Antennas And Microwave Engineering Set 1

Answer: complex design

Explaination:
designing a good quality frequency multiplier is more difficult since it non-linear analysis, matching at multiple frequencies, stability analysis and thermal considerations. considering all these issues for designing a multiplier makes it very complex.

Answer: true

Explaination:
as frequency increases to the millimeter wave range, it becomes increasingly difficult to build fundamental frequency oscillators with good power, stability and noise characteristics. an alternative approach is to produce a harmonic of a low frequency oscillator through the use of frequency multiplier.

Answer: true

Explaination:
a disadvantage of frequency multipliers is that noise levels are also increased by the multiplication factor.

Answer: 20 db

Explaination:
for a frequency multiplier, the increase in noise power is given by 20 log n, where n is the multiplication factor of the multiplier. substituting in the below equation, increase in noise level is 20 db.

Answer: reactive impedance

Explaination:
in a diode frequency multiplier, an input signal of frequency fo applied to the diode is terminated with reactive impedance at all frequencies other than required harmonic nfo. if the diode junction capacitance has a square –law i-v characteristic , it is necessary to terminate unwanted harmonics with short circuit.

Answer: false

Explaination:
resistive multipliers generally use forward biased schottky-barrier diodes to provide non linear characteristic. resistive multipliers have low efficiency but have better bandwidth.

Answer: true

Explaination:
at millimeter frequencies, varactor diode exhibits resistive property. hence, at high frequency the multiplier becomes lossy and also does not offer high bandwidth, which is a major disadvantage.

Answer: 25 %

Explaination:
for a resistive frequency multiplier of multiplication factor 2, the maximum theoretical conversion efficiency is given by 1/m2 where m is the multiplication factor. for a factor 2 multiplier, maximum theoretical conversion efficiency is 25 %.

Answer: antenna

Explaination:
antenna is a device that converts electrons into photons or vice versa. a transmitting antenna converts electrons into photons while a receiving antenna converts photons into electrons.

Answer: il= qv

Explaination:
basic equation of radiation is given by il=qv. i is the time change in current, l is the length of the current element, q is the charge v is the acceleration of the charge.

Answer: true

Explaination:
when the separation between

Answer: three

Explaination:
the three patterns required are, θ component of the electric field as the function of the angles as θ and φ, the φ component of the electric field as the function of the angles θ and φ, the phase of these fields as a functions of the angle φ and θ .

Answer: half power beam width

Explaination:
the beam width of an antenna measure at half of the maximum power received by an antenna or the 3 db beam width of the antenna is termed as half null beam width.

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

Answer: 900

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. twice the half power beam width gives the first null beam width. with the same steps applied, the half power beam width of the antenna is 450. first null beam width is 900.

Answer: beam area

Explaination:
the beam area is the solid angle through which all of the power radiated by the antenna would stream if p (θ, φ) maintained its maximum value over beam area and zero elsewhere. this value is approximately equal to the angles subtended by the half power points of the main lobe in the two principal planes.

Answer: true

Explaination:
power radiated from an antenna per unit solid angle is called radiation

Answer: transmitting antenna

Explaination:
a transmitting antenna is a device that converts a guided electromagnetic wave on a transmission line into a plane wave propagating in free space. it appears as an electrical circuit on one side, provides an interface with a propagating plane wave.

Answer: true

Explaination:
antennas can be used both as

Answer: wire antennas

Explaination:
dipoles, monopoles, oops, yagi-uda arrays are all examples for wire antennas. these antennas have low gains, and are mostly used at lower frequencies.

Answer: array antennas

Explaination:
array antennas consist of a regular arrangement of antenna elements with a feed network. pattern characteristics such as beam pointing angle and side lobe levels can be controlled by adjusting the amplitude and phase excitation of array elements.

Answer: 17.3 m

Explaination:
far field distance for a reflector antenna is given by 2d2/λ. d is the diameter and λ is the operating signal wavelength.

Answer: radiation pattern

Explaination:
radiation pattern of an antenna is a plot of the magnitude of the far field strength versus position around the antenna. this plot gives the detail regarding the region where most of the energy of antenna is radiated, side lobes and beam width of an antenna.

Answer: omni directional antenna

Explaination:
omni directional antennas radiate em waves in all direction. if the radiation pattern for this type of antenna is plotted, the pattern is a constant signifying that the radiated power is constant measured at any point around the antenna.

Answer: true

Explaination:
beamwidth and directivity are both measures of the focusing ability of an antenna. an antenna with a narrow main beam will have high directivity, while a pattern with low beam will have low directivity.