As we move into a new era of assuring continued air superiority, the combined impact of stealth aircraft, advanced weapons, and integrated avionics, including electronic warfare (EW), will be required to assure preeminence in air-combat capability. Stealth alone has created a decided advantage in intrinsic survivability. Coupled with advanced integrated avionics, including threat warning and electronic support measures (Esm) equipment, future air vehicles will strike with deadly precision. Undetected by the enemy and utilizing integrated on-board processing several orders ofmagnitude greater than earlier systems, on-board sensors will correlate multispectral sensor information, assess the entire air/land battle environment in real time, and provide the pilot crystal-clear awareness of anything that could be either a threat or a target.

YF-22 Cockpit

This article highlights the advantages of stealth in a combat environment and illustrates how electronic warfare has changed to complement stealth survivability and improve combat effectiveness.

Traditionally, aircraft have had very large radar signatures in comparison to stealth aircraft. And, weapon systems worldwide have been specifically developed and deployed to detect and engage conventional aircraft with airto-air and surface-to-air missiles (SAMS). Stealth technology has rendered these weapon systems ineffective, reducing the detection range of the radars to a fraction of their intended capability and leaving "holes" in the enemy air-defense network that can be exploited to perform a mission.

While new counter weapon systems can be developed, the effort required to achieve "pre-stealth" performance is technologically and economically more difficult than achieving stealth itself. Radar systems must compensate for the smaller reflection by increasing the transmitted power and sensitivity of the radar return. Both present problems for radar design, requiring larger transmitters and larger antennas, which are less mobile and reliable, consume more power, and are more expensive. Improving the sensitivity of a radar receiver also creates the need to process a greater number of radar returns in the presence of much more clutter or "false targets. " This, in turn, increases the processing load on the computer and has a direct impact on the ability of a weapon system to engage the targeted aircraft in a timely manner.

The problem has many analogies. Consider looking out across a field. A moth flying in tall grass is much more difficult to see than a bird flying above the grass. It is technically easier to create the moth than the technology to see it. Weapon systems attempt to exploit any observable characteristic that can be useful to detect and track the aircraft and, more importantly, gul 'de the missile. Stealth technology has been and will continue to be applied to reduce the signature of any observable characteristic, even infrared energy from the engines, to mitigate the effectiveness of heat-seeking missiles.

As with RF signatures, a reduction in infrared signature translates to a smaller engageable range and a shorter exposure-time to the threat. Countermeasures to any threat are more effective and easier to Implement as the observable features are reduced in magnitude. As threats continue to evolve, out of need, systems will be developed that attempt to counter the impact of stealth and regain weapons effectiveness. It will, in all probability, take a generation for the world to re-arm with yet undeveloped anti-stealth weapons. And, in that time, stealth technology will likewise continue to improve.

The real possibility of lethal engagement against stealth aircraft continues to exist, although at a much lower probability of occurrence. Threats can include "pop up" weapons deployed too quickly to avoid, shortrange visual contact, or a "leaker" which may get through in a "many-onmany" engagement in air-to-alr combat. If enemy aircraft are able to get close enough, engagements are possible. A chance observation by a ground gunner with optically guided missiles is also possible. Finally, no stealth aircraft is invisible to all radar systems at all ranges. This occurs only beyond a range where the radar return falls below the sensitivity of the receiver.

Some aircraft, by virtue of their mission, may need to remain undetected by all radars. Others may allow their existence to be known, but must remain unengageable by fire-control radars used to launch and guide mis'Ies. If fleeting evidence of the aircraft is seen, flashes, may tip the enemy to the aircraft's existence. However, persistence needed to track and engage may still be lacking. A stealth aircraft may be observable by an early- warning radar system operating at longer wavelengths, while remaining invisible to shorter-wavelength radar systems required to track and guide weapons.

Passive threat warning minimizes
exploitation by other weapon system

Risks to the pilot are quantified in statistical terms, not absolute values. Much like the threat of lightning, we would all like to believe we will not be struck, but we are, in reality, statistically at risk. The combined effect of stealth, electronic warfare, and fire power drives the statistical risk of being lost in combat to an all-time minimum, but not to a probability of zero.

Self-protection function is simplified -
Fewer engagements; reduced complexity and cost

The role of electronic warfare has changed significantly. Stealthy aircraft are no longer visible by all weapon systems, in danger of possible ' 'ie attack by any one of many missi surface-to-air weapon systems. Stealthy aircraft, however, will continue to use electronic-warfare equipment, operating in harmony with stealth, undetectable, yet fully effective. Passive sensors are maximized to provide the pilot with information required to successfully accomplish the mission. Missi 'le engagements remain a possibility, and countermeasures will still be needed, but at a lower probability of encounter and against a smaller subset of the world's weapons.

The traditional role of EW for selfprotection has been to deny or delay weapon systems from launching missiles by jamming the weapons radar systems used to acquire, track, and 'de missiles. With many weapon gul I 1 systems able to "see" the aircraft simultaneously, Ecm equipment has been quite complex, expensive, and always "chasing the threat" after it has been deployed. ECM techniques have been continually updated to maintain effective performance. With stealth, the effective range of weapons is greatly reduced. In addition, there are fewer encounters with air-defense weapons, reducing the need to apply ECM In a preemptive manner to assure survivability.

