Let's assume I have built a SMA-to-waveguide transition that flares out into a horn antenna. There's no flange between transition and horn, it's made of a single metal sheet. The antenna has tuning screws, and my goal is to find the screw position giving least reflected power.
Obviously, I don't have a suitable VNA with which I could measure the antenna S11 parameter. I do however have an uncalibrated power meter.
Which of the following methods gives best results?
Receiver: Connect power meter to horn antenna, aim it at another RF source, find screw position that maximises power indication.
Circulator: Connect TX to circ 1, circ 2 to horn antenna, circ 3 to power meter. Find screw position that minimises power indication.
Directional coupler: connect TX through coupler to horn antenna, s.t. part of the reflected power is coupled towards the power meter. Tune screws, find minimum power.
The underlying more general question is: given that I don't need accurate absolute S11 or VSWR values, what shortcuts can I take to get the best out of my antenna?