The unknown input impedance of a horn antenna operated at a frequency of 300MHz is measured using a slotted transmission line and a Smith Chart. When the antenna is connected to the slotted line, the VSWR on the line is measured to be 4, and voltage minima are observed at the points 10cm, 60cm, 110cm, on the ruler which is attached to the slotted line and which reads up as one moves from the load plane towards the generator. When the unknown load is replaced with a calibrated short circuit termination, the voltage minima have shifted to the points 5cm, 55cm, 105cm Find the unknown load impedance.