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Indonesian Journal of Electrical Engineering and Informatics (IJEEI)
Vol. 7, No. 3, Sep 2019, pp. 535~542
ISSN: 2089-3272, DOI: 10.11591/ijeei.v7i3.1012 535
Journal homepage: http://section.iaesonline.com/index.php/IJEEI/index
Performance Analysis of Low noise amplifier using Combline
Bandpass Filter for X Band Applications
Mohammed Lahsaini1, Islam Toulali2, Lahbib Zenkouar3
1Materials and Instrumentation Group, LASMAR, Faculty of Science, Moulay Ismail University, Meknes, Morocco
2,3Equipe de Recherche en Smart Communications (ERSC), E3S Research Center, Mohammadia School of Engineers
(EMI), Mohammed Vth University, Rabat, Morocco
Article Info
ABSTRACT
Article history:
Received Feb 04, 2019
Revised May 08, 2019
Accepted Sept 30, 2019
This paper describes a procedure for designing broadband low noise
amplifier for X-Band applications. The design and implementation are based
on HEMT transistors AFP02N2-00 of Alpha Industries®. The matching
circuit used for modeling the microwave amplifier is the quarter-wave
transformers impedance matching technique associated to combline
bandpass filter. The proposed amplifier is implemented on a substrate of
epoxy FR4 with a central frequency of 11GHz and a fractional bandwidth of
0.18% and is designed to be used in radar reception systems. The results
show that the proposed LNA is unconditionally stable with a simulated gain
of 20dB over the working frequency range of [9.5−12.5] GHz.
Keywords:
Low noise amplifier
Combline filter
Matching network
Microstrip technology
Quarter wave transformer
Copyright © 2019Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
Islam Toulali,
Equipe de Recherche en Smart Communications,
Mohammadia School of Engineers (EMI),
Mohammed Vth University, Rabat, Morocco
Email: islamtoulali@gmail.com
1. INTRODUCTION
Nowadays, the evolution of high data-rate communication systems and particularly the front-end
receiver systems creates new challenges for circuit designers. Since both, the transmitter and receiver require
high performance amplifiers and selective filters. In fact, microwave amplifiers with the characteristics of
high gain, low noise, good input and output matching and compact size play an important role in modern
wireless applications [1-2-3]. The main objective of our work consists of designing low noise and wideband
amplifier that meets the requirements described above. Previous studies of researchers present different
advantage. For example, detailed analysis of RF amplifiers has been presented by authors in [4-7]. Another
related study of LNA was performed by [8] which divided the method of lumped input and output matching
networks.
However, the most important factor while designing broadband microwave amplifiers is to
amplify the signal without causing any significant distortion [9]. The specific purposes of this study, is
developing a novel impedance matching technique, in order to solve the problems generally found in research
papers. The amplifier is adapted by a microstrip combline filter connected to a single quarter wave
transformer [10]. A step by step design implementation of the circuit is then presented. Combline filter is one
of the most commonly used bandpass structures. The combline bandpass consists of mutually-coupled
resonators which are physically less than a quarter wavelengths long and which are grounded at one end and
capacitively loaded at the other end [11]. A conventional combline filter is shown in Figure 1. The
contribution is a microstrip combline filter used as a matching network that can offers good selectivity and
adaptation. The final circuit was simulated using ADS (Advanced Design System) software and implemented
on FR4 epoxy substrate.
ISSN:2089-3272
IJEEI Vol.7, No. 3, Sep 2019: 535 – 542
536
The synthesis of combline bandpass filter is analyzed in Section II by using the mathematical
expressions. The design methodology of amplifier based on the combline filter is then described. Simulations
are presented in Section III to indicate the performance of the circuit. Finally, a conclusion is given in Section
IV.
Figure 1. Compact planar structure
2. RESEARCH METHOD
2.1. The matching network theory
The matching circuit used for modeling the microwave amplifier is the combline band pass filter.
Combline microwave filters are used extensively in mobile communication systems in recent years because of
their compact size, low cost, wide tuning range and relatively low loss. In fact, band pass filters that are
designed with combline cavity structure have several advantages [12]:
• Combline cavity filters are very compact.
• It is easier to realize high rejection for the stop bands.
• Combline filters are relatively easier to assemble ensuring faster production.
Figure 2. A combline, band pass filter [2]
Figure 2 represents a combline filter of N resonators in strip-line form. The resonators consist of line
elements which are short-circuited at one end, with a lumped capacitance between the other end of each
resonator line element and ground [13]. The resonators lengths are usually chosen to be between 20 and 80.
