Shun Yao, Xueli Liu, John Gibson and Stavros V. Georgakopoulos. Department of Electrical and Computer Engineering. Florida International University. Miami ...
Deployable Origami Yagi Loop Antenna Shun Yao, Xueli Liu, John Gibson and Stavros V. Georgakopoulos Department of Electrical and Computer Engineering Florida International University Miami, FL 33174 Abstract—A Yagi loop antenna, which is built on an origami spring structure, is presented here. The Yagi loop array can be compressed to 5 cm length by a servo motor which can reduce nearly 70% of the volume of the array. The antenna’s body is 20.5 cm long when it is expanded to the working state. The physical parameters of the antenna such as loop’s radius and distances between loops are analyzed. The antenna is designed to work at 1.31 GHz. A directional realized gain of 10.4 dBi is observed. The measurements agree well with the designed simulation model.
I.
m0
+ ∑ yi 2 n v2 cos nφ .
In this paper, a Yagi loop antenna is built based on an origami spring base made out of paper. The antenna can achieve a high gain (>10 dBi) and high front-to-back ratio. The whole length of the array can be controlled by a servo gripper. ORIGAMI YAGI ANTENNA DESIGN
For a Yagi loop array where the second loop is the only excited one, the resulting loop currents, the input admittance Y2, the radiation patterns, and the forward and backward directivities Gd and Gr, are given by [3]:
978-1-4799-7815-1/15/$31.00 ©2015 IEEE
(1)
n =0
Y2 = I 2 / V2 .
(2)
⎡ Eθ ⎤ ⎡cos θ ⎤ N η0 = − − exp jkr [ ] ⎢E ⎥ ⎢ 1 ⎥ ∑ kbi 4r ⎣ ⎦ i =1 ⎣ φ⎦
INTRODUCTION
Yagi antenna arrays have been widely used in fields of longdistance radio communications and point-to-point communications because of the high gain and simple structure. The properties of Yagi loop arrays have been studied by several investigators [1]-[3]. The antenna designers are able to optimize the parameters of the Yagi loop array under the constraints of the antenna size, directivity or bandwidth. However, the Yagi arrays currently on the market that operate at the lower frequencies (under 10 GHz) are too bulky. While the directors enhance the antenna’s gain also increase the volume of the antenna. Folding/unfolding origami antennas can be used to minimize the size of antennas and provide reconfigurability [4]-[6]. In [6], an origami spring based antenna was designed, where every level of the spring is round and all the levels are parallel. The structure of the origami spring is suitable for designing Yagi loop antenna array. The big advantage of the origami spring is that the whole spring body can be controlled by applying pressure at any level.
II.
⎡ ni ⎤ I i (φ ) = Vi ⎢ ∑ 1/ Z ii n + jωCgi ⎥ cos nφ ⎣ n= m0 +1 ⎦
∞
⋅ exp ( jkdi1 cos θ ) ∑ j n I i n ⎡⎣ J n −1 ( xi ) ± J n +1 ( xi ) ⎤⎦ n =0
⎡ sin nφ ⎤ ⋅⎢ ⎥ ⎣cos nφ ⎦
Gd ,r =
(3)
πη0
2
N
4 [ Re Y2 ] V2
2
∑ kb exp ( ± jkd ) I i
i1
i
(4)
i =1
where k and η0 are the propagation constant and the characteristic impedance of free space, respectively. In these equations (yijn) is the inverse of the impedance matrix (Zijn), Cgi is the gap capacitance, xi = kbi · sinθ, and the subscripts d and r in the directivity equation refer to the forward and backward gains along the array axis, respectively. The edge shape of every spring level is regular dodecagon. The distance between the dodecagon center and the edges is defined by bi. The exciter in this design is a loop antenna. The circumference of the exciter approximately equals one wavelength at its the resonant frequency:
2π ⋅ b2 ≈ λ .
