Design of Pyramidal Horn Antenna With Frequency 3 GHz and Gain 3 dB Siti Sahhiada Ashikin Binti Mohd Yasim B020910031 Faculty of Electronics and Computer Engineering , Technical University of Malaysia Melaka
[email protected] The purpose of this technical report is to present the Abstract — — The pyramidal horn antenna.This paper also discuss the calculation of horn antenna and the performance of antenna using simulation program CST ( Computer Simulation Technology) Horn antenna have very little loss so the directivity of this antenna is roughly equal to the gain
Index Terms – Pyramidal horn antenna , frequency is 3
GHz and gain is 13 dB, directivity
I.
INTRODUCTION
This report is covered how to design Pyramidal Horn Antenna based on gain and frequency selected. The objectives of this paper are :
To explore the operational principle of the pyramidal horn antenna To design a pyramidal horn antenna based on specification specification given which including calculation and simulation To measure the antenna radiation pattern, gain, directivity by simulation using CST software.
[1] Horn antenna is the most simplest and probably used. It widely used as a feed element for large radio astronomy, satellite, tracking and communication dishes found installed throughout the world. There are three basic types of horn antenna , E- plane sectoral horn ( flared in the direction of the E-plane only ) , H- plane sectoral horn ( flared in the direction of the H-plane only) and pyramidal horn antenna ( flared in both E-plane and H-plane).The horn antenna is mounted on a waveguide that is almost always excited in single mode operation. The waveguide is operated at frequency which is above the cutoff frequency of the TM 10 but below the cutoff frequency of the next highest mode
Figure 1 : (a) E-plane (b) H-plane (c) pyramidal sectoral II.
DESIGN AND CALCULATION
a. Design of rectangular waveguide waveguide
[2] In a rectangular waveguide, radio waves can propagate in many different modes. For this antenna design, dominant mode is has lower attenuation and its electric field is vertically polarized. In order to design the waveguide, firstly must calculate the cut- off frequency ( f C C) for the dominant mode of propagation. Value of a and b is assumed value in order to get the right cut-off frequency.
2
m n f c 2 a b 1
1
2
Unit Hertz (Hz)
Permeability ( ) = 1.2566x10 -6Henries/meter Permittivity ( ) =8.8541x10-12 Farad/meter
= 3.1415 a = 6cm , b = 3cm And the rules is ( a>b)
For dominant mode TM 10, m=1 and n=0 Formula for cut-off frequency after simplify according to the
dominant mode.
f c
1 2a
Unit Hertz (Hz)
Figure 2 :Designed Rectangular waveguide b. Design of the 3GHz Horn Antenna Antenna Aperture
A horn will be optimum when the aperture dimension are adjusted to give maximum gain for the slant length in the E and H planes.
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For the directivity of the horn antenna can defined in terms of directivity of E-plane and H-plane sectoral horn : Calculate value of A and B
a A 1 Figure 3 : Cross section of waveguide, cut in the E-plane
b 50 B 1 e
50
h
Find the value of GE and GH by using the value of A and B
GE
32
GH
32
A The directivity of the pyramidal horn ( D p ) can be written in
B
terms of the directivities of the E-plane and H-plane sectoral horns
G G E H D p 32 50 50 e h
Figure 4 : Cross section of pyramidal horn, cut in the H-plane In order to design the horn, the value is calculated by following the equation.
Result of calculation
Wavelength ,
c
c(speed of light in vacum) = 3x10 8
f
f (operating frequency) = 10GHz
Gain of antenna,
10 Go ( Go ( dB)
= 0.1
accurate 1.1384 cm
X(trial) = 1.266856cm
e =11.384 cm
=14.0983 cm h
a =20.565695 cm
b = 15.08907 cm
D p = 14.99 dBi
1
1
Determine value of X,
trial
p = p e =6.83102 cm h
G (unitless ) 0 2 2
III.
