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Ren, A 2.7-mW 1.36– 1.86-GHz LC-VCO with a FOM of 202 dBc/Hz enabled by a 26%- size-reduced nano-particle-magnetic-enhanced inductor, IEEE Trans Microwave Theory Tech 62 (2014), 1261–1268. V C 2016 Wiley Periodicals, Inc. BIO-INSPIRED DESIGN OF DIRECTIONAL LEAF-SHAPED PRINTED MONOPOLE ANTENNAS FOR 4G 700 MHz BAND P. F. Silva J unior, 1 P. H. da F. Silva, 2 A. J. R. Serres, 3 J. C. Silva, 4 and R. C. S. Freire 5 1 Federal University of Campina Grande (UFCG) Electrical Engineering Department CEP: 58429-140 Campina Grande, PB, Brazil; Corresponding author: paulo.junior@ee.ufcg.edu.br 2 Federal Institute of Paraiba (IFPB) Group of Telecommunications and Applied Electromagnetism Av. Primeiro de Maio, 720, Jaguaribe, CEP 58015-905, Jo~ ao Pessoa, PB, Brazil 3 Federal University of Campina Grande (UFCG) Electrical Engineering Department CEP: 58429-140 Campina Grande, PB, Brazil 4 Federal Institute of Paraiba (IFPB) Group of Telecommunications and Applied Electromagnetism Av. Primeiro de Maio, 720, Jaguaribe, CEP 58015-905, Jo~ ao Pessoa, PB, Brazil 5 Federal University of Campina Grande (UFCG) Electrical Engineering Department CEP: 58429-140 Campina Grande, PB, Brazil Received 31 October 2015 ABSTRACT: In this paper, a biologically inspired design methodology to develop directional leaf-shaped printed monopole antennas (PMA) for applications in the fourth-generation (4G) of mobile telecommunications technology is presented. Bio-inspired in the leaf shapes of a sugar cane plant, compact directional PMA are designed (with partial ground planes and flat rectangular reflectors) to cover the Brazilian 4G 700 MHz regulated band (698–806 MHz), with broadside radiation patterns and maximum directive gain up to 7.7 dBi. Simulated and measured results are presented for the proposed leaf-shaped antenna prototypes, and obtained results are compared with a square PMA. The use of bio-inspired leaf-shaped radiators and flat reflectors provides a fine tuning of ultra-wideband commonly presented by a conventional PMA, and the lowest resonant mode can be adjusted to cover the 700 MHz band. V C 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1529–1533, 2016; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.29853 Key words: bio-inspired design; leaf-shaped antennas; printed mono- pole antennas; 4G technology 1. INTRODUCTION According to Ref. [1] the “nature is effectively a giant labora- tory where trial and error experiments are taking place through evolution over 3.8 billion years”. Animals, plants, and other forms of life (that have been in existence for millions of years) are perfect engineers and natural designs are simple, functional, and remarkably elegant [1–3]. By taking inspiration from nature, biologically inspired (bio-inspired) engineering is an interdisci- plinary field that applies biological design principles to develop new engineering solutions. Biologically Inspired Design (BID), a kind of design by cross-domain analogy, is a promising para- digm for design innovation as well as sustainable design [2]. Bionics, biomimetics and biomimicry all follow nature for design ideas [3]. Such an engineering strategy is not a new con- cept. For centuries, we have looked at birds to mimic their flight. By looking to nature for solutions to engineering prob- lems, new and innovative products are being developed that influence all fields of engineering, including materials, energy, computing, robotics, biomedical, manufacturing, etc. In particular, within the plant kingdom, all natural photosyn- thetic organisms contain a light-gathering antenna system, which serves to increase the cross section for light absorption. There are several types of biological systems that capture the energy in sunlight and convert it to the chemical energy, but they all have two basic parts: the light-harvesting complex, or antenna, and the reaction center complex [4]. The biological light- harvesting antenna is analogue to a dish antenna (and others high gain reflector antennas), by collecting and focusing electro- magnetic radiations on a receiver. Leaves have been used as analogies to develop better solar-energy conversion [4], flow channels [5], and antennas [6]. With these ideas, bio-inspired concepts have also been used by microwaves engineers to design innovative bio-inspired antennas [7,8], which will draw upon the lessons learned from nature. Given the diversity of the animal and plant kingdoms, antenna bio-inspired design becomes a very promising design methodology to meet the requirements of modern wireless tech- nologies. In the context of bio-inspired design by analogy, leaf- shaped antennas have been attracting attention of microwave engineers and some papers have been published in specialized literature [6,9–15], mainly for ultra-wideband (UWB) applications. A compact UWB leaf-shaped printed monopole antenna was discussed in Ref. [6], with omnidirectional radiation pattern and constant group delay. In Ref. [9], a 69% bandwidth rose leaf- shaped microstrip patch antenna with capacitively coupled rec- tangular fed was designed, measured, and characterized in details. A maple-leaf-shaped PMA for UWB applications was presented in Ref. [10] with different band rejection techniques to achieve band-notch characteristic in the 5.0–6.0 GHz WLAN fre- quency band. In Ref. [11], an UWB antenna consisting of a leaf- shaped bowtie slot and a linearly tapered microstrip line was pro- posed. A holly-leaf-shaped monopole antenna with low RCS (radar cross-section) was designed in Ref. [12] with square notch etched in the ground plane to improve impedance matching. A 2- element quasi-millimeter wave (22–29 GHz) UWB array antenna composed by leaf-shaped bowtie elements was evaluated in Ref. [13]. Unidirectional UWB array antennas using a flat reflector and leaf-shaped bowtie 2- and 4-elements, with maximum gains of 11.2 and 13.3 dBi, [14,15], respectively, were proposed for impulse-based UWB systems. Section 2 introduces the proposed leaf-shaped PMA struc- tures and the bio-inspired design methodology based on sugar cane analogy. Simulated and experimental results are presented and discussed in Section 3. Finally, the conclusions of this paper are given in Section 4. DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 58, No. 7, July 2016 1529