Chapter_ one_III

•
•Microwave
Devices &
Systems
(ECEG4301)
Microwave Devices & Systems
Chapter-1
Microwave Circuit and Systems
Lecture -III
By
Yonas Desta (Lecturer)
Electronics & Communication Engineering
Stream
March 13, 2020 By: Yonas Desta (M.Sc.) 1
Aksum University
College of Engineering and Technology
Department of Electrical & Computer
Engineering

Contd…
Outline
• Design methods & difficulties
• Microwave Systems
• Microwave Applications
• Travelling waves and Transmission Line concepts

Design methods and Difficulties
Most design tools are available in many soft wares such as
 Microwave harmonica, Libra, Empire, COMPACT(Computer Optimization of
Microwave Passive and Active CircuiTs) and Super COMPACT, Handy COMPACT ,
Touchstone , CADEC, Sonnet Software, Ansoft, Speedy, etc
 We can design from analytical calculation of Maxwell’s equation applied to a
particular situation numerical solution using computers.
Difficulties Associated with the design
 Because of the high frequencies (and short wavelengths), standard circuit
theory often cannot be used directly to solve microwave network problems.
 In a sense, standard circuit theory is an approximation, or special case, of the
broader theory of electromagnetics as described by Maxwell’s equations [time-
varying currents → electromagnetic fields (or waves] ↔This is due to the
fact that, in general, the lumped circuit (L & C with low frequency)
element approximations of circuit theory may not be valid at high RF and
microwave frequencies.

 Microwave components often act as distributed elements, where the
phase of the voltage or current changes (Transmission line, Account for
propagation and time delays (phase change) significantly over the physical
extent of the device because the device dimensions are on the order of the
electrical wavelength.
 At much lower frequencies the wavelength is large enough that there is
insignificant phase variation(negligible phase change) across the
dimensions of a component (lumped circuit)
 The current and voltage along a transmission line may be considered
unchanged (which normally means the frequency is very low). The system
is called a lumped element system(Resistor, Capacitor, Inductor, Neglect
time delays (phase))
 The current and voltage along a transmission line are functions of the
distance from the source (which normally means the frequency is high),March 13, 2020 By: Yonas Desta (M.Sc.) 4

Conclusion:
Difficulties Associated with the design
I. Layout parasitic elements(electrical network) complicate the circuits basic
topology
• Parasitic inductance as main problem→Low value resistor
• Parasitic capacitance as main problem→ High value resistor
 Parasitic elements) (electronics) A circuit element or property that is present
within an electrical component, and has a negative effect on the performance
of the circuit.
 In electrical networks, a parasitic element is a circuit element that is possessed
by an electrical component but which it is not desirable for it to have for its
intended purpose. For instance, a resistor is designed to possess resistance,
but will also possess unwanted parasitic capacitance
⇒ Modeling of parasitic elements must be included in the layout

Parasitic elements of a typical electronic component package
II. Active devices are not completely reproducible
 Delivering/supplying energy to the external device.
 (V source, I sources , battery sources, generators, transistors(can amplify
power of a signal)), and OP-Amps
III. Ckt element of microwave frequency are distributed in nature.
N.B.
The distributed nature of so called lumped elements must be considered
(Passive device).
⇒ A circuit element is lumped, if its physical length(𝒍) is much smaller than
the wave length of the highest signal operation → (high frequency signal)

Example:
Consider the circuit below, having circuit 𝑙𝑒𝑛𝑔𝑡ℎ = 𝐿 = 5𝑐𝑚
Case (i): If 𝒇 = 𝟐𝟎 𝑲𝑯𝒛, 𝝀 =
𝒄
𝒇
=
𝟑𝑿𝟏𝟎 𝟖 𝒎/𝒔
𝟐𝟎𝒙𝟏𝟎 𝟑/𝒔
= 𝟏𝟓𝐱𝟏𝟎 𝟑
𝐦, hence
𝐿
λ
= 3.3𝑥10−6
≪ 1
i.e., The ckt length (𝟓𝒄𝒎) is very short as compared to 𝝀(𝟏𝟓𝐱𝟏𝟎 𝟑
𝐦), hence low
frequency approximations are applicable. ⇒[𝑉𝑜𝑢𝑡 = (
𝑅2
𝑅1 +𝑅2
) 𝑉𝑠]
Case (ii):
If 𝒇 = 𝟔 𝑮𝑯𝒛, 𝝀 =
𝒄
𝒇
=
𝟑𝑿𝟏𝟎 𝟏𝟎 𝒄𝒎/𝒔
𝟔𝒙𝟏𝟎 𝟗/𝒔
= 𝟓𝐜𝐦,
i.e., The circuit length is equal to wavelength (𝟓𝒄𝒎 = 𝟓𝒄𝒎) , so low frequency
approximations are not applicable.→(KCL, KVL) is not possible

