normal mode helical antenna
TRANSCRIPT
![Page 1: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/1.jpg)
Normal Mode Helical Antenna
Small Dipole:
Small Loop:
Therefore, Axial Ratio is:
For Circular Polarization, AR = 1
2 2
22E SSARE C C
4
jkrokI Se
E j sinr
2
2
2
4
D jkrok I e
E sinr
2C S
D
S
D
S
![Page 2: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/2.jpg)
Design of Normal Mode Helical Antenna
Radiation Resistance (Rs)2
21(790) 0.6 2
IavR h R
s sIo
AR = 2 Sλ / C λ2
= 2x0.01/0.04 2
= 12.5 = 21.94 dB
Axial Ratio (AR)
For Infinite Ground Plane:
Wire length ≈ λ / 4 – text book
> λ / 4 – in reality
Feed is tapped after one turn for impedance matching
![Page 3: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/3.jpg)
Normal Mode Helical Antenna (NMHA) on Small Circular Ground Plane
![Page 4: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/4.jpg)
NMHA Design on Small Circular Ground Plane
Resonance Frequency 1.8 GHz
Wavelength 166 mm
Spacing = 0.027λ 4.5 mm
Diameter of Helix = 0.033λ 5.5 mm
No of Turns (N) 7
Pitch Angle (α) 14.6 Degree
Length of Wire = 0.75λ 124.5 mm
![Page 5: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/5.jpg)
Effect of Ground Plane Size on NMHA
As ground plane radius increases from λ/30 to λ/20, resonance
frequency decreases and the input impedance curve shifts upward.
NMHA designed for 1.8 GHz and rwire = 1.6 mm (λ/100)
![Page 6: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/6.jpg)
Effect of Wire Radius on NMHA
As radius of wire decreases from λ/80 to λ/120, its inductance
increases so resonance frequency of NMHA decreases and its input
impedance curve shifts upward (inductive region).
NMHA designed for 1.8 GHz and rg = 5.5 mm (λ/30)
![Page 7: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/7.jpg)
Effect of Wire Radius on Bandwidth of NMHA
![Page 8: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/8.jpg)
Fabricated NMHA on Small Ground Plane and its Results
![Page 9: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/9.jpg)
Horn Antennas
Prof. Girish KumarElectrical Engineering Department, IIT Bombay
(022) 2576 7436
![Page 10: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/10.jpg)
Horn Antennas
H-Plane Sectoral HornE-Plane Sectoral Horn
Pyramidal Horn Conical Horn
TE10 mode in Rectangular Waveguide
![Page 11: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/11.jpg)
TE10 mode in Rectangular Waveguide
Rectangular Waveguide
b
a
For Fundamental TE10 mode: E-Field varies
sinusoidally along ‘a’ and is uniform along ‘b’
X-Band Waveguide WR90 (8.4 to 12.4 GHz):
a = 0.9” and b = 0.4”
Cut-off Wavelength = 2a = 2 x 0.9 x 2.54 = 4.572 cm
Cut-off Frequency = 3 x 1010 / 4.572 = 6.56 GHz
![Page 12: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/12.jpg)
E-Plane Sectoral Horn Antenna
![Page 13: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/13.jpg)
E-Plane Sectoral Horn: Side View
≈
![Page 14: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/14.jpg)
E-Plane Sectoral Horn: Directivity Curve
ρ1 6 10 20 100
b1 3.46 4.47 6.32 14.14
Max. Directivity:
![Page 15: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/15.jpg)
E-Plane Sectoral Horn: Max. Phase Error
Maximum Directivity occurs when
which gives ‘s’ approximately equal to:
δmax = 90°
δmax = 2πs, where≈
Maximum Phase error occurs when y’ = b1 / 2
Phase Error too high:
Not Recommended
![Page 16: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/16.jpg)
E-Plane Sectoral: Universal Pattern
E-Field for s = 1/4 (δmax = 90°)
E-Field for s = 1/8 (δmax = 45°) - Recommended
![Page 17: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/17.jpg)
H-Plane Sectoral Horn Antenna
δmax = 2πt, whereMaximum Phase
error at x’ = a1 / 2
![Page 18: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/18.jpg)
H-Plane Sectoral Horn: Directivity Curve
Max. Directivity: ρ2 6 10 20 100
a1 4.24 5.48 7.75 17.32a1 3λρ2
![Page 19: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/19.jpg)
H-Plane Sectoral Horn: Max. Phase Error
Maximum Directivity occurs when
which gives ‘t’ approximately equal to:
δmax = 135°
δmax = 2πt, where
Maximum Phase error occurs when x’ = a1 / 2
Phase Error too high:
Not Recommended
a1 3λρ2
![Page 20: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/20.jpg)
H-Plane Sectoral: Universal Pattern
E-Field for t = 1/4 (δmax = 90°)
E-Field for t = 1/8 (δmax = 45°)
Recommended
max. phase
error between
45° and 90°
![Page 21: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/21.jpg)
Pyramidal Horn Antenna
Side ViewTop View
![Page 22: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/22.jpg)
Pyramidal Horn Antenna
Condition for Physical Realization:
![Page 23: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/23.jpg)
Pyramidal Horn: Design Procedure
Directivity of
Pyramidal Horn
Antenna can be
obtained using
Directivity
curves for E-and
H-Planes
Sectoral Horn
antenna
Alternatively
![Page 24: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/24.jpg)
Pyramidal Horn Design Steps
![Page 25: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/25.jpg)
Pyramidal Horn Design: Example
![Page 26: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/26.jpg)
Pyramidal Horn Design: Example (Contd.)
![Page 27: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/27.jpg)
Pyramidal Horn Design: Example (Contd.)
![Page 28: Normal Mode Helical Antenna](https://reader034.vdocuments.mx/reader034/viewer/2022042311/625b77f1073d3d5b197d4756/html5/thumbnails/28.jpg)
Optimum Dimensions vs. Directivity
Gain (dBi)
aEλ
aHλ
Lλ