Overview

From APPLIED MICROWAVE & WIRELESS, VOL. 6, NO. 1, WINTER 1994

The development and testing of numerous products depends on accurate prototyping of the circuit boards. Not very long ago, the typical method of designing a microwave filter required that a microwave engineer spend hours using either a Smith Chart or a nodal CAD program, creating trial and error designs until the desired performance was calculated. Even then, there remained the necessity to render the design as an art work and to send the art to a circuit board etching shop. This process could take many days, even weeks, and might cost from $200 to $2,000 before an etched board was obtained for testing. Now, with RF simulation software and the use of a numerically controlled milling machine, an engineer can design and fabricate a prototype microwave filter in a few hours.

Filter Design

A fifth order hairpin filter with a 400 MHz bandwidth and center frequency of 3.3 GHz is shown in Figure 1. The hairpin filter was chosen because its size is 2 inches shorter in length than that of a comparable performance-edge coupled filter. The filter shown is ideal for use before or following a system preamplifier to eliminate out of band noise. This filter was made on Arlon s AR350L copper clad dielectric substrate material. For the CAD we used Eagleware s M/FILTER microwave synthesis software. Only three hours were required to design and fabricate the prototype filter.

Figure...