International Journal of Scientific & Engineering Research, Volume 4, Issue 12, December-2013

ISSN 2229-5518

781

Band Pass Filter and Low Noise Amplifier Design using Advanced Design System (ADS)

Vinay Divakar1, Manasa K2

Abstract— The paper presents the design of a lumped model of Low pass Filter (LPF) for 4.8 GHz and High pass filter(HPF) for

4.6 GHz using software tool ADS and then finally cascading the LPF and HPF to develop a Band pass filter(BPF), for passing
frequencies between 4.6 GHz to 4.8 GHz whose response is analyzed after simulation. It also describes the design of a HEMT
based Low noise amplifier (LNA) using the software ADS, on which a stability check and performance analysis is made on the
chosen model for the design of LNA. Once LNA design is ready, then it is cascaded with the BPF to produce an amplified
output with the least minimum noise figure.

Index Termshigh pass filter, low pass filter, Filter Design, Low noise amplifier, LNA, Advanced design system, HEMT.

—————————— ——————————

1 INTRODUCTION

Low Pass Filter (LPF) is used to block the high frequency components and pass only the low frequency signals. In

LPF, signals with frequencies higher than the cut off frequency are attenuated. High Pass Filters (HPF) is just the opposite of
fs2 = 4.8GHz + 0.2GHz
fs2 = 5 GHz

3 DESIGN CALCULATIONS FOR THE DESIRED SPECIFICATION:

IJSER

LPF as it blocks low frequency components and passes high
frequency signals. Cascading the LPF and the HPF, a Band
Pass Filter (BPF) can be obtained that passes frequencies with- in a certain range and attenuates or rejects frequencies outside that range. The Low Noise Amplifier (LNA) is a special type of electronic amplifier used in communication systems which amplifies very weak signals captured by an antenna. This is frequently used in microwave applications or systems such as GPS.

2 CUT-OFF FREQUENCIES FOR THE BANDWIDTH 0.2

GHZ (4.6 GHZ TO 4.8 GHZ):

Bandwidth (BW) = 0.2GHz
And

i. Low Pass Filter (LPF) design for 4.8GHz

R0 = 50Ω
Cut off frequency, fc = 4.8GHz
Wc = 2πfc
= 2*3.14*4.8GHz
= 30.163*109
L = 2R0/Wc
= 2*50/30.163*109
= 3.315nH ……(1)
C = 2/WcR0
= 2/30.163*109
= 1.326pF ……(2)
fp1 = 4.6GHz
fp2 = 4.8GHz
Now we determine the stop band frequencies fs1 and fs2 for
BW 0.2GHz for cut-off frequencies between 4.6GHz to 4.8GHz
as follows:
fs1 = fp1 – 0.2GHz
So fs1 = 4.6GHz – 0.2GHz
Therefore,
fs1 = 4.4GHz
Similarly,
fs2 = fp2 + 0.2GHz

————————————————

Author Vinay Divakar is currently pursuing M.sc (Engg) degree program in Electronic System Design Engineering in M.S Ramaiah School of Advanced Studies Affliated to Conventry University, U.K. PH- 9449835011. E-mail: vinaydivakar@hotmail.com
Co-Author Manasa.K is currently pursuing M.sc (Engg) degree program in Electronic System Design Engineering in M.S Ramaiah School of Advanced Studies Affliated to Conventry University, U.K. PH-9916010063. E-mail: kmanasa.rose@gmail.com

ii. High Pass Filter design (HPF) for 4.6GHz

R0 = 50Ω
Cut off frequency, fc = 4.6GHz
Wc = 2πfc
= 2*3.14*4.6GHz
= 28.90*109
L = R0/2Wc
= 50/2*28.90*109
= 0.8650nH ……(3)
C = 1/2WcR0
= 1/2*28.90*109*50
= 0.346pF …….(4)

IJSER © 2013

http://www.ijser.org

International Journal of Scientific & Engineering Research Volume 4, Issue 12, December-2013

ISSN 2229-5518

4 METHODOLOGY IN SIMULATING LUMPED MODEL BASED BAND PASS FILTER USING ADS:

 Open ADS and then create a new project, after creat- ing a schematic layout window opens.
 At the left hand side, top of the screen, Drop down by clicking and select Lumped components, and then all
the lumped components are displayed at the left hand side palette.
 LPF and HPF are designed by selecting the compo-
nents from the palette and placing it on the schematic.
 Once the components are placed and connected re-
spectively, then calculate the Inductance (L) and Ca- pacitance (C) values that needs to be assigned to the
inductors and capacitors.
 The values of L and C depends on the type of filter we
are designing i.e. LPF or HPF.
 Once calculated, these values are assigned to their re-
spective components. Then click and open the drop down box and select S-parameters. After this, select

Fig 1a Low Pass Filter (LPF)

782

terminal impedance from the palette and connect this to the source and load impedance of the circuit. Then select the S-parameter Engine, and place it on the lay- out. Make sure to connect the ground.

