Akimichi Hirota

A Compact Forward Coupler Using Coupled Composite Right/Left-Handed Transmission Lines

A novel forward coupler using coupled composite right/left-handed (CRLH) transmission lines (TLs) is presented. Forward coupling is enhanced by the CRLH TLs, which have a considerable difference between the effective phase constants in the even and odd modes. A 10-dB forward coupler using the coupled CRLH TLs is simulated and experimentally demonstrated in the S-band. Its coupled-line length is reduced to half that of the conventional right-handed forward coupler with the same coupling.

Direction-of-Arrival Estimation System for Multipath Propagation in Code-Division Multiple-Access Systems With Synthesized Virtual Planar Array Using Pilot Signals

Here, we propose a method for estimating the direction of arrival (DOA) using pilot signals in code-division multiple-access (CDMA) systems. We also report the evaluation of the performance of the proposed method by conducting simulations and experiments in an anechoic chamber and an outdoor environment. This method estimates the DOA of the arrival waves by synthesizing the data received by a virtual planar array using pilot signals. First, we describe a method for synthesizing the data received by the virtual planar array using pilot signals. Next, we present simulation results that confirmed that the accuracy of the estimation based on the virtual planar array was the same as that based on a real planar array. Last, we describe the effectiveness of the proposed system that is demonstrated through experiments in both the anechoic chamber and in an outdoor environment.

A stripline power divider with insensitive to resistance variations using a parallel resistor pair

The characteristics of a Wilkinson power divider frequently degrade when an isolation resistor in the Wilkinson power divider is formed by a resistance film because the resistance changes caused by manufacturing errors. In this paper, we present a stripline power divider that is insensitive to resistance variations, using a parallel resistor pair. In the proposed divider, two parallel resistors connected through 1/4-wavelength lines are placed between two output ports. When the resistance of the two resistors is changed because of manufacturing errors, the characteristics of the proposed divider remain stable because the total resistance of the resistor pair hardly changes owing to the connection of the two resistors through the 1/4-wavelength lines, which function as impedance transformers. The proposed divider was simulated and experimentally demonstrated in the X-band. The return loss and isolation in the experiments were lower than -20 dB in a 30.2% bandwidth when the resistance was changed to +50%.

Characteristics of Virtual Planar Array Antenna for Direction-of-arrival Estimation

In this paper, we report the evaluation of the performance of the methods for estimating the direction of arrival (DoA) with a virtual planar array antenna by conducting simulations and experiments in an anechoic chamber. These methods estimate the DOA of the arrival waves by synthesizing data received by a virtual planar array. First, we describe methods for synthesizing the data received by the virtual planar array using a T-shaped array antenna. Next, we present the simulation results that confirmed that the accuracy of these methods based on the virtual planar array. Finally, we demonstrate the effectiveness of the proposed systems through experiments in the anechoic chamber

DOA system with synthesized virtual planar array using eigenvectors

In this paper, we proposed a method of DOA estimation using eigenvectors and evaluated the proposed method by performing simulations and experiments in an anechoic chamber. DOA was estimated correctly in these simulations, and the effectiveness of the proposed method was confirmed. We evaluated the average of estimation errors to be about 1.4° in the anechoic chamber. These results confirmed that the proposed method provides an effective DOA estimation. Further studies are attempting to apply the proposed method to uncorrelated waves and estimate DOA from certain base stations through experiments.