Chapter 5

Explaining Phased Verticals to Others

Let’s understand how phased verticals work so we can explain it to others.

Our Quadrature Set Up

Quadrature Phasing—Using the Christman phasing scheme.

Two identical 1/4-wavelength verticals are spaced 1/4-wavelength apart and fed through a relay that adds an extra piece of cable into one of the vertical’s feedlines. When the relay energizes, the extra cable goes into the other vertical’s feedline. The spacing and extra cable provide the spatial and temporal delays needed to phase the verticals in quadrature.¹

Creating the Spatial Delay

The spatial delay comes from spacing the verticals 1/4-wavelength apart. When excited by the same signal, the electric fields emitted by each vertical arrive at the other vertical 90º behind the excitation signal. Click the image to understand.

The verticals are the two vertical lines. Below them is the polarity of the radio signal exciting them. The green arrows designate the passage of time every 90º of the signal’s oscillation. The yellow arrows show the polarity of the electric field radiated by one vertical upon its arrival at the other vertical. We can see these electric fields are 90º behind the excitation signal.This is because over the time it takes the electric fields to travel from one vertical to the other at the speed of light, the excitation signal advances 1/4 the way through one of its oscillations.

Over the time it takes these electric fields to span the 1/4-wavelength gap between the verticals, the excitation signal advances 90º of its 360º oscillation. This causes both verticals to be surrounded by electric fields that are 90º behind those they, themselves, are radiating.

Creating the Temporal Delay

After this, all we have to do is delay the signal being fed to one of the verticals. This is accomplished by inserting an extra 1/4-wavelength of cable into its feedline. This delays the signal feeding the vertical by 90º which causes it to now be in-phase with the electric fields sent to it from the other vertical. That vertical, in turn, now perceives the electric fields from the delayed vertical as being 180º out-of-phase with its excitation signal.

This Changes the Aerials Pattern

The electric fields around the “out-of-phase” vertical cancel each other out, producing the null in the phased vertical radiation pattern.² Electric fields around the “in-phase” vertical add-up, producing its broad, forward lobe. When the relay is energized, the verticals exchange roles which reverses the array’s directivity.³

Phased Vertical Pattern—On the left, we are looking down on the verticals and see that the two verticals emit energy in one compass heading. On the right, we are standing on the ground looking at the sides of the verticals. These plots are for phased verticals installed over land. When installed over salt water, the plot on the right extends down to the X-axis.

This might be the most straightforward way for readers to explain how their phased verticals work to others during on-air demonstrations.

1. Which essentially means “quarters”. Everything has to do with 90º.

2. By “the electric fields” we mean (i) the electric field which has traveled from the other vertical, and (ii) the electric field being radiated by the vertical.

3. The array points in the direction of the vertical with the extra cable in its feedline.