wirelesstutorial

Antennas Quite simply stated, the antenna is what puts the signal into the air and gets it back out again. It does this by converting the electrical energy being delivered to the antenna into electromagnetic waves that are then able capable of traveling over long distances. Antennas are reciprocal in nature, which means that they are capable of both transmitting and receiving a signal equally well. This allows the same antenna to be used for both transmission and reception of RF signals. When discussing different types of antennas, there are several characteristics that are used to describe an antenna's top-level behavior and performance. These characteristics are gain, radiation pattern, resonant frequency, polarization, and efficiency. The combination of these characteristics determines the types of applications in which an antenna can be effectively used. Conversely, if the desired application for an antenna is already known, these characteristics can be used to help select ...

The transceiver handles the process of converting the low-frequency baseband signal into a higher-frequency RF signal though a process called upconversion. Within the transceiver, an RF carrier signal is generated at the frequency that will be used for the final RF signal. This RF carrier is then combined with the baseband signal to upconvert the low-frequency baseband to the higher RF carrier frequency. Figure 2-2A shows both the low-frequency baseband signal and the RF carrier signal that are used in the upconversion process. Figure 2-2B shows the result of an ideal upconversion where the modulated RF signal is identical to the original baseband signal; except, it is now centered at a much higher frequency. In addition to upconverting outgoing signals, the transceiver also downconverts incoming RF signals to low-frequency baseband signals. The downconversion process is the inverse of the upconversion process. The process of upconverting a modulated baseband signal into a modulat...