Raspberry Pi 3 Model B+
The ANT500 is a telescopic antenna designed for operation from 75 MHz to 1 GHz with a total length that is configurable from 20 cm to 88 cm long. Each ANT500 is made of stainless steel and features an SMA male connector, rotating shaft, and adjustable elbow.
A GSM antenna really very fine and compact.
GSM / Cellular Antenna Quad Band Slim Sticker Type 3dBi uFL