ee223 microwave circuits fall2014 lecture1

7/21/2019 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.

ee223 microwave circuits fall2014 lecture1

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