H. Nakano

Hosei University · Department of Electronics and Electrical Engineering

Three different feeds are used to realize a loop antenna with wideband circular polarization. The loop is backed by the ground plane and analyzed using the moment method. It is found that the antennas with balanced and unbalanced feeds radiate left and right-hand circularly polarized waves with 3 dB axial ratio bandwidths of 13% and 3%, respectivel...

The conventional finite‐difference time‐domain (FDTD) method has been formulated in the Cartesian coordinate system. In this case, the staircase approximation should be used even for the analysis of arbitrarily shaped dielectric media. As a result, small meshes are required to accurately model these media. In this letter, we extend the contour‐path...

A meander metamaterial line (metaline) antenna, which consists of P- and C-type meta-atoms, is investigated to form a circularly polarized (CP) broadside beam across two frequency bands. The antenna has an extremely low-profile flat structure of approximately 0.01 wavelength and a small antenna area of less than 0.5 wavelength × 0.5 wavelength at t...

When the circumference of a round metaloop antenna (RoMLA), made of C-type meta-atoms, is one guided wavelength (1λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ) of the current on the loop, the RoMLA radiates a left-hand CP wave at frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/M...

The authors propose a novel dual-wire antenna with a balanced feed to increase a 3-dB axial ratio bandwidth. The antenna comprises loop elements with quasi two-sources, and the effects of the element distance on the axial ratio bandwidth are revealed using the method of moments (MoM). It is found that the antenna has a maximum bandwidth of 41% at a...

Curl and truncated spiral antennas are studied for input impedance matching a coaxial line. Each antenna is located at quarter wavelengths above the ground plane and analyzed using the moment method. It is found that the curl antenna shows a voltage standing wave ratio (VSWR) of less than two in a 3-dB axial ratio bandwidth of 30% using a crank fee...

Arbitrarily-shaped dispersive media can be treated with the dispersive contour-path (DCP) FDTD method. We extend the DCP-FDTD method for the analysis of a periodic structure to the case at oblique incidence. A trapezoidal recursive convolution technique is used to incorporate dispersive media into the DCP-FDTD method. The transmission characteristi...

We study three comb-line antennas to increase the bandwidth for a 3 dB axial ratio criterion. Each antenna comprises linear radiation elements with loops and a coplanar feedline above the ground plane. First, we analyze a reference antenna with a straight feedline using the method of moments. Next, the straight feedline is transformed into a round...

Abstract The finite‐difference time‐domain (FDTD) method based on the iterated Crank–Nicolson (ICN) scheme is extended to a frequency‐dependent version. The Drude model is used to express a metal dispersion, which is incorporated into the iterated Crank–Nicolson formulation with the trapezoidal recursive convolution technique. The validity of the p...

We study two array antennas to expand a 3 dB axial ratio bandwidth. Each array is located at a quarter wavelength above the ground plane and analyzed using the moment method. First, we use paired spiral elements fed by balanced parallel lines to avoid unwanted radiation from the feedline. It is found that the antenna shows an axial ratio bandwidth...

A low profile wideband spiral antenna array is presented for global mid-band 5G beam steering applications. In the global rollout of mid-band 5G, different frequencies have been licensed within each region (e.g. 3.4–3.8 GHz in the EU and 3.7–5 GHz in the USA). Therefore, antenna arrays must be able to cover a bandwidth of 3.3 GHz to 5 GHz to provid...

We analyze a novel dual-loop antenna with parallel wires using the moment method. The antenna is modified with a sequential rotation (SR), and a 3 dB axial-ratio bandwidth is evaluated versus loop height above the ground plane. It is found that the bandwidth with SR reaches 22%, which is 3.5 times as wide as that without SR. Subsequently, we design...

An efficient and accurate technique for evaluating the characteristics of a polarization converter consisting of a dielectric waveguide with a single asymmetric section is proposed and discussed with the aid of the imaginary-distance beam-propagation method. Detailed consideration regarding the optical-axis rotation angle reveals the necessity and...

A novel low-profile array antenna composed of two U-shaped metalines I and II is realized for a circularly polarized (CP) fan-beam. First, the radiation from metaline I is investigated. The investigation reveals that the metaline generates a right-hand (RH) CP broadside beam at two design frequencies of f <sub xmlns:mml="http://www.w3.org/1998/Ma...

A low profile wideband spiral antenna array is presented for global mid-band 5G beam steering applications. In the global rollout of mid-band 5G, different frequencies have been licensed within each region (e.g. 3.4–3.8 GHz in the EU and 3.7–5 GHz in the USA). Therefore, antenna arrays must be able to cover a bandwidth of 3.3 GHz to 5 GHz to provid...

We report here that spiral and curl antennas are essentially the same when using the moment method. This aids in the understanding and design of the two antennas, and serves as the groundwork for new ideas regarding antennas. First, the spiral antenna height above the ground plane was gradually reduced, and at each height, the spiral configuration...

