As I understand it;
If your unit has one internal radio (essentiall, anything other than the RUTX14 which has 2x internal radios)
Then the two antenna ports operate in this way:
The "main" antenna port is the primary TX/RX antenna for that single radio.
The "aux" antenna port is used as a "diversity" antenna for the main antenna.
This does a few things:
It enables 2x2 MIMO (both antennas used at the same time for DL -LTE Cat4)
It allows your radio to take better advantage of a concept called "signal diversity".
-essentially, it allows the radio to use both antennas at the same time for the SAME SIGNAL; ideally for LTE cell towers, you would have the two antennas in a "cross polarization" orientation. I.E. one antenna rotated 90 degrees relative to the other.
In order for these advantages to work to their maximal effect, BOTH antennas must be matched, I.E. exactly the same.
And, in any case, even if you use mis-matched antenna types, the SINGLE radio in your device can only connect to ONE band at a time (unless your unit support Carrier Aggregation -LTE Cat6 or higher- more on that below).
So, the radio will either connect to a low band frequency (I.E. ~800Mhz) or a mid band frequency (I.E. 1.8-2.1 Ghz).
It will NOT connect to one band on one antenna port, and a different band on the other antenna port.
Carrier Aggregation:
In Cat 6 and higher modems, "Carrier Aggregation" comes into effect if:
-Your device support it;
-your device will have SPECIFIC band combinations that it supports, you will have to look them up for your specific unit
-The tower you are pointed at supports it;
-the carrier equipment on the tower you are pointing two is emitting signals on multiple bands simultaniously AND that carrier has "turned on" the carrier aggregation feature on that particular tower
-And the bands that are POTENTIALLY being aggregated on the tower you are actually pointed to match the band combinations supported by your unit
-I.E. the tower supports CA on band 2+66, 12+66 and n41+66.
-You device only support CA on band 2+12 and 2+17
-In that case, even though your device technically support CA, and the tower you are pointing supports CA, you still wont see the advantage of it, because the band combinations supported by your device do not match the band combinations emitted by your tower.
Okay, so in the miraculous case that your unit supports CA on band combinations that are emitted by the tower you are pointed at, again as I undertand things (I could be wrong):
The band combination is done over each antenna channel;
So antenna channel 1 (main antenna port) would be seeing Band 2 + 12 (for example)
And antenna channel 2 (aux antenna port) would also be seeing Band 2 +12 (for example)
SO, for maximum signal integrity, you would want a matched pair of antennas that had wide enough bandwidth to cover the band combinations you intended to connect to.
All of that said; in your case:
I would recommend you test both antenna's independantly on the MAIN antenna port.
Determine through load testing/ speedtest's which Band has better service on the tower(s) you can connect to.
Once you have determined which Band is best for your location and the tower(s) you have available:
Lock the unit to only connect to that "preffered" band.
Connect the antenna matched to that band to the "main" antenna port.
Connect the stock omi-directional "stick" style antenna that came with the unit to the "aux" antenna port.
Tune the main antennas location and pointing direction.
LTE signal can be deceptive, especially at long range/ Non Line-Of-Sight.
It is often the case that obtaining the maximum signal STRENGTH does not actually result in the best data rates.
The reason?
NOISE.
For this reason it is also often the case that "just" placing the antenna as high as you can may not yield the best data rates.
You will need to experiment in your location with your antenna(s).
Things to consider:
The MOST IMPORTANT METRICS for you to looks at are in this order:
SINR:
-If you can't get this above +0 DBi then forget about every other measurement, your signal will be CRAP.
-If you can get this above +20 DBi AND your RSRP is -100 DBi or better, you will be able to achieve maximum data rates (the limit will be your units LTE modem, and the throughput available at the tower -congestion/backhaul etc.)
RSRQ:
-this is similar to SINR but doesnt include "general RF noise"
-this measures "noise" relative to signal stregth, but the only "noise" included in this measure are the OTHER cell towers you can also hear on the band you are currently connected to
-at -10 DBi or better (providing SINR is also +20 or better) you will be able to achie maximum data rates
RSRP:
-this is the stregth of the signal you are receiving from the tower you are currently connected too
-if SINR is +20 or better AND RSRQ is -10 or better, then once your get to -100 DBi RSRP you will be able to achieve maximum data rates
-that is to say, if SINR and RSRQ are at "excellent" levels then you will see NO BENEFIT from getting your RSRP better than -100
RSSI:
-for 4g LTE signals this measurement is almost ENTIRELY USELESS
-it is TOTAL WIDEBAND POWER
-it is the strength of ALL available signal added to the strength of ALL audible noise
-so, if you turn your antenna looking for MAX RSSI, you are probably going to find the area with the highest noise floor, and thus one of the worst directions for receiving a good signal
So, for tuning your antenna placement:
Try various location around your building/ structure;
You may find that placing the antenna on one side of the building such that the building itself blocks "noise" comming from a certain direction, you can obtain a better Signal to Noise Ratio (SINR) and thus better data rates, even if you sacrifice some TOTAL power of signal strength (I.E. SINR goes up, but RSRP and RSSI go down -that is actually a good thing)
Good luck in your RF journey!
