Kimio Sakurai

A radial line slot antenna for 12 GHz satellite TV reception

The analysis and design of novel planar antennas which can radiate circularly polarized pencil beams in x -band are presented for the application of receiving direct broadcast from a satellite (DBS). This antenna belongs to a class of slotted waveguide antennas and high efficiency is expected in principle. A circular two-dimensional aperture is located on the top plate of a twofold radial waveguide and is excited by a radially inward traveling transverse electromagnetic (TEM) mode in the upper waveguide. Slots are arrayed on the aperture spirally in such a way that they can couple with the radial currents flowing over the aperture plate to produce a circularly polarized broadside beam. Promising performances of the antenna are predicted theoretically. Experiments are performed with respect to basic characteristics of the antenna and they show the validity of the design and analysis.

An analysis of a waveguide T junction with an inductive post

The authors analyze the T junction with an inductive post, taking its diameter into account for the case where the current distribution is assumed on the surface of the post. A single cylindrical post placed in a T junction improves the impedance matching and compensates the junction discontinuity in a wide frequency band. The effects of the design parameters, such as the diameter of the post and its location, are clarified. The measured return loss is accurately predicted. On the basis of this analysis, an effective design procedure for the T junction is proposed, and the reflection below -30 dB is realized over 4% bandwidth. >

Characteristics of a radial line slot antenna for 12 GHz band satellite TV reception

Characteristics of a novel planar antenna which can radiate a circularly polarized pencil beam in x -band are presented for the application of receiving direct broadcast from a satellite. This antenna belongs to a class of slotted waveguide antennas and promising performances, especially its high efficiency, have already been predicted theoretically. The measured performance of a model antenna with a diameter of 0.6 m, is presented. Antenna gain of about 35 dBi and axial ratio of about 1 dB are realized at 12.2 GHz; the associated antenna efficiency of 57 percent is very high in comparison with that of the conventional microstrip antennas, in this range of gain.

Slot coupling in a radial line slot antenna for 12-GHz band satellite TV reception

Coupling between slots and slow-wave waveguides in a radial line slot antenna (RLSA) is discussed. Field analysis of the waveguide with a surface impedance wall revealed a considerable change in the propagation constant due to coupling. Experiments were performed to confirm these results and to obtain the surface impedance for actual slots. The change in the propagation constant caused the antenna efficiency to exhibit its maxima at two separated frequencies. An efficiency of 60% and 50% was measured at 11.6 and 12.4 GHz, respectively, which confirms a theoretical prediction. This effect suggests the possibility of broadband planar antennas. >

A matching slot pair for a circularly-polarized slotted waveguide array

The analysis and the design of the matching slot pair for a circularly polarized slotted waveguide array are described. The position and the size of the slots are numerically optimized to suppress reflection and to realize a desired polarization in the tilted beam direction, which contributes to the improvement of the antenna efficiency. A boundary value problem is analyzed for the matching slot pair taking the wall thickness of a waveguide into account in order to evaluate the phase of aperture fields accurately. The position and the size of the slots are determined on the basis of this analysis. The design is verified by measuring the reflection coefficient, the radiation patterns, and the axial ratio of a model slot pair. It was verified experimentally that the return loss is below -15 dB over 0.1 GHz at the 4-GHz band and the 3-dB axial ratio bandwidth is about 5% in the titled beam direction. >

Obliquely arranged feed waveguide for alternating-phase fed single-Layer slotted waveguide array

An alternating phase fed waveguide array with an oblique arrangement of feed waveguide is proposed. It belongs to single-layer waveguide arrays developed by the authors. Conventional arrays with radiation waveguides arranged perpendicularly to the feed waveguide suffer from accumulated reflection from coupling windows after round-trip propagation at the input port. In the proposed oblique arrangement, the reflections from each coupling window will not accumulate in phase but be diffused away out of phase. First, the design of obliquely arrayed T-junctions is conducted using two-dimensional finite element method (FEM). Then basic operations of the reflection canceling as well as improved voltage standing-wave ratio at the antenna input are confirmed by experiments. Almost the same radiation patterns and gain as the conventional arrays are observed in the measurements

