ANTENNAS AND WAVE PROPAGATION OBJECTIVE QUESTIONS

ANTENNAS AND WAVE PROPAGATION OBJECTIVE QUESTIONS

UNIT I 1. An antenna is (a) (a) Inductive (b) Capacitive (c) resistive above its resonance frequency (d) none 2. The input impedance of a λ/2 Dipole antenna is (c) (a)infinity (b) zero (c) 73.13 ohms (d) none. 3. The efficiency of an antenna increases with an increase (b) (a) Increase of ohmic resistance of an antenna (b) Increase of radiation resistance of an antenna (c) Increase of input reactance of an antenna (d) Increase of output reactance of an antenna 4. If D,G,η denote directivity, gain, efficiency then (b) (a) D= ηg (b) D=G/ η (c) DG= η (d) D=G+ η 5. For given aperture size beam width (b) (a) Increases with decreases in wavelength (b) Increases with increases in wavelength (c) Has no relationship with wavelength (d) All of the above 6. The directivity of an antenna is related as (b) (a) Directly proportional to its solid angle (b) inversely proportional to its solid angle (c) no relationship (d) none 7. effective area is (c) (a) Same as physical area (b) Greater than physical area (c) Less than physical area (d) None of the above 8. Effective area related to gain (c) (a) Ae=4πG /λ 2 (b)ae=g (c) G=4πAe /λ 2 (d) Ae=G 2 /2. 9. If Gd is direct gain,then gain in db is (a) (a) 20log 10 Gd (b) 10log 10 Gd (c) 30log 10 Gd (d) none of the above 10. MKS unit of radiation intensity is (c) (a) Watt/m (b) watt/m 2 (c) watt/sterradian (d) none of the above 11. Power density for isotropic radiator is given by (a) (a) W t /4πR 2 (b) W t /4πR (c) W t /4π (d) none of the above 12. Gain & directivity are related by G= ηd, where η (b) (a) η >1 (b) η 1 (c) η = (d) η=0 13. Radiation resistance(r r ) is related to power radiate (W t ) and peak value of current(i m ) as (a) (a) R r =2 W t / I m 2 (b) R r = W t / I m 2 (c) R r = W t / I m (d) R r =2W t 2 / I m

14. For a Lossless isotropic antenna (a) (a) G d =D (b) G d <D (c) G d >D (d) G d D 15. The most efficient antenna length is (c) (a) Eighth of a wave (b) quarter of a wave (c) half a wave (d) one wave 16. Which of the following makes the best feed line? (d) (a) Twisted pair (b) TV lead in (c) Single ware (d) Coax 17. Efficiency Factor η always lie between (a) a) 0 and 1 b) 1 and c) 0 and d) All the above 18. Electromagnetic waves are reflected when they (c) (a) Pass into a medium of different dielectric constant (b) Are polarized at right angle to the direction of propagation (c) Encounter a perfectly conducting surface (d) Pass through a small slot in a conducting plane. 19. When an electromagnetic wave is moving in free space, it suffers from (b) (a) Absorption (b) Attenuation (c) Refraction (d) none of the above. 20. To get efficient radiation, radiation resistance should be greater than (b) a) Inductance b) Ohmic resistance c) Ohmic conductance d) Reactance 21. The quality deciding factor of transmitting and receiving antenna is (a) a) Beam efficiency b) Resolution c) Gain d) Directivity 22. A dipole having a length 3cm is operated at 1 GHz. The efficiency factor is 0.6.Calculate the antenna gain? (b) ( a ) 1.5 ( b ) 0.9 ( c ) 1.642 ( d ) 2.34 23. The directivity of sources with hemispherical power patterns is (a) ( a ) 2 ( b ) 1.27 ( c ) 1.5 ( d ) 4 24. Length of a short wave dipole () (a) λ (b) λ/2 (c) λ/3 (d) λ/4 25. A Short dipole is called () (a) Nortorn dipole (b) Guassian dipole (c) Hertz dipole (d) Half wave dipole

26. Far field pattern is also called () (a) Induction field (b) Radiation field (c) Both (d) None 27. Near field also called () (a) Induction field (b) Radiation field (c) Both (d) none 28. Radiation resistance of a half dipole () (a)infinity (b) zero (c) 73.13 ohms (d) none 29. Gain of half wave dipole is 30. Effective length of a half wave dipole () (a) λ /π (b)π/ λ (c) 0.1 λ (d) none 31. Antenna theorem are applicable where () (a) Equality of directional patterns (b) Equality of directivity (c) Equality of effective length (d) all of the above 32. Energy stored in magnetic field is () (a) W= 1/2 µh 4 (b) W= µ H2 2 (c) W= µh 2 /2 33. Ohm s law is () (a) J=σ/E (b) J=σE (c) J=E/σ 34. A conductor is said to be perfect () (a) Zero conductivity (b) Infinite Conductivity (c) Uniform Conductivity 35. A Uniform Plane wave is one in which () (a) E & H perpendicular (b) E & H lies in a plane (c) E & H parallel

