Unit 3 SECA1701-microwave measurements.pptx

microwave measures

1. Unit :3 Microwave Measurements Sathyabama Institute of Science and Technology Department of ECE 1

2. Syllabus MICROWAVE MEASUREMENTS Microwave Bench general measurement set up, Measurement Devices and instrumentation: Slotted line, VSWR meter, power meter, spectrum analyzer, Network analyzer, Measurement of frequency, impedance, Attenuation, power and dielectric constant, measurement of VSWR, insertion loss ,EMI / EMC basics and measurement methods. The FCC and NTIA licensing process, Multi GBPS data communication and system requirements 2

3. Among the Microwave measurement devices, a setup of Microwave bench, which consists of Microwave devices has a prominent place. This whole setup, with few alternations, is able to measure many values like guide wavelength, free space wavelength, cut-off wavelength, impedance, frequency, VSWR, Klystron characteristics, Gunn diode characteristics, power measurements, etc. The output produced by microwaves, in determining power is generally of a little value. They vary with the position in a transmission line. There should be an equipment to measure the Microwave power, which in general will be a Microwave bench setup. 3

4. Microwave Bench General Measurement Setup 4

5. Signal Generator As the name implies, it generates a microwave signal, in the order of a few milliwatts . This uses velocity modulation technique to transfer continuous wave beam into milliwatt power. A Gunn diode oscillator or a Reflex Klystron tube could be an example for this microwave signal generator. Precision Attenuator This is the attenuator which selects the desired frequency and confines the output around 0 to 50db. This is variable and can be adjusted according to the requirement. Variable Attenuator This attenuator sets the amount of attenuation. It can be understood as a fine adjustment of values, where the readings are checked against the values of Precision Attenuator. 5

6. Isolator This removes the signal that is not required to reach the detector mount. Isolator allows the signal to pass through the waveguide only in one direction. Frequency Meter This is the device which measures the frequency of the signal. With this frequency meter, the signal can be adjusted to its resonance frequency. It also gives provision to couple the signal to waveguide. Crystal Detector A crystal detector probe and crystal detector mount are indicated in the above figure, where the detector is connected through a probe to the mount. This is used to demodulate the signals. 6

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8. Slotted Line In a microwave transmission line or waveguide, the electromagnetic field is considered as the sum of incident wave from the generator and the reflected wave to the generator. The reflections indicate a mismatch or a discontinuity. The magnitude and phase of the reflected wave depends upon the amplitude and phase of the reflecting impedance. The standing waves obtained are measured to know the transmission line imperfections which is necessary to have a knowledge on impedance mismatch for effective transmission. This slotted line helps in measuring the standing wave ratio of a microwave device. 8

9. Construction of slotted line The slotted line consists of a slotted section of a transmission line, where the measurement has to be done. It has a travelling probe carriage, to let the probe get connected wherever necessary, and the facility for attaching and detecting the instrument. In a waveguide, a slot is made at the center of the broad side, axially. A movable probe connected to a crystal detector is inserted into the slot of the waveguide. 9

10. Operation of slotted line The output of the crystal detector is proportional to the square of the input voltage applied. The movable probe permits convenient and accurate measurement at its position. But, as the probe is moved along, its output is proportional to the standing wave pattern, which is formed inside the waveguide. A variable attenuator is employed here to obtain accurate results. The output VSWR can be obtained by Where, V is the output voltage. 10

11. 11 1.Launcher –invites the signal, 2.smaller section of waveguide, 3.Isolator-prevents reflections to the source, 4.Rotary variable attenuator-for fine adjustments, 5.Slotted section-To measure the signal, 6.probe depth adjustment, 7.Tuning adjustments-To obtain accuracy 8.Crystal detector-detects the signal, 9.matched load-absorbs the power exited, 10.short circuit-Provision to get replaced by a load, 11. Rotary knob-to adjust while measuring, 12.Vernier gauge-For accurate results Different parts of slotted line

12. In order to obtain a low frequency modulated signal on an oscilloscope, a slotted line with a tunable detector is employed. A slotted line carriage with a tunable detector can be used to measure the following. -VSWR  -Standing wave pattern -Impedance -Reflection coefficient -Return loss -Frequency of the generator used 12

13. Tunable Detector The tunable detector is a detector mount which is used to detect the low frequency square wave modulated microwave signals. Figure shows a tunable detector mount . 13

