PICO-D4 SMA Antenna Matching

thethinker
Posts: 53
Joined: Thu Mar 01, 2018 1:26 am

PICO-D4 SMA Antenna Matching

Postby thethinker » Tue Jan 15, 2019 2:48 am

I'm designing a board with PICO-D4 and SMA connector. I'm also having the PCB fabricated with 50 ohm impedence control on the RF line and my RF line is only 7mm long. Do I need a pi matching network for this? I Would like to mention I'm using this device as a sniffer so I would like to get as accurate as I can.
Thanks.

thethinker
Posts: 53
Joined: Thu Mar 01, 2018 1:26 am

Re: PICO-D4 SMA Antenna Matching

Postby thethinker » Tue Jan 22, 2019 3:40 am

Please Help

ESP_Sprite
Posts: 2761
Joined: Thu Nov 26, 2015 4:08 am

Re: PICO-D4 SMA Antenna Matching

Postby ESP_Sprite » Tue Jan 22, 2019 9:43 am

Suggest you mail sales at espressif dot com for this, as I don't think any of our RF engineers are on this forum.

ESP_Angus
Posts: 1732
Joined: Sun May 08, 2016 4:11 am

Re: PICO-D4 SMA Antenna Matching

Postby ESP_Angus » Wed Jan 23, 2019 4:58 am

If you want maximum RF performance then a matching network will always help you achieve this.

One option is to contact sales and ask for advice from an RF engineer, as Sprite suggests. However, a good place to start first is the ESP32-PICO-KIT reference design which you can find on the espressif.com downloads page. This design uses a standard Pi matching network and gives the values for the capacitors and inductor as used on the board.

Do you have any facilities to analyse and tune the matching network performance? This is really the key point for optimising RF performance on your design, there is no substitute for testing and tweaking on an actual board. If you do not have this facility, you can start with the values from the PICO-KIT and see if performance is adequate for what you need.

The good news is, if it's a sniffer then you don't have to worry about TX performance. RX is generally less sensitive to impedance mismatches. (Although I'm not an RF engineer so don't consider this as expert advice.)

thethinker
Posts: 53
Joined: Thu Mar 01, 2018 1:26 am

Re: PICO-D4 SMA Antenna Matching

Postby thethinker » Wed Jan 23, 2019 11:58 pm

ESP_Angus wrote:
Wed Jan 23, 2019 4:58 am
If you want maximum RF performance then a matching network will always help you achieve this.

One option is to contact sales and ask for advice from an RF engineer, as Sprite suggests. However, a good place to start first is the ESP32-PICO-KIT reference design which you can find on the espressif.com downloads page. This design uses a standard Pi matching network and gives the values for the capacitors and inductor as used on the board.

Do you have any facilities to analyse and tune the matching network performance? This is really the key point for optimising RF performance on your design, there is no substitute for testing and tweaking on an actual board. If you do not have this facility, you can start with the values from the PICO-KIT and see if performance is adequate for what you need.

The good news is, if it's a sniffer then you don't have to worry about TX performance. RX is generally less sensitive to impedance mismatches. (Although I'm not an RF engineer so don't consider this as expert advice.)
Perfect,
Thank you for the response. I already have a PI network on the board. I have VNA and I'm familiar with the process of matching network for the PCB antennas. I was just wondering if SMA actually requires tuning at all. I will take your advice and email sales. Thanks!

ESP_Angus
Posts: 1732
Joined: Sun May 08, 2016 4:11 am

Re: PICO-D4 SMA Antenna Matching

Postby ESP_Angus » Thu Jan 24, 2019 1:34 am

OK, great to hear.

Yes, the process of tuning for an SMA connection should be similar to tuning for an onboard antenna. For example, the antenna on the PICO-KIT (Proant 440) is a 50 ohm antenna. For your SMA connection you presumably also want a 50 ohm characteristic impedance, so the tuning problem is very similar.

As far as I understand, PCB antennas are a special case because although they may also be designed for a 50 ohm impedance you have the possibility of a different characteristic impedance in the antenna itself (due to design tweaks, PCB properties, etc) as well as the feedline.

flashpackets
Posts: 7
Joined: Tue Jun 27, 2017 10:39 pm

Re: PICO-D4 SMA Antenna Matching

Postby flashpackets » Fri Jan 25, 2019 1:57 am

Having a pi network in place and finding that a straight short is perfect is better than not having the network, and needing it! If you have the room, put it in. Just because the component positions are available does not mean that they have to be populated. Remember that good ground stitching along the transmission line is important. Of course you might also consider the T network, however in the simplest case it requires 2 components while the pi on one.

thethinker
Posts: 53
Joined: Thu Mar 01, 2018 1:26 am

Re: PICO-D4 SMA Antenna Matching

Postby thethinker » Sat Jan 26, 2019 7:48 pm

Hi Guys,
Thank you very much for the reply. I think I'm not perfectly describing the question. I do have plenty of stitching and pi network in place and I'm not getting rid of them. My actual question is not about whether or not have them, it's about the actual tuning process. How could one go after tuning with such setup? Is it even needed? The reason I'm asking is because I have 50 Ohm impedance matched traces, PICO has the proper impedance, and my Antenna it self (tested with a VNA) has the right impedance as well. So what is left here to tune?
But @ESP_Angus's answer regarding the receive sensitivity being less sensitive to tuning mostly answers my question. I already know that I have good enough output power, I was just worried about receive sensitivity.

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