Introdaction;
In this blog we study how to measurment frequency of microwave the student must knoe how to measre the frequency.




Microwave frequency can be measured by either electronic or mechanical
techniques.


Frequency counters or high frequency heterodyne systems can be used. Here the unknown
frequency is compared with harmonics of a known lower frequency by use of a low
frequency generator, a harmonic generator and a mixer. Accuracy of the
measurement is limited by the accuracy and stability of the reference
source.


Mechanical methods require a tunable resonator such as an absorption
wavemeter, which has a known relation between a physical
dimension and frequency.


In a laboratory setting, Lecher lines can be used to directly measure the
wavelength on a transmission line made of parallel wires, the frequency can then
be calculated. A similar technique is to use a slotted waveguide or slotted coaxial line to directly
measure the wavelength. These devices consist of a probe introduced into the
line through a longitudinal slot, so that the probe is free to travel up and
down the line. Slotted lines are primarily intended for measurement of the voltage standing wave ratio on the line. However,
provided a standing wave is present, they may also be used
to measure the distance between the nodes, which is equal to half the wavelength.
Precision of this method is limited by the determination of the nodal
locations.

*what did you learn from this blog

Introduction:
In this blog we foucs in history of microwave the student must know how to discavre this tecnology.




The existence of radio waves was predicted by James Clerk Maxwell in 1864 from his equations.
In 1888, Heinrich Hertz was the first to demonstrate the
existence of radio waves by building a spark
gap radio transmitter that produced 450 MHz microwaves, in the
UHF region. The equipment he used was primitive, including a horse trough, a
wrought iron point spark, and Leyden jars. He also built the first parabolic antenna, using a zinc gutter sheet. In
1894 Indian radio pioneer Jagdish
Chandra Bose publicly demonstrated radio control of a bell using
millimeter wavelengths, and conducted research into the propagation of
microwaves.[16]


Perhaps the first, documented, formal use of the term microwave
occurred in 1931:



"When trials with wavelengths as low as 18 cm were made known, there was
undisguised surprise that the problem of the micro-wave had been solved so
soon." Telegraph & Telephone Journal XVII. 179/1
In 1943, the Hungarian engineer Zoltán Bay sent ultra-short radio waves to the
moon, which, reflected from there, worked as a radar, and could be used to
measure distance, as well as to study the moon.[17]


Perhaps the first use of the word microwave in an astronomical context
occurred in 1946 in an article "Microwave Radiation from the Sun and Moon" by Robert Dicke and Robert Beringer. This same article also made a
showing in the New York Times issued in 1951.


In the history of electromagnetic theory, significant
work specifically in the area of microwaves and their applications was carried
out by researchers .

*what did you understand from this blog

 Overview 
The Smith chart, invented by Phillip H. Smith (1905–1987) is a graphical aid or nomogram designed for electrical and electronics engineers specializing in radio frequency (RF) engineering to assist in solving problems with transmission lines and matching circuits. Use of the Smith chart utility has grown steadily over the years and it is still widely used today, not only as a problem solving aid, but as a graphical demonstrator of how many RF parameters behave at one or more frequencies, an alternative to using tabular information. The Smith chart can be used to simultaneously display multiple parameters including impedances, admittances, reflection coefficients,  scattering parameters, noise figure circles, constant gain contours and regions for unconditional stability, including mechanical vibrations analysis.] The Smith chart is most frequently used at or within the unity radius region. However, the remainder is still mathematically relevant, being used, for example, in oscillator design and stability analysis  

Mathematical basis
Actual and normalised impedance and admittanceA transmission line with a characteristic impedance of  may be universally considered to have acharacteristic admittance of  where

Any impedance,  expressed in ohms, may be normalised by dividing it by the characteristic impedance, so the normalised impedance using the lower case z, suffix T is given by

Similarly, for normalised admittance

The SI unit of impedance is the ohm with the symbol of the upper case Greek letter Omega (Ω) and the SI unit for admittance is the siemens with the symbol of an upper case letter S. Normalised impedance and normalised admittance are dimensionless. Actual impedances and admittances must be normalised before using them on a Smith chart. Once the result is obtained it may be de-normalised to obtain the actual result.

