Unveiling the Future of Antennas and RF Lenses using Radix 3D printable material!

Unveiling the Future of Antennas and RF Lenses using Radix 3D printable material!

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Ever since 3D printers hit the mainstream, I  dreamed of being able to print high-performance   Microwave antenna components. It was still  mostly a dream until I saw the announcement  about Rogers Radix™ 3D printable dielectric  UV resin material I got all over-excited and   made a video asking if I could have a sample to  try my own printer I was amazed when the lovely   folks from Rogers Corporation got in touch  and made me an offer I couldn't possibly   refuse! The deal was that if I created a  design for a gradient index antenna lens,   they'd get it processed and print some  examples for me. Sounded brilliant!  Surely there must be a catch? "There's a catch" they said,   "You have to collect the finished antennas in  person, from a facility in the United States, and we'd like you to make a  video about your experiences" Well AIMEE, that's an offer to  which the only right answer is:  "Sure! Brilliant! Let's do it!",  and so the adventure began .

This video is sponsored by Rogers   Corporation (I received payment, parts  and my travel expenses to the USA) I've used Rogers PCB materials for decades  and they're one of the brands that I trust   and rely on. As part of this collaboration I had  the opportunity to get a behind-the-scenes view,   follow the manufacturing workflow and interview  some of the hugely impressive team at Rogers and   Fortify, their 3D printing partner. I'm not an  antenna designer, nor an RF engineer. I've been   experimenting with microwave antennas and systems  for over 50 years, but never professionally.   If Rogers can give me the tools and workflow to  turn gradient index antenna lens designs that I've   dreamt up in my head into real working components,  then just imagine what a REAL RF design engineer   could achieve with Radix! Trust me. If Neil  can produce a successful design this way,   then literally ANYONE could. AIMEE, you're so rude.

I asked Karl Sprentall how Rogers is enabling RF  designers to create new and improved solutions for contemporary and future  applications using Radix. Yeah, one of the great things about being a  material supplier is you get to design something that basically expands the trade-offs  that are available to your customer and then watch them come up with  great ways to use your material. A few of the applications that  we're excited about right now:   One is low-K (or low dielectric constant)  substrates and so this is you know,   think of it as a replacement for foam but because  you're printing it you can print either complex   structures into it you can print it to have  good structural rigidity and you can even do   things like plated through holes directly into the  substrate which you couldn't do in a normal foam.  Gradient Index (GRIN) is obviously  a critical part. One of the most   well-known gradient index structures is called  the Luneburg lens. It starts with a dielectric   constant of 2 at the center, goes to 1 at the outside. You can put an antenna  

anywhere around the aperture of it and then steer  it by switching where you're feeding this from.   Another use case that we're seeing commonly is  complex geometry 3D parts. This is a structure   without a gradient index, but as you can see,  we've got an antenna that you want to have fit   directly to a surface with metallization. That's  also possible to do with Radix. The important   thing to us is not to have a great low-loss resin  that you then put a low conductivity metal on so   we focused on working on technologies that can  give you pure copper on the surface of Radix.  My brain was well on the way  to exploding at this point. That would be a rather small explosion.

Getting an antenna component with a position variable refractive index is exciting enough but the possibility of incorporating  3D metallization takes my ideas to another   level altogether. The team told me how Rogers  carry out rigorous quality control testing on   the resin and how Fortify performs tests  to ensure the printers are maintaining the   desired parameters of the cured dielectric  material. I first asked Phil about how the   printer technology ensures that the cured  material remains homogeneous and isotropic.   Many of the resins that we print are filled with  some type of fiber additive. Particle, fiber,   isotropic or not, and those fibers or particles  have a tendency to settle out as you're printing.  

