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.
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