1. VLF LF MF and HF ANTENNAS
CLASSIFICATION ACCORDING TO
FREQUENCY BANDS

2. VLF/LF Antennas and Antenna Systems

3. VLF Band EM waves penetrate well into the sea water.
(Communications with submerged submarines)
Low atmospheric attenuation.
Appropriate for long range communication.

4. VLF Antennas Ground and Sky waves Frequeny range: 3-30 KHz
Antennas : very large
Power: kW levels and even more

5. Some Problems Associated with VLF Antenna Systems
Small Bandwidth (usually less than 200 Hz)
Small radiation resistance.
High cost.
Antenna system covers a large area.
Need for very high power levels for transmission.

6. LF Antennas Ground and Sky waves Frequeny range: 30-300 KHz
Antennas: large
Power: kW levels and even more

7. Some Disadvantages High cost Large Dimensions
Trouble with efficiency, power capacity, bandwidth

8. VLF and LF antennas are “electrically small” antennas :
problem: high capacitive reactance and small antenna radiation resistance
remedy: top loading

9. Top-loading Top-loading
increases gain bandwidth (by decreasing reactance)
In VLF large top-loading
supported by towers

10. A simple VLF/LF Transmitting Antenna

11. VLF / LF Ground Systems Radial-wire: radial wires buried in the ground
Multiple-star:
small radial-wire systems forming a star topology

12. Basic Theory: The Vertical Electric Monopole Antenna

13. Vertical Electric Monopole Antenna
Assume uniform electric current I along a vertical monopole of
effective height he :
electric field
magnetic field

14. Vertical Electric Monopole Antenna -Radiated Power-
The vertical electric field in terms of radiated power is:

15. Vertical Electric Monopole Antenna -Equivalent Antenna Circuit-

16. Vertical Electric Monopole Antenna (Radiation Efficiency)
where
and
antenna total loss resistance
Effective power = (power capacity of the transmitter) x (antenna system efficiency)

17. Vertical Electric Monopole Antenna -Antenna Bandwidth-
The 3 dB bandwidth b in (c/s) for a single resonant circuit is:
f : resonant frequency
Q: the circuit reactance resistance ratio X/R0
R0: Total series resistance

18. Multiple Tuned VLF Antennas
To have sufficiently large bandwidths:
Huge antenna systems must be built. or
Several small multiple-tuned elements must be be used.

19. Multiple Tuned VLF Antennas

20. Multiple Tuned VLF Antennas
Ground losses are reduced.
Radiation resistance and efficiency are increased.
Instead of one and vulnerable antenna, several and smaller elements can achieve the same bandwidth-efficiency product.
If one element is out of service, the others can still operate.
The effective ground loss with multiple-tuning will be less than for a single element.
Tuning and retuning the system is difficult.
each antenna has to be matched to the transmitter.

21. Triatic Type Antenna

22. Cutler, Maine Antenna Installation

23. Goliath Antenna

24. Goliath Antenna

25. References References for the photos & figures:
(1) “VLF Radio Engineering”, A. D. Watt, Perg. Press, 1967
(2) “High Power Very Low Frequency/Low Frequency Transmitting Antennas”, P Hansen, Military Communications Conf., MILCOM '90, Conference Record, 'A New Era' IEEE, 30Sept.-3Oct.1990 Pages: vol.3
(3) Technology Conference, 1991.IMTC-91.Conference Record. ,8th IEEE , 14-16 May 1991 Pages:
(4) “Multiple Tuned VLF Antennas”, Manfred Schopp, IEEE Transactions on Broadcasting, Vol. 39, No.4, Dec
References for the photos & figures:
[1]
[2]

26. MF ANTENNAS & ANTENNA SYSTEMS
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27. INTRODUCTION
Usually: Vertical radiators operating in the MF band ( kHz).
The towers may be guyed or self-supporting.

