0018-926X (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/TAP.2018.2871964, IEEE Transactions on Antennas and Propagation > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Abstract—This paper presents a planar dual-band slim microstrip patch antennas. The antenna comprises four sections: a patch and shorting, centered, and offset pins with the overall size of 30×50 mm 2 . It is shown that the centered and offset pins help to improve antenna matching while providing efficient radiation performance. With the aid of shorting pins, lower band operation at 1900 MHz is achieved. Moreover, the higher frequency band is expanded from 3480 to 3570 MHz. Simulations show that at the lower band frequencies, the antenna gain and efficiency are 1.0 dBi and 28%, respectively. Whereas at the upper-frequency band, the antenna maximum gain is 2.4 dBi, and the efficiency of at least 25% is observed. The numerical simulation shows that the number of resonant frequencies is directly related to the patch width. In order to validate simulation results, a prototype of the proposed antenna is fabricated and measured. Good agreement has been achieved between the simulation and measurement results. Index Terms—Dual-band antenna, handheld/portable applications, slim antenna, radiation enhancement, shorted-pin microstrip patch antenna I. INTRODUCTION HE rapid growth of high mobility necessity and multifunctional wireless communication systems, increase the interest for compact, low-profile, integrated and multiband microstrip antennas in recent years. However, the main difficulties in front of engineers to design compact antennas include narrow bandwidth and low radiation efficiency. In recent years, many techniques have been reported for designing miniaturized microstrip patch antennas. One of the most promising methods is to add a shorting pin. A pin- loaded technique was first introduced in [1]. The problem is theoretically analyzed using transmission-line model [2] and Green’s function approaches based on cavity model [3]. This technique is applied to control input impedance [4] and implementing a dual-band [5], polarization-agile [6] and tunable [7] patch antennas. In [8], the authors suggested demonstrating a shorting post in proximity to the feed point to suppress surface wave propagation. Recently, the pin-loaded technique is utilized to present a wide 3-dB axial ratio beamwidth [9], high-gain [10], enhanced gain [11] and enhanced bandwidth [12]–[14] patch antennas. In these papers, the authors try to adjust the location of loading pins in order to modify current distribution and consequently manipulate antenna impedance (tuning the resonant frequency and broadening the antenna bandwidth) and radiation (decreasing Amir Jafargholi is with the Electromagnetic and Antenna Lab., Amirkabir University of Technology, 424 Hafez Ave., P.O. Box 15875-4413, Tehran, Iran (e-mail: Jafargholi@ieee.org). Ali Jafargholi is with Communication Company of Iran (MCI), P.O. Box: 19919-54651, Tehran, Iran (e-mail: the radiation beamwidth and improving polarization characteristics). However, it is notable that these structures generally do not address electrically small antennas. Even though these works have concluded that a shorting post will display resonance frequencies above the fundamental mode of the unloaded patch antenna. On the contrary to these designs, some researchers focused on miniaturizing patch antenna using the pin-loaded method, however, the obtained results suffer from a dramatically low gain [15]-[18]. The main objective of this paper is to present a simple, low- cost, miniaturized, efficient, slim antenna with a moderate gain and half-space radiation. From the practical point of view, the proposed structure could be mounted in several types of portable devices where the antenna has to be slim and hemispherical radiation should be required. In such applications, although the dipole-like antennas may be preferred, however, due to the ground plane existence that commonly implemented to support RF and digital front-end circuits; and their omnidirectional radiation pattern, the wire- type antenna is not applicable. At first, the pin-loaded antenna is studied to determine the possibility of reducing the patch length using pin-loaded technique and simultaneously decreasing the antenna resonant frequency. It is shown that the shorting pin could help to overcome the physical limitations observed in conventional microstrip patch antennas such as low gain and low efficiency, Second, a simple approach based on utilizing additional shorting pins is proposed to defeat low gain and low-efficiency drawbacks. It is shown by applying the proposed method, the radiation and matching of a shorted-pin single patch antenna enhanced simultaneously while it provides a single feed dual-/multiband compact antenna. Due to the shunt inductive effect of these pins, the resonant frequency of the dominant mode can be tuned to cover the desired frequency band. The numerical simulation shows that increasing the width of the proposed antenna causes decreasing resonant frequency while it provides half-space radiation pattern as expected in microstrip patch antennas. The number of resonant frequencies is directly related to the patch width. Moreover, at the lower frequency a greatly enhanced gain, >14 dB, and a low cross- polarization observed when it compared with an equivalent simple pin-loaded patch antenna (a pin-loaded patch antenna with the same resonant frequency). The proposed structure is demonstrated experimentally. The results of simulation and measurement are shown good agreement. a.jafargholi@mci.ir). Behbod Ghalamkari is with the Department of Electrical and Computer Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran (e-mail: ghalamkari@srbiau.ac.ir) Dual-Band Slim Microstrip Patch Antennas Amir Jafargholi, Member, IEEE, Ali Jafargholi, and Behbod Ghalamkari T