[edit]The normalised impedance Smith chartUsing transmission line theory, if a transmission line is terminated in an impedance () which differs from its characteristic impedance (), a standing wave will be formed on the line comprising the resultant of both the forward () and the reflected () waves. Using complex exponentialnotation:

 andwhere

 is the temporal part of the wave is the spatial part of the wave and where is the angular frequency in radians per second (rad/s) is the frequency in hertz (Hz) is the time in seconds (s) and  are constants is the distance measured along the transmission line from the generator in metres (m)Also

 is the propagation constant which has units 1/mwhere

 is the attenuation constant in nepers per metre (Np/m) is the phase constant in radians per metre (rad/m)The Smith chart is used with one frequency at a time so the temporal part of the phase () is fixed. All terms are actually multiplied by this to obtain the instantaneous phase, but it is conventional and understood to omit it. Therefore

 and The variation of complex reflection coefficient with position along the line
The complex voltage reflection coefficient  is defined as the ratio of the reflected wave to the incident (or forward) wave. Therefore

where C is also a constant.

For a uniform transmission line (in which  is constant), the complex reflection coefficient of a standing wave varies according to the position on the line. If the line is lossy ( is non-zero) this is represented on the Smith chart by a spiral path. In most Smith chart problems however, losses can be assumed negligible () and the task of solving them is greatly simplified. For the loss free case therefore, the expression for complex reflection coefficient becomes

The phase constant  may also be written as

where  is the wavelength within the transmission line at the test frequency.

Therefore

This equation shows that, for a standing wave, the complex reflection coefficient and impedance repeats every half wavelength along the transmission line. The complex reflection coefficient is generally simply referred to as reflection coefficient. The outer circumferential scale of the Smith chart represents the distance from the generator to the load scaled in wavelengths and is therefore scaled from zero to 0.50.

[edit]The variation of normalised impedance with position along the lineIf  and  are the voltage across and the current entering the termination at the end of the transmission line respectively, then

 and.By dividing these equations and substituting for both the voltage reflection coefficient

and the normalised impedance of the termination represented by the lower case z, subscript T

gives the result:

.Alternatively, in terms of the reflection coefficient

These are the equations which are used to construct the Z Smith chart. Mathematically speaking  and  are related via a Möbius transformation.

Both  and  are expressed in complex numbers without any units. They both change with frequency so for any particular measurement, the frequency at which it was performed must be stated together with the characteristic impedance.

 may be expressed in magnitude and angle on a polar diagram. Any actual reflection coefficient must have a magnitude of less than or equal to unity so, at the test frequency, this may be expressed by a point inside a circle of unity radius. The Smith chart is actually constructed on such a polar diagram. The Smith chart scaling is designed in such a way that reflection coefficient can be converted to normalised impedance or vice versa. Using the Smith chart, the normalised impedance may be obtained with appreciable accuracy by plotting the point representing the reflection coefficient treating the Smith chart as a polar diagram and then reading its value directly using the characteristic Smith chart scaling. This technique is a graphical alternative to substituting the values in the equations.

By substituting the expression for how reflection coefficient changes along an unmatched loss free transmission line

for the loss free case, into the equation for normalised impedance in terms of reflection coefficient

.and using Euler's identity

yields the impedance version transmission line equation for the loss free case:[8]

where  is the impedance 'seen' at the input of a loss free transmission line of length l, terminated with an impedance 

Versions of the transmission line equation may be similarly derived for the admittance loss free case and for the impedance and admittance lossy cases.

The Smith chart graphical equivalent of using the transmission line equation is to normalise , to plot the resulting point on a Z Smith chart and to draw a circle through that point centred at the Smith chart centre. The path along the arc of the circle represents how the impedance changes whilst moving along the transmission line. In this case the circumferential (wavelength) scaling must be used, remembering that this is the wavelength within the transmission line and may differ from the free space wavelength.