A periodic array of InSb spheres on a substrate is numerically analyzed at terahertz frequencies. The incident field is shown to be coupled to the substrate due to the guided-mode resonance. The effect of the background refractive index on the transmission characteristics is investigated for sensor applications.

We analyze a loop antenna array proximity coupled to a coplanar feed line using the method of moments. First, a novel-loop array at a uniform proximity distance (PD) from the feedline is investigated versus loop height above the ground plane. It is found that when the loop height is λ/5 (λ: wavelength), a 3 dB axial-ratio bandwidth reaches 11%, whi...

Using the method of moments, a dual-wire antenna with a single balanced feed is proposed. To enlarge a 3 dB axial ratio bandwidth, non-resonant radiation elements and a coplanar feedline for sequential rotation (SR) are used. It is revealed that the bandwidth reaches 49%, which is 1.7 times as wide as that without SR. Subsequently, the balanced fee...

We analyze three transmission-line antennas using the moment method. Each line antenna comprises a coplanar feed line, loops, and straight segments connecting the loops and feedline. First, we investigate bent and branched line antennas with loops on one side of the feedline. It is found that the segment length affects both the beam direction and a...

A novel method of exciting a circularly polarised (CP) loop antenna is proposed using the moment method. A horizontal square loop above the ground plane has two corners connected to a vertical, branched feedline with one source. First, the authors show the radiation characteristics of a reference antenna whose corners are excited with two sources h...

A novel, low cost, highly accurate, millimeter-wave RCS characterization method is developed and presented in this paper. In order to develop and verify the validity of the proposed method, full scale models and scale models of the horizontal-axis wind turbine (HAWT) and Crossflow turbines have been simulated and compared for a case study. The RCS...

A circularly polarized (CP), small, beam-steerable antenna is realized using bent metalines. The antenna has the following features: 1) dual-band operation at low frequency $f_{\mathrm {LOW}}$ (wavelength $\lambda _{\mathrm {LOW}}$ ) and at high frequency $f_{\mathrm {HIGH}}$ (wavelength $\lambda _{\mathrm {HIGH}}$ ); 2) a small antenna volume of l...

The area within a loop antenna can be used for inserting additional components (such as mounting hardware), if this does not cause the antenna characteristics to degrade. This paper discusses a circularly polarized (CP) metaloop antenna that has a loop circumference of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www....

Conventionally, the deterioration in the axial ratio (AR) for a circularly polarized antenna based on a traveling wave current is explained using backward currents reflected from the antenna arm end. This letter reveals the existence of a new cause for AR deterioration in a situation of no backward currents. For this, a theoretical loop antenna mod...

A beam-forming system for a patch antenna is proposed to realize a deeply tilted beam with high-gain, high aperture efficiency, and low sidelobe level. The proposed system uses only one novel metaplate, where the total system height is less than one wavelength. Firstly, a T-shaped metatwin is created as an element for the metaplate. It is revealed...

Using the method of moments, we analyze two types of loop antennas; they have loop circumferences of 1λ and 2λ ( λ : wavelength). Each loop is located above a ground plane at height h , and a 3dB axial-ratio bandwidth versus h is evaluated. It is found that the 1λ and 2λ loops have maximum bandwidths of 3% and 2% at h=0.18λ , respectively. Using 1λ...

Abstract An implicit Crank–Nicolson procedure can be replaced with an explicit iteration process. An explicit finite‐difference time‐domain method based on the iterated Crank–Nicolson scheme that has been widely used for solving Einstein's equations is newly developed. The formulation is presented with two iterations and its stability condition is...

The effects of adjusting the distance between a core and an air-cladding interface on the propagation properties are investigated in a bent Si-wire waveguide. The eigenmode analysis is carried out using the imaginary-distance beam-propagation method based on Yee’s mesh in the cylindrical co-ordinate system. The pure bend loss (PBL) is evaluated as...

A metaloop antenna (1FD-MetaLPA), made of C-type metaatoms and having a single feed point, FL’, is created to radiate a left-hand circularly polarized (LHCP) axial beam at a frequency of fLH-1FD = 2.55 GHz and a right-hand circularly polarized (RHCP) axial beam at a frequency of fRH-1FD = 3.45 GHz. It is revealed that the maximum gains at fLH-1FD a...

Abstract A novel dual‐wire antenna to obtain wideband circular polarisation is proposed. The antenna consists of curl elements with a balanced feed above a ground plane. Using the moment method, an antenna with balanced feedlines having two sources is analysed first. Analysis reveals that the antenna shows a 3 dB axial‐ratio bandwidth of 36%. Next,...

A 1 ×3 linear antenna array consisting of Quad-Arm Curl antenna with a High impedance surface (QACH) is presented. We believe that it is the first linear phased array solution which can provide 360° azimuth coverage. This array has been designed to operate at the L-band (1.518-1.675 GHz) and generate right-hand circularly polarized radiation to pri...

