International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 12 - Mar 2014
Analysis of Different Matching Techniques for
Microwave Amplifiers
Shreyasi S, Kushal S, Jagan Chandar
BE Student, DEPT of Telecommunication, RV College of Engineering, Bangalore INDIA
BE Student, DEPT of Telecommunication, RV College of Engineering, Bangalore INDIA
BE Student, DEPT of Telecommunication, RV College of Engineering, Bangalore INDIA
I. Abstract
input and output impedances are critical along with power
This paper describes different types of matching
circuits for microwave amplifiers at input and output side at
1GHz. This paper compares the results of all possible
combinations of ‘T’, ‘L’ and ‘π’ type matching circuits. The
designed circuit is simulated with Advanced Design System
(ADS) software. T- L matching configuration gives better
results than L-L, L-T, T-T, π-L, L-π, π-T, T-π, and π-π
circuits. Forward gain and stability factor for T-L match are
16.755 dB and 0.917 is observed which is better than other
output, gain and efficiency.
The main role in any impedance matching scheme
is to force a load impedance to look like the complex
conjugate of the source impedance, and maximum power
transfer to the load. When a source termination is matched to a
load with passive lossless two-port network, the source is
conjugate matched to the input of the network, and also the
load is conjugate matched to the output of the network. The
matching process becomes more difficult when real parts of
the terminations are unequal, or when they have complex
configurations.
Keywords-Advanced Design System (ADS), T, π,
impedances.
L matching networks, Low Noise Amplifiers (LNA),
III. Literature Survey
Scattering (S) Parameter
Recently lumped matching networks for matching a
II. Introduction
An amplifier is the most common electrical element
microwave amplifier have been studied by many researchers.
in any system. The requirements for amplification are as
varied as the systems where they are used. The key to
successful
microwave
amplifier
design
is
impedance
matching. In any high-frequency amplifier design, improper
impedance matching will degrade stability and reduce circuit
efficiency. At microwave frequencies, this consideration is
even more critical, since the transistor’s bond-wire inductance
and base-to-collector capacitance become significant elements
in input/output impedance network design. In selecting a
suitable transistor, therefore, it should be kept in mind that the
A symbolic approach and an optimization algorithm
for the optimal design of Low Noise Amplifiers (LNAs)
through S-parameters have been discussed in [1]. This paper
gives the idea of computing automatically the symbolic
expression of S parameters using Coates diagraph technique.
A new technique has been employed for improving the
stability of the Low Noise Amplifier. A RLC series circuit has
been employed to make the Low noise amplifier stable. The
simulation results of all possible combinations of L type
matching circuits are done. Each circuit is simulated for, with
ISSN: 2231-5381
http://www.ijettjournal.org
Page 625
International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 12 - Mar 2014
and without stabilizing circuit and feedback circuit. Under
RF/microwave frequencies because it allows maximum power
stability condition, forward gain and noise figure of L type
transfer to occur from source to load and signal-to-noise ratio
network are calculated.
to be improved due to an increase in the signal level. These
are the primary reasons to employ tuning in practically all
In paper [2], in this paper, the design of impedancematching
networks
by distributed
network synthesis
RF/microwave active circuit design. Ideally, the matching
is
network is lossless to prevent further loss of power to the load.
presented to achieve high-efficiency characteristics of
It acts as an intermediate circuit between the two non-identical
microwave and millimetre-wave amplifiers. The transfer
impedances in such a way that the source sees a perfect match
function for distributed network structures with an arbitrary
while the multiple reflections existing between the load and
electrical length is derived by the Chebyshev approximation.
matching network will be unseen by the source. Several types
The values of network elements synthesized to match the load
of matching network are available, however factors likes
impedance are tabulated in terms of the minimum insertion
complexity, bandwidth, implementation and adjustability need
loss (MIL) and ripple parameters. To validate the performance
to be considered in the matching network selection. In this
of matching circuits by the network synthesis, the results are
paper, “L” Matching, “T” matching and “π” matching circuits
applied to the design of an octave-band microwave transistor
and its all possible combinations are discussed.
amplifier.
