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Right choice is (a) \(VSWR =\frac{λ_g}{π(d_2-d_1)}\)

To explain: High VSWR measurements (S>10) there is a special METHOD CALLED double minimum method. \(VSWR =\frac{λ_g}{π(d_2-d_1)}\) where D2, d1 are the readings noted on the slotted line where dips (3-db power) is observed.

Right choice is (a) 1

Easiest EXPLANATION: The STANDING wave ratio is DEFINED as the maximum voltage to minimum voltage.

\(S=\frac{V_{max}}{V_{min}} =\frac{1+ρ}{1-ρ}\)

And reflection coefficient is \(ρ=\frac{P_{ref}}{P_{INC}} =0 \) (Since there are no REFLECTIONS).

\(S=\frac{1+ρ}{1-ρ}=1\)

The CORRECT option is (a) Absolute GAIN

To EXPLAIN: In absolute gain method, the prior KNOWLEDGE of gain of antennas used in the measurements is not necessary and it is used for standard gain calibration. Gain transfer or Gain compromise method requires the standard gains of the antennas used for measurements to compare the AUT.

The correct option is (B) hr ≥ 4D

Explanation: ELEVATED RANGE TEST is one of the outdoor ranges. The height REQUIRED to mount the AUT for the elevation range test is given by hr ≥ 4D, where D is the dimension of AUT.

Correct OPTION is (a) 300MHZ to 16GHz

To explain: Reflection range, Elevation range and SLANT range comes under outdoor ranges. The reflection range is an outdoor ANTENNA range test where the antennas are operated at UHF and 16GHz. Ground ACTS as a reflector.

Correct OPTION is (c) ∞

Explanation: The Reflection coefficient is \(ρ=\FRAC{P_{REF}}{P_{INC}} =1\) (Since there are reflections power and incident power are EQUAL). The SWR S is given by

\(S=\frac{1+ρ}{1-ρ}=\frac{1}{0}=∞\)

Right option is (d) Reactive Field

To elaborate: Radiative and reactive field regions are the PARTS of the NEAR field region.The Far field region is greater than \(\frac{2D^2}{λ}\)and near field region is LESS than \(\frac{2D^2}{λ}\). Reactive region is also known as NON- Radiative region and is next to antenna. The Radiative region is also known as Fresnel region.

The correct option is (a) Network analyzer

To elaborate: Network analyzer is used to MEASURE the amplitude of signal and phase over a frequency. Spectrum analyzer which is a frequency domain instrument GIVES the PLOT of signal amplitude versus the frequency. Oscilloscope is a TIME domain instrument. Klystron ACTS as a source for the microwave signal.

The correct ANSWER is (a) \(P_r = P_t G_r G_t (\frac{λ}{4πR})^2 \)

To explain: Friss transmission is basis for the ABSOLUTE GAIN measurement. The Friss TRANSFER equation is given by \(P_r = P_t G_r G_t (\frac{λ}{4πR})^2 \,where\, G_r,G_t \) are the gains of receiving and transmitting antenna respectively.

Right option is (b) ANECHOIC chamber

The best explanation: Reflection range, Slant range and ELEVATION range belongs to outdoor ranges. Anechoic, TAMPERED chambers and compact ranges are part of INDOOR ranges. Indoor ranges are used for the small antenna as the FAR field region criteria is achieved in limited space and outdoor ranges for larger antennas.

Correct CHOICE is (d) Slotted line

Explanation: The slotted line is not used in the SPECTRUM ANALYZER. Spectrum analyzer is a frequency domain instrument. It gives the plot of signal AMPLITUDE versus the frequency.

Correct CHOICE is (b) False

The best explanation: Spectrum ANALYZER is a frequency domain instrument. It gives the plot of SIGNAL amplitude versus the frequency. The amplitude is the Fourier TRANSFORM of the signal. It acts as a diagnostic tool for the RF and EMI MEASUREMENTS.

