Thick metal plate insertion make FR4 multilayer board a simple carrier for RF power circuits

In order to reduce sizes and costs of microwave circuits and to simplify their integration together with IF, control and power supply networks, we tested (1) a simple solution that allows using FR4 boards also for microwave circuits. Since FR4 boards are necessarily present in every equipment for power supplies, control, digital and IF circuits, it becomes possible to reduce the number of boards or modules collecting all the networks (operating from DC to tenth of Gigahertz) on the same FR4 multilayer. The typical RF requirements of good thermal and electrical ground and the need of a carrier for "chip on board" monolithic assembly are all achieved through the insertion of a copper plate a few tenth of millimetre thick. This copper plate replaces the second metal layer of FR4 multilayer remaining within standard FR4 process; monolithics can be mounted on it just opening a window on the first layer.