UNIT -4 (Guided waves between Parallel planes)

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1 SRI VENKATESWARA COLLEGE OF ENGINEERING DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING Date : PART-A QUESTIONS AND ANSWERS Subjet : Transmission lines & Wave Guides Sub Code : EC305 Staff Name: Dr.H.UMMA HABIBA,Prof./EC Class : V sem ECE Setion : A UNIT -4 (Guided waves between Parallel planes) 1. Compare TE and TM mode. (Nov/De 01,R8) TE Eletri field strength E is entirely transverse. It has a z omponent of magneti field Hz It has no z omponent of eletri field E z.( E z = 0) At ut off frequeny the wave impedane for TE waves beomes infinity. TM Magneti field strength H is entirely transverse. It has a z omponent of eletri field Ez. It has no z omponent of magneti field H z.( H z =0) At ut off frequeny the wave impedane for TM waves beomes zero.. What is the need for Attenuator? (Nov/De 01,R8) Attenuators are needed to redue impedane mismathes in high-frequeny iruits and systems. It provides isolation to stabilize osillators. It redues the power of a signal without appreiably distorting its waveform. 3. Write the Maxwell s equation. (Apr/May 01, R8), (May 009)

2 4. What is meant by dominant mode? What is the dominant mode for parallel plate waveguide? (Apr/May 01, R8) The mode having the lowest utoff frequeny is alled dominant mode. The dominant mode for parallel plate waveguide is TEM. 5. Write down the relationship between phase veloity and group veloity (Nov/De 011,R8) (May010/May 007) The produt of phase (Vp) veloity and group veloity (Vg) is the square of free spae veloity. Phase veloity * Group veloity = C Vp x Vg = C C Veloity of light The group veloity always less than veloity of free spae whereas phase veloity always greater than veloity of free spae. 6. Write down the equations for harateristi impedane for TE, TM, and TEM waves (Nov/De 011,R8) For TM Waves, Z0 = Z TM f 1 f For TE waves,, Z0 = Z TE f 1 f For TEM waves,, Z0 = η η- intrinsi impedane of the medium 377Ω; f ut-off frequeny 7. The eletri field in free spae is given by E= 50 os[10 8 t xβx ] ay v /m. Find the diretion of wave propagation and β [Apr/May 011,R8] 8. For the frequeny of 6 GHz and plane separation of 3 m find the group and phase veloities for the dominant mode [Nov-010,R8]

3 9. Define ut-off frequeny of a guide. (Nov 010, R8) (Nov007) (or) Define the utoff frequeny for the guided waves The utoff frequeny is the frequeny below whih wave propagation will not our.the frequeny at whih the wave motion eases is known as utoff frequeny of the guide. 10. What are the methods of Exitation of modes in retangular wave guides? [Nov-010] Possible methods for feeding retangular wave guides: TE10 waveguide mode TE11 waveguide mode TE0 waveguide mode TM11 waveguide mode 11. Find the ut off wave length of a retangular wave guide whose inner dimensions are a =.3m and b = 1 m operating at TE10 [NOV-010] = a/m = m m n a b a =.3m m=1 n=0

4 1. Give the examples of guided waves (May 010) An eletromagneti wave that are guided along or over onduting or dieletri surfaes are alled guided waves. Examples of guided waves are the eletromagneti waves along parallel wire and o-axial transmission lines, waves in waveguides and the waves that are guided along the earth surfae from a radio transmitter to reeiver 13. Write the expressions for the wave impedane of TE and TM waves between parallel planes (Nov 009) Z TE f 1 f Z TM f 1 f η- intrinsi impedane of the medium 377Ω; f ut-off frequeny 14. Give the expressions for the utoff wavelength and propagation onstant of TE waves between parallel planes (Nov 009) Cut-off wavelength (λ) = a/m a- distane between the two parallel planes; m- mode number 15. Plot the frequeny vs attenuation harateristis urve of TM and TE waves guided between parallel onduting planes (Nov 008)

5 16. Enumerate the properties of TEM wave between parallel planes of perfet ondutors (Nov 008/Nov 006) The TEM wave in whih both eletri and magneti fields are tranverse entirely but have no omponent of Ez and Hz. It is referred to as prinipal waves.the properties are 1. The TEM wave is independent of frequeny.the ut-off frequeny of TEM is zero.this means that all frequenies down to zero an propagate 17. Speify the signifiane of dominant mode of operation. (April 008) Dominant mode is a mode that has the lowest ut-off frequeny or lowest order mode Comment on: (a) Charateristis impedane. (b) Wave impedane (April 008) (a) Charateristi impedane: The harateristi impedane is given by Z0=V/I. But for a parallel plate waveguide the potential differene between two plates is given by Z0=Ex/Hy. The harateristi impedane for the parallel plate waveguide is dependent only on the geometry of the guide and the material parameters of the guide. (b) Wave impedane: The intrinsi impedane or wave impedane is defined as when looking in the diretion of propagation, that is, along the z axis it is defined as the ratio of transverse omponent of eletri and magneti fields. 19. What is Prinipal wave (April 008) The TEM wave is a speial ase of guided wave propagation. It is also alled as priniple waves. The eletri and magneti fields are entirely transverse. Along the diretion normal to the diretion of propagation, the amplitude of the field omponents are onstant. TEM waves are independent of frequeny. The ut-off frequeny of the wave is zero, indiating all frequenies down to zero an propagate along the guide 0. Plot the frequeny versus wave impedane urve for the waves between parallel onduting planes. ( April 008) (Nov 006)

6 1. What are the harateristis of prinipal wave? (Nov 007) (i) The phase onstant β varies linearly with frequeny and therefore the wave propagation takes plae with out dispersion. (ii) The ut-off frequeny for the TEM wave in a parallel plane waveguide is zero and all frequenies right down to d an propagate along the guide.. What is the utoff frequeny of TEM wave? (May 007) m f 0 a This means that all frequenies down to zero an propagate along the guide. 3. Define phase veloity and group veloity (Nov 006,Nov 005) The veloity with whih the phase hanges phase in a diretion parallel to the onduting surfae is alled phase veloity. It is denoted by Vp= ω/β ; ω=πf; β phase onstant Group veloity is the veloity with whih the group of waves as a whole propagate.. It is denoted by Vg; Vg=dω/d β ; 4. What do you understand by the dominant mode in waveguide? What is its importane? (May 006) Dominant mode is a mode whih has less attenuation. It is alled a dominant mode beause all the field onfiguration Ex, Ey, Hx and Hy exist. Dominant mode is a mode that has the lowest ut-off frequeny or lowest order mode..

SRI VENKATESWARA COLLEGE OF ENGINEERING DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING Date : UNIVERSITY QUESTIONS AND ANSWERS

SRI VENKATESWARA COLLEGE OF ENGINEERING DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING Date : 02.07.2015 UNIVERSITY QUESTIONS AND ANSWERS Subject : Transmission lines & Wave Guides Sub Code :