Grand Danois
Entertainer
I'm trying to get an idea of how close - or far away - GaN tech is for fielded systems. MASC is suggested in this article below. Since an AESA seem 10 years away for the Eurofighter, what about skipping GaAs in the E-Captor and go straight for GaN?
Anyone have something better than this article, which has a very good overview?
Radar revolution: the arrival of gallium nitride components opens up new applications for radars, including jamming and telecommunications.
by Dupont, Jean
Interavia Business & Technology • Summer, 2007 • DEFENCE
The active array antenna has virtually taken over the radar market--having won a berth on every new fighter or surveillance aircraft programme launched over the past 10 years. Even earlier programmes, such as the Rafale, Gripen, Typhoon or MiG-35 are preparing for the transition to active-array technology. The pressure do to so has been stepped up following the first US export sales of aircraft equipped with active-array radars--F-15s to Singapore in 2005, followed by Australia's recent order for the F/A-18E/F Super Hornet.
Weapons labs around the globe, however, are already gearing up for the next generation--antenna with the power and bandwith to perform offensive jamming and communications in addition to the radar function, and with a sufficiently compact and modular design to be housed not only in the nose of the fighter aircraft but also in conformal units elsewhere on the airframe surface.
The trigger for this revolution is a semiconductor material called gallium nitride (GaN), which, like the gallium arsenide (GaAs) used in current active antennas, is composed of elements from columns 3 and 5 of the periodic table and can be used to produce high frequency amplifiers.
The emergence of GaN from the laboratory has been delayed by epitaxy issues--growth of the semi-conductor layer on the silicon (Si) substrate, or silicon carbide (SIC) in the case of cutting-edge military applications. GaN and the substrate are made of crystals with different interatomic distances, hence the difficulty in assembling the two materials at a microscopic scale. The largest slices of high-performance GaN that have been obtained to date have a diameter of three inches, compared with six inches for GaAs and up to twelve inches for silicon. The size of the slice determines the number of chips that the machine can produce in a single pass.
GaN is clearly destined to remain expensive and its utilisation unlikely to expand beyond a limited number of applications, particularly since suppliers of SiC substrates are themselves limited. This situation could change, however, as GaN slices are expected to increase to four inches in the near future, and the arrival of new players should help to drive prices down, predicts Dominique Pons who heads the Alcatel Lucent/Thales III-V Lab. (The name reflects the columns of the periodic table mentioned above.) In any case, the intrinsic qualities of GaN have convinced the US Defense Advanced Research Projects Agency (Darpa) to invest heavily--tens of millions of dollars per year--in the technology.
The involvement of telecommunications giant Alcatel Lucent reflects the inherent duality of the technology--GaAs components are widely used in cell phones. Though power applications, such as radar, are largely confined to the military and space sectors, they are gradually finding their way into the civil domain. In the 1990s, EADS and Thales formed a joint company, United Monolithic Semiconductors (UMS), to produce GaAs chips and monolithic microwave integrated circuits (MMICs) for their new-generation radars.
Series production
UMS launched series production of MMICs for S- and C-band radars at the beginning of this decade, followed more recently by X-band radars like the active-array RBE2 AA that will equip the Rafale starting in 2012. On the civil side, lead times between technology incubation and application are much shorter, and the company has managed to find GaAs applications in a number of professional or top-end civil markets, such as wireless telecom infrastructures and anti-collision radars for cars.
In this way the military potential of GaAs has opened up an industrial capability that has found market openings in Europe ... the same openings that GaN will be able to exploit in its turn. Agreements are already in place with NXP (ex-Philips Semiconductors), explains Thierry Laboureau, UMS sales and marketing director, to develop power components for base stations for third- and fourth-generation cell phone networks and for WiMax base stations for mobile internet users. Ultimately, once prices have come down far enough, GaN could conceivably make its way into the kitchen, replacing the magnetron in the micro-wave oven.
However, these longer-term commercial perspectives will not be enough to cover the investment required to launch foundry operations. Nor is there any prospect of procuring components for military applications from the US or Japan--both countries have already placed an embargo on GaAs circuits, and there is no reason for them to be any more flexible concerning GaN. This explains why the defence procurement authorities in France and Germany are both helping to support industrial research efforts.