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15. In the field of Microwave engineering, there occurs many applications. Hence, while using different applications, we often come across the need of measuring different values such as Power, Attenuation, Phase shift, VSWR, Impedance, etc. for the effective usage. let us take a look at the different measurement techniques. 15

16. Measurement of Power The Microwave Power measured is the average power at any position in waveguide. Power measurement can be of three types. Measurement of Low power - 0.01mWto10mW0.01mWto10mW -Example − Bolometric technique Measurement of Medium power  -10mWto1W10mWto1W - Example − Calorimeter technique Measurement of High power - >10W>10W Example − Calorimeter Watt meter 16

17. Measurement of Low Power The measurement of Microwave power around 0.01mW to 10mW, can be understood as the measurement of low power. Bolometer  is a device which is used for low Microwave power measurements. The element used in bolometer could be of positive or negative temperature coefficient. For example, a barrater has a positive temperature coefficient whose resistance increases with the increase in temperature. Thermistor has negative temperature coefficient whose resistance decreases with the increase in temperature. Any of them can be used in the bolometer, but the change in resistance is proportional to Microwave power applied for measurement. This bolometer is used in a bridge of the arms as one so that any imbalance caused, affects the output. A typical example of a bridge circuit using a bolometer is as shown in the following figure. 17

18. The milliammeter here, gives the value of the current flowing. The battery is variable, which is varied to obtain balance, when an imbalance is caused by the behavior of the bolometer. This adjustment which is made in DC battery voltage is proportional to the Microwave power. The power handling capacity of this circuit is limited . 18

19. Measurement of Medium Power The measurement of Microwave power around 10mW to 1W, can be understood as the measurement of medium power. A special load is employed, which usually maintains a certain value of specific heat. The power to be measured, is applied at its input which proportionally changes the output temperature of the load that it already maintains. The difference in temperature rise, specifies the input Microwave power to the load. The bridge balance technique is used here to get the output. The heat transfer method is used for the measurement of power, which is a Calorimetric technique. 19

20. Measurement of High Power The measurement of Microwave power around 10W to 50KW, can be understood as the measurement of high power The High Microwave power is normally measured by Calorimetric watt meters, which can be of dry and flow type. The dry type is named so as it uses a coaxial cable which is filled with di -electric of high hysteresis loss, whereas the flow type is named so as it uses water or oil or some liquid which is a good absorber of microwaves. The change in temperature of the liquid before and after entering the load, is taken for the calibration of values. The limitations in this method are like flow determination, calibration and thermal inertia, etc. 20

21. VSWR meter The standing wave ratio meter, SWR meter, ISWR meter (current " I " SWR), or VSWR meter (voltage SWR) measures the standing wave ratio (SWR) in a transmission line The meter indirectly measures the degree of mismatch between a transmission line and its load (usually an antenna). Electronics technicians use it to adjust radio transmitters and their antennas and feed lines to be impedance matched so they work together properly, and evaluate the effectiveness of other impedance matching efforts. 21

22. SWR meter helps to determine how much of radiofrequency energy is reflected back to the transmitter compared to the amount of RF energy that is been sent out during operation. This ratio should not be high and the ideal rating is 1:1 such that the power reached the destination and reflects no power. The meter that is used to measure SWR is known as SWR meter. ISWR meter can measure current SWR and VSWR can measure voltage SWR. 22

23. The ratio of the maximum radio-frequency voltage to the minimum radio frequency voltage along the transmission line is known as Standing Wave Ratio (SWR). When SWR is recognized in terms of maximum and minimum AC voltage along the transmission lines, it is known as voltage SWR.  The ratio of the maximum RF current to the minimum RF current on the transmission line is known as current SWR. 23

24. Standing waves are known as stationary waves in physics. Such waves oscillate in time, but the amplitude does not move. Amplitude remains constant with time. In microwave engineering and telecommunications, the measure of impedance matching of loads to the impedance of a transmission line is known as SWR. When there is a mismatch in the impedance, it results in standing waves along the transmission line, which increases the transmission line losses. SWR is generally used to measure the efficiency of a communication line. This line can include other cables that allow radio frequency signals and TV cable signals. 24

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28. Directional SWR meter A directional SWR meter measures the magnitude of the forward and reflected waves by sensing each one individually, with directional couplers. A calculation then produces the SWR. Referring to the diagram, the transmitter (TX) and antenna (ANT) terminals connect via an internal transmission line 28

