Gripen E's data link mystery: solved
We've been debating what type of data link the Gripen E will have. Is it broadcasting? Is it directional? Is it a tight beam system like F35's MADL?
This SAAB slide deck from Farnborough 2014 seems to have the answer:
https://www.slideshare.net/...
The Gripen E will have a "smart directional communications". That sounds like it's not an area broad casting system and not a tight beam one but a directional system to manage signature and improve jam resistance. Makes sense for Gripen's signature management requirements and operational needs.
Not quite as hard to detect as MADL but still not broadcasting everywhere and difficult to jam.
UPDATE: Since we've identified the location of the Gripen's UHF antenna and with Axel's find of a paper with the exact dimensions of Gripen's AESA ecm array:
http://ieeexplore.ieee.org/...
https://saabgroup.com/media...
we can actually do a basic estimate the beam width capabilities of the UHF antenna, the Ku band antenna and compare it with the MADL array on the F35. This is because there is a simple relationship between antenna size, wavelength and beamwidth:
http://www.phys.hawaii.edu/...
BWin radians ~ lambda/L where lambda is the wavelength and L is the length of the antenna.
The Gripen's tail fin UHF antenna has 40 cm total height. Assuming useable height of 35 cm, the UHF phased array's theoretical beam width is ~45 degrees at the traditional legacy TIDLS / Link 16 frequencies near 1 GHz. If pushed to 3 GHz the best theoretical performance is ~ 15 degrees.
The Gripen's broadband AESA ECM antenna is 16 cm by 9 cm. SAAB patents show schemes using different antenna areas for transmit and receive to cut down on noise interference. Assuming for simplicity that they use a 9 cm by 9 cm area in the Ku band, that gives beam width performance of ~11 degrees at 18 ghz and 16 degrees at 12 GHz.
After carefully examining F35 photos, the MADL array is a hexagon with vertex to vertex width of ~9.5 cm. This gives theoretical beam width performance very close to the Gripen's wing tip antenna pods:
10 degrees at 18 GHz and 15 degrees at 12 GHz.
So we see that the UHF system is actually sized so that its beam width ranges from somewhat directional (45 degrees) to just starting to overlap with the low end beam width of a prospective Ku band beam forming antenna (~15 degrees).
For the high frequency antenna arrays, both the Gripen's AESA ECM antenna and the MADL antenna on the F35 have very similar dimensions. They are both designed to give 10 to 15 degree beams in the Ku band.
Although currently we can identify no concrete information from SAAB indicating that a Ku band narrow beam data link has been implemented, it would seem that were one to be added as a software update in a future block, the performance could be quite similar to MADL, at least in terms of beam width.
We can also surmise that current military thinking has settled on a consensus of 10 degrees to 15 degree beams as optimal for advanced low probability of intercept, high bandwidth, narrow beam data links.