Antenna efficiency at LTE 13 in different papers.
In this chapter, ASCCC fractal is defined. The name “ASCCC” is based on the process that the fractal is built. It is made by adding and subtracting circles to the circumference of a circle. Then the necessary formulas to build up the first and higher orders of ASCCC fractal are derived. By calculating the perimeter of each order, it is shown that the ASCCC fractal has a great capability in antenna miniaturization. Based on first-order ASCCC fractal, a systematic approach is designed to miniaturize an antipodal dipole at any arbitrary frequency. Then the proposed method is applied at band LTE13 (746–787 MHz), which is controversy for mobile antenna, because it causes the size of a common antenna to become very large for a handheld mobile. It is illustrated that not only the ASCCC fractal is successful in miniaturization of dipole antenna, but also it is very good at improving the antenna’s efficiency in comparison with its counterparts like Koch dipole/monopole.
- fractal antenna
- antenna miniaturization
- antenna’s efficiency
- antipodal dipole antenna
- mobile antenna
Nowadays, there is demand for antennas which fit in small space while have good radiation performance. Therefore, miniaturization techniques are inevitable in antenna design. Most of miniaturization techniques are based on slot loading, lumped loading, material loading, meandering, using fractal shapes or meta‐materials. Generally, these techniques cause radiation efficiency and bandwidth to reduce. The antenna performance can be improved if the available volume within the Chu’s sphere is used effectively. Fractal, meander and volumetric antennas are based on this method . However, volumetric antennas are not suitable for planar structures. The meander antennas  and some fractal antennas such as Hilbert  and Koch dipole/monopole [3, 4] have some sections of cancelling current from adjacent conductors that cause the efficiency not to improve significantly. Furthermore, the resonance frequency cannot be found analytically because the physical length is not equivalent with electrical length [1, 2].
In this chapter, a novel fractal named adding and subtracting circles to the circumference of a circle (ASCCC) is defined and the required formulas are derived to build it. The ASCCC fractal is made by adding and subtracting an even number of circles on circumference of a circle, in brief named as adding and subtracting circles to the circumference of a circle (ASCCC). Then, a procedure is shown to miniaturize an antipodal dipole based on first order of ASCCC fractal at any arbitrary frequency. A formula is extracted to determine the resonance frequency of the ASCCC dipole with excellent precision. The proposed procedure is used to design a mobile antenna at challenging band of LTE13 (746–787 MHz). Because of low frequency nature of LTE13, the in‐building penetration and area coverage are very good . On the other hand, the size of antenna becomes so large at LTE13 that it is not suitable for a handheld mobile . Therefore, some miniaturization techniques should be applied to the design. One of the great advantages of ASCCC dipole antenna is using the Chu’s sphere so effectively that the antenna’s efficiency improves considerably in addition to antenna miniaturization. Actually, the currents in adjacent teeth of ASCCC fractal dipole do not weaken the effect of each other, so very good efficiency is obtained. This advantage also makes the physical length to be approximately equal with electrical length.
The design is simulated by full‐wave software (Ansoft‐HFSS version 15). The results of simulation and measurement are in very good agreement. The efficiency of the proposed dipole antenna is higher than the existing works at LTE13 for handheld mobile antenna [8–25]. Also, the design obtains 40% size reduction compared with a common dipole. Furthermore, the ASCCC design has advantages of being planar and vialess .
In Section 2, the ASCCC fractal is explained. Then in Section 3, a procedure is shown to use ASCCC fractal in arms of an antipodal dipole. Theoretically, how to design an ASCCC dipole antenna for a special band is discussed. Next, a mobile antenna is designed, simulated and measured at LTE13. Finally, the conclusion is presented in Section 4.
2. ASCCC fractal
ASCCC fractal is based on adding and subtracting an even number of circles alternately on circumference of an initial circle. In brief, it is named as adding and subtracting circles to the circumference of a circle (ASCCC). It should be noted that radius of secondary circles (
Zero, first and second orders of ASCCC fractal for
Perimeter of the first‐order ASCCC (
For calculating the perimeter of the second‐order ASCCC fractal (
Eqs. (6) and (7) show the ratio of
Now, it is time to compare
3. An application of ASCCC fractal in antenna miniaturization
In this section, it is shown that an antipodal dipole antenna is miniaturized by applying the first‐order ASCCC fractal to arms of the dipole antenna. The procedure could be applied to any arbitrary frequency .
