SMT Ceramic Chip Antennas - Page 1
Forum section: electronics / rf-microwave

author: bson
author_rank: Unknown
timestamp: April 07, 2020, 09:40:38 pm
content: I was wondering if anyone has experience with SMT chip antennas? Specifically looking to use one for ANT, which uses the 2.4GHz ISM band. Looks cheaper and much simpler than an impedance controlled PCB. (Use is similar to ANT+ with similar device profiles, but not compatible with ANT+ and off on different frequencies and intended for machine telemetry rather than fitness products.) How do these compare to a plain old traced out PCB dipole?

author: ThomasDK
author_rank: Regular Contributor
timestamp: April 08, 2020, 12:47:57 pm
content: Quote from: bson on April 07, 2020, 09:40:38 pmWhy would you need an impedance controlled pcb?QuotePretty similar performance, smaller formfactor, higher price.They are rarely 50R impedance as-is so will need finetuning on your board, just like an F-antenna.

author: bson
author_rank: Unknown
timestamp: April 09, 2020, 08:58:21 pm
content: Yep, my bad, only the dielectric/VoP matters. Also, calculating the sizes it seems small changes in \$\epsilon\$ doesn't make much difference, nor does exact dimension (e.g. within 0.25mm or so). So it may not matter. Still, for 2.4GHz it comes out to the neighborhood of 28x32mm (forget the exact size off hand) with a nominal FR-4 \$\epsilon = 4.34\$ L=0.8mm. Kinda large area for a small PCB, but not large or expensive in absolute terms. And there's nothing to populate which is always nice.

author: charliedelta
author_rank: Regular Contributor
timestamp: May 02, 2020, 04:48:49 am
content: I tried some of the Murata versions at 2.9ghz and found them to be very poor as a general receive antenna using the antenna alone. However when I mounted the ship in front of a brass reflector to act like a corner reflector it work very well. In my application which was a zero IF receiver the pcb dipoles and reflectors worked the best.

author: E Kafeman
author_rank: Regular Contributor
timestamp: May 03, 2020, 06:18:02 pm
content: It is correct that performance is often low for small ceramic antennas but it is not always so.Here do I tune a ceramic antenna to 2.4GHz and afterward measure its efficiency:

author: cdev
author_rank: Super Contributor
timestamp: May 04, 2020, 12:58:25 am
content: The one on the Raspberry Pi 3 is pretty bad. Definitely replacing it is essential if you plan on using it over any distance more than "the next room".

author: E Kafeman
author_rank: Regular Contributor
timestamp: May 04, 2020, 03:17:29 pm
content: I do not fully agree that it had a poor antenna from engineering view, RPi 3 had an decent ceramic antenna. Its implementation was however poor designed at PCB so final result was not the best.That is a very common mistake for many of these ceramic antennas, it is assumed to be just a component, but in reality is it more critical to implement this type of antenna then even an IFA and needs careful tuning. Failed implementations are too common because this antenna type always will fail if not skilled implemented.That can be compared with a 30 mm wire soldered as monopole at PCB. Seldom as monopole max performance but will never be real bad without need of any thinking or tuning at all.Actual antenna was else a similar antenna as the one I tuned in video above with resulting measured efficiency around 70-80%.Antenna in PI 3B+ is not same as in PI 3 and is a non ceramic type.Guess it is same antenna as for R Pi zero W for which my efficiency measurement result looks like this:

author: cdev
author_rank: Super Contributor
timestamp: May 04, 2020, 10:57:28 pm
content: It is possible to replace the ceramic antenna on the Pi 3 with a hirose u.fl connector in fact it even has a footprint for it. But you better already have your antenna on a pigtail because making a pigtail from scratch for something that small at such a high frequency is almost guaranteed to not work well. There are lots of easy to make antennas for 2.4 GHz that can be made in a few minutes of time. Almost anything works better than that chip antenna.This handy calculator will give you a length to use if you want to use a quarter wave monopole.https://m0ukd.com/calculators/quarter-wave-ground-plane-antenna-calculator/>> 2430 Mhz = 2.9cm If you have the room in your case try to have it go away from the chassis as much as possible