Using the method of moments, we analyze three types of series-fed array antennas for circular polarization. First, we present radiation characteristics of a reference antenna with symmetrical dual loops fed by $balanced$ parallel lines. Next, we modify the symmetrical dual loops into asymmetrical ones to enhance a circularly polarized (CP) wave b...

The radiation generated by the current in an active region (ACT-R), specified by propagation phase constant $\beta $ , is investigated with special interest in its phase progression (PhasProg). The ACT-R is modeled by circular and square loops, and classified into two types: a right-handed ACT-R with positive $\beta $ and a left-handed ACT-R wi...

Using the moment method, we analyze a loop antenna with a perturbation segment in the presence of a ground plane. First, the radiation characteristics versus loop height above the ground plane are investigated. It is found that as the loop height increases to more than 0.2 wavelengths, a novel antenna other than a conventional one can exist, showin...

Kretschmann‐ and Otto‐type surface plasmon resonance (SPR) waveguide sensors are numerically investigated at terahertz frequencies. The reflectance of a three‐layer model for the Kretschmann‐type sensor is examined with the Fresnel equation, in order to determine the angle of incidence of the waveguide. Using the frequency‐dependent finite‐differen...

A dispersive contour-path (DCP) algorithm is newly introduced into the FDTD method for the analysis of arbitrarily-shaped dispersive media expressed by the Drude-Lorentz model. The frequency-dependent formulation is performed using the simple trapezoidal recursive convolution technique. A faster convergence of the numerical results for an Au cylind...

Radiation in the normal direction for a metaloop antenna is discussed. First, the radiation field generated from an N-type current distributed along a loop, EN, is investigated. The investigation clarifies the behavior of the unbalance between the left-handed circularly polarized (LHCP) component of EN at frequency f(−) and the right-handed circula...

A grating consisting of periodic arrays of InSb-coated dielectric cylinders on a substrate is analyzed at THz frequencies using the frequency-dependent finite-difference time-domain method based on the trapezoidal recursive convolution technique. The transmission characteristics of an infinite periodic array are investigated not only at normal inci...

A metacurl antenna made of C-type metaatoms (forming a C-type metaline), called the Cmetacurl antenna, is investigated. The investigation reveals that the gain for a left-handed circularly polarized wave, LHCP gain, has a maximum value at frequency fLH and the gain for a right-handed circularly polarized wave, RHCP gain, has a maximum value at diff...

We investigate a circularly polarized (CP) transmission-line antenna composed of loop radiation elements, called a loop-line antenna. To enhance the CP wave bandwidth, an isolated loop radiation element is first analyzed using the method of moments. It is found that a CP wave bandwidth for a 3 dB axial-ratio criterion has a maximum value of 8%. On...

Two types of modified crossed-wire antennas are investigated to enhance a circularly polarized (CP) wave bandwidth. The wire length of each antenna is increased twice as long as that of the original antenna. First, a bent-type antenna is analyzed using the method of moments. It is found that the CP wave bandwidth for a 3 dB axial ratio criterion is...

The circularly polarized axial and conical beams from a two-arm spiral antenna are investigated and the radiation phase distributions around the antenna axis are clarified. A tilted beam is created by superimposing the conical beam onto the axial beam. The tilted beam is steered in the azimuth plane when the two arms are excited by different amplit...

Using the method of moments, we investigate two types of circularly polarized loop array antennas with and without a coplanar feedline (CF). The loops and the CF are located above a ground plane at a height of a quarter wavelength. First, we analyze decoupling two-element array antennas. It is found that the antennas with and without the CF show re...

A three-dimensional plasmonic wavelength demultiplexer is investigated using slit- and stub-type filters consisting of metal–insulator–metal waveguides. To achieve a narrow bandwidth of the slit-type filter, a dielectric material is inserted into the slit section and the metal thickness is deliberately chosen to be 0.2μm. Then, a demultiplexer is c...

First, four N-type straight metalines, each radiating a circularly polarized wave, are arrayed in the shape of a cross, where one metaline is activated and the remaining metalines are non-activated. This antenna system is designated as the initial cross metaline antenna system (xMeTLNA system). By changing the activated metaline, the radiation beam...

The cylindrical hybrid implicit-explicit finite-difference time-domain method, in which the implicit scheme is adopted only in the circumferential direction, is improved in order to treat general electromagnetic problems. The connection of the field in a specific plane gives the problem with a cyclic matrix, the solution of which is performed with...

Four metamaterial line loop (metaloop) antennas, RND-MTLP-C, RND-MTLP-N, SQR-MTLP-C, and SQR-MTLP-N are investigated to clarify the antenna characteristics. Each metaloop is made up of either a C-type metamaterial line or an N-type metamaterial line, where the dispersion characteristics of the unit cell for the C- and N-type metamaterial lines are...