A method of and apparatus for mitigating adverse transmission and/or reception effects that an obstruction would otherwise have upon a RF signal to be transmitted or received, the RF signal being available at a feed point and wherein the obstruction is spaced from the feed point in a direction of desired transmission or reception. An artificial impedance surface is disposed adjacent the feed point and the obstruction, and the artificial impedance surface is designed (i) to have a spatially non-varying impedance function in a constant impedance region at least immediately adjacent the feed point and (ii) to have a non-constant impedance function in one or more regions spaced from the feed point and closer to the obstruction.