Abstractâ This paper presents a miniaturized, light-weight, log- periodic dipole antenna fabricated with 3-D printing techniques. The antenna substrate is built of ...
A 3-D Printed Miniaturized Log-Periodic Dipole Antenna Ibrahim T. Nassar and Thomas M. Weller
Harvey Tsang
Center for Wireless and Microwave Information Systems, Department of Electrical Engineering University of South Florida Tampa, Florida, USA
Department of Electrical Engineering University of Texas El Paso El Paso, Texas, USA
In what follows, an illustration of the antenna design is presented (Section II) followed in Section III by experimental results and discussion.
Abstract— This paper presents a miniaturized, light-weight, logperiodic dipole antenna fabricated with 3-D printing techniques. The antenna substrate is built of Acrylonitrile Butadiene Styrene material using the fused deposition modeling process and then metalized through direct print additive manufacturing using Dupont CB-028 silver ink. The antenna weighs 1.8 g and has a measured gain > 4 dBi and front-to-back ratio > 20 dB over the 2.25-3.75 GHz range. Compared to the standard log-periodic dipole antenna, the size is reduced by 13% with minimal gain degradation.
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II.
Fig. 1 illustrates the 3-D printed LPDA. The antenna is designed using Ansys/HFSS 15 to cover the 2-4 GHz frequency range. The number of the elements (N) used in this work is 7 and the geometry ratio between the elements length, width, and spacing (K) is 0.8. The spacing factor (σ) is selected to be 0.15. The length and width of the longest dipole are 70 mm (~λ/2 at 2 GHz) and 4 mm, respectively, and the lengths and widths of the other elements are found using the log periodicity of the structure. The arms are meandered in the vertical (Z) direction and rotated symmetrically around the center feed line in a periodic manner going from one element to another. The meander is shaped with a sinusoidal curve A × sin (0.1×π×t), where A is 2.5 mm and t varies from 0 to L for the first element and to L/Kn for the nth element, and L is the length of the first element. The width of the first element, the spacing, and A are optimized to maximize the gain over the 2-4 GHz frequency range. The dipoles are series fed with a 2 mmwide parallel plate transmission line that was optimized for the best impedance match. To improve the impedance matching, a ~λ/25 (at fo of 2 GHz) shunt shorted stub is also added at the end of the feed line. For measurement purpose, a coaxial feed line is added, Fig. 1. The coaxial line is running over the lower plate of the feed line conductor, and the coaxial center pin is attached to the upper plate of the feed line printed on top. This feeding technique ensures balanced currents on the dipole arms [1].
INTRODUCTION
The log-periodic dipole antenna (LPDA) is a classical broadband design that finds use in numerous applications including radar signal detection and radio broadcasting [1]. Given its popularity, reducing the LPDA size and weight is of significant interest. Various techniques to minimize the element length can be employed such as the use of high permittivity material if the antenna is printed on a dielectric substrate, loading the dipoles with lumped reactive elements [2], and loading the dipoles with cylindrical covers [3]. The most commonly used approach, however, is meandering the dipole length in a planar form by the introduction of different shapes, such as the Koch-shaped lines [4], rectangular meandered lines [5], and algorithm-generated shapes [6]. In [4], the antenna achieves 12% size reduction, VSWR < 2.5 bandwidth of 43.8%, and gain degradation of only 0.3 dB compared to a standard design. In this paper, a light-weight LPDA fabricated with 3-D printing technology is presented (Fig. 1). The size, weight, and cost are kept low by using 3-D printing to shape the dipoles with smooth sinusoidal curves and to deposit the dielectric material only to support the conductive parts. Instead of meandering the dipole length in a planar form as is typically done, with the 3-D printing the meandering is enabled in the vertical direction providing more spatial optimization freedom and more effective exploitation of the available volume. The printed antenna weighs 1.8 g, measures 0.5 λ ×1.42 λ× 0.03 λ at fo of 2 GHz, and has a measured maximum gain of ~6.75 dBi. The design provides VSWR (< 2.5) bandwidth of 100% and 13% size reduction at the expense of only 0.5 dB gain degradation according to [7].
