The 1700 to 2400 MHz band (M1 to M6) is a good band for the secondary control channel of air and ground robotic vehicles. Little radios made by Doodle Labs in Singapore are popular and this is an antenna solution specifically aimed at the Meshrider radios ( https://doodlelabs.com/products/mesh-rider-radios/nano/ ). I employed Ye Olde Fashioned technique of carving an antenna out of double sided board with a ruler and a scalpel, using copper tape for little optimization experiments and fixing the mistakes. Once one has the hang of it, it is possible to carve an antenna by hand in a day, vs waiting two weeks for a PCB factory. Etching it is good, if you have the chemicals and safety paraphernalia on hand and know what you are doing. This application requires an aerial system with a few important properties, notably: Wide bandwidth of 20% or more with a centre frequency of 2 GHz. Directivity of 8 to 12 dBi, to reduce clutter and interference from the surroundings, without making it
Autonomous planes, trains and cranes...