Motivation
In the antenna section you studied the slot antenna, which is more interesting than the simple dipole antenna. An array of slot antenna is very similar to a grating consisting of slots in a thick PEC wall. The slots in a thick wall can be considered as planar waveguides of finite length. A plane wave incident on such a grating excites propagating and evanescent modes. When the wall is sufficiently thick, the evanescent modes can be neglected for the computation of the transmitted field. When the slot is sufficiently thin, only the fundamental mode is propagates. The amplitudes of the modes in neighboring slots are equal in magnitude. When the plane wave is not incident perpendicular to the grating, there is a phase shift from each slot to its neighbor.
Modeling
Essentially, you can proceed as for the dipole antenna array, but your original cell looks quite different. Assume that the PEC wall ends at y=0 and that you have free space for y>0. Since the planar waveguides that feed the slot antennas extend to infinity in the -y direction, you have no bottom layer and the original cell extends to infinity.
In the slot antenna model you separated the slot area with two fictitious boundaries from the feed area and from free space. Essentially, you can do the same now. You might wish to start with the slot antenna model for obtaining a slot antenna array. To do that, you must, 1) remove the symmetry that was used in the slot antenna, 2) rotate all boundaries and expansions by an angle of 90 degrees (Use the "ROTate ALL" directive!), 3) move all expansions and boundaries to the desired location (Note that the original cell should be to the right hand side of the y axis.), 4) eliminate unnecessary parts of the boundary and unnecessary expansions, 5) modify the boundaries in such a way that they fit the desired cell, 6) add "symmetric" boundaries and expansions that are missing, 7) replace the fictitious boundary that separates the slot area from free space by a straight line that separates the original cell from the top layer, 8) add an appropriate periodic boundary, 9) set the desired periodic data in the Project dialog.
Validate the results
Since many steps were needed to obtain the model of the slot antenna array, it is important to carefully validate the results. Check the MMP errors and the field first. At low frequencies, the field radiated by a slot antenna is similar to a dipole field. Therefore, you can compare the results with the corresponding dipole antenna array. At high frequencies, the field near the slot of each antenna should be similar to the field of a single slot antenna. Finally, you can compare the results with the results of a corresponding slot grating.
Explore the physical properties
When you have a robust and reliable model, explore the physical properties of the slot antenna array by varying the frequency, the phase shift, and other parameters. Study the Rayleigh terms for obtaining an impression of the directional spectrum and compare them with those obtained for dipole arrays. Study the reflection coefficients and compare them with the coefficients of the single slot antenna.
SLOP100.PRO
The project SLOP100 on the CD-ROM contains all the essential files for a relatively simple model of a slot antenna array. Try to improve this model to obtain more accurate results in less computation time.
