【正文】 of the structure to provide best matching. The symmetrical slot antenna topology[see (b)]has an outer side length of 30 mm, an inner side length of 20 mm, and a slot width of 2 mm. The first downscaled structure[see (c)]has an outer side length of 20 mm, an inner side length of 10 mm, and a slot width of mm. Finally, the second downscaled structure[see (d)]has a side length of 10 mm and a slot width of 1 mm. For the purpose of parison, two basic similar structures having the same area as the proposed antenna are simulated. The first one is a single square ring slot antenna having an outer side length of 30 mm, and a slot width of 2 mm. The second one is a nested square rings slot antenna, presented in , with the same dimensions as that of the proposed antenna. The simulated return loss for the three structures,.,proposed antenna, single square ring, and nested square rings, is presented in . The measured return loss for the proposed antenna is also shown in . Both the single square ring slot and nested square rings slot antennas have multiple resonance behaviors. The bandwidth（VSWR 2) for the single square ring and nested square rings slot antennas are %and 29%, respectively. The proposed antenna has a broadband performance with a bandwidth of %. These results are totally expected since the final proposed antenna is posed of different resonant slot lengths providing the broadband performance. Good agreement between simulated and measured return loss is also demonstrated. A photograph of the fabricated slot antenna is shown in . The simulated magnetic current distribution along slots is presented in at two different frequencies corresponding to minimum returnloss points. All slots contribute to radiation with symmetrical behavior, which demonstrates the usefulness of spacefilling curves to provide multiresonant slot lengths(.,paths)over a wide frequency range. On the other hand, the contribution from upper slots is less significant at higher frequencies. The simulated radiation patterns of the proposed antenna, at two different frequencies, are presented in . The total electric field in the elevation is plotted at two different azimuth angles( = 0176。and =90176。). The puted maximum antenna gain at GHz is 5 dB. The main beam points vertically(at θ = 0176。and 180176。),.,broadside, which is similar to a magnetic dipole. However, the radiation patterns have some discontinuity near the antenna plane(θ= 90176。and 90176。)at high frequency[see (b)]. This is mainly due to the used thick dielectric substrate, where higher order modes are easily excited, which result in pattern shaping, in addition to the accuracy of the angular steps used by the simulator. Polarized Slot Antenna Based on the proposed broadband design, a circularly polarized slot antenna is investigated using the method of introducing asymmetry in the slot structure[9]. The asymmetry is implemented by replacing all vertical slots on one side of the symmetrical structure and all inner slots by a ground plane, together with the placement of the microstrip feed line along the diagonal direction. The configuration of the proposed circularly polarized antenna is shown in . The proposed circularly polarized slot antenna is implemented on a Taconic RF35 substrate（r = , h = ）with the same broadband structure dimensions. The simulated and measured return loss of the circularly polarized slot antenna is presented in . The antenna has a bandwidth（VSWR 2）of 66%, which is an expected result based on the used broadband topology. Good agreement between simulated and measured results is clearly observed. The simulated axial ratio is presented in . The antenna has a 3dB axial ratio bandwidth of 22% with VSWR 2. Based on a modified spacefilling curve, broadband and circularly polarized slot antennas have been developed. This has been achieved by inserting different downscaled copies of an“islandlike”spacefilling curve into each other to pose multiresonant slot lengths that provide the wideband performance. Furthermore, by introducing asymmetry in the proposed broadband structure, circular polarization has been achieved. Using three scaled versions of a modified seconditeration Moore spacefilling slot antenna, a broadband antenna that has an impedance bandwidth of % has been developed. The antenna has a total area of 3 3 cm and a gain of 5 dB. The circularly polarized version has a 3dB axial ratio bandwidth of 22%with, and occupies the same area. The achieved wideband performance depends on the area filling efficiency provided by the used spacefilling curve. Consequently, other spacefillingbased topologies have to be investigated for further bandwidth enhancement. 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