Planar transmission line is one of the physical medium used to transmit high frequency signal. The signal flow through the transmission line depends on the important electrical parameter, the frequency. As the signal frequency increases in a conductor, current carriers start to move towards the edges of the conductor. Flow of carriers on the conductor synchronizes with the substrate to achieve better efficiency. The signal flow in the transmission line depends on the dielectric constant of the material and the loss tangent value. The paper shows the simulation studies on return loss and insertion loss of planar transmission lines with constant frequency of 10GHz. To design planar transmission lines different dielectric materials are being selected. In our design, parameters like input impedance, conductor (silver) thickness and conductor height are kept constant. The design and analysis is done using Applied Wave Research (AWR) tool. The obtained results shows unique response and it depends on the type of dielectric medium selected.

1. GJTE-Vol(2)-Issue(4) April 2015 ISSN: 2393-9923
Global Journal of Trends in Engineering
68
Simulation Study on Insertion and Return Loss of Planar
Transmission Lines for Different Dielectric Substrates
Beeresha R.S1
, A.M.Khan2
, Manjunath Reddy H.V3
1
PG Scholar, Department of Electronics, Mangalore University, Mangalore, India
2
Professor and Chairman, Department of Electronics, Mangalore University, Mangalore, India
3
General Manager, ICON Design Automation Pvt Ltd, Bengaluru, India
E-mail Id: beereshakote@gmail.com, asifabc@yahoo.com, manju@icon-dapl.com
ABSTRACT: Planar transmission line is one of the physical medium used to transmit high frequency signal. The signal
flow through the transmission line depends on the important electrical parameter, the frequency. As the signal frequency
increases in a conductor, current carriers start to move towards the edges of the conductor. Flow of carriers on the
conductor synchronizes with the substrate to achieve better efficiency. The signal flow in the transmission line depends
on the dielectric constant of the material and the loss tangent value. The paper shows the simulation studies on return loss
and insertion loss of planar transmission lines with constant frequency of 10GHz. To design planar transmission lines
different dielectric materials are being selected. In our design, parameters like input impedance, conductor (silver)
thickness and conductor height are kept constant. The design and analysis is done using Applied Wave Research (AWR)
tool. The obtained results shows unique response and it depends on the type of dielectric medium selected.
Keywords: Planar Transmission Line, Applied Wave Research Tool, S-Parameters, Insertion Loss, Return noise, Printed
circuit board
I. INTRODUCTION
Transmission lines are used to transmit the signal efficiently from one point to another in integrated circuits (IC) [1-2].There
are different types of transmission lineslike coaxial cable, twisted pair wires, optical fiber and planar transmission lines. At
high frequency applications,planar transmission lineis preferable.Design of a transmission line depends on physical and
electrical characteristics of the dielectric material and on the conductor used. In our discussion, we consider the electrical
characteristics of the dielectric material. In an ideal dielectric material there is no leakage current and magnetic effect.There is
apossible way to reach near-ideal condition when better synchronization between conductor strip and dielectric material is
achieved. This synchronization helps to get low loss output [3]. The substrates have unique dielectric constant value. These
substrates are used to build different planar transmission lines [4]. The characteristics of transmission line can be analyzed
with respect to changing dielectric material. The analysis reflects changes in an insertion and reflection of signal flow on the
transmission line.
In our design we consider silver as conducting material and various dielectric materials like GaAs, Alumina, Germanium,
Silicon and RT/Duroid to study the insertion and reflection losses. The design of microstrip line, stripline and CPW is done
using Applied Wave Research (AWR) tool, and also the responses are graphed using S-parameters measuring technique.
The paper is organized as follows,in section II the basics of the planar transmission lines and types are discussed. Section III
briefly explains theory of scattering parameters. Section IV highlights designing a transmission lines by considering constant
frequency. In section V the simulation results are discussed.
II. BASICS OF PLANAR TRANSMISSION LINES
The planar transmission lines have a conducting metal strip placed entirely in parallel planes. The most common structure has
one or more parallel metal strips placed on a dielectric substrate over a conducting ground plane. Depending on the
application and frequency range, dielectric material is selected [5].
These transmission lines are fabricated using conventional printed circuit board techniques, this translates into good
mechanical tolerances and low cost. The planar transmission lines are mainly three types: microstrip line, strip line and
coplanar waveguide.
A. Microstrip
The microstrip line is a type of planar transmission line. It can be fabricated by using photo lithographic process and is easy to
miniaturize and integrate with both passive and active microwave devices [6].