According to Dominique Pons, the III-V Lab should produce its first X-band or wide-band GaN MMICs this year. Following validation and industrialisation by UMS, series production should get under way by 2009.
EDA funding
GaN is also one of the very first research areas to receive funding from the European Defence Agency (EDA) under a 40 million [euro] programme called Korrigan that brings together 23 companies and laboratories in seven countries to accelerate the development of one or more European GaN foundries with associated supply chain by 2009. The programme leader is Thales Airborne Systems. Other participants include EADS, Selex Sistemi Integrati, Saab Ericsson and BAE Insyte. Their role initially is to define requirements for the foundries, before becoming directly involved, from 2008 onwards, in integrating the microchips into a variety of specialised modules covering a range of land-based and airborne radar applications, as well as self-protection or offensive jammers.
In this way, explains Thales Airborne Systems technical director Pierre Fossier, it should be possible to launch the first system applications in 2010. In France, one of the leading candidates for the new technology is the offensive jammer, a capacity that the French Air Force has had its eyes on for several years, and which has already given rise to the Carbone airborne demonstrator. The performance of the system attracted a lot of attention at NATO's Mace X electronic warfare exercise in the year 2000.
The DGA procurement branch of the French MoD is continuing to provide limited funding for exploratory work by Thales while awaiting for national budgets to kick in to complete development. GaN would allow for a reduction in the size of the jammer, potentially clearing the way for integration into a combat aircraft. One of the first European acquisition programmes to integrate GaN technology could well be the Maritime Airborne Surveillance and Control (MASC) programme to replace Royal Navy Sea King Mk7 airborne surveillance helicopters, as required for the future CVF aircraft carriers. The three candidates for this mission are the Hawkeye aircraft, the EH-101 helicopter and the tiltwing V-22, though the Hawkeye would appear to be ruled out by the absence of a catapult in the current CVF definition. Both the other candidates would require a compact and powerful radar to meet missions requirements. The potential advantages of a GaN radar in this context have prompted the British MoD to finance some upstream development work in preparation for a programme launch in the 2009 timeframe--the same year that the first European GaN modules are scheduled to come off the production line.
Rafale lead
As far as Europe's combat aircraft programmes are concerned, the Rafale seems to have established a lead over Typhoon and Gripen in the race to integrate an active array antenna. This is primarily because--unlike its competitors--the transition to active-array technology on the Rafale's electronically scanned RBE2 was planned from the outset, avoiding the need for the more extensive (and expensive) modifications required on the mechanical antennas of the Typhoon and Gripen. The increase in range that the new technology will bring is deemed essential if the aircraft is to fully exploit the potential of the future ramjet-powered Meteor missile, due to enter service in the early years of the next decade. Without it, pilots will rely on target designation from another platform to strike targets at the limits of the Meteor envelope.
All aircraft will benefit from the collaborative work accomplished under the trinational Airborne Multirole Solid State Active Array Radar (AMSAR) programme, which was launched in 1993 to develop a European capability in GaAs power devices and subsequently gave rise to UMS (EADS/Thales). Work under AMSAR is currently focused on beam forming through computation. The goal is to cancel reception in jammed sectors and improve rejection of parasitic ground echos, though at the cost of a more complex antenna architecture.
In France, Thales launched its own active antenna radar demonstrator programme in the late 1990s incorporating US components. The resulting mockup was tested at the CEV flight test centre in 2002 on a Mystere XX test bed, and the following year on Rafale. In February 2004, the French MoD's DGA procurement branch awarded 85 million [euro] under the DRAMA programme to develop a prototype active-module radar representative of an operational system.
Thales is currently working on its first DRAMA antenna featuring UMS components. The antenna is scheduled to be delivered to the CEV test centre in midyear for flight testing on the Mystere XX and Mirage 2000 through 2009. The objective is to complete qualification of the new radar by 2009 and deliver two prototypes to Dassault the following year for integration into the aircraft and validation of the full standard. The first two production radars are currently scheduled for delivery in 2011; they will equip the last two Rafales in the current production batch. Half of the 400 million [euro] in funding for the Rafale "Roadmap"--the development of additional capabilities beyond the F3 standard--has been earmarked for the introduction of an active array antenna on the RBE2. This will involve an array of around 1,000 GaAs transmit/receive modules to replace the existing passive scanning antenna and the travelling wave tube (TWT) on the transmitter. The goal is to have the resulting AA version of the RBE2 ready for series production to equip Rafales delivered from 2012 under the next multi-year order, which is expected to be signed in early 2009.
