Nobuyoshi Kikuma

An adaptive array utilizing an adaptive spatial averaging technique for multipath environments

When the interference is coherent with the desired signal, the conventional adaptive arrays working under the guiding principle of output power minimization tend to cancel the desired signal by using the coherent interference. A technique is described which enables the adaptive array to function even under such an environment. The array is divided into subarrays, whose input correlation matrices are adaptively averaged so as to produce a Toeplitz matrix which would be obtained when the interference did not correlate with the desired signal. The averaged matrix is now free from correlation terms between the desired signal and interference, and therefore may be used to derive the optimum weight for the array element just as in the ordinary radio environment of incoherent interference. Numerical examples show that the new adaptive array is highly capable to suppress the coherent interferences as well as incoherent ones.

Millimeter-Wave Microstrip Comb-Line Antenna Using Reflection-Canceling Slit Structure

A microstrip comb-line antenna is developed in the millimeter-wave band. When the element spacing is one guide wavelength for the broadside beam in the traveling-wave excitation, reflections from all the radiating elements are synthesized in phase. Therefore, the return loss increases significantly. Furthermore, re-radiation from elements due to the reflection wave degrades the design accuracy for the required radiation pattern. We propose the way to improve the reflection characteristic of the antenna with arbitrary beam directions including strictly a broadside direction. To suppress the reflection, we propose a reflection-canceling slit structure installed on the feeding line around each radiating element. A 27-element linear array antenna with a broadside beam is developed at 76.5 GHz. To confirm the feasibility of the simple design procedure, the performance is evaluated through the measurement in the millimeter-wave band.

Grating Lobe Suppression of Narrow-Wall Slotted Hollow Waveguide Millimeter-Wave Planar Antenna for Arbitrarily Linear Polarization

A high-gain and high-efficiency slotted waveguide planar antenna is developed in the millimeter-wave band. Forty-five degree inclined polarization is required for automotive radar systems. In the design of slotted waveguide array for arbitrarily linear polarization, slot spacing is one guide wavelength which is larger than a wavelength in free space. Consequently, grating lobes appear in the radiation pattern. So, we developed a slotted waveguide planar antenna composed of post-loaded narrow-wall slots and a single-layer alternating-phase feeding circuit. A planar antenna with suppressed grating lobes has been fabricated and its RF performance has been measured. The measured gain is 33.2 dBi and antenna efficiency is 56% at 76 GHz. Grating lobe level is -28.6 dB lower than main lobe level. Since the proposed structure remains simple, the antenna is expected to be manufactured by metal injection molding for low cost

Beam-Scanning Performance of Leaky-Wave Slot-Array Antenna on Variable Stub-Loaded Left-Handed Waveguide

Metamaterial is an artificial material in which the effective phase constant can be controlled by the internal physical periodic structure of the transmission line. Effective phase constant is designed to be of any value, which may be small, large, approximately zero, or negative, attained by changing the dimensions of the periodic structure. Miniaturization of the antenna and wide design flexibility of radiation patterns can be expected from the use of metamaterials. In this work, we developed a leaky-wave slot-array antenna on a variable stub-loaded left-handed waveguide. The radiation pattern of the fabricated antenna was measured and the characteristics of the left-handed transmission line were observed. Moreover, performance of beam-scanning by changing the length of the stubs on the waveguide was confirmed experimentally.

A consideration of electro-magnetic-resonant coupling mode in wireless power transmission

The resonant mode of the wireless power transmission system is discussed to unveil a mechanism of wireless power transmission. We have analyzed electro-magnetic resonance phenomenon by using MoM to calculate input impedance, port currents, transmission efficiency, and near field distribution. We have checked that the system has two resonant frequencies, and the power transmission efficiency is maximized at those frequencies. The magnetic field distribution proves that the system has two different resonant modes. We have also considered far field to find that the higher frequency resonance is better for its high efficiency and low undesired emission.

Toeplitzization of correlation matrix in multipath environment

This paper deals with the technique to improve the performance of an adaptive array under the multipath environment. The adaptive array which works under the guiding principle of output minimization often assumes that the interference is not coherent with the desired signal. In this case, the correlation matrix of the input is Toeplitz. If, on the other hand, the interference is coherent with the desired signal, which is usually the case in multipath environment, the system tends to utilize this interference to cancel the desired signal. The correlation matrix in this case is not Toeplitz. Therefore, we introduce a new algorithm whose main concept is toeplitzization of the input correlation matrix for the purpose of determining the optimum weight for each array element without harming the desired signal. Numerical examples show that our adaptive array has high capability of suppressing the coherent interference as well as incoherent one.

Millimeter-Wave Transition From Waveguide to Two Microstrip Lines Using Rectangular Patch Element

A millimeter-wave transition from a waveguide to two microstrip lines and the design methodology are proposed. A rectangular patch element in a short-terminated waveguide is analyzed by the cavity model of a patch antenna and the dyadic Greens function of the waveguide. The analysis points out that the rectangular patch element has an optimum width for wideband, which only has the function of the broad wall width of the waveguide. The transition also works as a divider. A numerical investigation of a transition having two microstrip lines validates the analytical model in terms of wideband, and indicates that the distance between the two microstrip lines has an optimum length for suppressing higher order modes. A prototype transition exhibits an insertion loss of 0.5 dB from 76 to 77 GHz, and a bandwidth of 6.9% (5.29 GHz) for the reflection coefficient below -15 dB for the waveguide port

Millimeter-wave microstrip-to-waveguide transition operating over broad frequency bandwidth

A broadband microstrip-to-waveguide transition is developed in the millimeter-wave band. Since novel geometrical features are applied in the printed pattern on the substrate, the proposed transition operates over a quite broad frequency bandwidth due to its double resonance. The two resonant frequencies can be controlled independently according to dimensions of the structure for required bandwidth and reflection level. Two versions of transition are designed and reliability is confirmed by measurements in the millimeter-wave band. The design frequency is 76.5 GHz. The bandwidth 12.9 GHz (16.8 %) is obtained for reflection level lower than -30 dB. In the other design for broadband, the bandwidth for reflection level lower than -20 dB results in 24.9 GHz (32.5%).

Broadband and planar microstrip-to-waveguide transitions in millimeter-wave band

Broadband and planar microstrip-to-waveguide transitions are developed in the millimeter-wave band. Novel printed pattern is applied to the microstrip substrate in the ordinary back-short-type transition to operate over extremely broad frequency bandwidth. Furthermore, in order to realize flat and planar transition which does not need back-short waveguide, the transition is designed in multi-layer substrate. Both transitions are fabricated and their performances are measured and simulated in the millimeter-wave band.

Stub-Loaded Folded Dipole Antenna for Digital Terrestrial TV Reception

A stub-loaded folded dipole antenna is proposed for digital terrestrial TV reception. The antenna has a pair of lines as stubs inside a folded dipole. The prototype antenna printed on polyethylene terephthalate (PET) film has dimensions of 20 by 240mm with a line width of 1 mm. The antenna exhibits a relatively flat gain characteristic from 0.6 to 1.9 dBi with a stable figure-of-eight radiation pattern in the frequency range from 470 to 710 MHz. The voltage standing wave ratio (VSWR) is less than 2.6 in the frequency range