Abstract
Broadband Wireless Access systems, such as Local Multipoint Distribution Service (LMDS) and Multipoint Video Distribution Systems (MVDS) tend to operate at mm-wave frequencies where large allocations of spectrum are available. These frequencies were previously utilised by low volume applications such as radio astronomy and military systems. The techniques developed and the prices of parts reflected this. As the consumer market for Broadband Wireless Access equipment matures, new techniques are being developed which allow the production of mm-wave equipment in high volumes at low prices. This paper describes the design and development of upconverter and downconverter Multi- Chip Modules (MCMs) suitable for manufacture at low cost, in high volumes. The modules utilise printed filters, GaAs MMICs, discrete SMT components and a PTFE composite soft substrate.

Introduction
Equipment operating at mm-wave frequencies was traditionally the preserve of radio astronomy and the military. Systems were produced in low volumes and were normally hand-crafted; as such they tended to be very expensive. Today the use of mm-wave systems for commercial applications is growing rapidly. In particular, broad band multi-media services, such as LMDS and MVDS, have the potential to become very high volume markets for mm-wave electronics. This growth in the commercial use of mm-wave equipment has placed tremendous pressure on suppliers to reduce their costs.

GaAs Monolithic Microwave Integrated Circuits (MMICs) offer a means of fabricating large quantities of highly reproducible, low-cost mm-wave circuits. However, module assembly techniques, suitable for circuits operating at mm-wave frequencies, can be complex and costly. They also tend to be incompatible with low cost assembly methods, which could be adopted for the biasing, control and IF circuitry. This paper describes the development of a low cost route for producing mm-wave sub-system assemblies. A PTFE substrate is used, rather than ceramic and the attachment of bare die and SMT components can be performed in a single process step. Details of the design, fabrication and measurement of a 27.5 to 29.5GHz upconverter and a 27.5 to 29.5GHz downconverter, developed using these techniques, are presented.

Substrate Manufacture
Careful choice of substrate is vital. As well as being low cost, the substrate should possess the following properties for optimum use at mm-wave frequencies:
• Thin substrate height (to reduce dispersion and radiation losses)
• Low dielectric constant (helps reduce effects of tolerance variations and avoids dimensions of distributed structures becoming impractical)
• Well con