It’s a matter of wanting it all. Aircraft operators seek antennas that perform multiple functions with improved performance, yet are smaller and less obtrusive on the airframe.
Antenna manufacturers appear to be accommodating operators with technology that paves the way for increased information both in the cockpit and in the cabin. In some cases, the technology brings en-route weather reports to pilots, as well as live TV and high-speed Internet connectivity to passengers.
Advances in design include "conforming" antennas into the aircraft structure to reduce drag, producing specially tuned antennas for specific applications, and combining multiple functions into one antenna. And "phased array" antennas now are allowing much faster transfer of data and near-real time Internet access.
Antenna technology has helped make satellite communications (satcom) standard equipment on most long-haul commercial flights (and essential on intercontinental flights), providing air-to-ground voice and data communications for both crewmembers and passengers.
Satcom and accompanying high-gain antennas have become standard equipment on the Boeing 777. Satcom is a "no-charge option," says John Barker, CMC Electronics’ marketing manager for commercial aviation products. "If you want it removed, it costs you." Virtually all Airbus 340s, too, roll off the assembly line with satcom systems.
CMC produces both high-gain antennas, providing global coverage, and intermediate-gain antennas, providing continental coverage. Barker claims the company has delivered more than 1,400 antennas to 60 airline customers.
Swift64
The CMA-2102 high-gain antenna, combined with an onboard receiver/control processor (built by other companies), accommodates the existing Inmarsat Aero H satellite service. By installing a new modem circuit in the receiver/transmitter (transceiver) for wider-band capability, the CMA-2102 also accommodates Inmarsat’s new high-speed data service, called Swift64. The new service allows for much faster data transmission (64 kilobits/sec [Kbits/sec]) than does the older 2.4- Kbit/sec Inmarsat Aero H service. The system upgrade for Swift64 adds a voice and data channel with the capacity of up to six voice channels in the older Aero H service.
In April, Swift64 was first demonstrated on board Honeywell’s Citation V, using the CMA-2102 antenna. Among the capabilities demonstrated was video conferencing.
Rockwell Collins and EMS Technologies also are developing Swift64 systems. EMS Technologies has taken the extra step of combining two 64-Kbit/sec transceivers (two modems in the same box) to demonstrate a 128-Kbit/sec capacity. Although the company makes its own antennas, it employed the CMA-2102 model for the demonstration, according to Roger Reifler, CMC’s satcom program manager.
The older Aero H, or high-gain service, still may be used as a data downlink, no matter what type of uplink service is installed, because the downlink requires less capacity, according to Barker. "You could beam up via broadband all kinds of TV data, using a different satellite network," he explains. "But the link to communicate back to the ground would be Aero H [Inmarsat] narrowband."
How Phased Array Works
The core technology used in these high-gain antennas is based on phased array, according to Hannes Grobbelaar, program manager for CMC’s aeronautical communications group. With phased array, the pattern of antenna elements is adjusted to achieve the strongest gain. To enable more flexible steering of the antenna beam, "a number of small antenna elements are connected–with amplitude and phases combined–in a special way, thereby manipulating the antenna’s radiation pattern," Grobbelaar explains.
To illustrate, "instead of having a single TV antenna on a rooftop, you might have 30 up there," Barker explains. A big advantage of phased array, Grobbelaar adds, is that "you can steer the antenna main beam by adjusting the phases and not have any movement or movable parts required. You electronically manipulate the phases of the individual elements," he adds. "That is what electronically steered means, as opposed to mechanically steered, where servo or stepper motors are used to change the antenna’s position."
Benefits of Being Single
This is important because "the satellite is in a specific position and you’re flying somewhere in its footprint," Grobbelaar adds. "You need to point very accurately to the position of the satellite to optimize the signal strength you receive." The electronically steered antenna allows the instant movement of the antenna beam from one position to another, ensuring constant connection, no matter how the aircraft turns or maneuvers.
Barker claims CMC’s high-gain antenna "can be so effective that only one antenna is required on the aircraft." Other "side-mounted" systems require two antennas to pick up the satellite signal, depending on which way the aircraft banks, he adds. CMC’s surfboard-shaped, high-gain antennas are mounted on top of the aircraft, just aft of the cockpit or over the wing closer to the tail.
To facilitate broader bandwidths, CMC is working with Air TV to develop a satcom antenna that can accommodate "40 channels simultaneously, which would require a [receiver] speed of 80 megabits/sec [Mbits/sec] to achieve," says Grobbelaar. The new antenna’s transmit speed would be 64 Kbits/sec. "Internet will also be slipped into the channels, so you can configure the capacity of the antenna as required–to provide more TV channels or more Internet facility. What we basically provide is a pipe, and you can fill it up with your combo of data," he explains.
"With broadband, we’re talking real-time, says Barker. Broadband once was "a hot item," but it cooled down after 9/11, when emphasis was turned toward security items. But interest in broadband is heating up again, he claims. In the wake of 9/11, there may be a stronger need for live news, he surmises. Stock quotes also need to be updated quickly. In addition, broadband could provide live video feeds from surveillance cameras in the cabin or cockpit, with constant feedback to the ground for security purposes, he points out.
