2.4GHz amplifier, quadrature hybrid coupler - where/what to buy? - Page 1
Forum section: electronics / rf-microwave

author: Yansi
author_rank: Super Contributor
timestamp: March 23, 2019, 08:05:17 pm
content: Hello!just wanted to mess around a bit with some microwave power amplification (I have some interesting projects to use this for), but I am struggling with this task a bit.What I plan to do, is to make a simple balanced amplifier using two quadrature hybrids and two generic 2.4GHz integrated PAs - i.e. the target output power is at least 1W, which should be possible with this technique, as the typical integrated 2.4GHz ISM PA offers about 30dBm saturated power. Using the hybrid couplers I think will have the nice advantage of being more tolerant to source and load mismatch. I kind of like that as doing anything past a 50ohm transmission line on a standard FR4 board is a major pain in the ass for an individual.There is quite wide variety of different 2.4GHz amplifiers available for dirt cheap, but I can't say so for the quadrature hybrids.Easily available 2.4GHz 30dBm amplifiers for example are these: SST12LP15A (Microchip), SE2565T (Skyworks), LX5518LQ (Microsemi).However, sourcing the hybrid couplers is anything but difficult. So far I only discovered the existence of only one:C2327J5003AHF datasheet hereThis one is reasonably priced 4W capable coupler, that I think is suitable for combining the outputs of both amplifiers.I am having trouble finding any different ones. I think it is waste of resources to use the same, high power coupler to the inputs of the amplifiers, where there will be like 1mW of power present.How can I locate any other quadrature hybrids for the 2.4GHz band? Sorting of components at the distributor websites is mostly impossible, as they often mix directional couplers with the 3dB hybrids. I think I have sifted through all the Mouser and Digikey, but no suitable parts turned up for this. Only that one mentioned above.Do you have any tips for part numbers or where to look for these? (3dB hybrid coupler, just small signal one)Note I have not considered making any of the hybrids in microstrip on the PCB. I am certain it can be done, but I would not rather attempt it, due to lack of the resources to design these and also space on the PCB. Integrated couplers makes life much easier.Thank you for any help.Y.

author: BFX
author_rank: Frequent Contributor
timestamp: March 23, 2019, 11:22:00 pm
content: Here you arehttps://www.ebay.com/itm/10-St-XC2500E-03SR-X-Koppler-2300-2700MHz-Xinger-Anaren-B312/401458504916?hash=item5d78caa4d4:g:B~UAAOSwl2haLmz6

author: Yansi
author_rank: Super Contributor
timestamp: March 23, 2019, 11:32:17 pm
content: Thank you BFX, but I am looking more for the small signal ones, these large ones seem to be very abundant.I need a hybrid to split the signal before the pre-driver PA, where the signal levels are at mW level. So far I have only found a single specie (The C2327J5003AHF mentioned above, not a single one more).//EDIT: Going through AVX website, I've come across these two: DB0603N2400ANTR, DB0805A2325ASTR. Pretty expensive and the MS Paintbrush style straight line graphs in the datasheet does not instill much confidence in them either.

author: BFX
author_rank: Frequent Contributor
timestamp: March 23, 2019, 11:54:07 pm
content: Quote from: Yansi on March 23, 2019, 11:32:17 pmI think those what I mentioned are pretty usable and for this price and for you purpose absolutely fine.

author: Yansi
author_rank: Super Contributor
timestamp: March 24, 2019, 12:07:44 am
content: No, they are not. For the price of those ebay ones I can get handful of the integrated amplifiers. When I will be up to building a 50W PA, then yes, of course, these will become extremely handy!The only usable so far is the Anaren C2327J5003AHF, in a 0805 package. I am surprised I can't find any similar ones reasonably priced.

author: OwO
author_rank: Super Contributor
timestamp: March 24, 2019, 04:06:08 am
content: You wouldn't use these for the input divider (unless we are talking 200W amplifier with 2W drive) because it's easy to just design it into the PCB artwork. Also for <= 10W at these frequencies a 90 degree hybrid combiner is way overkill, it's much easier and cheaper to just use a Wilkinson combiner which also has robustness to mismatch.I used 4x SE5004L to get > 5W of output at 5.8GHz and used Wilkinson combiners at the output, and resistive power splitters at the input.

