Kazuaki Kawabata

A circularly polarized microstrip antenna using a crossed-slot feed

A simple configuration using a crossed-slot feed with a single microstrip line or a triplate line without a 90 degrees branch hybrid coupler to obtain the required phase shift is proposed. Measurement results on this circularly polarized microstrip antenna are presented. By using the crossed-slot feed method, a microstrip antenna with an axial ratio of less than 2 dB in a wide angle range was obtained. From these results, it was verified that circular polarization operation can be obtained by the proposed method.<<ETX>>

Scanning limitation in adaptive superresolution array

A fundamental limitation in an adaptive superresolution array, due to reciprocity between the angular resolution capability and the measurement time required, is discussed. For this purpose, a new concept for the measurement time, a scanning time concept, is introduced by considering a superresolution array consisting of an Applebaum-Howells adaptive processor with steering signal changing periodically with time. The measurement time is defined as the amount of time taken to perform one observation over the range of desired angle. Superresolution array output is defined according to the adapted angular response formulation. It is shown that the relationship between the resolution capability and the scanning time is reciprocal, i.e., the increased angular resolution is obtained at the expense of the scanning time. The relationship is discussed quantitatively for a narrow-band signal model.

A systolic array architecture for the Applebaum-Howells array

A systolic array architecture for the Applebaum-Howells array is derived. The problem to be solved is the elimination of the global signal feedback loop in the conventional Applebaum-Howells array processor. The procedure involved in deriving the architecture consists of two steps: orthogonalization of the input element signals and elimination of the feedback loop. In the first step, the input element signals are orthogonalized with regard to each other by using the Gram-Schmidt processor, placed ahead of the Applebaum-Howells processor. It is shown in the second step that the orthogonality in the Gram-Schmidt processor output signals can remove the global signal feedback loop and that the Applebaum-Howells array can be implemented effectively by using a systolic array with regular structure and local communication. Simulation results also show that the proposed processor features desirable characteristics for the radiation pattern with low sidelobe level common to the Applebaum-Howells array. >

Systolic array architecture of Applebaum-Howells array

A systolic array architecture for the Applebaum-Howells array is presented. The proposed architecture uses the preprocessor technique; the overall array consists of a preprocessor and an Applebaum-Howells processor. Assuming that the Gram-Schmidt processor is used as the preprocessor, it is shown that the orthogonality among the Gram-Schmidt processor outputs can remove the global feedback loop needed in the conventional Applebaum-Howells processor, which prevents the array from being used in systolic array implementation, and that the Applebaum-Howells array can be efficiently implemented by using the systolic array architecture.<<ETX>>