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Sidelobe Suppression

Antenna pattern of
directional antenna
Receiver
main channel
Antenna pattern of
omnidirectional antenna
Receiver
compensation
channel

Figure 1: Functional circuit diagram of a sidelobe suppression

Antenna pattern of
directional antenna
Receiver
main channel
Antenna pattern of
omnidirectional antenna
Receiver
compensation
channel

Figure 1: Functional circuit diagram of a sidelobe suppression

Antenna pattern of
directional antenna
Receiver
main channel
Antenna pattern of
omnidirectional antenna
Receiver
compensation
channel

Figure 1: Functional circuit diagram of a sidelobe suppression

Sidelobe Suppression

Sidelobe suppression is an important criterion for interference immunity in military radar equipment.

However, the radar is not able to distinguish between the main lobe and the side lobes from the signals of only one antenna and one receiver channel. Echo or interference signals received by a sidelobe are all displayed in the direction in which the antenna is aligned with its main lobe.

A second antenna with an omnidirectional or cardioid characteristic or simply with a much wider antenna pattern must be installed as a compensating antenna with its receiving channel. This receive channel is called the suppression channel or compensation channel and should have the same characteristics as the main channel.

An important difference: the received signals should be inverted from the main channel so that they can be subtracted from the received signals of the main channel. For good suppression, the gain of both channels must be controllable together, but the compensation channel must use an additional control stage. With the principle circuit shown in Figure 1, complete suppression of the side lobes is not possible. The level in the compensation channel can only be set to an average value. However, the side lobes are significantly reduced.

It is also possible to use several compensation antennas, each with its receive channel so that the suppression distributed to different channels allows a better result. The PRV-17 uses three compensation antennas: two of them are shown in Figure 3, the third one is located behind the main antenna and suppresses the back lobes.

A sidelobe suppression (SLS) is usually realized by a monopulse antenna in the secondary radar.

Picture gallery of antennas for side lobe suppression

Figure 2: PRV-13 with small compensation antenna next to the main antenna

Figure 3: PRV-17 at the Military History
Museum of Ukraine

Figure 4: In the radar AN/FPS-117 the compensation antenna is located to the right of the main antenna and is called “Auxiliary Antenna”