In order to combat that, Fortify developed  CKM which is a technology that you can think   of as plumbing in the system which consistently  circulates, mixes and heats the resin in order   to maintain the suspension of those particles  throughout the printing process so that you   have the same consistency from the beginning  of the build to the end. OK, the fruit cake   pic was a bit lame, but here's a real example of a  print with and without continuous kinetic mixing. I asked Phil about design considerations  when incorporating metalized elements. One thing you should consider when you're  trying to metalize something especially if it's a gradient refractive index device, is making sure there's a solid surface on which you can metalize. That means leveraging  the 3D printing technology that we have and   integrating all types of different geometries  that don't necessarily have to be lattice based   so that means you can have a lattice side by side  with a solid such as a skin or a mating feature   or a solid component to help you mount it to the  ultimate location where it's going to be in its   application. So, if a customer asks you to create  a skin or metallizable surface on their part,  

your workflow could incorporate that for  them. Yeah, exactly correct, that's what we're   doing here. So if you look at this device,  this is a Luneburg lens. On the top side,   you can see the exposed gradient refractive  index lattice geometry, but on the back side   here we have a solid skin, and this is all done  in the toolset that Fortify has developed and   it makes it easy for the RF engineer to  conceptualize their devices and quickly   go from concept to 3D printed part without  having to think too much about the process.  So now the ball was in my court.  I wanted a compact feed for a

parabolic dish to carry out moon  bounce experiments at 10 GHz in x-band.   The dish has a focal length to diameter ratio of 0.5 which means an illumination  angle around 112 degrees with an edge taper of   -12 dB. I wanted extremely low side lobes so  that the receiver wouldn't see any hot ground   or astronomical sources which were away from  the main beam axis. I also wanted the feed to  

work with a simple linear excitation in a round  waveguide using either a coaxial probe or an   oval iris to match from waveguide to a machined  round horn while avoiding the need to generate a   hybrid mode in the machined metal part of the  feed. I travelled to Rogers labs next and met   Chris who showed me some of the test fixtures and  instruments they used to validate the performance   of dielectric materials. Over here is showing some  of our additional capabilities in our R&D lab.   What you're looking at right here is a split post  dielectric resonator. What this allows us to do is   extract the permittivity of various materials with  dielectric constants anywhere from 2 to say 20,   50 or even 100. Whoa! It's time for a quick  sidebar moment here! A split post dielectric   resonator uses two ceramic pucks supported a  fixed distance apart inside a microwave cavity. RF  

energy is injected using a small loop fed with a  coax line a second identical loop samples a field   within the cavity. If you connect the fixture to  a vector network analyzer and set the position of   the loops correctly, you can measure the amplitude  and phase response of the cavity and pucks over a   range of frequencies. Now if you slide a sample of  dielectric into the air gap, so long as you know   its thickness and the size of the gap, you can  de-embed the fixture parameters and extract the   characteristics of the sample, as Chris explains. This is measuring at 10 GHz or X-band. The sample   will be inserted into our test fixture. Using some  of our internal software we can then measure the   coupon and using our Keysight Agilent Technologies  network analyzers it will extract the s-parameters   and an algorithm will then extract the  permittivity of the material and the loss tangent.

In addition to this fixture at 10 GHz, we also  have additional fixtures. This one is at 2 GHz,   and you'll see it allows a much thicker sample. This one's for 15 GHz. I asked Chris about calibration. He  explained that Rogers has an internal   calibration lab team dedicated to ensuring all  the instruments are maintained to the relevant   standards. Pretty cool huh? I asked Colby  to explain some of the technical quality   assurance tests carried out on production  prints using Radix. The first one of those  

is from the ASTM D2520 small sample  perturbation test. That involves this   waveguide fixture. This waveguide has two irises  brazed in about 2.4 inches apart and that sets   up a resonance a little bit under 10 GHz. The  idea is that that resonance will go down with   perturbation. Colby explained that as the volume  of the solid sample is known, the reduction in  

