D3A Dish Electromagnetic Design

GRASP Simulations

GRASP simulations using a simple model have been performed to get initial estimates of the radiation properties (such as gain, beamwidth, and sidelobe levels) of the D3A dishes. The radiation patterns were calculated for 3 frequencies: 0.4, 0.8, and 1.6 GHz over an angular range of -90° ≤ θ ≤ +90° in cut planes φ = 0°, 45°, and 90°. (θ = 0° is boresight.) Note that the feed used here has an ideal (circularly- symmetric) Gaussian radiation pattern with the illumination of the edge of the reflector at -12 dB with respect to the peak. These simulations do not include blockage or scattering by the feed.

GRASP model

Radiation patterns

3 dB beamwidths (full-width, half-maximum)

Frequency, GHz	Beamwidth
0.4	9.1°
0.8	4.6°
1.6	2.25°

Beam Deviation Factor

Here is the beam deviation at 800 MHz. This plot shows the deflection of the antenna beam as a function of angular displacements of the feed (measured from the vertex of the dish).

Δθ/Δφ = -0.65

Here is the beam deviation for transverse feed displacements in mm. This shows that for a beam deflection less than 1 arcmin, the position of the feed has to be within 0.3 mm of the focal point.

Δθ/Δφ = -3.0 [arcmin]/[mm]

-- WayneGretzsky - 2019-04-03