A novel technique for obtaining dual-hand circular polarisation (CP) radiation of a single-feed circular microstrip antenna in proposed and demonstrated . By embedding two pain of arcshaped slots of proper lengths close to the boundary of a circular patch, and protniding one of the arc-shaped slots with a narrow slit, the circular micr(strip antenna can perform dual-hand Cl' radiation using a single probe feed. Details of the antenna design and experimental results are presented.Introduction: Dual-frequency operations of microstrip antennas have received much attention, and many related designs have also been reported [1]. However, the dual-frequency designs available in the literature are mainly for linear polarisation (LP) operation. Little attention has been given to the dual-hand circular polarisation (CP) design, especially for the case using a single probe feed. This is probably because single-feed dual-band CP design is more complicated than that required for dual-band LP design. The typical dual-band CP microstrip antennas that have been reported include design using an aperture-coupled stacked microstrip antenna [2] or a combination of the spur-line filter technique and a nearly square patch antenna [3]. In this Letter, we propose a novel and simple design method using a single-layer circular microstrip antenna to achieve single-feed dual-band CP operation. The proposed antenna can easily be implemented by embedding two pairs of arc-shaped slots, with one of the arc-shaped slots having a narrow radial protruding slot, close to the boundary of the circular patch. Details of the proposed antenna desigr are described, and experimental results for CP performance are presented and discussed.

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A no¨el dual-frequency rectangular microstrip antenna with an inserted integrated reacti¨e loading is proposed and experimentally studied. The reacti¨e loading has the structure of a trapezoid microstrip-line section inserted at one of the radiating edges of the patch. By adjusting the flare angle of the trapezoid microstrip-line section, the frequency ratio of the two operating frequencies is tunable in the range INTRODUCTIONDual-frequency design for a rectangular microstrip antenna with an inserted short-circuited microstrip-line section at one w x of the radiating edges of the patch has been presented 1 . In such a design, the inserted short-circuited microstrip-line section serves as an integrated reactive loading to the mi- Figure 1 Geometry of a dual-frequency rectangular microstrip antenna with an inserted integrated reactive loading crostrip antenna. By selecting the length of the inserted short-circuited microstrip-line section, two resonant modes near the fundamental mode of the original unloaded microstrip antenna can be excited. However, because the inserted short-circuited microstrip-line section protrudes beyond the patch edge, the real size of this antenna is larger than that of the original unloaded microstrip antenna. Recently, dual-frequency operation of a single-feed rectangular microstrip antenna with an embedded reactive loading was w x also reported 2 . In such a case, the inserted short-circuited microstrip-line section is replaced by a microstrip structure of two cascaded microstrip-line sections embedded within a rectangular slot cut in the rectangular microstrip patch. The two cascaded microstrip-line sections also provide an intew x grated reactive loading to the microstrip antenna 3᎐5 . Moreover, because the embedded reactive loading requires no protrusions beyond the patch boundary, this design is w x more compact than that reported in 1 . In this letter, we report a new and promising design of a rectangular microstrip antenna with an inserted integrated reactive loading for dual-frequency operation. The inserted integrated reactive loading has the structure of a trapezoid microstrip-line section having a flare angle ␣ subtended by its two parallel sides, which can be easily constructed by inserting two narrow Ž . slits at one of the radiating edges of the patch see Fig. 1 . Since the inserted integrated reactive loading also requires no protrusions beyond the patch boundary, the proposed antenna has the same compact characteristic as the dualw x frequency design reported in 2 , but is simpler in structure. For the two operating frequencies of the proposed antenna, the same polarization planes and broadside radiation patterns are obtained. By using a trapezoid microstrip-line section of various flare angles, the frequency ratio of the two operating frequencies can also be adjusted. Details of the proposed antenna and experimental results are presented. Figure 1 shows the geometry of a dual-frequency rectangular microstrip antenna with an inserted integrated reactive loading....