GATE (Graduate Aptitude Test in Engineering) Electronics: Questions 599 - 602 of 1076

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Passage

Read the passage and answer the following five questions:

An antenna is generally a metallic object, often a wire or collection of wires, used to convert high frequency current into electromagnetic waves and vice-versa. Antenna serve either or both of the following two functions, generation or the collection of electromagnetic energy. In a transmitting system, a radio-frequency signal is developed, amplified, modulated and applied to the antenna. The R-F currents flowing through the antenna produce electromagnetic waves which radiate into the atmosphere. In a receiving system, electromagnetic waves “cutting” through the antenna induce alternating currents for use by the receiver.

Efficient operation also requires that the receiving antenna be of the same polarization as the transmitting antenna. Polarization is the direction of the electric field and is therefore, the same as the antennas physical configuration. Thus vertical antenna will transmit vertical polarized light, any antenna having a physical length that is one-half wavelength of the applied frequency is called a Hertz antenna. Hertz antenna are predominantly used with frequencies above 2MHz. usually, at frequencies below 2 MHz, a Marconi type of antenna is used. The Marconi antenna is usually a quarter-wave grounded antenna or any odd multiple of a quarter wavelength.

The Yagi-Uda antenna consists of a driver՚s element and two or more parasitic elements. Yagi-Uda has two parasitic elements, a reflector and a director. This Yagi-Uda antenna provides about 7 dB of power gain with respect to a half wavelength dipole reference. More complex antennas may be circularly polarized both vertically and horizontally polarized waves are radiated with equal power in both. If the powers are unequal the antenna is said to be elliptically polarized.

A horn is an ideal antenna for terminating a waveguide and may be conical, rectangular or sectorial. Wide band antennas either when the transmissions are wide band or when working of narrow channels over a wide frequency range is the major application. Helical antenna, which consists of a loosely wound helix backed up by a metal ground plane. Loop antennas are often used for direction finding. Loops have many shapes and generally consists of a single turn of wire. Disc one is a ground plane antenna evolved from the vertical dipole and having a very similar radiation pattern.

Question 599 (4 of 5 Based on Passage)

Appeared in Year: 2014 (UGC-NET)

Question

MCQ▾

Which is a non-resonant antenna? (June)

Choices

Choice (4)Response

a.

Rhombic

b.

Disc one

c.

Marconi

d.

Yagi-Uda

Question 600 (5 of 5 Based on Passage)

Appeared in Year: 2014 (UGC-NET)

Question

MCQ▾

An antenna is polarized in the plane of the field perpendicular to (June)

Choices

Choice (4)Response

a.

Both Electric and Magnetic field

b.

Electric field

c.

Magnetic field

d.

Field parallel to both electric and magnetic field

Question 601

Appeared in Year: 2014 (UGC-NET)

Question

Assertion-Reason▾

Assertion(Ꭺ)

In a two port network, with 4 terminals four types of parameters like impedance, admittance, hybrid and transmission are considered and they are related to each other. (June)

Reason(Ꭱ)

The assumption made for the above statement is that there are no independent sources and non-zero initial conditions within the linear port network.

Choices

Choice (4)Response

a.

Ꭺ is true but Ꭱ is false

b.

Ꭺ is false but Ꭱ is true

c.

Both Ꭺ and Ꭱ are true and Ꭱ is the correct explanation of Ꭺ

d.

Both Ꭺ and Ꭱ are true but Ꭱ is NOT the correct explanation of Ꭺ

Question 602

Polarization, Phase and Group Velocity

Appeared in Year: 2014 (UGC-NET)

Question

Match List-Ⅰ List-Ⅱ▾

Match the following lists: (June)

List-Ⅰ (Column-I)List-Ⅱ (Column-II)
(A)

0.8 nm

(i)

Visible light

(B)

200 nm

(ii)

100 GHz

(C)

400 - 700 nm

(iii)

193 T Hz

(D)

1550 nm

(iv)

Ultra violet

Choices

Choice (4)Response
  • (A)
  • (B)
  • (C)
  • (D)

a.

  • (iii)
  • (ii)
  • (iv)
  • (i)

b.

  • (ii)
  • (iv)
  • (i)
  • (iii)

c.

  • (iii)
  • (i)
  • (ii)
  • (iv)

d.

  • (iv)
  • (i)
  • (ii)
  • (iii)

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