the simulated and measured return losses, by using the optimized antenna parameters presented in Figure 3 and the bandwidth of the proposed antenna is 2.7-12 GHz. As shown in Figure 4, the maximum gain is 3.4-6.1 dBi in the whole frequency range and the 3 dB bandwidth of the axial ratio is 4.2-4.7 GHz, 5.9-6.8 GHz, and a minimum axial ratio level of 0.7 dB was obtained at 6.2 GHz. Figure 5 shows the measured radiation patterns of the designed antenna. The E h -patterns generally have omni-directional radiation patterns, viewed in the linear polarization [ Fig. 5(a)]. Moreover, viewed in the circular polarization ], the left hand circular polarization (LHCP) radiation patterns have been validated. In case of the planar two-arm Archimedean spiral antenna, they fed from the center of the spiral plane, radiating a circularly polarized wave in the direction normal to the spiral plane. However, the twoarm eccentric spiral antenna generates a circularly polarized wave with a main beam off-normal to the spiral plane [5]. The proposed antenna is similar to the eccentric antenna in that they are fed at the eccentricity. In addition, their radiation patterns are similar. The parameter P that is considered to obtain the broadband does not significantly decrease the gain at 12 GHz. CONCLUSIONSA new type of spiral slot antennas, fed by CPW, has been designed and fabricated using the magnetic phase difference. The advantages of this antenna are that its 3D volume is reduced using the CPW structure, and hence the balun circuit is not needed because the two spiral slots are fed by 180 out-of-phase sources with each other so that the magnetic cancellation caused by the different magnetic flow is minimized. This antenna is suitable for UWB antenna and dual band circularly polarized antenna. ABSTRACT: In this letter, design of compact size rat-race coupler (RRC), based on impedance-controlled simple transmission line structure is proposed for predetermined harmonic suppression. The present approach has the advantage that within the fabrication limit of high-impedance lines, a large number of harmonics are suppressed. Design guidelines are provided. Theoretical predictions are verified by implementing a prototype microstrip RRC, with up to twelfth harmonic of the operating frequency suppressed along with 75% size reduction compared with the conventional RRC.

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A novel structure for a frequency-independent steerable composite right/left-handed (CRLH) leaky wave (LW) antenna in the millimeter-wave band is proposed. This has the advantages of wide beam scanning and low profile, and is a suitable structure for mass-production. The proposed antenna has features wherein a movable dielectric slab is placed above the CRLH LW antenna, and the radiation angle can be steered by changing the distance between the slab and the antenna using compact actuators. Moreover, slots are added to the antenna to control the aperture amplitude distribution of the array antenna in order to enhance aperture efficiency. A prototype CRLH LW antenna has been fabricated with these slots, and backwardto-forward beam scanning characteristics at 76 GHz have been demonstrated successfully by measurement. A wide scanning angle from 73 to 114 deg. has been achieved experimentally. The aperture efficiency is 25.3 %.