Kenichi Hariu

A projection method providing low sidelobe pattern in conformal array antennas

The authors present a novel method for the analytical determination of the amplitude distribution providing the low sidelobe pattern of conformal array antennas. The proposed projection method considers both the nonuniform element density and element patterns on the aperture. Numerical results are given as well as results of experimental verification for an X-band, half-spherical array with 60 rectangular microstrip antennas.<<ETX>>

System design of wide swath, high resolution, full polarimietoric L-band SAR onboard ALOS-2

This paper describes SAR system design of the Advanced Land Observing Satellite-2 (ALOS-2), which is a next-generation Japanese L-band SAR satellite. Since one of an important mission of ALOS-2 is a global monitoring using its unique frequency of L-band, a capability of wider coverage is required. On the contrary, in the point of disaster monitoring especially for urban area, relatively higher spatial resolution is essential. To comply with such a contradictive requirement of wide swath and high resolution, ALOS-2 utilizes a dual-receive channel (DRC) technique, and achieved a coverage area of up to 50km with a spatial resolution of down to 3m. In the paper, the H/W design of ALOS-2 DRC mode is explained. For a wider coverage of polarimetric observation, ALOS-2 installs the fully redundant and “quad-receive channel” system to full-polarimetric mode, achieving a maximum coverage of 50km at 6m resolution. As an experimental mode, new polarimetric mode called “compact polarimetry” is installed for a wide coverage of polarimetric observation.

Pattern correction in large deployable reflector antennas with phased array feed

Recently, engineers have focused on developing mobile satellite communications systems using GEO, MEO and LEO satellites. We are now studying an on-board antenna for future S-band mobile satellite communications using hand-held terminals. This antenna is carried on a GEO satellite, and consists of a large deployable mesh reflector and a primary feed using an active phased array. It has the advantage of beam forming flexibility. For example, when its radiation pattern changes due to an amplifier problem, we can obtain the desired pattern by adjusting the only excitation phase of the array feed. We first present the satellite antennas configuration, then describe pattern correction by adjusting the excitation phase of the array feed.

Deployment test methods for a large deployable mesh reflector

The deployment characteristicsof large structures must be evaluated by ground tests. A deployment test system is described that enables high-precision gravity canceling, in contrast to the conventional radial support test method (hanging a ree ector by cables suspended from a high ceiling ). A large deployable ree ector composed of hexagonal pyramid-shaped modules is used in the deployment test. The ree ector is deployed by a coil spring force and controlled by motors and cables for a quasistatic stable deployment motion. A magnetically suspended slider test system was developed for accurate deployment tests. We cone rm that hanging at the pantograph bar is the most suitable test cone guration to simulate microgravity conditions, according to one-sided model experiments and deploying forceanalyses using mechanism analysissoftware. We also establish that a vertical support method, using thedevelopedmagneticallysuspendedsliders,enableshigh-precisiondeploymentfora largedeployablemesh ree ector.

Beam pointing error analysis for phased array antennas with true time delay modules

The beam pointing error theory for the phased array antennas (PAA) with true-time-delay (TTD) module is proposed in closed form and is confirmed to be valid. The proposed theory easily gives the optimum subarray size, which is a unit of a TTD module, and maximum delay length of the TTD module in order to attain the desired beam pointing accuracy.

Estimation of excitation amplitude and phase using radiation pattern for array antennas

In array antennas, sometimes the desired radiation pattern cannot be obtained due to coupling between element antennas, reflections from the surroundings, or amplitude and phase error of the power supply circuits or failures. In these cases, it is necessary to regenerate the desired radiation pattern by estimating the excitation amplitude and phase of the array antennas. Among methods of estimation of the excitation amplitude and phase, the rotation element field vector method of element antennas is used for the phased array antenna with variable phase shifters, and the planar near-field measurement method is used for the array antennas with no variable phase shifters. The former is limited to phased array antennas, and the latter requires a large-scale scanner for the measurement and results in increased measurement time with larger-scale array antennas. In this paper, we propose a method of estimation of excitation amplitude and phase using the radiation pattern of array element antennas and the measured radiation pattern of the array antennas. Two methods are proposed here; the first method of estimation is the least-squares method using the electrical field as the measured radiation pattern, and the second is the repeating calculation method using the electrical power as the measured radiation pattern. We describe here the principle and experimental results when the first method is used, and the principle and the effectiveness of selection of the initial value for the second method is confirmed by numerical results.

Deployment Test System Using Magnetically Suspended Sliders for Large Space Structures.

Various test methods have previously been adopted to test large deployable space structures. However, traditional methods are not applicable to a precise evaluation of three-dimensional deployment characteristics with quasistatic deployment motions. This paper describes the design and performance of a deployment test system using magnetically suspended sliders. The sliders support the deployable structure vertically, and each of them moves freely with negligible friction under the horizontal surface of a ceiling plate. All the sliders control the tension of their vertical cables independently using the feedback signals of the tension sensor to compensate for the gravity of the deployable structure. The test system using magnetically suspended sliders enables maximum drag with a horizontal motion of less than 0.25N and tension control precision from a suspension cable of within 0.25N. The adequacy of this test system is confirmed by a deployment test using a 7m test model.