28. APPLICATION AREAS AM Broadcasting Maritime Radio
Coast Guard Communication
Direction Finding

29. CHARACTERISTICS OF RADIATORS
Maximum radiation in the horizontal plane
Antennas taller than one-half wavelength have a minor lobe

30. Characteristics of the Radiators
Requirement for metallic ground plane to minimize losses
Vertical polarization is preferred due to superior propagation characteristics

31. Other features of the radiators
Shunt fed radiators
Top loaded radiators
Sectionalized radiators

32. Circuits for MF antenna systems
Antenna tuning units for matching purposes
Phase shifter networks for directional antenna systems
Power dividing networks

33. Ground Systems 120 buried (/4 length) copper wires
Extending radially outward
cm depth is sufficient
Individual ground systems are required for each tower of the array.
Copper-mesh ground system may also be used.

34. A typical ground system for a two-element directional antenna
Ground Systems
A typical ground system for a two-element directional antenna

35. HF Antennas & Antenna Systems

36. HF Antennas and Antenna Systems
Frequency Range: 3 to 30 MHz
( 10 to 100 meters; in wavelength)
For medium- and long- distance communications and broadcoasting

37. Characteristics of HF Antennas:
Signals are distorted as the ionosphere is neither regular nor smooth.
High powers and high antenna gains may be needed for communication.

38. Types of HF Antennas: Non-Resonant HF Antennas Long-wire Antenna
Vee Antenna
Rhombic Antenna
Resonant HF Antennas
Monopole Antenna
Dipoles and Slot Antennas
Loop Antennas
Log Periodic HF Antennas
Early Log-Periodic Antenna
Logarithmic Dipole Antenna
Directional HF Antennas
End-fire Arrays
Broadside Arrays
Circular Arrays

39. Non-Resonant HF Antennas:
wave propagates along the radiator in one direction only
remaining power is absorbed in a matched load
TYPES
Long-wire Antenna
Vee Antenna
Rhombic Antenna

40. Long-wire Antenna
A long terminated wire radiator
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41. Vee Antenna
Single mast (one wire radiator terminated in a resistive load
at the far end).
Radiation pattern exhibits large side lobes near the main beam.
The efficiency is low (almost half of the total input power may be exhausted in the matched load.
4/19/2017

42. Rhombic Antenna
4 radiating wires of equal length mounted on four masts
one of the wires are load-matched.
high directivity
the large rhombics are used for long-range communications.
4/19/2017

43. Resonant HF Antennas: Monopole Antenna Elevated-feed Monopole
Double-cone Monopole
Inverted-L and –T Antenna
Dipoles and Slot Antennas
Loop Antennas
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44. Monopole Antennas
Outside half-wave resonance, elevation pattern breaks up into main
lobes as input impedance becomes very high. Efficiency decreases
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45. Dipole Antennas

46. Loop Antennas
Usully used for reception and direction finding.

47. The Log-Periodic Antenna
Fed from the vertex.
Signal travells along the structure until reaches its resonant region.
The signal radiates from the resonant region

48. Directional HF Antennas:
End-fire Arrays
Horizontal Array of Dipoles
RCA Fishborne Antenna
Series Phase Array
Broadside Arrays
Broadside Dipole Array
Wide-Band Curtain Array
Circular Arrays

49. End-fire Arrays Higher directivity. Provide increased directivity in
elevation and azimuth planes.
Generally used for reception.
Impedance match difficulty in
high power transmissions.
Variants are:
Horizontal Array of Dipoles
RCA Fishborne Antenna
Series Phase Array

50. Broadside Arrays
Beam steering by phase variation is possible.

51. Circular Arrays Used for direction finding.
Consists of 30 – 100 elements, with equi-spaced and fed from a central source – goniometer.
Band-width seperation is possible:

52. References JASIK, H.: Antenna Engineering Handbook; Mc Graw Hill, 1961
Y.T., LEE S.W.: Antenna Handbook; Van Nostrand Reinhold, 1988.
RUDGE, A.W., MILNE K., OLVER A.D., KNIGHT P.: Handbook of Antenna Design (Volume 2); Peter Peregrinus, 1983.