(5)
A 5-element array is used in this design as shown in Fig. 1. The radius of the reflector is b1 = 0.183 λ. The radii of the three directors are b3 = b4 = b5 = 0.142 λ. The distance between the reflector and exciter is d12 = 0.2 λ. The distance between the exciter and the first director is d23 = 0.18 λ. The distances between directors are d34 = d45 = d23. By adjusting the loop’s position on the origami spring base, we can have different loop radius, and also we can modify the distance between loops on adjacent levels. We used copper
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tape to build the antenna. The width of the copper tape is 4 mm, and the thickness is 0.1 mm. When the origami spring is unfolded, we have b1 = 40 mm, b2= 35 mm, b3 = b4 = b5 = 31 mm, as shown in Fig. 1 (b).
antenna fully expands. The antenna can be compressed to 5 cm long, which will save nearly 70% of the antenna volume. The return loss versus frequency is shown in Fig. 3. The measurements agree well with the simulation results at the operating frequency. The measured return loss is -17.4 dB at the operating frequency of 1.31 GHz. More properties of this antenna such as input impedance versus frequency, far field radiation patterns and front to back ratio will be presented at the conference.
(a)
(b) Fig. 1. The simulation model of Yagi origami loop antenna at: (a) folded state and (b) unfolded state. Usually, the impedance of the full wave single loop antenna is in the vicinity of 100 ohms. The value can be reduced when there are reflector and directors. When d12 = 43 mm, d23 = d34 = d45 = 40 mm, the input impedance is 64 + 0.7j ohms at 1.31 GHz. This means a 50 ohms transmission line can be used to excite the antenna. III.
Fig. 3.
IV.
CONCLUSION
A Yagi origami loop array is presented. The antenna has high directional gain and high front to back ratio, and can selffold into small volume which is suitable for applications on spaceborne structures and satellites. ACKNOWLEDGEMENT
ANTENNA CONSTRUCTION AND RESULTS
The graphs in Fig. 2 show the manufactured prototype of the Yagi origami loop antenna. The permittivity of the paper that is used to build the origami spring base is 2.2. A 50 ohms coaxial line is connected to the driven loop.
This work was supported by the National Science Foundation under Grant EFRI 1332348. REFERENCES [1]
[2]
[3]
[4]
(a)
Return loss of the Yagi loop array.
[5]
(b)
Fig. 2. The manufactured prototype of the Yagi origami loop antenna at: (a) unfolded state and (b) folded state.
[6]
A ferrite choke is around the coaxial cable, working as a balun. A PLA gripper was printed by a 3D printer to control the spring body. The spring body length is 20.5 cm when the
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J. E. Lindsay, “A parasitic end fire array of circular loop elements,” IEEE Trans. on Antennas and Propagation, vol. 15, pp. 697-698, July 1967. S. Ito, N. Inagaki and T. Sekiguchi, “An investigation of the array of circular-loop antennas,” IEEE Trans. on Antennas and Propagation, vol. 19, no. 4, pp. 469-476, July 1971. A. Shoamanesh and L. Shafai, “Properties of coaxial Yagi loop arrays,” IEEE Trans. on Antennas and Propagation, vol. 26, no. 4, pp. 547-550, July 1978. S. Yao, S. V. Georgakopoulos, B. Cook and M. M. Tentzeris, “A novel reconfigurable origami accordion antenna,” IEEE International Microwave Symposium, Tampa Bay, FL, June 1-6, 2014. X. Liu, S. Yao, S. V. Georgakopoulos, B. Cook and M. M. Tentzeris, “Reconfigurable helical antenna based on an arigami structure for wireless communication system,” IEEE International Microwave Symposium, Tampa Bay, FL, June 1-6, 2014. S. Yao, X. Liu, S. V. Georgakopoulos and M. M. Tentzeris, “A novel reconfigurable origami spring antenna,” IEEE International Symposium on Antennas and Propagation, pp. 374-375, TN, July 6-11, 2014
