1. Basic Antenna Theory and Concepts
ICS 620 Communication Technologies
Class #11

2. Introduction
An antenna is an electrical conductor or system of conductors
Transmission - radiates electromagnetic energy into space
Reception - collects electromagnetic energy from space
In two-way communication, the same antenna can be used for transmission and reception

3. Antenna Definition
An antenna is a circuit element that provides a transition form a guided wave on a transmission line to a free space wave and it provides for the collection of electromagnetic energy.
Antenna research from Miller & Beasley, 2002

4. Antenna Definition-cont’d
In transmit systems the RF signal is generated, amplified, modulated and applied to the antenna
In receive systems the antenna collects electromagnetic waves that are “cutting” through the antenna and induce alternating currents that are used by the receiver

5. Reciprocity
An antenna ability to transfer energy form the atmosphere to its receiver with the same efficiency with which it transfers energy from the transmitter into the atmosphere
Antenna characteristics are essentially the same regardless of whether an antenna is sending or receiving electromagnetic energy

6. Polarization
Polarization is the direction of the electric field and is the same as the physical attitude of the antenna
A vertical antenna will transmit a vertically polarized wave
The receive and transmit antennas need to possess the same polarization

7. Types of Antennas Isotropic antenna (idealized) Dipole antennas
Radiates power equally in all directions
Dipole antennas
Half-wave dipole antenna (or Hertz antenna)
Quarter-wave vertical antenna (or Marconi antenna)
Parabolic Reflective Antenna

9. • Directional Antenna A beamwidth Max power
Radiated energy is focused in a specific direction
antenna
2 dipole
Power 3dB down from maximum point A

10. Beamwidth
Beamwidth is the angular separation of the half-power points of the radiated pattern

14. Half-wave Dipole (Hertz) Antenna
An antenna having a physical length that is one-half wavelength of the applied frequency is called a Hertz antenna or a half-wave dipole antenna. Hertz antennas are not found at frequencies below 2MHz because of the physical size needed of the antenna to represent a half-wave

15. Vertical (Marconi) Antenna
Vertical Antennas are used for frequencies under 2 MHz. It uses a conducting path to ground that acts as ¼ wavelength portion the antenna above the ground. The above ground structure represents a /4 wavelength

16. Vertical (Marconi) Antenna – cont’d
Poor grounding conditions of the earth/soil surrounding the antenna can result in serious signal attenuation. This problem is alleviated by installing a counterpoise

17. Counterpoise
Counterpoise is a grounding grid established where the earth grounding cannot satisfy electrical requirements for circuit completion. It is designed to be non-resonant at the operating frequency

18. Counterpoise-cont’d
radius = ¼ 
antenna
supports

19. Antenna Array
Antenna array is a group of antennas or antenna elements arranged to provide the desired directional characteristics. Generally any combination of elements can form an array. However, equal elements in a regular geometry are usually used.

20. Yagi-Uda Antenna
The Yagi-Uda antenna is a simple form of a directional antenna based off of a reflector placed /4 from the dipole antenna’s placement. Complex analysis to define the radiated patterns are experimental rather than theoretical calculations

21. Yagi-Uda Antenna-cont’d
reflector
/2
/4
dipole antenna

22. Radiated Directed Signal
antenna
2 dipole radiated signal without reflector
2 dipole radiated signal with reflector

23. The Antenna Formula   c  186,000 misec frequency of the signal
c is the speed of light
is the wavelength of the signal
use 3 x 108 when dealing in meters for the speed of light

24. The Antenna Formula - applied
If a half-wave dipole antenna needed to be constructed for a 60 Hz signal, how large would it need to be?
  c  ,000 misec
= 3100 mi 60
2 = 1550 miles!