36. The instinsic impedance of free space is () (a) 75 (b) 77 (c) 300 (d) 377 37. Polynting theorem is () (a) P=EH (b) P=E/H (c) P=ExH (d) None 38. The radiation resistance of an antenna is given by 50Ω& the current in it is 8 Amp, then the power radiated by the antenna is () a) 32 W b) 320 W c) 3200 W d) 3.2 W 39. The value of directivity alwayslies between () a) 0 & 1 b) 1 & c) to d) 0 to 40. The electric field strength produced by an antenna varies () a) Directly as radiated power b) Directly as the square root of radiated power c) inversely as the square root of radiated power d) inversely as radiated power 41. The relation between HPBW & BWFNis given by () a) HPBW = 2BWFN b) 2HPBW = BWFN c) BWFN = HPBW d) BWFN = 4HPBW 42. The directivity of small loop antenna is () a) 3/2 b) 5/2 c) 1/2 d) 7/2 43. Most preferred loop antenna is () a) Rectangular b) Circular c) Triangular d) Rhombic

44. The dipole has the following fields () ( a ) E r, E θ, E φ ( b ) E r, E θ, H φ ( c ) H r, E θ, E φ ( d ) E r, H θ, H φ 45. Radiation resistance of single turn loop is 0.5 ohms then the turns are increased to eight then the radiation resistance is () ( a ) 0.5 ohms ( b ) 4 ohms ( c ) 1 ohm ( d ) 32 ohms UNIT II 1. Which antenna givescircular polarized wave () (a) Yagi Uda (b) dipole (c) helical 2. To reduce end effect, the length of half wavelength conductor is () (a) 4a2(n-0.05)/f(nH) (b) 4a2/f (c) 492*f 3. Combination of two long wire antenna () (a) V (b) rhombic (c) both 4. Rhombic antenna is example of () (a) End fire (b) broadside (c) travelling wave 5. Height above ground h for Rhombic antenna is () (a) λ (b) 4sinB (c) λ/4sinb 6. Length of each side of rhombic antenna is () (a) λ/2sin2b (b) 2sin2B9 (c) λ 7. For helical antenna the radiation pattern along () (a) Ground plane (b) axis (c) none 8. The Pitch angle for helical antenna () (a) tan 1 [ s s ] (b) (c) tan 1 πd πd [πd]. 9. Axial ratio for hlical antenna () (a) 25 λ/πd2 (b) π2d2 (c) 25 λ 10. Terminal impedance of helical antenna () (a) 140c (b) c/ λ (c) 140c/ λ 11. BWFN for helical antenna () (a) 115/c λ3/ns (b) λ3/ns (c) λ3/ns/ns 12. Induction and radiation fields are equal at () (a) λ/4 (b) λ/2 (c) λ/6 (d) λ/2π 13. R r of λ/2 antenna in free space is () (a) 73 ohm (b) 377 ohm (c) 36.5 ohm 14. A half wavelength dipole of 30 MHz has length of () (a) 10m (b) 3m (c) 1m (d) 50 cm 15. Radar antenna usually ()

a) Parabolic (b) Yagi (c) helical 16. The radiated wave is linearly polarized wave with horizontal polarization for () a) AR = 0 b) AR = 1 c) AR= d) AR = -1 17. Orientation of electric-field vector along the straight line at every instant of time is () a) Linear polarization b) Circular polarization c) Elliptical polarization d) All of the above 18. Which of the following antennas is best excited from a waveguide? () ( a ) dipole ( b ) rhombic ( c ) horn ( d ) helical 19. To achieve circular polarization, primarily in the major lobe, the circumference of helix must be in the range of () ( a ) 3/4 <C/λ<4/3 ( b ) C/λ > 4/3 ( c ) 5 <C/λ<10 ( d ) 10 <C/λ<100 20. In normal mode of operation the field radiated by antenna is in plane. 21. In yagi-uda antenna, the length of dipole, reflector and director at resonance with respect to λ/2 is () (a) equal,greater,less (b) less,greater,equal (c) greater,less,equal (d ) equal,greater,equal 22. The spacing S, turn length L and pitch angle are related as 23. Helix responds as a loop for the tilt angle of 24. antenna gives circular polarization UNIT III 1. Length of reflector of Yagi uda antenna () (a) 0.45 λ (b) 0.5 λ (c) 0.55 λ (d) none 2. Length of director of Yagi-uda antenna () (a)0.45 λ (b) 0.5 λ (c) 0.55 λ 3. Length of driving element of Yagi-uda antenna () (a)0.45 λ (b) 0.5 λ (c) 0.55 λ 4. Distance between driving element and reflector () (a)0.23 λ (b)0.15 λ (c) 0.1 λ 5. Distance between driving element and director () (a)0.23 λ (b)0.15 λ (c) 0.1 λ 6. can be used as driving element in Yagi-uda antenna () (a) Yagi-uda (b0 Halfwave dipole (c) both 7. N element folded dipole has input impedance () (a) n*73 (b) n 2 *73 (c) n 3 *73 8. Input impedance () (a) 292 ohm (b) 343 ohm (c) 657 ohm 9. BWFN of paraboloid for circular aperture () (a) 140 λ/d (b) 115 λ/d (c) 58 λ/d 10. F/D ratio of parabolic reflector () (a) 1/4cotӨ/2 (b) 1/4cosӨ/2 (c) 1/4sinӨ/2

