Principles of Modern Radar - Volume 2 1891121537

11.3 Interleaved Scanning (Slow-Time Space-Time Coding) 51511.3 INTERLEAVED SCANNING (SLOW-TIMESPACE-TIME CODING)Another way to explore space is obtained by interleaved scanning, where successivepulses are sent is successive directions, thus interleaving different pulse trains - possiblywith different frequencies, or different codes. An example is shown Figure 11-20, with2 interleaved directions.This scheme, which can also be qualified as “slow-time” space-time coding, allowstrading a wider quasi-instantaneous coverage – and the possibility to implement adaptiveangular processing, by coherently processing the signals received from the adjacentbeams – against a lower repetition frequency (and consequently more Doppler ambiguities)in each direction, and blind ranges or eclipses. It has no significant impact on thepower budget: as for the previous space-time coding concepts, the loss in overall gain ontransmit is balanced by a longer integration time on target.With that interleaved scanning concept, it becomes possible to implement any adaptiveprocedure on receive, with only one channel on receive, if the transmitted signals areidentical (so that the samples received from the different direction can be coherentlyprocessed to extract angle information). However, one has to take into account the fact thatthe samples are not taken simultaneously, so Doppler information has to be incorporated inthe spatial filter. More specifically, the standard adaptive angular filter W (θ), to be appliedto the vector z of collected samples in one range gate, which is classically written [4]:now becomes a Doppler-angle filter:y(θ) = W H (θ)z (11.9)R −1 a(θ)W (θ) = √aH(θ)R −1 a(θ)(11.10)y(θ) = W H (θ)z (11.11)R −1 a(θ, f d )W (θ) = √aH(θ, f d )R −1 a(θ, f d )(11.12)a(θ, f d ) = ( f d )s(θ) (11.13)⎡⎤1 0 ... 00 e 2π jf d T r0with :( f d ) = ⎢⎣.. ..⎥(11.14)⎦0 e 2π j (N−1) f d T rTransmit θ1Transmit θ2FIGURE 11-20Interleavedscanning.Transmit Transmit Transmit Transmit Transmitθ1θ2θ1θ2θ1Receive θ1Receive θ 2 Receive θ 1 Receive θ 2 Receive θ 1