Right choice is (a) \(S=\FRAC{1+ρ}{1-ρ}\)

Explanation: Standing waves occur when there is mismatch or reflection due to uneven SURFACES. The standing WAVE ratio is DEFINED as the maximum voltage to MINIMUM voltage and its relation with the reflection coefficient is given as

\(S=\frac{V_{max}}{V_{min}} =\frac{1+ρ}{1-ρ}.\)

The correct choice is (a) Gtest antenna = Gstd antenna) + \(10log⁡(\frac{P_{Test}}{P_{Std}}) \)

To explain I WOULD say: In GAIN transfer method the UNKNOWN gain antennas are compared with the standard gain antennas. The relation between gains of test and standard antenna to the POWERS received by them are given by the equation

Gtest antenna = Gstd antenna) + \(10log⁡(\frac{P_{Test}}{P_{Std}}). \)

The correct answer is (c) 9

The explanation: The low VSWR measurement is ABLE to MEASURE the readings of the VSWR not exceeding 10. For High VSWR measurements (S>10) there is a special method called DOUBLE MINIMUM method.

The correct answer is (a) G = ∈r D

For EXPLANATION: Antenna gain refers to the AMOUNT of radiation intensity in the DESIRED direction to that of would have radiated when the isotropic antenna radiates. The relation between Antenna gain and Directivity is G = ∈r D, ∈r is the antenna EFFICIENCY.

The correct option is (a) True

To explain I WOULD say: Friss transmission is the method USED for the absolute GAIN measurement. The Friss transfer formula is given by \(P_r= P_t G_r G_t (\frac{λ}{4πR})^2 \,where\, G_r,G_t \) are the gains of receiving and transmitting ANTENNA respectively.

Correct answer is (a) Height of AUT should be equal to or more than four times the dimension of antenna

For explanation I WOULD SAY: The amplitude variation over AUT should be more than 0.2dB to get AUT ENCOUNTER UNIFORM illumination. To satisfy that the height criteria of AUT should be equal to or more than four times the dimension of antenna.

Correct answer is (a) 8m

Best explanation: The minimum height REQUIRED to mount ANTENNA under test for the ELEVATION RANGE is GIVEN by a relation hr ≥ 4D, where D is the dimension of AUT.

Minimum height required hr=4D=4*2=8m

The CORRECT answer is (d) Spectrum analyzer

Explanation: Spectrum analyzer frequency DOMAIN instrument and is contrast to the oscilloscope which displays in time domain. The Klystron acts as a microwave source and the by MOVING the SLOTTED line the maximum READING on the meter is observed. For high VSWR the frequency of operation is noted using the frequency meter.

Correct choice is (a) 0

Best EXPLANATION: For a LOSSLESS ANTENNA the whole peak power is radiated towards the RECEIVER without any LOSSES. So the antenna efficiency will be 100% so it is 0dB.

The CORRECT option is (a) Absolute gain

The explanation is: In absolute gain METHOD, the prior KNOWLEDGE of gain of antennas used in the MEASUREMENTS is not necessary. Gain transfer or Gain compromise method requires the STANDARD gains of the antennas used for measurements to compare the AUT.

The correct answer is (a) Anechoic CHAMBERS

Best explanation: Indoor ranges are used to avoid limitations due to electromagnetic INTERFERENCE and ALSO ignore the environmental changes in surroundings. Indoor ranges have space restrictions unlike outdoor ranges. Anechoic, tampered chambers and compact ranges come under indoor ranges. Reflection range, Slant range and elevation range COMES under outdoor ranges.

Correct choice is (a) Far field region

Explanation: The characteristics of EM fields vary with DISTANCE from the antenna. It is DIVIDED into TWO regions. The region next to the antenna is the near field region and the region Far field region > \(\frac{2D^2}{λ}\).

