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Front to Back Performance of a Hexagonal beam

Lighthouse in pretty sceneDirectional antennas perform better in one direction than others. If you can rotate the antenna, you will be able to target any area of the planet with the best performance of the hexagonal beam. This is a great advantage over fixed wire antennas that have generally good performance but usually in only a few directions of the compass. And it is better than vertical antennas that get poor performance in all directions unless they are over salt water or have an elaborate array of ground wires.

This is not an accident; we want to be able to focus the power in the direction we are transmitting and that is what a hexagonal beam will do. But did you know that the reception of an antenna is generally reciprocal with the transmitting? This means that if you can transmit better in a particular direction, you can receive from that direction better too. But what about front to back performance? What the heck is that?

Your hexagonal beam is just a variation of the Yagi beam antenna. It receives and transmits best in the direction it is aimed. In other directions, it does not transmit well and you really don’t care. But also it does not receive well either and this is usually a good thing. Why? Well, you really do not want to hear the signals from undesired directions because they would interfere with the signals you are looking for in the desired direction. That interference is called QRM. This discrimination of the hexagonal beam for desired directions and against undesired directions is called front to back performance. It is the ratio of signal strength of the front of the hex beam and the rear of the hex beam expressed in decibels or dB. Typically for a hexagonal beam the front to back performance is over ten dB. That is, the signals coming from undesired directions are one tenth of the strength from the desired direction. This means in many cases that strong signals from the undesired direction are suppressed to a much more tolerable level.

Front to side rejection of signals is also a good thing and fixed wire antennas frequently have good front to side rejection. But the problem is that for a fixed wire antenna, the side where the signals are rejected is often exactly where you want to go, such as an island in the south seas. But with a hexagonal beam, you can solve this problem by just rotating the beam to that direction and voila, you now have an amplified signal on both receive and transmit. This is the magic of a directional beam. How is this achieved by a hex beam? Well, the total power radiated from a transmitter is not increased by a hexagonal beam but rather it is focused, much like a lamp with a reflector focuses light.

The hexagonal beam performance is not as narrowly focused as a five element Yagi or even a three element Yagi but in most cases that is an advantage because it means you are not having to constantly tweak the beam direction to work stations from a particular quadrant of the globe. So the front to back performance is very good for a hexagonal beam but generally you can still hear signals well enough to recognize a desired station off the back or side. But not strong enough to interfere with the desired direction.

Modeling indicates that the hexagonal beam which is a two element Yagi beam with an unconventional shape, has front to back performance better than a conventional two element Yagi beam.  So don’t sell the hexagonal beam short when comparing it with other beam antennas. It is a good performer as well as a beam with a small physical footprint.

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