 Then double click on the S-parameter Engine and as-
 SIMULATION AND VERIFICATION :
The parameter S (2, 1) is the Gain Response and S (1, 1) is the
return loss.
sign the start, stop and step frequency values such that we obtain the desired response.
 And then finally we simulate and a simulation win- dow pops up, in this we select the graph from the pal- ette present on the left hand side of the screen. Then we have to select the response we desire to see i.e. S
(2, 1), which is gain and S (1, 1) is the return loss. Then a graph pops up and we can see and analyze the re- sponse shown in the graph.
 So the HPF and LPF is designed separately using the
above procedure and then the successfully designed
HPF and LPF is cascaded to develop a band pass filter
(BPF), whose frequency response is analyzed after
simulation.

5 DESIGN, MODEL, SIMULATE AND VERIFY THE DESIGNED BAND PASS FILTER (BPF) USING ADS:

i. Low Pass Filter (LPF):

 DESIGN:
L = 3.315nH ……From eqn (1)
L/2 = 1.657nH
C = 1.326pF ……From eqn (2)
 MODEL:
The LPF circuit in the Fig (1a) is modeled using the ADS soft-
ware.

Fig 1b Low Pass Response

The Fig (1b) verifies the Low pass filter designed for 4.8GHz, Since we can see that the gain response and the return loss is intersecting exactly at 4.8GHz.

ii. High Pass Filter (HPF):

 DESIGN:
C = 0.346pF …..From eqn (4)
2C = 0.692pF
L = 0.8650nH ……From eqn (3)
 MODEL:
The HPF circuit is modeled as shown in the Fig (2a) using the
ADS software.

IJSER © 2013

http://www.ijser.org

International Journal of Scientific & Engineering Research Volume 4, Issue 12, December-2013

ISSN 2229-5518

783

Fig 2a High Pass Filter

 SIMULATION AND VERIFICATION:
The parameter S (2, 1) is the Gain Response and S (1, 1) is the
return loss.

Fig 3a Band Pass Filter (BPF)


 SIMULATION AND VERIFICATION:
The parameters S (2, 1) is the Gain Response and S(1,1) is the
return loss.

IJSER

Fig 2b High Pass Response

The Fig (2b) verifies the High pass filter designed for 4.6GHz, since we can see that the gain response and the return loss is intersecting exactly at 4.6GHz.

iii. Band Pass Filter (BPF):

 DESIGN:
The designed LPF and HPF are cascaded in series together in
order to design a Band Pass Filter and then it is modeled and
simulated using the ADS software.
 MODEL:
The Band pass filter is modeled by cascading the model of LPF
and HPF using the software ADS, and it is shown in Fig (3a),

Fig 3b Band Pass Response

The Graph in Fig (3b) verifies the Band pass filter designed to pass 4.7GHz, since we can see the Fig (3b), that the only fre- quency returning S (1, 1) is 4.7GHz between 4.6GHz to 4.8GHz.

IJSER © 2013

http://www.ijser.org

International Journal of Scientific & Engineering Research Volume 4, Issue 12, December-2013

ISSN 2229-5518

784

6 SET UP TO PERFORM THE HARMONIC ANALYSIS FOR THE DESIGNED BAND PASS FILTER:

7 DESIGN OF LNA AND STABILITY ANALYSIS OF THE CHOSEN MODEL:


The stability of a High Electron Mobility Transistor (HEMT) depends on the Stability factor (K), and it is exhibited as follows,
 If K>1, it means the Hemt is stable.
 If K<1, it means the Hemt is unstable or oscillating.

Fig 4a Harmonic Set up

The Fig (4a) shows the set up to perform a harmonic analysis of a particular frequency. Since we have designed a BPF to pass a frequency of 4.7 GHz, so we perform a harmonic analy- sis on this frequency by determining the first three harmonics. In the Fig (4) set up, we use the designed BPF, and p_n harm is
connected at the source to obtain the harmonics and the set up
is terminated by a terminal impedance of 50Ω.

