Presentation on Design & Construction of 2.4GHz Axial Mode Helical Antenna to Establish WLAN
What is an Antenna?
An antenna is a transducer that converts electrical energy to electromagnetic energy in case of transmission and converts electromagnetic energy to electrical energy in case of receiving antenna. Apart from their different functions, transmitting and receiving antennas have similar characteristics, which mean that their behavior is reciprocal.
How Antenna Radiates
There must be a time varying current i.e. acceleration or deceleration of charge to create radiation. To create acceleration or deceleration the wire must be curved, bent, discontinuous or truncated. Two EM Fields – Induction & Radiation Induction Field is liable for storing energy and Radiation Field is liable for radiating that stored energy.
Antenna Parameters
- Resonant Frequency
- Gain
- Directivity
- Radiation Pattern
- Impedance
- Efficiency
- Bandwidth
- Polarization
- Reciprocity
Helical Antenna Theory
D = Diameter of helix
C = Circumference of helix = πD
S = Spacing between turns
α = Pitch Angle = tan-1 (S/πD)
n = Number of turns
L = Axial length = nS
a = Radius of helix wire conductor
- The Gain of Helical Antenna is, G=11.8+10*log{(C/l) 2*N*S} dB
- The HPBW of Helical Antenna- HPBW = 52/CλÖ(nSλ) degrees
- The input impedance is R = 140C/λ Ω
Design of 2.4 GHz Helix
Circumference, C = πD = λ = 12.5 cm
Pitch Angle, α = arctan (S/πD) =14°
Diameter, D = C/π = 3.97887 cm
Spacing between the turns, S = C tan α = 3.12 cm
Number of Turns, N = 28
Gain, G = 19.3 dBi
HPBW = 19.7 degree
Antenna Length, L = NS = 783 cm
Terminal Impedance, Z = 150 Ohm
Conductor Diameter, d ≥ 0.005λ = 0.625 mm
Problem with 2.4GHz Helix
- All the equations developed by John D. Kraus were for the helix in the air.
- But we build our antenna in a PVC pipe.
- The dielectric constant of dry air that is 1.000056 at 60Hz frequency and 30°C temperature whereas the dielectric constant for PVC concrete tube is 3.5 for 60Hz which at 2.4GHz is 1.5 approximately
- Suspension Factor = 1/√ εr = 1/√1.5 = 0.8164
- So, we build our antenna for 2.4/0.8164=2.92GHz
Design for 2.92GHz Antenna
For this design the required parameters are
Frequency, f = 2.92GHz
Wavelength, λ = 10.27 cm
Circumference, C = λ = 10.27cm
Diameter, D = 3.27 cm
Spacing between Turns, S = 2.56 cm
Pitch Angle, α = 14°
Number of Turns, N = 28
Conductor Diameter, d ≥ 0.005 λ ≥ 0.5135 mm
We used conductor of 1.26mm.
Diameter of the Ground Plane ≥ 0.75 λ ≥ 7.7cm
We used the Flat Circular Aluminium Ground Plane of 15cm Diameter.
Design for 2.92GHz Helix Antenna
For this design the required parameters are
Frequency, f = 2.92GHz
Wavelength, λ = 10.27 cm
Circumference, C = λ = 10.27cm
Diameter, D = 3.27 cm
Spacing between Turns, S = 2.56 cm
Pitch Angle, α = 14°
Number of Turns, N = 28
Conductor Diameter, d ≥ 0.005 λ ≥ 0.5135 mm
We used conductor of 1.26mm.
Diameter of the Ground Plane ≥ 0.75 λ ≥ 7.7cm
We used the Flat Circular Aluminium Ground Plane of 15cm Diameter.
Using the parameters stated previously,
- Gain, G = 19.3 dBi
- HPBW = 19.7 degree
- FNBW = 43.5 degree
- Antenna Length, L = 757 cm
- Terminal Impedance, Z = 150 Ohm
We used a Cu strip triangle of 72mm base and 17mm in perpendicular of it.
WLAN
A wireless LAN (WLAN) is a wireless local area network, which permits a network connection between two or more computers without using wires. It uses radio communication to accomplish same functionality that a wired LAN has. We used Ad-hoc network that uses IEEE 802.11b standard of 2.4GHz band. An ad-hoc network is a network where stations communicate only peer to peer (P2P). We used a wireless NIC that enables a client station capable of sending and receiving RF signals.
Before finishing, want to say something about our aspirations and the reasons for why we had to see our fancy hopes fritter away and our dreams were shattered like a shield……
Submitted by Shaikat Debnath And Kaisar Jamil