Contd…
Case (iii):
If 𝑓 = 300 𝐺𝐻𝑧, 𝝀 =
𝒄
𝒇
=
𝟑𝑿𝟏𝟎 𝟏𝟎 𝒄𝒎/𝒔
𝟑𝟎𝟎𝒙𝟏𝟎 𝟗/𝒔
= 𝟎. 𝟏𝒄𝒎,
i.e., The circuit length is very long compared to wavelength (𝟓𝒄𝒎 > 𝟎. 𝟏𝒄𝒎) ,
so low frequency a approximations are not applicable.
Hence, for case (ii) and (iii)
I. Voltage on the line will be a function of position along the line (considered
changed due to high frequency) or (depends on functions of the distance
from the source ⇒ distributed element system.)
II. The circuit seen by the source presents a length dependent i/p
impedance, which must be carefully matched for efficient power transfer.
III. Dispersion of the signal will degrade before it reaches the o/p.

Microwave Systems
 Earlier system used FDM voice (frequency-division multiplexing (FDM) is a
technique by which the total bandwidth available in a communication medium is
divided into a series of non-overlapping frequency bands each of which is used to
carry a separate signal. ⇒This allows a single transmission medium such as a cable
or optical fiber to be shared by multiple independent signals. Another use is to carry
separate serial bits or segments of a higher rate signal in parallel)band circuits and
used conventional non-coherent(In non coherent systems, the receiver
do not need the phase information of the transmitter carrier to recover the signal.
Do not require expensive and complex carrier recovery circuit. Lower bit error rate
of detection)frequency modulation techniques.⇒(better in band width and latency: is
generally measured in milliseconds 𝑚𝑠 and is unavoidable due to the way
networks communicate with each other, https://blog.stackpath.com/latency/
 In frequency-division multiplexing (FDM), 12 𝑠𝑒𝑝𝑎𝑟𝑎𝑡𝑒 𝒗𝒐𝒊𝒄𝒆 signals, each of 4 −
𝑘𝑖𝑙𝑜ℎ𝑒𝑟𝑡𝑧 bandwidth, are modulated onto carrier waves in the 60– 108 − 𝑘𝑖𝑙𝑜ℎ𝑒𝑟𝑡𝑧
range. These modulated signals are combined to form a single complex groupMarch 13, 2020 By: Yonas Desta (M.Sc.) 9

Microwave Systems
 Modern systems carry “Pulse Code Modulated TDM voice-band circuits use more
modern digital modulated techniques like phase shift keying(coherent system)
⇒(better in flexibility, efficiency and throughput: the rate at which data is transferred
through a system)
 Coherent system: if each components is relevant and its structure function is
monotone, consists of components that, when working never harm the system and
improve the system in at least some instance. Thus, each working component is
beneficial to the system
 A system is coherent if each of its components is relevant and its structure
function is monotone. A coherent system consists of components that, when
working, never harm the system and improve the system in at least some
instance. Thus, each working component is beneficial to the system.
 Coherent system perform better than non-coherent systems, provided that the
receiver can faithfully reproduce the same chaotic basic signals sent by the
transmitter.

Microwave Systems
Microwave system depends on:
a) Frequency Characteristics:
 Microwaves are very short frequency (as compared with ultra high radio waves
)radio waves that have many of the characteristics of light waves they travel in line
of sight paths and can be reflected and focused.
 By focusing these ultra high radio waves in to a narrow beam, their energies are
connected and relatively low transmitting power is required for reliable transmission
over long distance.
b) System Capacity
 The capacity of a microwave communication system varies from less than
𝟏𝟐 voice band channels to more than 𝟐𝟐𝟎𝟎𝟎 channels.