According to Thales, the RBE2 AA will offer 50% greater range than the current RBE2 and a huge increase in reliability--major overhaul every 7-10 years, compared with a current TWT service life of around 100 hours. It will also be possible to generate SAR images in air-to-ground mode with 1 m resolution or better, and to detect at long range low-reflection airborne targets, including stealthy UAVs and UCAVs.
No state funding has yet been made available to fund the active-array transition for Typhoon and Gripen. Euroradar (Selex SAS/EADS/Galileo Avionica/Indra) launched its own Caesar demonstrator programme for Typhoon in 2003. The demonstrator made its first flight on a BAC 1-11 testbed in February 2006. Caesar combines the back end from the existing Captor with an antenna partially featuring active GaAs modules from UMS (Germany) and Filtronic (UK). Captor air-to-air modes have been partially adapted to the new antenna. Caesar was flight tested on a Typhoon development aircraft (DA5) in May.
Industry is hopeful of an order as part of the Tranche 3 batch of Eurofighters, currently due to be ordered in 2009 for delivery starting in 2012. According to industry officials, the operating cost gains due to improved reliability would compensate for the extra cost due to development of the new antenna.
In Sweden, Saab Microwave Systems (the former Ericsson) is following a similar path, also without government funding. Saab, which hopes to start flight demonstrations this summer, aims to have an active antenna radar on Gripen by 2015, slightly later than the offer European programmes but with more ambitious technology goals. The antenna for its so-called Not Only Radar (NORA) concept would be mounted on a vertical axis allowing the scan angle (120[degrees] in pure electronic mode) to be extended to 200[degrees]. Nora would also offer jamming and data link functions, similar to what the Americans are testing today on the F-22's APG-77.
RELATED ARTICLE: Multifunction radars.
Much of the potential offered by GaN can be seen today with GaAs. It is already possible to produce very-high-bandwidth medium-power amplifiers for self-protection jammers covering the entire upper portion of the the electronic warfare spectrum (618-GHz). Thanks to a major technology investment, industry can now produce more powerful amplifiers, delivering around 10W at the high efficiency levels (around 50%) required for airborne X-band (8-12GHz) radar applications. In doing so, however, bandwidth has dropped to around 10% of the operating frequency. The experts predict that, within a relatively short timeframe, it will be possible to produce still more powerful GaN amplifiers ... with at least twice the bandwidth. The US Defense Advanced Research Projects Agency (Darpa) is targeting a six-fold increase in power compared with existing GaAs modules.
In Europe, the Korrigan project (see main article) aims to develop X-band power amplifiers in excess of 20W (i.e. suitable for radar and long-distance telecom applications) and with a bandwidth of around 2GHz, sufficient to jam other transmitters in the same frequency band.
In theory, modules with twice as much power could be used to produce radars with twice as much power, i.e. twice the range. However, engineers could well select another avenue, initially at least, since the useful range of a radar is related to the range of the weapons that it is being used to control. On the other hand, if the power of GaN is used to trim the number of modules, this means that the size of the antenna--and the nose section of the aircraft--can be significantly reduced, with an obvious payoff in terms of aerodynamics and stealth. The aircraft's stealth characteristics would be further improved by the fact that, by sharing the same antenna for radar, jamming and communications functions, there would be a reduction in the number of reflectors for enemy radars.
Another consequence of the smaller antenna is on increase in beam width. The tradeoff is a slight loss of resolution, but this is not a major problem in air-to-air situations where missiles have their own active seekers that can compensate for shortcomings in target designation. In air-to-ground modes, however, a wider beam enables a given area to be covered more quickly to establish cartography. Also, in jamming mode, the aiming accuracy in relation to a hostile transmitter would be less demanding.
