Interlace mode
The interlace mode in a secondary radar , often also referred to as mode interlace , denotes the possibility of transmitting different queries in successive pulse periods at different times. For the duration of the target's illumination time , these pulse periods are nested in a predetermined sequence.
The function of a secondary radar is that a transponder in an aircraft is queried and the answer is displayed on the radar screen in the vicinity of the target at the distance calculated by a transit time measurement . The secondary radar can carry out up to six different queries with different content, which are referred to as modes . The answers are known as a code and are ambiguous on their own. They only make sense if the associated question (here the fashion ) is known. Since the interrogation is temporally linked to the transmission pulse of the radar, only a single secondary radar interrogation can be carried out within a pulse period.
Of the current 6 common modes (Mode 1, Mode 2, Mode 3 A, Mode C, military Mode 4, Mode S ) are classified according to the interrogating device (interrogator) scanned quasi-simultaneously system used up to three in interlace mode. Since several transmission pulses are necessary with analog radar devices to generate a target symbol (pulse integration), the responses from the three different modes are available simultaneously for target processing.
In general, a 3-mode interlace is used, with modes 3A and C alternating from interrogation to interrogation and modes 1 and 2 used for military purposes being interrogated alternately from one antenna revolution to the other. The answers are saved and are therefore always available to the user.
| Order of query | one antenna turn long: |
in the next antenna revolution: |
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In the newer identification system Mode S , the classic order of the query is interrupted by the additional selective query. The interrogation devices of modern monopulse radar do not use the interlace mode. They are limited to the selectively queried Mode S responses from the transponders. Its information is permanently linked to the target sign and communicated to other radar devices via networks, so that only one query is necessary for a target as long as it is within the detection range of the radar or a group of radar devices.