Antenna System Laboratory is a very useful acquisition for any modern Electronics & Communications Laboratory. It can be used to practically demonstrate the basic principles of EM Theory.
Introduction:
What is an Antenna?
An antenna is a wire or a group of wires. It converts RF signals, generated by the transmitter, into electromagnetic waves for propagation through space. The receiving antenna receives these EM waves and reconverts them back into the original RF signals for further processing.
The antennas act like interfacing devices between a transmitter and space, and also between space and a receiver.
Thus, both transmitting and receiving antennas have entirely different functions to perform. But they also behave identically (i, e), their behavior is reciprocal.
Any communication system is as good as the antenna it uses. It is completely self-contained for conducting all experiments.
Using ASL-1, the student can understand the basic principles of polarization, directivity, gain and impedance of various types of antennas, in a laboratory environment. In reality, an antenna is a very complex device, with distributed components like inductance, capacitance and resistance spreading all over its length and breath.
They also vary continuously all over its surface and their spread determines the polarization, gain and radiation pattern etc., of an antenna.
Thus, an antenna is an LCR network.
The student can verify them in the laboratory.
Each antenna has its own special features and applications. There is no one best antenna design for all purposes.
Only about 70 types of antenna seem to have been developed so far in the world. Today, 90% of all antennas are vertical, 5% horizontal and 5% other types.
Objectives of Experiments:
Description:
Antenna System Laboratory consists of thirty varieties of antennas fabricated in several shapes and sizes, depending upon the operating frequencies and applications.
a) Eight Stands,
b) One Adjustable TRIPOD,
c) A VHF transmitter (1.5 watts power) with a frequency of about 135-175MHz is supplied for exciting these antennas.
d) One tuned VHF field strength meter. (FSM)
e) One untuned VHF field strength meter. (FSM)
f) VHF Amplifier
g) DIP Meter
h) Voltage Standing Wave Ratio (VSWR) meter.
i) 10meters of coaxial cable, having 50-ohms impedance.
j) A set of ten cables.
k) A detailed instruction manual, for conducting experiments.
Compact Disc (CD):
Compact disc is supplied to understand the details of all thirty antennae. This is simulation software. This is optional requirement. A compact disc (CD), to understand details of all thirty antennas.
Description of the system:
The following antennas are supplied with the ASL-1. Using these antennas, it is possible to study the behavior of each of them for a given transmission and reception medium. The antenna is mounted on a revolving stand. This stand can be manually revolved on a horizontal axis in 3600 with reference to ground plane. It is possible to record and observe the response on a field strength meter (FSM). Using these readings it is possible to draw the POLAR diagram for various angular positions of antenna. Each antenna is a dynamic demonstrator by itself.
Types of antennae supplied are:
1. Vertically Polarized Antenna.
2. Horizontally Polarized Antenna.
3. Circularly Polarized Antenna.
4. Quarter Wave Antenna.
5. Grounded Vertical Antenna.
6. Vertical Half-Wave Dipole Antenna.
7. Horizontal Half-Wave Dipole Antenna.
8. Full Wave Dipole Antenna.
9. Yagi Antenna
A) Folded dipole
B) Folded dipole, with a reflector
C) Folded dipole, with reflector and three directors
10. A loop (frame) Antenna.
11. Quad Loop Antenna.
12. Circular Loop Antenna.
13. AD Cock Antenna.
14. Ferrite Rod Antenna.
15. Helical Antenna.
16. Rhombic Antenna.
17. Endfire Antenna.
18. Broadside Antenna.
19. Collinear Antenna.
20. Log-Periodic Antenna.
21. Top-loaded Antenna.
22. Spiral Antenna.
23. Biconical Antenna.
24. Dipole Antenna, with corner reflector.
25. Turnstile Antenna,
26. Super turnstile Antenna,
27. Batwing Antenna,
28. Discone Antenna,
29. Slot Antenna,
30. Flush Disc Antenna,
31. Cellular Antenna,
32. Pager Antenna,
33. FM Antenna,
34. Horn Antenna,
35. V-Antenna,
36. Active Antenna,
37. Transmission Lines and a probe.
VHF Transmitter: This is a hand-held, variable frequency (135MHz to 175MHz) with 1.5 Watts of VHF output. It can be used both in the field and laboratory environments. It uses a re-chargeable battery. Any ?LOW? battery status is indicated, for recharging.
This PLL synthesized digital transmitter has a 4-digit frequency counter, with a 100 KHz resolution.
Its frequency can be varied by both SLOW/FAST controls. It can be modulated externally using a condenser microphone.
Tuned VHF Field Strength meter: This measures RF level of each received signal in mV, (between 1dB to 100dB) in steps of 1dB. This is also battery operated. Convenient for field/laboratory uses.
Tripod: This is used to mount transmitter antenna. This is fixed on a stand, whose height can be varied upto 2 Meters.
Software: This is an optional requirement. Using this simulated software, it is possible to plot radiation patterns on the computer.
What can a student learn? Using this trainer: The following are the objectives. After performing the following listed experiments the student learns
a. The evolution of antenna
b. Understand the current and voltage distributions along its entire length of transmission line and find its characteristic impedance.
c. Measure voltage and current distributions along the length and breadth of antenna.
d. Prepare a perfect earthing system, (an earth mat) or a simulated ground.
e. Understand types of polarization (vertical, horizontal and circular)
f. Understanding the field strength, radiation pattern, power gain and impedance of antennas.
g. Design a half wave dipole for a given frequency.
h. Understand the effect of perfect ground as a reflector.
i. Understand the principle of reciprocity.
j. Understand the principle of directional antennas, for navigational purposes.
k. Understand the effect of reflector and each director in a Yagi Antenna, in terms of gain and radiation pattern.
l. Determine the right type of BALUN.
m. Design at least ten types of antennas and construct them.
List of Experiments:
1) Determination of plane of polarization
2) Measurement of gain
3) Drawing of radiation pattern
4) Calculation of impedance.