author: OwO
author_rank: Super Contributor
timestamp: March 24, 2019, 04:11:30 am
content: For 2.4GHz I wouldn't bother with combining several wifi amplifier chips to get more power since I can get e.g. AFT23S160W02S for about $6, and it has better efficiency as well.

author: hendorog
author_rank: Super Contributor
timestamp: March 24, 2019, 05:54:57 am
content: Minicircuits perhaps?https://www.minicircuits.com/WebStore/90_180_degree_hybrid.htmlhttps://ww3.minicircuits.com/pdfs/QCS-332+.pdf

author: awallin
author_rank: Frequent Contributor
timestamp: March 24, 2019, 06:25:06 am
content: Quote from: hendorog on March 24, 2019, 05:54:57 ammini-circ has minimum order of 10-20 pcs for many smaller parts - and the distribution is through authorized dealers only (at least that's our experience...)so for DIY something available through digikey (mouser, RS, elfa, farnell, etc) in single qty is more convenient.if anyone knows where to get mini-circ parts easily let us know!

author: hendorog
author_rank: Super Contributor
timestamp: March 24, 2019, 07:08:08 am
content: There are some places you can get single quantities of MiniCircuits parts.I got some of their baluns from Kynix once.https://www.kynix.com/Search/QCS-332%2B.htmlThere are other places. Newark has filters but I didn't find the hybrid:https://www.newark.com/c/passive-components/more-passive-components?brand=mini-circuitsAlso for some parts e.g. filters there is an option to get a designer kit from MC direct. It costs probably about the same as ordering the MOQ, but you can get different part numbers at least.

author: OwO
author_rank: Super Contributor
timestamp: March 24, 2019, 07:34:09 am
content: Mini-circuits stuff are usually overpriced anyway. Why use an ex🅱️ensive coupler module when a pair of 70ohm transmission lines and a resistor on your PCB will do just fine? In my 5.8GHz 5W amplifier the output microstrip barely contributes to heating even though it's implemented on FR4.

author: Yansi
author_rank: Super Contributor
timestamp: March 24, 2019, 10:32:31 am
content: Thank you for some very interesting comments.Yes, I agree that most MiniCircuits stuff is way overpriced. I sometimes am able to source some of the stuff from china, although not very cheap either. I have seen that MCL has I think one or two suitable small hybrids, however their price is pure evil WTF!I haven't thought about using wilkinson. I want to avoid any such structure on the PCB, as FR4 is nothing but unpredictable and with limited access to test equipment, money and free time to tune just traces on the PCB, I want to avoid any microstrip structure as much as possible. At 2.4GHz, the pcb wavelength isn't that bad, just about 34mm for a 1/2 wavelength (sum of the wilkinson legs), so not large indeed.Okay, I will think about using this now.Yes, this is a driver PA for a larger one. It would be so nice to be able to make a couple of watts myself, but I do not have the balls nor the resources to do it.Where does one get a 45W 2.4GHz transistor for $6? I couldn't get even the first stage mixer for less than $6.

author: OwO
author_rank: Super Contributor
timestamp: March 24, 2019, 10:44:32 am
content: Quote from: Yansi on March 24, 2019, 10:32:31 amThey are usually pulls from old telecom gear, you might be able to get some PA boards locally if you know the right people. Here I just buy them from taobao, but it's a bit of a hassle because you have to message the seller to ask for the price.I've actually designed a 2.4GHz PA with 2 se2576 chips before for a custom USB wifi card:Circled in red is the output combiner, and green is the input splitter.The right side of the board is the ar9271 USB wifi card.

