Dish antenna is parabolic in shape and has meshy structure. Give reasons.

Dish antenna is parabolic in shape and has meshy structure. Give reasons.
by

1 Answer

Answer :

A Practical reflector employing the properties of the parabola will be a three dimensional bowl-shaped surface, obtained by revolving the parabola about the axis AB.

The resulting geometric surface is the paraboloid, often called a parabolic reflector or microwave dish. When it is used for reception exactly the same behaviour is manifested, so that this is also a high gain receiving directional antenna reflector. The principle of reciprocity which states that the properties of an antenna are independent of whether it is used for transmission or reception. The reflector is directional for reception because only rays arriving from BA direction i.e. normal to the directrix are brought together at the focus. On the other hand, rays from any other direction are canceled at that point, again owing to path length differences. The reflector provides a high gain because like the mirror of a reflecting telescope, it collects radiation from a large area and concentrates it all at the focal point.

Why dish antenna having meshy structure:

While installing the dish antenna look angles are taken into consideration.

Once look angle adjusted installation should not be disturbed.

Due to atmospheric changes like rain, winds there is a possibility of change a look angle of dish, due to meshy structure, rain and wind will go through holes by keeping fix position of dish antenna.
The parabola is a plane curve defined as the locus of a point which moves so that its distance from another point (called the focus) plus its distance from a straight line (directrix) is constant. These geometric properties yield an excellent microwave or light reflector. 
by

Related questions

Write one application of following antenna i. Rectangular antenna ii. Dish antenna iii. Yagi-Uda antenna iv. Horn antenna

Description : Write one application of following antenna i. Rectangular antenna ii. Dish antenna iii. Yagi-Uda antenna iv. Horn antenna 

Last Answer : i. Rectangular antenna is used in direction finding in portable recievers. ii. Dish antenna is used to transmit and receive signal from satellite. iii. Yagi-Uda antenna is used in HF and VHF range as a TV receiving antenna. iv. Horn antenna is used in satellite tracking.

Draw radiation pattern for following antenna i) Yagi-Uda antenna ii) Loop antenna iii) Dish antenna iv) Horn antenna

Description : Draw radiation pattern for following antenna i) Yagi-Uda antenna ii) Loop antenna iii) Dish antenna iv) Horn antenna

Last Answer : Type of antenna Radiation Patteren  Yagi-Uda antenna Loop antenna Dish antenna Horn antenna 

Draw the structure and state applications of: i) Ferrite loop (rod) antenna ii) Horn antenna

Description : Draw the structure and state applications of: i) Ferrite loop (rod) antenna ii) Horn antenna

Last Answer : Horn antenna: Application:- i) Used at microwave frequency. ii) Used in satellite tracking.  Ferrite loop antenna: Application:- In Am radio receiver to receive MW and SW band signals. In FM radio receiver

Draw the structure of horn antenna and its radiation pattern. List its any two applications.

Description : Draw the structure of horn antenna and its radiation pattern. List its any two applications.

Last Answer : The structure of horn antenna Radiation pattern of Horn Antenna Application:- i) Used at microwave frequency. ii) Used in satellite tracking 

Define the following terms related to antennas; (i) Antenna resistance (ii) Directivity (iii) Antenna gain (iv) Power density

Description : Define the following terms related to antennas; (i) Antenna resistance (ii) Directivity (iii) Antenna gain (iv) Power density

Last Answer : Antenna Resistance - The resistance of an antenna has two components: 1. Its radiation resistance due to conversion of power into electromagnetic waves 2. The resistance due to actual losses in the ... the transmitter power divided by the surface area of a sphere (4πR2) at that distance.

Define and explain the term beam width related to antenna with a sketch.

Description : Define and explain the term beam width related to antenna with a sketch.

Last Answer : Definition: The beam width of an antenna is described as the angles created by comparing the half power point (3dB) on the main radiation lobe to its maximum power point. As an example the beam width ... max voltage at center of lobe (these point are known as half power points.) Sketch-  

Draw construction of Yagi-Uda antenna and explain.

Description : Draw construction of Yagi-Uda antenna and explain.

