Principles of Electronic Warfare

Robert J. Schlesinger, Floyd E. Nixon, C. W. Besserer

• Publisher: Barakaldo Books
• Year: 2020
• eBook ISBN: 9781839745157
• Topic: History
• Subtopic: Military & Maritime History
• Index: History

Originally published in 1961, by a team of scientists and engineers from Convair led by Robert J. Schlesinger, this classic book still provides an excellent analysis of the principles of electronic warfare even today."During World War II, the rapid growth of military electronics had its start. Today, and in the foreseeable future, large-scale weapon systems depend and will depend on electronic technology.The importance of these electronic weapon systems to the overall concept of warfare is often obscured in detailed discussions of specific systems. For this reason, a broad understanding of the principles involved is essential. It is significant that these principles involve both engineering sciences and military strategy. In electronic warfare the terms "radiation" and "detection" must be considered in the same light as "offense" and "defense" are in strategic and tactical warfare."—From the Introduction

1—THE SCOPE OF THE PROBLEM

SOME ELEMENTS OF THE PROBLEM

It is our goal in this book to set down some of the existing theories, explore the current philosophies, and define the present problems connected with electronic warfare.

One of the first problems to consider is a definition of electronic warfare that will be acceptable in the situations to be discussed. In the context of this book, the interaction between two or more communication systems for the purpose of intentional interference will represent electronic warfare. A communication system is here understood to be any electronic device that radiates and/or receives information.

The problems concerned with when, where, and how to generate this electronic interference and, on the other hand, the action to be taken to counter its detrimental effects are of fundamental importance to electronic warfare. The former problem is generally referred to as Electronic Counter-Measures (ECM) and the latter as Electronic Counter-Counter Measures (ECCM).

It is the end purpose of ECM to interfere with the successful operation of an opponent’s weapon system; particularly weapon systems that might be used to destroy the vehicle (for example, an aircraft) on which the ECM equipment is carried.

Since the jamming of radar, communication, and missile guidance systems tends to accomplish this end purpose, these are the areas in which ECM has found its widest application.

It is natural to expect that as weapon systems came to place more reliance on the use of electromagnetic radiation as a connecting link among their elements, the weakness inherent to such a link would be exploited. Unfortunately for the user, one of the weaknesses of these systems lies in the fact that the radiation of Radio Frequency (RF) energy, in most of its applications, is not secure from detection and interference. To be sure, considerable effort is expended in some applications, notably communications, to provide some degree of security. However, since all weapon systems of the type considered here must transmit information in order to be useful, their security becomes a function of the detector used to intercept the signal. If the enemy has exactly the right type of receiver for the signal characteristics being transmitted, security is extremely difficult, if not impossible.

The subject of security is considered here because of its basic importance to the intelligent application of ECM methods. If the presence of a hostile signal cannot be detected, no jamming action can be initiated wisely. After detection has been accomplished, it is necessary to establish the information content of the signal to determine if jamming is required. Typical techniques of preventing these two steps from being carried out include high-speed transmissions and pseudo-noise generation with correlation to impede detection, and coded modulation methods to prevent information analysis. Many other techniques are used, some of which will be discussed in later sections of this text.

We have introduced two of the primary requirements for the employment of ECM: (1) it is necessary to detect the radiation from an enemy system; (2) it must be established that it is desirable to jam the signal detected.

It is not always in the best interest of the mission to jam every signal being emitted within enemy territory. For example, if an incoming bomber raid detected radiation, but did not analyze the signal, ECM transmitters might be turned on to jam a local UHF television station. This would hinder, more than aid, the success of the raid. Once the jamming transmitters are turned on, a public announcement is given that hostile aircraft are in the area. Because of the “beaconing” effect{1} of these transmitters, the area alerted is much larger than that covered by the surveillance radars alone.

In the foregoing discussion two important steps were defined that are necessary to the evaluation of the electronic environment with respect to the presence of hostile signals. This evaluation has up to this point depended only on the type of monitoring equipment carried aboard the penetrating aircraft and is therefore basically a reconnaissance function. If reconnaissance is the primary purpose of the flight it is not generally necessary to carry jamming transmitters.{2} A record of the signals intercepted can be stored on tape and/or film for use at a later time. (The application of reconnaissance information will be covered in the fourth chapter.) However, if the mission of the raid is to reach a specific target the use of active ECM techniques may be required to confuse and jam enemy air-defense systems.

When sufficient information has been received to determine that jamming tactics should indeed be employed, a second set of problems arises. These problems concern the actual ECM tactical considerations. For example, some of the questions that must be answered include: What mode of jamming should be used? How long should it be used? How many of the aircraft should use it? Exactly when should the jamming transmitters be turned on? To answer these questions, something must be known about the operational constraints imposed by the raid configuration, its mission, and the characteristics of the ECM equipment being carried.

It can be seen that the introduction of so many variable factors makes a general solution to the ECM tactics problem extremely difficult. However, if a specific raid is considered and previous reconnaissance data have given some details of the hostile electronic environment to be encountered in the target area, optimum ECM tactics may be established. Unfortunately, this information can seldom be provided in the detail desired.