[edit]Regions of the Z Smith chartIf a polar diagram is mapped on to a cartesian coordinate system it is conventional to measure angles relative to the positive x-axis using a counter-clockwise direction for positive angles. The magnitude of a complex number is the length of a straight line drawn from the origin to the point representing it. The Smith chart uses the same convention, noting that, in the normalised impedance plane, the positive x-axis extends from the center of the Smith chart at  to the point . The region above the x-axis represents inductive impedances (positive imaginary parts) and the region below the x-axis represents capacitive impedances (negative imaginary parts).

If the termination is perfectly matched, the reflection coefficient will be zero, represented effectively by a circle of zero radius or in fact a point at the centre of the Smith chart. If the termination was a perfect open circuit or short circuit the magnitude of the reflection coefficient would be unity, all power would be reflected and the point would lie at some point on the unity circumference circle.

[edit]Circles of constant normalised resistance and constant normalised reactanceThe normalised impedance Smith chart is composed of two families of circles: circles of constant normalised resistance and circles of constant normalised reactance. In the complex reflection coefficient plane the Smith chart occupies a circle of unity radius centred at the origin. In cartesian coordinates therefore the circle would pass through the points (1,0) and (-1,0) on the x-axis and the points (0,1) and (0,-1) on the y-axis.

Since both  and  are complex numbers, in general they may be written as:

with a, b, c and d real numbers.

Substituting these into the equation relating normalised impedance and complex reflection coefficient:

gives the following result:

.This is the equation which describes how the complex reflection coefficient changes with the normalised impedance and may be used to construct both families of circles.[9]

[edit]The Y Smith chartThe Y Smith chart is constructed in a similar way to the Z Smith chart case but by expressing values of voltage reflection coefficient in terms of normalised admittance instead of normalised impedance. The normalised admittance yT is the reciprocal of the normalised impedance zT, so

Therefore:

and

The Y Smith chart appears like the normalised impedance type but with the graphic scaling rotated through 180°, the numeric scaling remaining unchanged.

The region above the x-axis represents capacitive admittances and the region below the x-axis represents inductive admittances. Capacitive admittances have positive imaginary parts and inductive admittances have negative imaginary parts.

Again, if the termination is perfectly matched the reflection coefficient will be zero, represented by a 'circle' of zero radius or in fact a point at the centre of the Smith chart. If the termination was a perfect open or short circuit the magnitude of the voltage reflection coefficient would be unity, all power would be reflected and the point would lie at some point on the unity circumference circle of the Smith chart.

introduction : 
 
GAE microwave generators are available in two basic configurations, Laboratory and OEM, each offering local and/or remote control capability.

• Integrated microwave generators are turn-key systems that contain the magnetron, power supply and (if required) interconnect cables.
  
  
• Remote control modules are also available for some Lab and OEM generators.
  
  
• Magnetron and power supply modules are available separately. Contact GAE for more information.
  
  

Introduction 
 Microwave radio signals are electromagnetic waves with high frequencies (between 500 MHz to 300 GHz) and short wavelengths. According to "Electronic Communications System: Fundamentals Through Advanced, 5/e," approximately 35 percent of all terrestrial communication is maintained by microwave radio relay systems. There are various types of microwave radio communication systems, operating anywhere between 15 miles to 4,000 miles, including feeder service or intrastate microwave systems and long-haul microwave systems

Read more: Microwave Radio Communications Advantages & Disadvantages | eHow.com http://www.ehow.com/list_6137210_microwave-radio-communications-advantages-disadvantages.html#ixzz2EAXaOyZN 

Advantage: Able to Transmit Large Quantities of Data

• According to "Microwave Communication," microwave radio systems have the capacity to broadcast great quantities of information because of their higher frequencies. They use repeaters (a device that receives the transmitting signal through one antenna, converts it into an electrical signal and retransmits it) to transmit large volumes of data over great distances. Microwave radio communication systems propagate signals through the earth's atmosphere. These signals are sent between transmitters and receivers that lie on top of towers. This allows microwave radio systems to transmit thousands of data channels between two points without relying on a physical transmitting medium (optical fibers or metallic cables).
  
