The horn antenna is similar to the parabolic dish in theory. It is another highly directive antenna that can be made quite large to achieve heavy gains. Furthermore, the horn is actually not a true antenna, in and of itself. Just like the dish, it relies on another basic antenna incorporated into the horn to empower the complete horn assembly.
The Elements of a Horn
The horn consists of several parts. First, there is the flared element, the actual horn itself. The horn, in turn, is connected to a length of waveguide. The waveguide, in turn, is powered by a simple antenna — usually a monopole. The monopole driving the horn is straightforward, and the waveguide itself is also basic. The relation between the horn and waveguide, however, provides for some interesting results.
First, the tapered horn is necessary, for if the waveguide was simply left open-ended, a sharp impedance mismatch would occur at the end of the waveguide, causing reflections. The horn, then, allows a transition between the end of the waveguide and the open air. Not surprisingly, the design of the horn can be used to set the impedance of the system.
The Gain of a Horn
The parabolic dish works by reflecting a vast area of signal and reflecting it to the feed antenna. In the same way, the horn “scoops” a large area of signal and funnels it to its feed antenna. The result is a highly directional antenna with a high gain.
The gain of a horn can be increased simply by widening the horn, which allows it to intercept a larger area of signal. Just as with the parabolic dish, however, there is a limit to the amount of gain that can be achieved this way. The problem is that, as the horn grows, so grows the opportunity for and the detrimental effect of design flaws in the manufacture of the horn.
Advantages of Horn Antennas
As long as the horn is not too massive, the horn antenna is actually fairly easy to manufacture. It is a good choice where an inexpensive, simple, directional antenna is required. There are many types of horns as well, allowing for greater flexibility in applications.
The horn is also a broadband antenna, where the low frequency is size-dependent. This is why horns are more commonly used for high-frequency antennas than low-frequency ones.
All in all, it is not surprising that the horn is a popular choice for high-gain antenna applications.
ARSI 