AMSTERDAM — As the driver in the next lane swerves in front of you, you feel the gas back off and the brakes grab in the car you're driving — a Mercedes-Benz S-class luxury vehicle, the first passenger car equipped with a technology called adaptive cruise control. The technology makes these adjustments even though you haven't touch the brake or gas pedal.

At a safe distance behind, your Mercedes settles to a speed matching that of the driver in front of you. That's too slow, so after a look in your rearview mirror you pull into the empty outside lane and feel the acceleration as your car speeds up to the pre-set cruising speed. You still haven't press the accelerator pedal.

That's the beauty of this rising star of the auto industry, a millimeter-wave radar technology that promises not only to make driving easier, but to ignite a market for gallium-arsenide and other compound semiconductor components.

Beginning this month, buyers of S-class Mercedes vehicles will have the option of ordering their car with the "Distronic" proximity-control system. Although Greyhound buses and some heavy-goods vehicles have been fitted with automotive radar systems, the Mercedes is reckoned to be the first passenger automobile to sport this advanced use of electronics, and observers say it is likely to lead a proliferation of the technology.

"Adaptive cruise control is the first system in a network of sensors," said John Vaughan, vice president of business development at M/A-Com Inc. (Lowell, Mass.), which supplies sensors for the Mercedes system. "In time you will have a sensor field around the car which will be used by the vehicle's intelligence. It's the beginning of the microwave era in automotive electronics."

By coincidence, the European Microwave Week conference was being held in Amsterdam earlier this month at the same time as the Paris Automobile Show was held in the French capital, where Mercedes-Benz showed off its remodeled 1999-model S-class luxury cars. The Mercedes-Benz system uses a 77-GHz Doppler radar linked into the electronic control and braking systems to maintain a safe distance between a car with the system and the vehicle in front of it. Most of the new S-class vehicles are expected to ship with the radar, which carries a premium of about $1,500.

At European Microwave Week — which pulled together three previously separate conferences on GaAs, microwaves and wireless techniques — automotive radar came across as one of the hot areas in what is already an upbeat sector of the semiconductor industry.

E. Pettenpaul from Siemens Semiconductor, a keynote speaker at the conference, observed that the strength of mobile communications, satellite and broadband distribution systems are driving a boom market in GaAs components, in strong contrast to the doldrums in silicon semiconductors. Pettenpaul predicted that the worldwide GaAs market would average 31 percent annual growth between 1996 and 2002, with about 80 percent of the sales coming from the communications sector.

However, while GaAs wafer fabs are enjoying good business providing power amplifiers for mobile-phone applications at 900, 1,800 and 1,900 MHz, they are coming under pressure from silicon and silicon germanium, which can perform at these frequencies while offering the prospect of integration with other silicon analog components.

That's why higher-frequency applications, such as adaptive-cruise-control radar, are of great interest.

"The Europeans are taking the lead; Daimler-Benz first, BMW second," said Heinrich Daembkes, president of United Monolithic Semiconductors SA (UMS; Orsay, France). "Although soon the U.S. market will take off, as cruise-control radar fits much better with an automatic [transmission] car." Most automobiles in Europe still sport stick shifts.

UMS is the GaAs manufacturing joint venture between Thomson CSF (Paris) and Daimler-Benz AG (Stuttgart, Germany). Along with BMW, Volkswagen is expected to be the third automaker to enter the market for adaptive cruise control. The German company is preparing a new luxury vehicle that will use the technology.

"It's an interesting market, because at 77 GHz, you have to use III-V semiconductors," said Daembkes, who anticipates selling GaAs components to the recently formed LucasVarity Thomson-CSF Autocruise Ltd. Set up by LucasVarity and Thomson CSF, the company is chartered to design and manufacture sensors for adaptive cruise control and future collision-avoidance systems for passenger cars and light trucks.

Initially designed by Thomson-CSF Radars & Contre-Mesures, the radar sensor for the joint venture's adaptive-cruise-control system, to be marketed under the trade name Autocruise, is called by its designer the first radar sensor to utilize monolithic microwave integrated circuit (MMIC) technology. These sensors will support an adaptive-cruise-control contract awarded to the joint venture's parents for introduction in 2000.

