Vector calculus. Spend time studying cylindrical and spherical coordinates. Divergence and Stoke's theorem, line integral, surface integrals.
Look up cylindrical and spherical coordinates, it is NOT the ones you studied in your Calculus III multivariables. I know they talking about cylindrical and spherical stuff, but they are really still rectangular coordinates like:
[tex] \vec F=\hat x r\cos\theta+\hat y r \sin\theta +\hat z z \;\hbox { for cylindrical and }[/tex]
[tex] \hat x R \cos \phi \sin \theta +\hat y R \sin \phi \sin \theta + \hat z R \cos \theta\;\hbox { for spherical}[/tex]
These are not cylindrical and spherical coordinates in any stretch, they are just xyz coordinates with the amplitude of x, y and z represented in radial and angular components. I have a few EM books, they are not very detail in explaining these coordinates. If you can study this, you'll be ahead of the game, these are very very important.
Make sure you review and UNDERSTAND vector field, line integral, divergence and stoke's theorems and get good at it. EM is a very hard subject, you need to get these out of the way and concentrate on the EM part without having to struggle with the math. You are wise to get a 3 months head start......YOu really need it to get the most out of the class. If I am scaring you............Be scare.
I took a look at your book, it is an engineering EM book. If you are interested in EM theory, buy also "Introduction to Electrodynamics" by David Griffiths. I have 5 other engineering EM books, they are not very detail in a lot of things, I studied two of the books and still found I missed the picture. Then I studied the third time using Griffiths, it was like a light bulb just light up. Griffiths don't get too much into transmission lines, wave guide and antennas, but it make up in a lot more detail of the rest.