Microwave Systems
Working of Microwave System:
• Signal is transmitted through earth’s atmosphere. ⇒LOS
• Hence these systems have obvious advantage of carrying thousands of
information channels without the need for physical facilities such as co-
axial cables or optical fibers. ⇒it use Waveguide
 Microwave communication systems are used to carry telephony,
television and data signals.
 Majority of the system carry multi-channel telephone
signals(baseband).
 Individual telephone channels, 4𝐾𝐻𝑧 wide are multiplexed together in a
multiplexer equipment to get base band.
 At microwave due to high bandwidth capacity is more.

Microwave Systems
 A microwave system normally consists of a transmitter subsystem and
receiver subsystem ,
Transmitter subsystem
Includes. Microwave oscillator(Generating frequency source such as audio
signal, reference signal, measurement), waveguides, and transmitting antenna
Receiver subsystem includes Receiving antenna, transmitting line or waveguide,
a microwave amplifier,(used for HPA at low microwave frequency) and receiver
Microwave system

Microwave Systems
Microwave source: includes
Semiconductor Devices (solid state devices)→Lower power microwave sources (High
Frequency)
Tube Devices →High power microwave sources (Low frequency)
Wave meter: a device which uses to measure microwave frequency
Calibrated attenuator: reflection free wave guide terminals in the form of dissipating
resistance , transmission of RF power in to thermal energy.(is an example of
kinetic energy, as it is due to the motion of particles, with motion being the key, results
in an object or a system having a temperature that can be measured, can be
transferred from one object or system to another in the form of heat)
RF reference used in the calibration gain /loss of other RF components /paths⇒ Used
to reduce the power
Power meter: an instrument which measures the
electrical power at microwave frequencies.
Crystal mount: Its function is to act as a demodulator, rectifying the radio signal,
converting it from alternating current to a pulsing direct current, to extract the audio signalMarch 13, 2020 By: Yonas Desta (M.Sc.) 14

Microwave Systems
Advantage of Microwave System
 The gain of an antenna is proportional to its electrical size.
 A 1% bandwidth provides more frequency range at microwave frequencies
than that of HF.
 Microwave signals travel predominantly by LOS.
 There is much less background noise at microwave frequencies than at RF.
 Microwave systems do not require a right-of-way acquisition (finding new
way) between stations.
 Fewer repeaters are necessary for amplification.
 Underground facilities are minimized.
 Increased reliability and less maintenance

Microwave Systems
Disadvantage of Microwave System
 More difficult to analyze electronic circuits (Parasitic element)
 Conventional components (resistors, inductors, and capacitors) cannot be
used at microwave frequencies(not be valid at high RF and microwave
frequencies)
 There are physical limitations in creating resonant circuits at microwave
frequencies.
 Conventional semi-conductor devices do not work properly at microwave
frequencies because of
 Inherent inductances and capacitances of the terminal leads and
 Transit time(The time required for an electron or other charge carrier to
travel between two electrodes in an electron tube or transistor)
 For amplification, vacuum tubes are used such as klystrons, magnetrons
and traveling wave tubes (TWT).
 Distance of operation is limited by line of sight (LOS).
 Microwave signals are easily reflected and/or diverted because of the very
short wavelength.
 Atmospheric conditions such as rain/fog can attenuate and absorb the
microwave signal especially at 20 GHz and up.

