Reviewer in Microwave Communications | ECE Board Exam

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(Last Updated On: February 15, 2020)

Review Notes in Microwave Communications

This is the Reviewer in Microwave Communications as one topic in ECE Board Exam taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies (EST), Communications Books, Journals and other Communications References. This particular Coaching Notes in Communications Engineering has random Questions and Answers in random topics. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.

Summary of Important Microwave Communications Review Notes

Attenuation is the progressive decrease of signal strength with increasing distance

If K-factor is greater than 1, the array beam is bent towards the earth

The antenna separations (in meters) required for optimum operation of a space diversity system can be calculated from: S = 3λR/L

Rainfall is an important factor for fading of radio waves at frequencies above 10 GHz

Theoretically electromagnetic radiation field strength varies in inverse proportion to the square of the distance, but when atmospheric attenuation effects and the absorption of the terrain are taken into account the attenuation can be as high as the inverse sixth power of the distance

Slow fading – an attenuation that occurs over many different wavelengths of the carrier

Slow fading is not due to multipath

Large reflector causes multipath or frequency-selective fading

In microwave transmission using digital radio, delayed spreading causes most intersymbol interference

SONAR – a shipboard equipment which measures the distance between the ship’s bottom and the ocean floor

The cavity resonator is equivalent to an LC resonant circuit

The input signal of a traveling-wave tube is inserted at the cathode end of the helix

Coupling into and out of a traveling-wave tube can be accompanied by a waveguide match, cavity match and direct coax-helix match

A high-power microwave pulse of the order of megawatts can be generated by a magnetron

A traveling-wave tube (TWT) amplifies by virtue of the absorption of energy by the signal from an electron stream

The purpose of the electromagnetic field which surrounds a traveling-wave tube is to keep the electrons form spreading out

Tunnel diode and klystron tube are used as an oscillator device in the SHF band

Microwave frequencies are normally regarded as those in the range of 1 to 100 GHz

The highest frequency which a conventional vacuum-tube oscillator can generate is not limited by the degree of emission from the cathode

As the electron beam moves through a klystron’s intercavity drift space the velocity modulation at the input cavity creates density modulation at the output cavity

The frequency of the oscillation generated by a magnetron, is mainly determined by the dimension of each cavity resonator

If the instantaneous RF potentials on the two sides of a magnetron cavity are of opposite polarity, the operation is in the π mode

The Gunn diode oscillator depends on the formation of charge domain

Circular ferrite device can be used instead of duplexer to isolate a microwave transmitter and receiver when both are connected to the same antenna

To achieve good bearing resolution when using a pulsed-radar set, an important requirement is a narrow, antenna-beam width in the horizontal plane

When used in conjunction with a radar set, the purpose of an echo box is to provide an artificial target which may be used to tune the radar receiver

In a radar-set receiver, the usual mixer stage is a silicon crystal

Klystron oscillators are most often used in the frequency range of 3000 to 30000 MHz

Oscillations of a klystron tube are maintained by bunches of electrons passing the cavity grids

Ferrite emitter allows microwave to pass in only one direction

In an SHF pulsed radar set, a reflex klystron can be used as a local oscillator

A PPI cathode-ray tube as used on a radar set indicates both the range and azimuth of a target

The resonant frequency of a cavity resonator depends upon its physical dimensions

The maximum usable range of the usual radar set (on any particular range setting) is determined by the interval between transmitted pulses

A reflex klystron is oscillating at the frequency of its resonant cavity. If the reflector voltage is made slightly less negative, the frequency will decrease

The coarse frequency adjustment of a reflex klystron is accomplished by adjusting the flexible wall of the resonant cavity

In a pulsed radar set, the STC circuit is used to reduce interference from the effects of sea return

In a pulsed radar set, the function of the duplexer is to allow the transmitter and the receiver to operate from a common antenna

The aquadag coating on the inside of a PPI tube is used as a second anode and to prevent the build-up of secondary field

If the duration of the radar transmitted pulse, on a particular range of operation is increased, the required bandwidth of the receiver’s IF amplifiers may be decreased

The main frequency determining element of a klystron is its resonant cavity

A thin layer of dirt and grime covers the reflecting surface of the parabolic dish of a radar set. The practical effect on the performance of the radar will have no noticeable effect

Isolator permits a microwave signals to travel in one direction with virtually no loss, but severely attenuates any signal attempting to travel in the reverse direction

It is possible to increase the maximum range of a radar equipment by lower the pulse frequency, raising the peak power of the transmitter, and narrowing the beam width and increasing the pulse duration

When it is desired that short-range targets be clearly seen on a pulsed-radar set, it is important that the receiver and display system have the shortest possible time

Magnetron is used as a high-power microwave oscillator

Modern loran navigational system operates at loran C: 100 kHz

Circulator ferrite device can be used instead of a duplexer to isolate a microwave transmitter and receiver when both are connected to the same antenna

The pulse frequency is equal to duty cycle/pulse width

In a radar set, a blocking oscillator can be used to produce a trigger pulse for the transmitter

The intensity of the echoes (target definition) on a PPI display is determined by the pulse frequency and antenna rotation rate

A duplexer circuit allows a transmitter and a receiver to operate from the same antenna with virtually no interaction. This circuit may be replaced by a circulator

156.76 MHz and 156.8 MHz frequencies are used by a class-C Emergency Position-Indicating Radio Beacon

The repetition rate of a pulsed radar system indicates the frequencies of the duty cycle

