Introduction to RF Stealth

This book is based on material developed in the mid-1970s for stealth weapon systems.

The material remained classified for 20 years or more. All of the material in the text is from unclassified sources that have become available in the last 5 to 10 years.

Also, much of this material is in the public domain and first appeared in un-copyrighted

sources. It appears in many places, although I created much of it over the last 30 to 40 years. A few photos, tables, and figures in this intellectual property were made at Hughes Aircraft Company and first appeared in public documents that were not copyrighted. These photos, tables, and figures were acquired by Raytheon Company in the merger of Hughes and Raytheon in December 1997 and are identified as Raytheon photos, tables, or figures. The book is based on notes that the author and others prepared for Stealth Radar and Data Link courses, which the author taught between 1985 and 1996. There are several references to formerly classified documents.

The author may have the only copies in existence, because the government usually destroys them when they become unclassified. The “author” is the editor and compiler

of the material in this book. The ideas contained here are the products of an array of very bright people, and it is my privilege to summarize their work. Every attempt has been made to give credit where it is due, but the early originators were not as careful as they should have been in citing references, and some readers will undoubtedly find subjects in the text for which references aren’t properly cited. The author apologizes in advance for these errors, but 25 years in the black makes them difficult to correct. In addition, try as one will, there will always be mistakes that escape into the text; please notify me of those you find so that they may be corrected.

The author had the privilege of pioneering modern stealth techniques beginning in 1975. Because of the necessary requirements of security, this material is not widely known. As a result of this limited availability, people keep “reinventing the wheel,” keep “going down blind alleys” already explored, and keep making nonsensical claims. The book’s purpose is to provide a new generation of designers with a firm basis for new developments and to allow buyers of stealth technology to sort the charlatans from serious engineers. Much stealth technology is retrospectively obvious and mathematically simple but, before it is explained, it is not so easy to see. This introductory book presents first principles in a simple and approximate way. The author has tried to avoid repeating material easily found in other texts except where it is essential to understand the limitations of both stealth and counterpart threat sensors.

Some may find this book trivial and too simple even for an introductory text. Again, please accept apologies; the simplicity is because the author did not include anything

he couldn’t understand himself. Besides, if the book seems trivial, you’re already be yond the point of need, anyway. Mathematicians may be bothered by some of the approximations, but these approximations have proven to be adequate for real

applications. The text is oriented toward undergraduate seniors and graduate engineers

with some prior background in radar, communications, and basic physics. It approaches

each topic from a system engineering perspective. This is a labor of love, and it represents years of labor both teaching and writing.

ORGANIZATION OF THE BOOK

This book covers two major topics: low observables and low probability of intercept (LO

and LPI) of radars and data links, collectively sometimes called stealth. In most sections,

both are covered, because the signatures often interact. Each chapter has examples, student exercises, references, and counterpart appendices that describe the associated software on CDROM. Most of the analysis has been verified by experiment or computer

simulation by the “Famous Names of the Radar/Stealth World.” Much of the pertinent analysis in the form of computer programs is on the CDROM, which is described in Appendix A. Chapter 1 provides an introduction and history of RF/microwave LPI/LO techniques and some basic LPI/LO equations. Chapter 2 covers interceptability parameters and analysis. Chapter 3 covers current and future intercept receivers and some of their limitations. Chapter 4 surveys exploitation of both the natural and the threat environment and gives examples of one of the “great thoughts” of LPI/LO design, electronic order of battle (EOB) exploitation. Chapter 5 deals with LPIS waveforms and pulse compression. It covers another “great thought” of LPIS: Hudson-Larson complementary code pulse compression. Chapter 6 introduces some hardware techniques associated with LO/LPIS: low sidelobe/cross section antenna and radome design. It includes another of the “great thoughts” of LPI design: separable antenna illumination functions. Chapter 7 describes typical LPIS low-level RF and signal processing, which is often unique relative to conventional radar and data link processing.

 

David Lynch, Jr.

davidlynchjr@ieee.org

22000034

 

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