Microwave Communication Systems
What is micro wave communication
• A communication system that utilizes the radio frequency band spanning
2 𝑡𝑜 60 𝐺𝐻𝑧.
• As per IEEE, electromagnetic waves between 30 and 300 GHz are called
millimeter waves (MMW) instead of microwaves as their wavelengths are
about 1 to 10𝑚𝑚.
• Small capacity systems generally employ the frequencies less than 3 𝐺𝐻𝑧
• Medium and large capacity systems utilize frequencies ranging from 3 to
15 𝐺𝐻𝑧.
• Frequencies > 15 𝐺𝐻𝑧 are essentially used for short-haul transmission(b/c
its wave length is small)

Classification of microwave
 Nature
– Analog
– Digital
 Distance / Frequency
– Short Haul
• used for short distance microwave transmission usually at lower
capacity ranging from 64 𝑘𝑏𝑝𝑠 𝑢𝑝 𝑡𝑜 2𝑀𝑏𝑝𝑠
– Medium Haul
– Long Haul
• used for long distance/multi-hop microwave transmission. Used for
backbone route applications at 34 𝑀𝑏𝑝𝑠 𝑡𝑜 620 Mbps capacity
 Capacity / Bandwidth
– Light (Narrow Band)
– Medium (Narrow Band)
– Large (Wide Band)

 The main function of a microwave communication system is to ensure the
transmission of microwave signal from transmitter to receiver.
Microwave Communication Transmitter:
Block diagram of Microwave Transmitter
The transmitter consists of:
 Information source(baseband i/p)
• Baseband signal processing unit (Pre-emphasis ntk, Pre-emphasis circuit is a high pass
filter or differentiator which allows high frequencies to pass):→ Overcoming obstacles ,
making advancement , it includes one , more or all of the following
 An antialising,(minimizing distortion), ADC, Source coder, encryption unit(information to
make unreadable), error controller, multiplexer and a pulse shaper

• The antialising filter and ADC(IFFT, changes frequency to time) are only
required if the information source is analogue such as speech signal.
 Modulator :
The modulator impresses (processed) the baseband information on to the IF
carrier.→used b/c modulation, filtering and amplification are technologically
more difficult, and therefore more expensive, at the microwave RF)
 BPF(IF Amplifier )
 Stage of up conversion to the required RF(mixers + microwave oscillator) followed
by further filtering.⇒Up Converter: is a part to convert signal up for transmission.
Basically, mixer part for frequency upward conversion is called UP CONVERTER.
 When input signal combines LO signal, RF signal is generated as much as input
signal with LO signal.
 High power amplification(HPA) and Antenna

Microwave Communication Receiver :
Block diagram of Microwave Receiver
The Receiver consists of
 Antenna, Low nose amplifier (LAN, an electronic amplifier that amplifies a
very low-power signal without significantly degrading its signal-to-noise ratio,
Provides High-Quality RF & Microwave Components), Microwave filtering(BPF), Down
converter(is a part to convert RF signal down to IF or baseband. Basically, mixer
part for frequency downward is called down converter. When input signal combines
LO signal, IF or baseband signal is generated as much as Input signal to LO signal),
IF filtering and amplification, demodulator/detector, (Coherent or incoherent), baseband
processing unit (De-emphasis, de-emphasis circuit is a low pass filter or integrator which
allows only low frequencies to pass)

 Coherent signal/systems: need carrier phase in/on at the receiver and they used
matched filter to detect & decide what data was sent→same phase & freq →add up
constructively
 Non-coherent: don't need carrier phase in/on & use method like square law to
recover the data → different phase & freq →
𝐶𝑎𝑛𝑐𝑒𝑙 𝑒𝑎𝑐ℎ 𝑜𝑡ℎ𝑒𝑟 𝑜𝑟 𝑓𝑎𝑑𝑖𝑛𝑔 𝑜𝑐𝑐𝑢𝑟𝑠 (random)
 The signal processing unit will incorporate demultiplexing, error
detection/correction, deciphering (convert an encrypted or coded text or message
in to plain text) source decoding, DAC(FFT,(changes time to frequency,
appropriate), and audio/video amplification and filtering(appropriate).
 If detection is coherent, phase locked loops (PLLs) is necessary
Example: Automatic gain control(AGC/AVC ,closed loop feedback regulating circuit amplifier uses
to maintain suitable signal amplitude at o/p), may be also present in the receiver
N.B:
The various sub systems of the above two figures (the devices comprising) them whetherMarch 13, 2020 By: Yonas Desta (M.Sc.) 22

