I wasn't sure if you were looking for a product recommendation here, but I have been using the Poynting Cross Polarised 4G Omni LTE Antenna 4G-XPOL-A0001 (XPOL-1) for my RUT240 and have been very pleased with it. I am connecting to a tower about 3km away with some foliage in between, and am getting a signal of between -55dbm to -71dBm with it.
