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A discussion about optimizing beamforming, with gigahertz-clocking tree solutions, in order to enhance the performance of phased array antennas in satcom applications.
The Space Industry by satsearch - sharing stories about the businesses taking us into orbit.
We delve into the opinions and expertise of the people behind the commercial space companies of today, who could become the household names of tomorrow. Find out more about the companies and technologies discussed on this show at satsearch.com.
[00:00:00] Hywel: Hello everybody. I’m your host Hywel Curtis. And I’d like to welcome you to the space industry by satsearch, where we share stories about the companies taking us into orbit. In this podcast, we delve into the opinions and expertise of the people behind the commercial space organizations of today who could become the household names of tomorrow.
Before we get started with the episode, remember, you can find out more information about the suppliers, products, and innovations that are mentioned in this discussion on the global marketplace for space at satsearch.com.
Hello, and welcome to today’s episode. I’m joined today by Michael Seidl, Systems Engineer with a focus on space applications, and Adrian Helwig, Analog field application engineer, both from Texas Instruments.
Now Texas Instruments or TI as it’s often known is an electronics manufacturer that you’ve probably heard of. And today we’re gonna be talking about phased array antennas in satellite communications, and specifically about how to optimize beamforming when using such systems. Firstly, I’d just like to say hello to you both to Michael and Adrian. Thank you very much for being here today.
[00:01:02] Michael: Hello.
[00:01:05] Adrian: Glad to be here.
[00:01:06] Hywel: Great. Thank you. Okay. So let’s get into this topic. This is a very interesting topic, quite technical, but I think has quite a lot of applications and bearing on modern satellite communications applications. So clocking is receiving more and more attention in RF applications today. Can you explain why this topic is possibly more important today than it has been in the past? To, to Michael.
[00:01:28] Michael: Clocking has indeed become very important. This is mainly to the effect that the speed of data converters has reached extremely high rates of meanwhile, greater than 10 Giga samples per second, which is great as it enables designers to directly sample the RF signals without the need for any downmixing to an intermediate frequency anymore.
But sampling rates of greater than 10 Giga samples per second, translate into very short sampling periods of less than a hundred picoseconds. It is obvious that any clock jitter offers a few picoseconds or more does already degrade the system performance quite a bit.
[00:02:11] Adrian: Exactly. Another way to look at this is the SNR performance as a function of clock jitter. It’s dependent on the input frequency of the signal. So in other words, for a given amount of jitter SNR degrades more with a higher frequency signal than with a lower one. So we really see that for higher frequency systems. Low clock jitter becomes more and more important.
[00:02:41] Hywel: Okay. I see. So as we’re seeing more and more use of higher frequencies in the industry, then we need that low clock jitter to enable the applications to achieve the sensitivity they need.
But it’s not just higher frequencies that make clocking so important. Also the use of phased array antennas, as I mentioned, increases the importance of clocking. As far as I understand it. So could you give us a brief introduction to the use of phased array antennas in space applications, and specifically like what problems do they solve and what benefits they offer over alternatives?
[00:03:12] Michael: Correct phased array antennas are the second important trends. Phased array antennas offer electronic beam forming and steering capabilities that can bring a host of possibilities for emerging applications such as satellite broadband so that they remove the limitation of physically moving the antenna.
And they allow to adjust the beam to follow the highest concentration of users. Phase array Antennas are also referred to ESAs Electronically Steered Antennas. As there are no moving parts, ESAs provide much higher agility for steering the antenna beam.
[00:03:48] Hywel: Great. Which is a really important challenge because obviously achieving sensitivity of in attitude and in agile satellites requires a lot of a lot of additional hardware and control of the system.
So that’s interesting and I thank you for mentioning the satellite broadband application. It really makes it clear why these systems are in use. It sounds like there’s still a number of challenges that would exist in such systems. And yeah, I guess Adrian, this is your field. I wonder if you could explain some of the typical challenges designers facing when developing phased array antennas.