V. Parameters for comparison of different matching
In paper [3], Impedance matching for microwave
amplifiers have been investigated extensively using different
circuits
A. S-Parameters
methods such as stub matching for broadband applications. In
The network representation of a two port network at
the present communication broadband impedance matching
high
RF/microwave
technique has been developed by combining the amplifier
Parameters’. In view of linearity of the electromagnetic field
module with series microstrip transmission lines with
equations and the linearity displayed by most microwave
optimum characteristic impedance and electrical length.
components and networks, the scattered waves are linearly
Resistive loading are used at both the source and load
related to the incident wave amplitude. The matrix describing
terminals to ensure unconditional stability. Different variable
this linear relationship is called a “scattering matrix or [s]”.
parameters like resistance values, characteristics impedance
This linear relationship is expressed in terms of a ratio of two
and length of the transmission line are used to design the
phasors that are complex numbers with magnitude of the ratio
amplifier. The analysis of the design circuit has been carried
less than or equal to 1.
out using multiplication of transmission matrices. This unique
method hitherto unpublished can be used as a broad band
frequencies
is
called
‘Scattering
Each specific element of [S] matrix is defined
below:
technique for designing microwave amplifiers.
S11- Input reflection coefficient
S12- Reverse transmission coefficient
IV. Matching Networks
Connecting two circuits together via a coupling
device or network in such a way that the maximum transfer of
S21- Forward transmission coefficient
S22- Output reflection coefficient
energy occurs between two circuits is called matching.
Impedance matching is a very important concept in
ISSN: 2231-5381
http://www.ijettjournal.org
Page 626
International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 12 - Mar 2014
B. Stability
In a two-port network, oscillations are possible if
the magnitude of either the input or output reflection
VI. MATCHING CIRCUIT CONFIGURATIONS
coefficient is greater than unity, which is equivalent to
presenting a negative resistance at the port. This instability is
A. CASE 1: ‘L’ Type Input Matching and ‘L’ Type Output
Matching
characterized by either input or output reflection coefficient
greater than 1, which or a unilateral device implies |s11|>1 or
In Figure 2, the “L” type matching is used at the
input as well as on the output side.
|s22|>1. The requirements for stability are defined by circles,
called stability circles. The radius and centre of the output and
input stability circles are derived from the S parameters. The
concept of instability with varying input or output matching
conditions is significant, as an amplifier is desired to be
unconditionally stable under all expected conditions of source
and load impedances. Alternatively, stability is also verified if
the following conditions are met:
K=1-|s11|2-|s22|2-|∆|2 / 2(s12*s21)
---- (1)
And ∆=s11*s22 – s12*s21 where |∆| >1
Figure.2 “L” Type Input Matching and “L” Type Output
Matching
--- (2)
Figure.3 S11, S22, S12, S21, and stability factor for L-L Matching
After the simulation of the circuit shown in Figure
Figure.1 Input stability circles
2, the results are shown in Figure 3. The stability and forward
gain are as 0.917 and 16.219dB. The output reflection
coefficient is –13.945 dB, reverse transmission coefficient is 18.428 dB, and input reflection coefficient is -11.892 dB.
Since the stability circuit is not introduced, stability factor is
less than 1.
ISSN: 2231-5381
http://www.ijettjournal.org
Page 627
International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 12 - Mar 2014
B. CASE 2: ‘L’ Type Input Matching and ‘T’ Type Output
C. CASE 3: ‘T’ Type Input Matching and ‘L’ Type Output
Matching
Matching
In Figure 6, the “T” type matching is used at the
In Figure 4, the “L” type matching is used at the
input and on the output side the “L” type matching is used.
input and on the output side the “T” type matching is used.
Figure.6 “T” Type Input Matching and “L” Type Output
Matching
Figure.4 “L” Type Input Matching and “T” Type Output
Matching
Figure.7 S11, S22, S12, S21, and stability factor for T-L
Matching
Figure.5 S11, S22, S12, S21, and stability factor for L-T Matching
After the simulation of the circuit shown in Figure
After the simulation of the circuit shown in Figure
6, the results are shown in Figure 7. The stability and forward
4, the results are shown in Figure 5. The stability and forward
gain are as 0.917 and 16.043 dB .The output reflection
gain are as 0.917 and 16.283 dB .The output reflection
coefficient is -11.094 dB, reverse transmission coefficient is –
coefficient is -15.875 dB, reverse transmission coefficient is –
18.605 dB, and input reflection coefficient is -12.176 dB.