The CORRECT answer is (c) Reflection range

The BEST explanation: Free space or ELEVATION or Reflection range can be employed for the gain transfer method. Anechoic, tampered chambers and compact RANGES come under indoor ranges. In gain transfer method the unknown gain antennas are COMPARED with the standard gain antennas.

Right choice is (a) 1

Easy EXPLANATION: The RELATION between ANTENNA gain and DIRECTIVITY is G=∈r D, ∈r is the antenna efficiency.

⇨ ∈r= \(\frac{G}{D}=1\)

The correct answer is (a) Slant range

The explanation is: For small antennas whose far FILED criterion is obtained within in a limited range, indoor ranges are applicable. REFLECTION range, Slant range and elevation range BELONGS to outdoor ranges which is applicable for the larger antennas in OPEN environment. Anechoic, tampered chambers and compact ranges COME under indoor ranges.

The CORRECT option is (a) NEAR field

For explanation: The Near field region is less than \(\frac{2D^2}{λ}\) the FAR field region is GREATER than\(\frac{2D^2}{λ}\). Radiative and REACTIVE field regions are the parts of the near field region.Reactive region is also known as non- Radiative region and is next to antenna. The Radiative region is also known as Fresnel region.

Correct choice is (a) True

To explain I would say: The volume, in which the antenna parameters are measured, is called the antenna range. They are of two TYPES. Indoor ranges are USED to avoid LIMITATIONS due to ELECTROMAGNETIC interference. Outdoor ranges are used for larger antenna in environmental surroundings.

Correct choice is (a) Absolute gain

For EXPLANATION: Gain transfer and gain compromise methods require the STANDARD gain CALIBRATION of antennas for gain measurements to COMPARE the antennas under test. In Absolute gain METHOD, gain of the antennas which are to be compared are known priory and this is used for the standard gain calibration

Right option is (d) To GET AUT encounter uniform illumination, the amplitude variation should be more than 0.2dB

For explanation: To get AUT encounter uniform illumination, the amplitude variation should not be more than 0.2dB. The height required to MOUNT the AUT for the elevation range test is given by HR ≥ 4D, where D is the dimension of AUT. Range diffraction fences are used to reduce the antenna REFLECTIONS.

The correct choice is (a) True

For explanation I would say: The region next to the antenna is the near FIELD region and it is LESS than \(\FRAC{2D^2}{λ}\). Near field has inductive effect hence it is also known as the inductive field. The far field is known as the radiating field as RADIATION is high in that region.

Correct answer is (a) Standing WAVES occur when mismatches occurs

Explanation: When there is mismatch, reflections occur and this causes for the occurrence of the standing waves. The standing WAVE ratio is defined as the maximum voltage to MINIMUM voltage.

\(S=\frac{V_{max}}{V_{min}} =\frac{1+ρ}{1-ρ}\) And reflection coefficient \(ρ=\frac{P_{ref}}{P_{inc}}. \) Therefore S ranges from 1 to INFINITY.

The correct answer is (a) \(\frac{1}{λ_0} =\sqrt{\frac{1}{λ_g^2} +\frac{1}{λ_c^2}} \)

To elaborate: The RELATION between the λg, λc, λ0 is GIVEN by \(\frac{1}{λ_g^2} =\frac{1}{λ_0^2} -\frac{1}{λ_c^2} \)

⇨\(\frac{1}{λ_0} =\sqrt{\frac{1}{λ_g^2} +\frac{1}{λ_c^2}}\)

and \(λ_0=\frac{c}{f}.\)

Right ANSWER is (b) Reactive Field < 0.62\(\SQRT{\frac{D^3}{λ}}\)

To elaborate: The characteristics of EM fields vary with distance from the antenna. It is divided into two regions. The region NEXT to the antenna is the near field region and the region Far field region > \(\frac{2D^2}{λ}\). Reactive field < 0.62\(\sqrt{\frac{D^3}{λ}} < \,Radiative\, field\, < \frac{2D^2}{λ}\).