How read the HFSS results?

Hi,
I'm using HFSS for a little while simulating antennas. Now for the first time I need to plot Radiation patterns on gain, directivity and so on.
I've seen that HFSS gives me a lot of possibilities:gain, directivity,radiated power,radiation efficiency.
For the gain for example:I've plot a radiation pattern of gain for a fixed theta and variable Phi. The problem is...how I've to read that result? How can I for example say if the gain of this antenna is better of that of a dipole?
In the end...I've a lot of variables but how can I give them the right meaning
Thanks in adv.

P.S. I usually enclose my antenna in a cube of correct dimensions relating to lambda and assign to it a radiation boundary for the far field calculation...Is this correct or could I expect inaccurate results?

Directivity is calculated by integrating the pattern and doesn't include any losses in the antenna. Usually when directivity is referred to, it means the peak value of the directivity pattern. For example, the peak directivity of a half-wave dipole is 2.15 dBi.

Gain includes the effects of losses (conduction, dielectric, and also feedpoint mismatch loss unless the IEEE standard definition is used). The difference beween directivity and gain is the efficiency. Gain will always be lower than directivity.

For antennas, typically 2D cuts are made through the principal planes called the E-plane and H-plane. The E-plane contains the electric field vector and the direction of maximum propagation and the H-plane contains the magnetic field vector and the direction of maximum propagation. From these two cutplane plots, the general shape of the far-field pattern can be determined. Antenna design tools can also plot 3D antenna patterns. These are useful for showing where the power is being radiated.

In spherical coordinates, varying phi for a fixed theta value is a conical cut. Usually you will also see plots for varing theta for a fixed phi.

Check out the help menu of HFSS, it will explain what you need to know. Antenna textbooks will have the basic definitions for far-field quantities such as gain and directivity.

To model the antenna in HFSS, a numerical integration on the surface of the radiation boundaries (or PMLs) is performed to calculate far-field quantities. So be certain that your mesh is sufficient for getting the correct values (you may need to seed the mesh beforehand). I have seen radiation efficiencies slightly above 100% from HFSS even when the mesh is very good.

Depending on the type of antenna you are modeling, a moment-method tool may be better-suited for the problem since the Green's function includes the free space region. Only the conductors are meshed and the currents are directly solved for. In the finite element method (HFSS), the entire volume must be meshed and the electric fields are directly solved for. Then H-fields are computed and finally currents. I would go through an example antenna problem to check that you are setting up the problem correctly. Ansoft app engineers have the getting started tutorials that contain antenna examples.

Good luck.