This is the Review Notes in Antennas 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 Antennas Review Notes
The polarization of a discone antenna is vertical
When speaking of antenna, bay is a section which would be a complete antenna by itself
VHF and UHF range of frequencies are most omnidirectional horizontally polarized antennas used
If the current ratios of the two or more elements must be held 5% and the phase angle to 3°, the antenna is called a critical phased array
Antenna – a device that converts high frequency current into electromagnetic wave
Rhombic antenna – non-resonant antenna
Gain of a half-wave dipole antenna over isotropic 2.15 dB
Null – very low signal strength in antenna
The gain of the Hertzian dipole over isotropic antenna 1.76 dB
Beamwidth is the measurement of unilateral antenna properties of directivity
In testing transmitter to prevent interfering with other stations, dummy type of antenna must be used
The best solution to fading is space diversity
Entropy is the amount of uncertainly in a system of symbols
If an antenna has a gain of 30 dB, it increases the output of the transmitter by 1000 times
Top loading is used in an antenna in order to increase its effective height
A horizontal antenna is horizontally polarized
All elements in a beam collinear antenna are in line
FM broadcasting does not use vertical polarization antenna
Lightning rods must be mounted a top structure not less than 30 cm above the highest point
Antenna array is an antenna with a number of half-wave antenna on it
Marconi antenna radiates an omnidirectional pattern in the horizontal plane with vertical polarization
Parabolic dish antenna – an antenna with very high gain and very narrow bandwidth
The direction of the electric field vector determines antenna polarization
Azimuth is the horizontal pointing angle of an antenna
The estimated medium wind loading in the Philippines for antenna tower design is 200 kph
Discone radiation pattern is omnidirectional
Notch antenna is an open-ended slot antenna
Rhombic antenna is properly terminated
The radiation characteristic of a dipole antenna is bidirectional
The theoretical gain of Hertzian dipole is 1.76 dB
Isotropic – an antenna with unity gain
You can increase the gain of an antenna by focusing the radiated energy in one desired direction
Elementary doublet – an antenna which is one-tenth wavelength long
The minimum number of turns a helix antenna must have is 3
The gain of isotropic antenna is 1
Parasitic element improves antenna directivity
The antenna radiates horizontally polarized waves when the transmitter antenna is horizontally installed
Front-to-back ratio – comparing the signal strength arriving at the driven element from the desired direction to the signal strength reaching the driver from the opposite direction
Gain of an antenna is a measure of how the antenna concentrates its radiated power in a given direction
End effect – shortening effect of an antenna that makes it appear as if it were 5% longer
Low-pass filter – harmonic suppressor connected to an antenna
A simple half-wavelength antenna radiates the strongest signal at right angles to its axis
The current maximum in a Marconi antenna is found at the base of the antenna
If an antenna is too short for the wavelength being used, the effective length can be increased by adding inductance in series
Dummy antenna is used for testing and adjusting a transmitter for proper modulation, amplifier operation and frequency accuracy
It is possible to lower the resonant frequency of Hertz dipole antenna by connecting an inductor in series with the antenna
A vertical antenna which is a quarter-wavelength long receive signals in the horizontal plane equally well from all direction
If the length of a Hertz dipole is decreased its resonant frequency will be increased
A one-quarter wavelength shunt-fed vertical Marconi antenna must have a vertical receiving antenna for the best reception
A shunt-fed quarter-wavelength Marconi antenna has zero DC resistance to ground
The parasitic element of an antenna system will increase its directivity and give the antenna unidirectional properties
If the length of an antenna is changed from 2.5 meters to 2.8 meters, its resonant frequency will decrease
The effect of adding a capacitor in series with an antenna is that the antenna’s resonant frequency will increase
The electrical field strength of a standard broadcast station vary with the distance from the antenna by the field strength varies inversely as the distance from the antenna
Stacking element in a transmitting antenna system increases the field strength at the receiving antenna and increases the directivity of the transmitter antenna
A vertical loop antenna has a bidirectional radiation pattern in the horizontal plane