New from Ball
Ball Aerospace and Technologies, in Boulder, Colo., also provides phased array satcom antennas for the Inmarsat service. Since the early 1990s, the company has provided more than 500 systems for commercial airlines worldwide. Its 20-element AirLink system uses twin, side-mounted antennas.
Like CMC, Ball also has developed an updated high-speed data radio frequency unit (HSDRFU) to accommodate the faster-rate Swift64 digital transmission system. To date, Ball has sold three units to a classified government customer, with flight tests conducted last January.
These are two-channel units, "so when you multiplex the two channels you can have a data pipeline of about 128 Kbits/sec [twice that of the normal Swift64]," says Pierre Stoermer, Ball Aerospace program manager. Ball provided another, three-channel unit (with a capability of 192 Kbits/sec) to the military at Fort Bragg, N.C., for possible installation on a U.S. Air Force C-17.
And, like CMC’s system, no changes are required to the Ball antenna to accommodate the higher-speed Swift64 service. "You pull out the satellite data unit and existing Aero H, RF unit and put in the high-speed data RFU. Although Ball has yet to sell a commercial system, it has been working with another company to demonstrate the antenna on a commercial airliner in the near future, Stoermer maintains.
In the broadband area, Ball is under contract to the Defense Advanced Research Projects Agency (DARPA) to develop a broadband antenna with a single aperture that can be reconfigured to accommodate various functions, such as radar and communications.
Market is Broad
But older antenna technology remains popular, as well. Inmarsat Aero C service is used by the U.S. Air Mobility Command for electronic messaging and aircraft flight tracking, says Ken Ravenna, vice president of LandSea Systems, which distributes Aero C antennas for Thrane & Thrane. The omnidirectional, "jet blade" antenna–8 inches (20.3-cm) long by 6 inches (15.2-cm) high–receives GPS satellite data and pumps out position reports to ground-based tracking systems, providing a data rate of 600 bits/sec. The antenna also supports air/ground, air/air and ground/air e-mail.
New from Dayton-Granger
For VHF, HF and L-band airborne communications, the typical blade antennas are now being integrated into aircraft skins. For example, Dayton-Granger launched an HF antenna last summer for classic Boeing 727 aircraft (see photos, page 48). Major airlines have released the venerable B727, but it has entered new regions of the world (South America, Africa and Asia), where HF is the primary means of communication.
Built into the leading edge of the B727’s vertical stabilizer, the antenna allows increased aircraft performance through reduced drag. The Fort Lauderdale, Fla.-based company takes the old B727 leading edge in trade and provides a refurbished leading edge with the antenna installed, according to Karl Blomgren, Dayton-Granger’s marketing and contracts director. With no exterior parts exposed to the elements, the new B727 antenna, which is housed in a fiberglass radome, requires less maintenance than the old blade-type antenna, Blomgren adds.
Dayton-Granger is immersed in other new technologies for antennas, as well. For example, use of VHF digital link Mode 2 (VDL-2) for uplinking weather and other information to the cockpit in near real time has prompted the company to develop a 6-inch (15.2-cm) -long, aerodynamically structured antenna specifically tuned to the required frequency (136 MHz) for the VDL-2 uplink. The small antenna achieves the same performance "as you get out of a 17-inch [43-cm] whip [antenna]," Blomgren claims.
The VHF antenna works in conjunction with Honeywell’s new Bendix King KDR-510 Wingman Services VHF receiver, which takes in data from the ground, including the latest en-route weather. The airborne antenna is designed for the entire aviation market, from general aviation up to commercial transports, Blomgren claims.
Dayton-Granger also has designed a specially tuned antenna for the Merlin flight information system (FIS) service, produced by Satellink. The service, which requires an antenna operating in the 1.52- to 1.59-GHz frequency range, provides weather data and cockpit information, using a satellite data link, and is delivered to the user on a subscription basis. The Dayton-Granger antenna is 4.5 inches (11.4 cm) tall and weighs 5 ounces (0.14 kg). The Merlin FIS serves the entire aviation community, including general aviation. "AOPA [Aircraft Owners and Pilots Association] has wanted for years to get weather data in the cockpit," says Blomgren.
Further Dayton-Granger activity involves multiple-use antennas. Operators are "trying to reduce the number of antennas on the centerline of the aircraft, to clean up the airplane and reduce drag," Blomgren explains. By combining functions–for example, packaging a VHF and L-band antenna together, or combining a localizer and VOR–you have a single antenna that does two functions."
Keeping F-22 Stealthy
Use of conformal antennas to reduce drag in commercial aircraft has its counterpart in current military stealth aircraft. The U.S. Air Force’s F-22 air dominance fighter, built by a Lockheed Martin-led team, uses 156 antenna elements in four embedded apertures for its EW (electronic warfare) system. All are embedded into the aircraft’s surface to preserve its stealth characteristics.
For the CNI system, there are 21 apertures (antennas) that include all normal com, nav and identification functions, plus special-use antennas. BAE Systems provides all antennas for both the EW and CNI systems.