Fig 4b Harmonic Response

The Fig (4b) shows the harmonics of frequency 4.7 GHz. And m1, m2 and m3 are the marker indicating the plots where m1 is considered as the fundamental harmonic followed by m2 and m3. The harmonics generated depends on the form,
N*freq.
Where,
N = order or number of harmonics.
And freq = frequency

Fig 5a Stability Analysis (A)


Therefore it is necessary to analyze the values of “K” to check the stability of the HEMT. The HEMT model shown in Fig (5a) is ATF-35176_19921201 and we do a stability check on this chosen HEMT based LNA

Table 1 Unstable K

.
From the Table 1, it is seen that the values of “K” are less than
1 i.e. K<1, Therefore the above HEMT is not stable. Since it is
not stable, now it is necessary to make the above chosen model
stable using the method of sopt, In which we use an optimum
load, such as a resistor which is connected at the source of the
HEMT as shown in Fig (5b), in order to obtain stability.
The chosen resistance should be such that it provides stability
as well as adequate gain, in this case R1 = 18 Ohm as shown in
Fig (5b). In the Table.2, it is seen that the value of K is greater
than 1 i.e. K>1. Therefore we obtained the stability of the cho- sen model.

IJSER © 2013

http://www.ijser.org

International Journal of Scientific & Engineering Research Volume 4, Issue 12, December-2013

ISSN 2229-5518

785

Fig 5b Stability Analysis (B)

8 MINIMUM NOISE FIGURE AND MAXIMUM GAIN CIRCLES FOR THE CHOSEN LNA DESIGN:

i. Maximum Gain:

The Fig (6a) shows the design of LNA, in which the display template element is chosen to display the stability and noise gain circles.

Table 2 Stable K

IJSEFigR6a Low Noise Amplifier (LNA)

The Table 3 shows the noise figure values at port 1 and port 2.
Noise is the disturbance present along with the signal and it is measured in terms of signal to noise ratio. We can see the noise
figure’s nf (1) and nf (2) for the above design is negligible and does not distort the signal.

Table 3 Noise Figure

Fig 6b Maximum Gain

The above Fig (6b) shows the Maximum gain circles in the smith chart, and the value of the maximum gain and stability factor K at different frequencies between 4.4GHz to 5.00GHz. In the above Fig (6b), there is a Radio Frequency (RF) selector scale and a marker on it., the marker is at 4.4 GHz, and this marker is moved on the scale to specific frequencies in steps of
0.05 GHz, And the corresponding values of K and MaxGain are noted down and analyzed. The Table 4 below shows the val- ues of K and Maximum Gain for different frequencies.

IJSER © 2013

http://www.ijser.org

International Journal of Scientific & Engineering Research Volume 4, Issue 12, December-2013

ISSN 2229-5518

786

Table 4 Maximum Gain Values

Table 5 Minimum Noise Figure

ii. Minimum Noise Figures:

The Fig (7) shows the smith charts with plots of gain circles
and noise circles. These plots vary as the marker on the RF
frequency selector is changed to different frequencies. There-
fore varying the frequency, we note the corresponding mini- mum noise figure. The Table 5 shows the values of minimum noise figures at different frequencies.

Fig 7 Gain and Noise Cirles

IJSER © 2013

http://www.ijser.org

International Journal of Scientific & Engineering Research Volume 4, Issue 12, December-2013

ISSN 2229-5518

9 CASCADING THE DESIGNED BPF WITH LNA AND SIMULATE THE RESPONSE OF THE CASCADED

SYSTEM:

787

IFig 8Ja CascadingSBPF and LNA

In section 5, we designed Band pass filter by cascad- ing the low pass filter and the high pass filter. This Band Pass filter is cascaded with the designed Low noise amplifier and the response is analyzed after simulation. The Fig (8a) shows the cascading of the Band pass filter and the LNA. The BPF is connected at the source and load terminals of the LNA.The graph in Fig (8b) shows the gain response and the return loss. Since the design is developed, now this design is tuned to ob- tain a maximally flat and stable response. The process of tun- ing exhibited as we proceed further.

ER

Fig 8b Cascaded Response

IJSER © 2013

http://www.ijser.org

International Journal of Scientific & Engineering Research Volume 4, Issue 12, December-2013

ISSN 2229-5518

788

10 FINE TUNE THE LNA SOURCE AND LOAD FOR OPTIMUM S (1,1) AND S (2,1) PARAMETERS:

the components L7, C7 and C8. The above results analysed closely and the best possible values of L7, C7 and C8 are se- lected which gives maximum stability with adequate gain. From the Above values, we shall consider the values of L7, C7 and C8 which provides a gain of 10.928 dB.

Fig 9a Fine Tuning

IJSER

Fine Tuning is a process in which, we connect passive compo-
nents such as L and C to the cascaded circuit and then we vary
the parameters of these components, in order to get the most

suitable response of the S (2, 1) and S (1, 1) parameters.In the Fig (9a), the components (capacitance) C7, C8 and (Inductance) L7 parameters at the termination end are varied and simulta- neously the variation in S (2, 1) and S (1, 1) response parame- ters is analyzed and the chosen values of C8, C7 and L7 will be the ones which provide stability along with the desired gain response.