18.365 dB, and input reflection coefficient is -9.999 dB. Since
Since the stability circuit is not introduced, stability factor is
the stability circuit is not introduced, stability factor is less
less than 1
than 1
ISSN: 2231-5381
http://www.ijettjournal.org
Page 628
International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 12 - Mar 2014
D. CASE 4: ‘T’ Type Input Matching and ‘T’ Type Output
E. CASE 5: ‘L’ Type Input Matching and ‘π’ Type Output
Matching
Matching
In Figure 8, the “T” type matching is used at the
input and on the output side the “T” type matching is used.
In Figure 10, the “L” type matching is used at the
input and on the output side the “π” type matching is used.
Figure.8 “T” Type Input Matching and “T” Type Output
Figure.10 “L” Type Input Matching and “π” Type Output
Matching
Matching
Figure.9 S11, S22, S12, S21, and stability factor for T-T Matching
After the simulation of the circuit shown in Figure
8, the results are shown in Figure 9. The stability and forward
gain are as 0.917 and -18.957 dB .The output reflection
coefficient is -5.115 dB, reverse transmission coefficient is
15.690 dB, and input reflection coefficient is -13.157 dB.
Since the stability circuit is not introduced, stability factor is
less than 1
Figure.11 S11, S22, S12, S21, and stability factor for L-π Matching
After the simulation of the circuit shown in Figure
10, the results are shown in Figure 11. The stability and
forward gain are as 0.917 and 15.440 dB .The output
reflection coefficient is -6.976 dB, reverse transmission
coefficient is -19.208 dB, and input reflection coefficient is –
21.682 dB. Since the stability circuit is not introduced,
stability factor is less than 1
ISSN: 2231-5381
http://www.ijettjournal.org
Page 629
International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 12 - Mar 2014
F. CASE 6: ‘π’ Type Input Matching and ‘L’ Type Output
G. CASE 7: ‘π’ Type Input Matching and ‘T’ Type Output
Matching
Matching
In Figure 12, the “π” type matching is used at the
input and on the output side the “L” type matching is used.
In Figure 14, the “π” type matching is used at the
input and on the output side the “T” type matching is used.
Figure.14 “π” Type Input Matching and “T” Type Output
Matching
Figure.12 “π” Type Input Matching and “L” Type
Output
Matching
Figure.15 S11, S22, S12, S21, and stability factor for π-T
Matching
Figure.13 S11, S22, S12, S21, and stability factor for π-L Matching
After the simulation of the circuit shown in Figure
14, the results are shown in Figure 15. The stability and
After the simulation of the circuit shown in Figure
forward gain are as 0.917 and 14.755 dB .The output
12, the results are shown in Figure 13. The stability and
reflection coefficient is -10.438 dB, reverse transmission
forward gain are as 0.917 and 16.280 dB. The output
coefficient is -17.893 dB, and input reflection coefficient is -
reflection coefficient is -10.823 dB, reverse transmission
18.397 dB. Since the stability circuit is not introduced,
coefficient is -18.368 dB, and input reflection coefficient is -
stability factor is less than 1.
13.428 dB. Since the stability circuit is not introduced,
stability factor is less than 1
H. CASE 8: ‘T’ Type Input Matching and ‘π’ Type Output
Matching
In Figure 16, the “T” type matching is used at the
input and on the output side the “π” type matching is used.
ISSN: 2231-5381
http://www.ijettjournal.org
Page 630
International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 12 - Mar 2014
Figure.16 “T” Type Input Matching and “π” Type Output
Matching
Figure.18 “π” Type Input Matching and “π” Type Output
Matching
Figure.17 S11, S22, S12, S21, and stability factor for T-π
Matching
Figure.19 S11, S22, S12, S21, and stability factor for π-π Matching
After the simulation of the circuit shown in Figure
16, the results are shown in Figure 17. The stability and
After the simulation of the circuit shown in Figure
forward gain are as 0.917 and 15.161 dB .The output
18, the results are shown in Figure 19. The stability and
reflection coefficient is –9.012 dB, reverse transmission
forward gain are as 0.917 and 14.487 dB .The output
coefficient is -19.486 dB, and input reflection coefficient is -
reflection coefficient is –3.672 dB, reverse transmission
13.539 dB. Since the stability circuit is not introduced,
coefficient is -20.160 dB, and input reflection coefficient is -
stability factor is less than 1.