29. This main line is electromagnetically coupled to two smaller sense lines (directional couplers). These are terminated with resistors at one end and diode rectifiers at the other. The resistors match the characteristic impedance of the sense lines. The diodes convert the magnitudes of the forward and reverse waves to the terminals FWD and REV, respectively, as DC voltages, which are smoothed by the capacitors. It will be seen that the configuration of the two couplers is subtly different - one has the resistor at one end, whereas the other has the resistor at the other. This is to enable the power in different directions to be monitored. 29

30. 30 The three parallel coupled lines are visible. Diodes, Capacitors and termination resistors are mounted at the ends of the sense lines. Interior view of an SWR meter

31. The SWR bridge uses very few components Resistors:    The two resistors R are chosen to provide the required load for the bridge element of the coupler. Diodes:    These are small signal types. Germanium or Schottky diodes are best as they have a small turn on voltage and are suitable for small signals. Meter:    The absolute value is not defined, but it must have a suitably high sensitivity. Meters with 100µA full scale deflection are what is normally used. Directional coupler lines:    There are several ways of creating the coupler lines. The most common way is probably to use a printed circuit board and to run the main match 50Ω line on the PCB with a ground plane on the other side. 31

32. SWR Bridge Circuit SWR can also be measured using an impedance bridge. The bridge is balanced (0 Volts across the detector) only when the test impedance exactly matches the reference impedance. When a transmission line is mismatched (SWR > 1:1), its input impedance deviates from its characteristic impedance; Thus, a bridge can be used to determine the presence or absence of a low SWR. 32

33. 33 SWR Reflectometer Bridge circuit Internal view of SWR bridge showing the PCB and coupler lines

34. To test for a match, the reference impedance of the bridge is set to the expected load impedance (for example, 50 Ohms), and the transmission line connected as the unknown impedance.  RF power is applied to the circuit. The voltage at the line input represents the vector sum of the forward wave, and the wave reflected from the load If we know the characteristic impedance of the line is 50 Ohms, we know the magnitude and phase of the forward wave. It's the same wave which is present on the other side of the detector. 34

35. Subtracting this known wave from the wave at the line input yields the reflected wave. Properly designed, a bridge circuit can not only indicate a match, but the degree of mismatch – making it possible to calculate the SWR. This usually involves alternately connecting the reference wave and the reflected wave to a power meter, and comparing the magnitudes of the resulting deflections. 35

36. 36 Spectrum Analyzer A Spectrum analyzer measures the magnitude of an input signal Versus frequency within the full frequency range of the instrument It Usually display raw, unprocessed signal information such as voltage, Power, period Waveshape, sidebands and frequency. It can provide a clear and precise window in to the frequency spectrum

37. 37 Spectrum Analyzer Versus Oscilloscope Spectrum Analyzer Oscilloscope Spectrum analyzer gives amplitude v/s frequency display An Oscilloscope give amplitude v/s time display of a wave It displays frequency components of a wave and their amplitudes( a spectrum analyzer shows it with respect to frequency) It gives distribution of energy in wave with respect to time (an oscilloscope displays a signal with respect to time) To observe the frequency properties of a signal, a spectrum analyzer is required. An oscilloscope is used to find the relative time delay between two signals A spectrum analyzer can measure and display signals with analog modulation, such as amplitude modulation (AM) and frequency modulation (FM).  An oscilloscopes can only directly measure voltage, not current. One way to measure AC current with an oscilloscope is to measure the voltage dropped across a shunt resistor. .. The primary use is to measure the power of the spectrum of known and unknown signals. The spectrum analyzer is more accurate The primary function of an oscilloscope is to measure voltage waves The Spectrum Analyzer plots the Amplitude vs. Frequency of the signal. The oscilloscope plots the Amplitude vs. Time of the signal,

38. 38 Types of Spectrum Analyzers Filter Bank Spectrum Analyzer Superheterodyne spectrum analyzer Filter Bank Spectrum Analyzer The spectrum analyzer used for analyzing the signals are of AF range is called filter bank spectrum analyzer or real time spectrum analyzer because it shows any variations in all input frequencies, below block diagram shows this,

