PCB RF ROUTING

[Arunprakaash6]

Hello Mr.Robert,
I have a doubt in impedance matching. In my design GPS antenna with 50ohm impedance. I have calculated the values and then set in a PCB, But antenna does not work when mount in a PCB. But, It will work via cable soldered on a Pad. It is 2 Layer PCB.

I have calculated impedance with following parameters:
Track Width -2.85
Space between track and GND polygon - 1.58
Dielectric height - 1.6
Dielectic constant - 4.4

is there anything want to change


I have attached my PCB routing picture.

[Paul van Avesaath]

looks like you coverd the basics, calculations are correct btw.. but what is the value of R34? also why are C14 and C15 in there? you are adding a lot of stuff onto your RF signal..

whats also interesing What signal are you coupling through R32 and L2? suggest to remove those and test again.

in my opniion the problem is not with the impedance also since it is such a short track impedance should not matter that much..

also a GPS patch antenna is weaker than other types of antenna's right? (not 100% sure about this) maybe it is to weak for signal indoors?

[Arunprakaash6]

Design is make using as per datasheet. C14, R34 and C15 are reserved matching circuit for antenna impedance modification. By default, C14 and C15 are not mounted; R34 is 0Ω. The external active antenna is powered by GNSS_VCC. The voltage ranges from 2.8V to 4.3V, and the typical value is 3.3V. The inductor L2 is used to prevent the RF signal from leaking into the GNSS_VCC pin and route the bias supply to the active antenna and R32 can protect the whole circuit in case the active antenna is shorted to ground.

Is there any problem if track is in bottom layer since PATCH ANTENNA also in bottom side?

[Paul van Avesaath]

=Is there any problem if track is in bottom layer since PATCH ANTENNA also in bottom side?

there should not be although it is creating a stub, in some cases you are better of to go to the top layer with a via, (and GND via's next to it) and connecting it on the other side to reduce the stub length by 1.6mm in this case.

if you used a datasheet as reference.. woudl you mind sharing what components you used because now we don't know and its harder to help..? also you might want to contact a local FAE to help you..

[Arunprakaash6]

I am using Quectel MC60

[Paul van Avesaath]

do you have another antenna? maybe the current one is faulty? since the external antenna is working.. maybe there is a short somewhere..

[robertferanec]

Do they have reference board or is someone else using same chip and PCB antenna? Check existing board, maybe it could help - that is what I would do.

[Arunprakaash6]

Yes, I am also doing that now Mr.Robert

[Paul van Avesaath]

did you get it to work?

[Arunprakaash6]

[COLOR=rgba(0, 0, 0, 0.75)]Hello, Anyone Help me to complete this antenna routing. Is this routing ok? or want to change anything? I am using AcSIP S76S and RFM95 modules. I need to route antenna pins of both modules. I have put via on center of the top and bottom track. Is it ok?[/COLOR]

[Paul van Avesaath]

are these not two seperate modules? I do not think you want to combine those antenna's.
create a net for each independed antenna, and loose the via that connects the two..

[Arunprakaash6]

No, The customer need to combine the antenna

[Paul van Avesaath]

I do not think that wise... but if you must i would do this as close to the pin as possible..
you might want to put a 0 ohm serie resistor between the two so you can remove it if it does not work properly.. i know customers can be demanding of stuff.. but since they are antenna's they really need to know what they are doing..
in the end if they pay you for it.. then just do as they ask.. i would go for the resistor in between option.. just in case.. you can tell them it's a feature.. that if they do not want to combine the antenna in the end, you can easily do it..

if you go with the via then you need to do a redesign to disconnect it..

[Arunprakaash6]

[Arunprakaash6]

Is this OK?

[Paul van Avesaath]

i would suggest something like this.