DESIGN AND CONSTRUCTION OF A HYBRID BROADBAND ANTENNA
1SUNDAY, A.A; * EKPO, S.C; 2UDOANYA, E. O;
3WARA, S. T and 4OROVWODE, H.E
1,2 Department of Electrical and Electronics Engineering
University of Uyo, Uyo, Akwa Ibom state,
3,4 Department of Electrical / Electronics & Computer Engineering
IgbinedionUniversity, Okada,EdoState
Nigeria.
ABSTRACT
A hybrid (UHF/VHF) broadband antenna for various intelligence detections has been designed and constructed. This design has an inherent mechanical amplifier system that obviates the use of electronic amplifiers. The array gives a gain of about 20dB in the condition while the stacking technology7 employed in the UHF/VHF antenna returned a gain increase of about 3dB.
METHODOLOGY
The problem of providing an antenna at the high frequencies in use today is not as easily solved and required careful consideration of all the influencing factors.3As the frequency is increased the effects of diffraction around objects diminish, creating electrical shadows – barriers to the propagation of radio – frequency energy. The antenna dimensions can no longer be chosen arbitrarily but must be part of a systematic engineering design.3
VHF (30 – 300MHz) and UHF (300MHz – 3GHz) frequencies are usedprimarily for line-of-sight communications.6 thesefrequencies are typically used for local area and point-to-point communications. Useable
propagation range is usually limited to the radio horizon.4
Several antenna parameters (polar diagram, beam width, bandwidth and impedance) of interest contribute to a design specification.1 The mechanical specification of the antenna also contributes, such as its size, weight, shape and material.1 The design of a broadband antenna relies in part on the concept of a frequency – independent antenna.6 Broadband antennas are of the helical, biconical, spiral and log-Periodic types.6
DESIGN AND CONSTRUCTION
The most suitable antenna array system going by the radio frequency distribution2 systems requirements and attendant goals of the applications1-4 is the Log-Periodic Antenna (LPDA).
The design of an LPDA begins with the lowest frequency of the operating range and required gain. The length and spacing relationships are governed by a formula that incorporates a design ratio factor r, along with dipole length I and spacing d:5
r= I2/I1 = d3/d2 = … = In/In-2………1Where I1= גּ/2 is the length of the longest element and In must be shorter than the length for the upper and of the band.
r= d2 /d1 d3/d2 = … = dn-1/In-2………2
where d1 is the distance between I1 and I2. d1 is between 0.07גּ and 0.09גּ for the lowest frequency, andr is between 0.7 and 0.98 (with corresponding gains of 12dB to 7dB).5 The design ratio fixed the number of elements and the overall size of the antenna.5, 6
For this presentation, the parameters chosen are shown in table 1.0
CALCULATION
*Length of element
Upper useable frequency, fu = 890MHz
Lower useable frequency, fL = 170MHz
Speed useable light,
c = 300 x 106m/s
TABLE 1.0 DESIGN PARAMETERS FOR A HYBRID BROADBAND ANTENNA
Antenna type / UHF/VHFArray technology / LPDA
Design ratio factor, r / O.75
Spacing between elements, d / 0.09גּ
Length of longest elements, I1 / גּ/2
Frequency range / 170MHz – 890MHz
Bandwidth / 5.0
Centre-design frequency / 530 MHz
Reflector length / I1/ r
Director(s) / rIn *
Number of elements / 7
Directivity / 20dB
Channel range / 7 – 83
Fringe length / 5%In
This is the shortest length of element and there can be one or more directors.6
Upper useable wavelength, גּu = c/fu = 300/890 = 0.3370m
Lower useable wavelength, גּL = c/fu = 300/170 =
Longest element I1 = 1.765/2 = 0.8825m = 88.25cm
I2 = rI1 = 0.75 (88.25) = 66.19cm
I3 = 0.75I2 = 49.64cm
I4 = 0.75I3 = 37.23cm
I5 = 0.75I4 = 27.92cm
I6 = 0.75I5 = 20.94cm
I7 = 0.75I6 = 15.71cm
Reflector, I0 = I1/r = 88.25 =
0.75
117.67cm
Director I8 = 0.75I7 = 11.78cm
* Distance between elements
d = 0.09גּL
d1 = 0.09 (1.7650) = 0.1589m = 15.89cm
d2 = rd1 = 0.75 (15.89) = 11.92cm
d3 0.75d2 = 8.94cm
d4 0.75d3 = 6.70cm
d5 0.75d4 = 5.03cm
d6 0.75d5 = 3.77cm
d4 d1/0.75 = 21.19cm
TESTS AND RESULTS
The array system was deployed (both indoors and outdoors) and appropriate local stations detected.
Two receivers were utilized such that two different stations could be watched simultaneously.
The results of the actual simulated test conditions show that
*The LPDA technology enhances multi-channel capability with optimal audio and video qualities.
*Without electronic amplifier system, the array antenna gives a high gain of about 20dB while whit stacking technology employed; the gain is boosted by about 3dB.
* A 300Ώ twin cable terminated in a 75Ώ-800Ώ balun meets the transmission lie requirement.
*Radiation pattern of the LPDA array is as shown in figure 1 while the Log - periodic dipole array is shown in figure 2.
DISCUSSION:
The LPDA array has all its elements resonating over the entire spectrum with overlaps of the radiation patterns of the elements in the direction of maximum radiation. A gain margin of 20dB is optimum for all RF responses in electronic systems.
CONCLUSION
The hybrid (HUF/VHF) broadband antenna employing LPDA technology offers better bandwidth and gain responses besides multi-channel reception.
COST:
The manual production of a single hybrid broadband antenna employing the LPDA technology costs N4, 000.00(as at the year 2003)
COMPARATIVE COSTS FOR OTHER BRANDS(massly produced)
1.Sonnet -N2, 400.00
2.Antenna TV-N1, 500.00
3.Binatone-N3, 200.00
REFERENCES:
1.Dunlop, J. and Smith, D. G. (1998) “Telecommunications Engineering”, 3rd., Stanley Thornes (Publishers) Ltd, Cheltenham.
2.Mantner, L. (1952), “Multiple TV Antenna Coupler”, IN: Electronics for Communications Engineers; Marks, J. and Zeluff, V., Eds. McGraw-Hill, Toronto
3.Rhodes, R.D. (1952), “Flush-mounted Antenna for Mobile Application”, In: Electronics for Communication Engineers: Markus, J. and Zehuff, V. eds. McGraw-Hill Company, Toronto
Note: All correspondence be sent to Orovwode Hope .E/S.T. WARA
E-mail: /
4.Roddy, D. and Coolen, J. (1997). Electronic). Electronic Communications, 4th ed., Prentice-Hall New Delhi.
5.Schweber, W. (1996) Electronic Communication Systems – a complete course, 2nd ed., Prentice – Hall, New Jersay.
6.Whitaker, J. C. (1996) The Electronics Handbook, IEEE Press and CRC Press, Oregon