2. GJTE-Vol(2)-Issue(4) April 2015 ISSN: 2393-9923
Global Journal of Trends in Engineering
69
Fig. 1 Microstrip line structure and field lines
The construction of microstrip line is shown in Fig 1. A conductor of width W is placed on top layer on the dielectric material,
t is thickness of a conductor, h is height of dielectric. If the dielectric substrate is absent (thickness equal to zero) a
homogeneous medium exists between the layers [7, 8]. The dielectric material changes electrical behavior of transmission
lines and also has unique dielectric constant values.Fig 1 shows the field lines of microstrip line. Theheterogeneous dielectric
region exists around the conducting strip and hence it supports Quasi TEM waves.
The microstrip lines are designedusingstandard equations of theeffective dielectric ( ) is [7].
If the microstrip line dimension is known, then the characteristic impedance ( ) is calculated using below equations.
Where,
- Relative dielectric constant.
w - Width of the conductor.
h- Height of dielectric.
Using these equations, it is easy to design microstrip line for specific frequency applications.
B. Strip line
The strip line is being used for miniaturized microwave integrated circuits.The photo lithographic technique is used
tofabricate strip lines. The structure of the strip line is shown in Fig.2, b is the height of dielectric and t is the thickness of the
conductor. The dielectric is etched in its center to place the conductor.
Fig. 2 Strip line structure and Radiation pattern
Ifair is thedielectric media then lossreduces to lower values [7 - 9].
The strip line is designed usingcharacteristic impedance and effective width relations.These equations are as shown below.
i) Characteristic impedance,
ii) Effective width of the center conductor given by,
C. Coplanar Waveguide

3. GJTE-Vol(2)-Issue(4) April 2015 ISSN: 2393-9923
Global Journal of Trends in Engineering
70
Fig.3 Coplanar waveguide and radiation pattern
Coplanar Waveguide (CPW) is used to place more than one conductor on the substrate. The conductors form a central strip
separated by a narrow gap from two ground planes on either side [7, 9]. The dimensions of the center strip (w), the gap (s), the
thickness and permittivity of the dielectric substratedetermines the characteristic impedance and effective dielectric constant
of the transmission lines.
The characteristic impedance and effective dielectric constant equations are written as follows.
II.
III.
IV.
V.
VI. Where = characteristic impedance.
VII. = effective dielectric constant.
VIII. = relative dielectric constant.
IX. = elliptical integrals.
X. =components of .
III. S - PARAMETERS
S-parameter is the essential part of high frequency design. This is one of the techniques described to measure two port
networks [10]. Signal insertion loss and reflection loss can be measured effectively using S-parameters. A set of scattering
parameters can be seen in linear two port networks. For example, consider general two port network as shown below in figure
4. This network has two ports; port1 has a1and b1 terminals,and similarly port 2 has a2 and b2 terminals.
Fig. 4 Two port networks represent input and output waveforms.
The two port network can be analyzed usingS-parameters, namely S11, S12, S21 and S22, to measure losses in the
network.These parameters are calculated using the following equations [11].
+S12a2
+S22a2
Equivalently, these equations can be represented in matrix form as
The two port network technology shows the incident, reflected and transmitted electromagnetic waves. The port 1 and port 2
is given by its S-parameters equivalent as[12, 13].
Input reflection coefficient (Return loss)
Reverse transition coefficient (Insertion loss)
Forward transition coefficient (Insertion loss)
Output reflection coefficient (Return loss)
In this paper, we concentrate on S11 and S12 loss on planar transmission lines (but S12=S21).

