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A new method is introduced for the compensation of the mutual coupling effect of a linear adaptive dipole array employed in adaptive nulling of interference signals. The new method adopts a practical approach in that it needs only the measured voltages across the antenna terminal loads and an estimated current distribution for the calculation of the mutual impedances. The mutual impedance is defined and calculated differently from the conventional method and the results are more effective to remove the mutual coupling effect. The new method does not require the knowledge of the elevation angles of the signal of interest (SOI) and the interferences and still works if the elevation angles of the SOI and the interferences do not deviate too much from the horizontal direction. This increases the capability of the array to work in three-dimensional signal environments. Computer simulations for a number of rather extreme signal environments have been carried out to testify the robustness and the capability of the new method.

A low profile slot antenna array is designed to operate over a wide bandwidth with low sidelobe levels. Taylor synthesis is used to taper the power distribution among array aperture. An efficient approach to design an equal-phase but unequal-power symmetric waveguide divider is proposed for constructing an amplitude-tapering feed-network for the array. Phase differences are balanced by adjusting the waveguide phase velocities. The basic radiator is a 2×2 slot subarray, uniformly fed by such a waveguide divider. A 16×16 array is then constructed by 8×8 of such subarrays. A 1-to-64 way corporate-feed waveguide network is designed to excite all subarrays instead of individual slots, and the required power distribution is obtained by adopting a 30dB Taylor ̅ =4 synthesis. Measured results indicate that the array can achieve a 13.8% bandwidth and a gain of more than 29.5dBi. The first sidelobe level is -26.5dB in the E-plane and -30.4dB in the H-plane. The holistic sidelobe levels in both planes are better than -25dB with a better than -40dB cross-polarization.

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A novel polarization rotation technique based on an artificial magnetic conductor (AMC) structure is proposed. A new polarization rotating reflective surface (PRRS) is designed using a newly proposed AMC as the unit cell. The height of the so-constructed PRRS is only 0.04 . Our theoretical analysis shows that the polarization rotation property of the new PRRS is due to an impedance imbalance which can be analyzed using an equivalent circuit model. In addition, two polarization rotation bands and a large polarization rotation bandwidth of 29.1% can be achieved by using the new PRRS. Moreover, the new PRRS is applied for the first time to design a low-profile dipole antenna for the generation of circular polarization radiation. Three polarization states are readily achieved. Both simulation and measurement results demonstrate good right-handed circular polarization with a broad axial ratio bandwidth and a large axial ratio beamwidth in both the and planes.

Fig. 3(a) displays the measured return loss characteristic for thex-cut version of the LiNbO 3 hi-lo antenna. A measured bandwidth of 9.2% centered at approximately 12.8 GHz was observed, which is slightly lower than the z-cut antenna, but still adequate for most wireless communication systems.The far field radiation patterns at 12.75 GHz for the x-cut LiNbO 3 hi-lo antenna are given in Fig. 3(b). As the LiNbO3 wafer and the brass mounting block were approximately the same dimensions as in the z-cut case, the slight ripple in the patterns is still evident. The F/B ratio was measured to be approximately 26 dB, and a wide 3 dB beamwidth is again observed. The cross-polarization level in each plane of the x-cut LiNbO 3 hi-lo stacked patch was more than 30 dB below the copolarization level at broadside. The gain of the x-cut LiNbO3 hi-lo antenna was approximately 7 dBi. The computed gain differed by less than 1 dB from the directivity for both of the LiNbO 3 antenna structures, illustrating the efficiency of the hi-lo architecture, and implying low surface wave activity. IV. CONCLUSIONTwo hi-lo stacked patch antenna structures have been constructed employing z-cut/x-cut LiNbO3 wafers and a low permittivity foam dielectric. The use of the LiNbO 3 material enables the full integration of the antenna with electro-optic photonic devices. This can reduce the size, complexity and cost of base stations or remote antenna units in applications such as hybrid fiber-radio systems at high microwave and millimeter-wave frequencies. The LiNbO3 hi-lo configuration yields very good impedance and radiation characteristics. The simple nature of the hi-lo structure is compliant with the package requirements for OEICs, facilitating the realization of combined antenna/photonic/ microwave modules. ACKNOWLEDGMENTThe authors would like to thank Y. Visagathilagar, C. P. Wu, and S. Donovan for their assistance in the processing of the LiNbO3 wafers, and D. Welch for the mounting structures. REFERENCES[1] Y. Furuhama, "Research and developments of millimeter-wave technologies for advanced communications," in Proc. 3rd RIEC Symp.Abstract-The low-profile hemispherical helical antenna is studied experimentally and theoretically. This antenna can produce circular polarization radiation over a wide angular range of 90 . The current distribution, the input impedance, the axial ratio, the power gain, and the radiation pattern are rigorously studied. The 3-dB axial ratio bandwidth of a five-turn hemispherical helical antenna is found to be 14.6. In the range of 1 0 1 3, a relatively stable power gain of more than 9 dB is obtained. The radiation patterns typically consist of a large smooth main lobe with almost no sidelobes. These new antenna characteristics have a potential application in mobile satellite communications.

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