LOOP YAGIS

Loop yagis are similar in form to a quad antenna. Most quad antennas built for low frequencies have square form factors. Loop yagis employ round loop elements. Directive Systems loop yagis utilize brass driven elements fed with UT-141 semi rigid teflon coaxial cable. The feed system is inherently weatherproof, as any exposed teflon at the feed will not soak up any water. The only way for water to enter the system is through leaking coaxial connectors. (So what else is new?) A typical loop yagi driven element is shown below.

3318LYARM DRIVEN ELEMENT

The loop yagi can be either vertically or horizontally polarized. The polarization is determined by the "quad" feed system. In the photo above, the connector is located below the main boom. The actual driven element is "fed" at the top of the full wave loop. The maximum voltage points are 90 degrees away from the feedpoint. This puts the high voltage points on the left and right of the loop. This is horizontally polarized. If the entire antenna is rotated by 90 degrees, the polarization will be vertical. You can note that there are a second set of holes on the rear of this antenna, and the mounting bracket may be installed in the second set of holes for vertical polarization.

CONNECTOR ASSEMBLY 3318LYARM Front view

The connector assembly is clearly visible in this view. The type N rear "hood" is sealed with electronic grade RTV, and the UT-141 coax cable is sweat soldered to the hood making a great hermetic seal to keep water from places where it does not belong.

Loop elements can provide enhanced gain over conventional yagis, but only for very short boom lengths. Once you install several elements of either rod or loop elements, the aperture of either antenna is large enough that any gain advantage of the loop or quad element disappears, and both antennas will provide similar gain figures for a given boom length. There are advantages that tip the scales in favor of loop elements. At higher frequencies, full wave elements provide a lower Q structure than half wave rod elements. Half wave elements are also subject to considerable variation due to the end capacitive effect of rod elements. This means that loop elements are much more forgiving to production tolerances. While it is possible to make good conventional yagis at 2 GHz, the tolerances involved make them almost impossible to produce without a micrometer and sandpaper! Loop elements have been successfully used at 3456 MHz with negligible variation from antenna to antenna. In fact loop yagis have been made by several experimenters on both 5.7 and 10 GHz! Such exercises are not really possible with conventional yagis. The net effect is that loop yagis provide consistent performance at much higher frequencies than conventional yagis with rod elements. Extensive testing of our antennas for 3456 MHz proves this. Frequency response errors at 3.4 GHz are negligible. Consistency is good! In fact, loop yagis provide a better solution than parabolic dishes at 3456 MHz for gains up to about 30 dBi or so. The wind loading of parabolic antennas is about 6 to 8 times greater than a comparable gain loop yagi. Most amateur tower installations are not rugged enough for a high gain parabolic dish, but they can support a loop yagi (or more) with no problems.

We have included some actual patterns taken on a precision antenna test range in an anaechoic chamber. The antenna is the 45 element standard loop yagi popular on 1296, 2304, and the 3456 MHz. bands. This particular model is the 2304 version, the 1345LY. The patterns are for a quad array of 1345LYs, and they demonstrate the typical patterns that can be attained when stacked at the factory settings. Note that the sidelobes are quite low beyond the first sidelobe in the E plane. The H plane has a few more lobes, but the rest of the pattern is remarkably clean. Other lobes are at least 25 or 30 dB down for the most part.These plots were made at 2335 MHz, just above the band center for this antenna.

4 X 1345LY POLAR PLOTS E and H Planes

Directive Systems loop yagis are available in many sizes. You can look through the antenna directories on this web site and find the specifications that match your requirements. It is a simple matter then, to click on the accompanying link to view the complete antenna specification sheet or operating manual. Please be patient if the link is not operative. We are upgrading these links constantly with our goal to have much more information available to you.

 

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