center frequency of the resonance, plus the Q  factor change, can be used to characterize the   relative permittivity and loss tangent of the  material. After characterizing the empty cavity   and taking down the center frequency of the  resonance and the 3dB points, high and low,   the first thing we'll do is take this Rexolite  standard rod. It's a circular rod about 0.060   inches in diameter and we'll insert that into the  cavity and take a measurement there and calculate   the Dk and Df of the Rexolite. So that's like an  initial calibration check just to verify that the  

system is working as it should be? Yeah, exactly  that, and you mentioned the word "calibration",   it's a good time to point out that because all  we're looking at here is a resonance, that you   don't need to do any calibration of the network  analyzer cables or of the waveguide structures   itself it's just a turn on and go. So here's an  example of a solid that we can use to measure the   solid characteristics of the dielectric and  that's about 50 mil by 50 mil cross section   and we can drop that into the fixture in this way  but also you'll notice this sample is very tall   and so we can continue to drop the sample deeper  and deeper into the fixture and look for changes   over Z height. So this was printed in this  orientation on the Fortify printer and so   we can check over a four inch Z height whether  there's been any settling of the fillers in the   material because that would change the Dk over the  height of this toothpick. So oftentimes if we're   doing a print that's at least four inches we'll  print some of these what we call "toothpicks"   as well and do some of that characterization.  So, you can do that as part of a normal print   as a quality control check. Yeah exactly.  Colby then explained how you can create test  

blocks of different lattice density on the  build plate along with your parts to verify   the permittivity of lattices as printed. The  blocks are printed to be a good fit into the   chosen waveguide. This is WR90 for tests at  10 GHz. The fixture is connected to a vector  network analyzer (VNA) and calibrated. First with a through connection, then a short,   then a delay line of between 30 and 160 degrees  at the chosen frequency using shims. The sample   blocks are inserted in turn into a set of  shims and placed into the test fixture.  

The VNA then measures the response, and the  results are used to calculate the actual   permittivity, measuring the loss tangent (Df) is  tough, as the lattices are already full of air   and the resin has very low loss. From the phase  change we can calculate the effective Dk of the   material based on how much we're slowing the  incident wave down inside the waveguide fixture   and the ratio of dielectric to air can  come out of that and from that you get your effective Dk. Can you extract  the loss tangent from the s12,   or is it too small? We can certainly try.

Right now, the reliable method is to measure  the effective Dk and run this test with a solid   standard and compare the effective Dk to the  solid Dk and apply that ratio to the solid Df   to determine about where we think our effective  Df is living. We're also doing some work to   validate this fixture and to do that  we're going to these thin slabs. We're   using both an SPDR method, which is a  split post dielectric resonator and then   there's also something called  a Fabry-Perot Open Resonator. A Fabry-Perot Open Resonator uses a  pair of spherical RF mirrors,  one fixed, one movable, with an injection port and a sampling port,  both loosely coupled so as not to degrade the   unloaded Q factor of the cavity, which can be  over a hundred thousand. Inserting a layer of   dielectric material at the central zone affects  the Q factor and resonant frequency. The changed

values of those parameters can then be used to  calculate the relative permittivity and the loss   tangent of the dielectric sample. At 47 GHz, with  180 mm radius mirrors spaced about 300 mm apart,   the frequency varies by 150 kHz per micrometre of  offset. That's less than the half power bandwidth   of the unloaded cavity. The equations for  relative permittivity and loss tangent  

are scary looking. Transcendental  even, but hey, "Computers", right?   Now I want to make a Fabry-Perot  resonator of my own AIMEE! So many shiny projects. So few completed. Harsh. but true. So those are the methods we're using for some  validation that our lattice measurement in-house   is accurate. So, then a customer could print test  rods, blocks or coupons alongside the parts on  

the build plate to validate each of the different  relative permittivity zones? Yeah, exactly that.   If you were doing a lens with five different  effective Dks, there is likely room on the   build plate to print five of these little swatches  that we could test at X-band and like I mentioned   earlier, we also have the capability to test  at S-band, although for low loss materials,   Dk should really not change in a measurable way  between S and X-band. Maybe half of one percent at   the very most and Df should be pretty predictable  with a curve fit. I was curious about the relation  

