MOSFET BASED ABSORBER AT GHZ

FREQUENCY
Thesis Submitted
in the Partial Fulfilment of the Requirements for the
Degree of

MASTER OF TECHNOLOGY
in
Embedded System and VLSI
By

SHIVAM PATHAK
(2022PEV3213)

Under the Supervision of

DR. SHAILESH MISHRA

To the
Department of Electronics and Communications Engineering

NETAJI SUBHAS UNIVERSITY OF TECHNOLOGY

(Formerly Netaji Subhas Institute of Technology)
Azad Hind Fauj Marg, Sector-3, Dwarka, New Delhi-110078

JUNE, 2024

i
 CERTIFICATE

This is to certify that Shivam Pathak (Roll No. 2022PEV3213) has carried out his
research work on MOSFET BASED ABSORBER AT GHZ FREQUENCY in
partial fulfilment of the Master of Technology degree from Netaji Subhas University
of Technology, Dwarka, New Delhi. I verify that the student's work was authentic
and original and it was performed under my close observation and direction.
The thesis material has not been utilized for the conferral of any other degree, either
for the candidate or any other individual, at this university or any other institution.

Dr. Shailesh Mishra

Assistant Professor

Department of Electronics and Communications Engineering

Netaji Subhas University of Technology, Delhi-110078

ii
 COPYRIGHT TRANSFER CERTIFICATE

Title of the Thesis: MOSFET Based Absorber at GHz Frequency

Name of the Student: SHIVAM PATHAK

Copyright Transfer

The undersigned hereby assigns to the Netaji Subhas University of

Technology, (NSUT) New Delhi, all rights under copyright that may
exist in and for the above thesis submitted for the award of the
“MASTER OF TECHNOLOGY”:

Date: Signature of the Student

Place: (SHIVAM PATHAK)
(2022PEV3213)

Note: However, the author may reproduce or authorize others to

reproduce material extracted verbatim from the thesis or derivative of
the thesis for author’s personal use provided that the source and the
University Copyright notice are indicated.

iii
 ACKNOWLEDGEMENT

I extend my heartfelt thanks to my mentor, Dr. Shailesh Mishra, for his exceptional
mentorship, steadfast support, and inspiring encouragement during the course of my
research project. His profound knowledge, enduring patience, and consistent
dedication have played a pivotal role in the development of this thesis and have
greatly enriched my scholarly experience.I am also grateful to Ansys Elecronic
Desktop for providing the platform for creating and simulating the various
components and thus obtaining the results.
I am indebted to Netaji Subhas University of Technology, Delhi for providing the
necessary resources and conducive environment for conducting this research.

SHIVAM PATHAK
2022PEV3213
Master of Technology
Department of Electronics and Communication Engineering
Netaji Subhas University of Technology, Delhi

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 ABSTRACT

To minimize losses caused by RF signal reflection from the Reciever in 5G

Base_Station, an NMOS conncected to the rectifier is suggested as a solution. A

circulator has been constructed using the ANSYS HFSS software and simulation is

conducted to confirm the working of the various elements. Further,the reflected

signal through the circulator is pass on to the n-channel Mosfet via rectifier and the

pulsating DC signal is obtained.The simulation for the same is performed in the

ANSYS CIRCUIT software.This obatained DC signal is filtered using LC filter to

remove the pulses in the signal.. The research investigates the regularity of the

parameters and used for the absorber at Ghz frequency due to the reflected signal

from the ports of circulators in 5G base stations.It has been observed that mosfet

absorbs power of 9.007mw

v
 TABLE OF CONTENTS

CERTIFICATE

ACKNOWLEDGEMENT

ABSTRACT

List of Figures

1. CHAPTER1: Introduction…………………………………………(1-2)
1.1 Problem Statement
1.2 Structure of Thesis

2. CHAPTER 2: Literature Review…………………………………..(3-5)

3. CHAPTER 3: Methodology……………………………………….(6-11)

4. CHAPTER 4: Rectification Process………………………………(12-14)

5. CHAPTER 5: Rectification of Reflected Signal………………….(15-16)

6. CHAPTER 6: Filteration of DC Signal Literature………………..(17-19)

7. CHAPTER 7: Conclusion and Future Scope………………………..(20).

References

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 LIST OF FIGURES

Figure 1: Magic T……………………………………………..………………..(6)

Figure 2: Input Applied At E_Arm…………………………...………………..(7)

Figure 3: Input Applied At H_Arm……………………………………………..(7)

Figure 4: S Parameter of Magic T……………………………………………....(8)

Figure 5: 180 Degree Unidirectional Phase Shifter……………………………..(9)

Figure 6: Microstrip Line……………………………………………………....(10)

Figure 7: Circulator……………………………..………………………………(11)

Figure 8: Ports of Circulator…………………….……………………………...(14)

Figure 9: Full Wave Rectifier ………………………………………………….(16)

Figure 10: Output Waveform of Reflected Signal……………………………..(16)

Figure 11: Full Wave Rectifier with LC Filter and MOSFET…………………..(18)

Figure 12: Power Absorbed at the Drain Termial of the MOSFET………………(19)

vii
 CHAPTER 1

INTRODUCTION

5G technology is the latest advancement in the telecom sector, which aims to

provide ultrafast and reliable connections to a huge number of devices, enabling

large-scale IoT applications and more[1-3]. 5G works alongside 4G networks at

first, but will eventually become independent in later stages. Another key benefit of

5G is its low latency, which means how quickly it responds. Compared to 3G

networks, which typically had a latency of 100 milliseconds, and 4G networks,

which had around 30 ms, 5G can achieve as little as 1 ms[2-4]. This allows for faster

and more efficient connectivity. Besides these main applications, 5G enables a

communication system that is very reliable and has low latency, which means it can

control devices, robots, and vehicles in real time and safely[5-7].

The main challenge for the 5th Generation technology is the signal loss caused by the

reflection from the circulators in the receiving branch of the base station. The

mismatch between the source impedance of the Transmitter branch and the load

impedance of the Reciever branch results in reflection loss[8-10]. This reduces the

efficiency of the base station. A resolution to this problem is to create a circuit that

matches the impedance of the Reciever and the Transmitter branch of the station.

However, the solution introduces another difficulty in designing the circuit that

matches the impedance at high-frequency. The aim of the study is to employ the

NMOS to attenuate the signal reflection caused by impedance mismatch amid base

station’s transmitter and receiver.

1
PROBLEM STATEMENT
The aim is to solve the problem of reflection loss due to impedance mismatching

between the transmitter.

The solution proposes a circuit design that uses a MOSFET for the absorption of the

reflected Radio Frequency Signal from receiver branch and convert it into DC power

that can be used for other purposes. This circuit can improve the efficiency and

performance of the base station by reducing the losses and interference caused by

the reflection.

2
STRUCTURE OF THESIS

Thesis is standardized as follows. Sec-1 discusses the building up of the components

of the circulator and their interconnection. Sec-2 discusses the recctificaton process

ot the reflected signal from the circulator. Sec-3 introduce the absorption and

filtration process with the help of MOSFET and LC filter. Lastly, Sec-4 summarizes

the work suggest the subsequent directions.

3
 CHAPTER 2

LITERATURE SURVEY

The paper[1] by Omoru and Srivastava proposes a novel circuit design that uses a

MOSFET to absorb the reflected radio frequency (RF) signal from the RX branch of

a 5G massive MIMO base station. The authors claim that this circuit can improve

the efficiency and performance of the base station by reducing the losses caused by

impedance mismatching between the transmitter and receiver branches. The paper

provides mathematical analysis, circuit model, and simulation results to support their

idea.This paper is related to the field of 5G ,that promises lower latency, higher

capacity,faster speed and more reliability than 4G. One of the key features of 5G is

the use of massive MIMO, which is a technique that employs a large number of

antennas at the base station to serve multiple users simultaneously. However,

massive MIMO also poses some challenges, such as increased complexity,

interference, and power consumption. Therefore, it is important to find solutions that

can optimize the performance and efficiency of massive MIMO base stations.

4
The paper[2] by Omoru and Srivastava addresses one of these challenges, which is

the reflection loss due to impedance mismatching. Impedance mismatching occurs

when the load impedance of the receiver branch does not match the source

impedance of the transmitter branch, resulting in some of the transmitted power

being reflected back to the source. This reflection loss reduces the signal quality and

wastes energy. The authors suggest that using a MOSFET as an absorber can solve

this problem by converting the reflected RF signal into direct current (DC) power

that can be used for other purposes.

The paper[3] by Omoru and Srivastava contributes to the existing literature on 5G

technology and massive MIMO by proposing a novel and practical circuit design

that can improve the efficiency and performance of the base station. The paper also

provides theoretical and simulation analysis to validate their idea. However, the

paper has some limitations that could be addressed in future research. For example,

the paper does not consider the effects of noise, interference, or nonlinearity on the

circuit performance. The paper also does not provide experimental results or real-

world applications of their circuit. Moreover, the paper does not compare their

circuit with other existing solutions or discuss its advantages and disadvantages in

detail.

Therefore, a literature review on the research paper "MOSFET based absorber

reflected signal in 5G massive MIMO base Station" could conclude that the paper is

an original and innovative work that offers a potential solution for improving the

performance and efficiency of 5G base stations. However, the paper also has some

5
limitations that need further investigation and verification. The paper could inspire

more research on this topic and gave direction for more efficient and reliable 5G

communication systems.

6
 CHAPTER 3

METHODOLOGY

The proposed absorber consist of the Circulator, Rectifier and the MOSFET.The

construction of the circulator itself requires two Magic- T,a microstrip line and a 180

degree phase shifter.

CONSTRUCTION OF THE MAGIC T

The Magic T consist of E_plane and H-plane, and the coaxial arms are called the

sum and the difference ports. The magic T has the property that the power entering

any port is equally divided between the two adjacent ports, but not the opposite port.

For example, if power enters the E-plane, it will split between the sum and

difference ports, but not the H-plane.

MAGIC T

7
INPUT APPLIED AT E_ARM

INPUT APPLIED AT H_ARM

8
S PARAMETER TABLE OF MAGIC T

9
(B) CONSTRUCTION OF THE UNI-DIRECTIONAL 180_DEGREE_PHASE_

SHIFTER

A 180-degree phase shifter in a 4 port microwave circulator is a device that

introduces a non-reciprocal phase shift of 180 degrees between two ports of the

circulator.It is unidirectional shifter.To achieve this a PIN diode is used in one of the

arms of the phase shifter.

180 DEGREE UNI DIRECTIONAL PHASE SHIFTER

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(C) CONSTRUCTION OF THE MICROSTRIP LINE

A microstrip_line is a type of transmission_line that consists of a thin metal strip on

a dielectric substrate, separated from a ground plane by another dielectric layer. A

microstrip line is used in a circulator using a magic T by connecting it to one of the

coaxial arms of the magic T.

MICROSTRIP LINE

S PARAMETER PLOT OF MICROSTRIP LINE

11
(D) INTERCONNECTION OF THE ELEMENTS

Microwave Elements are interconnected to form a circulator.

CIRCULATOR

12
SCENARIO– 1 (Port 1 input, port 2 output) : The input signal
goes into port-4 of magic tee-2, which is the same as port-1 of the
circulator. It splits into two signals that have equal amplitude and
phase. These signals come out of port-1 and port-2 of magic tee-2 and
get to port-1 and port-2 of magic tee-1. They have the same phase
when they enter port-1 and port-2 of magic tee-1. The signal that
comes from port-1 of magic tee-2 does not change its phase when it
goes through a 180 phase shifter before getting to port-1 of magic tee-
1, because the phase shifter has no effect in that direction. The signals
that come from port-1 and port-2 of magic tee-1 are in phase, so they
combine and leave through port-4 (H-arm) of magic tee-1, which is
also port-2 of the circulator.

SCENARIO– 2 (Port 2 input, port 3 output) : The input signal

goes into port-4 of magic tee-1, which is the same as port-2 of the
circulator. It splits into two signals that have equal amplitude and
phase. These signals come out of port-1 and port-2 of magic tee-1 and
reach magic tee-2. The signal that comes from port-2 of magic tee-1
has the same phase and amplitude when it goes into port-2 of magic
tee-2, while the signal that comes from port-1 of magic tee-1 changes
its phase when it goes through a phase shifter and goes into port-1 of
magic tee-2. The signals that are at port-1 and port-2 of magic tee-2
have equal amplitude but opposite phase. Because the inputs are out
of phase, the signal leaves through the E-arm of magic tee-2, which is
also port-3 of the circulator.

SCENARIO– 3 (Port 3 input, port 4 output) : The input signal

goes into port-3 (E-arm) of magic tee-2, where it splits into two
signals that have equal amplitude and opposite phase. These signals
come out of port-1 and port-2 of magic tee-2 and reach port-1 and
port-2 of magic tee-1 with the same amplitude and phase as they had
at magic tee-2. The signal that comes from port-1 of magic tee-2 does
not change its phase when it goes through a 180 phase shifter,
because the phase shifter has no effect in that direction. The signals
that go into port-1 and port-2 of magic tee-1 combine and leave
through port-3 (E-arm) of magic tee-1, which is the same as port-4 of
the circulator.

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SCENARIO– 4 (Port 4 input, port1 output): The input signal goes
into port-3 (E-arm) of magic tee-1, which is the same as port-4 of the
circulator. It splits into two signals that have equal amplitude and
opposite phase. They are out of phase because they come from the E-
arm. The signals come out of port-1 and port-2 of magic tee-1 and
reach port-1 and port-2 of magic tee-2. The signal that comes from
port-2 of magic tee-1 has the same phase when it goes into port-2 of
magic tee-2, while the signal that comes from port-1 of magic tee-1
changes its phase when it goes through the 180 degree phase shifter.
The signals that are at port-1 and port-2 of magic tee-2 have equal
amplitude and phase. The signals are in phase, so they combine and
leave through the H-arm.

14
 CHAPTER 4

RECTIFICATION PROCESS

A circulator has four ports in which the signal flow in a clockwise manner. For

example, a signal that enters from port-1 will leave from port-2, and so on[11-14]. A

modulated RF signal obtain from the transmitter side of station enters the circulator

through port 1.

The signal then exits from port 2, where a band pass filter is attached. The filter

restricts the Radio Frequency Signal to the desired frequency range for transmission.

The filtered signal is then sent to a transceiver, which radiates the RF signal into the

air. A nearby base station receives the signal and sends it to its circulator through

port 2. The signal comes out from P3, where the Receiver branch is connected.

If there is any impedance mismatch between the Transmitter and Receiver end,

some of the signal will reflect back. The reflected waveform goes to P4 of the

circulator, where a rectifier is connected.

The simulation models did not have realistic ports, so a sine voltage source was used

to simulate the TX branch voltage of the incident RF Power. A voltage divider

circuit was used to generate the potential of the reflected power from the RXr

branch and apply it to the rectifier input terminal.

15
A voltage divider was used to create the potential equivalent to the reflected RF

power from the RX branch and feed it to the input terminal .

