Electronics > RF, Microwave, Ham Radio

Suggestions on circuit design for LTE-M

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diminatto:
Hello,

I´m design a board with Nordics NRF9160 to collect some data from a few sensors, i have already made a few boards for testing, but i´m having a problem with the LTE radio on it, it´s having a hard time obtaining and mantaining a connection to the tower, it takes a long time for making one and when it does the signal is so bad i can´t talk with the tower, or the connection drops after a few seconds. It also  has GPS wich can get a fix and it´s working. 

I´m using a flat antenna just like ANT-LTE-RPC-UFL from Linx, the antenna is connected via a IPX connector.

My board is quite small 24 mm (0.9') x 45 mm (1,77´), so i´m thinking maybe my ground plane is too small, i don´t have much experience with RF.

Here is my board:



Any suggestions on what could i do to try to solve my problem with the signal ?

Smile2016:
try to directly connect the antenna, no tuning/matching elements from NRF9160 to IPX. make sure the PCB stackup is for 50 Ohms. stick the antenna to a plastic enclosure as per datasheet. compare the return loss to datasheet plot if you have a VNA. check power supply and decoupling to support peak currents during Tx

diminatto:
It´s already connected without any tuning just a 0 ohm resistor, i think i may have fogotten to select controlled impedance during my order in the fab. I gonna buy a NanoVNA to check it up, currently i dont have one. Power supply is good.

Thanks!

Smile2016:

--- Quote from: diminatto on January 08, 2025, 04:13:34 pm ---It´s already connected without any tuning just a 0 ohm resistor, i think i may have fogotten to select controlled impedance during my order in the fab. I gonna buy a NanoVNA to check it up, currently i dont have one. Power supply is good.

Thanks!

--- End quote ---

How many layers? 4 layer or 2 layer PCB? I assume you have a GND reference plane in layer2. what's the trace width and Layer1 to Layer2 distance ?

Kean:
Some vendors have a free service where application engineers review your PCB layout for their RF modules.
I would guess that it is better for them to review designs for free early on, than deal with it later in the design stage and have disappointed (ex-)customers.

I'm not sure if Nordic offer it, but u-blox have done it for me with one of their nRF52 based modules.

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