Short-dipole Antenna Element

When you want to explicitly study the effects of polarization in a radar or communication system, you need to specify an antenna that can generate polarized radiation. One such antenna is the short-dipole antenna, created by using the phased.ShortDipoleAntennaElement.

The simplest polarized antenna is the dipole antenna which consist of a split length of wire coupled at the middle to a coaxial cable. The simplest dipole, from a mathematical perspective, is the Hertzian dipole, in which the length of wire is much shorter than a wavelength. A diagram of the short dipole antenna of length L appears in the next figure. This antenna is fed by a coaxial feed which splits into two equal length wires of length L/2. The current, I, moves along the z-axis and is assumed to be the same at all points in the wire.

The electric field in the far field has the form

$\begin{array}{l} E_{r} = 0 \\ E_{H} = 0 \\ E_{V} = - \frac{i Z_{0} I L}{2 λ} \cos el \frac{e^{- i k r}}{r} \end{array}$

The next example computes the vertical and horizontal polarization components of the field. The vertical component is a function of elevation angle and is axially symmetric. The horizontal component vanishes everywhere.

Short-Dipole Polarization Components

Open Live Script

Compute the vertical and horizontal polarization components of the field created by a short-dipole antenna pointed along the z-direction. Plot the components as a function of elevation angle from 0° to 360°.

Create the phased.ShortDipoleAntennaElement System object™.

antenna = phased.ShortDipoleAntennaElement(...
    'FrequencyRange',[1,2]*1e9,'AxisDirection','Z');

Compute the antenna response. Because the elevation angle argument to antenna is restricted to ±90°, compute the responses for 0° azimuth and then for 180° azimuth. Combine the two responses in the plot. The operating frequency of the antenna is 1.5 GHz.

el = -90:90;
az = zeros(size(el));
fc = 1.5e9;
resp = antenna(fc,[az;el]);
az = 180.0*ones(size(el));
resp1 = antenna(fc,[az;el]);

Overlay the responses in the same figure.

figure(1)
subplot(121)
polarplot(el*pi/180.0,abs(resp.V.'),'b')
hold on
polarplot((el+180)*pi/180.0,abs(resp1.V.'),'b')
str = sprintf('%s\n%s','Vertical Polarization','vs Elevation Angle');
title(str)
hold off
subplot(122)
polarplot(el*pi/180.0,abs(resp.H.'),'b')
hold on
polarplot((el+180)*pi/180.0,abs(resp1.H.'),'b')
str = sprintf('%s\n%s','Horizontal Polarization','vs Elevation Angle');
title(str)
hold off

Figure contains 2 axes objects. Polaraxes object 1 contains 2 objects of type line. Polaraxes object 2 contains 2 objects of type line.

The plot shows that the horizontal component vanishes, as expected.