E9B: Antenna patterns: E and H plane patterns; gain as a function of pattern; antenna design (computer modeling of antennas); Yagi antennas
E9B01:
What determines the free-space polarization of an antenna?
The orientation of its electric field (E Field)
The orientation of its magnetic field (H Field)
The orientation of its free-space characteristic impedance
Its elevation pattern
E9B02:
In the antenna radiation pattern shown in Figure E9-1, what is the 3-dB beamwidth?
50 degrees
75 degrees
25 degrees
30 degrees
E9B03:
In the antenna radiation pattern shown in Figure E9-1, what is the front-to-back ratio?
18 dB
36 dB
24 dB
14 dB
E9B04:
In the antenna radiation pattern shown in Figure E9-1, what is the front-to-side ratio?
14 dB
12 dB
18 dB
24 dB
E9B05:
What may occur when a directional antenna is operated at different frequencies within the band for which it was designed?
The gain may exhibit significant variations
Feed-point impedance may become negative
The E-field and H-field patterns may reverse
Element spacing limits could be exceeded
E9B06:
What usually occurs if a Yagi antenna is designed solely for maximum forward gain?
The front-to-back ratio decreases
The front-to-back ratio increases
The frequency response is widened over the whole frequency band
The SWR is reduced
E9B07:
If the boom of a Yagi antenna is lengthened and the elements are properly retuned, what usually occurs?
The gain increases
The SWR decreases
The front-to-back ratio increases
The gain bandwidth decreases rapidly
E9B08:
How does the total amount of radiation emitted by a directional (gain) antenna compare with the total amount of radiation emitted from an isotropic antenna, assuming each is driven by the same amount of power?
There is no difference between the two antennas
The total amount of radiation from the directional antenna is increased by the gain of the antenna
The total amount of radiation from the directional antenna is stronger by its front to back ratio
The radiation from the isotropic antenna is 2.15 dB stronger than that from the directional antenna
E9B09:
How can the approximate beamwidth of a directional antenna be determined?
Note the two points where the signal strength of the antenna is 3 dB less than maximum and compute the angular difference
Measure the ratio of the signal strengths of the radiated power lobes from the front and rear of the antenna
Draw two imaginary lines through the ends of the elements and measure the angle between the lines
Measure the ratio of the signal strengths of the radiated power lobes from the front and side of the antenna
E9B10:
What type of computer program technique is commonly used for modeling antennas?
Method of Moments
Graphical analysis
Mutual impedance analysis
Calculus differentiation with respect to physical properties
E9B11:
What is the principle of a Method of Moments analysis?
A wire is modeled as a series of segments, each having a distinct value of current
A wire is modeled as a single sine-wave current generator
A wire is modeled as a series of points, each having a distinct location in space
A wire is modeled as a series of segments, each having a distinct value of voltage across it
E9B12:
What is a disadvantage of decreasing the number of wire segments in an antenna model below the guideline of 10 segments per half-wavelength?
The computed feed-point impedance may be incorrect
Ground conductivity will not be accurately modeled
The resulting design will favor radiation of harmonic energy
The antenna will become mechanically unstable
E9B13:
Which of the following is a disadvantage of NEC-based antenna modeling programs?
Computing time increases as the number of wire segments is increased
They can only be used for simple wire antennas
They are not capable of generating both vertical and horizontal polarization patterns
All of these answers are correct
E9B14:
What does the abbreviation NEC stand for when applied to antenna modeling programs?
Numerical Electromagnetics Code
Next Element Comparison
National Electrical Code
Numeric Electrical Computation
E9B15:
What type of information can be obtained by submitting the details of a proposed new antenna to a modeling program?
All of these answers are correct
SWR vs. frequency charts
Polar plots of the far-field elevation and azimuth patterns
Antenna gain
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