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A mathematical model for the impedance of the cavity-backed slot antenna," IEEE Trans. A n t e m Propagar., vol. AP-25, pp. 829-833, Nov. 1977.C . Cockrell, "The input admittance of the rectangularcavity-backed slot antenna," Abstmct-Two methods are given for the determinaition of the phase center of aperture antennas. These methods are used to obtain @e phase centers of electromagnetic horn antennas treated ai * r t u r e antennas.The second-derivative method is more accurate and uses less eomputer time, while the two-point method is easier to understanil and to derive.Calculated and experimental results are compared.Abstracf-A new helical antenna design and its measord performance are presented. This modified helical antenna provides significant improvement in the purity of the circular pdarizatiou performance over its half-power beamwidth and is most suitable for space communication application where circular polarization purity and minimum-edge-coverage gain are often required. !vianuscript

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