Last Answer : Explanation A Yagi-Uda antenna, commonly known as a Yagi antenna, is a directional antenna consisting of multiple parallel elements in a line, usually half-wave dipoles made of ... receiver with a transmission line and additional parasitic elements called reflector and one or more directors.

Explain how modulation reduces height of antenna and avoid mixing of signals.

Description : Explain how modulation reduces height of antenna and avoid mixing of signals.

Last Answer : Modulation reduces antenna height: For the transmission of radio signals, the antenna height must be multiple of λ/4 ,where λ is the wavelength . λ = c /f where c : is the ... will occupy different slots in the frequency domain (different channels). Thus, modulation avoids mixing of signals.

Explain loop antenna with neat sketch. Draw radiation pattern. State its advantages and applications.

Description : Explain loop antenna with neat sketch. Draw radiation pattern. State its advantages and applications.

Last Answer : Loop antenna:-The single turn coil carrying RF current through it having length less than the wavelength.   Advantages:- 1. highly directive 2. Small size Applications:- 1. For direction finding 2. In portable receivers 3. In navigation 

Describe with respect to antenna (i) radiation pattern (ii) directive gain (iii) power gam (iv) polarization

Description : Describe with respect to antenna (i) radiation pattern (ii) directive gain (iii) power gam (iv) polarization

Last Answer : (i) Radiation pattern:-A graph or diagram which tells us about the manner in which an antenna radiates more power in different directions is known as the radiation patteren of antenna.  ( ... as the direction of the electric vector in the electromagnetic wave radiated by the transmitting antenna. 

Explain half dipole antenna ( Resonant antenna ) with its radiation patteren.

Description : Explain half dipole antenna ( Resonant antenna ) with its radiation patteren. 

Last Answer : Half wave dipole antenna Explanation:  1. It is a resonant antenna 2. It is exact half wavelength (λ /2) long & open circuited at one end. 3. The dipole antennas have ... pattern is bidirectional.  The radiation pattern of half wave dipole antenna is - The radiation pattern

Draw Yagiuda antenna with its radiation pattern.

Description : Draw Yagiuda antenna with its radiation pattern.

Last Answer : Construction of Yagi-Uda Antenna Radiation Pattern of Yagi-Uda Antenna

Define the following terms: (i) Polarization (ii) Antenna gain (iii)Antenna resistance (iv)Directivity

Description : Define the following terms: (i) Polarization (ii) Antenna gain (iii)Antenna resistance (iv)Directivity

Last Answer : i) Polarization:- It is defined as the direction of electric field vector in the EM wave radiated by the transmitting antenna. ii) Antenna Gain:- Antenna gain is defined as the ratio of ... in only one direction in which the radiation is maximum. That is directivity = Max. directive gain

An antenna has a radiation resistance of 72 Ω a loss resistance of 8 Ω and a power gain of 16. Find efficiency and directivity.

Description : An antenna has a radiation resistance of 72 Ω a loss resistance of 8 Ω and a power gain of 16. Find efficiency and directivity.

Last Answer : An antenna has a radiation resistance of 72 Ω a loss resistance of 8 Ω and a power gain of 16. Find efficiency and directivity.

Draw the radiation pattern for Dipole antenna: (i) Half wave dipole (ii) Folded dipole.

Description : Draw the radiation pattern for Dipole antenna: (i) Half wave dipole (ii) Folded dipole.

Last Answer : The radiation pattern for Half wave dipole antenna The radiation pattern for Folded dipole antenna.

An antenna with very high gain and very narrow beamwidth. A. Helical antenna B. Discone antenna C. Horn antenna D. Parabolic dish antenna

Description : An antenna with very high gain and very narrow beamwidth. A. Helical antenna B. Discone antenna C. Horn antenna D. Parabolic dish antenna

Last Answer : D. Parabolic dish antenna

How does the gain of a parabolic dish type antenna change when the operating frequency is doubled? A. Gain does not change B. Gain is multiplied by 0.707 C. Gain increases 6 dB D. Gain increases 3 dB

Description : How does the gain of a parabolic dish type antenna change when the operating frequency is doubled? A. Gain does not change B. Gain is multiplied by 0.707 C. Gain increases 6 dB D. Gain increases 3 dB

Last Answer : C. Gain increases 6 dB

A parabolic dish antenna isa(n)_______ antenna. A) omnidirectional B) bidirectional C) unidirectional D) horn

Description : A parabolic dish antenna isa(n)_______ antenna. A) omnidirectional B) bidirectional C) unidirectional D) horn

Last Answer : unidirectiona

Write two reasons of fading.

