# Delta loop

The * cubical quad* or

**is a square-shaped antenna. The gain of a**

*quad loop*freespace dipole with typical negligible copper losses is 2.13 dBi. Freespace quad element isotropic

referenced gain is 3.27 dBi. Thus the quad

element has 3.27 – 2.13 = 1.14 dBd gain over the dipole. We call

this 1.14 dBd gain.

Dipole

gain freespace

Quad element gain freespace:

The quad element is actually two stacked, shortened, bent dipoles

fed in phase. The fed dipole feeds power to the unfed half through the

attached ends. The square shape provides 1/4-wavelength broadside spacing between

the two short dipole’s current maxima. This more than offsets the immeasurable

gain decrease caused by bending the “dipole” antenna. The maximum possible gain

of a square quad element over a dipole at the same mean height is just over 1

dB. This peak gain difference occurs in freespace or at an optimum “sweet”

height. The “sweet” heights occurs where the dipole pattern has a strong broad

direct overhead lobe at heights around .75 wavelength. The quad has no gain over

a dipole, and actually can have loss, at heights where the dipole has a vertical

pattern null, such as 1/2 and 1 wavelength. The standard horizontally polarized

quad element is less effective than a dipole at mean heights below 1/2 wave.

Stacking Gain Graph

From this we see gain of two current maximas spaced .25 wavelengths is about

1 dB over a single element by itself. This agrees with models.

## Delta Loop

The delta loop is nothing more and nothing less than a reshaped quad element. The delta is pulled to a point at

one side, generally the apex. This either angles one of the high current area’s

angles to 120 degrees, which further reduces quad element gain, or it makes two

bends in high current areas (typically when vertically polarized).

**Advantages**

With a single apex point, the delta loop requires only one tall support. The

feedpoint, where the heavy coaxial line connects, can be placed at or near the delta loop

antenna bottom. The single tall support and low feed line connection point makes

delta loop construction and installation exceptionally simple and fast.

**Disadvantages**

Unfortunately, the delta has a pulled-in shape that reduces effective current

maxima area and current maxima spacing. The delta loop gives up some of the

quad’s 1 to 1.2 dB ** maximum** possible gain over a dipole:

The delta loop has 2.78 dBi gain, which is 0.65 dBd gain, *in freespace.
Freespace is the point of maximum delta gain advantage over a dipole at the same
mean height. That gain advantage is 0.65 dB. *

The quad element, on the other hand, has 3.27 dBi gain, which is 1.14 dBd gain, in freespace.

## Delta Loop vs. Dipole Over Earth, with fixed support height

Let’s assume we have a typical 70-foot tower or trees, allowing a maximum

height of 70 feet over typical flat, clear, earth. A dipole and delta loop have

the following pattern and gain:

At 28 degrees elevation angle, the dipole has 8.09 dBi gain. At the same 28

degree elevation angle, the delta loop has 4.57 dBi gain. Even at delta

loop’s maximum

gain angle of 43 degrees, the delta loop has only 5.5 dBi gain.

- Compared to an inverted Vee dipole, or dipole, the delta loop lowers
of the antenna considerably,*effective height*

increasing wave angle - The more compact area of the triangular-shaped full wave loop further reduces

the already small gain available from a full wave loop

**Flattened Delta Loop**

The Delta loop or quad loop effective operating height is really the mean

height of current maxima locations. With a 70-foot tall support, a delta or quad

loop’s antenna elevation pattern is one of much lower actual height. Often,

because height is limited, delta’s are installed in a “squashed” form. This

further reduces the maximum available gain of 0.65 dB over a dipole. The delta

starts to behave increasingly like a simple folded dipole as it is increasingly

squashed. It eventually becomes a folded dipole.

This is a delta squashed to 0.15 wavelength apex to base line height

difference. It has “horizontal polarization” (complimentary current maxima

in straight areas, apex feed) in freespace has about 0.1dBd gain:

## Vertically Polarized Delta Loop

Feeding the Delta slightly up from the corner, around 1/4 of the side length

up, results in vertical polarization.

Note the current minimum is at the apex, and in the middle of the bottom.

The often used “corner feed” skews the current and polarizations.

Feeding the delta loop on a sloped wire about 25% up either side from a

bottom corner produces the

following vertically-polarized pattern:

At 28 degrees elevation, the delta loop has -.53 dBi gain. This is -8.62 dBd

gain, or almost 9 dB weaker than a dipole.

At 16 degrees elevation, the vertically polarized delta has 1.37 dBi gain.

When compared to a horizontally polarized dipole at the same maximum height, the

delta has -4.72 dBd. Even at peak gain angle of the vertically polarized delta,

the

horizontally polarized dipole still has more gain.

The vertically polarized delta does not equal the dipole until around 5

degrees elevation angle.

Antennas radiate because of current over linear spatial distance. Antennas

obtain gain through proper spacing and phase of current maximums.

1.) When antennas are folded in a manner decreasing

current maximum spacing, or decreasing the linear (in line) spatial distance of

high current area, we reduce gain.

2.) When antennas are installed above earth, effective

antenna height is somewhere between peak height and minimum height of high

current areas.

3.) These effects apply to all antennas, and to arrays of

elements in more complex antennas.