1.2 The Importance of Intercepting and Analyzing Radar Signals 截获并分析雷达信号的重要性

The first large-scale use of radar occurred in World War II. No sooner had radar been deployed (by both sides) than the effort to counter it spawned electronic countermeasures (ECM), which included the interception of the radar’s signals. In today’s terminology, this is called electronic attack (EA). In the early 1940s, “the basic countermeasures principle was simple. A ship or aircraft carried a rapidly tunable receiver which could scan the wavelength bands in which enemy radars might be operating. If one was detected, its strength and characteristics gave clues as to the dangers involved and what the next tactic should be. If the operator was flying over enemy territory, he could switch on a jammer, a powerful transmitter which would overload the radar receiver rendering it ineffective, or he could dump bales of aluminum ‘chaff’ from the airplane, or he could dump and jam” [2]. A side effect of the large amounts of chaff cropped was that thousands of cows died in Germany from eating the foil as they grazed.

雷达在第二次世界大战中得到了广泛地使用，几乎与此同时，战争双方都开始采取有效的电子对抗措施保护己方目标，以躲避雷达的侦察。之所以当初称之为“Electronic CounterMeasures (ECM)”，关键在于当时的战术策略主要是干扰并躲避，即雷达是矛，ELINT是盾；但现在的情形已经发生了巨大的变化，对于侦查到的雷达设施，我们希望到达摧毁的目的，因此ECM进化成了“电子攻击（EA, Electronic Attack）”，这意味着ELINT已经占据了主动进攻的位置。在早期的电子对抗中，ELINT接收机是非常简单的，就如同我们经常使用的收音机一样，在一定的频段内进行搜索，如果发现信号则立即报警，这时候可以采取的反制措施包括：打开大功率发射机阻塞敌方雷达接收机或抛洒大量的金属箔条形成伪目标等。

 

The following illustrates the fundamental role of ELINT in preventing disastrous technological surprise [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 over which the radar echo could effectively be returned. The U-boat therefore had time to dive before actually being sighted by the searching aircraft. In turn, general effectiveness of the RAF antisubmarine 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.

二战中电子对抗的一个典型例子是英国皇家空军与德军潜艇的较量。1942年初，英国皇家空军采用L波段的雷达搜索海面上的德国U型潜艇，当德国人得知这一情报后，在潜艇上安装了L波段的接收机用于探测英国飞机上的雷达信号。由于接收机能够在雷达探测范围之外截获其发射的信号，那么德国潜艇能够在英国飞机捕获到目标之前下潜，从而避免英军飞机的袭击。随着战争的进行，英国人发现己方的反潜能力大幅度下降，他们找到了德国潜艇能够提前下潜的原因，同时将飞机上的雷达由L波段换成了S波段。德国潜艇上的接收机是工作在L波段的，自然接收不到S波段的信号，也就不能够察觉到英国飞机的威胁了。

 

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 new S-band radar was in use.

由于德国潜艇不断遭到英国飞机的袭击，德国人急于想弄清楚究竟是什么事情扭转了战局；根据侥幸生还的德国艇员的描述，他们一直以为是某种红外武器的作用，并针对这种幻想出来的武器制定了防护措施。毫无疑问，在德国人知道S波段雷达之前，这场战争无疑是他们的噩梦。这场简单的较量，包含了太多的引人深思的道理，也许我们应该谨记那句耳熟能详的古语：“知己知彼，百战不殆”。我的博客以前也写过这一事件，可参考：

http://www.sciencenet.cn/m/user_content.aspx?id=354361

 

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

  战争的本身不再于谁强谁弱，而在于谁能够发现自己的长处和对方的短处。

 

  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 often 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. It is obvious that the lack of information by the opponent side is the basic requirement of the so-called “secret weapon”.

  在上面这一段中我最注意的是这个短语“lack of information”，而现代社会的信息已经不仅仅只有雷达信号了。

 

  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 solution to the problem of generating high power for 10 cm radar, and simple crystal receivers for reconnaissance purposes were indeed available, if the Germans had cared to use them in this application. High sensitivity is not necessary for intercepting high-power sources.

  L波段是指电磁波频率为1~2GHz，S波段则为2~4GHz，大功率磁控管是S波段雷达研制成功的关键因素。

 

  Of course, one can find more recent examples of the value of radar interception than World War II. In the Vietnam War, there were heavy losses of aircraft because of the large-scale use of surface-to-air missiles. New tactics and the use of radar warning receivers designed with the aid of ELINT data helped reduce U.S. aircraft losses and allowed the North Vietnamese air defense to be destroyed with much lower losses on the U.S. side [4]. Similarly, the SA-6 missiles supplied by the Soviet Union to the Arabs in the October 1973 conflict with Israel proved a major factor in destroying low flying Israeli aircraft. New tactics and jammers eventually overcame the advantage achieved by the Arab combatants through technologies surprise [4].

