Hiroyuki Ohmine

Electromagnetically coupled coaxial dipole array antenna

A new type of collinear antenna called electromagnetically coupled coaxial dipole array antenna is proposed. The antenna has an advantage of structural simplicity due to a novel use of an electromagnetically coupled feed structure for the radiating element. An analysis of the radiating element is presented and compared with experimental results. Fabrication and measurement of a prototype array antenna are also presented.

Fast Measurement Technique for Phased Array Calibration

A novel measurement method is proposed in order to measure the active electric fields of the individual antenna elements in a phased array antenna. Fast and accurate measurements can be realized by the proposed method because the electric fields of multiple elements can be obtained simultaneously and no phase measurements are required. Hence, it can be easily applied to the on-board diagnostics and re-calibration in the operating phased array antenna systems. In the first step with this method, the phases of multiple antenna elements are successively shifted with the specified phase intervals while the array power variations are measured. Next, the measured power variation is expanded into a Fourier series and the terms are rearranged to put them into the form of the rotating element electric field vector (REV) method. Finally, the REV solution is used to identify the electric fields of the individual elements. Additionally, a theoretical study is carried out on the accuracy of the proposed measurement method. Simple, closed-form equations have been successfully derived for the measurement errors and the calibration accuracy is theoretically estimated. The proposed measurement method is validated with experimental results and the measurement accuracy is compared with the theoretical prediction.

An annular-ring microstrip antenna fed by a co-planar feed circuit for mobile satellite communication use

A new configuration of circularly polarized annular-ring microstrip antenna (ARMSA) fed by a branch-line hybrid coupler placed at the inner part of the ARMSA and its design method using an equivalent circuit are presented. Since the ARMSA has a narrow bandwidth and high-input impedance, a parasitic element placed above the ARMSA is employed for not only obtaining a broadband characteristic, but decreasing the input impedance down to 50 /spl Omega/. A hybrid coupler to generate circular polarization, therefore, can be connected to the co-planar space of the ARMSA directly without a large-size matching circuit and a very low profile and simple structure can be achieved. The ARMSA is excited at the TM/sub 21/ mode to produce a conical pattern, which has a high gain in a low-elevation angle for mobile satellite communications. An effective design method using the equivalent circuit is indicated and, as a result, it is obvious that a broadband characteristic is obtained when each resonant frequency of the ARMSA and parasitic element is identical. Experimental results in the L-band showed satisfactory characteristics for vehicle antennas.

Measurement of the Offset-Cassegrain Antenna of JEM/SMILES Using a Near-Field Phase-Retrieval Method in the 640-GHz Band

This communication describes the results of the measurements made for the flight model of the offset Cassegrain antenna of superconducting submillimeter-wave limb-emission sounder (SMILES) aboard the International Space Station. We have employed a near-field phase retrieval method in which the aperture phase distribution is estimated only from the amplitude distribution measurements over two near-field planes. The far-field patterns estimated from the estimated near-field patterns were compared with theoretical calculations based on physical optics in which the surface errors measured for the main and sub reflectors were taken into account. As a result of the comparison, the far-field patterns estimated from the phase retrieval method were found to be in very good agreement with the physical-optics calculations to the sidelobe levels as low as -55 dB. We have also found that patterns of machined flaws on the surface of the main reflector were clearly identified in the retrieved near-field phase pattern. This demonstrates that the phase retrieval is an effective method to evaluate aperture antennas in the submillimeter-wave region, where accurate phase measurement is rather difficult.

Performance test results of a manufactured submillimeter-wave offset cassegrain antenna at 0.64 THz band

This paper describes the design, manufacturing and performance test results of a submillimeter antenna (ANT) of SMILES at 0.64THz. The design of ANT is aiming at achieving high beam efficiency, low side lobe levels and a high thermal stability (Noguchi, 2003)(Noguchi et al., 2004). In this paper, a manufactured engineering flight model (EFM) of ANT and its measured performance, such as surface errors of reflectors, near- field distribution and far-field radiation pattern estimation from the near field measurements are presented. Measured performance has in good agreement with the design and the successful performance of EFM has been confirmed.

A small-sized waveguide horn with multi-ridge impedance transformer

This paper proposes a new configuration of small-sized horn having broad beamwidth with multi-ridge impedance transformer to realize small aperture size, which is to be near cut-off frequency. The small-sized aperture near cut-off frequency causes mismatch loss because of indication of high impedance like the open-ended waveguide. In order to overcome this problem, the multi-ridge part, which reduces the characteristic impedance, is introduced at the end of the horn aperture to transform the waveguide to free space smoothly. This novel configuration can achieve impedance matching at around the cut-off frequency and keeps the broad beamwidth.

Car-top annular-ring microstrip antenna

In Japan a car-top antenna for satellite communications is required to have high gain in the elevation angle range of 30 degrees -60 degrees . An annular-ring microstrip antenna (ARMSA) with a conical pattern which has high directivity in this angle range has been developed. The antenna gain is more than 3 dB in the elevation angle range of 30 degrees <or= theta <or=60 degrees .<<ETX>>

Resonant frequency of dipole antennas with crank sections in dual-band arrays

This paper presents the relation between the resonant frequency and the length of the dipole, which is an important parameter in antenna design. This relation is derived from a comparison between the inductance of the dipole and of a half wavelength dipole having the same resonant frequency. In addition, the theory is confirmed by numerical results.