author: radioactive
author_rank: Regular Contributor
timestamp: May 05, 2020, 05:26:53 am
content: Haven't worked on this for some time, but might be worth taking a look at. I think the default example is an inverted-f antenna. I never tested the inverted-f, but I did do extensive testing / production of something very similar to the bandpass filter shown. There definitely is some variation between runs of standard FR-4 boards due to process variations in epoxy / fiberglass ratio (at least conclusion I came to). For an antenna, these variations should be somewhat minor for most applications I would think. For something like the bandpass filter, I had to move to a more stable material: FR-408. Compatible with FR-4 process, still cheap, but much much more reliable for a good consistent match to numerical simulation once dialed in.https://github.com/tvelliott/jPCBSim/wiki

author: profdc9
author_rank: Frequent Contributor
timestamp: May 05, 2020, 03:02:52 pm
content: I don't know if this is too much of a hack or not, but I have taken cheap $3 RTL8188 Wifi dongles with ceramic antennas and soldered a roughly quarter wave wire onto the base where the ceramic antenna is fed. It's pretty imprecise, but it definitely seems to help the wifi performance. I haven't tried it with my Raspberry PI 3 though.

author: cdev
author_rank: Super Contributor
timestamp: May 05, 2020, 04:17:55 pm
content: You can and should definitely do that, if you are simply wanting a significantly better (quarter wave monopole) antenna and don't care about cosmetics.I edited my earlier post above and added a link to a calculator. But unless you are trying to transform it into an access point for general use (not a bad idea, actually) it shouldn't be critical.

author: cdev
author_rank: Super Contributor
timestamp: May 05, 2020, 04:51:12 pm
content: Quote from: radioactive on May 05, 2020, 05:26:53 amI am definitely going to check this out, thank you. Also thanks for the tip on FR-408

author: David Hess
author_rank: Super Contributor
timestamp: May 05, 2020, 06:33:32 pm
content: Quote from: cdev on May 04, 2020, 12:58:25 amAll loaded antennas have compromised performance compared to an unloaded full size antenna simply because of their smaller aperture. They are used for their small form factor and not performance.

