Page 232 - Electrical Engineering Dictionary

donor an impurity in a semiconductor Doppler linewidth characteristic width
that donates a free electron to the conduction of a Doppler-broadened spectral line; usually
band. the full width at half maximum when the line
is Gaussian.
door See lid.
Doppler power spectrum a function
dopant an impurity substance (such as characterizing the spread of average received
phosphorus or boron) added in very small power as a function of Doppler shift. Can be
controlled quantities to a semiconductor base obtained from the scattering function by in-
material (such as silicon or gallium arsenide), tegrating over the delay variable. See also
thereby changing the material conduction scattering function, multipath propagation.
characteristics by modifying electron and/or
hole concentration. A donor dopant is one Doppler radar radar-based technique
that gives rise to electrons and an acceptor used in measuring the velocity of a moving
dopant is one that gives rise to holes. target or wind by measuring the Doppler shift
(Doppler effect).
doping the process of introducing impu-
rity atoms into pure silicon to change its elec- Doppler shift a frequency shift in a re-
trical properties. The impurities may be ei- ceived signal caused by time-variant trans-
ther n-type (introducing an additional con- mission delay, or equivalently time-variant
ducting electron) or p-type (introducing the propagation path length. This in turn is
absence of a conducting electron, also called caused by movement of terminals with re-
a “hole”). spect to each other, or by movement of re-
flecting objects. In optics, frequency shifts
Doppler broadened lineshape function imposed on laser beams such as when used
spectral function that results from Doppler in laser radar or when diffracted by an acous-
shifts caused by the velocity distribution of tic wave.
atoms or molecules in a gas; a Gaussian func- The Doppler shift depends on the fre-
tion for a Maxwellian velocity distribution. quencyofthesignalandtheangleofarrivalof
the signal relative to the direction of move-
Doppler broadening broadening of a ment of the receiver. For a signal consist-
spectral line due to Doppler shifts caused by ing of a range of frequencies, each frequency
the random motion of atoms or molecules in component will experience a different shift.
a vapor. Hence the received signal will have a dif-
ferent bandwidth than the transmitted signal
Doppler effect See Doppler shift. (Doppler dispersion).
Foratone(continuous-wave)signaloffre-
Doppler filter a filter used to resolve tar- quency f , the Doppler shift f D observed on
gets from each other and from extraneous re- a single propagation path of changing length
turns from other objects (called clutter) by is given by
filtering in the velocity or Doppler domain.
fv
So-called because the Doppler effect causes f D = ,
c
frequency shifts proportional to velocity vari-
ations in tracked objects. where v is the rate (in m/s) of path length
change, and c is the speed of light.
Doppler frequency a shift in frequency of Also known as Doppler effect.
the returned power from a target as a result of
thetarget’smotionrelativetotheilluminating Doppler spread the increase of band-
source. width of a signal due to doppler shifting of

c
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