Masters Thesis Projects:
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"Active Bias, Power Detector, and Voltage Controlled Attenuator MMICs", 2003.
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"Antenna Data Acquisition System and Anechoic Chamber Characterization
", 2003.
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"A 24-42 GHz Monolithic Distributed Amplifier", 2001.
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"Output Power and Efficiency of Distributed Amplifiers", 2001.
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"A Distributed MESFET Source Injected Mixer", 2001.
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"A GaAs FET Distributed VCO", 2001.
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"An Active Antenna for Full-Duplex Operation", 1999.
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"Tapered Coplanar-strip Antenna and Log Periodic Balun", 1998.
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"A 2.4 GHz Phase Shifting Network", 1997.
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"A Class-B Microwave Distributed Push-Pull Amplifier", 1997.
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"A 2.5 GHz Programmable Frequency Divider", 1993.
Active Bias, Power Detector, and Voltage Controlled Attenuator MMICs
by : Scarlet Halabi
Advisor : Dr. Prasad N.Shastry
Summer 2003
ABSTRACT
The design and analysis of an Active Bias Circuit (ABC),
a Power Detector Circuit (PDC), and a Voltage Controlled Attenuator (VCA) implemented
using GaAs MMIC technology is presented in this thesis. These circuits are to be
implemented with a previously designed 24 to 42 GHz MMIC Band-Pass Cascode Cell
Distributed Amplifier. The active device used in these circuits is a 0.1 mm pHEMT.
The ABC encountered the challenge of having a current minor circuit used for
depletion mode FETs. The PDC encountered the challenge of designing the matching
network for the wide frequency band. Finally, the VCA encountered the challenge of
obtaining linear attenuation versus control voltage while achieving the specified
attenuation dynamic range over the frequency band. The novelty of the VCA circuit
is that a band-pass filter structure was used to achieve the bandwidth and eliminate
the effect of parasitic capacitances. All three circuits were designed as stand-alone
circuits and fabricated. Only the ABC and PDC have been tested, and the VCA is being
fabricated and will be tested later. These circuits along with the Distributed Amplifier
are to be used in European Local Multipoint Distribution Systems for driving power amplifiers.
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Antenna Data Acquisition System and Anechoic Chamber Characterization
by : Badria Elnour
Advisor : Dr. Prasad N.Shastry
Summer 2003
ABSTRACT
The thesis presents the design of an automated system
for the measurements of antenna radiation characteristics in an anechoic chamber.
The antenna data acquisition system enables one to plot the radiation patterns
of an antenna and determine its important parameters. The thesis further
addresses the issues of characterization of the anechoic chamber and presents
the results of characterization.
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A 24-42 GHz Monolithic Distributed Amplifier
Project Assistant : Shawn Parker
Project Director : Dr. Prasad Shastry
June 2001
This project was supported by a research grant from Fujitsu Compound Semiconductor, Inc.
ABSTRACT
The design and analysis of 24 to 42 GHz MMIC Band-Pass Cascode Cell Distributed
Amplifiers as presented in this thesis. The amplifiers make use of a novel mixed topology consisting of
a band-pass gate line and a low-pass drain line. The mixed topology provides the benefits of a band-pass topology
without requiring additional elements in the drain line. The amplifier makes use of a pHEMT cascode gain cell
capacitively coupled to the gate line. Two amplifiers, utilizing 200 micrometer and 300 micrometer pHEMTs, have been
designed, fabricated and tested. The amplifiers are suited for application in European Local Multipoint Distribution
Systems for driving power amplifiers.
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Output Power and Efficiency of Distributed Amplifiers
by : Amir S. Ibrahim
Advisor : Dr. Prasad N.Shastry
May 2001
ABSTRACT
The development of broadband systems created an increasing demand for use of wideband amplifiers.
Distributed amplifiers are critical components in many such systems because of their wideband performance.
However, the low efficiency and low output power of distributed amplifiers made them unsuitable for high power applications.
