Traveling Wave Antenna

Antenna Theory

Prepared byAbdelaziz Said

Electrical Engineering Department

New Cairo Academy

- Traveling wave antenna is non-resonant type antenna or aperiodic antenna

Definitions - The antenna in which the standing wave does not exist along the length of the antenna is called traveling wave antenna

Q1What is the difference between standing wave and traveling wave ?

Q2What is the difference between resonant and non-resonant antenna ?

1- Long Wire Antenna

An antenna is usually classified as a long wire antenna if it is a very straight conductor with a length from one to many wavelengths

Antenna Height (h)

Total field radiated by the wire It is found by multiplying the field radiated by the wire in free

space by the array factor of a two-element array the wave travels along the wire from the source toward the

load, it continuously leaks energy (attenuation coefficient)

Field radiated in free space

Radiated by long wire to free space

Current distribution along structure If = aˆz Iz (z΄) = z I0

By approx. : If = aˆz Iz (z΄) = z I0

K ==

it is evident that the power distribution of a wire antenna of length l is a multi lobe pattern whose number of lobes depends upon its length.

To calculate Peaks of lopes

For angles the peaks occur

To find nulls

Angles where the nulls occurs

Total radiated power

Radiation resistance

Directivity

Design long wires

Amplitude pattern , maxima and nulls

Input Impedance

Advantages

Provides strong Minor Lobes

Disadvantages

Easy to ConstructMore Cheap than V antennaMore simpleLarger Bandwidth Input impedance is High

Applications Commercial applications Mellatry applications For RF communications Microwave communications Long Closed places likes tunnels

2- V AntennaThe V antenna is made up of two wire antenna which are arranged in the form of the horizontal V and it is fed at the apex by the transmission feed line.

For some applications a single long-wire antenna is not very practical because(1) its directivity may be low.(2) its side lobes may be high.

These and other drawbacks of single long-wire antennas can be overcome by utilizing an array of wires, One very practical array of long wires is the V

There are two Types: Resonant V antenna Non-Resonant V antenna

Most V antennas are symmetrical (θ1 =θ2 =θ0 and l1 =l2 =l). Also V antennas can be designed to have unidirectional or bidirectional radiation patterns, as shown in Figures

Easy to ConstructCheap

Disadvantages

Advantages

Provides strong Minor Lobes

ApplicationsOn Light Aircraft Military appliancesCommercial appliances

3- Rhombic Antenna Two V antennas can be connected at their open ends to form a diamond or rhombic antenna, The antenna is usually terminated at one end in a resistor, usually about 600–800 ohms, in order to reduce if not eliminate reflections

- Radiation Pattern

Unidirectional Pattern Lobes = 2 to 8 long Directivity : 20 to 90

Power Gain : 50 to 60 β value = 17 to 24 degree

Assignment

- Design of Rhombic antenna

The tilt angle ()The leg length (L)The height above the ground (h)Two designs(a) Alignment design(b) Maximum output design

- Design of Rhombic antenna

(a) Alignment design h is chosen that max of the main lobe coincides with the desired angle of elevation

sin4

h

2sin37.0

L 90

(b) Maximum field intensity designh is chosen that max filed intensity is obtained at the desired

elevation angle

mh

sin4

mL

2sin2

90

Highly directional Simple & cheap

Disadvantages

Advantages

Needs larger space for installationEfficiency is Low

ApplicationsHF transmission & reception

Thank you…