Keenetic Hero 4G+ (KN-2311) has a built-in 4G modem cat.6, i.e. it supports aggregation of two frequencies (carriers) for reception while transmission goes on one frequency. The result of the aggregation is an increase in data transmission speed and a reduction in signal delay.
A prerequisite is that the operator's base station supports carrier aggregation.
List of supported aggregation combinations:
B1 + B1/B3/B8/B20
B3 + B3/B7/B8/B20
B7 + B7/B8/B20
B38 + B38; B40 + B40; B41 + B41
1*. Aggregation of two frequencies (carriers) within one band, e.g. B7+B7, is only supported for contiguous intra-band CA.
2*. The combination of B3(anchor PCC)+B8(SCC) is supported, but B8(PCC)+B3(SCC) is not.
The web interface of Hero 4G+ (KN-2311) shows the connection frequencies in the aggregation under 'Mobile' > 'Carriers'.
If your smartphone supports carrier aggregation, you can use the free NetMonster Android app to check the base station's carrier aggregation availability. The app will show on which frequencies the aggregation is currently active.
Many modern smartphones have a built-in 4G modem up to cat.20, i.e. they are able to aggregate up to 5 carriers. If during a speed test your smartphone shows higher speeds than the router with the same SIM card, this is most likely due to the higher number of frequencies in the aggregation.
Operators are upgrading their base stations to aggregate frequencies primarily in large population centres. In their information materials they use the terms 4G+ or LTE-Advanced to emphasise a network with frequency aggregation.
Note that the subscriber's device (smartphone, router) connects to the base station on a single frequency and aggregation is applied when the load increases. For example, while downloading a large file or testing the speed. The operator's network controller automatically determines whether to enable aggregation, and decides which carriers to include in the aggregation and which frequency will be anchor and which will be auxiliary.
During carrier aggregation, the subscriber device is always connected to only one base station. In theory, 4G technology allows a subscriber device to connect to one base station on one frequency and to another station on another frequency. But in practice, operators do not use this scheme.
Therefore, with and without frequency aggregation, the same 4G antennas are used, which are connected to the same base station. The example of street directional antennas can be given. In some cases a street antenna is installed to improve signal quality with a distant base station. Such an antenna is suitable for both cat.4 (without frequency aggregation) and cat.6 (with frequency aggregation) routers. One MIMO 2x2 antenna is sufficient in both cases. See this article for information on connection of outdoor directional antennas.