39. 39 Working of Filter bank spectrum analyzer It has set of BPF and each one is designed for allowing a specific band of frequencies. The output of each band pass filter is given to a corresponding detector All the detector outputs are connected to electronic switch This switch allows the detector sequentially to the vertical deflection plate of CRO,SO, CRO displays the frequency spectrum of AF signal on its CRT screen

40. 40 Superheterodyne spectrum analyzer The spectrum analyzer used for analyzing the signals are of RF range is called Superheterodyne spectrum analyzer, below block diagram shows it,

41. 41 Working of Superheterodyne spectrum analyzer The RF signal ,which is to be analyzed is applied to input attenuator. If the signal amplitude is too large, then it can be attenuated by an input attenuator Low pass Filter (LPF) allows only the frequency components that are less than the cut-off frequency Mixer gets the inputs from LPF and voltage tuned Oscillator. It produces an output, which is the difference of frequencies of the two signals that are applied The amplified IF signal is applied to detector. The output of detector is given to vertical deflection plate of CRO, So CRO displays the frequency spectrum of RF signal on its CRT screen So it is chosed to a particular spectrum analyzer based on the frequency range of the signal that is to be analyzed .

42. Network Analyzer A  network analyzer  is an instrument that measures the network parameters of electrical networks. Network analyzers commonly measure s–parameters because reflection and transmission of electrical networks are easy to measure at high frequencies. Network analyzers are often used to characterize two-port networks such as amplifiers and filters, but they can be used on networks with an arbitrary number of ports. Network analyzers are used mostly at high frequencies, operating frequencies can range from 1 Hz to 1.5 THz. 42

43. Concept of vector network analyzer The vector network analyzer utilizes the concept of measuring the transmitted and reflected waves as a signal passes through a device under test. Measuring the transmitted and reflected signals across the band of interest, and often beyond, enables the characteristics of a device to be determined. If both transmitted and reflected signals are used to characterize the input and also the output then the device can be fully characterized. This can form a key part of any design or test for an RF circuit. 43

44. ScalarNetworkAnalyzer  (SNA)—measures signal amplitude properties only, its accuracy is scalar error correction only VectorNetworkAnalyzer  (VNA)—measures both signal amplitude and phase properties, its accuracy elaborate vector error correction 44 Types of Network Analyzer

45. Spectrum Analyzer Versus Network Analyzer 45 Spectrum Analyzer Network Analyzer Measure signal amplitude characteristics, carrier level, sidebands, harmonics Measure response of components, devices circuits, sub assembles to applied stimulus Can demodulate and measure complex signals Contain sources and receivers Spectrum analyzers are receivers only(single channel Display ratioed amplitude and phase(frequency, power or time sweeps) Can be used for scalar component test (amplitude only) with tracking or external source Offers advanced error correction for high accuracy measurements

46. Difference between RF network analyzers and spectrum analyzers Spectrum analyzers A spectrum analyzer is intended for analyzing the nature of signals that are fed into them. spectrum analyzers are normally used to measure the characteristics of a signal rather than a device The spectrum analyzer is used to measure carrier power level, noise harmonics, etc RF network analyzers A network analyzer, on the other hand generates a signal and uses this to analyze a network or device RF Network analyzers are used to measure components, devices, circuits, and sub-assemblies. The network analyzer is used to measure the reflection, insertion loss,  S  parameters, and transmission and return loss    46

47. On the opposite end, spectrum analyzers measure the parameters of a signal and not a device. They are commonly configured without a source. Spectrum Analyzers are also more flexible in terms of their IF bandwidths to allow a complete range of signal analysis. Network analyzers consist of multiple receivers plus a source-receiver that measures the broadband frequency by sweeping power and frequency. It seeks a known signal/frequency of a device output and, using vector-correction, gives a more precise measurement than the spectrum analyzer. 47

48. Architecture of Network Analyzer The basic architecture of a network analyzer involves a signal generator, a test set, one or more receivers and display. Most VNAs have two test ports, permitting measurement of four S-parameters(s 11 ,s 12 ,s 21 ,s 22 )but instruments with more than two ports are available commercially. 48

49. Vector network analyzer block diagram 49 The diagram shows the very basic blocks of the VNA including the signal ports, the signal separation blocks, the receiver detector, and finally the processor and display. The VNA has precision connectors on the front panel of the unit itself and then precision cables are used to connect these to the device under test. Precision cables are required because the phase and loss of a standard cable would vary too much with even slight movement, etc.

