Quick answer: A 4G or 5G antenna does not boost signal like an amplifier. It improves the point of reception. The aim is to place the antenna where the usable radio signal is better, then carry that signal back to the router with as little loss and interference as possible.
The phrase that causes confusion
People often ask for an antenna to “boost the signal”. That wording is understandable, but technically poor. Most passive 4G and 5G antennas do not create extra signal. They receive and transmit from a better location, often outside a metal cabinet, behind less brickwork or higher up with a clearer path to the serving cell.
Signal strength is only part of the story
RSRP tells you something about received power, but performance also depends on RSRQ, SINR, congestion, band selection, carrier aggregation, modem capability, router settings and the SIM tariff. A site can show strong signal and still perform badly if signal quality is poor or the cell is overloaded.
Cable loss matters
A high-gain antenna connected through a poor cable can be worse than a sensible antenna with a short, low-loss cable. Long thin cable can throw away much of the benefit before the signal reaches the router. For serious installations, cable type and length need to be treated as part of the design, not an afterthought.
4×4 MIMO needs four proper antenna paths
Many 5G routers use multiple antenna connections. If the router is designed for 4×4 MIMO, performance can suffer when only two external antennas are connected and the remaining ports rely on small internal paddles in a poor location. A proper external 4×4 MIMO setup gives the modem a better chance to use the radio capabilities it was built with.
The practical takeaway
Good antenna work is not guesswork. Test outside, test at height, check signal metrics, watch real throughput, keep cable loss under control and avoid mixing random antenna types just because the connectors fit.