Studies on Microstrip Patch Antennas for

Cognitive Radio

Bhanwar SinghPrateek BatlaPratik Kumar

(Under the Guidance of Prof. M. V. Kartikeyan)

Overview

• Motivation and Scope• Problem Statement• Literature Survey• Work Done– Simulation– Hardware Realization

• Results and Discussions• Future Work• Publications

MOTIVATION & SCOPE

Cognitive Radio

• First proposed by Joseph Mitola III in 1998

• A radio that can change its transmitter parameters based on interaction with the environment in which it works.

• Currently under development

Need for CR

• Available wireless bandwidth is limited and most of it is already allocated to different wireless services.

• But some of the allocated spectrum remains idle most of the time.

• Cognitive Radio makes use of spectrum when it is idle.

Requisite for Antennas

• Monitoring of spectrum – To find out which part of spectrum is idle. Requires UWB antenna which can sense a broader bandwidth.

• Reconfigurablity – Change parameters to work in idle part of spectrum. Requires a narrowband reconfigurable antenna.

Problem Statement

• To design, fabricate and test a UWB antenna for CR with following specifications –

• BW = 3.1 to 10.6 GHz• S11 < -10 dB• Gain < 5 dB• Pattern = Approximately Omni directional

LITERATURE SURVEY

Some implementation of CR

UWB Antennas- Methods to improve BW

• Increase substrate height• Decrease permittivity• Introduce slots• Proper impedance matching• Unbalanced structure

WORK DONE

Process of Design

Design Specification

Initial Design

Parametric Analysis

Optimization

Final Parameter Selection

Initial Design

Initial Design….

Substrate Selection

• Minimum Epsilon– Radiation Max.– Bandwidth Increase– But losses increase

PTFE(Poly Tetra Fluro Ethylene) εr=2.5

Feeding – Why CPW, not MS ?

• Mode purity• Truly planar structure, can easily be mounted.• Less radiation and dielectric loss.• Higher impedances can be realized, 30 -140 Ω.• Same impedance can be realized using

different feed gap and feed width

Impedance Matching

• Input impedance should be close to 50 Ω.• Tapering – Changing feed width and gap.• Abrupt changes introduce parasitic reactive

elements which can be very high at higher frequencies, hence avoided.

Parametric Analysis

• Investigate antenna by varying one parameter and keep all others constant.

• Results to notice are |S11| and input line impedance.

• Important parameters are dimensions of ellipse, gap between ellipse and ground, feed length and tapering parameters.

Dimensions of ellipse

Ground Line Length

Gaps

Feed Widths

Optimization

HARDWARE REALIZATION

Hardware Realization

CST AutoCADCircuit Board Plotter

Confirm Dimensio

ns

Port Preparati

onMeasurem-ents

Hardware Realization

• Export design to CAD.• Print antenna using dry etching.

Antenna

Dimensions were confirmed using microscope

S11 Measurement

• R&S VNA• CaliberationProcess

Radiation Pattern Measurement

Calculation of Gain

• Using Friis’s Transmission Equation

Where Pr = Received power

Pt = Transmitted powerG0t = gain of transmitting antennaG0r = gain of receiving antenna

RESULTS & DISCUSSIONS

Results..

• An antenna can be looked as –1. A one port device2. An EM device

S11

S11

• The ripples in the experimental results are due to instrumental errors.

• Contact losses between the port and the antenna.

Analytical Line Impedance

Close to 50 OhmsTapering was done to make it close to 50 ohms.Causes reflections.

EM Behavior

Surface Current

Radiation Pattern

Electric Field

Gain

Surface Current

Surface Current Density

f= 3.46 GHz f=5.59 GHz f=6.5GHz

f = 8.46 GHz f=11 GHz

3D Radiation Pattern

f= 3.46 GHz f=5.59 GHz f=6.5GHz

f = 8.46 GHz f=11 GHz

Mode Coupling

2D Radiation Pattern

E - Plane

H plane

f= 3.46 GHz f=5.5GHz

2D Radiation Pattern

f= 11 GHz

E - Plane H plane

Electric Field

f= 3.46 GHz f=5.59 GHz f=6.5GHz

f = 8.46 GHz f=11 GHz

Gain

• Low frequencies -> Long Wavelength -> Standing Waves -> Oscillating mode -> Less Gain

• High frequencies -> Travelling mode -> More Gain

Frequency Simulated Gain Experimental Gain

3.46GHz 2.655dB 2.342dB

5.5GHz 4.076dB 3.985dB

11GHz 4.885dB 4.462dB

Limitations

• Radiation pattern bandwidth of antenna is very short.

• Contact losses are very high at high frequencies as port is simply soldered to the antenna feeding system.

Future Work

Other Antennas Studied

Publication Under Review

• National Conference on “RECENT TRENDS IN MICROWAVE TECHNIQUES AND APPLICATIONS”, organized by “University of Rajasthan, Jaipur”

• A Planar Elliptical Monopole Antenna for UWB Applications ( Ref. No. MW1258)

• Antenna System for Cognitive Radio Application (Ref No. MW1257)

Important References• Y. Tawk, and C. G. Christodoulou, Member, IEEE, A New Reconfigurable

Antenna Design for Cognitive Radio• Elham Ebrahimi, James R. Kelly, Peter S. Hall, Integrated Wide-Narrowband

Antenna for Multi-Standard Radio, IEEE TRANSACTIONS ON ANTEN-NAS AND PROPAGATION, VOL. 59, NO. 7, JULY 2011

• J. Liang, C Chiau, X. Chen and C.G. Parini, \Study of a Printed Circular Disc Monopole Antenna for UWB Systems", IEEE Transactions on Antennas and Propagation, vol. 53, no. 11, November 2005, pp.3500-3504.

• C.A. Balanis, Antenna Theory and Analysis, 2nd ed., Wiley, New York, 1997 D. M. Pozar, Microwave and RF Design of Wireless System, Wiley, New York, 2001.

• CST’s user manual “www.cst.com”

THANK YOU FOR

YOUR KIND ATTENTION