Many designs within these pages begin in software. More specifically, high-frequency designers now rely on software simulation tools to predict the performance of a design, or calculate the dimensions of transmission lines in a microstrip matching network, or create a high-quality-factor (Q) notch in a bandreject filter. Their software tools have evolved from home-grown code to more complex software "environments" combining circuit, system, electromagnetic (EM) simulators, and layout tools, as a sort of software-based method of "double-checking" deisgns.

Of course, with the growing sophistication of these software tools comes a corresponding increase in price. For larger companies, the higher cost of software is not an issue, since computer-aided-engineering (CAE) software is now an essential and accepted part of the high-frequency design process. But for smaller companies, or individuals with an entrepreneurial bent, the cost of a complete suite of CAE design tools can be prohibitive.

When funds are limited, there is still hope, since this industry offers a variety of free software programs. For designers of frequency synthesizers based on phase-locked loops (PLLs), for example, PLLSim is a free PLL simulator available from a number of different sites, while ADIsimPLL is a free design from Analog Devices based on the use of that company's synthesizer integrated circuits (ICs). The site www.microwavers.org offers a number of free software programs, including a transmission-line calculator, a microwave simulator, a synthesizer simulator andnot to be confused with their Advanced Design System (ADS) suite of design toolsthe classic ApCAD from Agilent Technologies.

Microwave Software offers six software programs at around $30 or less. The software programs include a Smith-Chart-based impedance-matching program (Smith- Match), a frequency-domain circuit-analysis tool (Sceptre), and a matching-network optimization program (OptiMatch). R. A. Wood Associates provides a number of low-cost tools, including RF Path Analysis Toolkit, SpurFinder, and RFSpecTest. Free trial versions are available on the R. A. Wood web site.

Even well-established software suppliers often offer free trial versions of their software, such as the EM simulator Sonnet Lite from Sonnet Software and Microwave Office and EM simulator AXIEM from AWR.

Of course, the old adage that "you get what you pay for" is usually true. But for some designs, basic software tools may be all that is needed, and without the sophisticated price tag.