Multiplexing an antenna
What you're probably looking for is a SPDT RF switch of some sort.  You can find RF relays that are designed for low loss and good isolation.  These are usually a few hundred dollars, but you may be able to find one on ebay or surplussed for cheap. The driving of a relay is very straightforward, but may require higher voltages than anything else in your system. Another option is using PIN diodes to act as RF switches. I'm not familiar with actual applications, but it may be easier or cheaper to try and make a switch.

At the frequencies you're interested in, a simple mechanical relay may give you issues with loss and isolation. I'm also guessing you couldn't manually swap out the antennas either. Good luck.