Chapter 14 - Electromagnetic Wave Propagation

BOO OOK K REVIEW EVIEW IN CO C OMMUNIC MMUNICAT ATIONS IONS

C HAP HAPTER 14

Electr Elec tronic C ommunications ommunic ations System By Wayne ayne Tomasi

ELEC TROMAG MAGNETIC WAVE PR PROPAGATION ION

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DEFINITIO DEFINITIONS NS

TERMS

1)

Propagation of electromagnetic waves often called radio-frequency (RF) propagation or simply radio propagation.

Free-space

2)

Elec tri tric a l ener ene rgy that has ha s esc esc ap ed into into free free spa c e.

3)

Electr lec troma omagne gneti tic c wave wa ve

The The ori orientation entation of the the electr elec triic field field vec tor in in respe espec ct to the surfac surfac e of the Ea rth.

4)

Pola Po larriza iza tion re mains ma ins c o nsta nstant nt

5)

Forms o f Linea Linea r p olar ola riza iza tion

6)

Polarization vector rotates 360◦ as the wave moves one wave-length through the space and the field streng trength th is is equa eq uall at a ll a ngles of pola p olarriza iza tion. tion.

7)

Fie Fie ld stre tre ngth var va ries with c hang ha nge e s in p o larization. larization.

8)

Used to show the relative electromagnetic wave propagation.

9)

10)

11)

Line Linea a r Polariz Po lariza a tion Horizontal Polarization a nd Vertica Vertica l Polariz Polariza tion tion

direction

C irc irc ula ula r Polariz Polariza tion tion

Elli Ellip p tic tic a l Polariz Po lariza a tio tio n of

Formed when two points of equal phase on rays propagated from the same source are joined together. A single single loc a tion tion from from which whic h ra ra ys propa ga te eq ually ually in all direc direc tio tio ns. ns.

Invi Invis sible forc forc e field field produc ed b y a magne ma gnet, t, such uc h a s a conductor when current is flowing through. Prepared repa red By : MA. MA. ELAINE AINE L. C ORTEZ

Polarization

Rays

Wavefront

Point Po int sourc source e

Magnetic Field

86

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12)

Strength of a magnetic field (H) produced around a conductor is expressed mathematically as:

H = 1/2d

13)

Invisible force fields produced by a difference in voltage voltage potent po tentiial between b etween two c onduc tors tors.

Elec tric tric field fields s

14)

Elec Elec tric tric filed stre tre ngth ng th (E) (E) is e xp ressed essed mathema ma thema tica tic a lly lly a s:

E = q/4d 2

15)

Dielectric constant of the material separating the two conductors.

Permittivity

16)) 16

The per pe rmitti mittivity vity o f a ir or free free sp sp a c e is is a p p ro ximately. imate ly.

-12 F/ m 8.85 x 10 -12

17)

The The rate a t whic whic h energy energy pa sses thr through a given given surfac urfac e a rea in free free spa c e.

Powe Po werr d ensit ensity y

18)

Intensity of the electric and magnetic fields of an electr elec troma omagneti gnetic c wave prop propa a ga ting ting in in free free spa c e.

Field intensity

M a themati thema tic c a lly lly powe po werr d ensity ensity is is express expressed a s: 19)

P = €H W/m W/ m2

The The char cha rac teri teristic tic impe impeda da nce of of a lossless transmission medium is equal to the square 20) roo t of the ratio of o f its its magne ma gne tic tic per pe rmea bility bility to to its e lec tric tric permit p ermitti tivity vity..

Zs =(µo/0)1/ 2

21)

Point source that radiates power at a constant rate uniformly uniformly in all a ll dire dire c tions. tions.

Isotr Isotrop opiic ra diator dia tor







23)) 23

Prop Prop a ga tion tion mediu med ium. m.

Isotropic Isotropic medium med ium

24)

Waves propagate through free space, they spread out, resul resulti ting ng in a red ucti uc tion on in powe po werr densit density. y.

25)) 25

Reduc tio tio n of Powe Po werr.

26)

Reduc tion tion in powe po werr dens de nsit ity y with with distanc distanc e is eq uiva uivalent lent to a power loss.

