Delta loop

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Quad element

 

 

The cubical quad or quad loop is a square-shaped antenna. The gain of a freespace dipole is 2.13 dBi, while the freespace quad element isotropic referenced gain is 3.27 dBi. Thus the quad element has 3.27 - 2.13 =  1.14 dBd (dB dipole) gain:

dipole lossless freespace

quad gain H-plane pattern

 

 

The quad element is nothing more than two stacked, bent, shortened-dipoles fed in phase. The square shape provides 1/4-wavelength broadside spacing between the two short dipole's current maxima.

Delta Loop

The delta loop is nothing other 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, is at or near the delta loop antenna bottom. The single tall support and low feedline 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 or current maxima spacing. The delta loop gives up some of the quad's 1 to 1.2 dB maximum gain over a dipole:

 

delta loop freespace gain

 

 

 

 

The delta loop has 2.78 dBi gain, which is 0.65 dBd gain, in freespace.

 

 

 

 

 

 

 

 

quad gain H-plane pattern

 

 

 

The quad element 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:

dipole over real earth 70 ft height      delta loop over real earth 70 ft apex

 

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 effective height of the antenna considerably, 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:

squashed delta from limited apex height

squashed delta freespace gain

 

 

Vertically Polarized Delta Loop

 

 

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:

 

 

delta loop vertically polarized 70 foot apex

 

 

 

 

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.

 

vertically polarized delta loop vs dipole gain

 

 

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.

 

 

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