Electronic Communications: A Systems Approach

Jeffrey S. Beasley

Chapter 14 ANTENNAS - all with Video Answers

Educators

Chapter Questions

Problem 1

How should a transmitting antenna be designed if a vertically polarized wave is to be radiated. and how should the receiving antenna be designed for best performance in receiving the ground wave from this transmitting antenna?

Manish Jain

Numerade Educator

01:14

Problem 2

If a field intensity of $25 \mathrm{mV} / \mathrm{m}$ develops $2.7 \mathrm{~V}$ in a certain antenna, what is its effective height? (108 m)

Tom Greenwood

Numerade Educator

01:16

Problem 3

If the power of a $500-\mathrm{kHz}$ transmitter is increased from $150 \mathrm{~W}$ to $300 \mathrm{~W}$, what would be the percentage change in field intensity at a given distance from the transmitter? What would be the decibel change in field intensity? $(141 \%, 3 \mathrm{~dB})$

Narayan Hari

Numerade Educator

01:51

Problem 4

If a $500-\mathrm{kHz}$ transmitter of constant power produces a field strength of $100 \mu \mathrm{V} / \mathrm{m}$ at a distance of $100 \mathrm{mi}$ from the transmitter, what would be the theoretical field strength at a distance of $200 \mathrm{mi}$ from the transmitter? $(50 \mu \mathrm{V} / \mathrm{m})$

Varsha Aggarwal

Numerade Educator

Problem 5

If the antenna current at a $500-\mathrm{kHz}$ transmitter is reduced $50 \%$, what would be the percentage change in the field intensity at the receiving point? $(50 \%)$

Check back soon!

01:44

Problem 6

Define field intensity. Explain how it is measured.

Ajay Singhal

Numerade Educator

01:29

Problem 7

Define polarization as it refers to broadcast antennas.

Ajay Singhal

Numerade Educator

Problem 8

Explain how antenna reciprocity occurs.

Check back soon!

Problem 9

Explain the development of a half-wave dipole antenna from a quarter-wavelength, opencircuited transmission line.

Check back soon!

01:16

Problem 10

Draw a diagram showing how current varies along a half-wavelength dipole antenna.

Mayukh Banik

Numerade Educator

Problem 11

Explain the voltage and current relationships in a one-wavelength antenna, one half-wavelength (dipole) antenna, and one quarter-wavelength grounded antenna.

Check back soon!

02:06

Problem 12

What effect does the magnitude of the voltage and current at a point on a half-wave antenna in free space (a dipole) have on the impedance at that point?

Ajay Singhal

Numerade Educator

03:20

Problem 13

Can either of the two fields that emanate from an antenna produce an electromagnetic field (EMF) in a receiving antenna? If so, how?

Sheh Lit Chang

University of Washington

Problem 14

Draw the three-dimensional radiation pattern for the half-wave dipole antenna, and explain how it is developed.

Check back soon!

Problem 15

Define antenna beamwidth.

Check back soon!

01:38

Problem 16

What is the effective radiated power of a television broadcast station if the output of the transmitter is $1000 \mathrm{~W}$, antenna transmission line loss is $50 \mathrm{~W}$, and the antenna power gain is 3? $(2850 \mathrm{~W})$

Narayan Hari

Numerade Educator

03:04

Problem 17

A $\lambda / 2$ dipole is driven with a $5-\mathrm{W}$ signal at $225 \mathrm{MHz}$. A receiving dipole $100 \mathrm{~km}$ away is aligned so that its gain is cut in half. Calculate the received power and voltage into a $73-\Omega$ receiver. $(7.57 \mathrm{pW}, 23.5 \mu \mathrm{V}$ )

Suhas Katkar

Numerade Educator

Problem 18

An antenna with a gain of $4.7 \mathrm{dBi}$ is being compared with one having a gain of $2.6 \mathrm{dBd}$. Which has the greater gain?

Check back soon!

02:02

Problem 19

Explain why a monopole antenna is used below $2 \mathrm{MHz}$

Keshav Singh

Numerade Educator

01:02

Problem 20

Explain what is meant by half-wave dipole. Calculate the length of a $100-\mathrm{MHz} \frac{2}{3} \lambda$ antenna.