Description : Write two reasons of fading.

Last Answer : Major reasons of Fading: 1. Interference between waves that have travelled by slightly different paths. 2. Multipath Propagation 3. Variation in atmospheric conditions along the path of waves. 4 ... signal very close to each other in the frequency domain will fade to a different extent.

Explain any four different frequency bands and give their two applications of each.

Description : Explain any four different frequency bands and give their two applications of each.

Last Answer : Explain any four different frequency bands and give their two applications of each.

Give the expression for modulation index for AM and FM.

Description : Give the expression for modulation index for AM and FM.

Last Answer : 1.Modulation index for AM ma=Vm / Vc Where Vm is modulating voltage Vc is the carrier voltage 2.Modulation index for FM mf=δ /fm where δ is the deviation fm is the modulating frequency

Define modulation index in AM and give its formula.

Description : Define modulation index in AM and give its formula.

Last Answer : In AM wave, the modulation index (m) is defined as the ratio of the amplitude of the modulating signal (Vm ) to the amplitude of carrier signal (Vc). m = Vm / Vc

Draw practical set-up and explain the procedure to measure selectivity of radio receiver.

Description : Draw practical set-up and explain the procedure to measure selectivity of radio receiver.

Last Answer : Procedure to measure selectivity of radio receiver: Throughout the measurement the receiver is kept tuned to desired frequency 950 Khz. Now the generator output frequency is deviated below ... the generator output voltage is adjusted to get a standard 50 miliwatt receiver output power.

Draw and label the circuit diagram of ratio detector

Description : Draw and label the circuit diagram of ratio detector 

Last Answer : Draw and label the circuit diagram of ratio detector  

Calculate the characteristics impedance for a transmission line having L=0.5 mH/Km, C=0.08 µF and negligible R and G.

Description : Calculate the characteristics impedance for a transmission line having L=0.5 mH/Km, C=0.08 µF and negligible R and G.

Last Answer : L=0.5 mH/Km C=0.08 µF

State the need of stub. Explain single stub and double stub matching.

Description : State the need of stub. Explain single stub and double stub matching.

Last Answer : Stub:- Stub is the piece of short circuited transmission line which is used to tune out the reactance of the load when connected across the transmission line as close as possible. ... but lengths are independently adjustable. The double stub matching provides wide range of impedance matching.  

Explain the working of amplitude limiter in FM receiver with circuit diagram.

Description : Explain the working of amplitude limiter in FM receiver with circuit diagram.

Last Answer : Amplitude limiter: The function of amplitude limiter is to remove all amplitude variation of FM carrier voltage that may occur due to atmospheric disturbances. Use of amplitude limiter makes the system less noisy  Circuit Diagram:

Explain duct propagation with neat sketch.

Description : Explain duct propagation with neat sketch.

Last Answer : Duct propagation is a special type and used for very high microwave frequencies. New phenomenon which occurs in super-refraction, also known as ducting. As the height above earth increases, ... in the standard atmosphere. The Duct propagation is used for very high frequencies in GHz range.

A superheterodyne radio receiver with an IF of 455KHZ is turned to 1000KHZ. Find: (i) Image frequency (ii) Local oscillator frequency

Description : A superheterodyne radio receiver with an IF of 455KHZ is turned to 1000KHZ. Find: (i) Image frequency (ii) Local oscillator frequency

Last Answer : Given Intermediate Frequency fi=455KHz Signal frequency =fs=1000KHz Local oscillator frequency fo=fs+fi  Fo=1000KHz+455KHz  =1455KHz Image frequency is the input frequency which produces the same intermediate frequency fsi=fs+2fi  =1000KHz+2*455KHz  =1910KHz 

Draw circuit diagram of transistor reactance modulator. Explain its working.

Description : Draw circuit diagram of transistor reactance modulator. Explain its working.