Vo = Vin * R2 / (R1 + R2)

where Vin is the terminal voltage of the incident Radio Frequency power from the

Transmitter branch and Vo is the reflected output voltage of Radio Frequency

power from the RX branch. An online software was used to calculate the values of

Resistor 1 and Resistor 2 that would obtain a potential drop equal to the voltage of

the reflected RF Power from the Receiver . Assuming a reflection loss of 19 dBm

from Receiving branch of the station, the values of R2 and R1 were found to be

1700 ohm and 108.95 ohm. Using these values in equation with Vin = 44.662 V, the

resulting output voltage was 2.69V.

16
PORTS OF CIRCULATOR

17
 CHAPTER 5

RECTIFICATION OF REFLECTED SIGNAL

The aim of 5G base_station is to optimize the capability of different components

used for its construction. Therefore, a FW Rectifier was preferred instead of half

wave rectifier because it has double the efficiency as compared to HW rectifier.

However, the drawback of using 2 more diodes is that each diode creates a potential

drop, which lowers the voltage at the rectifier output terminal[15-17]. Taking all

points into account, a source voltage that represents the reflected power from the

port IV of the circulator connected to the rectifier’s input terminal and a

combination of 2k ohm resistor and a combination of 4 non linear microwave diodes

performs the process of rectification considering the off and on status of the diodes

and the voltages on each node of the rectifier as shown in Fig.

During the first half cycle, D2 and D3 are in ON state, while for the other half

cycle, D1 and D4 are in ON state and the wave at the rectifier’s output is pulsating

in nature. In the configuration of the rectifier,diodes will keep changing contact to

the resistor through the different paths such that the current will flow

unidirectionally through the resistor.

18
FULL WAVE RECTIFIER FOR THE REFLECTED SIGNAL

OUTPUT WAVEFORM OF THE REFLECTED SIGNAL

19
 CHAPTER 6

FILTERATION OF PULSATING DC SIGNAL

A consistent and pure DC signal is essential for the proper operation of a MOSFET

device, but the signal received from the rectifier’s output is pulsating in nature[18-

19]. To obtain a DC signal, an inductor and a capacitor are connected in series and

in parallel with a load resistor[20-22]. The condensor smooths out the voltage

fluctuations at rectifier’s output, while the inductor smooths out the current

fluctuations. Without the capacitor, the DC signal would be pulsating, but with the

inductor and capacitor, the fluctuations are reduced. The capacitor charges and

discharges according to the voltage absorbtion and release of the energy to the

circuit. This prevents the potential from dropping or rising too sharply, and makes

the voltage more stable and smooth. The voltage fluctuations after filtering are

known as ripple voltage. The ripple voltage can be decreased by boosting the value

of the condensor or the load resistor value. Moreover, choosing the right capacitance

is a critical issue in the circuit, as it can affect the effectiveness of reducing the

ripple voltage.

The capacitor and the inductor both smooth out the fluctuations, but in different

ways. The inductor resists the change in current by taking in energy and expanding

its magnetic field when the current rises. When the current falls, the inductor gives

20
back the energy to the circuit by shrinking its magnetic field, thus maintaining the

current level.

FULL WAVE RECTIFIER WITH LC FILTER AND MOSFET

21
POWER ABSORBED AT THE DRAIN TERMINAL OF THE MOSFET

22
 CHAPTER 7

CONCLUSION AND FUTURE WORK

This model has demonstrated both theoretically and empirically that reflection from

the Receiver branch of the station can cause destructive interference, which can be

prevented by using MOSFET based absorber for the RF signal. Moreover, the

model’s reliability was verified by meeting the MOSFET absorption condition for

all reflection levels from the circulator’s port-4. Additionally, the model used a

MOSFET because it can function as a passive component like a resistor, capacitor,

or inductor. A possible future direction for this research is to design a DC-DC

booster for the source terminal of MOSFET, which can adjust the primary DC

current to the level needed to power high speed data converters such as DACs,

ADCs, and other 5G base station devices.

23
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