World Naval Developments

By Norman Friedman

The show also featured a variety of French and German missiles, some of them renamed in the past year. Over all of them hung the cloud of drastically slashed defense spending. The Germans in particular had not yet announced an order for the new Eurofighter 2000.

 

Russians offer EMP counter

By Norman Friedman

The Russians had little to show; they are still finding sales difficult. It was striking that they were continuing to ally themselves with the Israelis in developing new products. Israel Aircraft Industries (IAI) is offering an airborne early warning aircraft based on the old Soviet A-SO (Mainstay), using a new radar (presumably a variant of the company's Phalcon). IAI has been offering a MiG-21 upgrade package for some years.

The U.S. push toward high-definition digital television (HDTV) seems to have an important technological offshoot. Unlike the current analog system, digital television demands extremely precise control of the transmitted signal, much as a Doppler radar demands far more of its transmitter than does a conventional pulse radar. For radar and television, a relatively simple transmitting tube is replaced by a klystron, a very precise amplifier of the complex signal. Klystrons are expensive, and they wear out under continuous use. In military service they are tolerated because they are a relatively small part of the price of a few elaborate systems. Intensive work has made them reasonably reliable.

However, it has long been known that fully solid-state transmitters would be far more reliable and, ultimately, far less expensive. The transition to such transmitters has been slow because such good military klystrons already exist.

HDTV is a different proposition. Television stations have far higher duty rates than radars, so their tubes wear out far more easily. Stations have no fixed investment in klystrons. Instead, they are looking nervously at the likely cost of buying them by the thousand, as the federally-mandated beginning of HDTV approaches.

It now appears that an alternative semiconductor, silicon carbide (rather than silicon), may solve the problem. In all semiconductors, electrons can occupy any of many energy bands. In a semiconductor one band is full, so electrons have no mobility. The band above, the conduction band, normally is empty. Applying enough voltage pulls electrons up into the conduction band, at which point the semiconductor acts like a metal, a full conductor. Similarly, if enough heat is applied, many electrons in the normally-full band jump up to the conduction band. Again, the semiconductor acts like a metal. Neither state is desirable. Instead, the semiconductor is used as part of an electronic switch. To do that, it is made slightly conducting by adding a few atoms of another substance (doping). The new atoms may have fewer electrons than the semiconductor, in which case holes (which behave like positive electrons) appear in the band. Alternatively, they may have more electrons, so that a few appear in the conduction band. Transistors combine these two types of doped solids. The small numbers of holes and free electrons can be manipulated to amplify signals.

All of this means that the semiconductor works until it becomes too hot or until too much current is applied, at which point electrons flood up into the conduction band and control is lost. Hence the limit on the power output of semiconductor (solid-state) radar transmitters-and the device's vulnerability to the shock of high voltages imposed by electromagnetic pulse. Hence, too, the temperature limits on solid-state components, such as those to be found in personal computers.

Silicon carbide is interesting because it has a much wider gap than silicon itself. It can therefore operate at much higher temperatures or at much higher voltages. This has been known for years, but the use of the new semiconductor was blocked by production problems. But new techniques are improving these processes. More important, there is now a very important emerging potential civilian market in the form of HDTV.

Clearly, a semiconductor revolution financed by the television industry would have important military implications. The high-voltage character of silicon carbide would make solid state radar transmitters far more practical, and probably far less expensive. In that case, active radar arrays would probably become far more common. In theory, they offer enormous advantages over current types, in terms of simplicity and flexibility.

The high-temperature capacity of silicon carbide would offer drastic weight reductions in aircraft, where cooling is a significant consideration. According to a recent article, the Air Force estimates that an F-16 could shed 300 kg in electronics related weight by adopting silicon carbide, should that become practical. Silicon carbide chips also promise some protection against high-powered microwave (HPM) weapons and electromagnetic pulse (EMP).

It now has been reported that the Soviets have developed and fielded a variety of high-powered microwave weapons, from hand grenades up through missile warhead. Some years ago such a warhead was reported for the SS-21 tactical ballistic missile (to knock out radars), and about a year ago, the Russians published an article explaining how an HPM warhead on an antiship missile could be used.

Such devices produce localized forms of the electromagnetic pulses otherwise associated with nuclear weapons. During the Cold War, for example, it was widely believed that EMP attacks would begin any strategic assault on the United States, on the theory that our solid-state electronics would be particularly susceptible. Some suggested, for example, that the Soviets had held back from full conversion to modern solid-state devices for fear of EMP.

Certainly, we know that EMP can be produced without a nuclear explosion. In general, any violent change in an electric or magnetic field can trigger an EMP burst. For example, a capacitor can be made with explosive rather than air or some other insulator between its plates. When it is charged up, a strong static electric field forms in the explosive. If the explosive is now set off, the field feels a violent change, and EMP results. Presumably, the band width of the resulting radiation depends on how quickly the explosive acts. Much the same would probably be true if a magnetic field could be built up within some form of metallic explosive.

In either case, the energy of the EMP burst would be far less than that offered by a nuclear explosion. Voltage would fall off fairly quickly with range; maximum range would be defined by the voltage needed to make given components fail. It might still be far greater than the radius of damage to be expected of a similar weight of conventional explosive. Moreover, a successful EMP (HPM) attack might well disable defensive radars and other electronic systems, opening a target to conventional attack by follow-on weapons.

Certainly the threat of large-scale EMP attack by nuclear bombs was terrifying during the Cold War, because such weapons could cover a vast area with very high energies. A more localized attack might be a different proposition. The new netted systems, such as Cooperative Engagement Capability, might well be able to survive the loss of some of their nodes, and still be able to hit back effectively. Thus a non-nuclear EMP threat might well encourage further netting, which the Army already wants. On the civilian side, it might be wise to think through exactly what damage EMP is likely to do. It certainly is likely to wash out solid-state circuits, though it is not clear that they will not become usable again after the attack is over. It seems less clear that HPM bursts will wipe out magnetic memories. If the shift to such optical devices as CD-ROMs continues, then they certainly will not be very vulnerable. Perhaps most important, if the attack is localized, replacement equipment probably will be easy to obtain from nearby untouched areas. Clearly networks will suffer, since the attack will produce confusing signals. On the other hand, those signals also will make it quite obvious that something has happened.

How terrifying is the EMP hand grenade or bomb? As in most electronic catastrophes, those caught without back-ups will suffer badly, but they are already at risk from non-terrorist threats such as fires and earthquakes. .

And, of course, there are solutions. Formerly, the favored one was to enclose everything in a Faraday cage, a closed electrically-conducting box. EMP could flow through gaps in the enclosure, so they had to be carefully monitored and controlled. Perhaps now we should phase out silicon chips in favor of silicon carbide. That would be impossible in the civilian world, but it may not be so difficult in the military world, particularly if (as seems likely) silicon carbide becomes attractive for radars.

So maybe HDTV really is worth its cost.

 

Norman Friedman is a prominent naval analyst and the author of more than thirty books covering a range of naval subjects, from warship histories to contemporary defense issues. He is a longtime columnist for Proceedings magazine and lives in New York City.

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