Our May 1996 Beam Antenna Design results proved to be as interesting as we had guessed they would. We had previously experimented with and analyzed omni-directional antennas so as to get a better idea of antenna aperture as observed on a simpler radiating structure. At one of our pizza meetings a few months ago we discussed in general the idea of now doing assessments of uni-directional beam antennas. We wanted to be able to compare the gain figures of not only one uni-directional antenna compared to another, but also these same uni-directional antennas against omni-directional antennas with which we had become familiar.

All antennas develop signal gain as a result of their aperture area size. This is true of antennas no matter whether they are uni, or omni directional radiators. Aperture area merely means the area size of the radiating structure as it appears as a point in space. A half wavelength dipole represents an antenna of a given aperture size. If a reflecting element (a reflector) is placed behind that dipole a two element beam of larger aperture size and consequential gain is the result. If then a third element, a director is added, an even larger aperture antenna is created with yet even higher consequential gain. The same is also true of an omni-directional antenna. A 1/4 wavelength ground plane has a fixed aperture. A 5/8 wavelength ground plane has larger aperture, and higher signal gain. A detailed mathematical explanation of this function can be found in John Kraus's book, "Antennas".

For our purposes we used a much simpler formula to appraise or rank the aperture area of the beams measured. We described them in two dimensions, length and width. Simply stated all of the antennas we compared were either 1/4 or 1/2 wavelength wide, by "X" inches (or centimeters) in length.

The wavelength as measured at the lowest frequency on the band (as is the convention) is computed thusly. Velocity of propagation divided by frequency equals the wavelength. This would be 300/144 = 2.08 meters. If we then multiply this answer by 39.37 inches, which is the number of inches in one meter, we find that the wavelength of 144 MegaHertz (MHz.) in inches is 82.02 . A 1/2 wavelength Yagi-Uda antenna is 41.01 inches wide, and a Cubical Quad antenna is 1/4 wavelength wide or 20.51 inches wide. If we take either of these width constants as is appropriate and multiply it by the antennas boom length, we will arrive at a workable constant for assessing antenna aperture size. If we then compare this size against the gain figure realized we can state which of the antennas has the smallest aperture area for an observed signal gain figure.

The five antennas measured were a multi-element "Skeleton Slot" yagi of about 1 wavelength boom length, a 4 element Cubical Quad the design of which was published in our first edition of R&D, a 4 element Yagi-Uda with a 50 inch boom, a 4 element Quagi with an 85.5 inch boom, and a 2 element Cubical Quad with a 20.5 inch boom. The comparative gain figure of each of these antennas was compared and measured by the following means.

A signal source of .0001 Watts was fed to a typical copper "J" antenna at the far east end of our dry lake bed antenna range. A second "J" antenna was briefly installed at the far west end of the dry lake on the same mast and at the same height as the test antennas would be mounted. These are the same "J's" that we have used as standards for our previous omni-directional antenna tests. The resulting signal measured on the logarithmic "S" meter scale of our Yaesu FT-736 transceiver was 1.9, well below the Automatic Gain Control (AGC) compression level of the transceivers receiver. To assess the gain of each beam tested, an calibrated amount of signal attenuation was inserted to match this same S 1.9 reading. The attenuators used are the manufactured products of both Hewlett Packard, and the Allan companies. The table below shows the measured aperture area as described above, and the resultant gain observed.

Antenna and fabricator                Aperture     Gain

Skeleton Slot fabricator unknown      50454        25 db's

4 Element Cubical Quad by WA6BFH      1364         18  db's

4 element Quagi by WA6BFH             3506         16 db's

4 element Yagi-Uda by AC6SX           2051         15 db's

2 element Cubical Quad by WA6BFH      420          14 db's

Let me say right up front, we are not stating that these readings are or should be considered as dBd (Decibels as compared to a dipole)! We have in the past considered our J antennas as simply "end-fed dipoles". We now consider this assessment to either be naive, or some refractory mechanism was adding gain to our resultant measurements.

In 1976 the 4 element quad mentioned above was measured at 10 dBd. If we subtract the 8 dB's measured above that figure for that antenna as well as the others, we may have some better believable numbers. In fact this makes the 2 element wide spaced quad come in at 6 dB's. This is a figure often referenced for that sort of antenna. The 4 element Quagi then comes in at 8 dB's, the Yagi-Uda comes in at 7dB's, and the Skeleton Slot at 17 dB's. All of these are quite believable. The next question to answer of course is, where did the 8 dB's come from? This is a question that we want to answer in October.

Speculation suggests two possibilities. There is a problem with the reference antenna. In retrospect this seems possible. Another possibility is that some refractory nature of signals reflected from the source antenna down to the lake bed, and back up to the test site caused this effect.

In October we intend to look once again at these same antennas with two factors being changed and analyzed. 1) We will use simple dipoles as the reference antennas, and compare the signals against the J's. 2) We will check the antennas at a much closer elevation to the dry lake to rule out any refractory gain. We should also have several additional antennas to also inspect and assess! Build a design of your own!

So the last question is, which antenna won this contest. If we take our aperture figure and divide it by the gain of the antenna, the following numbers will result.

Skeleton Slot = 2018.16      Looks like the 2 element quad provides the
4 element Quad = 75.78       best gain over size.     
4 element Quagi = 219.13     Which antenna would you want at your station?
4 element Yagi = 136.73
2 element Quad=30