E9B-2012: Antenna patterns: E and H plane patterns; gain as a function of pattern; antenna design; Yagi antennas
In the antenna radiation pattern shown in Figure E9-1, what is the 3-dB beamwidth?
In the antenna radiation pattern shown in Figure E9-1, what is the front-to-back ratio?
In the antenna radiation pattern shown in Figure E9-1, what is the front-to-side ratio?
What may occur when a directional antenna is operated at different frequencies within the band for which it was designed?
The gain may change depending on frequency
Feed point impedance may become negative
The E-field and H-field patterns may reverse
Element spacing limits could be exceeded
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
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
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?
They are the same
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
How can the approximate beamwidth in a given plane 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
What type of computer program technique is commonly used for modeling antennas?
Method of Moments
Mutual impedance analysis
Calculus differentiation with respect to physical properties
What is the principle of a Method of Moments analysis?
A wire is modeled as a series of segments, each having a uniform 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
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
What is the far-field of an antenna?
The region where the shape of the antenna pattern is independent of distance
The region of the ionosphere where radiated power is not refracted
The region where radiated power dissipates over a specified time period
The region where radiated field strengths are obstructed by objects of reflection
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
What type of information can be obtained by submitting the details of a proposed new antenna to a modeling program?
All of these choices are correct
SWR vs. frequency charts
Polar plots of the far-field elevation and azimuth patterns
● = Unseen
● = Weak
● = Review
● = Learned
● = Incorrect answer