author: Yansi
author_rank: Super Contributor
timestamp: March 24, 2019, 11:10:56 am
content: Okay, so I can't get it for that price.Could you please explain the structures on the output of the SE2576L chips? I have never actually found any info about what kind of output matching is required for these (SE2576, SE2565,... ) Wifi chips from Skyworks. The input is matched - as far as I can tell, but the output need external matching.The datasheets of these chips do not contain any info on output impedance or recommended matching.

author: OwO
author_rank: Super Contributor
timestamp: March 24, 2019, 12:34:04 pm
content: There is a se2576 reference design which contains the output matching:

author: Yansi
author_rank: Super Contributor
timestamp: March 24, 2019, 12:58:29 pm
content: Thank you for the document. SE2576L-EK1 (the board reference in the datasheet) can not be located on the manufacturers website. I have located a different one, I think it was for the lower power SE2565T, the SE2565T-EK1, but only the device datasheet is provided.That output matching is NASTY. I have done a bit of research across similar chips for the 3.4GHz band, and these were much nicer and used simple stepped impedance line matching.I think it could be likely done here to, but the damn skyworks would have to provide the damn impedance charts!

author: OwO
author_rank: Super Contributor
timestamp: March 24, 2019, 01:41:39 pm
content: Yeah the higher frequency PA chips like the 5.8GHz SE5004L don't need any output matching at all, it's all integrated. I think 2.4GHz is still on the low side when it comes to on-chip matching. What I did is simulate the output matching network from the reference design in RFSim99, note the impedance, and modify the circuit while maintaining the impedance. For example I can substitute microstrip stubs for inductors or adjust positions of capacitors and then tweak lengths or values to compensate. I had to do that because I'm restricted to a set of capacitor and inductor values if I want them soldered by JLC SMT.

author: Yansi
author_rank: Super Contributor
timestamp: March 24, 2019, 01:57:10 pm
content: Do you still have somewhere noted what the output impedance of the chip at 2400MHz was?I think it could be worthy to blast a question to Skywworks abotu an impedance chart... but you know the corporates...//EDIT: So I've naively contacted them through the form on the web to "request info". Let's see where it gets us.

author: OwO
author_rank: Super Contributor
timestamp: March 25, 2019, 03:39:32 am
content: I see 2.6 - j6.4 ohms looking towards the load at 2.42GHz, referenced to the package pin of the chip. I'm not sure if this is accurate because it doesn't take into account parasitics of the chip caps and inductors. I would try to keep the design as close to the reference design as possible so that the parasitics are similar.

author: Yansi
author_rank: Super Contributor
timestamp: April 08, 2019, 10:16:19 am
content: So, lil update here: I have written a message to the Skyworks support. And guess what? I got a single grumpy answer of a men who could not even reply in a proper email, he attached the document we already have and nothing else.Who guessed this?This is what came into my inbox, quote:Quote

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: April 08, 2019, 11:23:38 am
content: Quote from: Yansi on April 08, 2019, 10:16:19 amOdd, my dealings with them have always been quite positive.

author: Yansi
author_rank: Super Contributor
timestamp: April 08, 2019, 11:58:39 am
content: Maybe because you mean money for them.

author: Yansi
author_rank: Super Contributor
timestamp: April 08, 2019, 12:39:35 pm
content: So, being dissappointed, I have written once more, if Mr. Godsiff have read my last question and received my email?Now I have received a reply within minutes. Same, short answer of "See below" type, but this time there is an email attached to it from another person, Mr. Du and actually something more was attached there.So for those still interested, this is what I got: A schematic of the EVB with the section circled in red, a note on the components (which actually is helpful) and a set of S-param images (S11, S22, S21) of SE2576 and SE2565 "Measured on the EVBoard".Do I understand those S-param graphs right, that these are the measurement of the matching network circled in red?Now maybe a dumb question - according to the note below I have received, many of those L-C-TML stuff are just stubs to filter harmonics - how can I transform that matching networks, if all I will do is to use a ceramic monolithic filter to get rid of the harmonics?As I understand it, I still do not have what I need - that is the output impedance of the amplifier itself.Shall I at least try to request the source data for the graphs in touchstone format (s2p)?Quote(Note: Graphs below for SE2576)

author: OwO
author_rank: Super Contributor
timestamp: April 08, 2019, 01:05:19 pm
content: No I think the S parameter graphs are for the board as a whole, because it's really a pain to measure S parameters at specific points on a PCB and do so accurately. Even worse is it's a very low impedance, so any errors in S11 get amplified. The best you can do is simulate that circuit in RFSim99, build a matching network that achieves the same impedance presented to the chip, then optionally do load pull yourself to determine optimal impedance.

