Think you need an ESA?
There is a common misperception that electronically scanned arrays (ESAs) are necessary to help unlock all the potential that the new GSO and NGSO networks bring to the SATCOM industry.
Despite many years and millions of dollars of R&D expenditures, no low-cost ESA appears to be ready for prime time. But beyond the lack of any tangible products, the reality is that ESAs have many technical shortcomings that make them unsuitable for most applications.
Below we dispel some pervasive myths about ESAs and why they cannot compare to the performance and value provided by ThinKom’s VICTS phased arrays.
ThinKom’s phased array has moving parts. Doesn’t that make it inherently less reliable than an ESA?
Actually, the ThinKom VICTS antenna, while being a mechanically steered phased array, has far superior reliability as compared to an ESA. Our airborne VICTS antennas have no belts or gears, instead employing a completely contact-less drive system.
Ball bearings are the only contacting parts and are extremely low velocity and lightly loaded, and therefore not a failure mode. ThinKom VICTS antennas have measured mean time between failures (MTBF) of >100,000 hours, with over 1,500 in service, tallying over 17 million operating hours through September 2020.
The first Ku3030, installed on Aeromexico in 2015, is still flying today and providing a robust IFE experience for hundreds of passengers daily, having never been removed or serviced.
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Those are some impressive reliability metrics. But everyone talks about ESAs having high reliability because of no moving parts. Is everyone wrong?
Publicly available reliability data is severely lacking for the few ESAs that have actually been put into service, so verifiable MTBF metrics are unknown.
But because an ESA has roughly 1,000 times more active components than a ThinKom VICTS antenna, overall reliability can only be high if the reliability for a very large subset of these components is very high.
Additionally, the average ESA has >10 times higher thermal dissipation than a VICTS antenna, and it is well known that heat is a primary driver in failure modes. ESAs require a receiver/exciter and power-supply LRUs – additional custom, low-reliability, single points of failure.
ESA manufacturers often claim that “as individual elements fail, there is graceful degradation.” In reality, antenna patterns change every time an element fails. Therefore, regulatory compliance is extremely difficult, if not impossible, to manage – and this is exacerbated if neighboring elements fail.
Size and Spectral Efficiency
Doesn’t an ESA provide the best hope for a small, low-profile and low-cost antenna for airborne and land-mobile applications?
ThinKom VICTS antennas are far superior in terms of spectral efficiency. For a given G/T, an ESA requires 2.5 to 8 times the aperture area required for a VICTS antenna.
This dramatically higher area (and spectral efficiency) advantage translates into annual bandwidth cost savings of $75K per aircraft or a net present value of $480K per aircraft over 10 years.
As far as low profile, VICTS antennas are 2 to 4 inches in total height (depending on frequency) and that’s comparable to ESAs.
Will ESA prices eventually be affordable, following a similar pricing model of consumer electronics, such as big screen TVs?
ESAs have been in development for many decades but have not been able to overcome the numerous technological challenges that limit their efficiency, cost effectiveness, excessive power demands and poor low-elevation performance.
Even if ESA manufacturers could overcome these challenges, the market for phased-array antennas is quite different (and smaller) than that of consumer electronics. Should the market change and the demand for phased array antennas take off, VICTS antennas are well suited for high volume manufacturing, meaning that VICTS antennas will continue to be a more cost-effective solution.
Extreme Scan Performance
At least an ESA’s scan performance is as good as a VICTS antenna, right?
That’s another myth. While all phased-array antennas experience a degradation in gain as the beam scans down towards the horizon (known as the “cosine roll-off”), ESAs exhibit additional degradation due to their densely packed, two-dimensional, discrete radiating elements.
At low look angles (below 30°), the proximity of the elements causes transmit and receive energy to be absorbed by adjacent radiators – an undesirable phenomenon that causes destructive interference and a decline in operating efficiency. Consequently, ESAs exhibit pronounced degradation due to their accelerated cosine roll-off (cosine^1.4-1.6), in contrast to a VICTS phased array that exhibits a roll-off of cosine^1.0.
As a practical example, every day our Ku3030 system supports multiple flights at latitudes above 70N (i.e., well above the Arctic Circle) reliably closing GSO links below 10° elevation.
Interoperability and Agility
To work with new LEO/MEO constellations that require switching satellites every 3 to 15 minutes, don’t you have to use an ESA antenna that has multiple beams?
