Instructions

For the following questions answer them individually

Question 73

The solid angle subtended by the sun as viewed from the earth is Ω =$$4 \times 10^{-5}$$ steradian.

A microwave antenna designed to be used for studying the microwave radiation from the

sun has a very narrow beam whose equivalent solid angle is approximately equal to that

subtended by the sun. What is the approximate directivity, D?

Question 74

A gain-standard horn is known to have a gain G = 10. It is being used to measure the gain of a large directional antenna by the comparison method. When the antenna being measured is connected to the receiver it is found to be necessary to insert an attenuator adjusted to attenuate by 23 dB in order to have the same receiver output that was observed with the horn connected. What is the gain of the large antenna?

Question 75

A paraboloidal-reflector antenna is designed for operation at 3 GHz. Its largest aperture dimension is 20 feet. It is desired to build a scale model of this antenna with the largest aperture dimension scaled to 18 inches. At what frequency must this model be operated in order to have the same pattern as the full-size antenna?

Question 76

An antenna has a radiation resistance of 72 Ω ,a loss resistance of 8 Ω and power gain of 16.Calculate its directivity.

Question 77

The current density at the surface of a thick metal plate is 100 $$\frac{A}{m^{2}}$$ What is the skin depth if the current density at a depth of 0.0059 cm is 0.272 $$\frac{A}{m^{2}}$$?

Question 78

An air filled rectangular waveguide $$R_{1}$$ is operating at the frequency 2 GHz and another air filled rectangular waveguide $$R_{2}$$ is operating at 4 GHz. The guide wavelengths of these waveguides at their respective frequencies are equal. If the cut-off frequency of waveguide $$R_{1}$$ is 1 GHz, what is the cut-off frequency of the waveguide $$R_{2}$$ in GHz?

Question 79

An electromagnetic wave propagates through a lossless insulator with a velocity $$1.5 \times 10^{10} \frac{cm}{s}$$ . Calculate the electric and magnetic properties of the insulator if its intrinsic impedance is 90 $$\pi$$ ohms

Question 80

A square waveguide carries $$TE_{11}$$ mode whose axial magnetic field is given by $$H_{Z}=H_{o} \times \cos (\frac{\pi x}{\sqrt{8}}) \times \cos (\frac{\pi y}{\sqrt{8}})$$ A/m where waveguide dimensions are in cm. What is the cut-off frequency of the mode?