50. To test the device, a variable frequency signal is generated within the vector network analyzer and the output is switched to test the DUT in either one direction or the other. In this case the left hand side on the diagram is selected. The signal passes to the splitter where one output is used as the reference signal for the receiver and the other side is passed to a direction coupler and then into the DUT via the external connection on the VNA and the precision cables. Power passes through the directional coupler (directional coupler 1) to the DUT, but the third port detects the reflected power and this is connected to the receiver again. Power that passes through the device under test is sampled by directional coupler 2 and this signal is connected to the receiver. 50 Vector network analyzer block diagram

51. Apart from generating a signal to power the device under test, the signal source also has an output that is connected to the receiver. This enables phase information to be gained from the detected signals. The signals are processed by the receiver are then fed to the processor and display. This section will again make heavy use of microprocessor technology to provide the control, functionality and user friendly displays that are needed for modern test instrumentation. 51

52. Block diagram of Scalar Network Analyzer 52

53. Measurement of wavelength and Frequency 53

54. 54 Switch on the klystron power supply and VSWR meter Adjust the reflector voltage to get some deflection in VSWR meter Maximize the deflection with AM amplitude and frequency control knob of power supply Tune the plunger of klystron mount for maximum deflection Tune the reflector voltage knob for maximum deflection. Tune the probe for maximum deflection in VSWR meter Tune the frequency meter knob to get a dip on the VSWR scale and note down the frequency directly from the frequency meter Replace the termination with movable short and detune the frequency meter Move probe along with the slotted line, the deflection in VSWR meter will vary,move the probe to a minimum deflection position, to get accurate reading; it is necessary to increase the VSWR meter range dB switch to higher position. Note and record the position Procedure

55. 55 Move the probe to next minimum position and record the probe position again Calculate the guided wavelength as twice the distance between two successive minimum positions obtained as above Measure the waveguide inner broad dimension ‘a’ which will be around 2.286 cm for X-band waveguide. Calculate the frequency by following equation f= =c + 𝞴 c =2a Where C=3X 10 8 -meter/sec is velocity of light in free space Verify with frequency obtained by frequency meter   Calculation

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62. 62 Measurement of Attenuation Microwave Attenuation Attenuation is a measure of the reduction in power level experienced by a signal as it passes through a circuit.  In engineering, attenuation is usually measured in units of decibels per unit length of medium (dB/cm, dB/km, etc.) and is represented by the attenuation coefficient of the medium. In practice, Microwave components and devices often provide some attenuation. The amount of attenuation offered can be measured in two ways . They are − Power ratio method and RF substitution method .  Attenuation is the ratio of input power to the output power and is normally expressed in decibels. Attenuation in dBs=10 log To measure the frequency of a microwave signal, the Resonant Cavity Frequency Meter is tuned until it resonates at the signal frequency. If a SWR meter is used as the indicator, resonance will reflect as a decrease (dip) in the signal level due to the storage of energy in the cavity at resonance .  

63. 63 Power Ratio Method

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65. 65 RF Substitution Method

66. 66 Measurement of Impedance

67. 67 Impedance measurement Using Slotted line

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74. 74 Measurement of Impedance using Reflectometer

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86. 86 Measurement of Dielectric Constant Various methods are used to measure the dielectric constant of a material Waveguide Method This method is used to measure the dielectric constant of a lossless or very low loss solid dielectric material that completely fills a length of a waveguide. The end of the sample is terminated in a short circuit. Due to the termination ,a standing wave is formed inside the waveguide. Let us assume that the first voltage minimum in the unfilled waveguide occurs at a distance l from the air-dielectric interface Therefore ,the position of the first voltage minimum in the unfilled waveguide is at a distance l e + l .