The combination of all these modes (radar, communications jamming) on a GaAs radar is also possible. In the US, trials have been performed using the Northrop Grumman APG-77 radar on the F-22 and the Raytheon APG-79 on the F/A-18E/F Block 2. However, local media reports have highlighted the limits of what can be achieved. First-generation APG-77s reached their temperature limits already in radar mode. This problem seems to have been resolved on more recent versions, but in jamming mode the APG-77 cannot transmit for more than one second without damaging the radar. Also, experts have commented that jamming is effective over a frequency band that is too narrow to effectively counter all airborne threats.
This helps to explain why the US, despite their lead in GaAs technology, is currently accelerating research into a future alternative.
RELATED ARTICLE: Power plus bandwith.
The intrinsic properties of gallium nitride (GaN) make it the designated successor to gallium arsenide (GaAs) for radar applications. The three major properties are: substrate thermal conductivity and breakdown electric field 10 times greater than GaAs, and a very high output impedance, allowing GaN transistors to operate across very large bandwidths.
The higher breakdown electric field means that components will be able to operate at higher voltages (typically 20 and 40V, compared with 10V for X-band GaAs components) and will possess greater tolerance to impedance mismatch, rendering them less sensitive to hyperfrequency aggressions.
Operating at higher voltages, GaN amplifiers should reduce heat losses--which the good thermal conductivity of the substrate will help to evacuate more effectively. Hence the possibility of either deriving more power from components, or reducing component size for the same power.
GaN can be used to produce amplifiers up to several hundred watts which could be used to replace travelling wave tubes on telecommunications satellites. A major advantage in this case would be the elimination of very-high-voltage power supplies and the risk that these represent for the onboard environment. Transmit/receive modules for radar antenna (which today measure 6-7cm in length, with a 15mm section) could be packaged in 13mm cubes ... small enough to insert into conformal antenna and open the way to "smart skin".
Finally, the high breakdown voltage of the semiconductors means that the low-noise amplifiers in the reception stages of the radar will be less sensitive, i.e. more resistant to external aggression, such as offensive jamming and leakage from the transmit circuit at the antenna stage. Today, GaAs receive module stages require protection in the form of bulky and expensive ultra-rapid ferrite circulators. These circulators could be replaced by simple switches, also using GaN technology. In this way, all the high-frequency components of the radar antenna modules could be built using the same process, thus further reducing production costs.
http://www.entrepreneur.com/tradejournals/article/166091651_2.html
Isn't it DRAAMA, btw?
Anyone have something better than this article, which has a very good overview?
Radar revolution: the arrival of gallium nitride components opens up new applications for radars, including jamming and telecommunications.
by Dupont, Jean
Interavia Business & Technology • Summer, 2007 • DEFENCE
The active array antenna has virtually taken over the radar market--having won a berth on every new fighter or surveillance aircraft programme launched over the past 10 years. Even earlier programmes, such as the Rafale, Gripen, Typhoon or MiG-35 are preparing for the transition to active-array technology. The pressure do to so has been stepped up following the first US export sales of aircraft equipped with active-array radars--F-15s to Singapore in 2005, followed by Australia's recent order for the F/A-18E/F Super Hornet.
Weapons labs around the globe, however, are already gearing up for the next generation--antenna with the power and bandwith to perform offensive jamming and communications in addition to the radar function, and with a sufficiently compact and modular design to be housed not only in the nose of the fighter aircraft but also in conformal units elsewhere on the airframe surface.
The trigger for this revolution is a semiconductor material called gallium nitride (GaN), which, like the gallium arsenide (GaAs) used in current active antennas, is composed of elements from columns 3 and 5 of the periodic table and can be used to produce high frequency amplifiers.
The emergence of GaN from the laboratory has been delayed by epitaxy issues--growth of the semi-conductor layer on the silicon (Si) substrate, or silicon carbide (SIC) in the case of cutting-edge military applications. GaN and the substrate are made of crystals with different interatomic distances, hence the difficulty in assembling the two materials at a microscopic scale. The largest slices of high-performance GaN that have been obtained to date have a diameter of three inches, compared with six inches for GaAs and up to twelve inches for silicon. The size of the slice determines the number of chips that the machine can produce in a single pass.