11. If efficiency of parabolic reflector is 0.25, radius is 5m. what is effective aperture () (a) 6.25 π (b) 12.5 π (c) 25 π 12. HPBW of parabolic reflector () (a) 140 λ/d (b) 115 λ/d (c) 58 λ/d 13. General feed of parabolic reflector () (a) Horn (b) Yagi-Uda (c) both 14. Cassegrain feed (a) Increases spill over (b) decreases spill over (c) both 15. In cassegrain feed the focus of paraboloid and focus of hyperboloid are () (a) coincides (b) different points (c) different planes 16. E-sectral horn antenna is flared in () (a) E-direction (b) H-direction (c) both 17. H-sectral horn antenna is flared in () (a)e-direction (b) H-direction (c) both 18. Pyramidal horn antenna is flared in () (a)e-direction (b) H-direction (c) both 19. The length of one side of horn antenna () (a) 4LS (b) 8LS (c) 16LS 20. Flare antenna for horn antenna () (a)2cos -1 [L/L+f] (b)2tan -1 [a/2l] (c) both 21. For horn antenna, optimum L () (a)f 0 Cos(Θ/2)1-Cos(Θ/2) (c) f 0 Cot(Θ/2)1-Cot(Θ/2) (c) both 22. The contour of lens in polar co-ordinate () (a)r=l(µ-1) µcos Θ-1 (b) r=lµ/ µcos Θ (c) none 23. In Zoning, the thickness of lens () (a) λ/ µ (b) λ-1/ µ (c) λ/ µ-1 24. with zoning () (a) weight reduces (b) weight increases (c) both UNIT IV 1. In uniform linear array, first side lobe level is () a) 0.51 b) 0.312 c) 0.121 d) 0.212 2. In broadside array, null-to-null beam width is () a) 2 2λ b) 2λ c) 2 λ d) 2λ

3. Why do we go for Antenna Arrays () a) To increase Directivity b) To increase Aperture area c) To increase Beam Area d) none 4. In Endfire array, null-to-null beam width is () a) 2 2λ b) 2λ c) 2 λ 2λ d) 5. The relative ratios of 5 element Broadside array in UNIFORM DISTRIBUTION is () a) 1:1:1:1:1 b) 1:0:0:0:1 c) 1:4:6:4:1 d) 1:1.6:1.9:1.6:1 6. The relative ratios of 5 element Broadside array in OPTIMUM DISTRIBUTION(Dolph- Chebyschef) is () a) 1:1:1:1:1 b) 1:0:0:0:1 c) 1:4:6:4:1 d) 1:1.6:1.9:1.6:1 7. The relative ratios of 5 element Broadside array in EDGE DISTRIBUTION is () a) 1:1:1:1:1 b) 1:0:0:0:1 c) 1:4:6:4:1 d) 1:1.6:1.9:1.6:1 8. The relative ratios of 5 element Broadside array in BINOMIAL DISTRIBUTION is () a) 1:1:1:1:1 b) 1:0:0:0:1 c) 1:4:6:4:1 d) 1:1.6:1.9:1.6:1 9. HPBW for UNIFORM DISTRIBUTION is () a) 23 b) 31 c) 27 d) 15 10. HPBW for EDGE DISTRIBUTION is () a) 23 b) 31 c) 27 d) 15 11. HPBW for OPTIMUM(Dolph-Chebyschef) DISTRIBUTION is () a) 23

