ANTENNAS AND WAVEGUIDES (C15 Tomasi)

CHAPTER 15

ANTENNAS AND WAVEGUIDES

1)A metallic conductor system capable of radiating and capturing electromagnetic energy

Antenna

2)Couples energy from a transmitter to an antenna or from antenna to a receiver

Transmission Lines

3)A special type of transmission line that consists of a conducting metallic tube through which high-frequency electromagnetic energy is propagated.

Waveguide

4)Electrical energy that has escaped into free space in the form of transverse electromagnetic waves

Radio Waves

5)The plane parallel to the mutually perpendicular lines of the electric and magnetic fields.

Wavefront

6)The ratio of radiated to reflected energy.

Radiation Efficiency

7)Antenna wherein two conductors are spread out in a straight line to a total length of one quarter wavelength.

Quarter Wave Antenna

8)Another name for quarter wave antenna.

Vertical Monopole or Marconi

9)A half-wave dipole.

Hertz Antenna

10)A special coupling device that can be used to direct the transmit and receive signals and provide the necessary isolation.

Diplexer

11)A polar diagram or graph representing field strengths or power densities at various angular positions relative to an antenna.

Radiation Pattern

12)Radiation pattern plotted in terms of electric field strength or power density.

Absolute Radiation Pattern

13)Radiation pattern plots field strength or power density with respect to the value at a reference

Relative Radiation

14)The primary beam of an antenna.

Major Lobes

15)The major lobes that propagates and receivethe most energy.

Front Lobe

16)Lobes adjacent to the front lobe.

Side lobes

17)The secondary beam of an antenna.

Minor Lobes

18)Lobes in a direction exactly opposite the front lobe

Back Lobe

19)The ratio of the front lobe power to the back lobe power.

Front to Back Ratio

20)The ratio of the front lobe to a side lobe.

Front to Side Ratio

21)The line bisecting the major lobe, or pointing from the center of the antenna in the direction of maximum radiation.

Line of Shoot or Point of Shoot

22)Antenna that radiates energy equally in all directions.

Omni-directional Antenna

23)Radiates power at a constant rate uniformly in all directions.

Isotropic Radiator

24)The direction in which an antenna is always pointing.

Maximum Radiation

25)It is defined as an equivalent transmit power. It stands for Effective Isotropic Radiated Power.

 EIRP

26)The equivalent power that an isotropic antenna would have to radiate to achieve the same power density in the chosen direction at a given point as another antenna.

Effective Radiated Power (ERP) or (EIRP)

27)The power density in space and the actual power that a receive antenna produces at its output terminals.

Captured Power Density

28)It describe the reception properties of an antenna

Capture Area

29)Another name for capture area.

Effective Area

30)The relationship of captured power to the received power density and the effective capture area of the received antenna.

Directly Proportional

31)It refers to the orientation of the electric field radiated from the antenna.

Polarization

32)The angular separation between the two half-power (-3dB) points on the major lobe of an antenna's plane radiation pattern.

Antenna Beamwidth

33)The frequency range over which antenna operation is satisfactory.

Antenna Bandwidth

34)Another name for antenna input terminal

Feedpoint

35)The feedpoint presents an ac load to the transmission line.

Antenna Input Impedance

36)The simplest type of antenna. Another names for elementary doublet

· Short Dipole,

· Elementary Dipole

· Hertzian Dipole

Elementary Doublet

37)Any dipole that is less than one-tenth wavelength

Electrically Short

38)Hertz antenna is name after him and he was the first to demonstrate the existence of electromagnetic waves.

Heinrich Hertz

39)A single pole antenna one quarter wavelength long, mounted vertically with the lower end either connected directly to ground or grounded through the antenna coupling network.

Marconi Antenna

40)Main disadvantage of Marconi Antenna.

Must be close to the Ground

41)A technique use to increase the electrical length of an antenna

Loading

42)A coil added in series with a dipole antenna which effectively increases antenna's electrical length.

Loading Coil

43)A loading coil approximately increases the radiation resistance of the antenna.

5 Ohms

44)An individual radiator, such as a half or quarter wave dipole.

Two types of antenna elements

· Driven

· Parasitic

Two Elements of a single antenna

· Two Wire

· Folded Dipole

Antenna Element

45)Its purpose is to increase the directivity and concentrate the radiated power within a smaller geographic area.

Array

46)Elements that are directly connected to the transmission line and receive power from the source.

Driven

47)Elements are not connected to the transmission line; they receive energy only through mutual induction with a driven element.

Parasitic

48)A parasitic element that is shorter that its associated driven element.

Director

49)Radiation pattern depends on the relative phase of feeds.

Driven

50)The simplest type of antenna arrays.

Broadside Arrays

51)A widely used antenna commonly uses a folded dipole as the driven element and named after two Japanese scientists.

Yagi Uda

52)Typical directivity of a yagi-uda antenna.

7 dB and 9 dB

53)Formed by placing two dipoles at right angles to each other.

Turnstile Antenna

54)A class of frequency-independent antennas.

Log Periodic

55)A broadband VHF or UHF antenna that is ideally suited for applications for which radiating circular rather than horizontal or vertical polarized electromagnetic waves are required.

Modes of propagation:

· Normal

· Axial

Helical Antenna

56)Antennas having half power beamwidths on the order of 1o or less.

Three important characteristics:

· Front-to Back Ratio,

· Side-toSide Coupling

· Back-to-Back Coupling

Microwave Antenna

57)Antenna that provides extremely high gain and directivity and are very popular for microwave and satellite communications link.

Two main part

· Parabolic Reflector

· Feed Mechanism

Parabolic Reflector Antenna

58)The effective area in a receiving parabolic antenna and is always less than the actual mouth area.

Capture Area