1536-1225 (c) 2013 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.2014.2355496, IEEE Antennas and Wireless Propagation Letters IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, 1 Abstract—A novel broadband unit-cell is proposed in this paper. This new cell element consists of three coupled circular rings where four quasi-spiral delay lines are connected to the outer ring to provide the required phase shift. The spiral shape of the delay lines exhibits more than 1000 o of phase swing. The cross polarization level of the presented element is considerably improved compared to previous designs with a similar phasing mechanism. The capability of operating in linearly or circularly polarized incident wave is an important advantage of the proposed cell. In other words, depending on polarization of the feed antenna, the present reflectarray can operate in vertical, horizontal or circular polarization. Finally a moderate size reflectarray, 27×27 cm 2 , is designed and fabricated based on the mentioned element. The measured results showed about 16.5% of 1 dB gain bandwidth. The antenna gain at 8.5 GHz is 26.4 dB which is equivalent to 59.2% efficiency. Also, the measured side- lobe level and cross polarization of this antenna are about -20 dB and -25 dB, respectively. Index Terms—Quasi-spiral phase delay line, phase shift mechanism, reflectarray antenna, delay line. I. INTRODUCTION EFLECTARRAY antenna is a good option for substituting reflector antennas in some applications. Their low cost, easier fabrication and planar structure make them advantageous in satellite communication. The most important drawback of this type of antennas is their narrow bandwidth. Recently, many efforts have been accomplished to improve the bandwidth of reflectarray antenna (RA) [1-2]. Several methods and unit-cells have been used as the phase shift mechanism such as, phase delay line[3], element rotation[4,5], and using element with variable size[6,7]. The sensitivity to fabrication in method of elements with attached delay line is lower than the element with variable size, due to their greater range of linear phase, but they have more cross polarization. However, the cross-polarization level can be mitigated in final array configuration. In [8] a technique based This paragraph of the first footnote will contain the date on which you submitted your paper for review. It will also contain support information, including sponsor and financial support acknowledgment. For example, “This work was supported in part by the U.S. Department of Commerce under Grant BS123456”. The authors are with the Department of Electrical Engineering, Iran University of Science and Technology, Tehran 16846-13114, Iran. (e-mail: iman_darafshi@elec.iust.ac.ir,n_komjani@iust.ac.ir,mohamadirad@ee.iust. ac.ir). on separation of the RA surface into four regions with mirror symmetric arrangement of elements, is used to reduce the cross polarization. Also, in [9] a new method for arrangement of elements was developed to achieve more reduction of cross polarization. In this article a wideband single-layer cell element composed of quasi-spiral phase delay lines is developed which offers about 1000 o variation of phase range. This structure has same phase response for vertical, horizontal and circular polarizations so that if a feed with linear or circular polarization illuminates the antenna aperture, the RA will operate in linear or circular polarization, respectively. Due to special shape of the unit cell the level of cross polarization is lower than ones in pervious works which have used delay line method. A 27×27 cm 2 (18×18 elements) reflectarray is designed and fabricated based on the suggested element and 1 dB gain bandwidth about 16.5% is measured which demonstrates wideband operation for present antenna. Measurement showed 26.4 dB of gain at 8.5 GHz and thus maximum efficiency of 59.2% for this size of RA. II. DESIGN OF UNIT CELL The designed cell element is shown in figure 1. As it can be seen, this element is composed of three circular rings. Four quasi-spiral phase delay lines are attached to the outer ring. Fig. 1.Proposed element geometry. A Single Layer Broadband Reflectarray Antenna by Using Quasi-spiral Phase Delay Line Iman Derafshi, Nader Komjani and Mohammad Mohammadirad R w s g s l s r i r m r o w s i l x l y a) b) d s d t RO_4003 Ground s i