EE223 Microwave Circuits Fall2014 Lecture1
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Transcript of EE223 Microwave Circuits Fall2014 Lecture1
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EE-223 Microwave Circuits
(Fall 2014)
Lecture 1
Dr. Atif Shamim
EE Program
King Abdullah University of Science andTechnology (KAUST)
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Course Description
Brief Summary
The course objective is to understand and predict how an electric circuit behaves when its
physical size is the same order of magnitude as the wavelength of excitation. The course
helps understand how electromagnetic waves in the microwave regime can be guided through
well-defined modes and how coupling, matching and filtering operations are key to efficient
microwave systems. Theory and design of key microwave components (passives and active)will be studied. Theory and design of key microwave components (passives and active) will be
studied. Probable topics are given below.
1. Transmission lines Theory and Design (Microstrip line, Coplanar waveguide)
2. Smith Chart and Impedance Matching (Quarter-wave Transformers)
3. Waveguides (Rectangular Waveguide, TE and TM modes)4. Microwave Networks (S-parameters)
5. Microwave System Level Fundamentals (Noise Figure, Dynamic Range)
6. Microwave Amplifier Design (Active Components, Low Noise and Power Amplifier)
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Course Details
Texts:
D. M. Pozar, Microwave Engineering, 3rdEdition
Course Slides/Additional Handouts
Reference Books: -Steer, Microwave and RF Design (A Systems Approach)
Wentworth, Fundamentals of Electromagnetics with Engineering Applications
Grading:
Assignments (3) 5% each and total of 15% (Mostly numerical and design
questions)
Midterm Exam 20% (short answers and numerical questions) (Date: To Be
Announced)
Design Project 30% (Simulations)or Individual Research Paper (in class
presentation)
Final Exam 35% (short answers and numerical questions)
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Wireless is all around us!
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Ever thought whats inside. . .?
World population ~ 7 Billion
Mobile subscriptions ~ 6 Billion
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Whats inside. . .?
A PCB with ICs, discretes..
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Building materials of cell-phones
Package
Discretecomponents
IC or chip
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RF TRX Package Discrete components
IC
Package
Bondwires, bondpads, ESD
Devices
Active: MOS & Bipolar Passive: R, C, L, diode,
transformer,
Transmission lines
Substrate
Building Blocks of cell-phones
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Microwave Engineering
What is microwaves?
The term microwaves refers
to alternating current
signals with frequencies
between 300MHz and
300GHz, with a
corresponding electrical
wavelength between 1m
and 1mm, respectively.
Signals with wavelengths on
the order of millimeters are
called millimeter waves.
Figure shows the location of
microwave frequency band
in the electromagnetic
spectrum.
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Why Microwaves Treated as a Special
Subject?
Because of the high frequencies and short wavelengths,standard circuit theory, generally, cannot be used
The lumped circuit element approximation of circuittheory are not valid at microwave frequencies
Microwave components are often distributed elements,where the phase of a voltage, or current changessignificantly over the physical extent of the device,because the device dimensions are on the order ofmicrowave wavelengths
At much lower frequencies, the wavelength is largeenough that there is insignificant phase variation acrossthe dimension of a component
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Advantages
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Typical Transceiver Block Diagram
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On the Tx, the back-end digital signal is used to modulate the carrier in the
IF stage.
A mixer converts the modulated signal and IF carrier up to the desired RF
frequency.A frequency synthesizer provides the other mixer input.
Since the RF carrier and associated modulated data may have to be
transmitted over large distances through lossy media (e.g., air, cable, and
fiber), a power amplifier (PA) must be used to increase the signal power.
Typically, the power level is increased from the milliwatt range to a level in
the range of hundreds of milliwatts to watts, depending on the particular
application.
A lowpass filter after the PA removes any harmonics produced by the PA to
prevent them from also being transmitted.
Transmitter
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Transmit side (Tx) and receive side (Rx) are connected to the antenna through duplexer.
The input pre-selection filter removes the signals not in the band of interest.
The LNA amplifies the input signal without adding much noise.
The image filter removes out-of-band signals and noise before the mixer.
The mixer translates the input RF signal down to the intermediate frequency, sincefiltering, as well as circuit design, becomes much easier at lower frequencies.
The other input to the mixer is the local oscillator (LO) signal provided by a voltage-
controlled oscillator inside a frequency synthesizer. The desired output of the mixer will be
the difference between the LO frequency and the RF frequency.
The IF stage then provides channel filtering at this one frequency to remove the
unwanted channels. The IF stage provides further amplification and automatic gain control(AGC) to bring the signal to a specific amplitude level before the signal is passed on to the
back end of the receiver.
It will ultimately be converted into bits (most modern communications systems use
digital modulation schemes) that could represent, for example, voice, video, or data
through the use of an analog-to-digital converter.
Receiver
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Impedance Concept
Electrical impedance, or simply impedance, describes a measure of opposition to
alternating current (AC). Electrical impedance extends the concept of resistance to AC
circuits, describing not only the relative amplitudes of the voltage and current, but also
the relative phases. When the circuit is driven with direct current (DC), there is no
distinction between impedance and resistance; the latter can be thought of as impedance
with zero phase angle.The symbol for impedance is usually |Z|
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Conversion from Rectangular to Polar
Z = R2 + X2
= arctan X
R
R = Z cos
X= Z sin
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Characteristic Impedance?
The characteristic impedance of a uniform transmission line,
usually written Z0, is the ratio of the amplitudes of a single pair of
voltage and current waves propagating along the line in the absence
of reflections. The SI unit of characteristic impedance is the ohm
(). The characteristic impedance of a lossless transmission line is
purely real, that is, there is no imaginary component (Z0= | Z0| +
j0). Characteristic impedance appears like a resistance in this case,
such that power generated by a source on one end of an infinitely
long lossless transmission line is transmitted through the line but isnot dissipated in the line itself. A transmission line of finite length
(lossless or lossy) that is terminated at one end with a resistor equal
to the characteristic impedance (ZL= Z0) appears to the source like
an infinitely long transmission line.
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Why 50 Impedance?
The standardization of fifty ohm impedance goes back to developing coax cables
for kilowatt radio transmitters in the 1930s. A good explanation for the choice of
fifty ohms is given in Microwave Tubes, by A. S. Gilmour, Jr. The quick answer is
that 50 ohms is a great compromise between power handling and low loss, for
air-dielectric coax.
The 50-Ohm compromise
The arithmetic mean between 30 ohms (best power handling) and 77 ohms
(lowest loss) is 53.5, the geometric mean is 48 ohms. Thus the choice of 50 ohmsis a compromise between power handling capability and signal loss per unit
length, for air dielectric.