3* Why is waveform’s type so important? The correct choice of waveform defines all the main characteristics of the radar as:- Performance of target detection.- Resolution (angular, range and frequency).- Measurement ( range, velocity & error).- Classification and recognition.
4*Factors of the selection of a particular waveform : Requirements of :Range coverage.Doppler coverage.Detection probability.Resolving capability.Measurement errors.Interference rejection.Enhanced modes of operation.Cost and complexity.
5* waveform’s Classification : Depends on the parameter chosen for classification :Character of variation in time domain.Usage of intra-pulse modulation or not.Pulse compression type.Frequency-coded waveforms types.Phase-coded waveforms types.Discretization.
6* The most popular pulse shapes : Sinusoidal.Rectangular.Gaussian.Triangular.Sawtooth.Exponential.
10Advantages : 1- CW Waveforms : Eqn. : Et = E0 cosw0t. Used: CW ,Doppler & Bistatic Radars.Advantages :Simplified design .Low power.Measure target velocity.Disadvantages:Need coding to determine range.Tx & Rx separation at high power.
11Generation: Active & Passive. Advantages : Disadvantages: 2- FMCW Waveforms :Eqn. : f(t) = f0 + αt.Used: In CW radars.Generation: Active & Passive.Advantages :Less sensitive to doppler shifts.Disadvantages:Has range-doppler cross coupling -> measurement errors.Range sidelobes are high -> weighting required -> 1-2 dB loss in SNR.
12Eqn. : Et = E0 cosw0t. (for Ton), Et = 0 (for Toff). 3- Simple Pulse :Eqn. : Et = E0 cosw0t. (for Ton), Et = 0 (for Toff).Used: Old Radars, Inexpensive Radars.Types: long & short.Advantages :Low cost.Long: doppler resolution.Short: range resolution.Disadvantages:Long: range resolution.Short: doppler resolution.
13Generation: Active & Passive. Advantages : 4- LFM Waveforms :Eqn. : f(t) = f0 + αt.Used: In pulse radars.Generation: Active & Passive.Advantages :Less sensitive to doppler shifts.The easiest to generate.Disadvantages:Has range-doppler cross coupling -> measurement errors.Range sidelobes are high -> weighting required -> 1-2 dB loss in SNR.
156- Phase-coded Waveforms : Types : binary & polyphase.Codes: Barker, P-codes.Advantages :low range sidelobes.Preferred in jamming conditions.Disadvantages:Poor resolution in presence of distributed clutter.The implementation is more complex than that of LFM.