The radar set, sensitivity-time control circuit can reduce sea-return response

Isolator is a ferrite device that buffers a microwave source from the effects of a varying load, and thereby prevents the formation of standing waves

Pulsed radar sets are primarily used to find the target’s range and bearing

Radio frequency is mainly concerned in the design of an antenna system for pulsed radar set

In a radar set receivers, an ac AFC system may be used to maintain the desired klystron frequency

The input signal is introduced into the traveling-wave tube at the cathode end of the helix

The display on the PPI scope of a radar set will have greater intensity at lower antenna rotation speeds and higher pulse repetition

The operating frequency of loran C lies within the LF band

The PPI tubes have an aquadag coating on the inside of the tube. The purpose of this coating is to act as the second anode

A traveling-wave tube is used at frequencies in the order of 8000 MHz

The main benefit of using microwave is more spectrum space for signals

Radio communications are regulated in the Philippines by the NTC

Mobile radio is not a common microwave application

Coaxial cable is not widely used for long microwave transmission lines because of its high loss

Stripline and microstrip transmission lines are usually made with PCBs

The most common cross section of a waveguide is a rectangle

Signal propagation in a waveguide is by electric and magnetic fields

When the electric field in a waveguide is perpendicular to the direction of wave propagation, the mode is said to be transverse electric

The dominant mode in most rectangular waveguide is TE1,2

A magnetic field is introduced into waveguide by a probe

A half-wavelength, close section of a waveguide that acts as a parallel resonant circuit is known as cavity resonator

Decreasing the volume of a cavity causes its resonant frequency to decrease

Hot carrier is a popular microwave mixer diode

Varactor and step-recovery diodes are widely used in frequency multiplier

Gunn diode is a popular microwave oscillator

Tunnel diode does not ordinarily operate with reverse bias

Low-power Gunn diodes are replacing reflex klystrons

Cathode-ray tube is not a microwave tube

In a klystron amplifier, velocity modulation of the electron beam is produced by the catcher cavity

A reflex klystron is used as an oscillator

For proper operation, a magnetron must be accompanies by a permanent magnet

The operating frequency of klystrons and magnetrons is set by the cavity resonators

A magnetron is used only as an oscillator

A common application for magnetron is in radar

In a TWT, the electron beam is density-modulated by a helix

The main advantage of a TWT over a klystron for microwave amplification is wider bandwidth

High-power TWTs are replacing Klystrons

Horn – the most widely used microwave antenna

MTBF is a measure of reliability expressed as the average number of hours between successive failures

Baseband repeater – an active microwave radio repeater that can provide drops and inserts

If the correction factor k equals 4/3 of the earth’s curvature, the microwave beam would have a curvature that is more than that of the earth

The optimum clearance from an obstacle in a microwave system is accepted as 0.6 of the first Fresnel zone radius

The microwave beam curves the same than that of the earth when the value of the correction factor k equals infinity

The ability of a radar to determine the bearing to a target depends upon the antenna directivity

The Doppler effect allows speed of a target to be measured

The Doppler effect is a change in frequency produced by relative motion between the radar set and a target

The most widely used radar transmitter component is a magnetron

Low-power radar transmitters and receivers use Gunn diode

Spark gap in a duplexer protects the receiver from the higher transmitter output

Most radar antennas use a horn and parabolic reflector

The most common radar display is the PPI

A radar antenna using multiple dipoles or slot antennas in a matrix with variable phase shifters is called a phased array

10 GHz is a typical radar operating frequency

A microwave system requires the use of repeaters when the distances involve are greater

Waveguides are transmission line which convey electromagnetic waves in highest frequencies

A microwave band of 10.9 to 36 GHz is considered as K-band

92.4 + 20 log F + 20 log D – a microwave communications system space loss calculation formula

A waveguide is also a high pass filter

Frequency diversity – a method of diversity reception where the signal is transmitted on two different frequencies over the same path

Litz wire – a wire used to reduce the skin effect

Space diversity transmission means transmitting and receiving on two or more antennas operating on the same frequencies

Frequency diversity – the best system configuration to overcome multipath fading of microwave system over the water

When the value of k increases, the effective result is flattening of the equivalent curvature

A traveling wave tube consists of electron gun, helix and collector

Advantage of periscope antenna in microwave: shorten waveguide length

The cut-off frequency of a waveguide is the lowest frequency the waveguide operates

When the clearance above the obstruction is equal to the radii of even Fresnel zones at the point of reflection, the RSL is decreased

The wavelength of a wave in a waveguide is greater than in free space

Water causes more attenuation particularly on 183 GHz frequency

Oxygen cause excessive attenuation at 60 GHz frequency

Terrestrial is a microwave link between the down-town terminal and another out of town terminal

Attenuator is used in the traveling wave tube to prevent oscillation

Space diversity is a method of diversity reception applied to reflective path to reduce fading

K X 4000 miles is the effective earth’s radius used in communications design

IF bandwidth of a radar system is inversely proportional to pulse width

EADI stands for Electronic Altitude and Director Indicator

DME aircraft navigational system determines the time to station (TTS) or time to go (TTG)

A radio altimeter operate at 43500 MHz frequency

Terrestrial Flight Telephone System allows passengers to make telephone calls, send faxes, and computer data shop and play computer games, etc

ADF stands for Automatic Direction Finder

RF carrier of the middle marker is modulated at 1300 Hz

The major advantage of using a helix traveling wave tube is its wide bandwidth

RADAR stands for Radio Detection and Ranging

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