Wow, where to start. Design: Many designs out there already, you would normally borrow one and adapt it for your location, application and frequency. There is an enormous difference between an antenna at 50KHz or 50Ghz, so adaption has to be thought through. You may need to do a finite element analysis (NEC for example)if the design is new, or an adaption is for a different frequency. There is still quite a bit of work being done on GHz antennae breaking new ground, you need access to IEEE journals and the like to find them. Building: Again there is a big difference between an antenna at 50KHz or 50GHz. The former is normally a wire strung up between some large poles, the latter might be planar on a ceramic substrate. The build and install are normally related, since the design often makes assumptions about the end application. Evaluating: These days vector network analysers are often used for measuring antenna characteristics, the prices have dropped, but they are still an expensive item if you need a wide frequency range. In the end real world testing has to be done, once the antenna is correctly matched, a transmit receive pair would be used, the power fixed on transmit, and another antenna deployed about the site on a receiver to measure received power. This would be done in an anechoic chamber where feasible to remove the effect of ambient RF radiation.
This is all very simplistic. For the frequency of interest you would normally do an internet search to find designs that have been used regularly and are well characterised.
Cheers,
Richard
