We have developed an application which uses the nRF9160 together with the same GPS and Ethertronics/Kyocera/AVX antennas as that of the nRF9160-DK. For the LTE antenna, we have used the matching values and configuration also as that of the DK (22 nH, 3.5 pF, 1.5 nH) and have used 1oz FR4. We also have additional Bluetooth and LoRa modules on the PCB, which we turn off for the testing procedure which uses the %XRFTEST set command in an anechoic chamber. Our unit had failed radiated emissions tests, exceeding the limits for harmonics on three LTE bands: 8 (880.7 MHz), 20 (833.7 MHz), and 28 (703.7 MHz). We have access to a simple DIY TEM cell and spectrum analyzer (TinySA) in our office, but could perhaps reach out to request some limited access for something better if we have a specific test in mind.
So far we have altogether found five different matching components on various related datasheets and tried a few of those values though we don't see any significant improvement/worsening in our simple TEM cell setup. We're now looking at modem commands to disable the GPS LNA, though it seems we're maybe probing too low-level.
We're willing to implement any suggestions/recommendations while we continue to learn what we can and make attempts.