UHF Panel Antennas - Equal vs. Un-equal bays

UHF Panel Azimuth Pattern Considerations

There are two major ways of controlling azimuth pattern shape; uneven number of panels with equal power dividers in the feed system and equal number of panels on all sides of the tower and adjust the power division in the feeder system. The obvious positive for using an unequal number of panels is cost savings. But there is a trade-off (isn't there always a trade-off for the cheaper way out?).

The ELEVATION PATTERN is not consistent in all directions with un-equal numbers of panels on the tower. The null fill and electrical beam tilt may, likewise, not be equal in all directions. At some azimuthal directions, nulls may form due to the interference between the radiation patterns from adjacent faces, even though these nulls do not show up in the elevation patterns as determined directly normal to the tower face. These nulls will generally form close to the tower (less than 1 kM), and as such, may not be a problem in some installations.

The formation of these nulls is due to the unlike-characteristics from adjacent faces of the tower:

 

Graph

 

Graph

The graphs show the relative radiation from a four bay and a three bay antenna array. At about 30 degrees below the horizon, the fields from each face are about the same amplitude, but are of opposite sign. Therefore, they would cancel, producing a null. This would happen at an azimuth about halfway between the two panels.

Click the link below to see a simulation of going around and un-equal array while plotting the elevation pattern:

 

 

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