What is the best way to match a 50 ohm unbalanced line to a 300 ohm balanced antenna at 1.7 GHz? The bandwidth of the matching circuit only need to be 40 MHz or so (~2.4%), but more is better. Intially I was thinking a coax half-wave balun since they are 4:1 transformers, but is this feasible at 1.7 GHz?
yes quite feasible, I use coax baluns just down the band a little way on 1296MHz
be precise in your cutting of the balun length, remember its an electrical half wave NOT a physical half wave
an electrical 1/2 wave will be a little shorter cuz of the velocity factor of the cable you use.
Speaking of which, the best cable for the job would be UT 141 0.141" diameter semi rigid coax