Studies on Microstrip Patch Antennas for Cognitive Radio Bhanwar Singh Prateek Batla Pratik Kumar (Under the Guidance of Prof. M. V. Kartikeyan)
May 27, 2015
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