[00:04:19] Adrian: The latest phased array systems are dealing with lots of elements. There may be dozens of elements in some systems and up to 100s or more in other cases. The higher the number of elements, the more directive the beam.
Each antenna element has an RF transceiver transmitting or receiving the signal. The biggest challenge in these systems is to maintain proper phase relationship between all of the elements for the beamformer to operate as intended. The phased array system adjusts the phase at each element to steer the beam to the desired direction.
[00:05:08] Michael: And you can do this in a couple of ways in a traditional analog beam forming system, you can use just one, split the signal to multiple elements and adjust the phase in an analog fashion at each element. That will be a lot of analog phase shifters which could be difficult to control and calibrate.
So the newer systems transition to a digital beamformer or hybrid beamformer where each element or a group of elements is supported by an independent receiver. This gives better control over the phase adjustment to each element since it’s done in the digital realm.
In these systems it is now the data converters that must properly be synchronized to maintain the proper phase relationship between elements and therefore clocking for those data converters is now very critical.
[00:06:06] Hywel: Okay. I understand. So yes, the move to a digital beam former can hopefully make this entire process of controlling to be more, more efficient and more controllable with requiring less systems. But why is clocking so important in these processes? And I guess how exactly does it work?
[00:06:24] Adrian: yes. So we really want to ensure that the skew between the data converters’ clocks must be minimized to ensure that all the devices are properly synchronized. Clocking skew at the data converter level translates to phase variation at the elements which impacts the directivity of the beam.
And in addition, you want those clock sources to have very low phase noise or clock jitter as we had discussed in the beginning.
So we need clock devices that maintain excellent low clock jitter performance at high frequency while minimizing skew are vital for the next generation of beamformers.
[00:07:18] Hywel: Got it. Okay. Yeah, that makes sense. So I guess, looking, thinking more broadly about the applications, RF designers are usually trying to pack in as many elements as possible that can operate at high frequencies, but with agile beam steering capabilities, but at the same time, they’re trying to reduce the PCB footprint and power consumption.
The SWAP-C budgets still vital and as always achieve the best signal chain performance. And I think when we are talking about satellite broadband, for example, the performance is gonna be vital because of the nature of the application. And as this is becoming more and more of a commercial use while this, the nature of the market that determines the success.
Could you share maybe some insights maybe to Michael about how clocking solutions can help achieve high performance and maintain the kind of typed synchronization across all the channels with as little development effort as possible required.
[00:08:11] Michael: We just discussed how the new systems are generally increasing the number of channels to get higher-performing systems.
And with that trend, you have to provide more integration to keep the systems compact and manageable while lowering also the power consumption so that the whole system doesn’t just melt down from thermal overload. New RF sampling transceiver devices are on the market now that integrate multiple channels onto one device and support RF frequency bands up to 12 GHz directly.
High-frequency RF synthesizers provide the clock signal for the RF sampling data converters. The transceivers need a high-frequency clock with very good phase noise, as we said before and the systems today will be clocking up to 12 GHz.
Future systems will push that to 20 GHz and beyond as technology moves on. Clocking devices that provide good phase performance and are configurable provide the designer a lot of flexibility to select the clocking rate that best suits the system and the ability to modify it for different bands or applications.
[00:09:26] Adrian: Maybe to add to this, the clocking devices not only need inherently low part-to-part skew variation, they need the ability to adjust the clock phase.
In a large array system there will be phase skew between elements caused by device tolerance variations, temperature variations, and interconnect length variations, for example. It is important to have the clock device adjust its phase to compensate for those variations in order to maintain tight synchronization across all of the channels.
And now if you fail to do this, you will have to transmit or receive more power to compensate for a less directive beam.
[00:10:16] Hywel: Right, absolutely, which is obviously a situation we wanna avoid. So that’s great. Thank you. Are there any other clocking elements that are typically used in a phased array, antenna systems that engineers need to know about?
[00:10:29] Michael: Yes, there are some other critical clocking parts typically used in the system.
A clock jitter cleaner synchronizes the synthesizer’s reference frequency to a system reference like 10 MHz. These devices provide synchronized outputs to support the synthesizer reference, FPGA clocks, and serializer system reference clocks.
