I urge everyone to read this!
Background
Image 1: APG-63(V)2 radar installed on an F-15C. The APG-63(V)2 was the first fighter mounted AESA radar to enter service worldwide. The first American F-15C unit to receive the new radars were stationed at Elmendorf in 2000. In comparison, the first European AESA entered operational service in 2012 and the first Russian AESA equipped fighters (Mig-35) will not enter service until 2016. The initial US technological lead in AESA technology is attributable to substantial investments made in the late stages of the Cold War.
Author's Note: During the research process on the J-31’s avionics (for the upcoming Threat Analysis of Foreign Stealth Fighters:J-31 Part II), it became apparent that very few credible, verifiable, and non-speculative English based source materials existed on the subject of PLA fighter radars. Basic information, such the proper name or designation of a radar system is utilized by a particular fighter often varies between sources; performance figures associated with domestically produced radars is even harder to verify. This article's intent was to compile a wide variety of information on expected future developments in Chinese actively scanned electronic array (AESA) radars. Furthermore, the current “Threat Analysis of Foreign Stealth Fighters: Part I Chengdu J-20” is largely dated with respect to developments with the J-20’s avionics suite and this article subsequently provides more up-to-date information on the J-20’s AESA.
AESA radars represent a significant increase in detection power, reliability, and electronic warfare capabilities when compared to older electronically scanned arrays (ESA) and mechanically scanned arrays (MSA). This article largely focus on more technical aspects of AESAs but the basics of AESAs are cogently detailed by Karlo Kopp in "Active Electronically Steered Arrays A Maturing Technology".
Three main determinants dictate the maximum number of transmit receiver modules a fighter radar can accommodate: the volume of the aircraft’s nose, the technological maturity of the firm/country’s T/R module packaging technology, and the effectiveness of the radar's thermal management system(s). The volume of the nose is a fairly intuitive constraint, the larger an aircraft’s nose is, the larger the radar can be. For example, the F-15C’s nose cone is able to accommodate the much larger 1,500 T/R element APG-63V(3) radar vs. the F-16C Block 60 with its comparatively smaller nose cone and its 1,000 T/R element APG-80 AESA. Packaging technology refers to how many individual T/R modules can be installed within the finite space usually accomplished by reductions in size of the individual T/R modules. The more technologically advanced a firm’s T/R packaging technology is, the smaller the individual T/R modules will be resulting in an increase density of the layout of T/R modules within the array. Thus, advancements in packaging technology enable engineers to accommodate more T/R modules within the fixed volume of the aircraft's nose.
Image 2: US early production quad packed transmit receiver modules. The United States no longer produces quad channel T/R modules and has since produced single T/R module designs. Less advanced AESAs such as the Zhuk-AE utilize multi-T/R channel designs, it is possible China's first generation of AESAs also utilize a multi-T/R channel design.
Lastly, thermal management systems are instrumental for the operation of high power AESA radars. Unlike MSA systems, air cooling systems are insufficient to prevent heat related system failures and frequent maintenance issues:
“Due to the behavior of microwave transistor amplifiers, the power efficiency of a TR module transmitter is typically less than 45%. As a result, an AESA will dissipate a lot of heat which must be extracted to prevent the transmitter chips becoming molten pools of Gallium Arsenide - reliability of GaAs MMIC chips improves the cooler they are run. Traditional air cooling used in most established avionic hardware is ill suited to the high packaging density of an AESA, as a result of which modern AESAs are liquid cooled.US designs employ a polyalphaolefin (PAO) coolant similar to a synthetic hydraulic fluid. A typical liquid cooling system will use pumps to drive the coolant through channels in the antenna, and then route it to a heat exchanger. That might be an air cooled core (radiator style) or an immersed heat exchanger in a fuel tank - with a second liquid cooling loop to dump heat from the fuel tank. In comparison with a conventional air cooled fighter radar, the AESA will be more reliable but will require more electrical power and more cooling, and typically can produce much higher transmit power if needed for greater target detection range performance (increasing transmitted power has the drawback of increasing the footprint over which a hostile ESM or RWR can detect the radar” – Kopp, 2014
Chinese AESAs
Image 3:The image which allegedly describes the number of TR modules within the J-10B, J-16, and J-20 has been posted on numerous defense forums since at least December of 2013.