Wave a ttenuati ttenuation on

27)

Spher phe ric a l spreading prea ding of the wave. wa ve.

Spa c e a ttenua ttenuati tion on

28)) 28

O ne with uniform uniform properti prop erties es throug throughout. hout.

Homog eneous ene ous medium med ium

29)

Absorption coefficient varies considerably with location, thus creating a difficult problem for radio systems engineers.

Inhomog Inhomog eneous ene ous medi med ium

30)) 30

O p tic tic a l properti prop ertie e s o f Ra dio Waves. Wa ves.

31)

Bendin end ing g of the the ra dio wave wa ve pa th.

32)

Square root of the dielectric constant and is e xp re sse d in:

33)

(k) Equiva Equivalent lent dielec tric tric c onsta onsta nt rela relati tive ve to free free space (vacuum).

Attenuation

Ab sorption Loss Loss

Refraction, Reflection, Diffraction and Interference

Refra efra c tion tion

Refra Refra c tive tive index inde x; n = (k)

K = (1- 81N/ f 2)1/ 2







35)

Ima Ima ginary ginary line line d ra wn perpend p erpendicular icular to to the interf interfa ac e a t the the po int of inc inc idence de nce .

Normal

36)

Angle formed formed b etween the inc inc ident de nt wave a nd the normal.

Angle of Incidenc Incidenc e

37)

Angle formed formed b etween the refr refra a c ted wave a nd the normal.

Angle Ang le of Refr Refra a c tion tion

38)

Ra tio tio of veloc ity ity of pr p ropa op a ga tion tion o f a light ra ra y in in free free spa c e to the veloc ity of pr p ropa op a ga tion tion of o f a light light ra ra y in in a given mater mate rial.

Refra efra c tive tive Inde x

39)

Perpendicular to the direction of propagation (pa ra llel llel to the wa w a veform) veform)

Densit Density y gr g ra dient die nt

40)) 40

To c a st or turn turn ba c k.

42)

Ratio of the reflected to the incident voltage intensities.

Reflection Coefficient

43)

Portion of the total incident power that is not reflected.

Power transmission coefficient

44)) 44

Fra Fra c tion tion of p ower ow er that pe netra netra tes medium med ium 2.

45)

Incide Inc ident nt wave wa ve front str strike ike s a n irr irre gula r surfa urfa c e , it is randomly scattered in many directions.

46)) 46

Reflec Reflec tion tion from from a per pe rfec tly tly smooth moo th surfa urfac c e.

Reflec t

Ab sorption c oe ffic ffic ient

Diffuse Diffuse refle reflec c tio tio n

Sp ec ular (mirr (mirro rlike) like) reflection







48)

Semiroug emirough h sur surfac fac e wil w illl reflec t as if it wer we re a smooth moo th surface whenever the cosine of the angle of incidence is greater than λ/8d, where d is the depth of the surface irregularity and λ is the wavelength of the the incident wave. wa ve.

49)

Modulation or redistribution of energy within a wavefront when it passes near the edge of an opa que objec objec t.

51)

Rayleigh Rayleig h c riterion iterion Cos θi > λ/8d

Diffr Diffra a c tion tion

Diffraction occurs around the edge of the obstacle, which a llows sec onda ond a ry waves wa ves to to “snea “snea k” ar a round the corner of the obstacle.

54)

States that the total voltage intens intensit ity y at a t a given point po int in in sp sp a c e is the sum sum of the indivi individua dua l wave wa ve vec tors tors.

52)

Electr lec troma oma gneti gne tic c atmosphere.

53)

C ommunic ommunic a tions tions be tween two or more more point p oints s on Earth.

54)) 54

Used for high-freq high-freq uenc y a p plica tions. tions.

