In a very basic sense, the radiating element of the Yagi is the only part that actually receives a signal. The other components bend and shape the pattern of RF energy for that single element. It works something like this: A transmitted signal comes up the cable and leaves the driven element. It hits the reflector and bounces toward the front of the antenna. Each directional element then carries that signal further while making it stronger.When the signal leaves the last element of the antenna, it’s focused in a single direction. The reverse is true for signals being received by the antenna.

The antenna you will build in this chapter is a Yagi antenna. There is a driven element, a reflector, and two directional elements.While the Yagi in Figure 2-8 uses aluminum and fiberglass, you will construct yours of steel and wood.

A parabolic antenna is very intuitive when you see one, like the one shown in Figure 2-9. The rear portion of the antenna is a curved reflector that bounces incoming signals into the focal point of the curve. A small antenna is placed at the focal point and becomes the antenna feed point. The feed point usually has a half-wave dipole or other basic antenna. For transmitted signals, the reverse is true as signals bounce off the reflector out into the distance.

A panel antenna is an array of rectangular flattened dipole antennas arranged in a pattern on a panel. These flattened dipole antennas are sometimes called patch antennas. Because the patches are laid out in an array, the shape of the radiation pattern is aligned and focused in one direction. The more patches in the array, the more focused the antennna and the higher the gain. Figure 2-10 shows the inside array of a very high-gain panel antenna.

Panel antennas work well in one direction off the face of the antenna. The metal backing surface is employed as a reflector and mounting point for the panel antenna. The face of the antenna is often covered in nonconducting plastic for weather proofing and to help prevent damage.

A waveguide antenna is very strange indeed. This type of antenna is actually formed by the space and the surface surrounding an electrically conductive enclosure. The size and shape of the waveguide determines the frequency at which the waveguide will operate best. A small driven element in a precise location near the rear of the waveguide creates the signal that is shaped by the metal surface of the enclosure. The shape of the enclosure directs the beam pattern outward, away from the opening. Figure 2-11 shows a basic homemade waveguide antenna made from a tin can. Waveguide antennas are often built from aluminum. However, a tin can is a very good conductor, and it’s the perfect size and shape for the waveguide antenna you will build in Chapter 3.

Antenna polarization stems from how an antenna radiates energy. The design of an antenna forces certain physical and electrical characteristics. As radio frequency (RF) energy is shaped and radiated by the antenna, the antenna changes the shape and beam pattern of the RF. Antennas are usually designated with vertical or horizontal polarization. At this point, the important thing for you to know is that polarizations like each other. For example, a vertically polarized antenna will work best receiving signals from another vertically polarized antenna (vertical-to-vertical). In fact, the signal strength can be 100 times less if you use mismatched polarization (vertical-to-horizontal). You can use mismatched polarization to your advantage when working with closely placed antennas. The solar-powered repeater you will buld in Chapter 9 uses two antennas mounted on the same pole.To help keep them from interefering with one another, they are placed in opposing polarizations (horizontal and vertical). The end-result of all this polarization talk is that you will want to hold your antenna vertically upright (vertically polarized) to pick up a typical store-bought access point (which is also vertically polarized).When we say “vertical” we mean that the paperclips are sticking straight up and down. “Horizontal” is when it is flat as compared to the ground.