What design engineers are able to achieve today would be unimaginable without software. Future high-end designs from advanced circuit architectures to System-in-Package based front-end modules to millimeter-wave RF CMOS designs will not be possible without software and the ongoing evolution of design software capabilities. The advances in software capability is often driven by the advances (and needs) in hardware development (at the component, sub-system and system levels)

Reconstructing the history of RF/microwave CAE/EDA software for our July cover story, “How Design Software Changed the World” through web-research and conversations with individuals who helped develop and support these tools uncovered some interesting reading. To learn more about the early days of RF/microwave software, refer to the list below, which includes some of the material used in writing this article.

A Heritage of Technology and Innovation: The History of Agilent EEsof EDA
by Gary Breed

Twenty years ago, electronic design automation (EDA) was an infant industry, particularly for high frequency RF and microwave engineering. Only a few tools were commercially available and many companies developed their own high frequency design tools. The foundation of Agilent EEsof EDA was established in these earliest days of design automation.
Read more

COMPACT – Microwave Circuit Optimization Through Commercial Time Sharing
By Les Besser

The SPICE program was developed at UC Berkeley in the early 1970s to computerize low-frequency analog circuit design. In those days, microwave designers did not have any significant commercially available CAD tools until the introduction of COMPACT (Computerized Optimization of Microwave Passive and Active CircuiTs) in 1973. Initially, the program was only available through commercial timesharing systems, but in a few years in-house versions were also offered. The ability to optimize complex microwave circuits eventually convinced many reluctant engineers to accept CAD as a practical design tool and as a result revolutionized circuit design.

Nonlinear Circuit Analysis Using the Method of Harmonic Balance – A Review of the Art. Part 1. Introductory Concepts
By Rowan Gilmore and Michael Steer

The harmonic balance method is a technique for the numerical solution of nonlinear analog circuits operating in a periodic, or quasi-periodic, steady-state regime. The method can be used to efficiently derive the continuous-wave response of numerous nonlinear microwave components including amplifiers, mixers and oscillators. It efficiency derives from imposing a predetermined steady-state form for the circuit response onto the nonlinear equations representing the network, and solving for the set of unknown coefficients in the response equation.
Read more

Nonlinear Circuit Simulation in the Frequency-domain
by Kenneth S. Kundert and Alberto Sangiovanni-Vincentelli

Simulation in the frequency-domain avoids many of the severe problems experienced when trying to use traditional time-domain simulators such as Spice [1] to find the steady-state behavior of analog, RF, and microwave circuits. In particular, frequency-domain simulation eliminates problems from distributed components and high-Q circuits by forgoing a nonlinear differential equation representation of the circuit in favor of a complex algebraic representation.

Parametric Harmonic Balance
By Yngve Thodesen and Ken Kundert

Harmonic balance has established itself as an important techniques for simulating high frequency circuits. However, this simulator struggles on strongly nonlinear circuits, particularly if there are several input signals at different frequencies.

An important observation is that multi-tone nonlinear circuits usually react in a strongly nonlinear fashion in response to one signal, but in near-linear fashion in response to others. In this paper we present an extension of harmonic balance that exploits these properties to reduce the time and memory required to perform accurate circuit-level frequency-domain simulation of mixers.