between unit cell size and effective Dk. Fortify  have shared some initial draft results with me,   showing the safe area for a range of cell sizes  and cutoffs. This is very much initial results   so please don't quote me! Colby then told me how  testing and validation of finished antennas was   being done using microwave and mmWave anechoic  chambers and about mechanical and environmental   testing of the printed resins. I'm going to be  testing my completed antenna lenses in a field   deployment. It's going to be exciting to find  out how they behave in a real-world application,  as long as I can keep the spiders out!  While I was working on the design,   I split the gradient index into subsections  of constant Dk and I asked Colby what sort   of feature size versus subsection size work best  he gave me a slightly quizzical look. That kind  

of depends on the designer and if this is someone  who is comfortable with defining a material Dk in   their simulation as an equation-based calculation  that's based on spatial area in their design, then   that would feed directly into a pure gradient with  no steps which is entirely feasible. Wait! What?   I made a rookie error, assuming I  need to do a pile of work creating   constant Dk zones in the EM solver  and CAD models! Oh dear did anybody   tell you that you couldn't do that?  No, but I didn't ask the question, so it serves me right, doesn't  it really? Never assume, or  you'll end up like Neil. AIMEE you're 100  percent right as usual. Lesson learned.   When you're working with innovative new  processes and materials, it's vital not   to make assumptions about any limitations. Simply  providing the equations to define the gradients   frees RF engineers and designers from a lot of  unnecessary grunt work. Don't be like me folks,   I should have thought of that and  not limited myself. Entirely my bad.  

Phil gave me a tour of the Fortify Print Lab.  I asked him to take us through the process of   setting up one of the printers to produce a  run of my lens designs. This is the reservoir   that goes into the machine to hold the resin  for the 3D printing and what we're doing right   now is assembling the reservoir so that I can  fill it with resin and put it into the machine, assemble the filter, and we're good to go into  the machine. This is a fully assembled reservoir.   I'll bring this over to the 3D printer now. I'm  going to put the reservoir into the machine,   seat it, then we close the reservoir manifold, the wiper slides right in. The wiper  will pass across the film during the  

printing cycle to help to maintain the resin's  particulate from sedimenting out and obscuring   the UV light At this point we need to add the  Rogers' material. So, it's been bottle-rolling   for a couple hours now, to make sure it's nice  and homogeneously mixed. We'll add just a bit. That's good for now. And we'll get that back on the bottle roller  for the next time we need to add material.   At this point we're going to warm up the printer  with this button here and what this does is it   starts the circulation and mixing that occurs in  the CKM, which is the continuous kinetic mixing   system. We are heating up the agitator and once  that step is complete, which we just saw the check   mark there, we're going to fill the reservoir. So  now what happens is we have a quantity of material  

and a reservoir back here behind the Z-axis and  it distributes material into the reservoir until   it reaches a set level in the reservoir and we  maintain that level throughout the build. And so   on the left side here you can see the inlet. This  is the inlet fluid flow nozzle on the left side of   the manifold. The resin is flowing in through a  mesh filter. The resin flows in from the left to   the right and then up the back side here There's  a peristaltic pump that pumps the resin out of   the outlet side of the reservoir back into our  circulation system to get reheated and remixed.   So, throughout the process, the resin will always  be flowing through the inlet to the outlet. The  

wiper will be moving periodically throughout  the build as well to help to maintain the   homogeneity of the material and help to keep the  film clear of any obstruction so that the UV light   will penetrate through and make a good part. All  right so we have our build plate, we're going to   assemble it into the system, place it in here and  close the clamp and we see on the user interface   that the build plate check box just went from  yellow to green, so we are ready to start a build. Looks like the build is done.

