University of Tripoli
Electrical & Electronic Engineering Department
EE521
Properties of Microwave Devices
Name : Riyad A. Alhejni
ID : 022120968
Group : 3
Introduction :
Microwaves are generally defined as electromagnetic waves with a frequency between
300 MHz to 300 GHz. Typically, the wavelengths of these electromagnetic waves are
defined as well, with the range being from 1m to 1mm.
Microwaves obey the laws of optics, such as Snell’s law and the law of reflection, and
thus can be transferred, assimilated, or reflected, which is extremely important when
considering how microwaves operate.
Modern Usage:
Microwaves are ubiquitous in modern technology, with one of its most popular
industries being television. As one may realize upon noting that television programs are
available across the globe, the wide frequency/wave length of microwaves allows for
the transcontinental transference of television content. Using a variety of intricate
networks (i.e. transmitter and receiver) local stations receive television signals and
instantly transfigure the signal to a more appropriate, lower signal so personal television
sets can broadcast the desired content.
Microwaves are also popular amongst national and local security channels. For
example, missile guidance infrastructures utilize microwaves in order to control the
parameters and speed of their missiles.
Loss Mechanisms
There are a multitude of mechanisms through which microwave energy can combine or
be lost within a system, with the four most popular being
Dielectric
Conduction
Hysteresis
Resonance
Understanding which loss mechanism occurred in which sample can be extremely
difficult; yet, there still are a distinguishable difference between these mechanisms
when it comes to elements such as microstructure, frequency, or temperature.
Devices :
Circuits
Circuits, which can be considered as a series of electronic components, are one of the
most important elements of microwave infrastructures. In general terms, circuits are
made to configure electromagnetic occurrences to send different signals to the
appropriate location.
The origins of microwave circuits derived slightly after World War II when clunky,
massive pipes were used. Engineers soon found these metallic pipes to be too heavy and
expensive, so they created the lighter planar circuits, which remain particularly popular
to this day.
Yet with novel techniques and technological advancements, engineers are seeking to
further diminish the cost, size, and density of microwave circuits. For example,
engineers have designed a system in which multiple layers of circuits are stacked on top
of each other for maximum efficiency.
Antenna
Microwave antennas are components of a microwave system that send and receive data
between various sites. So, in continuing the television example mentioned above,
television antennas allow the personal television to receive data from local, national, or
international broadcasters, and vice versa.
In order to properly receive signals, antennas should be place at a location where it will
not be blocked. Thus, microwave antennas of high importance are typically place on top
of large hills, towers, or mountains so they can have supreme access to long distance
signals.
Resonators
When in reference to microwaves, resonators are typically called radio frequency
cavities (or microwave cavities). A radio frequency cavity traps electromagnetic
phenomena within the microwave vector of the wave spectrum. Thus, without radio
frequency cavities, it would be extremely difficult to send or receive microwave signals
on a consistent basis.
Objectives :
Measurement of the insertion loss of few terminations.
Measurement of the properties of a three port circulator.
Measurement of the properties of a microstrip directional coupler.
Measurement of the insertion loss of a low pass filter.
Equipment and Tools :
Microstrip trainer box (Feedback).
DC power Supply .
Voltage controlled oscillator (VCO).
Spectrum analyzer (SA).
Assignment (1) :Measurements of the properties of a three port circulator
Measurement of the Transmission power:
1- We make connection of the circuit shown in Fig 1 for the basic test system by
connecting the VCO , the circulator and Spectrum Analyzer . Terminate port 3 of the
circulator with 50Ω coaxial termination , we measured P1 = -16.4dBm .
2- Connect the port 2 , which is the output port of the circulator to the spectrum analyzer
(SA) which is to be set at frequency f1, we used f = 2.6Ghz , the attenuator of SA set
at 20 dB . we found the output power of the circulator, P2 =-16.4dBm
Insertion loss = P1-P2 = 0dB
Measurement of the insertion loss of few terminations:
1- We interchanged SA and the 50Ω termination and measured the power at port 3 at the
same frequency . this gives us the insertion loss of the 50Ω , P3 = -36.4dBm.
Insertion loss = P2-P3 = 20dB.
We repeated this measurement for the other 50Ω terminations . we find the same result.
2- Replace the 50 Ω coaxial termination with the coaxial short circuit and measure the
power P3 at port 3.
P3 short = -16.4dBm
Insertion loss = P2 - P3 short = 0dB.
By replacing the short circuit with the coaxial open circuit and measure the power at
port-3 we can find the insertion loss of the open circuit terminal:
P3 open = -16.4dBm
Insertion loss = P2 - P3 open = 0dB.
Measurement of the power P1 (at port 1 when the circulator is reversed) :
We measured the power at port 2 . after that we reversed the circulator so that port 2 is
connected to the VCO and port 1 is connected to SA . port 3 is connected to the 50 Ω
termination . P1 = -55.2dBm .
Insertion Loss = P2-P1 = 38.8 dB.
This value expected. Because port 1 work as isolation.
Assignment (2) :Measurements of the properties of a directional coupler
(coupling factor , directivity , isolation , insertion loss):
1- We repeated measurement of power at port 2 of the circulator and still the same value.
2- Connect the input port of the directional coupler to the output port of the circulator
(port 2) , with ports 2 and 4 terminated with 50Ω terminations , we measured the
power at port 3 (the coupled port ) at the same frequency , f = 2.6Ghz .
P3
C3,1 = -10 log 10 P1 dB
Coupling factor = P3 - P1 = 27.20-16.4 = 10.8 dB
3- With ports 2 and 3 terminated in matched loads , we measured the power at port 4(the
isolated port) .
I4,1 = -10 log 10¿ ) dB
Isolation = 56-16.4 = 39.6 dB.
4- With ports 3 and 4 terminated in matched loads , we measured the power at port 2 (the
through port ) .
PT
Insertion loss(dB) = 10 log 10 PR
Insertion loss = 16.4-19.2 = 2.8 dB.
The directivity of Directional coupler : P3c –P4c = 28.8dB.
Assignment (3) :Measurements of the insertion loss of low pass filter (LPF)
1- Before connecting the LPF , we measured the power P2 at port2 of the circulator.
P2 = -16.4dBm , this is the input power to the filter , the Pout of filter = -19.2dBm.
2- Connect the filter and measure power Pout at the output port of the LPF .
P2
Insertion loss = -10 log 10 P 1 dB.
Insertion loss = P1F – Pout = 2.8dB.
: Conclusion
a circulator is a three-port microwave device that can be lossless and matched at all
ports.
the circulator directs the power with low loss into port-(n+1) but not in the reverse,
if power were to be reflected at port-(n+1) it will be directed to port(n+2)
The three-port circulator can be transferred to isolator by terminating one of the
ports using matched load but at certain frequency band.
A Directional coupler is a device that samples a small amount of Microwave power
for measurement purposes. The power measurements include incident power,
reflected power, VSWR values, etc.
The directivity, the coupling factor, the isolation factor and insertion loss are the
main parameters of the directional coupler and they were calculated.
