10 Kent Ridge Crescent, Singapore, 119620. 1. Introduction. Phased array antennas have found an increased application in radar and, more recently, in satellite ...
A High Performance Phased Antenna Array Design and Analysis using Fast Algorithm Tao Yuan, Le-Wei Li, Jian-Ying Li, Ning Yuan, Mook-Seng Leong Department of Electrical and Computer Engineering National University of Singapore at Singapore 10 Kent Ridge Crescent, Singapore, 119620
1. Introduction Phased array antennas have found an increased application in radar and, more recently, in satellite and cellular communications. The most recent application concerns smart antennas in cellular base stations. Despite increased popularity, the design and development of a planar phased array antenna remains a challenging task. In this paper, a high preference phased antenna array is designed. Compared with the traditional one, this type antenna array has a lower sidelobe characteristic. The sidelobe lever is reduced by using the taper structure. For different scanning angle, the comparison between calculated and measured results is in general very good agreement. Moreover, the precorrected fast Fourier transform (P-FFT) method is employed to accelerate the entire computational process to reduce significantly both the memory requirement and computational time for large arrays. Very good agreement has been obtained between calculated and measured performance of such arrays. Calculated results of radiation patterns return loss, and gain of the arrays are
shown and the experimental results show reasonable agreement with the theory and simulation.
2. Design Procedure A. Series-fed taper antenna array design The seven-element series-fed taper microstrip antenna array is shown in Fig. 1(a), which was used as the starting point of this work. The array is designed to resonate at 10GHz. The dielectric substrate of the microstrip array has a relative dielectric constant of 2.2 and thickness of 31mil. An array with a uniform excitation produces the narrowest possible beamwidth along with the highest sidelobe level. Sometimes it is necessary to reduce the sidelobes. High sidelobes can increase interference or result in spurious signal reception. Here the sidelobe level can be reduced by introducing a taper in the amplitudes of the elements [1]. When tapering the amplitude distribution, the excitation is highest at the center of the array and then decreases as one move toward the edge. If the array has
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an odd number of elements, then the center element has the largest excitation. For an even number, the two elements adjacent to the center share the largest excitation. With end-fed arrays, the elements nearest the feed couple only a small amount of power and therefore must be fairly narrow. The feed line must be small compared to the narrowest patch. In this case, a 80Ω line will be used. This is a 1.111mm wide line that is considerably smaller than the square patch width [2]. Two-dimensional arrays are designed as shown in Fig. 1(b) which is composed with eight single series-fed taper arrays. The element spacing is chosen as 2 / 3λ0 which can prevent grating lobes.
(a) (b) Fig. 1 (a) Configuration of single series-fed taper antenna array (b) Configuration of the 7x8 series-fed taper antenna arrays
B. Implementation of phased shift As shown in Fig. 2, RF signal is emitted by antennas through the feeding network and phase shifter. By adjusting the phase shifter, the radiation pattern (H-Plane) could be continuously steered over a range of angles and the beam-scanning function can be achieved. Antenna Phase shifter
RF Feed Network
High-power Source Fig. 2 Block diagram of the phased-array system
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3. Results and Analysis To be able to judge the performance of this 7x8 phased antenna arrays properly, the single seven-element series-fed taper antenna array is first designed and analyzed ( ε r = 2.2 , substrate thickness: h = 31mil ), as shown in Fig. 1 (a). The series-fed taper antenna array is designed as shown in Fig. 3. The detail geometric parameters are listed in Table I.
W1
W2
W3
W4
W5
W6
L1
L2
L3
L4
L5
L6
W0
Fig. 3 Configurations of the single antenna array
TABLE I Array
1
2
3
4
5
6
7
Width (mm)
4.8
6.55
8.385
10.35
8.385
6.55
4.8
Length (mm)
10.133
9.93
9.787
9.682
9.787
9.93
10.133
W (mm)
1.111
1.111
1.111
1.111
1.111
1.111
1.111
L (mm)
11.12
11.12
11.12
11.12
11.12
11.12
11.12
Fig. 4 shows the measured pattern when the phase shifters were adjusted to scan the beam to 0o (broadside), -7o, 11o, respectively. For E-plane, the radiation patterns are the same because of no shifted phase involved. From the Fig. 4, for shift angle, the comparison between calculated and measured results is in general very good agreement. 0
simulation measurement
-10
-20
-30
simulation measurement
-10
Radiation Pattern (dB)
Radiation Pattern (dB)
0
-40
-20
-30
-40
-50
-50 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
Angle (degree)
-60 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
Angle (degree)
(a) E-Plane (Scanning angle=0o)
(b) H-Plane (Scanning angle=0o)
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0
0
-10
Radiation Pattern (dB)
-10
Radiation Pattern (dB)
simulation measurement
simulation measurement
-20
-30
-40
-20
-30
-40
-50
-50
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
Angle (degree)
Angle (degree)
(c) H-Plane (Scanning angle=-7o) (d) H-Plane (Scanning angle=11o) Fig. 4 The radiation patterns of the antenna arrays in different scanning angles
4. Conclusion In this paper, a high preference phased antenna array is designed. Compared with the traditional one, this type antenna array has a lower sidelobe characteristic. The sidelobe lever is reduced by using the taper structure [3]. For different scanning angle, the comparison between calculated and measured results is in general very good agreement. Moreover, the precorrected fast Fourier transform (P-FFT) method is employed to accelerate the entire computational process to reduce significantly both the memory requirement and computational time for large arrays. Very good agreement has been obtained between calculated and measured performance of such arrays. Calculated results of radiation patterns
return loss, and gain of the arrays are shown and the experimental results show reasonable agreement with the theory and simulation.
References [1] Robert A. Sainati, “CAD of microstrip antennas for wireless applications”, Artech House, Boston. London, 1996. [2] Edwin K. L. Yeung, J. C. Beal, and Y. M. M. Antar, “ Multilayer microstrip structure analysis with matched load simulation,” IEEE Trans on Microwave Theory Tech., vol. 43. no. 1, pp. 143 –149, Jan., 1995. [3] David M. Pozar, Barry Kaufman, “Design considerations for low sidelobe microstrip arrays”, IEEE Trans on Antennas Propaga, vol. 38. no. 8, pp. 1176 –1185, Aug., 1990.
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