/--/ Basicaly what I'm looking for is something similar to an usual 2.4Ghz transmitter/receiver, but 2-way and if possible, by serial in order to connect it to the laptop and raspberry. --/

Any suggestion?

Do these look like they would do the job?
https://assets.lairdtech.com/home/brandworld/files/Product Brief - RM024.pdf

 

Probably yes, probably no, it is so rare thing that no experience with Leird in the fiongertips. Better take the LORA where it are. For example, if You are too lazy to solder DIY: - https://www.ebay.com/itm/LoRa-SX127...728108?hash=item2cc459002c:g:Fz8AAOSw8IpcdUhu for price of 2 and half USD. By the way, that spirallic antenna seems rather good.

 

XBee 868/900? XBee 2.4GHz can achieve quite a range in open space. 1-km is asking for trouble if you lose connection

 

In level of principle, for identic power and antennas efficiency, as lower the frequency, as longer signal is beating through. Especially in case of physical barriers like walls, wood etc. However with this one may loose the speed what for serial data transfer is most crucial thingy, often. Thus, with the appropriate modulation system sometimes the effect may be got far stronger than by change of frequency. And FSK is not in the last place. Yet the algorithm makes an iimpact as well, see, 2,4 MHz NRF24L makes a 1 km in clear field with a deadly efforts, whilst 868 LoRa may get the 3 km even at intra-city obstacles, however both have a FSK and similar power. Yet for battery use efficiency, first are taking average some maybe 10-fold less current (I hesitate to name a accurate number, just it serves a several years with one battery making a one telegram per minute with NRF and LoRa spends the battery about at year with the same once-a-minute telegrams. Probably, one may meditate about 470 MHz??? At least walkie-talkies at that range serves no less than 3km afar. However I havent searched yet, do exist any FSK compatible IC dedicated for that frequency.