SIMULATION
a. Horn antenna design
For e and h
e x(trial )
2 0 1 h 3 8
G
For a1 and b1
a 1
3 h
b 1
For Pe and Ph
2 e 1 Pe b b 1 b 4 1
1 2
2 e
2 1 h p a a 1 h a 4 1
1 2
Figure 5 : View of Pyramidal Horn Antenna Design (aPerspective, b-Front, c-Back, d-Left, e-Right, f-Top, gBottom)
2
b. Return Loss
Figure 6 : Return loss of the pyramidal antenna Simulation frequency = 2.8244 GHz , Simulation Return Loss = -19.91 dB
Phi = 0 is 38.0 degree , Phi = 90 is 33.9 degree Figure 8 : HPBW of the radiation pattern
c. Bandwidth
FNBW for phi = 90 is 6 6 degree Bandwidth = 0.2577GHz Figure 7 : Return loss of the pyramidal antenna
Figure 9 : FNBW of the radiation pattern e.
Gain and Directivity
d. Radiation pattern
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Figure 10 : Gain and directivity The simulated gain = 12.96 dB, The simulated directivity = 12.99dBi
IV.
RESULT ANALYSIS AND DISCUSSION
[3] A horn antenna with the horn in the shape of a foursided pyramid, with a rectangular cross section. They are the most widely used type, used with rectangular waveguides, and radiate linearly polarized radio waves. The gain of a horn is usually very close to its directivity because the radiation efficiency is very good (low losses). The from simulation is 12.96 dB and while the corresponding gain is 13 dB. The gain of an antenna in a given direction is the amount of energy radiated in that direction compared to the energy an isotropic antenna would radiate in the same direction when driven with the same input power Directivity is the ability of an antenna to focus energy in a particular direction when transmitting, or to receive energy better from a particular direction when receiving. The calculated directivity is 1.499 dBi and the measurement is 12.99 dBi. It show that the calculated have higher than measurement.. The bandwidth of an antenna refers to the range of frequencies over which the antenna can operate correctly. From simulation, the bandwidth that obtain is 0.417 GHZ. The greater the bandwidth, more accurate result that obtain for horn antenna.
A null is a zone in which the effective radiated power is at a minimum. A null often has a narrow directivity angle compared to that of the main beam. An antenna's beamwidth is usually understood to mean the half-power beamwidth. The peak radiation intensity is found and then the points on either side of the peak which represent half the power of the peak intensity are located. The angular distance between the half power points is defined as the beamwidth. Half the power expressed in decibels is — 3dB, so the half power beamwidth is sometimes referred to as the 3dB. HPBW for phi = 0 is 38.0 degree while for phi = 90 is 33.9 degree. FNBW is taken from the major lobe of the radiation pattern which is equal to 66 degree. V.
CONCLUSION
Horn are the versatile microwave antenna and easy to design and build with predictable performance. They should be the antenna choice for all but the highest gain application. The gain of horn antenna is often increased , while the beamwidth decrease as the frequency of operation in increased. This happens because the size of the horn aperture is always measured in wavelengths where at higher frequencies the horn antenna is "electrically larger" and this is because a higher frequency has a smaller wavelength. REFERENCES
[1]
Constantine A. Balanis, Antenna Theory Analysis & Design. 3 rd editions John Wiley & Sons.
[2]
http://smartech.gatech.edu/jspui/bitstream/ 1853/34414/1/PG_TR_040813_YL.pdf
[4] The return loss is another way of expressing mismatch. It is a logarithmic ratio measured in dB that compares the power reflected by the antenna to the power that is fed into the antenna from the transmission line .The return loss from the simulation is below than -10dB which is -19.874689 dB . [5]The radiation pattern of the horn antenna is similar to the theoretical pattern. The radiation pattern of a horn antenna will depend on B and A value (the dimensions of the horn at the opening) and (the length of the horn, which also affects
[3]
http://en.wikipedia.org/wiki/Horn_antenna
[4]
http://wireless.ictp.it/handbook/C4.pdf
[5]
http://www.antennatheory.com/antennas/aperture/horn.php
[6]
http://www.ece.msstate.edu/~donohoe/ ece4990notes12.pdf
[7]
http://www.qsl.net/n1bwt/chap2.pdf
the flare angles of the horn), along with b and a (the dimensions of the waveguide). The pattern consists of a main lobe with many side lobes adjacent to it. Minor lobes usually represent radiation in undesired directions, and they should be minimized, the peaks are referred to as sidelobes
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