# Design of Dual Circularly Polarized Sequentially-Fed Patch Antennas for Satellite Applications  
[PERSON]  
1 Department of Electrical, Electronics, and Computer Engineering (DIEEI), [PERSON] 6, 95125 Catania, Italy; [EMAIL_ADDRESS] (L.D.D.); [EMAIL_ADDRESS] (G.S.)  
[PERSON]  
3 National Institute for Nuclear Physics (INFN), National Southern Laboratories (LNS), Via S. Sofia 62, 95123 Catania, Italy; [EMAIL_ADDRESS] (Dipartimento di Informatica Engineering, Infractructures, and Sustainable Energy, \"Mediterranea\" University of Reggio Calabria, Salita Melissari, 89124 Reggio Calabria, Italy (Correspondence: santi.  
Such requirements are of primary importance especially for satellite or RADAR [12; 13] applications, in which the effects of ionosphere and rain have to be carefully taken into account in antenna design.  
However, two important drawbacks of single-feed patch antennas are their reduced axial ratio (AR) bandwidth and their poor polarization purity. To mitigate such effects, it is sometimes useful to exploit sequentially-rotated multi-feed patch antennas, as outlined in [14; 15].  
To deal with these issues, in the first part of the paper we propose the design and fabrication of a sequentially-fed [15; 16] circular patch antenna with relative phases of \(0^{\circ}\), \(120^{\circ}\) and \(240^{\circ}\) and operating at \(f=8.25\) GHz. The antenna radiates dual-CP by connecting alternatively the two input ports of the microstrip feeding network printed on the antenna back. Useful and comprehensive techniques to design both antenna arrays and feeding networks in microstrip technology can be found in [17]. Thanks to their inherent compactness, microstrip feeding networks have been adopted both for applications at relatively low frequencies, i.e., in UHF band [18] and also in the range of microwaves [19].  
Moreover, to increase antenna compactness and to allow more flexibility in aperture distribution shaping, in the second part, the sequentially-fed patch antenna was properly scaled and adopted as building block for the design of a 2-by-2 array for applications in the higher UHF band, at the operating frequency of \(f=2.2\) GHz. The array configuration increases antenna gain and can be also used to synthesize the difference (delta, \(\Delta\)) radiation pattern normally used to track satellites from ground stations. It is worth noting that a set of properly designed passive monopoles has been included in the antenna design to compensate unavoidable gain loss for large elevation angles. Indeed, passive monopoles are usually adopted to compensate antenna gain loss and to preserve also CP purity at high elevation angles (\(\theta\)) [20].  
The resulting low axial ratio (AR) and the symmetric broad radiation pattern allow the antennas to be profitably used as a reflector primary feeders for satellite applications.  
The paper is organized as follows. In Section 2, the operating principles of a dual-CP polarized sequentially-fed patch antenna loaded by a fence of passive monopoles are discussed, considering the design and realization of a prototype operating at \(f=8.25\) GHz. In Section 3, the proposed single radiating element is used as a building block for the design of a 2-by-2 array operating in the higher UHF band at \(f=2.2\) GHz for satellite applications, and in Section 4 the proposed array is experimentally tested. Finally, conclusions are drawn.