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90. EMI / EMC basics and measurement methods . EMI  is  measured  in special rooms called "RF anechoic chambers" There are strict regulations regarding unwanted electromagnetic emissions, and all commercially-produced electronic devices must pass emission certification, to meet FCC and other international standards. This is true for all developed countries. The terms  Electromagnetic interference  ( EMI ) and  electromagnetic compatibility  ( EMC ) are often used interchangeably when referring to the regulatory  testing  of electronic components and consumer goods. During  EMC testing , radiated emissions  measurements  are made using a spectrum analyzer and or an  EMI  receiver and a suitable  measuring  antenna. Radiated Emissions (H-field): The magnetic component of the electromagnetic wave is using a spectrum analyzer and or an  EMI  receiver and a suitable  measuring  antenna . 90

91. Differences between EMC/EMI EMI  stands for  electromagnetic interference  and is an electronic emission that interferes with components, RF systems, and most electronic devices. ... The  difference between EMI  and  EMC  is that  EMI  is the term for radiation and  EMC  merely is the ability for a system to operate within the presence of radiation. Causes of EMI Electromagnetic interference ( EMI ) is a disturbance  caused  by an electromagnetic field which impedes the proper performance of an electrical device.  EMI  can come from man-made or natural sources such as the sun or the Earth's magnetic fields . 91

92. Design guidelines for EMI and EMC reduction in a PCB Trace spacing and layout. ... Ground planes. ... Shielding. ... Arrangement of PCB layers: ... Segregate sensitive components. ... Decoupling capacitor. ... Controlled impedance for transmission line design 92

93. What is EMC Electromagnetic Compatibility Basics EMC is of increasing importance as the number of wirelessly connected devices increase. Defining what EMC is and understanding the concepts enable electromagnetic compatibility to be achieved from the outset. Electromagnetic compatibility, EMC is the concept of enabling different electronics devices to operate without mutual interference - Electromagnetic Interference, EMI - when they are operated in close proximity to each other. All electronics circuits have the possibility of radiating of picking up unwanted electrical interference which can compromise the operation of one or other of the circuits. EMC definition :    EMC is defined as the ability of devices and systems to operate in their electromagnetic environment without impairing their functions and without faults and vice versa. Electromagnetic compatibility, EMC ensures that operation does not influence the electromagnetic environment to the extent that the functions of other devices and systems are adversely affected. 93

94. EMC basics The aim of employing EMC measures is to ensure that a variety of different items of electronics equipment can operate in close proximity without causing any undue interference. The interference that gives rise to impaired performance is known as Electromagnetic Interference, EMI. It is this interference that needs to be reduced to ensure that various items of electrical equipment are compatible and can operate in the presence of each other. There are two main elements to EMC: Emissions:    The EMI emissions refer to the generation of unwanted electromagnetic energy. These need to be reduced below certain acceptable limits to ensure they do not cause any disruption to other equipment. Susceptibility & immunity :   The susceptibility of an item of electronics to EMI is the way it reacts to unwanted electromagnetic energy. The aim of the design of the circuit is to ensure a sufficiently high level of immunity to these unwanted signals. 94

95. EMC standards With the growing awareness and need to maintain high standards of electromagnetic compatibility many standards have been introduced to help manufacturers meet the levels they need to maintain full electromagnetic compatibility. Many years ago the levels of EMC were low and interference often occurred - taxis driving past a house whilst using their radio telephone were quite likely to disrupt the operation of a television, and there were many other instances. As a result, it became necessary to introduce EMC standards to ensure the required levels of compatibility were attained. EMC is now an integral part of any electronics design project. With standards now implemented and enforced across the world, any new product needs to meet and have been tested to ensure it meets the relevant EMC standards. While this presents an additional challenge to the electronics design engineer, it is essential that good EMC practices have been employed and that the EMC performance of the product is sufficient to ensure it operates correctly under all reasonable scenarios. 95

96. EMI Electromagnetic Interference: the fundamentals Electromagnetic Interference, EMI is the interference caused by one electrical or electronic device to another by the electromagnetic fields set up by its operation. Electromagnetic interference, EMI Electromagnetic interference, EMI is the name given to the unwanted electromagnetic radiation that causes potential interference to other items of electronics equipment. There are many ways in which electromagnetic interference can be carried from one item of equipment to another. Understanding these methods is a key to mitigating the effects of the electromagnetic interference 96

97. EMI can be divided into two categories : Continuous interference:    The continuous interference is often in the form of a radio signal or oscillation that is maintained. It could be from an unscreened oscillator, or it may be in the form of wideband noise. Impulse interference:    This form of interference consists of a short impulse. It may arise from an electrostatic discharge, lightning, or a circuit being switched. Apart from understanding the form of the interference, it is also necessary to know how the interference is travelling from the transmitting device to the receiving device. Unfortunately this is not always easy to discover as many of the paths are difficult to define. However good initial design alleviates many problems. 97

