TABLE OF CONTENTS Alan Bensky
The antenna is the interface between the transmitter or the receiver and the propagation medium, and it therefore is a deciding factor in the performance of a radio communication system. The principal properties of antennas directivity, gain, and radiation resistance are the same whether referred to as transmitters or receivers. The principle of reciprocity states that the power transferred between two antennas is the same, regardless of which is used for transmission or reception, if the generator and load impedances are conjugates of the transmitting and receiving antenna impedances in each case.
First we define the various terms used to characterize antennas. Then we discuss several types of antennas that are commonly used in short-range radio systems. Finally, we review methods of matching the impedances of the antenna to the transmitter or receiver RF circuits.
Understanding the various characteristics of antennas is a first and most important step before deciding what type of antenna is most appropriate for a particular application. While antennas have several electrical characteristics, often a primary concern in choosing an antenna type is its physical size. Before dealing with the various antenna types and the shapes and sizes they come in, we first must know what the antenna has to do.
As stated in the introduction, the antenna is an interface between circuits and space. It facilitates the transfer of power between space and the transmitter or receiver. The antenna impedance is the load for the transmitter or...