Types Of Microwave Stations
Terminals
 are points in the system where the baseband signals either originate or
terminate
Repeaters
 are points in the system where the baseband signals maybe reconfigured
or simply repeated or amplified.
Passive Microwave repeaters
• A device that re-radiates microwave energy without additional electronic
power.
– back to back
– billboard type
Active Microwave repeater
• A receiver and a transmitter placed back to back or in tandem with the
system.
• It receives the signal, amplifies and reshapes it, then retransmits the signalMarch 13, 2020 By: Yonas Desta (M.Sc.) 23

 Depending upon the stage at which they amplify the signal, the repeaters
can be classified into following three types
 IF repeaters
 Baseband Repeaters
 RF repeaters
.
Repeater stations
• Points in a system where baseband signals may be reconfigured.
• Points in a system where RF/IF carriers are simply "repeated" or
amplified.

Microwave IF Repeater
 Called heterodyne repeaters⇒works at the level of intermediate frequency (IF)
 Received RF carrier is down-converted to an IF frequency only,
amplified, reshaped, up-converted to an RF frequency, and then
retransmitted.
.

IF section
• Generates a frequency-modulated IF carrier.(found in Heterodyne
receiver)
RF section.
• The IF signal enters the transmitter through a protection switch.
• The IF and compression amplifiers help keep the IF signal power constant
and at approximately the required input level to the transmit modulator
(transmod).
Transmod
• A balanced modulator that, when used in conjunction with a microwave
generator, power amplifier, and Band pass filter, up-converts the IF carrier
to an RF carrier and amplifies the RF to the desired output power.
Microwave generator
• Provides the RF carrier input to the up-converter.
• It is called a microwave generator rather than an oscillator because it is
difficult to construct a stable circuit that will oscillate in the gigahertz range.

Microwave Baseband repeaters:
• The received RF carrier is down-converted to an IF frequency, amplified, filtered,
and then further demodulated to baseband.
• The baseband signal, which is typically frequency-division-multiplexed voice-band
channels, is further modulated to a master group, super group, group, or even
channel level.⇒ amplified and converted back to IF and finally to RF signals ⇒
amplified signal is Retransmitted
.

Contnd
Microwave RF repeater
• The received microwave signal is not down-converted to IF or baseband
levels.
• The signal is simply mixed (heterodyned) with a local oscillator frequency in
a nonlinear mixer.⇒Converted to out put radio
frequency⇒amplified⇒Retransmitted

Why are microwave frequencies of interest?
 Perhaps the best way of answering this is to consider a primary application
of microwaves -- wireless communication
 The first application of microwaves that often comes to mind is wireless
transmission of information. As we go higher in frequency, fractional
bandwidth increases.
Example:
 let’s assume that we wish to transmit a number of 4 𝑘𝐻𝑧 wide voice signals
through a wireless link. Further let’s assume that we have two wireless
systems to chose from, one operating at 500 𝑀𝐻𝑧 and the second at 4 𝐺𝐻𝑧,
each with a 10 % 𝑏𝑎𝑛𝑑𝑤𝑖𝑑𝑡ℎ around its center frequency.
 In theory, the 500 𝑀𝐻𝑧 system could carry:
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐ℎ𝑎𝑛𝑛𝑒𝑙𝑠 =
𝒐𝒑𝒆𝒓𝒂𝒕𝒊𝒏𝒈 𝒇𝒓𝒆𝒒𝒖𝒆𝒏𝒄𝒚 ∗ 𝒑𝒆𝒓𝒄𝒆𝒏𝒕 𝑩𝑾
𝑩𝑾 𝒑𝒆𝒓 𝒄𝒉𝒂𝒏𝒏𝒆𝒍
=
𝟎. 𝟓𝑮𝑯𝒛 ∗ 𝟎. 𝟏
𝟒𝑲𝑯𝒛
=
𝟏𝟐, 𝟓𝟎𝟎 𝑪𝒉𝒂𝒏𝒏𝒆𝒍𝒔
For 4GHz
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐ℎ𝑎𝑛𝑛𝑒𝑙𝑠 =
𝒐𝒑𝒆𝒓𝒂𝒕𝒊𝒏𝒈 𝒇𝒓𝒆𝒒𝒖𝒆𝒏𝒄𝒚 ∗ 𝒑𝒆𝒓𝒄𝒆𝒏𝒕 𝑩𝑾
𝑩𝑾 𝒑𝒆𝒓 𝒄𝒉𝒂𝒏𝒏𝒆𝒍
=
𝟒𝑮𝑯𝒛 ∗ 𝟎. 𝟏
𝟒𝑲𝑯𝒛
= 𝟏𝟎𝟎, 𝟎𝟎𝟎