4. GJTE-Vol(2)-Issue(4) April 2015 ISSN: 2393-9923
Global Journal of Trends in Engineering
71
The graph shows comparative results for three planar transmission lines microstrip line, strip line and coplanar waveguide.
IV. DESIGN AND ANALYZED RESULTS
The planar transmission lines design using standard equation is discussed in section II. The design includes variable
parameters and constant parameters. The constant parameters are metal thickness (t) conductor height (h), input impedance
(Rin) and frequency (f).
The variable parameter isthe dielectric substrate of the transmission lines. Changing the dielectric substrates affects the
insertion and return loss of the transmission line. The change of dielectric substrate results in the change of dielectric constant
and loss tangent values. This also influences the change in width (W) and length (L) of transmission lines.The overall effect
that can be observed by changing these parametric values is the variation of insertion and reflection losses in a transmission
line.
The graph shows insertion loss and return loss of planar transmission lines. The graphs are plotted in negative dB scale.
Similar substrate is used for designing different planar transmission lines. The responses of the planar transmission lines are
plot in a single graph for particular loss. The design is done to observe the insertion and reflection lossat frequency of 10GHz
and the obtained results are tabulated in Table. 1.
Fig.5 Return loss using GaAs substrate
Fig.6 Insertion loss using GaAs substrate
Fig.7 Return loss using Alumina substrate
Fig.8 Insertion loss using Alumina substrate

5. GJTE-Vol(2)-Issue(4) April 2015 ISSN: 2393-9923
Global Journal of Trends in Engineering
72
Fig.9 Return loss using Germanium substrate
Fig.10 Insertion loss using Germanium substrate
Fig.11 Return loss using Silicon substrate
Fig.12 Insertion loss using Silicon substrate

6. GJTE-Vol(2)-Issue(4) April 2015 ISSN: 2393-9923
Global Journal of Trends in Engineering
73
Fig.13 Return loss using RT/Duroide 5880 substrates
Fig.14 Insertion loss using RT/Duroide 5880 substrates
Table 1
A plot of loss versus dielectric substrates for planar transmission lines is given below. Fig 15 corresponds to reflection loss
and Fig. 16 to insertion loss.
Substrates
Planar transmission lines
Microstrip line Stripline Coplanar waveguide
Loss Type
Return loss
(- dB)
Insertion
loss (- dB)
Return
loss (- dB)
Insertion
loss (- dB)
Return
loss (- dB)
Insertion loss
(- dB)
GaAs
Loss T = 0.0005
76.98 0.0081 53.79 0.024 85.82 0.81
Alumina
Loss T = 0.0005
77.96 0.0081 55.66 0.021 104.50 0.70
Germanium
Loss T = 0.0005
76.24 0.0085 52.04 0.120 125.8 0.93
Silicon
Loss T = 0.001
77.00 0.0120 55.09 0.027 79.36 0.77
RT/Duroide 5880
Loss T = 0.001
75.64 0.0100 62.32 0.017 32.59 0.35

