Crossed-dipole Antenna Element

Another antenna that produces polarized radiation is the crossed-dipole antenna, created by using the phased.CrossedDipoleAntennaElement System object™.

You can use a cross-dipole antenna to generate circularly-polarized radiation. The crossed-dipole antenna consists of two identical but orthogonal short-dipole antennas that are phased 90° apart. A diagram of the crossed dipole antenna appears in the following figure. The electric field created by a crossed-dipole antenna constructed from a y-directed short dipole and a z-directed short dipole has the form

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

The polarization ratio E_V/E_H, when evaluated along the x-axis, is just –i which means that the polarization is exactly RHCP along the x-axis. It is predominantly RHCP when the observation point is close to the x-axis. Moving away from the x-axis, the field becomes a mixture of LHCP and RHCP polarizations. Along the –x-axis, the field is LHCP polarized. The figure illustrates, for a point near the x, that the field is primarily RHCP.

LHCP and RHCP Polarization Components

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This example plots the right-hand and left-hand circular polarization components of fields generated by a crossed-dipole antenna at 1.5 GHz. You can see how the circular polarization changes from pure RHCP at 0 degrees azimuth angle to pure LHCP at 180 degrees azimuth angle, both at 0 degrees elevation angle.

Create the phased.CrossedDipoleAntennaElement object.

fc = 1.5e9;
antenna = phased.CrossedDipoleAntennaElement('FrequencyRange',[1,2]*1e9);

Compute the left-handed and right-handed circular polarization components from the antenna response.

az = [-180:180];
el = zeros(size(az));
resp = antenna(fc,[az;el]);
cfv = pol2circpol([resp.H.';resp.V.']);
clhp = cfv(1,:);
crhp = cfv(2,:);

Plot both circular polarization components at 0 degrees elevation.

polar(az*pi/180.0,abs(clhp))
hold on
polar(az*pi/180.0,abs(crhp))
title('LHCP and RHCP vs Azimuth Angle')
legend('LHCP','RHCP')
hold off