Narayan Hari

Numerade Educator

01:02

Problem 21

Determine the distance from a $N / 2$ dipole to the boundary of the far-field region if the $\lambda / 2$ dipole is being used in the transmission of a $90.7-\mathrm{MHz}$ FM broadcast band signal. $(R=1.653 \mathrm{~m})$

Narayan Hari

Numerade Educator

03:32

Problem 22

Determine the distance from a parabolic reflector of diameter $D=10 \mathrm{~m}$ to the boundary of the far-field region. The antenna is being used to transmit a 4.1-GHz signal. $(R=2733.3 \mathrm{~m})$

Khoobchandra Agrawal

Numerade Educator

Problem 23

Define near and far fields.

Check back soon!

01:50

Problem 24

Define radiation resistance and explain its significance.

Ajay Singhal

Numerade Educator

03:48

Problem 25

The ammeter connected at the base of a vertical antenna has a certain reading. If this reading is increased 2.77 times, what is the increase in output power? (7.67)

Khoobchandra Agrawal

Numerade Educator

04:45

Problem 26

How is the operating power of an AM transmitter determined using antenna resistance and antenna current?

Ameer Said

Numerade Educator

04:45

Problem 27

Explain what happens to an antenna's radiation resistance as its length is continuously increased.

Ameer Said

Numerade Educator

02:20

Problem 28

Explain the effect that ground has on an antenna.

Shahab Ullah

Numerade Educator

06:42

Problem 29

Calculate the efficiency of an antenna that has a radiation resistance of $73 \Omega$ and an effective dissipation resistance of $5 \Omega$. What factors could enter into the dissipation resistance? $(93.6 \%)$

Eduard Sanchez

Numerade Educator

01:52

Problem 30

Explain the following terms with respect to antennas (transmission or reception):
(a) Physical length.
(b) Electrical length.
(c) Polarization.
(d) Diversity reception.
(e) Corona discharge.

Arpit Gupta

Numerade Educator

Problem 31

What is the relationship between the electrical and physical length of a half-wave dipole antenna?

Check back soon!

02:00

Problem 32

What factors determine the resonant frequency of any particular antenna?

Arpit Gupta

Numerade Educator

01:03

Problem 33

If a vertical antenna is $405 \mathrm{ft}$ high and is operated at $1250 \mathrm{kHz}$, what is its physical height expressed in wavelengths? $(0.54 \mathrm{X})$

Prabhu Ramji

Numerade Educator

02:03

Problem 34

What must be the height of a vertical radiator one half-wavelength high if the operating frequency is $1100 \mathrm{kHz}$ ? $(136 \mathrm{~m})$

Alex Moore

Numerade Educator

Problem 35

What is an antenna feed line? Explain the use of resonant antenna feed lines, including advantages and disadvantages.

Check back soon!

Problem 36

What is a nonresonant antenna feed line? Explain its advantages and disadvantages.

Check back soon!

01:27

Problem 37

Explain the operation of a delta match. Under what conditions is it a convenient matching system?

Ankur S

Numerade Educator

Problem 38

Draw a simple schematic diagram of a push-pull, neutralized radio-frequency amplifier stage, coupled to a vertical antenna system.

Check back soon!

01:16

Problem 39

Show by a diagram how a two-wire radio-frequency transmission line may be connected to feed a half-wave dipole antenna.

Mayukh Banik

Numerade Educator

Problem 40

Calculate the characteristic impedance of a quarter-wavelength section used to connect a $300-\Omega$ antenna to a $75-\Omega$ line. ( $150 \Omega$ )

Check back soon!

03:38

Problem 41

Explain how delta matching is accomplished.

Bryan Lynn

Numerade Educator

00:53

Problem 42

Which type of antenna has a minimum of directional characteristics in the horizontal plane?

Mayukh Banik

Numerade Educator

04:45

Problem 43

If the resistance and the current at the base of a monopole antenna are known, what formula can be used to determine the power in the antenna?

Ameer Said

Numerade Educator

Problem 44

What is the difference between a half-wave dipole and a monopole antenna?

Check back soon!

01:16

Problem 45

Draw a sketch and discuss the horizontal and vertical radiation patterns of a quarter-wave monopole antenna. Would this also apply to a similar type of receiving antenna?

Mayukh Banik

Numerade Educator

Problem 46

What is an image antenna? Explain its relationship to the monopole antenna.

Check back soon!

02:17

Problem 47

What would constitute the ground plane if a quarter-wave grounded (whip) antenna, $1 \mathrm{~m}$ in length, were mounted on the metal roof of an automobile? Mounted near the rear bumper of an automobile?