Now I'm going to take the build plate off. Phil showed me how the parts are removed  from the build plate with a razor blade,   then washed in a solvent to remove any  residual resin. For these small parts of mine,   a simple agitator table with  a two-stage wash was perfect. This is a cleaner wash, to get the  last little bit of the resin out. Phil allowed the parts to drain, then  used compressed air to drive out any   solvent traces and prepare  the parts of final curing. Well, I think it's fair to say that "That'll  do!" It looks remarkably like the CAD model that   I designed. All right, now that we have a clean  part, the first step is to cure it in the UV oven.  

That uses 405 nm long-wave ultraviolet light  to ensure the resin is completely cured The parts are then finished off  with a bake in a thermal oven. Now that looks absolutely gorgeous!  Just before I flew to the United States   to visit Rogers and Fortify, I designed  another gradient index dielectric lens,   it's a Mikaelian cylindrical lens, with an index  that varies across the diameter according to an   inverse hyperbolic cosine expression. The idea was  to use it as a basis for discussing the production   workflow. I submitted the design, and the team  suggested some manufacturability improvements,  

but then I thought no more about it. Imagine my  amazement when Phil showed me a freshly completed   print of three of these lenses. They were just  out of the printer and not washed or cured,   but they looked BRILLIANT! A few weeks later  a delivery van arrived with a parcel for me No YouTube video is truly complete without an  unboxing scene. Ooh, this is like birthdays   and Christmas all rolled into one. I need to  check the weight so I can get the balance of   the mount correct. I'd estimated it in my  CAD program at between 250 and 500 grams,   perhaps three-fourths of a pound Wow! These things  feel like they're made from fired ceramic. Amazing  

That's a little under 13 ounces,  perfect. The texture and finish   are just breathtaking! I love how the gyroid  lattice structure looks up close it's gorgeous I think it's fair to say that "That'll do!" One of the applications for the Mikaelian  lens is a handheld source of microwave   signals rather like a flashlight. I  built a transceiver into a flashlight   body. This was the first one I bought, but  it's a bit on the small side. As The Great   Australian philosopher poet (M Dundee)  once said: "Call that a flashlight?" "THIS is a flashlight!!!" Karlo is one of the co-founders of Fortify.  I asked him about their vision and the work   with Rogers on Radix. We exist as a company  to bring to market what we consider the first  

production-capable Additive Manufacturing System.  By combining advanced materials, fibers, fillers,   and the unique processing conditions that we  built into our system, we're able to create   shapes and tackle applications that no other  Additive Manufacturing company has been able   to tackle. Through the creation of this platform,  we've had the fortune of partnering with Rogers   who have developed some really interesting  high performance, but very tough-to-print   resins like the Dk 2.8 material. By combining  their unique materials and our platform, we're   able to produce these shapes, these devices, that  are unmatched in the Additive Manufacturing space.   Many of the RF engineers and designers I know,  need to be personally convinced before asking   their businesses to invest in the capital  equipment to support a new manufacturing   technology. As Karlo put it, they have a "Prove  it to me!" mindset, and quite rightly so. The  

combination of Rogers' excellent Radix material  and Fortify's advanced printing systems will   give engineers and designers an entry point into  the benefits of advanced 3D printed dielectric   materials for lenses, foam-replacement substrates  and complex metalized forms, without incurring a   huge financial risk. My experience of using the  workflow was immensely positive. One of the best   things was being accepted as a peer despite me  being the least intelligent person in the room.   It's hard to imagine ANY gathering where  you're NOT the least intelligent person.   Unlike AIMEE, the teams at Rogers and Fortify are  flexible, smart, helpful and have a razor-sharp   focus on customer success. Full information on how  to get details on Radix and the printing system   are on the end screen in the description and on a  card up at the top of the screen. The next step is

to show the test results and how I machined the  mounts and cavities for the lenses. That'll be in   Part Two, which will appear up THERE. Huge thanks  to Rogers and Fortify, and especially to my host   Vitali, whose hands starred in several scenes.  Click the link to find out more about Radix

2023-02-23 15:12

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