Two of the software developments represent improvements on the method-of-moments calculation used to simulate radiation patterns in metal interconnects and antennas. The method-of-moments calculator examines the eddy currents flowing through a metal interconnect such as an antenna, then looks at the radiation fields these surface currents create and determines their impact on adjacent fields.

But method of moments is largely a two-dimensional analysis, said Sonnet Software senior engineer James Willhite. In addition to computer run-time penalties, the method-of-moments calculation can introduce inaccuracies. The calculation typically uses two cells to represent one area: one cell for electrical currents, the other cell for magnetic fields, Willhite said.

One answer to this problem is an Eigenmode simulator, which uses what Sonnet calls an "integral analysis" in the time domain. The Eigenmode solver uses linear and nonlinear equations to infer field effects from resonant 3-D structures, and an integral analysis builds the radiation effects from the equations. Computer Simulation Technology (Darmstadt, Germany), Sonnet's software development and marketing partner, manufactures Microwave Studio. As embodied in Microwave Studio, an Eigenmode solver can depict the radiation patterns from cell phones, coaxial cable connectors or IC lead frames in a fraction of the time required by full method-of-moments calculators, Sonnet said.

Ansoft's answer to the method-of-moments calculation is SVD FastSolve, a singular-value decomposition algorithm developed at Bell Labs and licensed to Ansoft. SVD FastSolve is essentially a matrix decompression algorithm that reduces the complexity of the calculations, said Richard Hall, Ansoft's director for planar product development. The SVD algorithm, as embodied in version 7.0 of Ansoft's Ensemble planar structure simulator, allows the simulation of larger, more complex structures. An electrically large structure — like the layout for a cellar handset power amplifier — would take 15 to 20 Gbytes of memory without compression. The SVD algorithm reduces the memory requirement to about 800 Mbytes, Hall said. Thus, an equation with 50,000 unknowns that would take the Jet Propulsion Laboratories a week to solve on an advanced supercomputer could now be solved on a PC, Ansoft said.

Xpedion launched two product developments at MTT-S. One is neural network technology that was developed for use with RF modeling and will be integrated with other environments, said Rich Curtin, director of product marketing.

Circuit-level simulation of RF devices has been regarded as something of a black art, Curtin said. Applied to device modeling, neural net technology can be used to develop highly accurate "equivalent circuits" to replace current-voltage elements. The model of an RF IC, even a GaAs transistor, can include dozens of nonlinear circuit elements such as inductive and capacitive elements, as well as nonlinear resistors and diodes. Xpedion is working with Fujitsu Compound Semiconductor, a manufacturer of GaAs devices, to develop behavioral models with improved accuracy-a C-language function that can substitute for the otherwise complex physics of the device.

Predefined models in the new Golden Gate software include GaAs MESFETs, MOSFETs, JFETs and diodes. These models take into account charge and current effects, delay and memory effects, Curtin said. They define equations for lumped elements and voltage-dependant current sources. By building on these detailed models (based on IV measurements), Xpedion tool users like Fujitsu can create their own device-equivalent circuit for larger multidevice subsystems like power amplifiers and low-noise amplifier receivers.

The neural net technology enables a significant reduction in engineering time spent developing model equations, Curtin said. The equivalent models are accurate, easily parameterized and can be used with any simulator supporting C-code interface, he said.

Another Xpedion goal, according to Curtain, is to make the Xpedion modeling tools function with Cadence's SPW and the MathWork's MatLab modeling tools.

Applied Wave Research, a startup which debuted at MTT-S two years ago, was on hand this time with Microwave Office 2000, a Windows-based simulation and layout suite for RF system design. The new release combines an IC and pc-board layout editor, called Artisan, with circuit simulation and electromagnetic analysis tools. It includes the Voltaire XL linear and nonlinear RF circuit simulator, which in turn includes Harmonic Balance and Volterra series simulation engines. The harmonic balance simulator — ordinarily a computer run-time burden because it uses an iterative error function to converge on a solution — runs fast in the Microwave Office environment, said Applied Wave Research vice president Steve Evans-Pughe. That's because the simulator was developed directly for the Windows environment, rather than ported from another platform, Evans-Pughe said.

The Volterra series calculator offers a fast means of analyzing intermodulation in "mildly nonlinear" circuits, according to Evans-Pughe, and is 10 to 100 times faster than a multitone harmonic balance simulator. In addition, Volterra series analysis integrates easily with linear analysis, allowing noise figure and other linear characteristics such as gain, port VSWR and the like, to be optimized simultaneously with intermodulation.

The Microwave Office 2000 expands the functionality of the original design suite with physical layout for MMIC, RF IC and RF printed circuit boards. In addition to an intelligent routing engine, printed circuit boards and LTCC, the new version of Microwave Office includes tweakable models of GaAs ICs that can be fabricated by UMS in Europe and by TriQuint in the United States. An optional data migration tool allows users to import designs from Agilent EEsof's Series IV and ADS tools, Evans-Pughe said.