EXPERIMENT NO.5

Analysis of Parabolic Reflector

 Time ( min) Content Learning Aid / Methodology Faculty Approach Typical Student Activity Skill / Competency Developed 10 Relevance and significance of experiment Chalk & Talk , Presentation Introduces, Facilitates, Monitors Listens, Participates, Discusses Knowledge, Communication, intrapersonal 20 Explanation of experiment Chalk & Talk , Presentation Introduces, Facilitates, Explains Listens Knowledge, Communication, intrapersonal, Application 60 Reading Demonstration Explains, Monitors Participates, Discusses comprehension, Hands on experiment 20 Calculations N/A Explains, Monitors Participates, Discusses Knowledge, Communication, Intrapersonal, Application 10 Results and conclusions Keywords Lists, Facilitates Listens, Participates, Discusses Knowledge, Communication, intrapersonal, Comprehension

Practical Session Plan

Title: Analysis of Parabolic Reflector

Objectives: Mount and set up the connections of Parabolic Reflector antenna to analyze the performance parameters

Aim:

1) To sketch the radiation pattern of Parabolic Reflector antenna

2) To compute gain ,beam width ,return loss & impedance of Parabolic Reflector antenna

Apparatus: Antenna Trainer Kit, Half Wavelength Dipole antenna, Directional Coupler, coaxial connectors.

Theory:

1) Basic type of antenna: Reflector antenna

2) Theoretical Information:

A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish. The main advantage of a parabolic antenna is that it has high directivity. It functions similarly to a searchlight or flashlight reflector to direct the radio waves in a narrow beam, or receive radio waves from one particular direction only.

Parabolic antennas have some of the highest gains, that is they can produce the narrowest beam width, of any antenna type. In order to achieve narrow beamwidths, the parabolic reflector must be much larger than the wavelength of the radio waves used, so parabolic antennas are used in the high frequency part of the radio spectrum, at UHF and microwave (SHF) frequencies, at which the wavelengths are small enough that conveniently-sized reflectors can be used.

Fig.1: Parabolic Reflector

Parabolic antennas are used as high-gain antennas for point-to-point communications, in applications such as microwave relay links that carry telephone and television signals between nearby cities, wireless WAN/LAN links for data communications, satellite communications and spacecraft communication antennas. They are also used in radio telescopes.

The other large use of parabolic antennas is for radar antennas, in which there is a need to transmit a narrow beam of radio waves to locate objects like ships, airplanes, and guided missiles.

Procedure

1) Mount the Parabolic Reflector antenna on receiver stand of antenna trainer kit; connect a coaxial cable between antenna and input section of transreceiver meter.

2) Mount Half wavelength dipole antenna on stand of transmitter stand of antenna trainer kit, connect a coaxial cable between antenna and output section of transreceiver meter.

3) Apply a frequency of 1250 MHz (1.25 GHz) to transmitter antenna by varying knob on transreceiver meter.

5) Rotate the receiver antenna mount with an increment of 5 degree and take respective readings.

7) To find VSWR of antenna connect the coaxial cable from antenna under test to input terminal of directional coupler,

8) Output terminal of directional coupler is connected to input terminal of transreceiver meter, and common terminal is connected to input terminal of transreceiver meter.

9) Press VSWR button on transreceiver meter you get value of Vi (incident Voltage).

10) Now reverse the direction of input & output of directional coupler and press VSWR button you get value of Vr (Reflected voltage) & VSWR.

Observations:

The observation table of reading obtained is,

 Angle (Degree) Field Strength Angle (Degree) Field Strength Angle (Degree) Field Strength 0 130 260 5 135 265 10 140 270 15 145 275 20 150 280 25 155 285 30 160 290 35 165 295 40 170 300 45 175 305 50 180 310 55 185 315 60 190 320 65 195 325 70 200 330 75 205 335 80 210 340 85 215 345 90 220 350 95 225 355 100 230 105 235 110 240 115 245 120 250 125 255

By observing the radiation pattern of antenna & obtained readings, we have value of maximum & minimum reading, value of Vi & V r, with these data we have to calculate antenna parameter as:

Calculations:

1) VSWR = Vi / Vr =

2) Front to Back ratio = maximum reading / minimum reading =

3) Return Loss = (VSWR-1) / (VSWR+1) =

4) Gain of antenna = ( Maximum reading of AUT â€“ Maximum reading of dipole antenna) +7=

5) Beam width can be calculated by observing 2D radiation pattern.

HPBW =

FNBW =

Result:

1) VSWR =

2) Front to Back ratio =

3) Return Loss =

4) Gain of antenna =

5) HPBW =

FNBW =

Conclusion: The parabolic reflector antenna was analyzed on antenna trainer kit. Field Strength of various angle were obtained and radiation pattern were plotted for same: highly directional having maximum lobe in one direction.

Upon completion of experiment students will be able to:

Students will able to demonstrate the radiation pattern of the Parabolic Reflector antenna, compute the performance parameters practically and compare the performance parameters with the standard parameters

Oral Question Bank

Theory Question Bank

 Q. No Description 1 Explain parabolic reflector antenna. 2 What are the different types of parabolic reflectors? 3 What are factors affecting parabolic reflector antenna gain 4 Parabolic reflectors are generally used for which frequency range? 5 List the formulae for a) First null beam width b) HPBW c) Directivity Of parabolic reflector 6 List different feeds used for parabolic reflector. 7 What is the advantage of cassegrain feed? 8 What is the main advantage of parabolic reflector antenna? 9 Draw the radiation pattern for parabolic reflector antenna?