2-30
Q30. The actions of the tr and atr circuits depend on the impedance characteristics of what length of
transmission line?
Q31. During which of the transmit or receive cycles are both the tr and atr tubes of a parallel-
connected duplexer ionized (arcing)?
Q32. In a series-connected duplexer, what tube (tr or atr), if any, fires during the receive cycle?
Q33. To propagate energy down an arm of a hybrid ring duplexer, the two fields at the junction of the
arm and the ring must have what phase relationship?
RECEIVERS
The energy that a distant object reflects back to the antenna in a radar system is a very small fraction
of the original transmitted energy. The echoes return as pulses of rf energy of the same nature as those
sent out by the transmitter. However, the power of a return pulse is measured in fractions of microwatts
instead of in kilowatts, and the voltage arriving at the antenna is in the range of microvolts instead of
kilovolts. The radar receiver collects those pulses and provides a visual display of object information.
Information about the position of the object is present visually when the reception of an echo causes
the movement or appearance of a spot of light on a cathode-ray tube (crt). The crt requires a signal on the
order of at least several volts for proper operation and will not respond to the high frequencies within a
return pulse. Therefore, a receiver amplifier and detector must be used that are capable of producing a
visible indication on the cathode-ray tube under the following conditions: (1) when the input signal to the
amplifier is in the form of pulses of extremely high-frequency, (2) the amplitude of the pulses is in the
microvolt range, and (3) the pulses last for only a few microseconds.
The radar receiver evolved directly from the simple radio receiver. The radar receiver operates on
exactly the same principles as the radio receiver. However, the overall requirements and limitations of a
radar receiver differ somewhat from those of a radio receiver because of the higher frequencies involved
and the greater sensitivity desired.
In studying the radar receiver, we will first examine the overall requirements of a radar receiver.
Second, we will examine a typical radar receiver that satisfies these requirements. Finally, we will discuss
the individual components of the receiver.
RADAR RECEIVER REQUIREMENTS
The following characteristics determine the design requirements of an effective radar receiver:
Noise
Gain
Tuning
Distortion
Blocking
