Circularly Polarized Antenna With Reconfigurable Broadside and Conical Beams Facilitated by a Mode Switchable Feed Network

A pattern-reconfigurable slot-augmented patch antenna is reported that radiates circularly polarized (CP) fields and is switchable between a broadside and a conical radiating mode. Two novel design strategies were adopted to realize these advantageous performance characteristics. First, a mode switchable feed network which includes a set of eight L-probes was developed that facilitates the proper excitation of either the patch's TM11 or TM21 mode and yields symmetric radiation patterns. Second, their operating bands were made to overlap by augmenting this patch with an annular slot. Consequently, the radiation pattern is easily switched between the broadside and the conical modes within the overlapping operational bandwidths. A prototype was fabricated and tested. The measured results are in good agreement with their simulated values, verifying the design concepts. The measured operating bandwidth, 7.8% from 2.45 to 2.65 GHz, was determined from the overlap of the impedance and axial ratio bandwidths for both modes. The measured realized gain values are stable for both radiating states within this operational bandwidth, the broadside (conical) peak value being 8.5 dBic (5.8 dBic). The CP pattern reconfigurability of this antenna with its favorable performance characteristics makes it an ideal candidate for many RFID and satellite communication applications.