In this thesis, investigation of techniques to increase the efficiency and out power
of distributed amplifiers is presented. A 20 dBm tapered drain line distributed amplifier is designed. The amplifier
has a bandwidth of 4.5 GHz and power-added-efficiency of 24%. The performance of the amplifier is found to be
comparable to a reactively matched power amplifier using the same number of transistors.
The amplifier was fabricated on a 30-mil thick board with dielectric constant of 3.1 for the
gate line and a 25-mil thick board with dielectric constant of 10 for the drain line. The use of two different
board materials was necessary to avoid inconsistencies in microstrip widths. Measured results of the fabricated
amplifier have been found to be comparable to simulation results.
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A Distributed MESFET Source Injected Mixer
by : Edward W. Cullerton
Advisor : Dr. Prasad N.Shastry
May 2001
ABSTRACT
Recent developments in broadband communications systems have led to the development
of broadband components. A mixer is a critical component in any communication system, and with
the development of broadband communication systems, a broadband mixer is needed.
In this thesis, the design and performance of a broadband active mixer is presented.
The mixer is called "Distributed MESFER Source Injected Mixer". Two GaAs MESFETs perform the mixing operation in
the mixer. The mixing operation is achieved by injecting the LO signal into the source of each MESFET, and
injecting the RF signal into the gate of each MESFET. A distributed topology is used to inject the RF signal
into the gate of each MESFET, and Chebyshev impedance transformers are used to inject the LO signal into
the source of each MESFET. The IF signal is extracted from the drain of each MESFET using a lumped
element matching network.
The mixer was fabricated on a 20 mil dielectric substrate using photolithography.
Packaged MESFETs and lumped components were soldered to the microstrip circuit board to create a hybrid
circuit. The design of the mixer and measured results are described in the following chapters.
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A GaAs FET Distributed VCO
by : Sunil Modur
Advisor : Dr. Prasad N.Shastry
July 2001
ABSTRACT
A novel design of a voltage controlled oscillator (VCO) based on the distributed
amplifier topology for the ISM (Industrial, Scientific, Medical) band is presented. The VCO
includes a distributed amplifier and a power divider built on Rogers RO3003 substrate and
a varactor tuned passive bandpass filter with an amplifier gain block built on TMM10i ceramic substrate,
in the feedback path. The amplifier and the varactor tuned bandpass filter in the feedback path
provide and the appropriate magnitude and phase of loop gain necessary for oscillations.
The distributed oscillator design and measured results are discussed. The novel idea can be implemented
in the MMIC form and has great potential in the growing wireless communication market.
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Active Antenna for Full Duplex Operation
by : Thirendra Rayamajhi
Advisor : Dr. Prasad N.Shastry
May 1999
ABSTRACT
Active antennas have been of growing interest in
recent years. The use of active devices in passive antenna elements have
helped to reduce cost and size, and improve the overall performance of
the antenna. In practically all communication systems, full duplex operation
has been achieved by using different frequencies for transmitting and receiving.
Active antennas with full duplex functionality at the same frequency are
relatively new. Bidirectional amplifiers such as distributed amplifiers
though well known for their duplexing capability, have not been investigated
for such applications.
This thesis work involved investigations into the
possibility of integrating a distributed amplifier with an antenna for
full duplex operation. In this presentation, the active antenna concept
will be introduced. The possible system configurations for integrating
a distributed amplifier and passive antenna, and design and performance
issues involved therein will be discussed.
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Tapered Coplanar Strip Antenna And Log-Periodic Balun
by : Mahmoud Basraoui
Advisor : Dr. Prasad N.Shastry
May 1998
Publications : 1) M.Bsaraoui and Prasad N.Shastry, "
Wideband Planar Log AntennaLog-Periodic Balun",
International Journal of RF and Microwave Computer-Aided Engineering,
Vol. 11, Issue 6, November 2001, pp. 343-353.
