by: KA5WNX
Quarter Wave Phased Vertical Antennas
Designing the Phased Verticals
It is said that every time you add 3dbi gain to an antenna system, you double the strength of the antenna in theory.
You see, two or more phased vertical antennas can be considered to be a single antenna in theory. By using two antennas you can feed the antenna in 3 ways.
They are, double stacked (broadside fed), end-fire fed, and collinear fed. By stacking the verticals as seen here in the illustration you will create a figure 8 transmission and reception pattern.
If you end-fire feed the antennas you will get a unidirectional pattern, and a omni directional pattern when collinear fed (one atop another).
Anytime you use two antennas in these patterns, you will need to keep them separated by 1/4 wavelength apart or more to prevent feedback causing high SWR's.
You see, two or more phased vertical antennas can be considered to be a single antenna in theory. By using two antennas you can feed the antenna in 3 ways.
They are, double stacked (broadside fed), end-fire fed, and collinear fed. By stacking the verticals as seen here in the illustration you will create a figure 8 transmission and reception pattern.
If you end-fire feed the antennas you will get a unidirectional pattern, and a omni directional pattern when collinear fed (one atop another).
Anytime you use two antennas in these patterns, you will need to keep them separated by 1/4 wavelength apart or more to prevent feedback causing high SWR's.
1/2 wave
Each leg is 1/4 of one wavelength long. The feed point will provide approximately 72 ohms at the feed point.
The formula for each leg of the ground plane is as follows:
234/frequency in MHz.
At 28.4MHz it would be....
234/28.4 = 8 feet, and 2.75 inches.
The total length of the antenna would then be 16 feet and 2.75 inches in length.
The total length formula for half wave is 468/frequency in MHz
Also the separation between the two phased verticals would also be 468/frequency in MHz .
To get the inches instead of a decimal point, just subtract the feet, and multiply 12 times the decimal point left over.
The formula for each leg of the ground plane is as follows:
234/frequency in MHz.
At 28.4MHz it would be....
234/28.4 = 8 feet, and 2.75 inches.
The total length of the antenna would then be 16 feet and 2.75 inches in length.
The total length formula for half wave is 468/frequency in MHz
Also the separation between the two phased verticals would also be 468/frequency in MHz .
To get the inches instead of a decimal point, just subtract the feet, and multiply 12 times the decimal point left over.
492/frequency