In order to get maximum radiation to all the surrounding points in the horizontal plane, the antenna used is a vertical quarter-wavelength rod
If the antenna current is doubled, the field strength at a particular position is doubled
The rhombic antenna is primarily used for sky wave propagation
Isotropic antenna radiates equally in all directions
Actual height of antennas should be at least quarter wavelength
Resonant antenna is not properly terminated
Broadcast array is an antenna array which is highly directional at right angles to the plane of the array
The directivity pattern of an isotropic radiator is a sphere
An isotropic radiator is a hypothetical, omnidirectional antenna
The purpose of stacking elements on an antenna sharper directional pattern, increased gain, and improved bandpass
The advantage of using top loading in a shortened HF vertical antenna is improved radiation efficiency
The voltage nodes in a half-wave antenna is at the feed point
Isotropic radiator – a theoretical reference antenna that provides a comparison for antenna measurements
In horizontal-dipole antenna, the polarization is in the horizontal direction
Increasing the electrical length of an antenna means adding an inductor in series
Stacking antennas at various angles results in a more omnidirectional reception
Driven element – the element fed by the transmission line
Antenna bandwidth – the frequency range over which an antenna can be expected to operate satisfactorily
To lengthen an antenna electrically, add a coil
The usual electrical length of a driven element in an HF beam antenna is ½ wavelength
The bandwidth of an antenna increases as it is shortened through the use of loading coils
To electrically decrease the length of an antenna, add a capacitor in series
Strong interference from one particular station can be eliminated by the use of wave traps in the antenna circuitry
It is useful to refer to an isotropic radiator when comparing the gains of directional antennas
A disadvantage of using a trap antenna is it will radiate harmonics
The input terminal impedance at the center of a folded dipole antenna is 300 ohm
When a capacitor is connected in series with a Marconi antenna the antenna resonant frequency increases
The current nodes in a half-wave antenna is at the ends
For a shortened vertical antenna, loading coil should be placed near the center of the vertical radiator to minimize losses and produce the most effective performance
The effect of adding parasitic elements of a Hertz dipole is to increase the antenna’s power gain
Stacking antenna elements increases sensitivity to weak signals
In the case of Marconi antenna, the actual length of the radiating element is one-quarter wavelength
The antenna efficiency of an HF grounded vertical antenna can be made comparable to that of a half-wave antenna by installing a good ground radial system
An antenna “efficiency” is computed by using Efficiency = (radiation resistance / total resistance) x 100%
Increasing the resonant frequency of an end-fed Marconi antenna can be done by adding a capacitor in series and reducing the physical length
Factor that determines the radiation resistance of an antenna: the location of the antenna with respect to nearby objects
Beamwidth is the angle between the half-power radiation points
Directivity gain is the ratio of the maximum radiation intensity to the average radiation intensity
Good grounding is important for vertical antennas
An ungrounded antenna near the ground acts as antenna array
Log-periodic is very useful as a multiband HF receiving antenna
Horn antennas is best excited from a waveguide
The following reasons for using metal counterpoise with antenna are impossibility of a good ground connection, provision of an earth for the antenna and rockiness of the ground itself
Protection of personnel working underneath is not a reason for using metal counterpoise with antennas
Reason for the use of an antenna coupler: to make the antenna look resistive, to provide the output amplifier with the correct load impedance and to discriminate against harmonics
To prevent reradiation of the local oscillator is not a reason for the use of an antenna coupler
Marconi antenna is not a wideband
Adding C in series makes an antenna physically long but electrically short
When antennas are closed to the ground, vertical polarized polarization is ideal
Long wire is an antenna made up of a number of full wavelengths
Electromagnetic – any energy which radiates in the form or radio waves, infrared waves, light waves, x-rays, etc
Diplexer is an antenna coupling unit
Vertical polarization is employed in AM broadcasting
Horizontal polarization is employed in FM broadcasting
Dipole antenna is not grounded at one end
Yagi antenna does not use the ground
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