2) M.Bsaraoui and Prasad N.Shastry, "
Tapered Coplanar-Strip Antenna",
proceedings of 1998 IEEE-APS
Conference on Antennas and Propagation for Wireless Communications, Waltham, MA, November 1998,
pp121-124.
3) M.Basraoui and Prasad N.Shastry, "Wideband, Planar,
Log-Periodic Balun", IEEE MTT-S International
Microwave Symposium Digest, Baltimore, June 1998, pp 785-788.
ABSTRACT
Advancement in miniaturizing integrated electronic
circuits has led to a new generation of antennas. In microwave applications,
planar antennas provide printed radiating structures that are compatible
with integrated circuits. These antennas offer the advantages of structural
strength, reduced size, ease of fabrication, and simplicity of layout.
These antenna structures embody a radiating element and a feed circuit
for proper excitation.
In this thesis, a complete design and performance
characteristic of a new antenna structure is presented. This antenna is
called "Tapered Coplanar Strip Antenna (TCSA)" and it is based on Chebyshev
impedance transformation theory. This is first time that a compact, wideband,
tapered coplanar-strip antenna has been developed.
This thesis also presents the design and performance
characteristics of a new planar balun structure that operates over a wide
frequency band. The design is based on the log-periodic antenna theory.
The design guidelines, as well as simulated and measured results are presented.
It is shown that the new balun has greater than one octave bandwidth. The
log-periodic balun will find applications in wireless communication circuits
such as mixers, amplifiers and antennas.
The design and measured performance characteristics
of TCSA as well as the Log-periodic balun will be described in the chapters
of the report.
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M.Basraoui's work at MTT-98 Student Research Exhibition
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Design of a 2.4 GHz Digital Phase Shifting Network
by : John S. Novak, III
Advisor : Dr. Prasad N.Shastry
May 1997
ABSTRACT
A 2.4 GHz digital phase shifting network has been
designed, simulated, and fabricated for use in phase shifting antenna arrays.
The design technique incorporates the hyperbolic nature of the geometry
of the Smith chart to create arbitrary phase shifting networks from arbitrary
PIN diodes. The fabrication is accomplished in microstrip technology, and
uses surface mount component technology where available.
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A Class-B Push-Pull Distributed Microwave Amplifier
by : G.Brubaker
Advisor : Dr. Prasad N.Shastry
May 1997
ABSTRACT
A Class-B Push-Pull Distributed Amplifier for use in the
2-4 GHz band using NEC NE76084 GaAs MESFETs has been designed, simulated,
fabricated and tested. A differential distributed amplifier (also with the NEC
NE76084 GaAs MESFET), used as an active balun at the input, has been designed
and simulated. Physical restrictions prevented fabrication of this design.
Passive microstrip baluns were used to phase split the input signal and
recombine the balanced output. The Curtice Cubic model was used to model the
active devices during the design process. Guidelines to assist in the
application of the Curtice Cubic model are presented.
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A 2.5 GHz Programmable Frequency Divider
by : Srinivas Reddy Ponnala
Advisor : Dr. Prasad N.Shastry
May 1993
ABSTRACT
A 2.5 GHz Programmable frequency divider has been
designed and simulated, for use in microwave frequency synthesis applications.
The frequency divider uses a 1µm gate length E/D MESFETs, and Schottky
diodes. The basic building block of the frequency divider is Direct - Coupled
FET Logic (DCFL) gate. Graphical design approach is used for the design
of frequency divider logic circuits. Using this approach test circuits
have been designed, laid out and simulated. Transmission line interconnect
designs are implemented in layout and its effects are simulated. A new
analytical design approach for the design of DCFL inverter is presented.
The frequency divider is capable of dividing an input frequency from DC
to 2.5 GHz with any divisor between 2 to 127. The delays obtained from
the test circuit simulations are used in the simulation of a 7-bit programmable
frequency divider.
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