An annular-slot coupling feeding technique for dual-feed circularly polarized patch arrays

In microwave radio links, circular polarization is able to reduce multipath effects as well as to allow more flexible reciprocal orientation of the transmitter and the receiver antennas. For the above reasons circularly polarized (CP) antennas are used in a number of communication systems, as for example GPS (Global Positioning System) terminals and satellite-to-mobile wideband communication links, as well as most UHF RFID (Radio Frequency IDentification) readers. Moreover, several ATC (Air Traffic Control) radars and SAR (Synthetic Aperture Radar) systems adopt CP antennas, by bringing into play some interesting properties of the polarimetric scattering. CP patch antennas are generally divided into two categories, named as single-feed [1] and dual-feed [2]-[3]configurations, both able to excite the patch orthogonal principal modes with a quadrature phase shift. Dual-feed layouts resort to an external power splitter (for example a reactive power divider or a 90° quadrature hybrid). On the other hand, single-feed configurations are based on some perturbations that are applied to the patch boundary. Typical single-feed configurations are the corner truncated patch and the nearly square patch with the feeding point located along the patch axes or diagonals. Single-feed solutions are simpler but usually exhibit a limited Axial Ratio (AR) bandwidth. On the contrary, the dual-feed technique results in a larger AR bandwidth at the expense of a more complex feeding network, which is a substantial drawback in electrically large array antennas. In this paper, a circular patch antenna using a novel slot-coupling technique is used to realize a CP 2×2 array with wide impedance matching and AR bandwidths. Specifically, a dual-feed technique is used for each array element, and it is combined with a sequential rotation array feeding technique [5]. The sequential rotation technique consists in sequentially rotating each patch element together with an appropriate offset in the feed excitation phase. Array simulation results are compared with those for a similar array which is made of 4 square patches coupled to the microstrip feeding through square ring slots (such a configuration has been firstly introduced in [4], for dual-linear polarization square patch antennas). Numerical simulations obtained with Ansoft DesignerTM are used to compare the AR performance of the two 2×2 arrays designed to operate at the 3.5GHz WiMAX(TM) frequency band. In the following, the antenna is described and numerical results are shown before the final conclusions. © 2010 IEEE.