Most radar antennas use a

Horn Antenna:

• Horn antenna converts the electric power into radio waves and vice versa. It is usually used with a radio transmitter or radio receiver.
• One particular use of horn antennas is for short-range radar systems. The horn antenna provides the useful amount of directivity to prevent other reflections interfering with the required response.
• Its structure is designed to match the impedance of a tube to the impedance of free space, enabling the waves from the tube to radiate efficiently into space.

Parabolic Reflector:

• The parabolic dish antenna is the form most frequently used in radar engineering.
• A parabolic antenna consists of one circular parabolic reflector and a point source situated in the focal point of this reflector. This point source is called “primary feed” or “feed”.
• This forms a reflective surface in the antenna that enables RF energy traveling towards the antenna to be reflected and remain in phase at the focal point. This is as shown: