This article proposes a fast far-field estimation method of electrically long antenna in compact measurement space. The presented method estimates a far-field pattern on an orthogonal cut plane from the linear equivalent electric current and circular current distribution. The equivalent electric current data is measured in a reactive near-field region using a small loop probe. In the proposed method, the linear equivalent current distribution is extended by a simple numerical extrapolation formula for improving the accuracy of the estimated far-field in the broadside direction. In the horizontal plane, the far-field pattern is calculated from both the circular equivalent electric and magnetic distribution approximating equivalent magnetic current with equivalent electric current. We confirmed the validity of the proposed method from the numerical simulation and measurements results. The method allows accurate directivity measurement in a small space in about a few minutes.

A broadband differential-line-to-waveguide transition covering the 260-300 GHz band was developed in this study. This transition consists of a differential line inserted from the narrow wall of the waveguide that excites an X-shaped patch located at the waveguide center. As the two corners of the patch are excited electromagnetically via differential signal lines in the opposite phase, orthogonal current components that radiate the TE 10 mode into the waveguide are generated. Broadband operation is achieved via the double resonance of the X-shaped patch and a cavity formed by the via-hole arrangement with apertures patterned in a multi-layer substrate. The transition geometries are optimized via electromagnetic simulation using a finite element method. Transition performance is evaluated through measurements and simulations.

This paper presents a new kind of finline in double-layer dielectric substrate and its beamforming circuit of Butler matrix in the millimeter-wave band. The finline is constructed by inserting a slotline between two dielectric substrate layers. In this configuration, it is bounded within a closed structure composed of a double-layer dielectric substrate and two rows of via-hole arrangement, contributing to low dispersion and low radiation loss of the finline characteristics. The proposed finline design aims to provide a low-complexity and low-loss transmission line which is applied to the Butler matrix design. A 4×4 Butler matrix for 4 switchable beams is realized by using the finline in the double-layer dielectric substrate. In addition, a waveguide-to-finline transition is developed as a feeding circuit for the Butler matrix. Characteristics of the proposed transition and the Butler matrix were analyzed by electromagnetic analysis of the finite element method and demonstrated by experiments at 79 GHz. The proposed Butler matrix obtains a wideband characteristic and an acceptable insertion loss of 2.42 dB. The array factor which is calculated from the measured amplitude and phase outputs 4 swichable beams with the beam directions of +14 • , −46.5 • , +46.5 • and −14 • , respectively. The proposed beamforming circuit using finline in double-layer dielectric substrate would be attractive for millimeter-wave applications due to its performance and low cost.

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