CHAPTER 14: Antennas and Wave Propagation Flashcards
The interface between the transmitter and free space and between free space and the receiver is the ______________.
Antenna
A radio signal is called an ___________________wave because it is made up of both electric and magnetic fields.
Electromagnetic
A radio signal is called an electromagnetic wave because it is made up of both electric and ________________.
Magnetic fields
Whenever _________________ is applied to the antenna, an electric field is set up.
voltage
This voltage causes ____________ to flow in the antenna, producing a magnetic field.
current
The strength and direction of the magnetic field depend upon the _______ and ________ of the current flow.
magnitude and direction
__________________ is the dielectric constant of the material between the two conductors.
Permittivity
During one-half cycle of the ac input, one wire is positive and the other is negative.
During the negative half-cycle, the polarity __________.
reverses
Transmission lines do not radiate signals efficiently. The closeness of the conductors keeps the ________________ concentrated in the transmission line dielectric.
electric field
The electric field spreads out from conductor to _________.
conductor
The higher the Q, the narrower the _________________.
bandwidth
The __________________ of any antenna is the shape of the electromagnetic energy radiated from or received by that antenna.
radiation pattern
___________ is a phenomenon caused by any support insulators used at the ends of the wire antenna and has the effect of adding capacitance to the end of each wire.
End effect
A _______________ uses multiple transmitters, receivers, or antennas to mitigate the problems caused by multipath signals.
diversity system
With __________________, two separate sets of transmitters and receivers operating on different frequencies are used to transmit the same information simultaneously.
frequency diversity
______________________________ uses two receive antennas spaced as far apart as possible to receive the signals.
Space or spatial diversity
__________is the variation in signal amplitude at the receiver caused by the characteristics of the signal path and changes in it.
Fading
In a ___________________, multiple repeaters are under the control of a computer system that can transfer a user from an assigned but busy repeater to another, available repeater, thus spreading the communication load.
trunked repeater system
Communication ____________ act as fixed repeater stations.
satellites
The receiver-transmitter combination within the satellite is known as a _________.
transponder
________________ waves leave an antenna and remain close to the earth.
Ground or surface
AM broadcast signals are _________ primarily by ground waves during the day and by sky waves at night.
propagated
Two basic types of antenna arrays are used to achieve
gain and directivity:
Parasitic array and driven array
A ______________ consists of a basic antenna connected to a transmission line plus one or more additional conductors that are not connected to the transmission line.
parasitic array
_______________ usually consist of two or more half- wave dipoles mounted end to end.
Collinear antennas
A __________________ is a stacked collinear antenna consisting of half-wave dipoles spaced from one another by one-half wavelengths.
broadside array
The end-fire array uses two half-wave dipoles spaced one-half wavelength apart.
