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

$$\begin{array}{l}{E}_r=0\\ E_H=-\frac{i{Z}_{0}IL}{2\lambda }\cos \text{az}\frac{e^{-ikr}}{r}\\ E_V=\frac{i{Z}_{0}IL}{2\lambda }(\sin \text{el}\sin \text{az + }i\cos \text{el})\frac{e^{-ikr}}{r}\end{array}$$

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

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.

Note: This example runs only in R2016b or later. If you are using an earlier release, replace each call to the function with the equivalent step syntax. For example, replace myObject(x) with step(myObject,x).

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 Azithmuth Angle')
legend('LHCP','RHCP')
hold off

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