98. There are many forms of electromagnetic interference, EMI that can affect circuits and prevent them from working in the way that was intended. This EMI or radio frequency interference, RFI as it is sometimes called can arise in a number of ways, although in an ideal world it should not be present. EMI - electromagnetic interference can arise from many sources, being either man made or natural. It can also have a variety of characteristics dependent upon its source and the nature of the mechanism giving rise to the interference. By the very name of interference given to it, EMI is an unwanted signal at the signal receiver, and in general methods are sought to reduce the level of the interference. Types of EMI - Electromagnetic Interference EMI - Electromagnetic Interference can arise in many ways and from a number of sources. The different types of EMI can be categorised in a number of ways. One way of categorising the type of EMI is by the way it was created: Man-made EMI :   This type of EMI generally arises from other electronics circuits, although some EMI can arise from switching of large currents, etc. 98

99. Naturally occurring EMI:    This type of EMI can arise from many sources - cosmic noise as well as lightning and other atmospheric types of noise all contribute. Another method of categorizing the type of EMI is by its duration: Continuous interference:    This type of EMI generally arises from a source such as a circuit that is emitting a continuous signal. However background noise, which is continuous may be created in a number of ways, either manmade or naturally occurring. Impulse noise:    Again, this type of EMI may be man-made or naturally occurring. Lightning, ESD, and switching systems all contribute to impulse noise which is a form of EMI. It is also possible to categories the different types of EMI by their bandwidth. Narrowband:    Typically this form of EMI is likely to be a single carrier source - possibly generated by an oscillator of some form. Another form of narrowband EMI is the spurious signals caused by intermodulation and other forms of distortion in a transmitter such as a mobile phone of Wi-Fi router. These spurious signals will appear at different points in the spectrum and may cause interference to another user of the radio spectrum. As such these spurious signals must be kept within tight limits. Broadband:    There are many forms of broadband noise which can be experienced. It can arise from a great variety of sources. Man-made broadband interference can arise from sources such as arc welders where a spark is continuously generated. Naturally occurring broadband noise can be experienced from the Sun - it can cause sun-outs for satellite television systems when the Sun appears behind the satellite and noise can mask the wanted satellite signal. Fortunately these episodes only last for a few minutes . 99

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106. The FCC and NTIA Licensing Process The FCC ruling also permits a simplified licensing scheme for millimeter-wave radios, allowing cheap and fast allocations to prospective users: You can apply for a 10-year license, get accepted, and pay for it in less than 30 minutes for only a few hundred dollars. The FCC will issue an unlimited number of non-exclusive nationwide licenses to non-federal government entities in the 12.9 GHz of spectrum allocated for commercial use. These licenses will serve as a prerequisite for registering individual point-to-point links. The 71-95 GHz bands are allocated on a shared basis with federal government users. Therefore, in order to operate a link under its non-exclusive nationwide license, licensee will have to: Coordinate with the National Telecommunications and Information Administration (NTIA) with respect to federal government operations. Register as an approved link with a third party Database Manager . On September 29, 2004, the Wireless Telecommunications Bureau (WTB) appointed Comsearch, Frequency Finder, and Micronet Communications as independent Database Managers responsible for the design and management of the third-party 71- 95 GHz bands Link Registration System (LRS). Proposed links must be coordinated with NTIA. NTIA has developed an automated coordination mechanism that can determine whether a given non-federal government link has any potential conflict with federal government users. A proposed link entered into NTIA’s automated system will result in either a “green light” or a “yellow light” based on the proposed parameters. Licensing MMW radios is simple and inexpensive: A 10- year license costs a few hundred dollars and only takes about a half-hour to apply for.

107. Despite some issues and technical challenges, MMW radios are promising candidates for multigigabit rates in point to-multipoint and point-to-point applications. The huge unlicensed bandwidth, coupled with higher allowable transmission power and advances in integrated circuit technology, have made millimeter wave radios promising candidates for multi-gigabit rates in point-to-multipoint and point-to-point applications. A number of open issues and technical challenges have yet to be fully addressed. In particular, propagation and implementation issues require further optimization and research in order to obtain a truly efficient and low-cost millimeter wave communication system Multi GBPS data communication and system requirements

108. Research & Development https://www.drdo.gov.in/labs-and-establishments/microwave-tube-research-development-centre-mtrdc 108

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