Hi all, I have used moats on a couple of designs. Basically to "direct" the RF return currents where you want them to go. Use the same moat on all layer. You can check the book: "EMC and the Printed Circuit Board. Design, Theory, and Layout Made Simple" by Mark I. Montrose. IEEE press, ISBN 0-7803-4703-X. Hope this can help, Best Regards, Jean Cayer, Design Techn. Cetso inc. 150 Duquet Ste-Thérèse, Québec, Canada J7E 5B3 fax: 450 971-7802 mailto:[log in to unmask]