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Some months ago I did the layout of a board with a GSM module SIM800L and below is shown the antenna circuit that was used. We assembled 200 PCBs with R22 = 0R jumper and C28 and C29 not populated and the GSM communication worked in all of them with good results.

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Now I want to use a NB-IoT module SIM7020C, the hardware design PDF of it shows the reference circuit for the ANT pin / antenna, the difference for the previous circuit is that there is an extra resistor (R2).

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Could I for the circuit above, in my circuit, do not place R1,R2,C1,C2? And place only the TVS diode and place the RF connector (I will use uFL/IPEX) very close to the ANT pin like 2mm far if I am going to always use antennas with 50 ohms of output impedance?

I did a search for "SIM7020C" on Aliexpress, found a board where they did not used the impedance matching circuit, I wanted to use this way, but I am asking about anyway...

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Regards.

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The Main_Ant pin is 50 Ohm, it connects directly to a 50 Ohm connector, and it probably has a matching network under the shield. The matching network is used to match on-board antennas (ceramic or printed) to 50 Ohm. If you don't use an on-board antenna, you don't need that matching network. You might want to implement a matching network between the RF connector and the module, just in case.

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Good luck without any matching circuit, unless the module is already pre-matched to 50 ohms (it seems so from the hardware manual) did you at least made a controlled impedance line?

As for R2 yes, you can omit it or place a zero ohm for later matching (if you have a suitable test rig).

The idea would be to build the circuit, measure with a VNA and then tune the parameters to optimum match (thats one of the reason for having an RF test connector like shown in the manual). The usual 3 components provide place for an L or Pi network, the additional resistor could be used for a double-L matching.

If your antenna/uFL assembly is already well matched to 50 ohms and you don't need to certify the product (a personal hobby product, for example) you could risk your 2mm trace right out of the module.

If you need to go in a lab for GSM certification or emission testing I strongly recommend to do a proper impedance controlled line and reserve space for at least a 3 component matching network (typically 0402 size or smaller for that band). RF power for GSM is not trivial (that module can output 23dBm, 200mW) and the design guide recommends some very small insertion losses (like less than 0.5dB for the low UHF band). I don't think you could obtain that with sheer luck

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