Why are microwave frequencies of interest?
• From the above, we see that as the system’s operating frequency
increases, ideally its capacity increases.
• Another advantage in going to higher frequency is antenna size.
• For a given aperture size, the gain of an antenna increases with frequency.
• To make portable wireless communications possible, we must operate at a
frequency at which the required antenna size is reasonable
• Another advantage of increased antenna gain with frequency is the
potential for higher-resolution imaging systems.
• While it may seem that one can simply increase the operating frequency of
a microwave link to increase capacity, issues such as equipment cost,
spectrum licensing, and atmospheric attenuation must be considered.

Contnd
Conclusion:
Advantages of using higher frequency
 Larger instantaneous bandwidth for much information
 Higher resolution for radar imaging and sensing
 Less interference by near by application
 Higher speed for digital communication, signal processing and
transmission
 Less crowded spectrum
 Difficulty in jamming (military application)
Disadvantages of using high frequency
 More expensive component
 Higher atmospheric loss
 Reliance in GaAs technology rather than Si technology
 Higher component losses, lower output power from active devices

Applications of Microwaves
 Microwaves have a wide range of applications in modern technology
 Most common applications are with in the range 𝟏𝑮𝑯𝒛 𝒕𝒐 𝟒𝟎 𝑮𝑯𝒛
1. Broadcasting and Telecommunication Transmission
 Due to their short wavelength, highly directional antennas are smaller
 Mobile phone network, like GSM, use the low microwave/UHF frequencies
around 1.8 𝑎𝑛𝑑 1.9𝐺𝐻𝑧
 Intercontinental Telephone and TV, space communication (Earth – to –
space and space – to – Earth), telemetry communication link for railways
etc.
 Microwave used in television signal to transmit a signal from a remote
location to a television station from a specially equipped van
 Used for communication, from one point to another via satellite
 Satellite TV either operates in the C band for the traditional large dish fixed

2. Remote Sensing
Radars (Radio detection and ranging) : uses a transmitter to illuminate an object
and a receiver to detect its position & velocity, detect aircraft, track / guide
supersonic missiles, observe and track weather patterns, air traffic control
(ATC), burglar alarms, garage door openers, police speed detectors , radio
astronomy (sub class of astronomy that studies celestial(sky /space)objects at radio
frequencies etc.
3.Home, Commercial and industrial applications
 Microwave energy is a means for rapid heating and excellent processing efficiency
Microwave cooking, Oven
 Drying machines – textile, food and paper industry for drying clothes, potato chips,
printed matters etc.
 Food process industry – Precooling /cooking, pasteurization/sterility, hat frozen/
refrigerated precooled meats, roasting of food grains / beans.March 13, 2020 By: Yonas Desta (M.Sc.) 33

 Biomedical Applications (diagnostic/therapeutic ) – diathermy for
localized superficial heating, deep electromagnetic heating for treatment of
cancer, hyperthermia ( local, regional or whole body for cancer therapy).
 Rubber industry / plastics / chemical / forest product industries
 Mining / public works, breaking rocks, tunnel boring, drying /
breaking up concrete, breaking up coal seams, curing of cement.
 Drying inks /drying textiles, drying / sterilizing grains, drying /
sterilizing pharmaceuticals, leather, tobacco, power transmission.
4. Microwave semiconductor
 Light generated charge carriers in a microwave semiconductor make it
possible to create a whole new world of microwave devices, fast jitter free
switches, phase shifters, HF generators, etc.