A circularly polarized waveguide narrow-wall slot array using a single layer polarization converter

A linearly polarized radar antenna made by a slot array on the narrow wall of a rectangular waveguide has been widely used for shipborne applications. This paper proposes a circularly polarized waveguide narrow-wall slot array with a single layer dipole array mounted on it as a polarization converter. We can switch from linear polarization to circular polarization by mounting the dipole array in front of an existing linear polarization array. In a narrow-wall slot array, each slot has a different angle with respect to the waveguide axis to control the radiation power. This variation in the slot angle results in a large phase difference in the circularly polarized wave, when each dipole mounted on the inclined slot is designed to optimize the axial ratio of the element pattern and is making a constant angle with each slot. Grating lobes of -14 dB and -20 dB appear in the -35 dB Taylor distribution design of 1.2 m (47 elements) and 3.6 m (150 elements) in the 9.41 GHz band. The phase correction is realized by changing the angle between the slot and dipole though the axial ratio of the element in the boresight direction is degraded up to 4.0 dB in the worst case. The array pattern is still perfect circularly polarized. The level of the grating lobes after the phase control is about -18 dB and -26 dB for the circularly polarized antenna with 47 elements and 150 elements, respectively.

Study of material loss in mm-wave RLSA with honeycomb structure

Analysis of the electrical properties of dielectric materials, which were used to fill an oversized radial waveguide of the RLSA, was carried out at 32 GHz. The use of multiple layers is indispensable to meet the requirements for space-use RLSA, and the electrical properties (permittivity, loss factor) need to be specified accurately in order to design the slot array and optimize the antenna performances. Simulation results of the waveguide filled with NOMEX® honeycomb structure suggested a significant material loss at 32 GHz. The measurement results of fabricated antennas supported this anticipation.dielectric materials,oversized radial waveguide

Estimation and measurement of cylindrical wave propagation in parallel plate with honeycomb spacer for the use in mm-wave RLSA

Analysis of non-metallic honeycomb structures to be used as the waveguide at 32 GHz in a satellite on-board Radial Line Slot Antenna (RLSA) was carried out. Incorporating honeycomb structure for the waveguide is indispensable to meet the requirements for space-use while maintaining the electrical characteristics. At 8.4 GHz this was successfully done using Quartz honeycomb structure, where the cell size was much smaller than the guided wavelength. At 32 GHz, with the design frequency 4 times larger, estimation of propagation characteristics in the millimeter wave region was a necessity. Simulation results anticipated anisotropic propagation around 32 GHz for larger cell sizes and significant material loss for smaller cell sizes. These results were partly confirmed by measurements of honeycomb structure and antenna measurements supported significant material loss.

Design of 1 m^2 Order Plasma Excitation Single-Layer Slotted Waveguide Array with Conducting Baffles and Quartz Glass Strips Using the GSM-MoM Analysis

The authors have proposed a 1 m 2 single-layer slotted waveguide array consisting of conducting baffles and quartz glass strips positioned in front of the slot aperture, which is referred to as a vacuum window, for microwave plasma excitation. The effect of the complicated outer vacuum window hinders the realization of uniform distribution. In this paper, a unit-cell of the alternating-phase fed single-layer slotted waveguide array with the vacuum window is analyzed by generalized scattering matrix method (GSM)-method of moments (MoM) hybridization analysis, and the array is designed to realize uniform aperture electromagnetic field distribution, where the plasma and the chamber is neglected. The GSM-MoM analysis gives reliable numerical results while the MoM has numerical errors due to singularities of Greens function for a long cavity. Uniform aperture EM field distribution outside of the vacuum window is observed in near field measurements using a 1/5 scale model antenna, and the validity of the analysis and design is verified.