Refer to figures.
Learning Objective 062.01.02.03.01: Name the common different types of directional antennas: loop antenna used in old automatic direction-finding (ADF) receivers; parabolic antenna used in weather radars; slotted planar array used in more modern weather radars.

Radars such as AWRs (Airborne Weather Radars) have to be able to send pulses of electromagnetic radiation in one direction all at once. This is more difficult than it sounds, due to the way that these waves are produced.

Parabolic Antenna

The older method of directing this energy was by using a parabolic reflector dish, which is a shape that reflects all radiation from the focal point in the middle outwards in the same direction, and vice versa, any radiation from that direction is reflected onto the focal point in the middle. This allows for a transmitter/receiver device to be placed in the focal point, facing backwards towards the dish, and for its transmissions to go forwards, ahead of the aircraft, and receive the reflected pulses indicating the presence of weather.

One of the biggest problems with the parabolic antenna is the side lobes. The formation of this "main beam" of radiation does cause some unwanted extra radiation, called side lobes, which send some of the energy in a different direction than intended, and can cause some spurious and incorrect responses on the radar screen.

Slotted Planar Array / Flat Plate Antenna / Phased Array

These types of radars use a more efficient modern technique, by having a flat plate with numerous waveguide-size slots cut into it, it can produce a similar beam to the parabolic antenna with much smaller sidelobes. The lesser side lobes means that there are less spurious returns and that there is less wasted energy, meaning that less energy is needed for the same radar scan.

The main beam (main lobe) of a slotted planar array can also be made thinner than the parabolic antenna beam, which would use even less energy, allowing for increased range, or just lower energy consumption.