Unusual Antennas

Unusual Antennas

There are many other antenna types. Most of these are beyond the scope of this report, but knowledge about some may be useful for LMR users. While not as commonplace as wire or rod antennas, aperture antennas are by no means unusual. These antennas are implemented as an opening in a relatively large, conductive metal) surface.

Figure 24. A vertical-plane radiation pattern without “tilt”

Figure 25. A vertical-plane radiation pattern with 8/ “tilt”

The simplest aperture antenna is the slot antenna, which is equivalent to a dipole. As shown in figure 26, it is a long, narrow opening with terminals located at the middle of the long sides of the slot. This simple slot and more complex versions are well-suited to covert operations. They can be located on vehicle surface and concealed behind a cover of thin insulating material. Slot antennas are common on aircraft and missiles.

Figure 26. A slot antenna

Not so much antenna types as antenna features, broadband and multiband antennas are the result of design efforts to make an antenna perform well over a wide band of channels. There may be a trade-off in making an antenna broadband, such as a reduction in gain or an increase in physical size. The usual design goals for this type of antenna are to make the gain and radiation pattern, as well as the terminal impedance, relatively constant over the frequency range of operation. The log-periodic array is an example of a broadband antenna.

Multiband antennas are designed to operate on several bands, for example, at both VHF high-band and UHF. These antennas often involve clever designs where one part of the antenna is active for one band, and another part for a different band. Again, there will be compromises. The antenna may have lower average gain or may be physically larger than an equivalent single-band antenna.