For upcoming LEO/MEO constellations, antennas must be able to re-steer their beam up to 180° in azimuth to move from a “setting” to a “rising” satellite in less than one second to avoid service lapses.
VICTS antennas, while being mechanical, are nevertheless very agile, slewing from satellite to satellite in under 800 milliseconds, which is less than a typical GEO ping time that people are accustomed to today, and can easily be buffered by the modem for a seamless transition and smooth user experience.
Can a VICTS antenna support true make-before-break?
With separately pointable transmit and receive apertures, a VICTS antenna supports true make-before-break (MbB) in half duplex, or very fast break-before-make (BbM) at full duplex.
Further, if two truly simultaneous full-duplex beams are required, two separate antennas can be utilized, while still occupying a significantly smaller footprint as compared to a single multi-beam ESA.
ThinKom VICTS antennas have proven the ability to “seamlessly roam” between NGSO and GSO satellites via recent demonstrations on Telesat’s LEO1 test satellite, OneWeb’s LEO test constellation and the SES GEO/O3b MEO constellation.
Don’t all phased-array antennas have narrow instantaneous bandwidth (IBW) that limit their use for many government applications and next-generation HTS GSO and NGSO satellite constellations?
While most ESAs do indeed have narrow IBW limitations (generally less than 125 MHz), ThinKom VICTS antennas actually have an IBW 4 to 8 times greater than a conventional ESA, ranging from 500 MHz to 2 GHz, depending on the frequency band and use case.
User bandwidth demands only trend upwards, so current and future generations of satellites are constantly pushing the envelope with frequency reuse, narrower spot beams and larger transponders. These new satellite architectures demand antennas support a minimum of 500 MHz channel bandwidth today, and likely to be higher in the future.
While a narrow-channel-bandwidth ESA would need to continually repoint for frequency changes, ThinKom phased arrays simply see the entire frequency spectrum all at once, with no antenna beam re-steering required.
Is the ThinKom VICTS phased array power hungry?
Active ESAs are quite power hungry, but a VICTS antenna – being passive – consumes very little power. For example, ThinKom’s Ka2517 airborne antenna consumes only 70 W of power (used for beam steering while the aircraft is in flight). Separately, the inside aircraft equipment (IAE) antenna controller and HPA consumes 50 W and 375 W, respectively.
To meet the same performance as the Ka2517 at 25° elevation, an active ESA would require 3 kW or more of power. And high power consumption equates to high heat dissipation which limits long-term reliability of electronic components.
Power-guzzling ESAs require thermal management to prevent the electronics from overheating. This burdens the aircraft’s power system, limits gate-to-gate operation (unless liquid cooling is incorporated) and ultimately negatively impacts MTBF due to high component-junction temperatures. A VICTS antenna requires no active cooling.
Regulatory Compliance and 5G Interference
What, if any, regulatory restrictions are there on airborne antennas to ensure they don’t interfere with terrestrial 5G or with GSO satellites when trying to work with NGSO satellites?
Major regulatory bodies (ITU and WRC) have awakened to the interference threats to satellites in the GSO arc posed by aircraft, maritime and other mobile terminals operating broadband services via NGSO satellites, as well as interference threats to 5G terrestrial networks employing the same shared frequencies on the ground.
Terminals operating on NGSO satellites (which can be located anywhere in the sky) must limit their emissions so as not to interfere with GSO satellites.
An additional regulatory challenge for phased-array antennas is that many countries plan to (re)use the same frequencies for terrestrial 5G point-to-point backhaul and distribution services as for satellite systems. Hence, the most recent drafting of the WRC-19 “ESIM” rules which establish new standards to protect terrestrial 5G networks from interference from airborne and other mobile terminals.
The elevated sidelobes emitted by gimbaled flat-plate antennas and some ESAs are problematic when operating with NGSOs and make them unlikely to meet these new and more challenging ITU requirements.
ThinKom VICTS phased arrays uniquely meet both the ITU Article 22 and WRC 19 interoperability requirements, as they exhibit unusually low “below-horizon” emissions and well-managed above-horizon emissions with no grating lobes or elevated sidelobe floors.
The unique design of our VICTS antenna results in a surprising series of advantages over today’s (and tomorrow’s) ESAs. The VICTS antenna has a large area efficiency advantage, is more reliable, performs much better at low look angles and has proven itself on a large number of commercial aircraft.