A 10-turn helical antenna is simulated in XFdtd^® to demonstrate the far-field circular polarization plotting capabilities of the software.

The antenna design and dimensions are taken from Example 6-1 on page 270 of “Antenna Theory and Design” by Stutzman and Thiele (John Wiley and Sons, 1981).  The center frequency is 8GHz giving a helix circumference of 3.45cm.  The helix is constructed with a right hand (clockwise) twist to produce a Right Circular Polarized far-field pattern.  The spacing between turns is 0.796 cm.  The theoretical half-power beam width is computed as 38.8 degrees.

The antenna is constructed in XFdtd using the helix primitive. The helix will expand along the Z-axis and will have a radius of 0.549cm. The entered parameters are shown in Figure 1.

In addition to the helix, a small ground plane is added at the base of the helix using the parameters shown in Figure 2.

The resulting geometry is as shown in CAD mode and after meshing with a cubical cell size of 1mm.

The feed is applied to the cell edge that connects the helix to the base plate as shown in Figure 5.

A sinusoidal signal at 8GHz is used as the waveform with a convergence criteria of-35 dB. Following the simulation the far zone patterns are computed in several planes and in three dimensions.

The right circular polarized pattern is shown in Figure 6. The radiation is right polarized, so the left circular polarized pattern is much lower.

The gain of the main beam is plotted in a two-dimensional line plot to determine the half-power beam width. The plot indicates it is approximately 39 degrees as shown in Figure 8 which matches quite well with the theoretical value.