1536-1225 (c) 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/LAWP.2019.2904795, IEEE Antennas and Wireless Propagation Letters AWPL-01-19-0159.R1 1 Abstract— A fast and accurate method is proposed for the design of rectennas. It combines the use of a full wave electromagnetic simulator, for the analysis of the antenna, and a harmonic balance simulator, for the analysis of the rectifying circuit, with a single point experimental calibration procedure. The proposed method can be used to speed up the development of general rectenna configurations. Two case studies are presented to illustrate the proposed concept. The first one is general whereas the second is efficiency optimization oriented. A modified planar printed dipole without a matching network is used in both cases. An efficiency of 48% is achieved for a power density of 57 μW/cm² around 5 GHz. Good agreement is obtained between simulation and experimental results. Index Terms—Energy harvesting, rectennas, wireless power transmission I. INTRODUCTION ireless power transmission (WPT) is a longstanding theme in electrical engineering, tracing its roots to Heinrich Hertz and Nikola Tesla [1]. The growing number of wireless devices and their need for powering have renewed the interest for WPT research area [2], [3]. With the development of 5G and the Internet of Things (IoT), many everyday objects and sensors will be connected to the internet. A large number of services is emerging from the interaction with, and between, these "things". The forecasted number of IoT devices for 2020 is between 20 and 30 billion. Each IoT device or network node requires a power source to realize data acquisition and transmission. The usual source is a battery that will someday be depleted by the device operation. Sometimes the only way to assure the continuity of operation is to harvest energy from another source to feed the device [4]. The use of WPT as energy harvesting is a sustainable alternative [5]. The main idea is to capture radio frequency (RF) energy from the ambient and convert it into DC using a rectifying antenna (rectenna) [6]. Considering the number of devices, their size, and diversity, any viable proposal needs to be low cost, low size and flexible in terms of load to feed [7], [8]. The rectenna cost is affected by the materials and Manuscript submitted in August 5, 2018. This work was supported by CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico – Brasil under scholarship 235062/2014-6, and FCT - Fundação para a Ciência e a Tecnologia under grant UID/EEA/50008/2019. The authors also like to thank Instituto Federal da Paraíba (IFPB), Brasil and Instituto de Telecomunicações (IT), Instituto Superior Técnico (IST), University of Lisbon (UL), Portugal. components used (mainly diodes, and inductors) and also by the development time. In this paper, a fast design method for low-cost, low profile and load flexible rectennas is proposed. The method is focused on reducing the number of laboratory tests necessary to determine the most efficient operation region in terms of frequency, power density, and load. The method requires only the measurement of one calibration point for each analyzed frequency, determining the system behavior by simulation. The advantage of the proposed method is the possibility of providing an accurate simulation of the complete rectenna system. The results can be compiled into a simple figure of merit, here named power map, that allows fast analysis of the rectenna behavior with frequency and load. In [9] and [10] only measurement results are presented for the complete rectenna system. Simulation results for the complete system are presented in [11] and [12] for a single frequency and fixed load, in [13] for a single load varying the frequency, and in [14] for a single frequency varying the load. In [15], where both power level and load are varied, the efficiency results are presented as a function of power level and load separately, and the frequency is lower (up to 2.7 GHz). To the best of authors’ knowledge, no other publication provides the same power map simulation approach. By using the proposed method, it is possible to simulate structures without a matching network (MN), in which the diode is integrated into the antenna. This is a novel approach in the development of rectenna systems. To simulate the complete system, the method requires a full wave simulator (FWS) and a harmonic balance simulator (HBS), in this paper respectively CST Microwave Studio and AWR Microwave Office. To show the effectiveness and flexibility of the proposed method two case studies are presented. The first one is general and is used to explain the details of the method, whereas the second is efficiency optimization oriented reaching a maximum efficiency of 48 % for a power density of 57 μW/cm² around 5 GHz. The efficiency values of the proposed rectenna are in line with the literature [16-18]. A more efficient rectenna is proposed in [13] for ultra-low power densities, but a much more complex and large structure is used. Erik Farias da Silva is with IT/IST, UL, Portugal, and IFPB, Brasil (e-mail: erik@ifpb.edu.br). Alfredo Gomes Neto is with IFPB, Brasil (e-mail: alfredogomes@ieee.org). Custódio Peixeiro is with IT/IST, UL, Portugal (e-mail: custodio.peixeiro@lx.it.pt). Fast and Accurate Rectenna Design Method Erik Farias da Silva, Alfredo Gomes Neto, and Custódio Peixeiro, Member, IEEE W