State coulomb’s law
Coulomb stated that the force between two very small charges separated in a vacuum or free space by a distance r (which is large compared to the size of the charge) is proportional to the multiplication of charges and inversely proportional to the square of the distance between them.State Stokes theorem
It states that the circulation of a vector field A around a closed path C is equal to the surface integral of the curl of A over the open surface ‘S’ bounded by ‘C’ provided that A and curl of A are continuous on ‘S’.State Gauss’s law for electric field
It states that the electric flux passing through any closed surface is equal to the total charge enclosed by that surface.State Biot-Savart law
It states that, the magnetic field intensity dH produced at a point ‘P’ due to a differential current element IdL is,Proportional to the product of the current I and differential length dL.The sine of the angle between the element and the line joining point ‘P’ to the element.
And inversely proportional to the square of the distance R between point P and the element.
State Ampere’s Circuital law
It states that, the line integral of magnetic field intensity ‘H’ around a closed path is exactly equal to the direct current enclosed by that path.Define the line parameters?
The parameters of a transmission line are:Resistance (R) is defined as the loop resistance per unit length of the wire. Its unit is ohm/Km
Inductance (L) is defined as the loop inductance per unit length of the wire. Its unit is Henry/Km
Capacitance (C) is defined as the loop capacitance per unit length of the wire. Its unit is Farad/Km
Conductance (G) is defined as the loop conductance per unit length of the wire. Its unit is mho/Km
What are the types of line distortions?
The distortions occurring in the transmission line are called waveform distortion or line distortion. Waveform distortion is of two types:a)Frequency distortion
b)Phase or Delay Distortion.
How frequency distortion occurs in a line?
When a signal having many frequency components are transmitted along the line, all the frequencies will not have equal attenuation and hence the received end waveform will not be identical with the input waveform at the sending end because each frequency is having different attenuation. This type of distortion is called frequency distortion.What is a distortion less line? What is the condition for a distortion less line?
A line, which has neither frequency distortion nor phase distortion is called a distortion less line. The condition for a distortion less line is RC=LG. Also,a)The attenuation constant a should be made independent of frequency.
b)The phase constant β should be made dependent of frequency.
c) The velocity of propagation is independent of frequency.
Define reflection coefficient
Reflection Coefficient can be defined as the ratio of the reflected voltage to the incident voltage at the receiving end of the lineReflection Coefficient K=Reflected Voltage at load /Incident voltage at the load K=Vr/Vi
Define reflection loss
Reflection loss is defined as the number of nepers or decibels by which the current in the load under image matched conditions would exceed the current actually flowing in the loadWhat is Impedance matching?
If the load impedance is not equal to the source impedance, then all the power that are transmitted from the source will not reach the load end and hence some power is wasted. This is called impedance mismatch condition. So for proper maximum power transfer, the impedances in the sending and receiving end are matched. This is called impedance matching.Define the term insertion loss
The insertion loss of a line or network is defined as the number of nepers or decibels by which the current in the load is changed by the insertion . Insertion loss=Current flowing in the load without insertion of the network/Current flowing in the load with insertion of the networkWhen reflection occurs in a line?
Reflection occurs because of the following cases:1)when the load end is open circuited
2)when the load end is short-circuited
3)when the line is not terminated in its characteristic impedance
When the line is either open or short circuited, then there is not resistance at the receiving end to absorb all the power transmitted from the source end. Hence all the power incident on the load gets completely reflected back to the source causing reflections in the line. When the line is terminated in its characteristic impedance, the load will absorb some power and some will be reflected back thus producing reflections.
Define An Antenna?
Antenna is a transition device or a transducer between a guided wave and a free space wave or vice-versa. Antenna is also said to be an impedance transforming device.What Is Meant By Radiation Pattern?
