Actually either will work but there are practical and electrical differences to consider. Stranded wire with a diameter over 16 AWG is easier to work with since thicker solid wire is too stiff. But either type will work for a PIT tag antenna. Solid and stranded wire have different electrical characteristics.
Solid Core Cable uses one solid copper wire per conductor. It is used for permanent infrastructure links between two points. It has low attenuation and costs less than stranded cable. Its design suits horizontal or vertical cabling routes and should not be disturbed once installed.
Stranded Cable uses multiple strands of wire wrapped around each other to form one conductor. It is considerably more flexible than solid core cable, consequently it is suited to applications where the conductor may be moved during use. It has higher attenuation so better used over shorter distances.
