This paper presents the design methodology for the micromachined circuits operating in the microwave and mm-wave frequency region. The design is based on dividing the circuit into membrane-supported components, bulk components and membrane to bulk transitions. Every region is modeled using appropriate and techniques using full-wave electromagnetic simulation software. As illustrative examples, the design of band-pass filter structures and double-folded slot antenna arrays are briefly described. The micromachined structures were fabricated and measured results are presente