Abstract: A microwave circuit module, more particularly an antenna, comprised of a polyethylene foam substrate having a loss tangent less 0.001 and a dielectric constant less than 1.3, a predetermined pattern of one or more elements, such as an array of n.times.m radiator elements, formed of electrically conductive material, deposited on a first surface of the substrate, and an electrically conductive ground plane secured to the opposite surface of the substrate. In the antenna embodiment, a feed network formed of electrically conductive material is deposited on said said first surface of the substrate for electrically interconnecting the radiator elements in the array; and I/O means are coupled to the feed network for supplying a signal to be transmitted by the antenna or for receiving a signal received by that antenna.