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ANTENNA DESIGN
The antenna substrate was fabricated using a Dimension SST 768 printer at the College of Engineering of the University of South Florida with the fused deposition modeling (FDM) process. The material used is Acrylonitrile Butadiene Styrene (ABSplus) which has a relative dielectric constant (εr) of ~2.4, loss tangent (tanδ) of ~0.0038, and a thickness of 60 mils. The antenna was then metalized with Dupont CB-028 through a 75ID/125OD ceramic tip, using an nScrypt 3D-450 machine using fiducial and conformal printing settings. While Dupont CB-028 ink has low conductivity (~2.1 × 105 S/m) when cured at 80 Co, herein we show that it is possible to achieve high gain antenna with this material.
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AP-S 2014
REFERENCES 70 mm [1]
D. Isbell, “Log periodic dipole arrays,” IRE Transactions on Antennas Propagation, vol. 8, no. 3, pp. 260–267, May 1960. [2] Y. Zhengguang, S. Donglin, and L. Shanwei, "A novel size-reduced strip line log periodic dipole arrays," IEEE International Symposium on Microwave, Antenna, Propagation and EMC Technologies for Wireless Communications, vol. 1, pp. 56-59, Aug. 2005. [3] H. Jardon-Aguilar, J. Tirado-Mendez, R. Flores-Leal, and R. LinaresMiranda, "Reduced log-periodic dipole antenna using a cylindrical-hat cover," IET Microwaves Antennas & Propagation, vol. 5, no. 14, pp. 1697-1702, Nov. 2011. [4] D. Anagnostou, J.Papapolymerou, M. Tentzeris, and C. Christodoulou, "A printed log-periodic Koch-dipole array (LPKDA)," IEEE Antennas and Wireless Propagation Letters, vol. 7, pp. 456-460, 2008. [5] A. Gheethan, and D. Anagnostou, "Reduced size planar Log-Periodic Dipole Arrays (LPDAs) using rectangular meander line elements," IEEE Antennas and Propagation Society International Symposium, pp. 1-4, Jul. 2008. [6] M. Mangoud, M. Aboul-Dahab, A. Zaki, and S. El-Khamy, "Genetic algorithm design of compressed log periodic dipole array," IEEE 46th Midwest Symposium on Circuits and Systems, vol. 3, pp. 1194-1197, Dec. 2003. [7] P. C. Buston and G. T. Thompson, “A note on the calculation of the gain of log-periodic dipole antennas,” IEEE Transaction on Antennas and Propagation, vol. 24, Jan. 1976.
105 mm
Silver printed 2 mm on bottom
Coaxial feed
Silver printed on top
Shunt Shorted Stub
Fig. 1. Illustration of the proposed antenna. EXPERIMENTAL RESULTS
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Fig. 2 (left) shows the measured and simulated S11 of the LPDA. The antenna has a good impedance match over the 2-7 GHz frequency range. The measured gain is > 4 dBi over the 2.25-3.75 GHz frequency range and > 2 dBi over the 2.25-5.5 GHz range, Fig. 2 (right). The measured maximum gain is 6.75 dBi and occurs at 2.5 GHz. According to [7], the presented design provides 13% size reduction at the expense of 0.5 dB gain degradation in comparison to a standard wire element design. The measured co-to-cross-pol ratio remains > 16 dB over the 2-6 GHz range in the endfire direction. Using ink material with conductivity similar to the conductivity of copper cladding, the gain over the 2-6 GHz range is only improved by < 0.4 dB.
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The measured E-and H-plane radiation patterns of the antenna at different frequencies are shown in Fig. 3. The HPBW over the E-plane is 60o, 60o, 50o, and 40o for frequencies of 3, 4, 5, and 6 GHz, respectively. The front-toback ratio is > 20 dB over the 3-6 GHz frequency range.
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Fig. 2. Simulated and measured S11 (left) and gain (right) of the antenna. IV.
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CONCLUSION
A 3-D printed log-periodic dipole antenna is presented. Using advanced 3-D printing manufacturing technology, more spatial optimization freedom is enabled and high gain antennas with reduced weight, cost, size, and material usage can be realized. The use of different meandering functions and shapes can be enabled and investigated using 3-D printing.
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Fig. 3. Measured radiation patterns; E-plane (top) and H-plane (bottom).
ACKNOWLEDGEMENT This is an NSF-sponsored project (#ECCS-1232183). The authors are thankful to Sciperio and nScrypt corporations for their support in printing the antenna.
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