permittivity of 2.65) with its size 70 ϫ 57 mm 2 . Its dimension parameters are listed in Table I. RESULTS AND DISCUSSIONTo examine the performance in terms of impedance bandwidth, the return loss for the fabricated antenna was measured using an HP8510C network analyzer. The simulated and measured return losses of the antenna are shown in Figure 2. It can be seen that the investigated antenna can approach an impedance bandwidth from 2.0 to over 12 GHz for S 11 Յ Ϫ10 dB, and a notch centered at 5.76 GHz (about 260 MHz higher than that of the simulated one) is also observed. The difference between simulations and measurements is mainly due to the substrate errors (including its thickness and relative permittivity) and fabrication tolerances.The measured radiation patterns in the E-plane and H-plane at 3.0, 5.0, 7.0, 9.0, and 10.5 GHz are illustrated in Figure 3. Notice that the proposed antenna has almost bi-directional patterns, especially at lower frequencies, in the E-plane, and omni-directional patterns in the H-plane at the lower or higher frequencies. Meanwhile, the measured antenna gain, given in Figure 4, shows the antenna has a gain of about 3.8 -6.8 dBi across the UWB frequency band. A sharp notch, centered at 5.76 GHz, is also observed with the rejection level approximately 10 dB. CONCLUSIONA planar elliptical slot antenna has been investigated. The proposed antenna has a compact size of 70 ϫ 57 mm 2 because of employing FG-CPW structures. To co-exist with the WLAN systems, a V-shaped slot is introduced. The antenna offers UWB performance with frequency band-rejection characteristic and suitable radiation patterns, which is met for UWB applications.

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Abstract-A low profile double-layer polarizer structure is presented for planar patch antennas to obtain circular polarization in 3.5 GHz WiMAX band (3.4-3.6 GHz ≈ 5.7% bandwidth). Each polarizer layer is composed of 45 • tilted metallic strips on a printed circuit. A bandwidth widening is obtained due to a significant reduction of the distance between polarizer and patches. The associated effects from the interaction of the two structures have been studied. A 2 × 2 array prototype has been implemented and measured, with a 8% average bandwidth in reflection and dual linear/circular polarization.

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A circularly polarized slotted array antenna is presented. The array is fed by a circular waveguide propagating the TM01, to properly generate the required polarization. An omnidirectional azimuth radiation pattern is obtained, as well as a −10°/+30° elevation antenna coverage. Low losses are achieved because of the waveguide feed. The slot array is mechanized over the metallic wall of the circular waveguide. Furthermore, the antenna presents a solid and rigid mechanical structure, which guarantees an optimum and repetitive response in a manufacturing process. A prototype antenna has been designed and measured. Satisfactory results have been obtained. The slotted array takes part from a signal detection system centered in 36.85 GHz. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 638–642, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22207