Indeed when the value of the load capacity increases, the length of the line decreases, thus resulting in a more
compact filter with a larger rejection band. The main advantage is an excellent stopband because the
resonators are electrically short. The combline filter is compact, as the resonators may be significantly shorter
than one quarter wavelength and are closer together than in an interdigital filter with the same bandwidth and
ground plane spacing [14].
The design method of combline filter requires solving equations in order to obtain the important physical
dimensions, namely the spacing, the width, the length of the resonators and the capacitance values. In this
study, we provide an analysis of combline filters based on the method of graphs and a design method based
IJEEI ISSN: 2089-3272
Performance Analysis of Low noise amplifier using Combline Bandpass Filter … (M Lahsaini, et al)
537
on a bandpass prototype circuit [15]. The design procedures are indicated below; the first step is to suggest a
low pass to band pass transformation for estimating the attenuation characteristics of combline filter [13] as
indicated in (1), (2), (3):
(1)
With:
(2)
And
(3)
The design equations for combline filter are given by:
=
(
) (4)
Where is the electrical length of the resonator elements at the midband frequency.
′ (5)
′
(6)
′ (7)
Where is the fractional bandwidth defined below and represents the element values of a lowpass
prototype filter with a normalized cutoff frequency
. is the characteristic admittance of the
terminating lines.
The resonators consist of line elements that are short-circuited at one end, with a localized
capacitance between the other end of each resonator line element and the ground. In Figure 2 lines 1 to n,
along with their associated lumped capacitances
to
comprise resonators, while lines 0 and n + 1 are not
resonators but simply part of impedance transforming sections at the ends. The normalized capacitances per
unit length between each line and ground are as follows [13]:
(8)
(9)
(10)
(11)
(12)
Where is the dielectric constant and ε is the relative dielectric constant of the medium of propagation. The
normalized mutual capacitances
per unit length between adjacent line elements are:
(13)
(14)
ISSN:2089-3272
IJEEI Vol.7, No. 3, Sep 2019: 535 – 542
538
(15)
The lumped capacitances
are:
(16)
It is usually desirable to make the capacitances in this type of filters sufficiently large that the
resonator lines will be
or less, long at resonance. After the normalized capacitances, ε
and ε
,
have been computed, we use the charts of Figure 3 and Figure 4 and (17), (18) to determine the dimensions
and of the lines for specified and [13]. Figure 3 can be used to determine
, then is
obtained.
The cross-sectional dimensions of the bars and spacings between them are determined as follows
[13]:
(17)
And the normalized width of the bar is:
′
′
(18)
Figure 3. Normalized even-mode fringing capacitance
and interbar capacitance
for coupled
rectangular bars [13]
IJEEI ISSN: 2089-3272
Performance Analysis of Low noise amplifier using Combline Bandpass Filter … (M Lahsaini, et al)
539
Figure 4. Normalized fringing capacitance for an isolated rectangular bar [13]
2.2. Fiter design process
A stripline [16] combline band pass filter was designed to have fractional bandwidth of 27% or
FBW=0.27 at the midband frequency of 11 GHz. Tschebyshev low pass prototype filter of order with
pass band ripple of 0.1 dB was chosen. The low pass prototype parameters given for a normalized low pass
cutoff frequency are:, and.
The band pass filter topology is shown in Figure 5 and analyzed using the ADS software of Agilent
Technologies relying on the S-parameters. A dielectric substrate [16] with a relative dielectric constant of
4.32 and a thickness of 1.6 mm was chosen for the filter design. The dimensions and of the lines and
capacitances between each line and ground are represented.
Figure 5. Structure of the third-resonator combline filter
The simulated results of the designed filter are satisfying; the filter is capable of passing the
frequencies between range with minimum loss as it is described on Figure 6.
Figure 6. Structure of the third-resonator combline filter
910 11 12 13814
-40
-30
-20
-10
-50
0
freq, GHz
dB(S(1,1))
dB(S(2,1))
ISSN:2089-3272
IJEEI Vol.7, No. 3, Sep 2019: 535 – 542
540
3. CIRCUIT ANALYSIS AND INTERPRETATIONS
Based on the matching circuit explained in the previous section, the broadband low noise amplifier
was modeled as indicated in Figure 7. The proposed LNA comprises two transistors separated by a
transmission line, and a matching networks [17] which are located in the input and output.
