Workshopon

Antenna Design

Helical antennaHelical antenna

Helical AntennaHelical Antenna traveling wave antenna in the

shape of a corkscrew produces radiation along the axis

of the helix antenna.referred to as axial-mode helical

antennas.has a wide bandwidth, easy to

construct, has a real input impedance, circularly polarized

Parameters of the helix Parameters of the helix antenna antenna D - Diameter of a turn on the helix

antenna.C - Circumference of a turn on the helix

antenna (C=πD).S - Vertical separation between turns for

helical antenna. α- pitch angle, which controls how far the

helix antenna grows in the z-direction per turn, and is given by

N - Number of turns on the helix antenna.H - Total height of helix antenna, H=NS.

Design ConsiderationsDesign Considerationsat least 3 turns will have close to

circular polarization when the circumference C is close to a wavelength

0.75λ≤C ≤ 1.33 λ 12°<α<14° (typical value 13°)S=C tan(α)D=c/pi

Axial Ratio,Gain,HPBWAxial Ratio,Gain,HPBW

Radiation Pattern Radiation Pattern

Design Helical Antenna Operating At 10 Ghz (N=5)

Microstrip Patch AntennaMicrostrip Patch Antennalow profile antennalightweight, inexpensive, and

easy to integrate with accompanying electronics

elements are usually flat; hence their other name, planar antennas (planar antennas not always a patch antenna)

Side View of Microstrip Patch Antenna with Probe Feed

Microstrip Patch Antenna

Design Methodology of Rectangular Design Methodology of Rectangular Patch AntennaPatch Antennapractical width that leads to good radiation

efficiencies is found using equations of W

Determine the effective dielectric constant of the microstrip antenna using

Once W is found using determine the extension of the length using

0 2

2 1r r

vw

f

1

21 1

[1 12 ]2 2

r r wreff

h

( 0.3)( 0.264)0.412

( .258)( 0.8)

reff

reff

wL h

whh

The actual length of the patch can now be determined by solving for L

Where W =width of patch L=length of patchh=height of dielectric substrateέr = dielectric constantV0=free space velocity

0 0

12

2 r reff

L Lf

Design a rectangular microstrip antenna using a substrate (RT/duroid 5880) with dielectric constant of 2.2, h = 0.1588 cm (0.0625 inches) so as to resonate at 10 GHz

Design methodology of Circular Design methodology of Circular Patch antennaPatch antenna

h=height of dielectric substrateέr = dielectric constantfr=resonance frequencya= radius of the circular patch

Design a circular microstrip antenna using a substrate (RT/duroid 5880) with a dielectric constant of 2.2, h = 0.1588 cm (0.0625 in.) so as to resonate at 10 GHz.

Yagi-Uda (Array) antennaYagi-Uda (Array) antenna

Yagi-Uda AntennaYagi-Uda AntennaArray antennas can be used to

increase directivity.Parasitic array does not require a

direct connection to each element by a feed network

The parasite elements acquire their excitation from near field coupling by the driven element

A Yagi-Uda antenna is a linear array of parallel dipoles.

The basic Yagi unit consists of three elements:1. Driver or driven element2. Reflector3. Director

Radiation Pattern of Yagi-Uda Array Antenna

Design MethodologyDesign MethodologyOptimum spacing for gain of a reflector and

driven element is 0.15 to 0.25 wavelengthsDirector to director spacings are 0.2 to 0.35

wavelengths apart.Reflector length is typically 0.05

wavelengths longer or a length 1.05 that of the driven element.

The driven element is calculated at resonance without the presence of parasitic elements. Driven element is a ½ wave dipole.

The directors are usually 10 to 20% shorter than at resonance.