  

Advantage: Relatively Low Costs

• Microwave communication systems have relatively low construction costs compared with other forms of data transmission, such as wire-line technologies. A microwave communication system does not require physical cables or expensive attenuation equipment (devices that maintain signal strength during transmission). Mountains, hills and rooftops provide inexpensive and accessible bases for microwave transmission towers.
  
  
  
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Disadvantage: Line of Sight Technology

• Microwave radio systems are a line of sight technology, meaning the signals will not pass through objects (e.g., mountains, buildings and airplanes). This drawback limits microwave communication systems to line of sight operating distances. Signals flow between one fixed point to another, provided no solid obstacle disrupts the flow.
  
  
  

Disadvantage: Subject to Electromagnetic and Other Interference

• According to "Rural America at the Crossroads: Networking for the Future," microwave radio signals are affected by electromagnetic interference (EMI). EMI is any disturbance that degrades, obstructs or interrupts the performance of microwave signals. Microwave signal disruption EMI is caused by electric motors, electric power transmission lines, wind turbines, television/radio stations and cell phone transmission towers. Wind turbines, for instance, scatter and diffract TV, radio and microwave signals when placed between signal transmitters and receivers. Microwave radio communication is also affected by heavy moisture, snow, vapor, rain and fog due to rain fade (the absorption of microwave signals by ice, snow or rain, causing signal degradation and distortion).
  
  

Read more: Microwave Radio Communications Advantages & Disadvantages | eHow.com http://www.ehow.com/list_6137210_microwave-radio-communications-advantages-disadvantages.html#ixzz2EAYBET96 

* what did you learn about this lesson ? 

introduction:
In this blog we talking about important information of this the student short explication about it:  
To be transmitted, Information (Data) must be transformed to electromagnetic signals.

introduction:
In this blog we talking about radio wave propagation modes and explication about it:  

2  Sky Wave Propagation
Signal reflected from ionized layer of atmosphere. Signal can travel a number of hops, back and forth. Examples  SW radio

3  Line-of-Sight Propagation
Transmitting and receiving antennas must be within line of sight.
Example :-
Satellite communication
Ground communication

* Take one of them and explain it in more details.
 

introduction:
In this blog we talking about electromagnetic spectrum in general the object of this the student know kind of electromagnetic:  

introduction:
In this blog we talking about elements of a communication system in general the object of this the student know kind of it and short explication about it:  

Input Transducer: The message produced by a source must be converted by a transducer to a form suitable for the particular type of communication system.
Example: In electrical communications, speech waves are converted by a microphone to voltage variation.

Transmitter: The transmitter processes the input signal to produce a signal suits to the characteristics of the transmission channel.
Signal processing for transmission almost always involves modulation and may also include coding. In addition to modulation, other functions performed by the transmitter are amplification, filtering and coupling the modulated signal to the channel.
Channel: The channel can have different forms: The atmosphere (or free space), coaxial cable, fiber optic, waveguide, etc.
  The signal undergoes some amount of degradation from noise, interference and distortion

Receiver: The receiver’s function is to extract the desired signal from the received signal at the channel output and to convert it to a form suitable for the output transducer.
  Other functions performed by the receiver: amplification (the received signal may be extremely weak), demodulation and filtering.

Output Transducer: Converts the electric signal at its input into the form desired by the system user.
Example: Loudspeaker, personal computer (PC), tape recorders.

Communication is the transfer of information from one place to another.

This should be done :-  
  - as efficiently as possible
  - with as much fidelity/reliability as possible
  - as securely as possible  
Communication System: Components/subsystems act together to accomplish information transfer/exchange.