Measurement Measurement of Reflection and Radiation Characteristics of Antenna Antenna
Kushmanda Saurav and Debdeep Sarkar
Department of Electrical Engineering, IIT Kanpur
What is an Antenna? •
A means for radiating radiating or receiving receiving radio waves ( IEEE Standard Definitions Definitions of Terms for Antennas) Antenna s) http://ieeexplore.ieee.or http://ieeexp lore.ieee.org/stamp/stamp.jsp? g/stamp/stamp.jsp?tp=&arnumber=3065 tp=&arnumber=30651 1
1. Antenna acts as a transitional structure between structure between free-space and a guiding device 2. Antenna optimizes or accentuate the radiation energy in some directions and suppress suppress it in others. others. Thus the antenna must also serve as a directional device in device in addition to a prob a probing ing device. device.
Single Antenna Configurations
Dipole Antenna
Pyramidal Horn Antenna
Loop Antenna
Microstrip Patch Antenna
Antenna Array Configurations
Yagi Uda Array
Array of Microstrip Patch Antenna
Slotted Waveguide Array
Main Performance Metrics of any Antenna •
Return Loss Input Reflection Coefficient (S11)
•
Radiation Pattern
•
Directivity / Gain
•
Radiation Efficiency
•
Polarization characteristics: Linear / Circular
S11 measurement using Vector Network Analyzer
•
•
•
•
•
•
Approximate reflection characteristics of antenna in the entire operating range of VNA Preset the VNA Connect the antenna under test to the port 1 of VNA Measure the S11 Once the desired operating frequency range is known Perform the one port calibration of the VNA in the desired frequency range Connect the antenna under test to the port 1 of VNA Measure the S11
Radiation Pattern of Antenna •
•
Defined as mathematical function or a graphical representation of the radiation properties of the antenna as a function of space coordinates. Radiation Properties include Power density, Radiation intensity, Field strength, Directivity.
•
•
Radiation pattern is generally determined in far-field of antenna Challenge: Automatic Measurement of Radiation Pattern.
Linearly Polarized Printed Dipole Antenna acting as AUT
Balun Dipole
Theoretical Radiation Pattern of the AUT
Radiation pattern measurement setup in anechoic chamber
Position Controller
Antenna stand mounted on the turn table
Control through RS232
Control through GPIB
Radio Frequency
Vector Network Analyzer Position controller
Acknowledgement
S. Vinoth Naidu PhD Student EE Department, IIT Kanpur
Position controller
Position controller
Position controller
Position controller
Friis transmission equation P r P t
4 R
2
Got Go r Pt
R
Pr
Got
P t = Input power of transmitting antenna P r = Power delivered to the receiving antenna R = Distance between transmitting and receiving antenna Got = Gain of transmitting antenna Gor = Gain of receiving antenna
4 R λ
2
= Free space loss factor
corresponds to the operating wavelength R
2 D
2
(Far-field region of antenna)
Gor
S 2 1
P r P t
If we make use of VNA for antenna radiation characteristics measurement
Gain measurement Absolute method: A pair of identical test antennas are required Identical test antennas are used as transmitters and receivers P r P t
4 R
Thus,
Got
2
Got Go r
Gor
And
P r Go t P / 4 R t
Pt
R
Got
Relative method: Standard gain antenna with known value of gain in the desired frequency range is required 2 P r Go t P / 4 R Gor t
