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Phased Array Toolbox and directivity of IsotopicAntennaElement

Cannot you explain how and in what units directivity is calculated in MATLAB Phased Array Toolbox?

I run their simple example with IsotropicAntennaElement.

myAnt = phased.IsotropicAntennaElement();
ang = [-30,-20,-10,0,10,20,30; 0,0,0,0,0,0,0];
freq = 1e9;

d = directivity(myAnt,freq,ang)

It gives me this:

d =

   1.0e-03 *

    0.1102
    0.1102
    0.1102
    0.1102
    0.1102
    0.1102
    0.1102

MATLAB manual tells that directivity is the ratio of the intensity in given direction and the intensity of an isotropic antenna of the same power.

But what's the hell, why it does not give 0 dB on the directivity of an isotopic antenna itself?

Does it mean that an isotropic antenna radiates less, than an isotropic antenna? Or how should I understand it?

Solution

  • It's in dBi units, as stated in the the documentation:

    directivity Compute element directivity

    D = directivity(H,FREQ,ANGLE) computes the directivity (in dBi) of the element for the directions specified in ANGLE (in degrees) and frequencies specified in FREQ (in Hz).

    So it should be 0 for an isotropic antenna. You are getting 0.0001102, which is acceptably close to 0.