Introduction to Radar Basics - MATLAB Simulations for Radar Systems Design - page 37

where is the aperture radius and is the wavelength. In practice, Gaussian
antenna patterns are often adopted. In this case, if denotes the antenna
3dB beamwidth, then the antenna gain can be approximated by

r λ

θ 3 dB

2.776θ 2
θ 3 dB

 

G () = exp  – ------------------- 

(1.89)

2

 

If the antenna scanning rate is so fast that the gain on receive is not the same
as on transmit, additional scan loss has to be calculated and added to the beam
shape loss. Scan loss can be computed in a similar fashion to beam shape loss.
Phased array radars are often prime candidates for both beam shape and scan
losses.

Figure 1.23. Normalized (sin x / x) antenna pattern.

1.8.3. Atmospheric Loss

Detailed discussion of atmospheric loss and propagation effects is in a later
chapter. Atmospheric attenuation is a function of the radar operating frequency,
target range, and elevation angle. Atmospheric attenuation can be as high as a
few dB.

1.8.4. Collapsing Loss

When the number of integrated returned noise pulses is larger than the target
returned pulses, a drop in the SNR occurs. This is called collapsing loss. The
collapsing loss factor is defined as