"Jerry Martes" wrote
A properly done colinear array of 8 half wave elements will sure have a
highly directive pattern in the Elevation plane. With some luck and low
loss components you might get 8 or 9 dBi. But, the pattern will have a
pattern max thats broadside to the axis of the colinear array at only one
frequency. That pattern max will squint up and down (with respect to the
horizon) as the frequency varies from that center frequency.
_______________

The change with frequency in the angle of the elevation pattern maximum
field is the result of the varying relative r-f phase vs the operating
frequency that is applied to the radiating elements in this design.

This can be eliminated by using a vertically stacked array of identical
radiators fed via an n-way power divider, whose output connects to feed
cables of equal electical lengths to each element of the array. The
directivity (gain) and sidelobe distribution of this type of array will
change with operating frequency, but the elevation angle at which the peak
field is directed will remain the same, regardless of the input frequency.

This approach is used in broadcast transmit antenna designs giving good
signal coverage over large sections of the UHF TV band, or the entire FM
band.

RF