Measurement of Reflection and Radiation

Characteristics of Antenna

Department of Electrical Engineering,

IIT Kanpur

Kushmanda Saurav and Debdeep Sarkar

What is an Antenna?

A means for radiating or receiving radio waves (IEEE Standard Definitions of Terms for Antennas)

http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=30651

1. Antenna acts as a transitional

structure between free-space and a

guiding device

2. Antenna optimizes or accentuate the

radiation energy in some directions and

suppress it in others. Thus the antenna

must also serve as a directional

device in addition to a probing device.

Single Antenna Configurations

Dipole Antenna Loop Antenna

Pyramidal Horn 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.

PC loaded with LabVIEW 2010.

Antenna under test (AUT) and reference antenna.

Vector Network Analyzer (HP 8712ET).

Position Controller (HOLMARC ver 2.0)

Turn table

Radiation pattern measurement set-up (transmitting and probe antenna, cables, connectors etc.)

Automatic Radiation Pattern measurement setup

Linearly Polarized Printed Dipole Antenna

acting as AUT

Dipole

Balun

Theoretical Radiation Pattern of the AUT

Radiation pattern measurement setup in

anechoic chamber

Position Controller

Antenna stand mounted on the turn table

Position controller

Control through GPIB Control through RS232

Radio Frequency

Vector Network Analyzer

Acknowledgement

S. Vinoth Naidu

PhD Student

EE Department, IIT Kanpur

Position controller

Position controller

Position controller

Position controller

orot

t

r GGRP

P2

4

Pt = Input power of transmitting antenna

Pr = Power delivered to the receiving antenna

R = Distance between transmitting and receiving antenna

Got = Gain of transmitting antenna

Gor = Gain of receiving antenna

= Free space loss factor

corresponds to the operating wavelength

(Far-field region of antenna)

2

4

R

22DR

Friis transmission equation

Pt Got

Pr Gor

R

t

r

P

PS 21

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

Thus,

And

Relative method: Standard gain antenna with known value of gain in the desired

frequency range is required

orot

t

r GGRP

P2

4

orot GG

RP

PG

t

rot

4/

or

t

rot G

RP

PG

2

4/

Pt Got

Pr Gor

R

6 April, 2015 Metamaterial Antenna: Demo