Contnd
Travelling waves and Transmission Line
 A travelling wave may be defined by
𝑬 𝒛, 𝒕 = 𝑬 𝒐 𝒄𝒐𝒔(𝜔𝒕 − 𝒌𝒛)
 Due to the variation of 𝑬 with both time 𝒕 and space variable 𝒛, we may
plot 𝑬 as a function of 𝒕 by keeping 𝒛 constant and vice versa.
Where
𝑬 𝒐 is amplitude, 𝜔 is angular frequency (𝜔 = 2𝜋𝑓), λ wave length in meter, 𝒕 is
time in sec, 𝒛 is 𝒛 -axis, displacement on 𝒛 -axis(space on 𝒛 ), 𝑘 is constant
(propagation constant or wave number.), 𝒗 𝒑 is velocity of the wave or phase
velocityMarch 13, 2020 By: Yonas Desta (M.Sc.) 35

Contnd
 If 𝑓 is low , 𝑇 is high, 𝜔 is low, so Phase variation is negligible⇒(Lumped
parameters, R,L,C are used ) and (Ohms low, KCL, KVL used)
 If 𝑓 is high , 𝜔 is high , hence phase variation is high ⇒ Distributed
Parameters ⇒( R/unit length , C/unit length, L/unit length) are used ⇒
microwave components
 Propagation constant=wave no. =
𝟐𝝅
𝝀
= 𝒌
 Velocity of the propagation wave = phase velocity= 𝒗 𝒑 =
𝜔
𝒌
=
𝟐𝝅𝒇
(
𝟐𝝅
𝝀
)
= 𝒇𝝀 = 𝒇𝒖𝑻 =
Path travelled by wave Phase change
λ 2𝜋
𝜆/2 𝜋
λ/4 𝜋/2
L ∆𝟇=(2𝜋/λ)*L=(k)*L, 2𝜋/λ is Propagation constant

Contnd
 Free space Intrinsic impedance =𝞰 𝒐 =
𝝁 𝒐
𝜺 𝒐
=
𝟒𝝅∗𝟒∗𝟏𝟎−𝟕 𝑯/𝒎
𝟖.𝟖𝟓𝟒∗𝟏𝒐−𝟏𝟐 𝑭/𝒎
= 𝟑𝟕𝟕Ω
 𝒄 = 𝒗𝒆𝒍𝒐𝒄𝒊𝒕𝒚 𝒐𝒇 𝒍𝒊𝒈𝒉𝒕 =
𝟏
𝝁 𝒐 𝜺 𝒐
𝒊𝒏 𝒗𝒂𝒄𝒖𝒎
 Intrinsic impedance of the medium = 𝞰 =
𝝁
𝜺
or
 Wave impedance =
𝑬
𝑯
= intrinsic impedance of medium

Contnd
Transmission Line:
 A transmission line is the structure that forms all or part of a path from
one place to another for directing the transmission of energy, such as
electrical power transmission and microwaves.
 Conventional two-conductor transmission lines are commonly used for
transmitting microwave energy.
 If a line(Txn line) is properly matched to its characteristic impedance (𝑧) at
each terminal, its efficiency can reach a maximum
 Transmission lines are commonly met on printed-circuit boards.
A microwave integrated circuit

Contnd
Fundamental mode
(A) Transverse Electric Mode (TEM): 𝑬 𝒛𝒔 = 𝟎 𝑯 𝒛𝒔 ≠ 𝟎
 The electric field, 𝑬 is transverse to the direction of propagation of wave
and the magnetic field, 𝑯 has components transverse and in the direction
of the wave.
• Exists in waveguide modes.
(B)Transverse Magnetic Mode (TMM): 𝑬 𝒛𝒔 ≠ 𝟎, 𝑯 𝒛𝒔 = 𝟎
 The magnetic field, 𝑯 is transverse to the direction of propagation of wave
and the electric field, 𝑬 has components transverse and in the direction of
the wave.March 13, 2020 By: Yonas Desta (M.Sc.) 39

Contnd
(C) Transverse Electromagnetic (TEM)
• The electric field, 𝑬 and the magnetic field, 𝑯 are oriented (direct towards)
transverse to the direction of propagation of wave.
• Exists in plane waves and transmission lines (2 conductors).
• No cut-off frequency.
(D) quasi-TEM mode :
 If the wavelength larger than the cut-off wavelength or
 non-uniform dielectric constant

