Normal Mode Helical Antenna

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    17-Apr-2022
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Transcript of Normal Mode Helical Antenna

Slide 12 2




E sin r
Radiation Resistance (Rs) 2
= 2x0.01/0.04 2
> λ / 4 – in reality
Normal Mode Helical Antenna (NMHA) on Small Circular Ground Plane
NMHA Design on Small Circular Ground Plane
Resonance Frequency 1.8 GHz
No of Turns (N) 7
Pitch Angle (α) 14.6 Degree
Length of Wire = 0.75λ 124.5 mm
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)
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)
Effect of Wire Radius on Bandwidth of NMHA
Fabricated NMHA on Small Ground Plane and its Results
Horn Antennas
[email protected]
Pyramidal Horn Conical Horn
Rectangular Waveguide
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
E-Plane Sectoral Horn Antenna

Max. Directivity:
Maximum Directivity occurs when
δmax = 90°
Phase Error too high:
E-Field for s = 1/8 (δmax = 45°) - Recommended
H-Plane Sectoral Horn Antenna
Max. Directivity: ρ2 6 10 20 100
a1 4.24 5.48 7.75 17.32a1 3λρ2
H-Plane Sectoral Horn: Max. Phase Error
Maximum Directivity occurs when
δmax = 135°
Phase Error too high:
Recommended
Optimum Dimensions vs. Directivity