GaN is clearly destined to remain expensive and its utilisation unlikely to expand beyond a limited number of applications, particularly since suppliers of SiC substrates are themselves limited. This situation could change, however, as GaN slices are expected to increase to four inches in the near future, and the arrival of new players should help to drive prices down, predicts Dominique Pons who heads the Alcatel Lucent/Thales III-V Lab. (The name reflects the columns of the periodic table mentioned above.) In any case, the intrinsic qualities of GaN have convinced the US Defense Advanced Research Projects Agency (Darpa) to invest heavily--tens of millions of dollars per year--in the technology.
The involvement of telecommunications giant Alcatel Lucent reflects the inherent duality of the technology--GaAs components are widely used in cell phones. Though power applications, such as radar, are largely confined to the military and space sectors, they are gradually finding their way into the civil domain. In the 1990s, EADS and Thales formed a joint company, United Monolithic Semiconductors (UMS), to produce GaAs chips and monolithic microwave integrated circuits (MMICs) for their new-generation radars.
Series production
UMS launched series production of MMICs for S- and C-band radars at the beginning of this decade, followed more recently by X-band radars like the active-array RBE2 AA that will equip the Rafale starting in 2012. On the civil side, lead times between technology incubation and application are much shorter, and the company has managed to find GaAs applications in a number of professional or top-end civil markets, such as wireless telecom infrastructures and anti-collision radars for cars.
In this way the military potential of GaAs has opened up an industrial capability that has found market openings in Europe ... the same openings that GaN will be able to exploit in its turn. Agreements are already in place with NXP (ex-Philips Semiconductors), explains Thierry Laboureau, UMS sales and marketing director, to develop power components for base stations for third- and fourth-generation cell phone networks and for WiMax base stations for mobile internet users. Ultimately, once prices have come down far enough, GaN could conceivably make its way into the kitchen, replacing the magnetron in the micro-wave oven.
However, these longer-term commercial perspectives will not be enough to cover the investment required to launch foundry operations. Nor is there any prospect of procuring components for military applications from the US or Japan--both countries have already placed an embargo on GaAs circuits, and there is no reason for them to be any more flexible concerning GaN. This explains why the defence procurement authorities in France and Germany are both helping to support industrial research efforts.
According to Dominique Pons, the III-V Lab should produce its first X-band or wide-band GaN MMICs this year. Following validation and industrialisation by UMS, series production should get under way by 2009.
EDA funding
GaN is also one of the very first research areas to receive funding from the European Defence Agency (EDA) under a 40 million [euro] programme called Korrigan that brings together 23 companies and laboratories in seven countries to accelerate the development of one or more European GaN foundries with associated supply chain by 2009. The programme leader is Thales Airborne Systems. Other participants include EADS, Selex Sistemi Integrati, Saab Ericsson and BAE Insyte. Their role initially is to define requirements for the foundries, before becoming directly involved, from 2008 onwards, in integrating the microchips into a variety of specialised modules covering a range of land-based and airborne radar applications, as well as self-protection or offensive jammers.
In this way, explains Thales Airborne Systems technical director Pierre Fossier, it should be possible to launch the first system applications in 2010. In France, one of the leading candidates for the new technology is the offensive jammer, a capacity that the French Air Force has had its eyes on for several years, and which has already given rise to the Carbone airborne demonstrator. The performance of the system attracted a lot of attention at NATO's Mace X electronic warfare exercise in the year 2000.
The DGA procurement branch of the French MoD is continuing to provide limited funding for exploratory work by Thales while awaiting for national budgets to kick in to complete development. GaN would allow for a reduction in the size of the jammer, potentially clearing the way for integration into a combat aircraft. One of the first European acquisition programmes to integrate GaN technology could well be the Maritime Airborne Surveillance and Control (MASC) programme to replace Royal Navy Sea King Mk7 airborne surveillance helicopters, as required for the future CVF aircraft carriers. The three candidates for this mission are the Hawkeye aircraft, the EH-101 helicopter and the tiltwing V-22, though the Hawkeye would appear to be ruled out by the absence of a catapult in the current CVF definition. Both the other candidates would require a compact and powerful radar to meet missions requirements. The potential advantages of a GaN radar in this context have prompted the British MoD to finance some upstream development work in preparation for a programme launch in the 2009 timeframe--the same year that the first European GaN modules are scheduled to come off the production line.
