DIAMOND STACKING F0R MORE GAIN (DUBUS 3/2010)

by Slobodan Bukvic, YU7XL, yu7xl@nadlanu.com

Always looking for better performace, I have tried many different configurations. One deserves to be more widely known, because it helps achieving extremely low antenna noise temperatures.

Instead of classic style of stacking where antennas are placed side by side or one above the other, the antennas are mounted diagonally, or in diagonal configuration, as shown on figure 1.

The results are very interesting. Higher gain and much lower noise temperature are obtained. Let me demonstrate this by an example using two of my LFA yagi models – Y21105XL7B and Y20805XL6.

LFA ANTENNA Y21105XL7B

The radiation pattern (no losses) of a single Y21105XL7B antenna is in the following figure 2:

Fig 2

For a classic H-stack arrangement the optimum spacing is 340cm horizontally and 300cm vertically. Figur 3 shows the resulting radiation patterns, assuming no-losses:

Fig 3

Now look at the pattern for a diamond configuration. with a horizontal spacing of 420cm and a vertical spacing of 530cm, again assuming no losses (Fig. 4):

Fig. 4

LFA ANTENNA  Y20805XL6

Here is the radiation pattern of a single Y20805XL6 antenna (Fig. 5, no losses):

Fig. 5

For a classic H/stack arrangement the optimum spacings are 280 cm horizontally and 260 cm vertically. Here are the radiation patterns for no-loss condition (Fig. 6):

Fig. 6

Finally, look at the pattern for a diamond stacking configuration with a horizontal spacing of 260cm and vertical spacing of 540cm (Fig. 7):

As you can see, side lobe supprssion is much much better and antenna gain is much higher. In fact here are four side lobes which are invisible on the 2D patterns. They are located between the horizontal and vertical planes at 45 degrees (see Fig. 8), but these four needle-like side lobes do not contribute much to the overall antenna temperature. The results table shows that:

Not every diagonal stacking arrangement gives good results. Beside the two above mentioned forms, the other possible configurations are shown in Fig.9 below:

Not every antenna design can give good results, just those with very good side lobe suppressio. Finally, as the boom length increases, the difference in performance between the two stacking arrangements becomes less. Therefore, the use of  the diamond stack is only justified if the boom is shorter then 3 or 4 wavelengths.

Every hard-core VHF amateur will immidiately see the problems arising from this configuration. The most severe is the difficulty of elevating such a system, and thereforeit is not suitable for serious EME work. The second problem is the mechanical imbalance in the system.

I think the most likely use of four-diamond stack will be in VHF/UHF contests, because of the higher gain and much better receive performance, because the horizontal main lobe is wider, and QRM from/to nearby stations is reduced. In this case, look at the patterns of Y20805XL6, stacked in the diamond format at 260cm horizontally and 540cm vertically. The main horizontal lobe is 26,2 deg wide, and the vertical one is just 14,8 deg wide! Ideal for tropo, contests, etc.

The explanation of how the diamond stack works can be seen in Fig 10:

As seen on the drawing for the diamond stack, the radiation patterns for left-side and right-side antennas (elipsoides) are touching each other. It is obvious that the antenna apertures in a diamond configuration are better utilised, giving higher gain, better side lobes suppression and, finally, preserving the width of the horizontal main lobe. Table 1 explains all!