A compact bandstop frequency selective surface (FSS) using fractal structure is proposed. This flexuous design elongates the cell perimeter of the ring-shaped FSS, which means the cell size gets smaller at the same resonance frequency. Furthermore, the unit cells adopt regular hexagon and the array employs equilateral triangle form. Because of its symmetric configuration, good frequency stability has been achieved for both horizontal and vertical polarizations at different oblique angles. For the stable bandstop character, this FSS can be used for protecting the staff of S-band radars against electromagnetic radiation, while the 900/1800/1900 MHz mobile bands and the 5.2/5.8 GHz wireless local area network signals are not affected. Minimal size FSS for long wavelength, Electron Lett 44 (2008), 394 -395. 9. K.Q. da Costa and V. Dmitriev, Theoretical analysis of a modified Koch monopole with reduced dimensions, IEE Proc-Microw Antennas Propag 5 (2006), 475-479. ABSTRACT: A 15-by-20-mm 2 dual-broadband printed monopole antenna fed by a coplanar waveguide is presented. With a numeral-7 slit etched from the rectangular radiating element, the antenna can excite for its lower and upper impedance bands two and one resonant modes, respectively. With a back-patch appropriately printed on the other side of the substrate, a lower (upper) impedance band with a bandwidth of 39.3% (19.5%) can be obtained. These two impedance bands can cover the frequency bands required by UMTS/IMT-2000/IEEE802.11a/b/g/ WiMAX.

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Circular symmetrical ground planes such as square and circular ones are always utilized in the design of circularly polarized antennas. However, carriers in practical applications are mostly circular asymmetrical, which will impose an effect on the circular polarization performance of the circularly polarized antenna. The characteristics of a circularly polarized microstrip patch antenna with a circular asymmetrical ground plane are analyzed through simulation in this paper. The reason for deterioration of the circular polarization performance is discussed, on the basis of which an improved method is proposed to design a dual-feed circularly polarized rectangular microstrip patch antenna on a circular asymmetrical carrier. The antenna is fabricated and measured. Measured results show that performance of the antenna is remarkably improved.

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