The design and development of a multilayer RF circuit card

The goal of this project was to design an airborne radio frequency circuit card that was very light weight, occupied a small volume, and operated from 20 Mhz to 1500 Mhz. The circuit card being reported on is called an RF multicoupler, and is one of two cards used in a radio frequency distribution unit (RFD). This unit interfaces a large number of receivers to various antennas.

In the past this type of circuitry was done by cascading discrete connectorized RF components together with coaxial cable. As technology progressed the discrete surface mount or pin through RF components were mounted on single layer fiberglass or Duroid circuit cards. The next generation improved circuit density by incorporating a multilayer RF circuit card in which RF and digital control signals were run on the internal layers.

The RF multilayer circuit card in this project represents the state-of-the-art for high density RF circuitry. The board material is a teflon/fiberglass composite. The discrete RF components are surface mount and the passive higher frequency components are physically incorporated into the RF circuit card itself as stripline RF circuits.

Thus, by using advanced board materials, a multilayer construction, integral stripline components, and a light weight aluminum housing, it was possible to achieve dramatic weight reductions.

Finally, much effort was expended in "up front engineering" to ensure that this RFD was capable of being transitioned from a laboratory prototype to a production unit capable of being manufactured in large quantities.