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Cylindrical Antenna

A center-fed cylindrical antenna is the simplest example that we can simulate. It consists of a straight wire with a source at its center and becomes a half-wave dipole when the frequency is such that the length of the antenna is half the wavelength. Follow the steps below to model this antenna.

Step 1 | Setup

Go to Tools > Preferences > in the main menu for selecting suitable units for frequencies and lengths. In this example, frequencies will be measured in MHz and lengths in mm. Then, go to the Setup tabsheet. In the Frequency panel choose Sweep and fill the Frequency Sweep box as shown in Fig. 1. Make sure None is selected in Environment panel > Ground Plane box and Discrete Sources is selected in the Excitation panel.

Fig. 1: A frequency sweep is set in the Frequency panel. The calculations will be performed at the frequencies: 50, 55,… ,295, 300 MHz.
Step 2 | Draw

Right click on the workspace and choose Line from the displayed pop-up menu >. The Draw dialog box for the Line will be shown. Fill the Line and Attributes pages as shown in Figs. 2 and 3. A straight wire with 17 segments and 5 mm in radius will be drawn in the workspace. Right click on the wire and choose the Source/Load command from the pop-up menu. Follow the procedure described in Adding Sources > and put a voltage source in segment number 9 (at the wire center). The source voltage is 1 (0º) V. The center-fed cylindrical antenna in the workspace is shown in Fig. 4.

Fig. 2: Line page in the Draw dialog box. The wire will be drawn starting from point (0,0,-750) [mm] and ending at point (0,0,750) [mm]. Thus, it lies along the z-axis and is 1500 mm long, which corresponds to half-wavelength at 100 MHz. Press F7 to view the main axes.
Fig. 3: Attributes page in the Draw dialog box. The wire is divided into 17 segments, and it has a circular cross-section with 5 mm in radius.
Fig. 4: Cylindrical antenna in the workspace.
Step 3 | Run

Click on the Run Currents and Far-Field (F11) button on the toolbar. After the calculations are complete, right click on the wire and choose Plot Currents from the displayed pop-up menu and select the desired frequency. The current distribution along the wire will be plotted, Fig. 5. Follow the procedures described in Displaying Results > for obtaining other parameters of interest.

As an example, the current distribution in amplitude and phase, the input impedance vs. frequency, the gain, and E-field patterns at 100 MHz are shown in the following figures. Note that the antenna length is half a wavelength at 100 MHz, so the current distribution approaches a semi cycle of a sine function, as expected for a half-wave dipole.

Fig. 5(a): Amplitude of the current distribution along the cylindrical antenna at 100 MHz.
Fig. 5(b): Phase of the current distribution along the cylindrical antenna at 100 MHz.
Fig. 6(a): Real part of the input impedance vs. frequency.
Fig. 6(b): Imaginary part of the input impedance vs. frequency.
Fig. 7(a): Gain [dBi] pattern at 100 MHz.
Fig. 7(b): Total E-field pattern at 100 MHz.
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