3.1. The proposed design
In this section, it is shown that an antipodal dipole antenna is miniaturized by applying the first‐order ASCCC fractal to arms of the dipole antenna. Figure 5(a)–(d) presents the utilized method. In the first step, two first‐order ASCCC fractals with the same
In a common dipole antenna, the length in which current travels along the two arms is equal to
To design a balanced feedline, the method described in Refs.  and  is used. The line parameters are given in Figure 6. The exponential part of line is made by Eqs. (12) and (13).
3.2. Simulation and measurement results
The method described in Section 3.1 is used to design a handset mobile antenna at the LTE13 band (746–787 MHz). The antenna is printed on an FR4 substrate with
A fabricated prototype of the proposed antenna is shown in Figure 8. The overall size of the printed antenna is 62 × 115 × 1.6 mm3 that is suitable for a handheld mobile. The simulated and measured results of
Figures 10 and 11 present the 3‐D and polar radiation patterns of the proposed antenna at 769 MHz, respectively. As they show, the antenna has a dipolar radiation pattern. Figure 12 shows the efficiency of antenna. The measured efficiency is obtained by the improved Wheeler‐cap method . Antenna efficiency varies from 79.28 to 88.01%. As it is seen, the antenna has very high efficiency at LTE13, on the contrary of the other designs for this band that are listed in Table 1 [8–25].
Finally, the antenna exhibits 40% size reduction in comparison with a common dipole. This is evidence that the proposed procedure is a good technique in antenna miniaturization .
In this chapter, ASCCC fractal is defined and its driving formulas are extracted. It is shown that ASCCC fractal has a great potential in antenna miniaturization and improving efficiency. A miniaturization method was designed for a dipole antenna at any arbitrary frequency. Then, the method applied to the dipole antenna at band LTE13 which is very challenging for reduction in size of mobile antennas. The total size of antenna is 62 × 115 × 1.6 mm3, which is appropriate for handheld mobiles. The efficiency of antenna is greater than 79% with
Volakis J, Chen CC, Fujimoto K. Small Antennas: Miniaturization Techniques & Applications. 1st ed. New York: McGraw‐Hill; 2010. p. 428
Hansen RC, Collin RE. Small Antenna Handbook. 1st ed. Hoboken, New Jersey: John Wiley & Sons, Inc.; 2011. p. 346
Best SR. On the performance properties of the koch fractal and other bent wire monopoles. IEEE Transactions on Antennas and Propagation. 2003; 51(6):1292–1300. DOI: 10.1109/TAP.2003.812257
Vinoy KJ, Abraham JK, Varadan VK. On the relationship between fractal dimension and the performance of multi‐resonant dipole antennas using Koch curves. IEEE Transactions on Antennas and Propagation. 2003; 51(9):2296–2303. DOI: 10.1109/TAP.2003.816352
Eskandari Z, Keshtkar A, Ahmadi‐Shokoh J, Ghanbari L. A novel fractal for improving efficiency and its application in LTE mobile antennas. Microwave and Optical Technology Letters. 2015; 57(10):2429–2434. DOI: 10.1002/mop.29346
Sharawi MS, Numan AB, Khan MU, Aloi DN. A dual‐element dual‐band MIMO antenna system with enhanced isolation for mobile terminals. IEEE Antennas and Wireless Propagation Letters. 2012; 11:1006–1009. DOI: 10.1109/LAWP.2012.2214433
Zhang Z. Antenna Design for Mobile Devices. 1st ed. Singapore: John Wiley & Sons (Asia) Pte Ltd; 2011. p. 280
Meshram MK, Animeh RK, Pimpale AT, Nikolova N K. A novel quad‐band diversity antenna for LTE and Wi‐Fi applications with high isolation. IEEE Transactions on Antennas and Propagation. 2012; 60(9):4360–4371. DOI: 10.1109/TAP.2012.2207044
Yu Y, Kim G, Ji J, Seong W. A compact hybrid internal MIMO antenna for LTE application. In: 2010 Proceedings of the Fourth European Conference on Antennas and Propagation (EuCAP); 12–16 April 2010; Barcelona, Spain: IEEE; 2010.