author: E Kafeman
author_rank: Regular Contributor
timestamp: May 06, 2020, 12:13:25 am
content: This tread is going a bit too wild and below basic RF knowledge.It is comparing oranges with apples. They can be assumed to be similar in size but it is a bad idea to use an appel-calculator to calculate size of oranges or use a GP-calculator to calculate an embedded antenna.GP is a free space antenna designed for 50 Ohm by increasing impedance with 3-4 bent quarterwave ground radials. An embedded antenna have its impedance much decided by ground plane properties at its PCB location, which not is bent or have quarterwave length and wires and enclosure in antenna nearfield makes it long way from "free space" and therefor reducing antenna natural resonance frequency for a given length. Due to this differ antenna impedance a lot between these antenna types and while a GP antenna assumes a 50 Ohm interface is it seldom the case for an optimal embedded monopole.Optimal monopole antenna size inside an specific enclosure do I neither know anything about as there are too many parameters. A few of them:It is very common that an existing ceramic antenna is tuned by reactive components and it can be long way from 50+j0 Ohm at both sides of these components and if you intend to place a quarter-wave monopole is its expected impedance 36 + j21 Ohm if PCB ground can be assumed ideal. It is seldom ideal.It is not like an GP antenna in free space, with bent ground radials to adjust its impedance to be close to 50 Ohm.As I wrote above, 30 mm length is ok. It is surely not perfect but the closest anyone can guess. Better result requires measurements and tuning components, not a calculator of any kind.RTL8188 have a from data sheet impedance of 25-j5 Ohm. Even if a GP antenna is designed for 50 Ohm and placed in free space must it then be impedance matched to 25-j5 Ohm for minimizing losses. Another problem is that 8188 seems to have DC bias at its antenna pin and can probably kill IC if antenna creates a ground loop if no decoupling is included.However havewww.RF-link.net(now dead link) designed a FCC certified impedance network for this IC to provide a 50 Ohm interface.Do not know if it is correct values but it gives an idea what is needed to get a 50 Ohm interface from that chip.There is clearly an capacitor intended for DC decoupling in that circuit and remaining components seems to result in neighborhood of 50 Ohm.It is not values that I had selected even if including stray variations but it can be a transmission length from chip to matching network that affect chosen values.30 mm is an rough assumptions not taking in account for environment, ground and IC impedance for actual circuit, but it is just as good guess as something else.It is likely that this mis-design will reduce else possible optimal signal with several dB without real measurement and design job.Reason that it will increase result by chance is that original design job was worse done. It could be due to antenna space was too limited, ground was to short to be a stable RF ground or much more including that no one did a skilled design job. I have also done several less optimal antenna jobs due to that environment not allowed better design.In case of RPi3 was it not a problem with antenna that caused bad radiation performance. It was more likely someone using GP-calculator to implement the antenna and its ground.I wrote " RPi 3 had an decent ceramic antenna."Your reply: "Almost anything works better than that chip antenna."If it had been a forum for "gardening" so yes, noisy FM radio-reception, it can be described as a problem with whole radio.No one knows if noise is due to oxide in audio-pot or due to that antenna is missing and have no skill to understand difference.From technical view do I always differ hardware from its implementation for electronic circuits and antennas.No shade over any antenna type because it had been implemented by a monkey and these antennas are very depending on ground-plane size, they have minimal own antenna properties and they must be uniquely matched for each PCB design, but for RPi3 was that part forgotten, no matching components was even implemented and antenna was probably not even connected at correct antenna pad.Not really a problem with the antenna as it was its surrounding that failed.If a transistor is burning due to bad implementation is it a design problem, not a transistor problem.If someone asks if ceramic antennas are simpler then other antenna types to implement, which was the question in this tread, is my general answer no. It is based on that I have done such jobs many times.My general opinion if ceramic antennas are less effective then other antenna types, yes they are somewhat less effective in general, all ceramic material have higher losses then air, but most common type of losses are due to that RF design job is more demanding or not even have been performed.Ceramic antennas are mainly used because they are assumed to cost less PCB space then other antenna types. It is partly true but for same performance as for an IFA is needed PCB space often similar.These tiny USB BT plugs that only occupy a few mm outside of plug do often contain an IFA-antenna as a more effective alternative,. Similar PCB but with ceramic antenna require additional few mm space behind USB plug.How a ceramic implementation can be done is shown in my video, linked above, which includes measured result for a ceramic antenna performing real good.Video-demo is showing for TS what he asked for, what typical job that is needed to implement a common type of ceramic antenna.To implement other types of antennas at a professional level, whatever type of antenna, actual job is rather similar.Advntage is that IFA/PIFA are typical antennas that easy can be designed at PCB to optimal use existing space for a unique design. A ceramic antenna is in most cases bought in a specific size and with at least assumed limitations in frequency range and how its nearfield PCB must be designed. Much for that reason did I show that an antenna that by manufacturer is said to be designed for, in this case 868 MHz, sometimes easily can be tuned for other frequencies but opposite is also true, sometimes can not any retuning be done because radiation efficiency becomes useless low.If not doing any measurements and design-job at all can a ceramic antenna probably can have losses of more then 5-10 dB while a unknown performing monopole of 30 mm at least performs better then that if it also unmeasured and unskilled implemented, but also for monopole, most likely several dB from optimal possible performance.Using a calculator to calculate antenna length better then that without measurements of chip impedance and ground properties and such, is then not a productive idea.A somewhat better idea if no measurement tools are available but software allows to read RSSI, is to make antenna much longer then 30 mm and shorten it with 1 mm and read RSSI for each cut and that way find a somewhat better result but impedance matching will still be very poor as this is matching along a 1-dimensional trace while impedance is 2-dimensional (resistive&reactive) and if poor matching is also peak performance harder to find as RSSI due to mismatch can be more flat in its frequency behavior.Correct way to implement an antenna, embedded or external, for a circuit that not originally have a dedicated 50 Ohm port is to use correct measurement tool for this kind of job, a VNA.A decent VNA for amateur use is not that far away in cost nowadays. Everything I did in my video can be done even with cheap VNA's at cost of a bit longer time to perform each step.>All loaded antennas have compromised performance compared to an unloaded full size antenna simply because of their smaller aperture.Yes it is true but some ceramic antenna types are in my view almost no antennas at all. They are more a counterweight to RF current in ground plane and have due to its size almost no own aperture at all.It can still be a relative effective antenna, even if it is the ground plane that mainly radiates.Another video,https://www.antune.net/demo/bluetooth/index.html, shows when I designs a tiny 2.4GHz non ceramic antenna, just a small strip of PCB.It is a relative small antenna but do still radiate decent with less occupied space, less footprint, then StrongFirst antenna in RPi3.