25. Radiation & Induction Fields
The mechanics launching radio frequencies from an antenna are not full understood. The RF fields that are created around the antenna have specific properties that affect the signals transmission. The radiated field field is known as the (surprisingly!) radiation field

26. Radiation & Induction Fields-cont’d
There are two induction fields or areas where signals collapse and radiate from the antenna. They are known as the near field and far field. The distance that antenna inductance has on the transmitted signal is directly proportional to antenna height and the dimensions of the wave
R 
2D2 

27. Radiation & Induction Fields-cont’d
Where: R = the distance from the antenna
D = dimension of the antenna
 = wavelength of the transmitted signal

28. Radiation Resistance
Radiation Resistance is the portion of the antenna’s impedance that results in power radiated into space (i.e., the effective resistance that is related to the power radiated by the antenna. Radiation resistance varies with antenna length. Resistance increases as the  increases

29. Effective Radiated Power (ERP)
ERP is the power input value and the gain of the antenna multiplied together
dBi = isotropic radiator gain
dBd = dipole antenna gain

30. Radiation Pattern
Radiation pattern is an indication of radiated field strength around the antenna. Power radiated from a /2 dipole occurs at right angles to the antenna with no power emitting from the ends of the antenna. Optimum signal strength occurs at right angles or 180° from opposite the antenna

31. Radiation Patterns Radiation pattern
Graphical representation of radiation properties of an antenna
Depicted as two-dimensional cross section
Beam width (or half-power beam width)
Measure of directivity of antenna
Reception pattern
Receiving antenna’s equivalent to radiation pattern

32. Radiation Pattern for Vertical Antennas
/4
/2
antenna

33. Antenna Gain Antenna gain Effective area
Power output, in a particular direction, compared to that produced in any direction by a perfect omnidirectional antenna (isotropic antenna)
Effective area
Related to physical size and shape of antenna

34. Antenna Gain
Antenna gain is the measure in dB how much more power an antenna will radiate in a certain direction with respect to that which would be radiated by a reference antenna

35. Antenna Gain Relationship between antenna gain and effective area
G = antenna gain
Ae = effective area
f = carrier frequency
c = speed of light (» 3 ´ 108 m/s)
 = carrier wavelength

37. Propagation Modes Ground-wave propagation Sky-wave propagation
Line-of-sight propagation

38. Ground Wave Propagation

39. Ground Wave Propagation
Follows contour of the earth
Can Propagate considerable distances
Frequencies up to 2 MHz
Example
AM radio

40. Sky Wave Propagation

41. Sky Wave Propagation
Signal reflected from ionized layer of atmosphere back down to earth
Signal can travel a number of hops, back and forth between ionosphere and earth’s surface
Reflection effect caused by refraction
Examples
Amateur radio
CB radio

42. Line-of-Sight Propagation

43. Line-of-Sight Propagation
Transmitting and receiving antennas must be within line of sight
Satellite communication – signal above 30 MHz not reflected by ionosphere
Ground communication – antennas within effective line of site due to refraction
Refraction – bending of microwaves by the atmosphere
Velocity of electromagnetic wave is a function of the density of the medium
When wave changes medium, speed changes
Wave bends at the boundary between mediums

44. Line-of-Sight Equations
Optical line of sight
Effective, or radio, line of sight
d = distance between antenna and horizon (km)
h = antenna height (m)
K = adjustment factor to account for refraction, rule of thumb K = 4/3

45. Line-of-Sight Equations
Maximum distance between two antennas for LOS propagation:
h1 = height of antenna one
h2 = height of antenna two

46. LOS Wireless Transmission Impairments
Attenuation and attenuation distortion
Free space loss
Noise
Atmospheric absorption
Multipath
Refraction
Thermal noise

47. Thermal Noise Thermal noise due to agitation of electrons
Present in all electronic devices and transmission media
Cannot be eliminated
Function of temperature
Particularly significant for satellite communication

48. Noise Terminology
Intermodulation noise – occurs if signals with different frequencies share the same medium
Interference caused by a signal produced at a frequency that is the sum or difference of original frequencies
Crosstalk – unwanted coupling between signal paths
Impulse noise – irregular pulses or noise spikes
Short duration and of relatively high amplitude
Caused by external electromagnetic disturbances, or faults and flaws in the communications system

49. Other Impairments
Atmospheric absorption – water vapor and oxygen contribute to attenuation
Multipath – obstacles reflect signals so that multiple copies with varying delays are received
Refraction – bending of radio waves as they propagate through the atmosphere

50. Multipath Propagation

51. Multipath Propagation
Reflection - occurs when signal encounters a surface that is large relative to the wavelength of the signal
Diffraction - occurs at the edge of an impenetrable body that is large compared to wavelength of radio wave
Scattering – occurs when incoming signal hits an object whose size in the order of the wavelength of the signal or less