When dealing with large array systems, often a low phase noise clock distribution chip is needed to disseminate the low jitter clock to multiple devices without introducing any degradation of its own. A good clock distribution device minimizes the number of RF synthesizers needed.
And all of these clocking devices work together to form a complete clocking solution that maintain optimum performance for the phased array system.
[00:11:25] Adrian: That’s well explained, Michael, thanks. In summary, you are looking for clock devices with low jitter, low skew variation, and programmable to mitigate variations in other parts of the system.
[00:11:41] Hywel: Excellent. Low jitter, low skew variation and high programmability or programmable to yeah, give you great control efficiently. So that makes sense. Now I understand that there is some kind of established standards for high-speed data captured designs that use F PGAs. And you mentioned the importance of using FPGA clocks and how they can help the synchronization of the system.
I’m aware, for example, of JESD204, which I understand is becoming more popular for terrestrial high-speed applications. How suitable is this standard because of its, because it is established and being used, how suitable is it or equivalent standards to be used in satellites as opposed to on the ground?
[00:12:21] Adrian: Yes. So actually for ultra-high-speed data sampling, there is not really an alternative to JESD204. We are really living in a very data-hungry world and we must transfer multiple Gigabit per second in a single modulated data stream.
So a new trend to cover this is RF sampling. This trend supports very flexible form of modulation but it needs high bandwidth between the FPGAs and the data converters. This is where JESD204 comes into play. It supports serial connections with embedded clocks.
And now with JESD204C, we can easily reach 10 to 32 Gbit per second on each lane between FPGA and converter. A similar principle is known by PCI express in the PC world. So, multiple of these lanes could be combined to form even higher speed connections if needed.
[00:13:34] Hywel: I see. I see. Okay. So JESD204 helps support the serial connections with embedded clocks. I understand, enables higher ultra-high speed data sampling, but how exactly does JESD204 support space applications. Maybe if we could translate it to the applications themselves, that would be great. And Michael, perhaps you could answer.
[00:13:53] Michael: Yea Good question, let’s look now how the standard supports space applications. Starting with JESD204B the standard contains synchronization methods which are very relevant for space. Let me explain now why.
First, we must take a quick look at some of the typical space problems. Besides the well-known thermal issues, we have mainly one big problem and that is radiation. If a high-energy particle is hitting our well-designed and crafted circuit it could displace some electrons and by that cause some false switching.
That is not a big deal. False data from false switching is typically corrected by some error correction. However, there is one severe condition from which recovery is not so easy. It is called latch-up. This is when an integrated device, any IC, suddenly causes kind of a “soft” short circuit on its power rails.
The only safe way to resolve this issue is by cutting the power from the affected part for a short moment. This power cycle ends the latch-up and lets everything work fine again.
[00:15:01] Adrian: Here comes the catch. A complete system shutdown interrupts all thousands of data streams instantly. And it takes quite some time until all is up and running again.
We want something with less impact like for example a partial solution. It would be cool to just restart the component which failed because it goes rather quick compared to a full system shutdown.
[00:15:28] Michael: Yes, exactly, this is where JESD204B helps us with its synchronization methods like a SYSREF signal. It re-establishes system clock phases and it also helps quickly recover communication on the lanes between converter and FPGA.
This makes it possible to power cycle exactly the one affected device while keeping the remainder of the system alive. The partial system can maintain functionality during the event so the impact is minimal and restore full usability in very short time.
This is more like switching off and on a light bulb compared to a complete reboot of a PC.
[00:16:09] Hywel: That’s great. That’s yeah, that’s very understandable. Thank you as always the harsh environment of space and it requires us to do some crazy things on the engineer inside to uncover, to account for problems that we don’t face in the ground. But that’s great. Thank you. I wonder if you’d give us some, an example or some examples of space-related applications or any case studies that would really require this use of high-performance, tightly synchronized clock into each of the channels using gigahertz, clocking tree solutions.
