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Software Advances As Computers Improve

Engineers relied on the knowledge of fundamental electrical relationships, such as Ohms Law, until improvements in computers enabled practical modeling and circuit analysis by means of software.

Computer-Aided-Engineering (CAE) software is a recent development when viewed over the past 50 years of this industry. What is now known as the commercial CAE software part of the RF/microwave industry only started to take root in the early 1980s. much of the credit for this goes to Les Besser, often referred to as the "Father of Microwave CAD," due to his creation of what was effectively the first commercial microwave software, COMPACT. Previously, high-frequency engineers who had computer access could use the SPICE (Simulation Program with Integrated Circuit Emphasis) program developed at the University of California at Berkeley in the early 1970s (sometimes referred to as "Berkeley SPICE"), but this was really a tool developed for lower-frequency analog circuit simulations.

Besser had spent time at Fairchild Semiconductors, Farinon Electric Co., and Hewlett-Packard Co., writing programs in BASIC and working on the available computers of that time (which were time-share systems). He developed circuit simulation programs to solve the equations applied by high-frequency engineers for such tasks as developing impedance matching networks for transistors. Besser's first software program was completed while he was at Fairchild, a tool called SPEEDY which was nominally intended to promote the company's transistors by making them easier to use. The program was backed by available scattering (S) parameter files for the firm's transistors, enabling simulations of circuits using those transistors and their S-parameter files.

Besser would eventually start a business to sell a program called COMPACT, an acronym formed of letters from the phrase "computerized optimization of microwave passive and active components." This program included performance optimization, which was not part of SPEEDY. the business was called Compact engineering, later to be renamed Compact Software. Its time-sharing COMPACT microwave simulation program became an industry standard for many leading electronics companies. When Compact Software merged with Communication Satellite Corporation (COMSAT), Besser stayed on board for another three years to manage microwave software development, including the creation of a next-generation version of COMPACT known as SuperCOMPACT.

Meanwhile, SPICE software continued to improve. Created by Lawrence Nagel at the University of California at Berkeley with help from his research advisor, Professor Donald Pederson, the software was designed to translate the various elements in a circuit into a series of nonlinear differential equations that would then be solved to predict the electrical behavior of those circuits. The earliest version of SPICE (SPICE1) was written in FORTRAN computer code and relied on nodal analysis of a circuit to create the nonlinear differential equations. The early SPICE programs had only a handful of model representations for circuit elements. But as the software was enhanced in subsequent versions, such as SPICE2, and became more capable of modeling complex circuits, such as integrated circuits (ICs), more industry companies became involved in developing models for SPICE. In addition, more variants of SPICE became available. These included HSPICE, which is now supported by Synopsis, and PSPICE, which is now owned by Cadence Design Systems.

As computing power became more available, software quickly moved from mainframes and time-sharing systems to programs written for individual PCs, and smaller companies, such as CIRCUIT BUSTERS (later to become Eagleware) started by Randy Rhea. Around the same time, significant efforts at converting Maxwell's equations into computer code had begun. Zoltan Cendes, who started Ansoft and developed the code for the early High- Frequency Structure Simulator (HFSS), and Jim Rautio, whose company Sonnet Software and code of the same name, were among early champions of microwave EM simulation.

For an extended look at the history of microwave CAE, don't miss our exclusive report in the special 50th Anniversary Issue of Microwaves & RF.

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