We adopted the HEMT transistors AFP02N2-00 of Alpha Industries®, the block of impedance
transformation was used to adapt the impedance at 11 GHz. This transmission line can eliminate the
imaginary part of the impedance to adapt. After that a second transmission line designed by a single quarter
wave transformer was used to approach the center of the Smith chart. Finally, we integrated the third-
resonator combline filter at the input and the output of the circuit.
We have simulated the two stages LNA constituted by the physical parameters of each block and
implemented on FR4 epoxy substrate using ADS (Advanced Design System) software. Tuning and
optimization tools of ADS software have been used to optimize results.
Figure 7. Scheme of the modeled amplifier
Figure 8 illustrates the simulated results of gain and reverse transmission coefficient which is
given by . The gain is about 20.5 dB from to and is less than -35 dB over the band
of interest.
Figure 8. Transmission Parameters
The simulated results of input and output reflection coefficients are shown in Figure 9. The input
reflection coefficient is less than -23dB and the output reflection coefficient is widely inferior to -25dB.
10.0 10.5 11.0 11.5 12.09.5 12.5
-30
-20
-10
0
10
20
-40
30
freq, GHz
dB(S(1,2))
dB(S(2,1))
IJEEI ISSN: 2089-3272
Performance Analysis of Low noise amplifier using Combline Bandpass Filter … (M Lahsaini, et al)
541
Figure 9. Reflection Parameters Figure 10. Noise figure
The noise factor is the degradation of signal to noise ratio (SNR). The noise figure obtained is
around at as shown in Figure 10. The designed amplifier is unconditionally stable; the stability
coefficients (Mu1 and MuPrime1) are greater than 1 as indicated in Figure 11.
Figure 11. Stability coefficients
Table 1 presents a comparison of the results with those of other researchers. Our proposed amplifier
presents suitable simulations results compared with other design techniques [18-21].
Table 1. Summary of the LNA performances
Frequency
(GHz)
Bandwidth
Technology
This work
[9.5-12.5]
< -23
>20.5
< -25
<- 35
HEMT
[18]
[7-12]
<-9
>12
<-15.12
-
Narrow band
FET
[19]
[8-12]
<-10
>15
<-10
-
CMOS
[20]
[10-12]
< -18.9
> 20.37
< -19.10
< -36.29
HEMT
[21]
[10-12]
< -32
>20
< -40
<- 35
HEMT
4. CONCLUSION
In this paper, an appropriate approach for designing low noise amplifier using the concepts of
quarter wave transformers and combline filter has been proposed. The fast and accurate tools of ADS based
on optimization, allows obtaining directly optimal parameters of combline band pass filter. Thus, the
amplifier was configured and the simulated results achieve high performance features. As a prospect of
development of research, we will analyze a new component of the communication block which is the
comparator as proposed in [22].
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ISSN:2089-3272
IJEEI Vol.7, No. 3, Sep 2019: 535 – 542
542
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BIOGRAPHY OF AUTHORS
Mohammed Lahsaini was born in Sidi Slimane, Morocco, in 1984. He received the Master's
degree in Telecommunication and Microwave Devices from National School of Applied Sciences,
Fes, Morocco, in 2011 and Doctoral degree from Mohammadia School of Engineers, Mohammed
V University, Agdal, Rabat, Morocco. He is currently a professor at the faculty of Science,
Moulay Ismail University, Meknes, Morocco. His research interests include Microwave Circuits,
Transmission and Reception Systems.
Islam Toulali was born in Rabat, Morocco, in 1990. She studied mathematics and physics at Ibn
Ghazi Higher School Preparatory Classes in Rabat, Morocco. And obtained the engineer degree in
telecommunications and networks from National School of Applied Sciences in 2014, Oujda,
Morocco. She is preparing her PhD in Mohammadia School of Engineers, Mohammed V
University, Agdal, Rabat, Morocco. Her research interests include Microwave Circuits and
Systems.
Lahbib Zenkouar was born in Meknes, Morocco. He received the Doctoral degree in CAD-VLSI
from University of Sciences and Techniques of Languedoc, Montpellier, France and Ph.D.
Sciences and Techniques in Telecommunication from Institute of Electricity of Montefiore, Liege ,
Belgium, He is currently Leader of research team TCR of the Laboratory Electronic and
Communication -LEC- and Professor at Electrical Engineering Department, Mohammadia School
of Engineers, Mohammed V University, Agdal, Rabat, Morocco. His research interests focuses on
the design of Microwave Circuits and Systems and Information Technology.