Khoobchandra Agrawal

Numerade Educator

00:29

Problem 48

What is the importance of the ground radials associated with standard broadcast antennas? What is likely to be the result of a large number of such radials becoming broken or seriously corroded?

Luis Rios

Numerade Educator

01:19

Problem 49

What is the effect on the resonant frequency of connecting an inductor in series with an antenna?

Luis Mendoza

Numerade Educator

02:48

Problem 50

What is the effect on the resonant frequency of adding a capacitor in series with an antenna?

Vishal Gupta

Numerade Educator

01:59

Problem 51

If you desire to operate on a frequency lower than the resonant frequency of an available monopole antenna, how may this be accomplished?

Lisa Tarman

Numerade Educator

Problem 52

What is the effect on the resonant frequency if the physical length of a $\lambda / 2$ dipole antenna is reduced?

Check back soon!

00:49

Problem 53

Why do some standard broadcast stations use top-loaded antennas?

Carlos Henrique De Lima

Numerade Educator

01:24

Problem 54

Explain why a loading coil is sometimes associated with an antenna. Under this condition, would absence of the coil mean a capacitive antenna impedance?

Penny Riley

Numerade Educator

View

Problem 55

Explain how the directional capabilities of the elementary antenna array shown in Figure 14-19 are developed.

Lainey Roebuck

Numerade Educator

02:27

Problem 56

Define the following terms:
(a) Driven elements.
(b) Parasitic elements.
(c) Reflector.
(d) Director.

Shahab Ullah

Numerade Educator

Problem 57

Calculate the ERP from a Yagi-Uda antenna (illustrated in Figure 14-20) driven with $500 \mathrm{~W}$. $(2500 \mathrm{~W})$

Check back soon!

03:42

Problem 58

Calculate the $F / B$ ratio for an antenna with
(a) Forward gain of $7 \mathrm{~dB}$ and reverse gain of $-3 \mathrm{~dB}$.
(b) Forward gain of $18 \mathrm{~dB}$ and reverse gain of $5 \mathrm{~dB}$.

Willis James

Numerade Educator

01:16

Problem 59

Sketch a Yagi-Uda configuration.

Mayukh Banik

Numerade Educator

Problem 60

Describe the physical configuration of a collinear array. What is the effect of adding more elements to this antenna?

Check back soon!

Problem 61

Describe the physical configuration of a broadside array. Explain the major advantage they have compared to collinear arrays.

Check back soon!

04:46

Problem 62

What is the direction of maximum radiation from two vertical antennas spaced $\lambda / 2$ and having equal currents in phase?

Farhanul Hasan

Numerade Educator

03:20

Problem 63

How does a directional antenna array at an AM broadcast station reduce radiation in some directions and increase it in other directions?

Sheh Lit Chang

University of Washington

00:57

Problem 64

What factors can cause the directional pattern of an AM station to change?

Keshav Singh

Numerade Educator

Problem 65

Define phased array.

Check back soon!

Problem 66

Explain how a parasitic array can be developed.

Check back soon!

Problem 67

Describe the major characteristics of a log-periodic antenna. What explains its widespread use? Explain the significance of its shortest and longest elements.

Check back soon!

01:00

Problem 68

Describe the directional characteristics of the following types of antennas:
(a) Horizontal half-wave dipole antenna.
(b) Vertical half-wave dipole antenna.
(c) Vertical loop antenna.
(d) Horizontal loop antenna.
(e) Monopole antenna.

Raj Bala

Numerade Educator

01:24

Problem 69

What is the directional reception pattern of a loop antenna?

Penny Riley

Numerade Educator

View

Problem 70

What is a ferrite loop antenna? Explain its application and advantages.

Victor Salazar

Numerade Educator

06:42

Problem 71

What is the radiation resistance of a standard folded dipole? What are its advantages over a standard dipole? Why is it usually used as the driven element for Yagi-Uda antennas instead of the half-wave dipole antenna?

Eduard Sanchez

Numerade Educator

Problem 72

Describe the operation of a slot antenna and its application with aircraft in a driven array format.

Check back soon!

Problem 73

An antenna has a maximum forward gain of $14 \mathrm{~dB}$ at its $108-\mathrm{MHz}$ center frequency. Its reverse gain is $-8 \mathrm{~dB}$. Its beamwidth is $36^{\circ}$ and the bandwidth extends from 55 to $185 \mathrm{MHz}$. Calculate:
(a) Gain at $18^{\circ}$ from maximum forward gain. (11 dB)
(b) Bandwidth. (130 MHz)
(c) $F / B$ ratio. $(22 \mathrm{~dB})$
(d) Maximum gain at $185 \mathrm{MHz}$ ( $11 \mathrm{~dB})$

Check back soon!