The Strategic Air Command (SAC) force required to penetrate deep into enemy territory would like very much to have a general tactic to employ in the face of an unknown electronic environment. This is a basic problem that has been of major concern to both military and civilian planners engaged in establishing electronic-warfare strategies. Before further consideration of this problem is undertaken, one additional complication and some illustrative examples will be discussed.

TECHNICAL SUPREMACY AND THE SECRET WEAPON

In many studies it has been shown that “technical supremacy” is a critical factor. Should SAC bombers encounter an air-defense system using tracking and missile-guidance radars operating at a frequency of 40 kmcs, when the highest-frequency ECM equipment they carried was 30 kmcs, the results could be fatal! Generally, since the monitoring receivers do not search higher in frequency than their companion jamming transmitters, the first indication the raid would have of their being illuminated by the enemy defense system would be the explosion of surface-to-air or air-to-air missiles. In this case, even if they had employed their ECM transmitters blindly, no amount of jamming would have reduced the effectiveness of the enemy air-defense system. The SAC bombers were not technically equipped to defeat the threat they encountered in this example. However, the correct employment of chaff at the proper time may have been of some aid. It is not uncommon to find chaff and active ECM used simultaneously in certain cases. For deep penetration raids, requiring many hours of flying time over enemy territory, it is impossible to carry enough chaff for continuous dispersal. Therefore, some operational information to establish the correct time to disperse the chaff is still required.

Perhaps the most interesting case of technical supremacy is the now classical example of submarine searching carried on during World War II.{3}

In early 1942, the RAF Coastal Command used L-band radar as an aid for locating German U-boats recharging batteries on the surface. The overall effectiveness of the RAF in this task was quite good until the U-boats began using L-band search receivers. These receivers allowed the submarine to hear transmitted radar signals at a range greater than that over which the radar echo could effectively be returned. The U-boat therefore had time to crash-dive before actually being sighted by the searching aircraft. In turn, the general effectiveness of the RAF anti-submarine effort decreased. The Allies, realizing what had happened, installed new S-band search radars aboard their aircraft during early 1943. As a result of the effectiveness of new equipment the intercept rate rose sharply. German submarines sitting on the surface, listening to L-band search receivers, became vulnerable targets for S-band radar directed aircraft.

As the U-boat sinkings increased, the Germans tried frantically to determine the method of detection the Allies were using. Since reports from surviving submarines stated that no radiation had been heard in their L-band search receivers prior to the attack, it was thought that perhaps an infrared detection device of some type was being employed. Considerable effort was spent in an attempt to combat a non-existing infrared threat. U-boat activity was greatly reduced by the time the German High Command realized that a new high-frequency radar (S-band) was in use.

This is an interesting example of a weapon (L-band radar), a counter measure (L-band search receiver), and an improvement (S-band radar) providing a clear margin of technical supremacy.

There is another point to be considered. To be sure, the use of S-band radar employing magnetrons and extending the useable frequency by a factor of ten provided a definite advantage. However, had the Germans had information as to what was being used, the time lag until they were able to develop an effective S-band search receiver would have been greatly reduced. An added advantage was gained by the Allies because of the Germans’ lack of information. It is obvious then that the enemy’s lack of information is the basic requirement of the so-called “secret weapon.”

This point is mentioned here because illustrated in this example is one of the important roles of electronic reconnaissance. Had the Germans been conducting an extensive reconnaissance program at the time, it is probable that they would have intercepted S-band signals from magnetron oscillators in the development and testing stages during flights over England. The development of the magnetron was, of course, the crux of the problem of generating high power for 10 cm radar, but simple crystal receivers for reconnaissance purposes were indeed available, if the Germans had cared to use them in this application. Sensitivity is, of course, not necessary for intercepting high-power sources. Therefore, special requirements of a reconnaissance system include being general enough to intercept the unexpected and providing intelligence inputs for an advanced ECCM program. Other relationships between ECM, ECCM, and reconnaissance will also be taken up in the fourth chapter.

DYNAMIC DEVELOPMENT OF AN ECM TACTIC

It was stated, prior to these examples, that it is difficult to specify a general ECM tactic to be employed on any and all raids. When intelligence information is complete and exact on the defenses of any given area or target (the precise types and location of all air-defens...

Table of contents

• Title page
• TABLE OF CONTENTS
• DEDICATION
• PREFACE
• 1-THE SCOPE OF THE PROBLEM
• 2-TECHNIQUE AND TACTICS
• 3-NOISE, PROBABILITY, AND INFORMATION RECOVERY
• 4-ELECTRONIC RECONNAISSANCE
• 5-RADAR CONSIDERATIONS
• 6-THE ROLE OF ANTENNAS IN ELECTRONIC WARFARE
• 7-OPTIMIZATION-CONSTRAINTS AND INCOMPLETE INFORMATION
• 8-SOME ASPECTS OF ELECTRONIC WARFARE IN THE SPACE ERA
• BIBLIOGRAPHY