Novel Dual-Band Antenna with Simultaneous Linear and Circular Polarizations Faiza Kanwal, Hamail Sultan, Moazam Maqsood and Qamar ul Islam Department of Electrical Engineering Institute of Space Technology Islamabad, Pakistan moazam.maqsood@ist.edu.pk Steven Gao School of Engineering and Digital Arts University of Kent Canterbury, CT2 7NT, UK s.gao@kent.ac.uk Abstract— A multi-function microstrip antenna for simultaneous operation at two different frequency bands (centered at 1.575 GHz and 2.4 GHz) is presented. In contrast to the traditional dual-band antennas, the presented antenna design is unique as it can achieve two different polarizations simultaneously. Such a configuration makes the proposed antenna suitable for receiving signals from entirely different systems using a single antenna. In order to achieve the dual-band operation, a stacked configuration of microstrip antennas has been used where the top patch is designed to operate at 2.4 GHz with linear (vertical) polarization while the bottom patch is designed to operate at 1.575 GHz with right hand circular polarization. Although the proposed antenna is a typical dual- band stacked configuration, it is the antenna feed that makes it a novel design. The antenna feed consists of a broadband branch- line coupler but its connection to the antenna is non-symmetric thereby forcing the two different patches to produce different polarizations. Antenna simulation results show that the dual- band antenna achieves greater than 5 dBi gain at both frequency bands whereas the axial ratio remains less than 3 dB at the GNSS band (1.575 GHz). The axial ratio at the ISM band (2.4 GHz) is shown to be greater than 35 dB demonstrating a linearly polarized operation. The antenna has a compact size and low cost, suitable for portable terminal antennas receiving signals at both GNSS and ISM frequency bands. Keywords—dual-band antenna; GNSS; stacked patch; dual polarization I. INTRODUCTION Antennas are commonly used in our daily life. However, with the ever increasing number of wireless systems around us, there is clearly need of antennas that are capable of connecting to more than one systems either by switching from one frequency to another or by achieving simultaneous multiband operation. Multi frequency operation in a system can be achieved by either using a multiband antenna providing resonance at multiple frequencies or using a wideband antenna covering a larger band width. The use of wide band antenna seems simpler of the two however the system needs to employ an efficient filtering mechanism in order to reject the unwanted interference. The use of multi-band antennas eliminate the need of filtering but such a mechanism increases the design complexity of the antenna as multi-band operation requires multiple resonating elements. Although the subject of dual- band / multi-band antennas or antennas with multiple polarizations has been extensively covered in the literature [1- 3], the presented antennas either achieve multi-band operation with the same polarization or multiple polarization states for the same frequency. Since different systems are characterized by unique frequency band and polarization, an antenna to be used with more than one system simultaneously will require resonance at more than one frequency bands with separate polarizations (unique to each frequency band). The antenna designs presented in [2] and [3] are capable of switching from one frequency band to another, with more than one selectable polarization states. The presented antennas use PIN diodes to alter the antenna size or shape in order to switch between multiple frequency bands and polarization states. However, the integration of PIN diodes directly on the antenna surface requires complex DC biasing mechanism thereby rendering the overall antenna design impractical. This paper presents the design of a dual-band antenna capable of receiving signals in the GNSS and ISM bands simultaneously. The proposed antenna resonates at 1.575 GHz and 2.4 GHz with right hand circular polarization at former and vertical polarization at the latter frequency band. Such an antenna can be used in the satellite communication for receiving navigation and telemetry signals simultaneously. In contrast to the designs presented in [2] and [3], the proposed antenna design is simple and easy to fabricate where the dual band operation is achieved by passive stacked patch configuration and the polarization switching is achieved by manipulating the feed network only. This arrangement is advantageous as the antenna is kept isolated from the parasitic of the active components. II. ANTENNA DESIGN The proposed antenna design uses a stacked patch configuration with a broadband branchline coupler integrated at the bottom. The top patch is designed to operate at 2.4 GHz producing vertical polarization while the bottom patch operates at 1.575 GHz producing right hand circular polarization. A broadband branch-line coupler [4] is integrated at the bottom of the antenna. The dimensions of the square patches (for both 1.575 GHz and 2.4 GHz) were calculated using design 2014 Loughborough Antennas and Propagation Conference (LAPC) 10 - 11 November 2014, UK 978-1-4799-3662-5/14/$31.00 ©2014 IEEE 509