TECHNICAL NOTE / STACKING / PHASING
Two antennas do not become a superior array simply because their feed lines join together. Identical polarization, direction, amplitude, relative phase and mutual coupling determine whether stacking improves the intended pattern.
Equal feed power is only the beginning
For identical antennas in a symmetrical two-way arrangement, equal electrical path lengths are a useful baseline. An unequal three-way combination can distribute power, but using dissimilar 6- and 11-element antennas invites differences in element pattern and phase center. A commercial power divider is not automatically a phasing solution.
What determines stack spacing
- Individual antenna beamwidth and gain; how much vertical or horizontal pattern narrowing is desired.
- Electrical position of each antenna and mutual coupling.
- Feed-line loss and relative phase across the desired bandwidth.
- Mast stiffness, rotor load, wind, clearance and mechanical safety.
What to measure
Check individual antenna match, each feed path, combined input match and actual far-field direction. A perfect 50-ohm input can conceal unequal amplitude or a deep pattern null. Compare designs at the operating frequency with the whole support structure included.
For K0AXX, phased Directive Systems loopers at 902 MHz and higher-gain 1296 MHz antennas remain active design topics, with dimensions and performance to be validated rather than declared final.