LOG PERIODIC ANTENNA

Designing of 200MHz to 1000MHz Log Periodic Antenna

MUHAMMAD ILYAS SAEED-UR-RAHMAN SAJID ALI TUFAIL AHMED

Engr. Sardar Ali

Antenna Introduction Log periodic Antenna Parameters of LP Antenna Calculations of our Antenna Construction of LP Antenna Advantages of LP Antenna Applications

An antenna is a conductor capable of transmitting and receiving electromagnetic waves.

As a transmitter ◦ radiates electromagnetic energy into space

As a Receiver ◦ collects electromagnetic energy from space

A transmitting antenna can also be used for reception and vice versa. In two-way communication, the same antenna can be used for transmission and reception.

This property of transmit/receive EM waves is known as antenna reciprocity.

Definition A log-periodic antenna is a broadband, multi-

element, unidirectional antenna, that has impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency.

The individual components are often dipoles, as in a log-periodic dipole array (LPDA).

l : Length of elements(l),L: Length of antenna(L),d: Spacing b/w the elements,C: Coaxial feed line,

Bandwidth

Directivity

Gain

Polarization

Impedance

LPA ParametersLPA Parameters

Bandwidth: The bandwidth of an antenna is the

range of frequencies over which it is effective, usually centered around the resonant frequency.

Directivity: Directivity show us that how well an

antenna Transmit and receive EM waves in particular direction.

Gain: Gain is the comparison of TX and RX Em

waves. Gain of Log Periodic antenna is very high.

Polarization: LP antenna has linear polarization.

Impedance: As the electric wave travels through the

different parts of the antenna system,it may encounter differences in impedance.

SWR: The ratio of maximum power to minimum

power in the wave can be measured and is called the standing wave ratio (SWR).

Radiation Pattern: Radiation pattern shows us that how an

Antenna transmit and receive EM energy in different directions.

There are two types of LP Antenna.

LPDA Straight type

LPDA Vee type

log periodic offers reasonably good gain over an extremely wide range of frequencies.

It is also highly directional.

log-periodic provides a very wide bandwidth as compared to yagi-uda antenna’s.

Frequency range: 200MHz – 1000MHz Design factor: 0.8 Longest element: λ/2=3*10^8/200*10^6=0.75m Limiting Factor: λ/2=3*10^8/1000*10^6=0.15m Length of other element is li+1=*li

Distance b/w two consective elements D1=0.09λ Di+1=0.7Di

Equipments: Aluminium pipe (0.25diameter) accoording

to calculations.

Aluminium wire for connection b/w the elements.

End caps

70Ω Coaxial cable + BNC connector

Wood Boom

  ReferencesReferences

Kraus john D, Antennas, second edition

NOWATZKY,D .: Logarithmisch periodische Antennen. Technische Mitteilungendes (http://home.tonline.de/home/Dieter.Nowatzky/doc.htm)

R. L. Carrell, “The Design of Log-Periodic Dipole Antennas,” 1961 IRE International Convention Record, Part 1.