An antenna with a directive gain of  is radiating a total power of . The amplitude of the electric field in free space at a distance of  from the antenna in the direction of  gain (rounded off to three decimal places) is _______

Radiation resistance of a small dipole current element of length I at a frequency of 3GHz is 3 ohms. If length is changed by 1% then the percentage change in the radiation resistance, rounded off to two decimal places, is _____%

Consider a wireless communication link between a transmitter and a receiver located in free space, with finite and strictly positive capacity. If the effective areas of the transmitter and the receiver antennas, and the distance between them are all doubled, and everything else remains unchanged, the maximum capacity of the wireless link

A half wavelength dipole is kept in the x-y plane and oriented along 45° from the x-axis. Determine the direction of null in the radiation pattern for . Here the angle is measured from the z-axis, and the angle is measured from the x-axis in the x-y plane

Two lossless X-band horn antennas are separated by a distance of 200λ. The amplitude reflection coefficients at the terminals of the transmitting and receiving antennas are 0.15 and 0.18, respectively. The maximum directivities of the transmitting and receiving antennas (over the isotropic antenna) are 18 dB and 22 dB, respectively. Assuming that the input power in the lossless transmission line connected to the antenna is 2 W, and that the antennas are perfectly aligned and polarization matched, the power (in mW) delivered to the load at the receiver is______________        

The far-zone power density radiated by a helical antenna is approximated as:

The radiated power density is symmetrical with respect to ∅ and exists only in the upper hemisphere: is a constant. The power radiated by the antenna (in watts) and the maximum directivity of the antenna, respectively, are

A radar operating at 5 GHz uses a common antenna for transmission and reception. The antenna has a gain of 150 and is aligned for maximum directional radiation and reception to a target 1 km away having radar cross-section of  . If it transmits 100 kW, then the received power (in μW) is ________________

Two half-wave dipole antennas placed as shown in the figure are excited with sinusoidally varying currents of frequency 3 MHz and phase shift of π/2 between them (the element at the origin leads in phase). If the maximum radiated E-field at the point P in the x-y plane occurs at an azimuthal angle of 60°, the distance d (in meters) between the antennas is _________.  

The directivity of an antenna array can be increased by adding more antenna elements, as a larger number of elements

In spherical coordinates, let  denote unit vectors along the θ, ϕ directions.

And

Represent the electric and magnetic field components of the EM wave at large distances r from a dipole antenna, in free space. The average power (W) crossing the hemispherical shell located at r=1km,  is____________.

For an antenna radiating in free space, the electric field at a distance of 1 km is found to be 12mV/m. Given that intrinsic impedance of the free space is 120π Ω, the magnitude of average power density due to this antenna at a distance of 2 km from the antenna  is ____.

Match column A with column B.        

The radiation pattern of an antenna in spherical co-ordinates is given by

The directivity of the antenna is

For a Hertz dipole antenna, the half power beam width (HPBW) in the E-plane is

At 20 GHz, the gain of a parabolic dish antenna of 1 meter diameter and 70% efficiency is

Adipole is kept horizontally at a height of  above a perfectly conducting infinite ground plane. The radiation pattern in the plane of the dipole (plane) looks approximately as

A mast antenna consisting of a 50 meter long vertical conductor operates over a perfectly conducting ground plane. It is base-fed at a frequency of 600 kHz. The radiation resistance of the antenna in Ohm is:

Two identical and parallel dipole antennas are kept apart by a distance of  in the H-plane. They are fed with equal currents but the right most antenna has a phase shift of. The radiation pattern is given as

Consider a lossless antenna with a directive gain of +6db. If 1mW of power is fed to it the total power radiated by the antenna will be

Two identical antennas are placed in the  plane as shown in figure. The elements have equal amplitude excitation with 180º polarity difference, operating at wavelength λ. The correct value of the magnitude of the far-zone resultant electric field strength normalized with that of a single element, both computed for, is

The line-of-sight communication requires the transmit and receive antenna to face each other. If the transmitted antenna is vertically polarized, for best reception the receive antenna should be

A person with a receiver is 5 Km away from the transmitter. What is the distance that this person must move further to detect a 3-dB decrease in signal strength?

Consider a linear array of two half-wave dipoles A and B as shown in Figure. The dipoles are  apart and are excited in such a way that the current on element B legs that on element A by 90º in phase.

(a) Obtain the expression for the radiation pattern for the radiation pattern for  in the XY plane (i.e. )

(b) Sketch the radiation pattern obtained in (a).

If the diameter of a  dipole antenna is increased from  to , then its

For  8 feet (2.4 m) parabolic disk antenna operating at 4 GHz, the minimum distance required for far field measurement is closest to

 A transmitting antenna radiates 251 W isotopically. A receiving antenna, located 100 m away from the transmitting antenna, has an effective aperture of 500. The total received by the antenna is

The average power of an omni directional antenna varies as the magnitude, where  is the azimuthal angle. Calculate the maximum Directive Gain of the antenna and the angles at which it occurs.

The vector H in the far field of an antenna satisfies

An antenna in free space receives  of power when the incident electric field is  rms. The effective aperture of the antenna is

The maximum usable frequency of an ionospheric layer at 60° incidence and with 8MHz critical frequency is

The far field of an antenna varies with distance r as

A parabolic dish antenna has a conical beam 2° wide, the directivity of the antenna is approximately

A dipole antenna has  radiation pattern where the angle  is measured from the axis of the diode. The diode is vertically located above an ideal ground plane the figure is. What should be the height of the diode H in terms of wavelength so as to get a null in the radiation pattern at an angle of  from the ground plane? Find the direction of maximum radiation also.

A transverse electromagnetic wave with circular polarisation is received by a dipole antenna. Due to polarisation mismatch, the power transfer efficiency from the wave to the antenna is reduced to about

The critical frequency of an ionospheric layer is 10MHz. What is the maximum launching angle from the horizon for which 20 MHz wave will be reflected by the layer?

A 1 km long microwave link uses two antennas each having 30 dB gain. If the power transmitted by one antenna is 1W at 3 GHz, the power received by the other antenna is approximately

An antenna, when radiating, has a highly directional radiation pattern. When the antenna is receiving, its radiation pattern

For a short wave radio link between two stations via the ionosphere, the ratio of the maximum usable frequency to the critical frequency

For a dipole antenna

Consider an array of two non-directional radiators with spacing . Determine the directions of maximum radiation when the radiators are excited as shown in figure. Calculate the phase shift required for turning the direction of the maximum radiators by, keeping the separation, d, unchanged.        

Two dissimilar antennas having their maximum directives equal,

The beam width between first null of uniform linear array of N equally spaced (element spacing = d), equally excited antennas is determined by

Elements of a linear array of three equally spaced (element spacing = ) vertical mast radiators, are excited as given in figure. For the horizontal plane radiation pattern of the array, determine the direction of the major lobe (main lobe or principal lobe), and calculate its half-power beam width in degrees

A radio wave is incident on a layer of ionosphere at an angle of 30 degree with the vertical. If the critical frequency is 1.2 MHz, the maximum usable frequency is

In a broad side array of 20 isotropic radiators, equally spaced at a distance of  the beam width between first nulls is

In the radiation pattern of a 3-element array of isotropic radiators equally spaced at distances of  it is required to place a null at an angle of 33.56 degrees off the end-fire direction. Calculate the progressive phase shifts to be applied to the elements. Also calculate the angle at which the main beam is placed for this phase distribution.