Microwave System Design Tools

and EW Applications

Preface

Based on extensive use of embedded interactive graphic Java applets, this project represents a new approach to technical electronic books. Applets greatly simplify the presentation of information, and their interactivity significantly speeds up the understanding and learning process.

The topics and applets have been selected to cover technical requirements likely to be met in the microwave radar and EW system design fields. With the widespread use of fast personal computing there is now no reason for engineers to use approximate rules in the design of broadband microwave systems. Several very good Mathematical CAD packages are available which cope with complexity of modern microwave system analysis but require considerable experience in their use and a good understanding of mathematical modelling processes. This e-book toolbox exploits Java applets as a very convenient graphical method for not only calculating accurate design parameters, but also serving as a valuable interactive learning aid. They permit the limits of a design to be ascertained without the need to delve deeply into the supporting mathematics and cope extremely well handling many variables in real time.

The applets are backed up by short background summaries and derivations of the key analysis equations used to model the subject. The technical text is not intended to be as detailed or as comprehensive as a conventional textbook, but is intended to complement the excellent descriptive works available. The bibliographies and references at the end of each topic point the user to conventional technical support. The aim has been to make the applets as intuitive as possible so that the user can learn or design by interaction.

Whilst the applets all start with a reasonable set of default parameter settings, the user can vary these over very wide ranges to explore corner limits and ask what-if questions. The models used in the applets are as close to real operation as possible, although in some cases good mathematical approximations have been made to speed processing. Some are very comprehensive and almost like having a real system to test. With most applets, there is a facility for saving design data to a built-in data console and extracting this to the Windows clipboard for use in other applications, or for incorporation directly into a customer design specification.

Section 1, Components, covers basic microwave components and addresses basic component noise figure, demodulators, cascaded component VSWR, parabolic antenna design, the microwave filter, noise compression in limiting amplifiers, dynamic range of RF gain stages, video compression amplifiers, and finally, intermodulation performance of common mixers. There are nine applets associated with this section. The first two are simple calculating aids, but the third has proven to be one of the most useful and illuminating. The topic is VSWR of cascaded mismatches. Throughout my experience, microwave engineers have been advised to use the linear combination method but this applet clearly highlights its limitations for wideband use. Comprising a source, two transmission line components, separated by an attenuator, driving a resistive load, these five VSWR-specified devices produce a possible 32 different impedance combinations and clearly all load one another. The proper analysis is tedious but easily carried out in real time by a personal computer running an interactive applet. The result is sometimes surprising. Analysis of signal and noise suppression in an amplifier is a complex topic that is often avoided by considering only the linear and hard-limited regions. The applet throws light on what happens through the limiting region and, by treating the noise as having in-phase and quadrature parts, one can understand the effect of unequal compression on following demodulators. The applet on amplifier dynamic range is also worth discussing. It treats third-, fifth-, and seventh-order intermodulation component generation. The analysis problem is solved by first fitting a polynomial to the transfer characteristic and then collecting the components generated by each of the exponential terms and weighting them by the polynomial coefficients. In this way, it is easy to cover a very wide dynamic range, which also makes visible the interference between the contributions of the various exponential terms as the signal amplitude is varied. Users can input their own amplifier transfer characteristics for analysis.

Section 2, Receivers, is divided into two groups. The first applet compares the sensitivity of eight types of microwave receivers,
followed by others to aid the design of some of the more modern EW applied receivers. These include wideband RF detector-video, digital FFT,
and the compressive receiver.

The digital FFT applet is a good example that demonstrates the strengths of Java applets for rapid design prototyping.
There are 12 applet variables, all having an impact on the receiver design. Once a suitable design is achieved, the designer
can then immediately check the signal-to-noise performance in conditions of signal overdrive, signal frequency and time offset,
ADC linearity, and clock jitter. ADC spurii? They are all in there!

The second group of seven applets comprehensively cover aspects of signal digital thresholding, detection, and false alarms.

Section 3, EW Systems, details the design of IFM, interferometer, and amplitude comparison DF systems. The amplitude comparison applet compares the three main algorithms and users can input their own antenna patterns for evaluation.

Finally, Section 4, Field Performance, examines the real-world performance and application of microwave systems to the radar, EW, and communication fields. Applets include antenna near-field power, antenna polarisation coupling, ESM and radar detection range, evaluation of DF error sources and ESM clutter, passive location accuracy, ESM range advantage, and jammer protection zones.

The primary aim of the project was to provide a working and learning tool for microwave and EW design engineers. It may also be useful as an evaluation and demonstration tool for managers and marketing managers as well as a training and development tool for graduates and EW System operators.

My enthusiasm for Java applets has not waned since my first discovery and I hope others are bitten by the bug and run with this e-book concept.

Acknowledgements

The Java applet approach exploited in this e-book was inspired after visiting Fu-Kwun Hwang’s instructive tutorial on how rainbows are formed, and discovering how useful his Rainbow Applet was in the learning process.

Early applets in this project were based on a well-structured mathematical equation plotting applet called SimplePlot.java written by Elizabeth Odekirk; without such excellent grounding, it might not have taken off.

Applet suggestions and presentations have benefited from comprehensive vetting by my erstwhile colleague, Charles Arnold.

P W East May 2005