b) 31 c) 27 d) 15 12. HPBW for BINOMIAL DISTRIBUTION is () a) 23 b) 31 c) 27 d) 15 13. The Field Components of a loop antenna are () a) E Ø, H Ɵ b) E Ø,H Ø c) E Ɵ,H Ɵ d) E Ɵ,H Ø 14. The maximum radiation of end fire array is directed to the axis of the array 15. In array the maximum radiation can be oriented in any direction 16. Direction of maximum radiation is normal to the axis of array, it is array 17. Ψ in the case of radiation pattern of 8-isotropic elements fed in phase spaced λ/2 apart is 18. In radiation pattern measurement, the power at primary in antenna is () (a) different (b) constant (c) varies 19. The minimum distance between T*r and R*r for radiation pattern measurement () (a)>2d/ λ (b)<=2d 2 / λ (c) >=2d 2 / λ 20. Allowable phase difference for end of primary antenna is () (a) λ/4 (b) λ/ 8 (c) λ/ 16 21. Frisss s transmission equation is () (a) W R /W T =A er *A ct / λ 2 d 2 (b) W R /W T =G T *G R *λ 2 (c) both (d) none 22. Directivity D=? () (a)41257/o E (b) 41257/O H (c) 41257/O E O H 23. Parabolic and lens antenna are mainly used at () (a)sw (b)mw (c) Microwave UNIT V 1. Direction of electric field and magnetic field () (a) Parallel (b) perpendicular (c) none 2. Expression for path loss () (a) L s =[4π/d] 2 (b) [4π/ λ] 2 (c) [4πd/ λ] 2 3. Ground wave propagation take place upto () (a) 2KHz (b)2mhz (c)2ghz 4. Due to wave tilt, the strength of signal () (a) Increases (b) decreases (c) same 5. For b<5 0 attenuation factor A is given as () (a)2+0.3p/2+p+0.6p 2 (b)2/2+0.3p (c) 0.3p/2+6p 2

6. Sky wave propagation takes place () (a)2-20khz (b)2-200 KHz (c) 2-30 MHz 7. Space wave propagation takes place between () (a)below 30 MHz (b0above 30 MHz (c) above 50MHz 8. During day time dominant regions are () (a) E,F (b)d,e,f 1,F 2 (c) F 1,F 2 9. During night time dominant regions are () (a) E,F (b)d,e,f 1,F 2 (c) F 1,F 2 10. F layer is also called () (a) Appleton (b) Kenelly (c) Heaviside 11. Electron density in region () (a) 10-20 (b)10 5-10 6 (c) 10 14-10 16 13. In D region ionization is due to photo ionization of () (a) hydrogen molecule (b) oxygen molecule (c) nitrogen molecule 14. E region is formed by ionization of all gases with () (a)uv ray (b) Xray (c) α ray 15. For angle of incidence I, the muf is () (a)cosif c (b) seif c (c) tanif c 16. Television broadcast generally uses () (a) LOS (b) Ionosphereic propagation (c) ground wave propagation 17. The relative permittivity of ionosphere at radio frequency () (a) >1 (b) <1 9c) =1 18. D Layer starts from () (a) 50-90 Km (b) 20-50 Km (c) 90-110 Km 19. Long distance short-wave radio broadcasting uses () (a) Tropospheric scatter (b)direct wave (c) ground wave 20. Scatter transmission is used at frequency () (a) UHF & VHF (b) UHF (c) VHF 21. Which of the wave unaffected during day or night () (a) Troposheric scatter (b) sky wave (c) ground wave 22. Microwave signal follow the curvature of earth that phenomenon is called as () (a) Tropospheric scatter (b) sky wave (c) ground wave 23. During day which layer do not exist () (a) D (b) F1 (c) F2 (d) E (e) F 24. During day time ionosphere consist of () (a) D,E,F layers (b) D,E,F2 layers (c) D,E,F1,F2 layers 25. LOS distance in miles is given as () (a) 2( ht + hr) (b) 2(ht+hl) (c) (2 hr ht ) 26. Earth s radius R related to µ () (a)dh/d µ (b) d µ/dh (c) dh/d µ (d) -d µ/dh 27. Expression for k in terms of R & r is () (a) 1(1+r/R) (b) 1/(1-r/R) (c) 1/(1-R/r) 28. Received electric field strength at R*r for ground wave propagation ()

(a) only direct ray (b) only reflected ray (c) resultant (d) none 29. Frisss s transmission equation is () (a) W R /W T =A er *A ct / λ 2 d 2 (b) W R /W T =G T *G R *λ 2 (c) both (d) none 30. The path loss for ground wave propagation () (a) (λ/4πd) 2 (b)( 4πd/ λ) 2 (c) none