Antenna and Microwave Engineering Question Bank2 PDF

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EC8701- ANTENNA AND MICROWAVE ENGINEERING IV YEAR ECE / VII SEMSESTER QUESTION BANK PART A 1. What are microwaves? Micro waves are electromagnetic waves, with their frequency falling in gighertz range i.e. frequency ranging between 3Ghz and 300GHz with a corresponding wavelength between 10cm and 1mm respectively 2. write the frequencies of the following Microwave bands i) L band

ii) ku band

iii) U band

iv) W band

L band: 1-2GHz ku band 12-18GHz U band 40-60GHz W band 75-110GHz 3. Why standard Circuit theory can not be used to directly to solve microwave network problems? Because of high frequency and short wavelength, the microwave act as a distributed elements. Distributed elements along with transmission theory concepts are relevant and useful for circuit design and analysis of microwave Engineering. Microwave theory is almost completely based on field theory quantities 4. What are the features of microwaves? 1. 2. 3. 4. 5.

Possibility of larger bandwidth possibility of smaller sized system frequency reusability reliability or achievability of larger antenna gain Resonance Phenomenon

5. Define Antenna. As per IEEE standards of terms Antenna is defined as "A means for radiating or receiving radio waves. in other words the antenna is a transitional structure between freespace and guiding device An antenna can also be defined as a transducer which converts radio frequency electrical current into electromagnetic waves of same frequency

6. What are standing waves and how it can be reduced? The reflected waves from the interface create, along with the traveling waves from the source toward the antenna, constructive and destructive interference patterns, referred to as standing waves, inside the transmission line which represent pockets of energy concentrations and storage, typical of resonant devices The standing waves can be reduced, and the energy storage capacity of the line minimized, by matching the impedance of the antenna (load) to the characteristic impedance of the line. 7. what is Isotropic radiator? An isotropic radiator is defined as “a hypothetical lossless antenna having equal radiation in all directions.” Although it is ideal and not physically realizable, it is often taken as a reference for expressing the directive properties of actual antennas. 8. What is directional antenna? A directional antenna is one “having the property of radiating or receiving electromagnetic waves more effectively in some directions than in others. This term is usually applied to an antenna whose maximum directivity is significantly greater than that of a half-wave dipole.” 9. What is a resonant antenna?  A resonant antenna are the antennas with a length in exact multiples of /2. Such antenna open at both ends and none of the ends is terminated in any resistance.  They operate at fixed frequency  In these antennas, reflected wave and standing wave exist  The voltage and current along the length are not in phase. the radiation pattern of such antenna is multidirectional 10. What are the functions of antenna?  Antenna act as a transducer. IT converts electrical energy into electromagnetic energy at transmitting end, while it converts an electromagnetic energy back into the form of an electrical energy in the receiving end  Act as an impedance matching device  Antenna functions as a device which direct radiated energy in most desired direction with suppressing energy in undesired direction  Antenna act as a transitional structure ar region where transition between guided waves and free space and vice versa  It functions as a remote sensing temperature measuring device 11. What are the most common types of antenna  Wire antenna  Aperture antenna  Microstrip Antenna

 Array antenna  Reflector antennas  lens antenna 12. Define reactive-near field Reactive near filed region is defined as that portion of the near-field region immediately surrounding the antenna where in the reactive field predominates.

Outer boundary of the region exist at a distance R, where

𝑅 < 0.62

𝐷3



from the surface of antenna. - wavelength D - Largest dimension of the antenna. 13. Define Radiation Pattern  An antenna radiation pattern or antenna pattern id defined as mathematical function or a graphical representation of the radiation properties of the antenna as a function of space co-ordinates  It is determined in the far field region  It is represented as a function of the directional coordinates  The radiation property is a two or three dimensional spatial distribution of radiated energy as a function of observers position along a path or surface of constant radius 14. What is Beam width of an antenna? Antenna beam width is the measure of the directivity of an antenna . Beam width is an angular width in degree, measured on a radiation pattern on major lobes The beam width is defined as the angular separation between two identical points on opposite side of pattern maximum 15. What is Half power Beamwidth? The Half Power Beam Width (HPBW is defined by IEEE as "In a plane containing the direction of maximum of a beam, the angle between two directions in which the radiation intensity is one-half value of the beam. It is also called as 3dB beam width. 16. What is a radian? The radian is a measure of plane angle. One radian is defined as the plane angle with its vertex at the center of a circle of radius r that is subtended by an arc whose length is r 1 radian = 180/ degree = 57.29 degree

17. Define radiation intensity  Radiation intensity in a given direction is defined" as the power radiated from an antenna per unit solid angle"  The radiation intensity of an antenna doesnot depend on distance from antenna. It is denoted by U  It is a far-field parameter expressed in Watts / steradian  it us defined as time average power per unit solid angle U 

𝑈=

𝑃𝑟𝑎𝑑 4

18. What is directivity:  The directivity of an antenna is defined as the ratio of radiation intensity in a given direction from the antenna to the radiation intensity averaged over all direction.  the average radiation intensity is equal total power radiated by antenna divided by 4  If the direction is not specified, the direction of maximum radiation intensity is implied.

 𝐷=

𝑈 𝑈0

=

4𝜋𝑈 𝑃𝑟𝑎𝑑

19. What is FBR? The Front to back ratio is defined as the ratio of power radiated in desired diretion to the power radiated in opposite direction. 𝐹𝐵𝑅 =

𝑃𝑜𝑤𝑒𝑟 𝑟𝑎𝑑𝑖𝑎𝑡𝑒𝑑 𝑖𝑛 𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝑑𝑖𝑟𝑒𝑐𝑡𝑖𝑜𝑛 𝑃𝑜𝑤𝑒𝑟 𝑟𝑎𝑑𝑖𝑎𝑡𝑒𝑑 𝑖𝑛 𝑂𝑝𝑝𝑜𝑠𝑖𝑡𝑒 𝑑𝑖𝑟𝑒𝑐𝑡𝑖𝑜𝑛

The desired FBR vale is very high as it is expected to have large radiation in the front or desired direction then in back or opposite direction 20. Define Effective length of an antenna. The effective length of an antenna is defined as the ratio of open circuit voltage induced at the open terminals of an antenna to the incident electric field intensity Ei producing Voc

𝐿𝑒𝑓𝑓 =

𝑉𝑜𝑐 𝐸𝑖

An effective length id the length of a thin straight semiconductor oriented perpendicular to the given direction and parallel to antenna polarization having a uniform current equal to that at the antenna terminals and producing the same far field strength as the antenna in that direction 21. What is antenna polarization?

Polarization is nothing but physical orientation of electromagnetic waves in free space. The antenna polarization in a given direction refers to the polarization of electromagnetic waves radiated or transmitted by the antenna PART B 1. Describe the antenna parameters. (a) Gain (b) Bandwidth (c) Input Impedance (d) Effective aperture 2. (i)List out the concept of (a) Radiation pattern (b) Gain (c) Directivity (ii)Show the condition under which the fields are classified as near field and far field and explain the same 3. Mention the various classification of antennas as well as the types of antennas. 4. Summarize radiation pattern with a three dimension model. Also explain HPBW , FNBW and the various lobes. 5. (i) Illustrate the concept of (a) Bandwidth (b) Beam efficiency (c) Antenna Temperature (ii) Solve the maximum effective aperture of an antenna which is operating at a wavelength of 2 meters and has a directivity of 100. 6. Summarize radiation pattern with a three dimension model. Also explain HPBW , FNBW and the various lobes PART C 1. Elaborate the various fundamental parameters of antenna with equations and diagrams...