Moreover, stealth aircraft could "blow their cover" to other enemy sensors by applying electronic ountermeasures against a threat that appears to be locked onto the aircraft. Exposure time to the threat is the critical factor. If the exposure time is known to be small, inadequate time may be aval 'lable for missile launch. Safe exposure time may be much greater than the technical reaction time of many weapon systems. The elements of surprise, fatigue, air-defense saturation by standoff jammers, and morale may substantially impact the reaction time of forces operating the weapon systems, and extend the exposure time available to the aircraft without having a missle launched.

Stealth aircraft can optimize their invisibility to radar, finessing their way through areas where weapons are deployed. Given knowledge of the existence, type, status, and location of radar threats, aircrews can plan a mission route which deny SAM systems an opportunity for detection. Or, at a minimum, they can fly a route that minimizes the temporal window of opportunity avaliable for a weapon system to react. In-flight dynamic route replanning is also possible by correlating the current real-time threat deployment seen by the aircraft against the pre-flight laydown, and making adjustments in flight direction to minimize the chance of an engagement.

Threat-warning systems that operate passively, detecting emissions from the threat, will provide warning to the pilot. Such sensors will provide unambiguous assessment of the threat. Processing functions will perform lethality assessment and recommend an optimum response. If the recommended response is defensive, manuevers and timely countermeasures are employed for maximum effectiveness to divert the missile in the end-game. The reduced signature of the stealthy aircraft, in every observable parameter, simplifies the task of seducing the missile, masking the signature, and drawing the missile away from the aircraft.

Providing the pilot a high-fidelity knowledge base of activity around the aircraft is called situation awareness. With knowledge of the environment, the pilot can choose to attack, perform a defensive manuever, or not react at all to the threats as they present themselves. The pilot has to obtain situation awareness of both the airborne and the SAM weapons environments without being seen. The pilot wants to know: What's out there? Who is it? Where is it? Is it something unexpected? Is it a potential threat? Can it see me? What is the intent? Should I engage or avolid? Are other aircraft in danger? Has a missile been launched? What kind is it? Can it hit me? How long do I have to maneuver and counter the missile? To answer these questions, stealth platforms must make use of passive sensors, multispectral in design, that do not emit energy and therefore can not be detected by the enemy, to provide situation awareness of the environment to assure survivability.

Electronic warfare provides varied ways for the pilot to obtain situation awareness. Included are passive sensors that detect radar emissions, communications, and radiation of infrared and ultraviolet energy from engines and hot body structures of aircraft and missiles. A combination of correlated sensors can overcome the limitations of individual sensors and provide an accurate picture of the situation. Some sensors may be very accurate in spatial resolution, but offer little in the identification of the threat. The infrared detection of aircraft is one example. Radio-frequency sensors may offer high-quality identification with less resolution. Multispectral sensor correlation brings out the best features of each sensor to establish an optimum track file on each entity.

EW sensors support passive engagement -
First look, first kill advantage.

Responses to integrated Ew-sensor information can be offens've or defensive. The power of passive sensors, combined with stealth, can provide an offensive capability that assures "first look, first kill." The overall effectiveness of the aircraft weapon system will be enhanced without engaging the enemy with active emissions that could trigger a counter-engagement maneuver.

EW sensors support passive engagement -
First look, first kill advantage.

Passive sensors provide the pilot with 'nformation to optimize response, both offensive and defensive. These sensors detect, locate, identify, and track potential threats and targets, both land-based and airborne. The information can be used directly, for offensive or defensive action, or cue other sensors without jeopardizing the observability or lethality of the aircraft. Lower observability, which allows surgical threading between threats, requires passive sensors to supply the "vision into the threat field." And, when weapon systems can't see the platform, jamming techniques that delay or deny engagements become less important.

With stealth, the focus for selfprotection is on the terminal fly-out engagement due to the statistically small frequency of occurrence. Passive missile warning, coupled with manuevers, and timely use of decoys take on added importance and provide highly effective countermeasures. Electronic warfare will continue to evolve, enhancing the survivability and effectiveness of the pilot and performing a critical and complementary role with current and future stealth aircraft.

Variants od Sanders' broadband expendable decoy develped for the U.S. Nany straight through repeater antenna performance program (STRAP)

GARY W. WAY is Director - Systems Engineering, Countermeasures Division, Lockheed Sanders. Way joined Sanders in ig68 as a microwave antenna design engineerfor electronic countermeasures systems. From 1972 to 1973, be worked as an antenna engineer at Adams Russell, returning to Sanders Surveillance Systems Division in 1973 where, until 1987, be worked as a systems engineer on the development of acquisition and direction-finding systems for SIGINT applications on land, sea, and air.

Since 1987 Mr. Way has been Director of Systems Engineering in the Countermeasures Division where he has provided technical-systems leadership within the integrated electronic warfare system (INEWS) for the F-22 and related applications.

© copyrights 1992 by Lockheed Corporation, 4500 Park Granada Boulevard, Calabasas, CA 91399-0610
published by plweb publications - Gregor Mima, Technical University Vienna.