In general, radars work by sending out pulses of electromagnetic waves and timing when they get returns back that have reflect off certain objects. This allows them to calculate how far away the object is, and by spinning continuously and sending out a new pulse in each direction, they can work out where the object is in relation to the radar antenna, by both direction and distance.

Primary Surveillance Radar (PSR) operates based on pulse radar principles. The raw data obtained from a PSR includes:

• Bearing – Determined by the direction in which the antenna is pointing.
• Range – Calculated from the time delay between the transmitted and received pulse, allowing the system to measure the aircraft’s distance from the antenna.

As for the other options:

• The pulse pair interval is set by the radar designer to choose the maximum range of the radar (how long does it wait for a return before sending the next pulse).
• The frequency shift of the received pulse can be used to calculate the speed of the object relative to the antenna (only towards or away from the antenna) due to doppler shift. This is used in some primary ground radar systems, but more often for pilots, we use this in airborne weather radars to spot areas of windshear.