Antennas And Microwave Engineering Set 3

Answer: hertz antenna

Explaination:
one of the most widely used antenna types is the half-wave dipole antenna. this antenna is also formally known as the hertz antenna after heinrich hertz, who first demonstrated the existence of electromagnetic waves.

Answer: radiation resistance

Explaination:
the transmission line is connected at the center. the dipole has an impedance of 73 v at its center, which is the radiation resistance. at the resonant frequency, the antenna appears to be a pure resistance of 73 v.

Answer: swr is minimum

Explaination:
when the radiation resistance of the antenna matches the characteristic impedance of the transmission line, the swr is minimum and maximum power reaches the antenna. this allows maximum power to be transmitted.

Answer: conical antenna

Explaination:
a common way to increase bandwidth in the antenna is to use a version of the dipole antenna known as the conical antenna. the overall length of the antenna is 0.73λ or 0.73(984)/f = 718.32/f. this is longer than the traditional one-half wavelength of a dipole antenna, but the physical shape changes the necessary dimensions for resonance.

Answer: doughnut

Explaination:
the radiation pattern of any antenna is the shape of the electromagnetic energy radiated from or received by that antenna. typically that radiation is concentrated in a pattern that has a recognizable geometric shape. the radiation pattern of a half-wave dipole has the shape of a doughnut.

Answer: 90°

Explaination:
the beam width is measured between the points on the radiation curve that are 3 db down from the maximum amplitude of the curve. the maximum amplitude of the pattern occurs at 0° and 180°. the 3-db down points are 70.7 percent of the maximum. the angle formed with two lines extending from the center of the curve to these 3-db points is the beam width. the beam width is 90°. the smaller the beam width angle, the more directional the antenna.

Answer: directivity

Explaination:
the measure of an antenna’s directivity is beam width, the angle of the radiation pattern over which a transmitter’s

Answer: effective radiated power

Explaination:
the power radiated by an antenna with directivity and therefore gain is called the effective radiated power (erp).

Answer: sphere

Explaination:
an isotropic radiator is a theoretical point source of electromagnetic energy. the e and h fields radiate out in all directions from the point source, and at any given distance from the point source, the fields form a sphere.

Answer: 300Ω

Explaination:
a popular variation of the half- wave dipole is the folded dipole. like the standard dipole, it is one-half wavelength long. however, it consists of two parallel conductors connected at the ends with one side open at the center for connection to the transmission line. the impedance of this

Answer: marconi antenna

Explaination:
the same effect as dipole antenna can be achieved with a one-quarter wavelength antenna or marconi antenna. a vertical dipole with the doughnut-shaped radiation pattern, in which one-half of the pattern is below the surface of the earth. this is called a vertical radiation pattern.

Answer: dipole antenna

Explaination:
wires of half wavelength are termed as dipoles. their radiation resistance is about 73 Ω. if only half of this length is used, then it is called quarter-wave monopole with a radiation resistance of 36.5 Ω.

Answer: wire antenna

Explaination:
in a wire antenna, the location of the feed determines the direction of the lobe and the orientation of the wire determines the polarization. these wires can be thick or thin. thickness of the wire determines the radiation resistance of the antenna.

Answer: false

Explaination:
loop antennas are classified based on various antenna parameters. to name a few, small and large loops, circular and square loops, loops having single or multi turns, loops with turns wound using a single wire or multiple wires.

Answer: none of the mentioned

Explaination:
all of the above mentioned antennas belong to the horn antenna family. horn antennas may be made of pointed or rounded waveguides. the waveguides may contain disc at an end or some dielectric.

Answer: true

Explaination:
reflector antennas are used to modify radiation patterns of radiating elements. reflector antennas are classified into two categories. they are passive reflectors and active reflectors. based on the type of the radiating element and the modification in the radiation pattern required, accordingly either active or passive reflectors are chosen.

Answer: secondary pattern

Explaination:
in a reflector antenna, the feed pattern is called primary pattern and the pattern of the reflector is called secondary pattern. these antennas are widely employed in radars and other types of point to point communication links.

Answer: lens antennas

Explaination:
lens antennas are complex in nature but are able to scale wider angles. in comparison to reflectors, their gain is 1 or 2 db less, but these have more lenient tolerance on surfaces. these have less rearward reflection, relatively low loss and can be easily shaped to the desired contours.

Answer: delay antenna

Explaination:
in delay lenses, the electrical path length is increased or the wave is retarded by the lens medium. dielectric lenses and h-plane metal lenses fall in this category.

Answer: wide band antennas

Explaination:
in this class of antennas, constancy of impedance and radiation characteristics is maintained over a wide range of frequencies. to be wide band or frequency independent, antennas should expand or contract in proportion to the wavelength.

Answer: antenna arrays

Explaination:
higher directivity is the requirement in point to point communication. this can be achieved by increasing the size of the antennas in terms of electrical length.

Answer: 50 Ω

Explaination:
the terminal impedance zs of the slot is given by the relation z 2/ 4z ) zₒ is

Answer: true

Explaination:
when the separation between two lines that chary the tem wave approaches λ the wave tends to be radiated so that the opened – out line act as an antenna which lunches a free space wave.

Answer: 660

Explaination:
half power beam width of the antenna is obtained by equating the field pattern of the antenna to 0.707 (half power point) and finding θ. 2θ gives the value of beam width. solving the given problem in the same flow, half power beam width of the antenna is 660.

Answer: true

Explaination:
power radiated from an antenna per unit solid angle is called radiation intensity. unit of radiation intensity is watts per steridian or per square degree.