Last Answer : Explanation- A reactance modulator is illustrated in figure. It is basically a standard commonemitter class A amplifier. Resistors R1 and R2 from a voltage divider to bias ... frequency, whereas a lower capacitance increases the frequency. The circuit produces direct frequency modulations.

State and explain the concept of transmission bandwidth.

Description : State and explain the concept of transmission bandwidth.

Last Answer : Bandwidth is defined as the portion of the electromagnetic spectrum occupied by a signal We may also define the bandwidth as the frequency range over which as information signal is transmitted. Bandwidth is the ... to 15 KHZ. Therefore the bandwidth is(f2-f1) BW= f2 - f1= 15000-20=14980Hz

Define critical frequency w.r. to wave propagation.

Description : Define critical frequency w.r. to wave propagation.

Last Answer : Define critical frequency w.r. to wave propagation.

Define VSWR with refernce to standing waves.

Description : Define VSWR with refernce to standing waves.

Last Answer : Voltage Standing Wave Ratio: The voltage standing wave ratio (VSWR) is the ratio of max voltage to min voltage. VSWR= VMAX /VMIN

State two disadvantages of TRF receiver over superheterodyne receiver.

Description : State two disadvantages of TRF receiver over superheterodyne receiver.

Last Answer : Disadvantages of TRF Receiver: 1. Instability due to oscillatory nature of RF amplifier. 2. Variation in bandwidth over tuning range. 3. Insufficient selectivity at high frequencies 4. Poor adjacent channel rejection capability 

Define sensitivity with graph.

Description : Define sensitivity with graph.

Last Answer : Define sensitivity with graph.

Compare between simplex and full duplex communication on the basis of: 1) Definition 2) Sketch

Description : Compare between simplex and full duplex communication on the basis of: 1) Definition 2) Sketch

Last Answer : Compare between simplex and full duplex communication on the basis of: 1) Definition 2) Sketch

Explain operation of balanced slope detector with „s‟ curve.

Description : Explain operation of balanced slope detector with „s‟ curve.

Last Answer : Diagram: Explanation:   Curve:  

Draw block diagram of FM receiver and explain the use of limiter circuit.

Description : Draw block diagram of FM receiver and explain the use of limiter circuit.

Last Answer : Diagram Explanation Amplitude limiter: The function of amplitude limiter is to remove all amplitude variation of FM carrier voltage that may occur due to atmospheric disturbances. Use of amplitude limiter makes the system less noisy.

Compare PAM, PWM, and PPM on the basis of i. Variable characteristics ii. Bandwidth iii. Information contained in iv. Transmitted power

Description : Compare PAM, PWM, and PPM on the basis of i. Variable characteristics ii. Bandwidth iii. Information contained in iv. Transmitted power

Last Answer : Compare PAM, PWM, and PPM on the basis of i. Variable characteristics ii. Bandwidth iii. Information contained in iv. Transmitted power

Explain “BALUN” with neat sketch

Description : Explain “BALUN” with neat sketch

Last Answer : Diagram- Explaination

Explain working of envelope detector with suitable diagram and waveform.

Description : Explain working of envelope detector with suitable diagram and waveform.

Last Answer : Envelope Detector: An Envelope Detector is an electronic circuit that takes a high frequency signal as input and provides an output which is as envelopes of the original signal. The capacitor ... decreases the responsiveness thus, real-world designs must be optimized for the application.

A load of 200 ohm is used to match 300 ohm transmission line to achieve SWR=1. Find out the required characteristic impedance of a quarter of a quarter wave transformer connected directly to the load.

Description : A load of 200 ohm is used to match 300 ohm transmission line to achieve SWR=1. Find out the required characteristic impedance of a quarter of a quarter wave transformer connected directly to the load.

Last Answer : Solution :

Why should local oscillator frequency be greater than signal frequency in AM receiver? Also explain why IF has constant value?

Description : Why should local oscillator frequency be greater than signal frequency in AM receiver? Also explain why IF has constant value?

Last Answer : Reason for LO frequency to be greater than signal frequency The local oscillator frequency (f0) is made greater than signal frequency (Fs) in radio receiver: Local oscillator frequency range is 995 ... frequency of desired signal because the IF is constant and same for all the incoming RF signal.