author: Yansi
author_rank: Super Contributor
timestamp: April 08, 2019, 01:23:10 pm
content: Makes sense, I haven't noticed the positive gain of 30dB is S21! (Haven't really looked at the data, bad on my side)Now, how would you combine the power of these two devices (SE2576) the easiest way?I have already figured out, Wilkinson shall be enough for this. But, what to do about the matching networks (that are more like harmonic filters, than matches)?I have a ready made ceramic filters available, namely BF3216-B2R4DAAT (but that one seems to have unacceptable loss of 2.5dB) and RFBPF2012080A7T with even worse insertion loss figure. So to preserve the maximum power available, better to keep hands off of these and leave what the manufacturer recommends there.It should be probably wise to make a prototype of the amplifier itself first. Probably only as a single unit board (make one like the original eval kit) and then a double one (wilkinson combined), before implementing it on a complex full PCB.

author: OwO
author_rank: Super Contributor
timestamp: April 08, 2019, 01:49:06 pm
content: What I did was first match each chip to 50ohms, then use a 50ohm Wilkinson combiner. You can put the filter before or after the combiner depending on whether or not you can get high power rated filters.

author: Yansi
author_rank: Super Contributor
timestamp: April 08, 2019, 02:12:10 pm
content: Obtaining a filter for a couple of watt should not be a problem, but if one can avoid them... Those small SMD 0805 device with 2-3dB loss would likely de-solder from the board when presented with those power levels we are talking here - so, these are kind of ruled out. I could likely get better ones, by why to bother... (I will use those further back in the signal chain).So back to the good old transmission lines and lumped passives.Do you think it would be a good idea to transform the design from 0402 to 0603? I am not that equipped with 0402 kit and have high dislike for having just a tiny part of board assembled in 0402, while the rest in 0603. (I'd guess 2.4G shall not present much problems for 0603 here).

author: OwO
author_rank: Super Contributor
timestamp: April 08, 2019, 02:28:30 pm
content: At the low impedance parts of the matching network the body effects are significant, for example the 1mm length of a 0402 capacitor is a significant error when you put it into the simulation. It's not trivial to account for it either because the equivalent circuit will differ depending on which terminal of the capacitor is connected to the outermost "plate" facing the PCB. I would personally stick with 0402 for this part. The Wilkinson combiner resistor is an exception and I used 0805 for that.

author: Yansi
author_rank: Super Contributor
timestamp: April 08, 2019, 03:05:34 pm
content: Well, 0603 parts are 0.6mm longer than 0402 ones, meaning one could account for that by adding tiny bit of inductance in series, on the order of <1nH. (But I am sure it would not be as simple as that)If one wanted to be nitpicking, you would have to account even for variation of SMD PAD lengths, as my certainly will be different than the OEM ones.Hence why I wanted to avoid this output matching spaghetti mess altogether, get the output impedance, and make a simple impedance-step match as typicaly is done with common GHz power transistors. (ie. resonate out the real part using 1/4 wave line, then parallel R or series C and be done with it - I can't characterize and measure any better than that at home)

author: Yansi
author_rank: Super Contributor
timestamp: June 01, 2019, 10:49:21 pm
content: I have just found out the existence of this wifi amplifier chip: YP242034, datasheet hier:http://pro366bdc.pic21.websiteonline.cn/upload/innotionyp242034datasheet_ekzd.pdfIt seems it has a really easy impedance matching circuit. But the problem is, these chips seem nowhere to be found :-OAny ideas where could one buy a couple of these for a test?