I'm building a helical antenna at 1.7 GHz from scratch. Theory says that its characteristic impedance is 140 Ohm. The RF transmission line is 50 Ohm so there has to be an impedance transformer in between. What is the proposed custom implementation of such a transformer? I have come across the LC circuit as a possible transformer, but is it enough for 5 MHz of bandwidth that i require from the antenna? What's the simplest transformer that will do the job for me?
Thank you for your time