Short one today, as we had a test and Jerry talked quite a bit on unrelated stuff. Also, sorry about the format, the keyboard I had was sticky and I could not type well, I had to copy/paste from the powerpoint slides.
Antenna
Characteristics
Types, sizes and shapes
Passive antennas
–The most common type
–Constructed of a piece of metal,
wire, or similar conductive material
–Does not amplify the signal in
any way
–Directional gain
•Passive antennas radiate the RF
energy supplied by the transmitter in one direction
•Exhibits an effective gain that is similar to amplification of
the signal
–Essentially passive antennas with
an amplifier built-in
–Amplifier is connected directly
to the piece of metal that forms the antenna itself
–Most active antennas have only one electrical connection
•RF signal and the power for the amplifier are supplied on the
same conductor
Size and shape of an antenna depend on:
–Frequency on which the antenna will
transmit and receive
–Direction of the radiated
electromagnetic wave
–Power with which the antenna must transmit
•Antenna size is inversely proportional to the wavelength it is
designed to transmit or receive
–Lower frequency signals require larger antennas
Omnidirectional antennas
–Used to transmit and receive
signals from all directions with relatively equal intensity
–Longer omnidirectional antennas have a higher gain
•Directional antennas
–Transmit a signal in one
direction only
–Yagi antenna emits a wider, less
focused RF beam
–Parabolic dish antenna emits a narrow, more concentrated beam of
RF energy
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