Chinese defense forums have posted copies of the image above which claim to cite the J-20’s AESA T/R module count at 1,856, the J-16’s at 1,760, and the J-10B at 1,200 T/R modules. It is likely the J-10B is the first Chinese fighter aircraft to feature an AESA; J-10B units achieved initial operational capability (IOC) in October of 2014. The volume of the J-10s nose cone is not substantially different from that of the F-16 or the Israeli Lavi from which the J-10 is partially based. Therefore, if one were to assume China had reached parity with the United States in packaging technology, the 1,200 T/R module figure would be plausible but slightly high. For comparison, the APG-80 AESA for the F-16C/D Block 60 has 1,000 T/R modules (DSB, 2001). However, it is unlikely that China has been able to reach parity with the United States in terms of packaging technology on their first generation AESA design. Neither Russia nor Israel was able to field 1,000 T/R element arrays within their first generation fighter mounted AESAs for similar nose volumes as the F-16 with the Mig-35 and Israeli F-16 respectively.
Russia’s first fighter mounted AESA radar, the Zhuk-AE, contained 652 T/R modules and was unveiled in 2007. The Israeli ELM-2052 AESA radar, which has been marketed for both the F-16 and the FA-50 – a joint Korean Aerospace Industry and Lockheed Martin F-16 derivative, has roughly 512 T/R modules (Trimble, 2014). The only firm outside of the United States that was able to produce a 1,000 T/R element within one generation was the French avionics firm Thales with its RB2E radar (Avionics Today, 2009). While the relative technological maturity of European, Israeli, and Russian AESAs is not directly indicative of the relative technological maturity of China’s packaging technology, it is an indicator that the first generation AESA produced by China is likely not on par with the US which is generally recognized as having the most technological mature T/R packaging technology (Kopp, 2014).
Image 4: T/R module count of US AESAs based upon the 2001 Defense Science Board report "Future DoD Airborne High-Frequency Radar Needs/Resources"(link provided in Source 1 citation, refer to page 6). Image Credit: Air Power Australia, 2008.
The prospect of China’s TR packaging technology being on par with US firms within a single generation of radars is even more dubious when one examines the preference for an incremental technological development within the Chinese aerospace industry. Several Chinese aviation authors have hypothesized that the J-10B serves as a “technological stepping stone” with respect to the development of the more advanced J-20. For example, Feng Cao argues the J-10B and the J-16 AESAs were likely used to test technology related to the J-20’s AESA which would be a second generation Chinese design. By virtue of the larger nose volumes in the J-16 and J-20 airframes, it is highly probable the two aircraft will feature radars with more T/R modules than the J-10B’s radar.
The J-16 utilizes the Su-27BS airframe which has room for a 0.9-1.1 meter aperture in the nose which is on par with the F-15 and F-22 in terms of volume (Kopp, 2012). The 1,500 element N036 Tikhomirov NIIP AESA has a similar aperture size to the electronically scanned array (ESA) Irbis-E radar featured in the Su-35 series of fighters which shares the base Su-27 airframe. If the 1,760 T/R figure is correct it would indicate the Chinese aerospace industry has eclipsed Russian T/R module packaging technology as the N036 is arguably the most advanced Russian fighter mounted AESA. Similarly, the most advanced US fighter mounted AESAs such as the APG-77(V)2 and APG-82(V)1 contain 1,500 T/R modules*. While the prospect of Chinese avionics firms reaching parity with US and Russian firms is more plausible within two generations of designs, the author is skeptical the 1,760 figure is correct given the unsubstantiated nature of the image and the fairly substantial 260 T/R discrepancy between the J-16 radar figure compared to the most advanced US and Russian AESA designs. Therefore, the author speculates it would be more reasonable to assume a figure between 1,200 and 1,500 TR modules for the J-16 rather than the 1,760 figure.
Image 5: The sixth and most recent (as of January 2015) unveiled J-20 testing aircraft model "2015".