Contnd
• Important transmission lines classified according to the number of
conductors they contain, and according to the general class of
electromagnetic wave or propagation ‘mode’ that they support.
Metal and dielectric can be represented by:
 has no conductors at all – it is just a rod of dielectric, but it can still trap and
guide an electromagnetic wave. This is extremely important practically in
the form of an optical fiber. It can also be used at ‘high’ radio frequencies,
i.e. in microwave or millimetre-wave bands, when it would be referred to as
a ‘dielectric waveguide’.
 There is no very obvious way we could apply concepts like voltage and

Contnd
A transmission line with only one conductor – a conventional rectangular
waveguide.
 Finline or ‘𝐸 − 𝑝𝑙𝑎𝑛𝑒’ structure. Here there is a central section with a
printed conductor pattern, lending itself to the production of a microwave
integrated circuit. This is considered an attractive structure for work at
millimetric frequencies.
 The enclosed structure of the coaxial cable, largely prevents this and
makes it suitable as a general-purpose radio frequency line.

Contnd
• The parallel wire line, may be seen in old-fashioned open telephone lines,
overhead power lines (electric power txn & distribution to transmit elec
energy along large distance), and sometimes as lines connecting high-
power, low and medium frequency radio transmitters to their antennas.
• In the figure we have a structure suitable for microwave integrated circuits,
where the ‘live’ conductor may be given a complex pattern by printed circuit
methods. However, it is mechanically awkward to include other electronic
components in it and to assemble.
• Suitability for ‘printed’ production methods and microwave integrated
circuits (MICs) while avoiding the mechanical drawbacks of stripline .
Microstrip, is by far the most widely used.

Contnd
Suitability for ‘printed’ production methods and microwave integrated circuits
(MICs) while avoiding the mechanical drawbacks of stripline . Is gaining in
popularity.
Suitability for ‘printed’ production methods and microwave integrated circuits (MICs)
while avoiding the mechanical drawbacks of stripline. Is used only for a few special
purposes.
Suitability for ‘printed’ production methods and microwave integrated circuits
(MICs) while avoiding the mechanical drawbacks of stripline. Especially useful

Contnd
⇒ The line in figure is a variant of the parallel wire line where the mechanical support is
built in. It is mainly used for relatively short runs linking radio equipment and antennas
at VHF frequencies.
⇒Note that, in the microstrip form of line, it is easy to break the ‘live’ conductor in order
to insert a component in series with it, but if we want to connect a component in shunt
between the live conductor and ground, we have to cut or drill the dielectric. Coplanar
waveguide and coplanar strips do not suffer from this problem.
⇒ The slot line, in the figure, can be, and is, used for complex MICs but it remains
rather specialized and is not particularly easy to use.
⇒ Slot line, in the figure looks as though it should be classed as a quasi-TEM line, and it would
support DC excitation. It turns out, however, to be a special case that is not adequately described
by quasi-TEM mode theory. (This is because the conductors are nominally infinite in extent. ⇒(the
magnetic field lines in the slot line mode cannot form complete loops in a transverse
plane, because they would have to penetrate the conductors to do so.)

Contnd
⇒The following important points can be made about the classification of
transmission lines:
1. All the two-conductor lines (except slotline), and only these, are classified
as transverse electromagnetic (TEM), or quasi-TEM mode, lines.
2. The lines in this class can be recognized as those that could carry DC
excitation(producing a electrical magnetic field, to provide a continuous (DC)
current to the field) and which conform to the idea of a complete circuit with
‘go’ and ‘return’ conductors(form complete loops )
3. In the two-conductor family, TEM lines can be recognized as those in which
the dielectric constant is uniform over the cross-section of the line, while
those with a non-uniform dielectric are quasi-TEM lines.
(In a few special cases, magnetic materials may also be involved, and here
the permeability also has to be uniform for a true TEM line.)
A further important point is that:
4. All the TEM and quasi-TEM lines can treated, to a good first approximation
at least, by distributed circuit theory

Contnd
THANK YOU!

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