Victor Rice, chief executive of LucasVarity, said, "The combination of Thomson-CSF's radar capabilities with our expertise in automotive electronics and braking positions the new company well to capture a significant part of the emerging market demand for high-performance adaptive-cruise-control systems."

Not collision avoidance
Holger Meinel, senior researcher at Daimler Benz Aerospace AG (Ulm, Germany), was quick to make a point stressed by all the companies working in this field. "This is not anti-collision radar," he said. "It's not a safety feature, it's a comfort feature."

The source of this distinction is concern that if adaptive cruise control is marketed as a safety feature, the first accident that occurs involving a vehicle equipped with millimeter-wave radar will bring a damaging liability suit. That's why companies are at great pains to point out that the driver retains control and responsibility.

At a special tutorial session on automotive radar held at European Microwave Week, Meinel discussed the main architectural approaches used for automotive radar. These include hybrid construction based on discrete components, quasi-optical systems and monolithic integration. Systems can also use a variety of radar-signal formats including frequency-modulated continuous wave, frequency-shift keying, pulse-Doppler or a combination of these.

"The most efficient millimeter-wave oscillators still utilize Gunn diodes in waveguide cavities," he said. All the remaining front-end components are housed in a single hybrid assembly.

Meinel explained that automotive radar has been developed at a number of frequencies, including 35, 60 and 86 GHz, but he said that 76 to 77 GHz is now a globally available frequency for the application. "I started work at AEG in Ulm in October 1973. On my third day I was told to design a 35-GHz receiver for automotive radar," Meinel said. "That's 25 years ago. It takes that long for something like this to come into production."

Daimler-Benz Aerospace has completed the design of a hybrid 77-GHz radar, called Tempomat, which is being considered for deployment. In his tutorial Meinel said that "the low-cost, very high-volume production of collision-avoidance sensors has to rely on the availability of millimeter-wave GaAs MMICs, which has become a reality today."

Meinel also spoke of work at Daimler-Benz Research which uses scanning radar to build up an image. The technique can "see" vehicles beyond the car directly in front, which are obscured optically. That's because the space between the underside of the vehicle in front and the road acts like a waveguide, piping a radar image back to the sensor, he said.

When allied to image and behavior-recognition processing, such scanning radar systems will be able to detect the road edge, gauge road conditions and provide much more interaction with the vehicle-control system, Meinel said.

But for now, simpler single- or triple-beam systems are ready for deployment. And although European automakers are credited with leading the move, it is not without benefits to manufacturers in the United States.

Indeed, it is the M/A-Com division of AMP Inc. that is providing the sensor unit for the Mercedes S-class 1999 model, based on a design derived from the work of Automotive Distance and Control Systems GmbH (Friedrichshafen, Germany). Initially, M/A-Com is using an indium-phosphide Gunn diode for the primary oscillator, rather than a GaAs diode.

M/A-Com's Vaughan said InP was used because of power output requirements. But "we'll be migrating over time to GaAs MMIC solutions," he said.

"All the big automakers are interested in this and a variety of similar applications," said Vaughan. "The adaptive cruise control happens to be something particularly European; perhaps because it's useful in situations where there is more traffic."

Sketching a future of vehicle sensors, Vaughan added, "But there are also blind-spot detectors, parking aids, pre-arming for airbag deployment and seat-belt tensioning." He explained that radar forewarning of a potential crash could be used to arm an airbag and pull a vehicle's occupants into an appropriate sitting position prior to airbag deployment. Vaughan said that an accelerometer sensor would still be used to fire the airbag, as it is today, but with reduced risk of injuring occupants.

"Ultrasonics are good for one or two meters, for parking aids and so on, but we are looking for microwave technology to replace ultrasonics," he said. "Then sensors will be joined together in a network."

Vaughan was reluctant to predict how many of the Distronic sensors M/A-Com would be supplying per year. The number will depend on takeup of the Distronic option on Mercedes S-class autos, he said. "There's not been many millimeter-wave systems that are shipped in tens of thousands."