The tentative designation for the J-20's AESA is the Type 1475. While the nose volume of the J-20 is certainly large, the jet overall is longer and heavier than the F-22, no credible figures for nose volume were available at the time of this publication. As with the J-16 T/R figure, the J-20 figure is substantially greater than that of the most advanced US and Russian designs. Even if the Nanjing Research Institute of Electronics Technology (NRIET) or the China Leihua Electronic Technology Research Institute (607 Institute) was able to develop sufficient packaging technology that would enable 1,856 T/R modules within the J-20's nose, the density of the T/R modules would create significant cooling problems. For example, Phazotron's single greatest difficulty in designing the Zuk-AE was the AESA's thermal management system (Kopp, 2008). Without an effective cooling system, the Type 1475 would not be reliable at peak power output and would cause significant maintenance issues. Furthermore, with such a high number of T/R modules, the Type 1475 would be vulnerable to radar warning receiver (RWR) systems such as the ALR-94 without a very capable low probability intercept (LPI) mode.
Many discussions with respect to the "relative stealthiness" of fighter aircraft are limited to merely comparing radar cross section estimates while entirely neglecting alternate means of detecting aircraft such as RWRs or other emission locator systems. David Axe succinctly compares the process of how RWRs function to how a flash light carried by another person is easily visible in a dark room. AESAs emit a substantial amount of energy, especially designs with a greater number of T/R modules, which enables passive emission locator systems to detect an AESA. The addition of an LPI software for AESAs mitigates the risk of RWR detection.
"The radar's signals are managed in intensity, duration and space to maintain the pilot's situational awareness while minimizing the chance that its signals will be intercepted.More distant targets get less radar attention; as they get closer to the F-22, they will be identified and prioritized; and when they are close enough to be engaged or avoided, they are continuously tracked" - Bill Sweetman, 2001
Image 6: Engagement boundaries for the AN/APG-77. Targets automatically receive higher tracking accuracy as they enter engagement boundaries in proximity to the F-22. The boundary concept facilitates automated sensor tasking and efficient sensor usage which contributes towards increased situational awareness and fewer emissions by the array (Ronald W. Brower, 2001). Image Credit: Ronald W. Brower & USAF, 2001.
However, LPI software is not foolproof as demonstrated between tests involving F-22s and a CATbird avionics testbed equipped with the F-35's avionics package*. The F-35's avionics were able to jam and track multiple F-22 and F-15 radars during the exercise (Fulghum, Sweetman, Perrett & Wall, 2011).
Background
Image 1: APG-63(V)2 radar installed on an F-15C. The APG-63(V)2 was the first fighter mounted AESA radar to enter service worldwide. The first American F-15C unit to receive the new radars were stationed at Elmendorf in 2000. In comparison, the first European AESA entered operational service in 2012 and the first Russian AESA equipped fighters (Mig-35) will not enter service until 2016. The initial US technological lead in AESA technology is attributable to substantial investments made in the late stages of the Cold War.
Author's Note: During the research process on the J-31’s avionics (for the upcoming Threat Analysis of Foreign Stealth Fighters:J-31 Part II), it became apparent that very few credible, verifiable, and non-speculative English based source materials existed on the subject of PLA fighter radars. Basic information, such the proper name or designation of a radar system is utilized by a particular fighter often varies between sources; performance figures associated with domestically produced radars is even harder to verify. This article's intent was to compile a wide variety of information on expected future developments in Chinese actively scanned electronic array (AESA) radars. Furthermore, the current “Threat Analysis of Foreign Stealth Fighters: Part I Chengdu J-20” is largely dated with respect to developments with the J-20’s avionics suite and this article subsequently provides more up-to-date information on the J-20’s AESA.
AESA radars represent a significant increase in detection power, reliability, and electronic warfare capabilities when compared to older electronically scanned arrays (ESA) and mechanically scanned arrays (MSA). This article largely focus on more technical aspects of AESAs but the basics of AESAs are cogently detailed by Karlo Kopp in "Active Electronically Steered Arrays A Maturing Technology".
Three main determinants dictate the maximum number of transmit receiver modules a fighter radar can accommodate: the volume of the aircraft’s nose, the technological maturity of the firm/country’s T/R module packaging technology, and the effectiveness of the radar's thermal management system(s). The volume of the nose is a fairly intuitive constraint, the larger an aircraft’s nose is, the larger the radar can be. For example, the F-15C’s nose cone is able to accommodate the much larger 1,500 T/R element APG-63V(3) radar vs. the F-16C Block 60 with its comparatively smaller nose cone and its 1,000 T/R element APG-80 AESA. Packaging technology refers to how many individual T/R modules can be installed within the finite space usually accomplished by reductions in size of the individual T/R modules. The more technologically advanced a firm’s T/R packaging technology is, the smaller the individual T/R modules will be resulting in an increase density of the layout of T/R modules within the array. Thus, advancements in packaging technology enable engineers to accommodate more T/R modules within the fixed volume of the aircraft's nose.