Radiation pattern is the relative distribution of radiated power as a function of distance in space .It is a graph which shows the variation in actual field strength of the EM wave at all points which are at equal distance from the antenna. The energy radiated in a particular direction by an antenna is measured in terms of FIELD STRENGTH. (E Volts/m)Define Beam Efficiency?
The total beam area (WA) consists of the main beam area (WM) plus the minor lobe area (Wm).Thus WA = WM+ Wm.
The ratio of the main beam area to the total beam area is called beam efficiency.
Beam efficiency (SM) = WM / WA.
Define Directivity?
The directivity of an antenna is equal to the ratio of the maximum power density P (q,f)max to its average value over a sphere as observed in the far field of an antenna.D = P (q,f)max / P(q,f)av. Directivity from Pattern.
D = 4p / WA. Directivity from beam area (WA).
What Is Meant By Front To Back Ratio?
It is defined as the ratio of the power radiated in desired direction to the power radiated in the opposite direction. i.e FBR = Power radiated in desired direction / power radiated in the opposite direction.Define Antenna Efficiency?
The efficiency of an antenna is defined as the ratio of power radiated to the total input power supplied to the antenna. Antenna efficiency = Power radiated / Total input Power.What Is Meant By Antenna Beam Width?
Antenna beamwidth is a measure of directivity of an antenna. Antenna beam width is an angular width in degrees, measured on the radiation pattern (major lobe) between points where the radiated power has fallen to half its maximum value. This is called as "beam width" between half power points or half power beam width.(HPBW).Define Gain?
The ratio of maximum radiation intensity in given direction to the maximum radiation intensity from a reference antenna produced in the same direction with same input power. i.e Maximum radiation intensity from test antenna (G)= Maximum radiation intensity from the reference antenna with same input power.Define Self Impedance?
Self impedance of an antenna is defined as its input impedance with all other antennas are completely removed i.e away from it.Define Mutual Impedance?
The presence of near by antenna no.2 induces a current in the antenna no.1 indicates that presence of antenna no.2 changes the impedance of the antenna no.1. This effect is called mutual coupling and results in mutual impedance.Define Radiation Field?
The radiation field will be produced at a larger distance from the the current element, where the distance from the centre of the dipole to the particular point is very large. It is also called as distant field or far field.What Is A Dipole Antenna?
A dipole antenna may be defined as a symmetrical antenna in which the two ends are at equal potential relative to the midpoint.What Is A Half Wave Dipole?
A half wave antenna is the fundamental radio antenna of metal rod or tubing or thin wire which has a physical length of half wavelength in free space at the frequency of operation.Define Sky Wave?
Waves that arrive at the receiver after reflection in the ionosphere is called sky wave.Define Tropospheric Wave?
Waves that arrive at the receiver after reflection from the troposphere region is called Tropospheric wave (i.e. 10 Km from Earth surface).
Define Ground Wave?
Waves propagated over other paths near the earth surface is called ground wave propagation.
Near Field
The field, which is nearer to the antenna, is called as near-field. It has an inductive effect and hence it is also known as inductive field, though it has some radiation components.Far field
The field, which is far from the antenna, is called as far-field. It is also called as radiation field, as the radiation effect is high in this area. Many of the antenna parameters along with the antenna directivity and the radiation pattern of the antenna are considered in this region only.Types of Antenna
1. Omni-directional antennaThe Omni-directional antenna radiations radio power equally in all the directions. The power emitted is perpendicular to the axis. It further declines to zero towards the axis. It is commonly used in applications that require communication with multiple devices.
2. Semi-directional antenna
Semi-directional antennas also radiate the power in a particular direction providing the radiations across a large area. It is generally a point-to-point communication used for short-to medium distance communications.
3. Directional antenna
The directional antenna radiations power in a specific direction. The power radiated thus has a strong beam. It prevents the radiations from any interference due to the radiations in a particular direction. It has a narrow beam and double gain as compared to the Omi-directional antenna.
The application of directional antenna includes GPS (Global Positioning system), cellular networks, etc.
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