ANTENNAS (Antena)

Up until now, we have not asked ourselves how EM waves are produced. Recall that electric
charges are the sources of EM fields. If the sources are time varying, EM waves propagate
away from the sources and radiation is said to have taken place. Radiation may be
thought of as the process of transmitting electric energy. The radiation or launching of the
waves into space is efficiently accomplished with the aid of conducting or dielectric structures
called antennas. Theoretically, any structure can radiate EM waves but not all structures
can serve as efficient radiation mechanisms.
An antenna may also be viewed as a transducer used in matching the transmission line
or waveguide (used in guiding the wave to be launched) to the surrounding medium or vice
versa. Figure 13.1 shows how an antenna is used to accomplish a match between the line
or guide and the medium. The antenna is needed for two main reasons: efficient radiation
and matching wave impedances in order to minimize reflection. The antenna uses voltage
and current from the transmission line (or the EM fields from the waveguide) to launch an
EM wave into the medium. An antenna may be used for either transmitting or receiving
EM energy.

Bab 13 ANTENNAS (Antena) 3rd element sadiku (buku berbahasa inggris, dilengkapi contoh (soal+pembahasan )

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