Image 2: US early production quad packed transmit receiver modules. The United States no longer produces quad channel T/R modules and has since produced single T/R module designs. Less advanced AESAs such as the Zhuk-AE utilize multi-T/R channel designs, it is possible China's first generation of AESAs also utilize a multi-T/R channel design.
Lastly, thermal management systems are instrumental for the operation of high power AESA radars. Unlike MSA systems, air cooling systems are insufficient to prevent heat related system failures and frequent maintenance issues:
“Due to the behavior of microwave transistor amplifiers, the power efficiency of a TR module transmitter is typically less than 45%. As a result, an AESA will dissipate a lot of heat which must be extracted to prevent the transmitter chips becoming molten pools of Gallium Arsenide - reliability of GaAs MMIC chips improves the cooler they are run. Traditional air cooling used in most established avionic hardware is ill suited to the high packaging density of an AESA, as a result of which modern AESAs are liquid cooled.US designs employ a polyalphaolefin (PAO) coolant similar to a synthetic hydraulic fluid. A typical liquid cooling system will use pumps to drive the coolant through channels in the antenna, and then route it to a heat exchanger. That might be an air cooled core (radiator style) or an immersed heat exchanger in a fuel tank - with a second liquid cooling loop to dump heat from the fuel tank. In comparison with a conventional air cooled fighter radar, the AESA will be more reliable but will require more electrical power and more cooling, and typically can produce much higher transmit power if needed for greater target detection range performance (increasing transmitted power has the drawback of increasing the footprint over which a hostile ESM or RWR can detect the radar” – Kopp, 2014
Chinese AESAs
Image 3:The image which allegedly describes the number of TR modules within the J-10B, J-16, and J-20 has been posted on numerous defense forums since at least December of 2013.
Chinese defense forums have posted copies of the image above which claim to cite the J-20’s AESA T/R module count at 1,856, the J-16’s at 1,760, and the J-10B at 1,200 T/R modules. It is likely the J-10B is the first Chinese fighter aircraft to feature an AESA; J-10B units achieved initial operational capability (IOC) in October of 2014. The volume of the J-10s nose cone is not substantially different from that of the F-16 or the Israeli Lavi from which the J-10 is partially based. Therefore, if one were to assume China had reached parity with the United States in packaging technology, the 1,200 T/R module figure would be plausible but slightly high. For comparison, the APG-80 AESA for the F-16C/D Block 60 has 1,000 T/R modules (DSB, 2001). However, it is unlikely that China has been able to reach parity with the United States in terms of packaging technology on their first generation AESA design. Neither Russia nor Israel was able to field 1,000 T/R element arrays within their first generation fighter mounted AESAs for similar nose volumes as the F-16 with the Mig-35 and Israeli F-16 respectively.
Russia’s first fighter mounted AESA radar, the Zhuk-AE, contained 652 T/R modules and was unveiled in 2007. The Israeli ELM-2052 AESA radar, which has been marketed for both the F-16 and the FA-50 – a joint Korean Aerospace Industry and Lockheed Martin F-16 derivative, has roughly 512 T/R modules (Trimble, 2014). The only firm outside of the United States that was able to produce a 1,000 T/R element within one generation was the French avionics firm Thales with its RB2E radar (Avionics Today, 2009). While the relative technological maturity of European, Israeli, and Russian AESAs is not directly indicative of the relative technological maturity of China’s packaging technology, it is an indicator that the first generation AESA produced by China is likely not on par with the US which is generally recognized as having the most technological mature T/R packaging technology (Kopp, 2014).
Image 4: T/R module count of US AESAs based upon the 2001 Defense Science Board report "Future DoD Airborne High-Frequency Radar Needs/Resources"(link provided in Source 1 citation, refer to page 6). Image Credit: Air Power Australia, 2008.
