Joint Probabilistic Data Association technique is used to associate each blip with one of the tracked aircraft. If there are unassigned blips, a new model is set up to track the newly discovered aircraft.
Each aircraft's model is updated with the associated blip's position. This includes updating each Kalman Filter as well as selecting which of the filters should be used for the next prediction (the one that predicted the current blip more accurately).