[00:16:37] Adrian: Yes, no problem, Hywel, so probably the most prominent applications are the recently launched LEO constellations to bring broadband access to any region of the world. In these constellations, the phased array antennas bring value to both ends of the communication channels terminated inside the satellites: to the user link, and also to the feeder link, which connects the satellite with the operator’s ground stations.
[00:17:06] Hywel: Okay. How does this work? How does beamforming help in each of these or in this use case? How does beam forming help?
[00:17:14] Michael: Yes, let me start with the user link. the user link establishes the connection between the individual subscribers and the satellite. With the ability of electrically steering multiple beams each satellite can divide the area it serves and provide each of these sub-areas their own frequency band.
Now, the high agility is needed as the satellites in the Low Earth Orbit are flying by with quite some speed over ground. This means the beams sent to Earth must move with the inverse of the ground speed to keep an optimal connection. And let me add to this, the user link’s endpoint may not necessarily be on ground. It can also be on an airplane to provide broadband access to flight passengers.
[00:17:58] Adrian: Exactly, the second link, the feeder-link builds the connection between the satellite and the ground stations which are connected to operator’s terrestrial network. Also for this link the beam must steer inverse to the satellite’s movement over ground to keep the best possible field strengths between the two antennas. The moment the satellite moves close to the horizon it will lose that connection and the beam must quickly turn to the next base station on its way.
[00:18:35] Hywel: Okay. Got it. Michael, I wonder if you could elaborate on any other applications besides the satellite broadband?
[00:18:49] Michael: Yeah, of course. There are many more applications, of course, that benefit from phased array antennas. One to highlight is of course, the earth observation missions. A very prominent example for this would be the Rose-L mission as part of ESA’s latest additions to the Copernicus earth observation program. Rose-L carries a synthetic aperture radar with a phased array antenna operating at roughly 1.3GHz.
[00:19:17] Adrian: We can even add a third application field we could mention here, the radar observation systems. The multi-beam capability enables these systems to follow multiple objects, such as airplanes, or other satellites, at the same time. In future such applications could also be used for collision avoidance to mitigate the increasing risk for satellites from space debris.
[00:19:45] Hywel: Interesting. Yeah, obviously a, an area of huge interest in today’s industry. So thank you, Adrian. That leads into my next question. Really. You mentioned the potential future applications. So I wondered how you saw this idea of, using gigahertz clocking tree solutions in phase array and antennas, how you saw this evolving in space applications over the next, I don’t know, like five years or so. Adrian, if you want to continue?
[00:20:17] Adrian: Yeah, that’s very interesting. There are indeed several trends that will make high-performing clocking trees even more important.
We see RF sampling up-to X-band (8-12 GHz) being already a reality as of today. As technology advances RF-sampling will also be possible at even higher frequencies and we do see a strong trend towards even higher utilization of the higher bands such as the Ku, K and Ka bands.
Obviously, this will always come with the need for clocking at such frequencies, and as mentioned in the beginning of our conversation, the higher the frequency, the more stringent the requirements on the clock signal in terms of phase noise and skew.
[00:21:02] Michael: Let me add to this. The second major trend is the growing demand of phased array antennas that enable electronically steered RF beams with high agility and strong spatial selectivity as we discussed.
Interestingly the spacing between antenna elements is inversely proportional to the frequency phased array antennas operate at. For example, if you double the frequency you must reduce the spacing by half, in other words, you will have four times the number of elements in the same area.
As a result, we will see the need for even more data converters per antenna system that will need to be supplied with a high-quality and perfectly synchronized clock.
This will also create a need for even higher integration for smaller footprints and lower power consumption.
In summary the trend goes clearly to higher frequencies, hence stricter performance requirements in terms of phase noise and skew and towards an increasing number of end-points that must be synchronized.
[00:22:04] Hywel: Interesting. Yeah. And obviously we’re looking at. Satellite systems with a specific physical footprint budget that needs to be filled. Then these considerations very important to the RF designers, to the, how it integrates with the rest of the satellite system, how these things are powered and controlled ultimately by the, by the satellite computer system. So that’s great.
