Chip antenna RFECA3216060A1T, gap in feed line - Page 1
Forum section: electronics / rf-microwave

author: nuclearcat
author_rank: Unknown
timestamp: March 27, 2021, 10:51:36 am
content: I'm looking to JLC library and in antennas i found suitable chip antenna RFECA3216060A1T.But in datasheet there is very weird gap in feed line. There is no dimensions for this gap as well.Someone asked this question, but seems he didnt got complete answer.https://electronics.stackexchange.com/questions/432688/2-4-ghz-chip-antenna-layoutAlso not clear, what they mean under matching component?Datasheet:https://datasheet.lcsc.com/szlcsc/1808272258_Walsin-Tech-Corp-RFECA3216060A1T_C127620.pdf

author: E Kafeman
author_rank: Regular Contributor
timestamp: March 31, 2021, 06:01:32 am
content: Application design in that datasheet is omitting important details and lack design values.Gap is undefined space for matching components.Matching component placed after antenna shows that they have no clue how to make this ceramic thingy to radiate.Presented undocumented matching values and a nice VSWR curve means that you will never have a chance to confirm that VSWR or if it is just made up.If producer of this antenna not can provide real world values for needed tuning topology and its values for in the example simplified ground plane and a incomplete PCB pattern is it up to you to do this the development job for them.Most of these kinds of very small antennas are less antenna and more a kind resonators that use your PCB ground as antenna.If your PCB ground is lossy from RF view will antenna radiation be lossy.Ceramic chip in it self is all too small to be able to radiate with any efficiency and that is limited by physical laws.Include needed free footprint for this antenna and space for tuning components is not that small and will not either be a decent antenna.For same PCB space can an antenna of type IFA be made just as effective and it is a a very cheap antenna as it is part of your PCB pattern.It will cost you design work to create a such antenna pattern and these small antennas do need to be tuned either by careful PCB design needing a VNA for tuning or the most common solution, adding a tunable network a pi network for antenna feeding, where actual component values are decided after PCB antenna is designed and placed in an intended enclosure so that all thing that affect antenna tuning in its near-field can be included when deciding and verifying best tuning values.See section 7.1 in this PDF as an example of an IFA structure:https://www.cypress.com/file/136236/downloadIf footprint still is too big, see this design example:https://www.antune.net/demo/bluetooth/index.htmlAs all PCB dimensions and tuning component values are included in above example does it mean that this antenna design can be repeated and stated antenna performance will be possible to verify.Tuning values are not likely to be the same if this antenna design is implemented on a different shaped PCB ground plane. Above ground plane is very ideal, a big shape with no other components placed at PCB.For a fully populated PCB with maybe less ideal ground plane will needed tuning values be very different.As an practical example how these tuning values are decided for a more complex PCB:https://youtu.be/RyMFun_KhAcIt is not necessary to have an expensive VNA , there are cheaper alternative such as nanoVNA, good enough to measure actual antenna impedance and single frequency tuning values can be calculated from measured antenna impedance with a pen, a ruler and a printed Smith diagram.If tuning measurement seems too complicated, sorry but it is a must for all embedded small antenna structures if good antenna performance is needed.Do you really need an embedded antenna due to limited available space? Else are there a number of alternatives.A very simple antenna, no need for tuning and still almost embedded or at least not an external antenna is possible. Some performance will be sacrificed relative a well tuned PCB antenna but it will still be a decent performing antenna:This antenna only need one single measurement and it cost no VNA: use a ruler and cut a 35 long wire. That's all.Use few mm of the wire length for soldering. Solder antenna at PCB and make sure it points away from PCB and in "free space".Use a kind of wire that can keep it self straight but else no special needs for type of cable even if it is common to use a thin coaxial cable, using braid as antenna element, leave center wire as it is and even plastic isolation can with advantage be left as a stiffener and for protection.Using coaxial cable braid as antenna gives a bit better bandwidth and less losses then a single thin CU-strand, but difference is marginal and of less interest as antenna impedance in any case not is tuned.

author: nuclearcat
author_rank: Unknown
timestamp: March 31, 2021, 06:24:27 am
content: Wow. My deepest gratitude and thank you to you for such a detailed explanation.My fears were confirmed that this "chip antenna" is another not-so-well-documented nonsense.I'm trying now to buy a NanoVNA that "can" 2.4ghz, but unfortunately they are out of stock. Until then, i guess not worth even to try copying swra117d from TI, without VNA.I will use your advice about the wire, but do you think it is ok in some cases to make u.fl on a board (or SMA / RP-SMA) and just take a ready-made antenna from digikey? (if i need to do it "nicely looking")Of course, with the very short trace from the chip to the antenna.About chip antenna it will be cool to have it, as i dont want something hanging from PCB, but no big deal, i can live even with SMA!

author: E Kafeman
author_rank: Regular Contributor
timestamp: March 31, 2021, 06:44:22 am
content: Yes ufl connector is relative simple to implement and from there can either an adapter to a chassie-mount SMA be used or can a dipole antenna with ufl be directly inserted.Most external antenna will be ok to use but if using a ufl to reverse polarity SMA (RP-SMA), then can many of the antenna from old used WiFi routers be re-used. These antenna are in most cases antenna of dipole-type. It is even possible that it exist a short cable inside the old router with ufl to RP-SMA cable, ready to be reused.