The prospect of China’s TR packaging technology being on par with US firms within a single generation of radars is even more dubious when one examines the preference for an incremental technological development within the Chinese aerospace industry. Several Chinese aviation authors have hypothesized that the J-10B serves as a “technological stepping stone” with respect to the development of the more advanced J-20. For example, Feng Cao argues the J-10B and the J-16 AESAs were likely used to test technology related to the J-20’s AESA which would be a second generation Chinese design. By virtue of the larger nose volumes in the J-16 and J-20 airframes, it is highly probable the two aircraft will feature radars with more T/R modules than the J-10B’s radar.
The J-16 utilizes the Su-27BS airframe which has room for a 0.9-1.1 meter aperture in the nose which is on par with the F-15 and F-22 in terms of volume (Kopp, 2012). The 1,500 element N036 Tikhomirov NIIP AESA has a similar aperture size to the electronically scanned array (ESA) Irbis-E radar featured in the Su-35 series of fighters which shares the base Su-27 airframe. If the 1,760 T/R figure is correct it would indicate the Chinese aerospace industry has eclipsed Russian T/R module packaging technology as the N036 is arguably the most advanced Russian fighter mounted AESA. Similarly, the most advanced US fighter mounted AESAs such as the APG-77(V)2 and APG-82(V)1 contain 1,500 T/R modules*. While the prospect of Chinese avionics firms reaching parity with US and Russian firms is more plausible within two generations of designs, the author is skeptical the 1,760 figure is correct given the unsubstantiated nature of the image and the fairly substantial 260 T/R discrepancy between the J-16 radar figure compared to the most advanced US and Russian AESA designs. Therefore, the author speculates it would be more reasonable to assume a figure between 1,200 and 1,500 TR modules for the J-16 rather than the 1,760 figure.
Image 5: The sixth and most recent (as of January 2015) unveiled J-20 testing aircraft model "2015".
The tentative designation for the J-20's AESA is the Type 1475. While the nose volume of the J-20 is certainly large, the jet overall is longer and heavier than the F-22, no credible figures for nose volume were available at the time of this publication. As with the J-16 T/R figure, the J-20 figure is substantially greater than that of the most advanced US and Russian designs. Even if the Nanjing Research Institute of Electronics Technology (NRIET) or the China Leihua Electronic Technology Research Institute (607 Institute) was able to develop sufficient packaging technology that would enable 1,856 T/R modules within the J-20's nose, the density of the T/R modules would create significant cooling problems. For example, Phazotron's single greatest difficulty in designing the Zuk-AE was the AESA's thermal management system (Kopp, 2008). Without an effective cooling system, the Type 1475 would not be reliable at peak power output and would cause significant maintenance issues. Furthermore, with such a high number of T/R modules, the Type 1475 would be vulnerable to radar warning receiver (RWR) systems such as the ALR-94 without a very capable low probability intercept (LPI) mode.
Many discussions with respect to the "relative stealthiness" of fighter aircraft are limited to merely comparing radar cross section estimates while entirely neglecting alternate means of detecting aircraft such as RWRs or other emission locator systems. David Axe succinctly compares the process of how RWRs function to how a flash light carried by another person is easily visible in a dark room. AESAs emit a substantial amount of energy, especially designs with a greater number of T/R modules, which enables passive emission locator systems to detect an AESA. The addition of an LPI software for AESAs mitigates the risk of RWR detection.
"The radar's signals are managed in intensity, duration and space to maintain the pilot's situational awareness while minimizing the chance that its signals will be intercepted.More distant targets get less radar attention; as they get closer to the F-22, they will be identified and prioritized; and when they are close enough to be engaged or avoided, they are continuously tracked" - Bill Sweetman, 2001
Image 6: Engagement boundaries for the AN/APG-77. Targets automatically receive higher tracking accuracy as they enter engagement boundaries in proximity to the F-22. The boundary concept facilitates automated sensor tasking and efficient sensor usage which contributes towards increased situational awareness and fewer emissions by the array (Ronald W. Brower, 2001). Image Credit: Ronald W. Brower & USAF, 2001.
However, LPI software is not foolproof as demonstrated between tests involving F-22s and a CATbird avionics testbed equipped with the F-35's avionics package*. The F-35's avionics were able to jam and track multiple F-22 and F-15 radars during the exercise (Fulghum, Sweetman, Perrett & Wall, 2011).