13.344 dB. Since the stability circuit is not introduced,
stability factor is less than 1.
I. CASE 9: ‘π’ Type Input Matching and ‘π’ Type Output
VII. SIMULATION RESULTS
Matching
In Figure 18, the “π” type matching is used at the
input and on the output side the “π” type matching is used.
In this paper, combination of different input and
output matching networks have been developed for a
microwave Amplifier circuit at 1 GHz range and simulated
using ADS software. The results are shown in Table 1.
ISSN: 2231-5381
http://www.ijettjournal.org
Page 631
International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 12 - Mar 2014
parameters like output reflection coefficient (S22) = –
VIII. CONCLUSION
The simulation results of all possible combinations of
10.438 dB, input reflection coefficient (S11) = -18.397 dB
“L”, “T” and “π” type matching circuits are shown in
and reverse transmission coefficient (S12) = -17.893 dB
Table 1 for without stabilizing circuit (SC). From Table 1
are also comparatively better than other matching
the “π” type input matching with “T” type output
sections. Since stability circuit has not been included, the
matching gives better results without much degradation in
stability factor is less than 1.
terms of forward gain, and stability point of view. It gives
gain as 16.755 dB and stability as 0.917. Other
REFERENCES
[1] D. Senthilkumar, Dr.Uday Pandit knot, Prof. Santosh Jagtap / International
[5] Chris Bowick, RF Circuit Design, Newnes imprint of Butterworth
Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622
Heinemann, 1982, Ch. 4 - 5.
Vol. 3, Issue 1, January -February 2013, pp.403-408
[6] Joseph F. White, High Frequency Techniques / An Introduction to RF and
[2] Microwave and optical technology letters, Volume 27, issue 2, 25 august
Microwave Engineering, John Wiley & Sons 2004.
2000
[7] Randy Rhea, “Yin-Yang of Matching: Part 2- Practical Matching
[3] S K Khah, Pallavi Singh, Sweta Rabra, Tapas Chakarvarty IEEE01/2007;
Techniques,” High Frequency Electronics, April 2006.
DOI:10.1109/AEMC.2007.4638055
[8] J. F. White, High Frequency Techniques / An Introduction to RF and
In
proceeding
of:
Applied
Electromagnetics Conference, 2007. AEMC 2007. IEEE
Microwave Engineering, JohnWiley & Sons 2004, pp. 70-71.
[4] “Philip H. Smith: A Brief Biography” by Randy Rhea, Noble
[9] Agilent Technologies, Advanced Design System.
[10] B. Becciolini, Impedance Matching Networks Applied To R-F
Publishing 1995.
Power Transistors, Motorola AN-721, Motorola Inc., 1974.
Parameters
L
analysed
LL
S11
-11.892
S12
-18.428
S21
16.219
S22
-13.945
Stability Factor
.917
L
LT
T
TL
T
Lπ
TT
π
L
πL
π
T
πT
-
9
-
-
j
j
-9.999
-12.176
-13.157
-21.68
-13.428
-18.397
-
-
-
-
-
-
-18.365
-18.605
15.690
-19.208
-18.368
-17.893
1
J
1
-
-
1
16.283
16.093
-18.957
15.440
16.280
16.755
-
-
-
-
-
-15.875
-11.094
-5.115
-6.976
-10.823
-10.438
0
0
0
0
0
0
.917
.917
.917
.917
.917
.917
Tπ
-
ππ
o
-13.539
-
-13.344
-
-19.486
H
-20.160
1
15.161
-
14.487
-
-9.012
0
-3.672
0
.917
0.917
Table I Comparative Results of microwave amplifier Circuit (without Stabilizing circuit) using different matching techniques.
[11] Agilent Technologies, win-Smith 2.0, Noble Publishing 1998.
[12] linSmith, John Coppens, 1999- 2008, www.jcoppens.com/soft/linsmith.
ISSN: 2231-5381
http://www.ijettjournal.org
Page 632