Lopez N, Lee C‐J, Gummalla A, Achour M. Compact metamaterial antenna array for long term evolution (LTE) handset application. In: IEEE International Workshop on Antenna Technology( iWAT) 2009; 2–4 March 2009; Santa Monica, CA, USA: IEEE; 2009. DOI: 10.1109/IWAT.2009.4906933
Bae H, Harackiewicz FJ, Park MJ, Kim T, Kim N, Kim D. Compact mobile handset MIMO antenna for LTE700 applications. Microwave and Optical Technology Letters. 2010; 52(11):2419–2422. DOI: 10.1002/mop.25507
Zhao X, Choi J. Design of a MIMO antenna with low ECC for a 4G mobile terminal. Microwave and Optical Technology Letters. 2014; 56(4):965–970. DOI: 10.1002/mop. 28196
Cheon Y, Lee J, Lee J. Quad‐band monopole antenna including LTE 700 MHz with magneto‐dielectric material. IEEE Antennas and Wireless Propagation Letters. 2012; 11:137–140. DOI: 10.1109/LAWP.2012.2184517
Ban YL, Chen JH, Yang S, Li JLW, Wu YJ. Low‐profile printed octa‐band LTE/WWAN mobile phone antenna using embedded parallel resonant structure. IEEE Transactions on Antennas and Propagation. 2013; 61(7):3889–3894. DOI: 10.1109/TAP.2013.2258879
Wong KL. 4G/Multiband handheld device ground antennas. In: Microwave Conference Proceedings (APMC); 5–8 November 2013; Asia‐Pacific: IEEE; 2013. DOI: 10.1109/APMC.2013.6695215
Wong KL, Chang YW. Internal WWAN/LTE handset antenna integrated with USB connector. Microwave and Optical Technology Letters. 2012; 54(5):1154–1159. DOI: 10.1002/mop.26788
Jeon S, Kim H. Mobile terminal antenna using a planar inverted‐e feed structure for enhanced impedance bandwidth. Microwave and Optical Technology Letters. 2012; 54(9):2133–2139. DOI: 10.1002/mop.27035
Jo Y, Park K, Lee J, Kim HH, Kim H. Mobile handset antenna with parallel resonance feed structures for wide impedance bandwidth. In: Proceedings of the International Symposium on Antennas & Propagation (ISAP); 23–25 October 2013; Nanjing, China: IEEE; 2013.
Lee J, Liu Y, Kim HH, Kim H. PIFA with dual‐resonance feed structure for enhancement of impedance bandwidth. Electronics Letters. 2013; 49(15):921–922. DOI: 10.1049/el.201 3.1432
Chu FH, Wong KL. Planar printed strip monopole with a closely‐coupled parasitic shorted strip for eight‐band LTE/GSM/UMTS mobile phone. IEEE Transactions on Antennas and Propagation. 2010; 58(10):3426–3431. DOI: 10.1109/TAP.2010.2055807
Wong KL, Chen WY, Wu CY, Li WY. Small‐size internal eight‐band LTE/WWAN mobile phone antenna with internal distributed LC matching circuit. Microwave and Optical Technology Letters. 2010; 52(10):2244–2250. DOI: 10.1002/mop.25431
Ban YL, Liu CL, Chen Z, Li JLW, Kang K. Small‐size multiresonant octaband antenna for LTE/WWAN smartphone applications. IEEE Antennas and Wireless Propagation Letters. 2014; 13:619–622. DOI: 10.1109/LAWP.2014.2313353
Lu JH, Guo JL. Small‐size octaband monopole antenna in an LTE/WWAN mobile phone. IEEE Antennas and Wireless Propagation Letters. 2014; 13:548–551. DOI: 10.1109/LAWP. 2014.2311797
Luo J, Gong SX, Duan P, Mou C, Long M. Small‐size wideband monopole antenna with CRLH‐TL for LTE mobile phone. Progress in Electromagnetics Research C. 2014; 50:171–179.
Takemura N. Tunable inverted‐L antenna with split‐ring resonator structure for mobile phones. IEEE Transactions on Antennas and Propagation. 2013; 61(4):1891–1897. DOI: 10.1109/TAP.2012.2232894
Antoniades MA, Eleftheriades GV. Multiband compact printed dipole antennas using NRI‐TL metamaterial loading. IEEE Transactions on Antennas and Propagation. 2012; 60(12):5613–5626. DOI: 10.1109/TAP.2012.2211324
Bourqui J, Okoniewski M, Fear EC. Balanced antipodal vivaldi antenna with dielectric director for near‐field microwave imaging. IEEE Transactions on Antennas and Propagation. 2010; 58(7):2318–2326. DOI: 10.1109/TAP.2010.2048844
Geissler M, Litschke O, Heberling D, Waldow P, Wolff I. An improved method for measuring the radiation efficiency of mobile devices. In: Antennas and Propagation Society International Symposium. IEEE; 22-27 June 2003; Columbus, Ohio, USA: IEEE; 2003. DOI: 10.1109/APS.2003.1220380