55)

Ea rth –guided elec troma tromagne gneti tic c wave wa ve that tra tra vels over ove r the the sur surfac e of e a rth.

waves wa ves

tr tra velling velling

within within

Ea Ea rth’s

Shado ha dow w zone zone

Linea Linea r Supe up e rp o sitio itio n

Terr errest estial waves

Terr errest estial ra ra dio communications

Sky wa ves

Surface wave

Surfac e

56)

Relative Relative C ond ucti uc tivit vity y of Ea Ea rth Surfa urfac c es

Seawater Fla Fla t, loamy loa my soil Large bodies of freshwater

Relative C onduct onductivity Good Fair Fair






57)) 57

58)


Disa Disa dva ntages ntag es of surfac urfac e waves. wa ves.

Advantage Ad vantages s of ground ground wave wa ve propaga propa ga tion.

1. G round wa ves re re quire quire a relatively transmission power. 2. Gr G round waves wa ves a re limi limited ted to ver ve ry low, low, low , a nd mediu med ium m fr freq uencies uenc ies.. 3. Requiring large antennas. 4. Gr G ro und loss losse s var va ry c onside onsiderra b ly with surfac urfac e materia materia l and composition.

1. Given e nough noug h tra tra nsmit nsmit power po wer,, ground ground waves wa ves c a n be used used to c ommuni ommunic c ate between a ny two two loc a tions tions in the world. 2. Gr G round waves wa ves are relatively elatively una unaff ffec ec ted b y c hangin hang ing g a tmos tmosphe pherric conditions.

59)

60)

61)

62)

Tr Travel ess essentia entia lly in a straight traight line between be tween the the transmit and receive antennas.

Spa c e wave wa ve propa ga tion tion with with direc direc t waves wa ves..

The The curvatur curvature e of Eart Earth h presents presents a hori horizon to to spa spa c e wave propa propa gat ga tion.

Occurs when the density of the lower atmosphere is such that electromagnetic waves are trapped be tween it and Ea rth’s surfac urfac e.

Direct waves

LineLine-ofof-S Sight (LOS) transmis transmiss sion ion

Ra dio Horiz Horizon on

Duct propagation









64)

Located approximately between 60 miles and 85 mile mile s (100 (100 km km to 14 140 0 km) ab o ve Ea rth’s sur surfa fac c e.

65)) 65

The uppe up pe r p ortion ortion of the E layer.

66)

M a d e up o f two layer la yers s, F 1 and F 2 layers. layers.

E La La yer

Sp orad ic E layer

F La La yer

67)

Highest frequency that can be propagated directly upward and still be returned to Earth by the ionosphere.

Critical frequency

68)

Maximum vertical angle at which it can be propagated and still be refracted back by the ionosphere.

C ritic tic a l Angle

69)

A measurement technique used to determine the c riti itic a l freq freq uenc y.

Ionos Iono sp heric heric Sounding ound ing

70)

Height above the Earth’s surface from which a refrac efrac ted wa ve app a ppea ea rs to have be en refl reflec ec ted.

Virtual Height

71)

Highest frequency that can be used for sky wave propagation between two specific points on Earth’s

M a ximum imum Usa Usa ble Frequency (MUF)







75)

The area between be tween where where the the surfac urfac e waves are c ompletely omp letely dis diss sipated ipa ted a nd the p oint where where the firs first sky wave returns to Earth.

Quiet, or skip, zone

76)

Formed by the ionosphere is raised, allowing sky wa ves to tr tra vel highe higherr b efor efo re bein be ing g retur returned ned to Earth.

C eiling eiling

77)) 77

Define a s the loss loss inc inc urr urred by b y a n elec troma troma gneti gne tic c waves as it propagates in a straight line through a vac uum with with no a bsorpti bsorption on or reflec reflecti tion on of o f ener ene rgy from from nea ne a rby objec o bjec ts.

78)) 78

O c c urs urs simply imply b ec a use use o f the invers inverse squa re law. law .

79)) 79

Va riation ia tion in signal igna l loss loss.

80)

To a c c ommoda ommod a te tempor tempo ra ry fadin fad ing, g, a n a dd itiona tionall loss loss is a dd ed to the no rmal ma l pa th loss loss

Free-s ee -spa pa c e p a th los loss s

Sp rea ding loss loss

Fad ing

Fade margin Fm = 30 logD + 10log (6ABf) – 10lo 10lo g (1-R) (1-R) – 70

Chapter 14 - Electromagnetic Wave Propagation

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