Rafale lead
As far as Europe's combat aircraft programmes are concerned, the Rafale seems to have established a lead over Typhoon and Gripen in the race to integrate an active array antenna. This is primarily because--unlike its competitors--the transition to active-array technology on the Rafale's electronically scanned RBE2 was planned from the outset, avoiding the need for the more extensive (and expensive) modifications required on the mechanical antennas of the Typhoon and Gripen. The increase in range that the new technology will bring is deemed essential if the aircraft is to fully exploit the potential of the future ramjet-powered Meteor missile, due to enter service in the early years of the next decade. Without it, pilots will rely on target designation from another platform to strike targets at the limits of the Meteor envelope.
All aircraft will benefit from the collaborative work accomplished under the trinational Airborne Multirole Solid State Active Array Radar (AMSAR) programme, which was launched in 1993 to develop a European capability in GaAs power devices and subsequently gave rise to UMS (EADS/Thales). Work under AMSAR is currently focused on beam forming through computation. The goal is to cancel reception in jammed sectors and improve rejection of parasitic ground echos, though at the cost of a more complex antenna architecture.
In France, Thales launched its own active antenna radar demonstrator programme in the late 1990s incorporating US components. The resulting mockup was tested at the CEV flight test centre in 2002 on a Mystere XX test bed, and the following year on Rafale. In February 2004, the French MoD's DGA procurement branch awarded 85 million [euro] under the DRAMA programme to develop a prototype active-module radar representative of an operational system.
Thales is currently working on its first DRAMA antenna featuring UMS components. The antenna is scheduled to be delivered to the CEV test centre in midyear for flight testing on the Mystere XX and Mirage 2000 through 2009. The objective is to complete qualification of the new radar by 2009 and deliver two prototypes to Dassault the following year for integration into the aircraft and validation of the full standard. The first two production radars are currently scheduled for delivery in 2011; they will equip the last two Rafales in the current production batch. Half of the 400 million [euro] in funding for the Rafale "Roadmap"--the development of additional capabilities beyond the F3 standard--has been earmarked for the introduction of an active array antenna on the RBE2. This will involve an array of around 1,000 GaAs transmit/receive modules to replace the existing passive scanning antenna and the travelling wave tube (TWT) on the transmitter. The goal is to have the resulting AA version of the RBE2 ready for series production to equip Rafales delivered from 2012 under the next multi-year order, which is expected to be signed in early 2009.
According to Thales, the RBE2 AA will offer 50% greater range than the current RBE2 and a huge increase in reliability--major overhaul every 7-10 years, compared with a current TWT service life of around 100 hours. It will also be possible to generate SAR images in air-to-ground mode with 1 m resolution or better, and to detect at long range low-reflection airborne targets, including stealthy UAVs and UCAVs.
No state funding has yet been made available to fund the active-array transition for Typhoon and Gripen. Euroradar (Selex SAS/EADS/Galileo Avionica/Indra) launched its own Caesar demonstrator programme for Typhoon in 2003. The demonstrator made its first flight on a BAC 1-11 testbed in February 2006. Caesar combines the back end from the existing Captor with an antenna partially featuring active GaAs modules from UMS (Germany) and Filtronic (UK). Captor air-to-air modes have been partially adapted to the new antenna. Caesar was flight tested on a Typhoon development aircraft (DA5) in May.
Industry is hopeful of an order as part of the Tranche 3 batch of Eurofighters, currently due to be ordered in 2009 for delivery starting in 2012. According to industry officials, the operating cost gains due to improved reliability would compensate for the extra cost due to development of the new antenna.
In Sweden, Saab Microwave Systems (the former Ericsson) is following a similar path, also without government funding. Saab, which hopes to start flight demonstrations this summer, aims to have an active antenna radar on Gripen by 2015, slightly later than the offer European programmes but with more ambitious technology goals. The antenna for its so-called Not Only Radar (NORA) concept would be mounted on a vertical axis allowing the scan angle (120[degrees] in pure electronic mode) to be extended to 200[degrees]. Nora would also offer jamming and data link functions, similar to what the Americans are testing today on the F-22's APG-77.
RELATED ARTICLE: Multifunction radars.
