Horn Antennas

Basic Concept The horn antenna gains its name from its appearance

Type of Aperture antenna

A horn antenna is used for the transmission and reception of microwave signals

                                       

The horn antenna may be considered as an RF transformer

RF transformers match the Impedance to achieve maximum power transfer and to suppress undesired signal reflection.

Tapered or flared end enables the impedance to be matched

Spot Area Coverage

Basic Concept Cntd….

Design Used in conjunction with waveguide feeds

Waveguides A waveguide is a special form of transmission line consisting of a hollow,

metal tube Works only for signals of extremely high frequencies

Radiation Pattern

Major Types Of Horn Antenna Pyramidal Horns

Conical Horns

Corrugated Horns

Multiflare Horn

Lens Corrected Horn

Hog Horn

Dual Mode Horn

Some Other Types

Pyramidal Horn

Basic Properties

Rectangular

Gain 10-25 DB

Easy Fabrication

Radiation Pattern

Pattern For Phase And Amplitude

Conical Horn

Basic Details

Also called Open Ended Waveguides

Used commonly with multiple beam antennas(MPAs)

Wide Bandwidth

Has an excellent VSWR for large aperture

Easy Fabrication

Used as Array elements

Directivity Gain Pattern

Corrugated Horn

Basic Details The name “Corrugated” means shaped into alternating parallel grooves

and ridges

Used in most of all communication satellites

Complete earth coverage

FOV +- 9*

Medium Antenna Gain

Difficult Fabrication

Corrugated Horn

Radiation Pattern

Uses Of Horn Antennas Horn antennas are commonly used as the active element in a dish

antenna, the horn is orientated towards the reflector surface, and is able to give a reasonably even illumination of the surface without allowing radiation to miss the reflector, minimizing loss of energy around the edges of the dish reflector

Used in Almost all of the Satellites

Horn antennas are used in short-range radar systems, to measure the speeds of approaching or retreating vehicles

It provides a significant level of directivity and gain

Some Pictures

Helix Antenna

Introduction

The helix antenna, invented in the late fourties by John Kraus (W8JK)

Specially for frequencies in the range 2 - 5 GHz

Design is very easy, practical, and, non critical.

Cntd……… Frequencies around 2.4 GHz which can be used for e.g. high speed

packet radio (S5-PSK, 1.288 Mbit/s), 2.4 GHz wavelans, and, amateur satellite (AO40)

Developments in wavelan equipment result in easy possibilities for high speed wireless internet access using the 802.11b (aka WiFi) standard.

Theory The helix antenna can be considered as a spring with N turns with a

reflector

The circumference (C) of a turn is approximately one wavelength (l)

The distance (d) between the turns is approx. 0.25C

The size of the reflector (R) is equal to C or l, and can be a circle or a square

Theory Cntd…..

The design yields circular polarization (CP), which can be either 'right hand' or 'left hand' (RHCP or LHCP respectively), depending upon how the helix is wound

To have maximum transfer of energy, both ends of the link must use the same polarization, unless you use a (passive) reflector in the radio path

Gain

The gain (G) of the antenna, relative to an isotrope (dBi), can be estimated by:

G = 11.8 + 10 * log {(C/l)^2 * N * d} dBi 

Characteristic Impedence

The characteristic impedance (Z) of the resulting 'transmission line' empirically seems to be:

Z = 140 * (C/l) Ohm

Radiation pattern

Single & Double Helix Patterns

Different Uses