52. The Effects of Multipath Propagation
Multiple copies of a signal may arrive at different phases
If phases add destructively, the signal level relative to noise declines, making detection more difficult
Intersymbol interference (ISI)
One or more delayed copies of a pulse may arrive at the same time as the primary pulse for a subsequent bit

53. Types of Fading Fast fading Slow fading Flat fading Selective fading
Rayleigh fading
Rician fading

54. Error Compensation Mechanisms
Forward error correction
Adaptive equalization
Diversity techniques

55. Forward Error Correction
Transmitter adds error-correcting code to data block
Code is a function of the data bits
Receiver calculates error-correcting code from incoming data bits
If calculated code matches incoming code, no error occurred
If error-correcting codes don’t match, receiver attempts to determine bits in error and correct

56. Adaptive Equalization
Can be applied to transmissions that carry analog or digital information
Analog voice or video
Digital data, digitized voice or video
Used to combat intersymbol interference
Involves gathering dispersed symbol energy back into its original time interval
Techniques
Lumped analog circuits
Sophisticated digital signal processing algorithms

57. Antenna Height
Antenna height above the ground is directly related to radiation resistance. Ground reflections causing out-of-phase signals to be radiated to receiving antennas will degrade the transmission. Physical length and electrical length of most antennas are approximately 95% of the physical length. Ideal antenna height is usually based on trial and error procedures

58. Smart Antennas

59. Smart Antennas
smart antennas are base station antennas with a pattern that is not fixed, but adapts to the current radio conditions
smart antennas have the possibility for a large increase in capacity: an increase of three times for TDMA systems and five times for CDMA systems has been reported.

60. Smart Antennas-cont’d
Major drawbacks and cost factors include increased transceiver complexity and more complex radio resource management

61. Smart Antennas-cont’d
The idea of smart antennas is to use base station antenna patterns that are not fixed, but adapt to the current radio conditions. This can be visualized as the antenna directing a beam toward the communication partner only

63. Smart Antennas-cont’d
Smart antennas add a new way of separating users, namely by space, through SDMA (space division multiple access)
By maximizing the antenna gain in the desired direction and simultaneously placing minimal radiation pattern in the directions of the interferers, the quality of the communication link can be significantly improved

64. Elements of a Smart Antenna
Smart antennas consists of a number of radiating elements, a combining/dividing network and a control unit

65. Phased Array Antenna
Phased Array antennas are a combination of antennas in which there is a control of the phase and power of the signal applied at each antenna resulting in a wide variety of possible radiation patterns

66. Types of Intelligent Antennas
Switched lobe (SL): This is also called switched beam. It is the simplest technique, and comprises only a basic switching function between separate directive antennas or predefined beams of an array. The setting that gives the best performance, usually in terms of received power, is chosen

67. Intelligent Antennas-cont’d
Dynamically phased array (PA): By including a direction of arrival (DoA) algorithm for the signal received from the user, continuous tracking can be achieved and it can be viewed as a generalization of the switched lobe concept

68. Intelligent Antennas-cont’d
Adaptive array (AA): In this case, a DoA algorithm for determining the direction toward interference sources (e.g., other users) is added. The radiation pattern can then be adjusted to null out the interferers. In addition, by using special algorithms and space diversity techniques, the radiation pattern can be adapted to receive multipath signals which can be combined. These techniques will maximize the signal to interference ratio (SIR)

70. SMDA
Space Division Multiple Access (SDMA) implies that more than one user can be allocated to the same physical communications channel simultaneously in the same cell, only separated by angle. In a TDMA system, two users will be allocated to the same time slot and carrier frequency at the same time and in the same cell

71. SMDA-cont’d
In systems providing full SDMA, there will be much more intracell handovers than in conventional TDMA or CDMA systems, and more monitoring by the network is necessary

72. Antenna Installation Considerations
Safety
standard operating procedure priority
Grounding
lightning strikes
static charges
Surge protection
lightning searches for a second path to ground

73. Antenna Installation Considerations-cont’d
Adaptive array antenna placement needs to be considered differently than current technologies serving the mobile environment. They need to be place so they have a greater angular approach to the receiving units. Existing tower placement with close proximity to roads and highways would need to be reconsidered.

75. Antenna Installation Considerations
Base, mast, and supporting structure needs clearance, serviceability (access), and complies with state, federal, and municipal guidelines