Question

Consider an MTD processor with a bank of eight contiguous doppler filters installed in an airport surveillance radar operating at S band (2.8GHz). The MTD uses two different pulse repetition frequencies to unmask a moving target whose echo signal might be in the same doppler filter as moving weather clutter. Let one of the two prfs be 1100 Hz. Weather clutter is assumed to have a spectrum of radial velocities extending from 0 to 25kt. An aircraft flying at a radial velocity of 250kt is aliased in doppler and falls into the same doppler filter (near the middle of filter no. 2-please verify this) as the weather clutter. It is masked by the clutter and not detected. (Note that filter no. 1 is designated as the filter centered at zero frequency.) (a) What should be the second prf (smaller than the first, so as not to decrease the maximum unambiguous range) in order to move the aliased aircraft velocity completely outside of the main response of filter no. 2 and into the middle of filter no. 4 ?

Answer 1

To move the aliased aircraft velocity outside of filter no. 2 and into filter no. 4, the required second PRF needs to be calculated using the aliasing velocity and the formula provided.

Step-by-step explanation:

The second PRF (Pulse Repetition Frequency) should be chosen to move the aliased aircraft velocity completely outside of the main response of filter no. 2 and into the middle of filter no. 4. To determine the required second PRF, we need to calculate the aliasing velocity, which is the velocity that is aliased or folded into the same Doppler filter as the clutter.

Given that the first PRF is 1100 Hz and the aliasing velocity is 250 kt, we can use the formula:

Aliasing Velocity = (Second PRF / first PRF) × Nyquist Velocity

Here, the Nyquist velocity is half of the maximum unambiguous velocity, which is 25 kt. By solving this equation, we can calculate the second PRF required to move the aliased aircraft velocity outside of filter no. 2 and into filter no. 4.