  通过列举越南战争和中东战场上的一些例子，进一步说明电子情报侦查的重要性。

 

  Radar uses have proliferated, particularly for military applications, but also for civilian air traffic control, harbor surveillance, weather monitoring, and so on. Prudence requires knowledge of the military capabilities of potential adversaries, and this means continued use of receivers to listen for radar transmissions and all of the other aspects of ELINT. For this reason, the accumulation of knowledge of radar signals has a peacetime role in proportion to the development of modern weapons, many of which incorporate radar target detection and tracking.

  即使是在和平年代，对于电子情报（不限于雷达信号）的截获和分析都是非常重要的，情报分析的结果有利于我们国防建设的针对性；战争的胜负是在一瞬间决定的，但这一瞬间的事情完全取决于平时的勤奋与否。

 

  Consider the following remarks of Soviet authors, Rear Admiral Peronmov and Captain First Rank-Engineer A. Partala from their essay “A Look at Development of Means of Electronic Warfare” [5]:

  The military effectiveness of electronic countermeasures, even with emphasis on real life experimentation, must be regarded as confirmed only under the condition that basic characteristics of the electronic weapons of the opponent have been revealed with sufficient accuracy. But the possibility of dependably uncovering and obtaining this information is an extremely difficult task, according to American specialists; “… Experience in battle with application of means of ‘electronic warfare’ in Southeast Asia”, writes the American press, gave evidence that even the most modern reconnaissance [intelligence] is not able to secure timely disclosure of all nomenclatured radio-electronic means, their tactical-technical characteristics, and special military employment. And, therefore, from the beginning of military operations various surprises are probably inevitable. For prevention of large material losses and tactical operational failures, questions about preparation for ‘electronic warfare’ cannot really be left without attention.

In [5], these remarks are interpreted to mean: “If you don’t know the exact details of the electronic threat and fail to prepare effective countermeasures in advance, you will be shot down or sunk.”

以上的一段文字十分有趣，这位美国作者引用了前苏联军事专家的文字来阐述电子情报侦查的重要性，而在前苏联军事专家的文字中又包含了一部分引述的美国专家的语句。看来这两个超级大国之间的战争是永远不会停息的，它们永远都在窥探着对方的一举一动。最后一句话的措辞是很严厉的，它严肃地警告我们：如果你不清楚当前电子威胁的细节，从而无法预先采取有效的防护措施，那么你将面临的是失败或死亡。

 

ELINT has an important role in maintaining defensive capabilities and preventing surprises – in this very real sense, knowledge is power, and where hostile radar is concerned, ELINT provides a great deal of knowledge. The path to that knowledge begins with antennas, receivers, and strategies for search, which are major topics of this book, and continues through the measurement of signal parameters and the recording and reporting of the interceptions for more detailed analysis.

分析ELINT数据是必须的，也是非常有用的，我们需要从中获取尽可能多的对手的信息。

 

The data gathered is typically about a potential rival’s defense network, such as radars, surface-to-air (SAM) systems, and aircraft. ELINT can be gathered from ground stations near the hostile country, from ships near the coast, from aircraft near the airspace, or from satellites in space. This may lead to incidents where aircraft or ships stray into hostile waters or airspace. In one particularly dangerous incident, a Chinese fighter collided with a U.S. reconnaissance aircraft and forced it to land in China.

对于情报信息的获取，可以采用多种多样的方式，而美国人总是骚扰我国边境的目的就是要截获尽量多的电波信号（以雷达信号为主）。看这位作者的口气，他似乎不认为这是非法入侵，而是在保护他们美国的利益不受我们的侵害。

 

ELINT data is valuable in the event of a conflict. Knowledge of the location and type of SAM and antiaircraft artillery (AAA) systems allows planning to avoid heavily defended areas, making use of flight profiles which will give the penetrator the best chance of avoiding hostile fire. It also enables intelligent jamming of an enemy’s defense work. Knowledge of the whereabouts of ships, command and control centers, surface-to-air missile systems, and other assets of the enemy permits them to be attacked if need be. ELINT is important to stealth operations because stealth aircraft are not totally undetectable and also need to know which areas to avoid. Of course, ELINT data is an important part of network-centric warfare. One way it is used is “traffic analysis” of ELINT signals. In ELINT, it is not the message that is of interest as it is in communications intelligence (COMINT); rather, it is the type of signal, the location of its transmitter, and the timing of the transmissions relative to other events which may be taking place.

为了避免雷达的追踪，隐形武器逐渐得到追捧，但隐形并不意味着完全消失，它只能削弱雷达回波的能量。随着雷达新技术的不断涌现，隐形武器也面临着巨大的挑战，而迎接这一挑战的最简单的措施也许就是ELINT信息的积累与更新。

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