7. GJTE-Vol(2)-Issue(4) April 2015 ISSN: 2393-9923
Global Journal of Trends in Engineering
74
Fig. 15 Reflection loss (referring to the Table.1)
Fig 16 Insertion loss (referring to the Table.1)
V. CONCLUSION
The dielectric materials and metal strips are used to design transmission lines;the dielectric has unique dielectric constant and
loss tangent value. The design is centeredon 10GHz frequency. Various dielectric substrates were tried for design and the
corresponding results are tabulated and graphed for three different planar transmission lines.
From the obtained results, the following observations are made:
1. For microstrip line and strip line, GaAs dielectric substrate induces low return loss and Al substrate induces low
insertion loss.
2. For a CPW, RT/Duroide dielectric substrate causes low return and insertion loss.
The design can also be extended to analyze printed circuit board, hybrid integrated circuits and monolithic microwave
integrated circuits.
ACKNOWLEDGMENT
The authors would like to thank the ICON design Automation Pvt Ltd, for their assistance in carrying this work
REFERENCES
[1] Joachim N. Burghartz, Daniel C. Edelstein, Keith A. Jenkins, Young H. Kwark, “Spiral Inductors and Transmission
Lines in Silicon Technology Using Copper–Damascene Interconnects and Low-Loss Substrates,” IEEE
Transactions on Microwave Theory and Techniques, Vol. 45, No. 10, October 1997.
[2] Dane C. Thompson, Olivier Tantot, Hubert Jallageas, George E. Ponchak, Manos M. Tentzeris, “Characterization of
Liquid Crystal Polymer (LCP) Material and Transmission Lines on LCP Substrates From 30 to 110 GHz,” IEEE
Transactions on Microwave Theory and Techniques, Vol. 52, No. 4, April 2004.
[3] J. Zhang, M. Y. Koledintseva, G. Antonini, J. L. Drewniak, Rolla, A. Orlandi, K. N. Rozanov, “Planar
Transmission Line Method for Characterization of Printed Circuit Board Dielectrics,” USA, PIER 102, 267-286,
2010
[4] Richard Brown, RF/Microwave Hybrids Basics, Materials and Processes,Richard Brown Associates, Inc. Shelton,
CT Kluwer Academic Publishers New York, Boston, Dordrecht, London. ISBN: 1-4020-7233-3, 2003, PP29-30.
[5] N.A. Hoogc, M.J.J. Mayerb,1, H. Miedemac, W. Olthuisa, F.B.J. Leferinkd, A. van den Bergaa, “BIOS Modeling
and Simulations of the Amplitude–Frequency Response of Transmission Line Type Resonators Filled With Lossy
Dielectric Fluids,” Elsevier Sensors and Actuators A: Physical. Nov 2014.
[6] Jan Zehentner, Jan Mrkvica, Jan Machac, “Spectral Domain Analysis of Open Planar Transmission Lines,” Europe,
2009.
[7] David M. Pozar, Microwave Engineering, 4th
Edition, John Wily and Sons, Inc.USA, ISBN 978-0-470-63155-3,
2012.
-150
-100
-50
0
GaAs Al Ge Si RT/D
Microstrip
Stripline
CPW
-1
-0.8
-0.6
-0.4
-0.2
0
GaAs Al Ge Si RT/D
Microstrip
Stripline
CPW

8. GJTE-Vol(2)-Issue(4) April 2015 ISSN: 2393-9923
Global Journal of Trends in Engineering
75
[8] Inder Bahl, Lumped Elements for RF and Microwave Circuits, Artech House Boston, London. ISBN 1-58053-309-
4(alk paper). 2003. PP 429-435.
[9] Brian C, Wadell, Transmission Line Design Book, British Library Cataloguing Data, Norowood, 685 Canton Street,
Artech House,Inc, ISBN 0-89006-436.9. 1991, pp 73-136.
[10] Mukesh kumar, Rohini Saxena, Anil Kumar, Pradyot Kala, Reena Pant. “Theoretical characterization of Coplanar
Waveguide Using IJS Conformal Mapping,” IJARCSEE Volume 1, Issue 4, June 2012. ISSN: 2277 – 9043.
[11] Vendelin, Anthony M. Pavio, Ulrich L. Rohde,. A John Wiley, “Microwave Circuit Design Using Linear and
Nonlinear Techniques,” Second Edi., New Jersey., 2005, pp198-200.
[12] K. A John Wiley, Radio-Frequency and Microwave Communication Circuits Analysis and Design, Second Edi.,
Devendra & Sons, Inc, Publication. Hoboken, New Jersey. 2004. PP 304-311.
[13] Richard Brown, RF/Microwave Hybrids Basics, Materials and Processes, Richard Brown Associates, Inc. Shelton,
Kluwer Academic Publishers, London, 2003, pp10-11.