Table 6 Fined Tuned Parameters

The graph in Fig (9b), shows the Gain response S (2,1) of 10.928 dB achieved by components L7, C7 and C8 having values of
1.805nH, 1.97pF and 1.94pF respectively, and also provides
better stability with adequate gain compared to the other val-
ues of L7, C7 and C8.
The Table 6 shows the best possible values of gain S (2,1) that can be achieved along with stability for the different values of

Fig 9b Tuned Response

Note that a maximum gain of 11.165 dB can be achieved, but the design may not provide the desired stability, whereas the others provide good stability but insufficient gain such as
10.771 dB and 10.200 dB. Therefore we prefer to achieve a gain of 10.928 dB with good stability.

IJSER © 2013

http://www.ijser.org

International Journal of Scientific & Engineering Research Volume 4, Issue 12, December-2013

ISSN 2229-5518

789

11 CONCLUSION:

The designed LPF blocks high frequency components and passes frequencies below 4.8GHz, while the HPF blocks low frequency components and passes frequencies above 4.6GHz, thus the cascaded LPF and HPF will pass frequencies only be- tween 4.6GHz and 4.8GHz making it a BPF. From the harmon- ic setup and analysis, it’s concluded that the fundamental harmonic with maximum amplitude is at 4.7GHz followed by the attenuated harmonics at 9.4 GHz and 14.10GHz. The cho- sen HEMT model for LNA design becomes stable with a re- sistance load 18 Ohm connected at the source. Maximum gain value is at 4.4GHz of 16.518 with a stability factor of 1.021. The cascaded response of LNA and BPF is tunned for different values of L7 (nH), C7 (pF) and C8 (pF) to obtain maximum gain with stability, therefore the selected tunned parameters or values of L7, C7 and C8 are the ones that provides a gain of
10.928 db or 11.165 db.

microwave filters” Microwave J, vol.31, pp.183-192, February [11]Sudipta Das and Dr. S.K. Chowdhury, (2009) “Design Simu- lation and Fabrication of Stepped Impedance Microstripline Low Pass Filter for S-band Application using IE3D and Matlab” Inter- national Journal of Electronics and Communication Technolo- gy, Vol. 3, pp. 98-100, January

REFERENCES

[1] Davud M.Pozar (2005) “Microwave Engineering”, 3rd Edi- tion, John wiley sons, Inc, USA.
[2] D. Swanson and G. Macchiarella (2001), “Microwave filter

design by synthesis and optimization” IEEE Microwaves Mag, vol.

8, no. 2, pp.55-69, Apr. 2007. Inc., New York.
[3] Joseph F. White.(2004), “Filter Design, In: High Frequency Techniques-An Introduction to RF and Microwave Engineering” Ch.9, pp.335-390, John Wiley & Sons, Inc., Hoboken, New Jer- sey, Inc. Canada.
[4] Jolly Rajendran, Rakesh Peter, and K. P. Soman (2012) , “Design and Optimization of Band Pass Filter for Software Defined Radio Telescope” International Journal of Information and Elec- tronics Engineering, Vol. 2, No. 4, Coimbatore, India, July
[5] Liew Hui Fang , Syed Idris Syed Hassan, Mohd Fareq Bin
Abd. Malek, “New Approach of Transforming Lumped Element Circuit of High-order Chebyshev Low Pass Filter Into Microstrip Line Form” International Journal of Engineering & Computer Science IJECS-IJENS Vol:13 No:03, University Malaysia Perlis [6] Ludwig, Reinhold and Bretchko, Pavel (2000) “RF Circuit Design- Theory and Application” Prentice-Hall, Inc. New Jersey, USA
[7] N. Durga Indira, K. Nalini, Habibulla Khan (2013) “Design of Interdigital Bandpass Filter” International Journal of Engineer- ing and Advanced Technology (IJEAT) ISSN: 2249 – 8958, Vol- ume-2, Issue-4, K L University, Guntur DT, A.P, India, April
[8] OmidBorazjani and ArmanRezaee, (2012) “Design, Simula-

tion and Construction a Low PassMicrowave Filters on the Micro Strip Transmission Line” International Journal of Computer Theory and Engineering, Vol. 4, No. 5, October.

[9] R.Levy and S.B.Cohn, (1988) “A history of Microwave filter

research, design and development” IEEE Trans.Microwave Theory

Tech., vol.MTT-32, pp.1055-1067, September
[10] R.Levy,(1988) “Design considerations for lumped- element

IJSER © 2013

http://www.ijser.org