null at the horizon

[souldigger]

Пожалуйста, помогите перевести.

Выражение встречается в следующем контексте:

null at the horizon - ?
place a null at the angular location -?

In the absence of multipath, the performance of a GPS receiver can be restored either by an intelligent antenna design (i.e., one which has a null on the horizon) or by using an antenna array that can adaptively place a null at the angular location of the jammer.

Заранее спасибо