how to implement antenna/antenna tuning? (is it required?) - Page 1
Forum section: electronics / rf-microwave

author: Nightreaver
author_rank: Newbie
timestamp: October 30, 2024, 04:05:49 pm
content: So I'm quite a noob with PCB design really, but i like challenges so I'm trying to design a small expressLRS board with ESP32-S3 + SX1280 for the ELRS control.Both - esp and sx1280 - require an antenna so i went out looking for that fits my board design.I found thisRFECA3216060A1T(https://www.lcsc.com/datasheet/lcsc_datasheet_1808272258_Walsin-Tech-Corp-RFECA3216060A1T_C127620.pdf), it is stated that the frequency is 2.4GHz~2.4835GHz which is mostly all Wifi channels.But it seems the documentation is very lacking and the antenna is not recommended here.But I came acrossPulse Elec W3008(https://wmsc.lcsc.com/wmsc/upload/file/pdf/v2/lcsc/2007071008_Pulse-Elec-W3008_C581402.pdf), theYAGEO ANT3216LL00R2400A(https://www.lcsc.com/datasheet/lcsc_datasheet_1810241140_YAGEO-ANT3216LL00R2400A_C293767.pdf) and maybe theJohanson Dielectrics 2450AT07A0100001Thttps://www.johansontechnology.com/docs/3823/antenna-2450AT07A0100001T-rev4.0.pdfMy focus was the small package and the feedline coming from along the pcb edge, not from the side.I dont have a lot of space available, and would not like to increase the size anymore.The current gaps are around 3mmx7mm, i might get another 1 or 2mm with moving components.So my question is, what else do I need to take care of, besides implementing the "footprint" quite accurately.I already have a matching circuit for the esp32-s3and I have matching circuit for the sx1280What else do I need to do to "attach" an antenna?How to set the frequency of an antenna? DoIdo that, or is it done by the chip ? (Like selecting wifi channels)Is there some oversight in my antenna implementation?(in another thread it was said that even a badly implemnted chip antenna will be better than a bad meander antenna -https://www.eevblog.com/forum/rf-microwave/help-to-identify-small-pcb-trace-wifi-antennaso i'm taking him by his words, maybe?)As seen in this topic as well, there are many expressLRS designs using a similar setup, many of them dont seem to use big matching circuits between the chip and the antenna as well, so Im very confused about what is required, what is nice to have and what is just "peak design" practice. I would really love to use expensive gear like VNA but I dont have the money nor the capabilities at the moment.Im just trying to design something that works, without need to be perfect.The antenna range can be less than 10 meters, its not mandatory to get a few hundred meters for like FPV drones.

author: uer166
author_rank: Super Contributor
timestamp: October 31, 2024, 04:07:55 pm
content: I never said badly implemented chip antenna is better than meandered. I said a "poor chip antenna" is better, but you still need a decent implementation.By poor I meant efficiency: the smaller the chip, the higher K dielectrics and lossier it would be. Your layout overall is in pretty good shape for a chip antenna that requires a slot-style antenna PCB layout.Remember that with these chips, PCB is still usually part of the radiator structure, so follow recommended layout as close as you can.

author: uer166
author_rank: Super Contributor
timestamp: October 31, 2024, 07:09:08 pm
content: Looking at your options, the only one that doesn't fit the layout is the YAGEO ANT3216LL00R2400A, it's more of a monopole style, the rest are slot-type antenna layouts. Copy the layoutEXACTLYfor whichever chip you choose, and use recommended matching components if any, and you'll be orders of magnitude ahead of what the original design you showed with the meander antenna.

author: uer166
author_rank: Super Contributor
timestamp: October 31, 2024, 07:13:03 pm
content: Quote from: Nightreaver on October 30, 2024, 04:05:49 pmThe chip itself, combined with the recommended layout, create the resonant structure. As long as your layout is correct, it'll resonate at the correct frequency. Both need to be correct to "set" the frequency.

author: virtualparticles
author_rank: Regular Contributor
timestamp: November 26, 2024, 11:41:19 am
content: Beware of a groundplane requirement for the antenna. I'm aware of at least one "chip" antenna that is quite small but requires a 4"x2" ground plane around it to function properly. Completely negates the benefit of the small size.

author: MartinL
author_rank: Regular Contributor
timestamp: November 26, 2024, 12:18:38 pm
content: Quote from: virtualparticles on November 26, 2024, 11:41:19 amThis isn't just an issue with "at least one" chip antenna, it's an issue withallchip antennas. The chip isn't the antenna! The antenna is the whole reference design, including the ground plane.I wrote a bit about thisin a previous threadbecause it's a really common misunderstanding (that's somewhat deliberately encouraged by manufacturers marketing their "tiny" chip solutions).

author: tszaboo
author_rank: Super Contributor
timestamp: November 26, 2024, 12:52:50 pm
content: Quote from: Nightreaver on October 30, 2024, 04:05:49 pmThose parts are matching the output of the chip to 50 Ohms. You also need to match the antenna to 50 Ohms. It depends on your FR4, size housing, so it's almost impossible to ballpark a circuit like that, especially without very expensive simulation circuit. What sets the frequency is the ESP. What sets the impedance of the antenna is the matching circuit. If it's not there, and your antenna is ie. 10 Ohm, most of the energy will "bounce back" from the antenna, and you will get a very bad range.If you are new to PCB design, use a radio module.