Problem 74

Explain the difference between antenna beamwidth and bandwidth.

Check back soon!

Problem 75

Microwave antennas tend to be highly directive and provide high gain. Discuss the reasons for this.

Check back soon!

01:16

Problem 76

What is a horn antenna? Provide sketches of three basic types, and explain their important characteristics.

Mayukh Banik

Numerade Educator

00:38

Problem 77

Describe how a radar beam is formed by a paraboloidal reflector.

Norman Atentar

Numerade Educator

00:38

Problem 78

With sketches, explain three different methods of feeding parabolic antennas.

Norman Atentar

Numerade Educator

Problem 79

A160-ft-diam parabolic antenna is driven by a $10-\mathrm{W}$ transmitter at $4.3 \mathrm{GHz}$. Calculate its effective radiated power (ERP) and its beamwidth. (29.3 MW, 0.10 ${ }^{\circ}$ )

Check back soon!

01:55

Problem 80

A parabolic antenna has a $0.5^{\circ}$ beamwidth at $18 \mathrm{GHz}$. Calculate its gain in $\mathrm{dB}$. (50.7)

Narayan Hari

Numerade Educator

02:45

Problem 81

What is a radome? Explain why its use is often desirable in conjunction with parabolic antennas.

Mohamed Mohamed

Numerade Educator

Problem 82

Explain the principles of a zoned lens antenna, including the transformation of a spherical wave into a plane wave.

Check back soon!

01:56

Problem 83

The antenna in Figure 14-32 has a resonant frequency of $1.3 \mathrm{GHz}$. Calculate the bandwidth of this patch antenna. $(\approx 130 \mathrm{MHz})$

Meghan Miholics

Numerade Educator

01:55

Problem 84

The beamwidth of a $4.0 \mathrm{GHz}$ signal is $1.1^{\circ}$. Determine the $\mathrm{dB}$ power gain. $(43.8 \mathrm{~dB})$

Narayan Hari

Numerade Educator

00:37

Problem 85

Determine the focal length of a 5 -m parabolic reflector with a curve depth of $1.23 \mathrm{~m}$.

Zachary Warner

Numerade Educator

01:55

Problem 86

Determine the approximate gain of a $10-\mathrm{m}$ antenna operating at $14 \mathrm{GHz}$. Express your answer in $\mathrm{dB}$.

Narayan Hari

Numerade Educator

Problem 87

Determine the approximate beamwidth of a 10-m parabolic antenna operating at (a) $14 \mathrm{GHz}$ and (b) $4 \mathrm{GHz}$. Compare the two results.

Check back soon!

Problem 88

Find the effective aperture of a 3-m parabolic antenna, given a reflection efficiency of 0.6 .

Check back soon!

08:14

Problem 89

A ship radio-telephone transmitter operates on $2738 \mathrm{kHz}$. At a distant point from the transmitter, the $2738-\mathrm{kHz}$ signal has a measured field of $147 \mathrm{mV} / \mathrm{m}$. The second harmonic field at the same point is measured as $405 \mu \mathrm{V} / \mathrm{m}$. How much has the harmonic emission been attenuated below the $2738-\mathrm{kHz}$ fundamental? $(51.2 \mathrm{~dB}$ )

Mayukh Banik

Numerade Educator

Problem 90

You are asked to calculate effective radiated power. What data do you need to collect and how do you perform the calculation?

Check back soon!

01:28

Problem 91

Design a log-periodic antenna to cover the complete VHF TV band from $54 \mathrm{MHz}$ to $216 \mathrm{MHz}$. Use a design factor ( $\tau$ ) of 0.7 , and provide a scaled sketch of the antenna with all dimensions indicated.

Salamat Ali

Numerade Educator

02:51

Problem 92

A loop antenna used for DF purposes detects a null from a signal with the loop rotated $35^{\circ}$ counterclockwise (CCW) from a line of latitude. When the antenna is moved $3 \mathrm{mi}$ west along the same line of latitude, it detects a null from the same signal source when rotated $45^{\circ}$ clockwise (CW) from the line of latitude. You have been asked to identify the exact location of the signal source with respect to the two points when readings were taken. Provide this information. (You may use a sketch.)

Teresa Fuston

Numerade Educator