Printed antennas are increasingly becoming popular thanks to their low-profile and ease of fabrication. However, they are limited to operate over a very narrow bandwidth. In this example, the antenna is a printed circular monopole: We analyze and compare their simulated performances to the published results. The printed monopole antenna is in essence a substrate backed with a ground plane on one side and printed with a patch on the other.  The open air around the antenna is included and truncated with radiation boundaries, simualting an anechoic chamber. In this study, we exploited the symmetry of the model to lessen the number of mesh elements and therfore the simualtion required time through the use of symmetry boundary conditions.

Figure 1 - Circular Disc Monopole Antenna (3D SolidWorks view)

Simulation

To simulate the behavior of this antenna, we create an antenna study, and specify the frequency range at which the antenna operates. Here we use the "fast sweep": The fast sweep greatly reduces the simulation time of an S-parameter study through the use of the reduced-order model. By solving the matrix equations of a single frequency, the reduced-order model is produced. Other surrounding frequencies in the band of interest are then solved using the reduced model instead of the full matrix solution. In HFWorks, the fast sweep option has been further developed into the adaptive fast sweep. This advanced feature which is exclusive to HFWorks, employs new expansion points whenever the error of the reduced order model exceeds a certain threshold. The only thing that the user needs to provide is the maximum number of expansion points. 

Solids and Materials

In figure 1, we have shown the discretised model of the antenna. As mentioned in the description of the model, the substrate of the antenna has on both of its sides two printed planes: the ground and the patch. The air is included and conveniently truncated (Minimum distance is the double of the wavelength.

Figure 2 - Boundary conditions of the antenna

On the figure, we can spot the different boundary conditions; from the right we have the symmetric PEM. The port is highlighted and marked with red arrows pointing to two faces. The arrows in yellow show the PEC faces which are the two printed conductors of the antenna; The arrows in red from the righ side show the PMCSsymmetry surface. The radiation boundaries are applied to the remaining air box faces.

Meshing

The mesh is finer on the ports and PEC faces. Meshing these surfaces helps the solver refine its precision on the eddy parts, and take their  forms into account.

Figure 3 - Mesh of the half DR filter

There is always a compromise between accuracy and time consumption. Applying an over-accurate mesh control may result in much time consumption and causes long simulation. 

Results

Various 3D and 2D plots are available to exploit, depending on the nature of the task and on which parameter the user is interested in. As we are dealing with an antenna simulation, plotting the radiation intensity at the best match frequency alongside with the reflection coefficient sounds like an intuitive task.

HFWorks plots the electrical parameters on 2D plots as well as on Smith Charts : The antenna in this example is best matched at 5.5 GHz, with a return loss of 27 dB.

Figure 4 - Variations of return loss (S11)

The 3D plots for the antenna studies cover a wide range of parameters: we can view the electric field distribution, its components in different coordinate systems, and parameters peculiar to antenna studies such as radiation and directivity.

Figure 5 - Radiation pattern at 4 GHz  and at 6.5 GHz

On this figure, the radiated electric field (radiation pattern) is plotted on the plane Phi=90° for both frequencies. 

References

A Novel Disc Monopole Antenna for UWB Applications Mohamed Nabil Srifi, O.El-Mrabet, and Mohamed Essaaidi - Electronics                     and Microwaves Group, faculty of science, Abdelmalek Essaadi university, Tetuan 93000, Morocco