Kazutaka Kikuta

Compact Folded-Fin Tapered Slot Antenna for UWB Applications

In this letter, a novel antipodal tapered slot antenna (TSA) for ultra-wideband (UWB) applications is proposed. A folded fin structure is employed in the design for realizing wider bandwidth. Generally, UWB antennas have difficulty in its miniaturization because the lower-limit frequency reaches to 3.1 GHz. The lower-limit is determined by its total fin width. The folded fins realize both the lower limit and a compact size. We demonstrate the wideband characteristics in experiments. Its dispersion characteristic is also measured and discussed.

An Active Metamaterial Antenna With MEMS-Modulated Scanning Radiation Beams

In this letter, for the first time, we report a microelectromechanical system (MEMS)-modulated scanning beam metamaterial antenna based on surface micromachining process. The antenna is implemented by cascading periodical metamaterial modules with a unit length of less than λg/5 to make an electromagnetically homogeneous waveguide, of which the MEMS cantilevers are monolithically integrated in each unit as a radio frequency (RF) switch to modulate the phase constant β, and thereby to realize the scanning beams in the fixed frequency around 8 GHz. Experiments that verified the MEMS-modulated scanning radiation beams are tuned from the backward (around -15°) to the broadside (around 0°) and to the forward (around +15°) directions as the RF-MEMS switches are, respectively, actuated from the states of 0000-0000 (switches in all of the eight units are OFF) to 1010-1010 (switches in the unit of numbers 1, 3, 5, and 7 are ON) and to 1111-1111 (all switches are ON).

Interference mitigation in UWB receivers utilizing the differences in direction of arrival and power spectrum density

High-definition localization has the potential to create broad applications in various field. Ultra wideband (UWB) technology achieves high ranging accuracy through signal time of arrival (TOA) measurements. TOA estimation can be challenging when operating in the environment with narrow band interference (NBI). In this paper, we propose a practical interference mitigation scheme using direction of arrival estimation method. Reduction of the wave incoming only from the direction and in the frequency band of interference wave can be achieved using two-element compact array antenna with small amount of calculation. Simulation results demonstrate that the proposed method realizes interference mitigation effectively.

Narrowband Interference Mitigation in UWB Systems Utilizing Frequency Dependence of Null Formation in Array Antennas

The high precision ranging using ultra wideband (UWB) signals is expected for various applications. However, UWB requires mitigation of narrowband interference (NBI) from other wireless systems. There have been many studies of adaptive notch filters to cope with NBI at various frequencies. This paper proposes a novel NBI mitigation method which utilizes frequency dependence characteristics in array antennas. We use power inversion to direct nulls to large-power input, which realizes NBI only suppression with a small calculation cost. The results show that the proposed method can obtain lower bit error rate. The proposed method can cope with variously directional and multiple-frequency NBIs without a priori knowledge of the incident waves.

An active metamaterials antenna controleld by RF-MEMS switches

This paper reports an active metamaterials-based CRLH (Composite Right Left Handed) antenna, in which RF-MEMS cantilevers are used as RF switches to reconfigure the radiation patterns. We implement leaky-wave antenna with cascaded metallic patterns of a J-shaped unit that possess an effective electromagnetic homogeneity and tunable metamaterial properties. Owing to the microstrip-based periodic structures that are compatible with micro-machining process, RF-MEMS cantilevers arrays are integrated in each cell to control the electromagnetic boundary conditions. By actuating the RF-MEMS switches between ON and OFF in each unit, the metamaterials properties are tuned and thereby the spatial radiation patterns are correspondingly controlled from backward (around -30°) radiation to forward (around +30°) at a fixed frequency around 9 GHz.

Direction-of-Arrival Estimation of Ultra-Wideband Signals in Narrowband Interference Environment Based on Power Inversion and Complex-Valued Neural Networks

We propose two-stage null-steering direction-of-arrival (DoA) estimation of ultra wideband (UWB) signals with power inversion algorithm and complex spatio-temporal neural network (CVSTNN). This method can estimate DoA more accurately than conventional methods in narrowband interference (NBI) environment. For null steering in UWB systems, it is necessary to adjust the amplitude and phase of tapped delay lines (TDLs) of CVSTNN. However, with a conventional CVSTNN, it often fails to estimate the arrival direction because of the NBI. We aim to reduce the influence of NBI in the learning process to avoid falling into a local solution by setting the initial weights of the TDLs with power inversion. In simulation results, it is shown that the two-stage method can realize higher DoA estimation accuracy than conventional methods.

High Precision Direction-of-Arrival Estimation for Wideband Signals in Environment with Interference Based on Complex-Valued Neural Networks

We propose a null steering scheme for wideband acoustic pulses and narrow band interference NBI using direction of arrival DoA estimation based on complex-valued spatio-temporal neural networks CVSTNNs and power inversion adaptive array PIAA. For acoustic imaging, pulse spectrum should be wide to make the pulses less invasive. When a pulse has a wide frequency band, narrow band interference causes DoA errors in conventional CVSTNN. We use the weights of PIAA as the initial weights of CVSTNN to achieve higher precision in DoA estimation. Simulations demonstrate that the proposed method realizes accurate DoA estimation than the conventional CVSTNN method.