On reading your post, you state that the receiver is approximately 1.5 meters from the router radio antenna in about the same plane. Unless there is some obstruction in between the router transmitter and the receiver device, I do not believe you will see any improvement in wireless performance by changing the antenna. The way to tell that is to measure the signal attenuation (signal strength) at the receiver at different distances from your router transmitter. If the transfer rate does not increase when you move the receiver closer to the router transmitter, you will not benefit from a different antenna.
I suggest that you simply use a CAT6 Ethernet cable between the router and the device. If the device does not have a Ethernet RJ-45 port, perhaps a USB 3.0 patch cable between the devices for that distance?
I have not found any high gain antennas which work to increase the signal of both the 2.4GHz and 5.2/5.8GHz band over the stock antennas simultaneously.
The best I could do was replace one, or two, of the stock antennas with a high gain omnidirectional antenna optimized for 2.4GHz while keeping the stock antennas for the 5.2/5.8GHz band. This gave me a significant improvement in the 2.4GHz band while keeping most, or all, of the 5.2/5.8GHz band performance.
There really are no small, high performance 5.2/5.8GHz antennas that perform better than the stock antennas. The 16dBi 2.4GHz antennas I use work better but are much longer (38-40 cm) than the stock antennas. I am willing to accept that for the performance gain in 2.4GHz. The 5.2/5.8GHz antennas that really outperform the stock antennas are like 4-5X the size of the stock antennas and much more expensive. Plus, they do not readily mount directly to the router, requiring a cable.