Draw waveform for standing waves on an open and shorted line. Prove that impedance is inverted at every quarter wavelength interval.

Description : Draw waveform for standing waves on an open and shorted line. Prove that impedance is inverted at every quarter wavelength interval.

Last Answer : Waveform- Explanation When the transmission line is short circuited voltage is zero and current is maximum.The variation is according to the wavelength. When the ... The pattern repeats for every half wavelength. Thus impedance is inverted at every quarter wavelength interval.

Explain virtual height with respect to wave propagation with neat sketch.

Description : Explain virtual height with respect to wave propagation with neat sketch.

Last Answer : In ionization layer the incident wave refracts and bends down gradually than sharply.   The incident and refracted rays follow paths that are exactly the same as they would have been if reflection had taken place from a surface located at a greater height called virtual height of this layer. 

a) For a transmission line, Find SWR and reflection coefficient R if, i. There is no reflected voltage. ii. Reflected voltage and incident voltage is equal. iii. If reflected voltage=20V and incident voltage=10V. iv. If reflected voltage=10V and incident voltage =20V.

Description : a) For a transmission line, Find SWR and reflection coefficient R if, i. There is no reflected voltage. ii. Reflected voltage and incident voltage is equal. iii. If reflected voltage=20V and incident voltage=10V. iv. If reflected voltage=10V and incident voltage =20V.

Last Answer : reflection coefficient R=Vr/Vi i. There is no reflected voltage. i.e,Vr=0 R=0 SWR= 1+R/1-R=1 ii. Reflected voltage and incident voltage is equal. Vr=Vi; R=1 SWR= 1+R/1-R=1+1/1-1=infinity iii. If reflected ... and incident voltage =20V. Vr=10 and Vi=20 R=10/20=0.5 SWR= 1+R/1-R=1+.5/1-.5=3 

In a FM system, the maximum deviation is 75KHz. Find bandwidth for modulating frequency i. fm=500Hz ii. fm=5KHz iii. fm=10KHz Draw conclusion for bandwidth of FM from answer.

Description : In a FM system, the maximum deviation is 75KHz. Find bandwidth for modulating frequency i. fm=500Hz ii. fm=5KHz iii. fm=10KHz Draw conclusion for bandwidth of FM from answer.

Last Answer : Given deviation∆=75kHz i) fm=500Hz bandwidth B.W=2(∆+fm)  =2(75k+500)=151kHz  ii). fm=5KHz bandwidth B.W=2(∆+fm)  =2(75k+5k)=160KHz iii) fm=10KHz bandwidth B.W=2(∆+fm)  =2(75k+10k)=170KHz As the modulating frequency increases bandwidth also increases.

Define PAM, PWM, and PPM. Draw waveforms.

Description : Define PAM, PWM, and PPM. Draw waveforms.

Last Answer : Pulse amplitude modulation is defined as a process of varying the amplitude of the carrier pulse in accordance to the modulating signal variations. Pulse width modulation is defined as a ... of varying the position of the carrier pulse, in accordance to the modulating signal variations.

Explain isotropic radiator with neat sketch.

Description : Explain isotropic radiator with neat sketch. 

Last Answer : An isotropic radiator is a point source that radiates equally in all the directions. It is a hypothetical antenna used as a reference to describe real antenna. The radiation is represented by a sphere with center coincides with location of isotropic radiator.

A telephone cable has following primary constants per loop kilometer ,R=30Ω, L=20mH,C=0.06µF,G=0.If the applied signal has an angular frequency of 5000 rad/sec.., Determine (i) Characteristics impedence (ii) Attenuation constant

Description : A telephone cable has following primary constants per loop kilometer ,R=30Ω, L=20mH,C=0.06µF,G=0.If the applied signal has an angular frequency of 5000 rad/sec.., Determine (i) Characteristics impedence (ii) Attenuation constant

Last Answer : A telephone cable has following primary constants per loop kilometer ,R=30Ω, L=20mH,C=0.06µF,G=0.If the applied signal has an angular frequency of 5000 rad/sec.., Determine (i) Characteristics impedence (ii) Attenuation constant