This is a really interesting topic, as I said, this is very technical, but the potential that is bringing to applications that I think you’ve explained really clearly with things like the satellite broadband area are great. So I guess finally, if any, if people are really interested particularly satellite RF designers who were really looking to incorporate some of these systems and ideas and technologies into their own systems. Do you have any pointers on resources or information where they could follow up this topic?
[00:22:53] Adrian: Yes Yes, TI has a wealth of material on this topic at ti.com. First of all, I would strongly suggest to take a look at TI’s leading clocking products such as the LMX2615-SP, which is also a Space grade 40-MHz to 15-GHz wideband synthesizer with phase synchronization and JESD204B support, or LMK04832-SP, our space grade ultra low-noise, also with JESD204B compliant clock jitter cleaner, and several others you can find on ti.com.
All these come with their respective EVM and a great wealth of software support, including the new online-tool CLOCK-TREE-ARCHITECT. This is help generating a clock tree solution that meets your requirements.
[00:23:58] Michael: Further, I would recommend designers to take a look at the material on TI’s space applications web page, ti.com/space, where you can find plenty of application materials and reference designs including test and measurement results. These help getting a quick impression on the performance potential or to get a head start into development with example schematics and layouts to refer to.
So for example you will find here a complete high-speed data acquisition system based on TI’s ADC12DJ3200QMLV-SP which is 12-bit, 6.4-GSPS, RF-sampling ADC. The design also includes a full space-grade power tree and clocking.
[00:24:51] Adrian: Finally, I would like to encourage designers to take advantage of the very popular precision lab training series provided on training.ti.com. There are several short trainings on high-speed clocking and high-speed data conversion systems. These short videos provide great insights on how the semiconductor products work and how the characterization parameters are defined and why they are important.
The precision lab trainings are actually very popular! The target audience for these is very broad. We see newcomers that appreciate to get started on the topic quickly, or experienced engineers that want to refresh their memories from school or are just interested to get a deeper look into the semiconductor products they work with. Even for those who have worked on RF technology for decades it is sometimes good to take a step back and see what design challenges could meanwhile be resolved with an integrated circuit where several years ago only discrete solutions were thinkable.
[00:26:15] Hywel: Absolutely. I think the industry’s moving so fast that even the most experience RF designers maybe have not had to think too specifically about how they’re gonna enable satellite broadband connection on airplanes or multi-element radar tracking of space debris in LEO. That’s That and these sort of applications are now possible.
So I think that refresh your knowledge and trainings like this is great. And just to say to the listeners, we link to all of these resources that I mentioned in the show notes. So you don’t have to worry too much about remembering those acronyms and we can link through to the ti.com tools and resources we’ve found here.
So that’s fantastic. Thank you. I think that’s a really great place to wrap up. So our listeners will have learned a great deal today about the use of phased array antennas the processes that need to be carried out to optimize beamforming and the importance of clocking solutions at all stages.
And I think it’s great to understand how these technologies are changing aspects of the industry, how they could also make a difference in the applications of tomorrow. And importantly how the kind of fundamental physics and engineering that goes behind, what decisions have to be made by engineers when developing space-based their solutions to this.
And indeed as you’ve pointed out the importance of beamformin on the terrestrial side, on the end user side. I’d like to thank you both very much for spending time with us today on The Space Industry podcast and sharing these insights and knowledge. Thank you.
[00:27:35] Michael: Our pleasure.
[00:27:37] Adrian: Thank you very much. Thank you.
[00:27:38] Hywel: And to all of our listeners out there, I’d also like to thank you for spending time with this on the space industry podcast. You could find out more about text instruments, of course, at ti.com as well as on the pages on satsearch that we have for the company. And as I mentioned, we’ll link to the resources that have been referenced in the show notes.
And if you have any further questions for our speakers in, or any questions on procurement and on the portfolio of Texas Instruments, we will be more than happy to help you get answers to those. So thank you very much and have a great day.
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