Re: ESP07 with strange 3.5G? chip antenna...  solved - Page 1
Forum section: electronics / rf-microwave

author: hazzer
author_rank: Regular Contributor
timestamp: June 27, 2025, 01:46:55 pm
content: Purchased some ESP07s from an online retailer, arrived and all looks good except I was suspicious about the onboard chip antenna,since I planned to use with an external antenna I decided to investigate.to my surprise it was resonant above 3.5Ghz?3.5 to 3.8 Ghz depending on the fixture - does anyone know of a chip antenna resonant at 3.5Ghz (narrow band - not wide band?)H

author: tszaboo
author_rank: Super Contributor
timestamp: June 27, 2025, 01:52:09 pm
content: Quote from: hazzer on June 27, 2025, 01:46:55 pmYou will get the best measurement results this way:You need to measure that antenna on that FR4 board.Calibrate your VNA to a IPEX connector. Disconnect the chip (scalpel and cut the trace) going to the ESP, and make sure that the antenna is connected to that IPEX connector on the board. You might need a 0402 or 0201 jumper or something, depends on the board. Measure S11.The ceramic element alone is not just the antenna, it includes the GND gap and other layout features.Nice VNA.

author: hazzer
author_rank: Regular Contributor
timestamp: June 27, 2025, 03:55:46 pm
content: Found my error - the antenna has no ground connection, its perhaps a stub or 1/4 wave antenna? (.....update its actually a monopole)When measured as a stub (update...monopole) with a ground plane it is indeed resonant at 2.4Ghz, SWR of 2.5 but perhaps better when on the PCB.Problem solved, a wrong assumption....HPS not convinced about my onboard measurement, getting a good calibration at the end of an IPEX connector is a challenge I've yet to solve :-)

author: hazzer
author_rank: Regular Contributor
timestamp: June 27, 2025, 03:58:39 pm
content: Thanks yes I will need to invest in some IPEX connectors and try this with a good IPEX calibration, thanks for the pointer.

author: tszaboo
author_rank: Super Contributor
timestamp: June 27, 2025, 04:11:39 pm
content: Quote from: hazzer on June 27, 2025, 03:58:39 pmIPEX calibration is extremely cheap for antennas like these. If you are not chasing every 0.1dB in measurements.A few tings to consider:Consider the cable disposable. Unlike other RF connectors, they are only good for few tens of connections, so you might need to throw it out after a day.Buy a basic calibration kit, that uses 0402 or 0603 resistors. Typically they call this NanoVNA RF demo kit. They are like 10 EUR. Also disposable.Otherwise you can make your own calibration kit, it's just some IPEX connectors and some resistors. It's like 5 EUR to make one. I do that when doing antenna matching for any board, just use a blank PCB to make one. Then the stackup and layour around that IPEX is already compensated.

author: hazzer
author_rank: Regular Contributor
timestamp: June 27, 2025, 05:39:42 pm
content: Thanks yes good pointsHaving read a bit more and as you mentioned earlier these chip antennas really need to be mounted onto a PCB for any meaningful measurements.for anyone interested here's a good manufactures descriptionhttps://www.2j-antennas.com/antennas/single-internal-antennas/2je07g-2-4-ghz-ism-surface-mount-compact-antenna/298Note its described as a monopole antenna.Thanks again for the suggestions.H