Horn Antenna Design Nurbaiti bt. Abd Aziz B020610143 Faculty of Electronic and Computer Engineering Universiti Teknikal Malaysia Melaka, Karung Berkunci No 1752, 76109 Durian Tunggal, Melaka
[email protected]
— This This paper presents the observation and Abstract — identification of aperture horn antenna of gain 20dB with 10GHz frequency and directivity of 22dB. The observations involve the gain, return loss and bandwidth of the antenna designed. Besides, the radiation pattern analyzed includes the major lobe, side lobe, directivity, HPBW and FNBW of the aperture horn antenna. Horn Antenna, gain, return loss, bandwidth, radiation Index — Horn pattern, directivity, HPBW, FNBW
II. CALCULATION There are 3 parameters that has been set to design the aperture horn antenna; Gain = 20dB, Frequency =10GHz, Directivity=22dB. The value of a and b of the waveguide part of the horn antenna are 6cm and 3cm respectively. The wavelength; c
I. INTRODUCTION
A
horn antenna is used for the transmission and reception of microwave signals. It derives its name from the characteristic flared appearance. The flared portion can be square, rectangular, or conical. The maximum radiation and response corresponds with the axis of the horn. In this respect, the antenna resembles an acoustic horn. It is usually fed with a waveguide.
0.03 m
f
Resonance Frequency; 2
c
f r
2
a
Value of b
2
Figure 1: Horn Antenna
is found using equation; 2
2
2
Go
1
3
2
e
h
;
e
0.1702
h
0.2132
a1
3
h
0.1385
b1
2
e
0.1011 2
1
a
2
pe
b1
b
ph
a1
a
Go
2
8
3
1
e
1
b1
4 2
Horn antennas are used all by themselves in short-range radar systems, particularly those used by law-enforcement personnel to measure the speeds of approaching or retreating vehicles.
5.5902GHz
b
Go
2
6
3
1
1
From the calculation obtained; x= 5.673
In order to function properly, a horn antenna must be a certain minimum size relative to the wavelength of the incoming or outgoing electromagnetic field. If the horn is too small or the wavelength is too large (the frequency is too low), the antenna will not work efficiently. Horn antennas are commonly used as the active element in a dish antenna. The horn is pointed toward the center of the dish reflector. The use of a horn, rather than a dipole antenna or any other type of antenna, at the focal point of the dish minimizes loss of energy (leakage) around the edges of the dish reflector. It also minimizes the response of the antenna to unwanted signals not in the favored direction of the dish.
2
2
0.11427 1
h
1
a1
4
1
2
0.11429
Pe and Ph must be equal for a pyramidal horn to be physically
realizable.
A
a1
D. HPBW & FNBW
50
12.24746
h
B
b1
50
9.99995
e
G E G H D p
32
B
32
101.8587
A 124.7516 G E G H
32
G E G H
50
50
e
h
10.1859
158.418 10 log158.418
50
50
e
h
21.9980dB
III. SIMULATION
Figure 5: Radiation Pattern in Polar View
A. Return Loss
FNBW = 135o; HPBW= 16.2o E. Gain
Figure 2: Return Loss of Horn Antenna
S11 = -30.167dB at frequency 9.61GHz. B. Radiation Pattern
F. Directivity
Figure 3: Radiation Pattern in 3D
C. Bandwidth
For this design, bandwidth is referring to the difference between upper and lower cut-off frequency at -10 dB because the transmitted power is assumed to be 90% of the received power. Bandwidth for this horn design is assumed to be more than 10GHz.
Directivity in dB= 19.46+2.7= 22.16dB
IV. DISCUSSION 1.
10. The waveguide length is assumed based on the value must be less than the assumed value of a which is 6cm for this design.
Simulation of the designed aperture horn antenna is done using CST Microwave Studio.
V. CONCLUSION 2.
In terms of return loss, the horn antenna produced return loss S 11 of -30.167dB , drop at frequency 9.61GHz which is close to the set value of frequency; 10GHz.
3.
The bandwidth of the antenna is the difference between upper and lower cut off frequency at -10dB, for this designed, the S-parameter Magnitude doesn‟t shows at range -10dB, by that, bandwidth is assumed to be more than 10GHz for this horn antenna.
4.
As the return loss drop at frequency 9.61GHz, the gain obtained at the frequency is 19.40dB, compared to gain at 10GHz is 19. From the simulation of the designed horn, the value of gain obtained is 19.40dB which is slightly different to the theoretical gain, 20dB.
The horn antenna is designed with measurement a=6cm and b=3cm, waveguide length is 11.43cm. With reference value chose for directivity 22dB, gain 20dB and frequency 10GHz, the return loss for this antenna is lower than -10dB which is -30.167dB. This antenna can perform at frequency 9.61GHz and radiates well according to radiation pattern obtained. The horn antenna is a particularly useful form of antenna for use with RF microwave applications and waveguide feeder. Although it is not used below RF microwave frequencies because waveguides are not used at low frequencies as a result of the sizes needed, the horn antenna is nevertheless a very useful form of RF antenna design for use at high frequencies.
REFERENCES 5.
6.
7.
The directivity of the antenna observed is 19.46dBi. As converted in dB, the directivity is 22.16dB which is slight different from the set value of 22dB directivity.
[1] [2] [3]
From the observation of the radiation pattern of the designed horn antenna, there are major lobe and side lobes. Major lobe is the maximum lobe in radiation pattern which is intended to be along the forward axis and which gives effect of a beam while the side lobe is a radiation lobe in any direction other than main beam.
[4]
Full null beam width (FNBW) is the angle between two vectors, originating at the pattern‟s origin and tangent to the main beam at its base.. Half power beam width (HPBW) is angle between two vectors, originating at the pattern‟s origin an d passing through these points of the major lobe where the radiation intensity is half its maximum. For this antenna, the FNBW is 135o and HPBW obtained is 16.2 o.
[7]
8.
Theoretically, HPBW is FNBW/2, but for this design, the FNBW/2 is 67.5 o, a large different compared to the simulated result which is 16.2 o.
9.
There are slight different of directivity, gain and frequency obtained from the designed antenna compared to the calculation value. The HPBW simulated also different to the theoretical value. This might be due to assumption of value a and b and the waveguide length also is an assumption value. Besides, the return loss drops at 9.61GHz instead of 10GHz.
[5] [6]
[8]
[9]
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[10] M. Kanda, “The Effects of Resistive Loading of „TEM‟ Horns,”
IEEE Transactions on Electromagnetic Compatibility, EMC 24,2, May 1982, pp. 245-255. [11] R. J. Wohlers, “The GWIA, An Extremely Wide Banawidth Low-Dispersion Antenna,” Calspan Corp., Buffalo, NY, Tech. Rep., 1971. [12] R. T. Lee and G. S. Smith, “On the Characteristic Impedance of the TEM Horn Antenna,” March 2004, to he published in IEEE Transactions on Antennas and Propagation.