Much of the potential offered by GaN can be seen today with GaAs. It is already possible to produce very-high-bandwidth medium-power amplifiers for self-protection jammers covering the entire upper portion of the the electronic warfare spectrum (618-GHz). Thanks to a major technology investment, industry can now produce more powerful amplifiers, delivering around 10W at the high efficiency levels (around 50%) required for airborne X-band (8-12GHz) radar applications. In doing so, however, bandwidth has dropped to around 10% of the operating frequency. The experts predict that, within a relatively short timeframe, it will be possible to produce still more powerful GaN amplifiers ... with at least twice the bandwidth. The US Defense Advanced Research Projects Agency (Darpa) is targeting a six-fold increase in power compared with existing GaAs modules.
In Europe, the Korrigan project (see main article) aims to develop X-band power amplifiers in excess of 20W (i.e. suitable for radar and long-distance telecom applications) and with a bandwidth of around 2GHz, sufficient to jam other transmitters in the same frequency band.
In theory, modules with twice as much power could be used to produce radars with twice as much power, i.e. twice the range. However, engineers could well select another avenue, initially at least, since the useful range of a radar is related to the range of the weapons that it is being used to control. On the other hand, if the power of GaN is used to trim the number of modules, this means that the size of the antenna--and the nose section of the aircraft--can be significantly reduced, with an obvious payoff in terms of aerodynamics and stealth. The aircraft's stealth characteristics would be further improved by the fact that, by sharing the same antenna for radar, jamming and communications functions, there would be a reduction in the number of reflectors for enemy radars.
Another consequence of the smaller antenna is on increase in beam width. The tradeoff is a slight loss of resolution, but this is not a major problem in air-to-air situations where missiles have their own active seekers that can compensate for shortcomings in target designation. In air-to-ground modes, however, a wider beam enables a given area to be covered more quickly to establish cartography. Also, in jamming mode, the aiming accuracy in relation to a hostile transmitter would be less demanding.
The combination of all these modes (radar, communications jamming) on a GaAs radar is also possible. In the US, trials have been performed using the Northrop Grumman APG-77 radar on the F-22 and the Raytheon APG-79 on the F/A-18E/F Block 2. However, local media reports have highlighted the limits of what can be achieved. First-generation APG-77s reached their temperature limits already in radar mode. This problem seems to have been resolved on more recent versions, but in jamming mode the APG-77 cannot transmit for more than one second without damaging the radar. Also, experts have commented that jamming is effective over a frequency band that is too narrow to effectively counter all airborne threats.
This helps to explain why the US, despite their lead in GaAs technology, is currently accelerating research into a future alternative.
RELATED ARTICLE: Power plus bandwith.
The intrinsic properties of gallium nitride (GaN) make it the designated successor to gallium arsenide (GaAs) for radar applications. The three major properties are: substrate thermal conductivity and breakdown electric field 10 times greater than GaAs, and a very high output impedance, allowing GaN transistors to operate across very large bandwidths.
The higher breakdown electric field means that components will be able to operate at higher voltages (typically 20 and 40V, compared with 10V for X-band GaAs components) and will possess greater tolerance to impedance mismatch, rendering them less sensitive to hyperfrequency aggressions.
Operating at higher voltages, GaN amplifiers should reduce heat losses--which the good thermal conductivity of the substrate will help to evacuate more effectively. Hence the possibility of either deriving more power from components, or reducing component size for the same power.
GaN can be used to produce amplifiers up to several hundred watts which could be used to replace travelling wave tubes on telecommunications satellites. A major advantage in this case would be the elimination of very-high-voltage power supplies and the risk that these represent for the onboard environment. Transmit/receive modules for radar antenna (which today measure 6-7cm in length, with a 15mm section) could be packaged in 13mm cubes ... small enough to insert into conformal antenna and open the way to "smart skin".
Finally, the high breakdown voltage of the semiconductors means that the low-noise amplifiers in the reception stages of the radar will be less sensitive, i.e. more resistant to external aggression, such as offensive jamming and leakage from the transmit circuit at the antenna stage. Today, GaAs receive module stages require protection in the form of bulky and expensive ultra-rapid ferrite circulators. These circulators could be replaced by simple switches, also using GaN technology. In this way, all the high-frequency components of the radar antenna modules could be built using the same process, thus further reducing production costs.
http://www.entrepreneur.com/tradejournals/article/166091651_2.html
* * *
Isn't it DRAAMA, btw?
