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The arms of a spiral antenna are printed on the bottom surface of a dielectric substrate and are placed in contact with an absorbing strip installed in a shallow cavity. The antenna characteristics when a slot is cut into each of the arms are investigated with the permittivity of the dielectric substrate as a parameter. The investigation shows that, as the permittivity is increased, the center frequency...
The fundamental scheme is applied to reformulating the locally one-dimensional finite-difference time-domain method in cylindrical coordinates and the full-vectorial beam-propagation method. It is shown that the formulations are significantly simplified in the right-hand sides of the resultant equations, maintaining the equivalence to the original problems.
It is known that a loop antenna of one wavelength circumference radiates a linearly polarized wave in the direction normal to the antenna plane. It is also known that, when perturbation elements are added to the loop, the linearly polarized wave can be changed to a circularly polarized wave [1]. For mobile communications, the circularly polarized wave at low elevation angles is often required to have...
The antenna characteristics of helices for the normal and axial modes [1] have been theoretically revealed using numerical techniques. However, little theoretical analysis has been performed for revealing the antenna characteristics of the conical mode [2][3]. With this background, this paper presents the antenna characteristics of the conical mode helix. The antenna characteristics presented here...
The loop antenna is well known as a fundamental element that radiates a linearly polarized wave. Recently, some unique properties have been discussed for a loop antenna capable of radiating a circularly polarized wave (CPW) [1]-[4]. CPW radiation is obtained using two perturbation elements on the loop.
Slots are cut into the arms of an Archimedean spiral antenna in order to generate a stop band. The center frequency of the stop band is determined by the slot resonance, which occurs when the slot length is close to one-quarter wavelength. It is found that the gain drastically drops at the center frequency of the stop band. It is also found that the radiation characteristics outside the stop band...
A planar antenna consisting of four bent arms on a thin dielectric substrate is investigated. The arms are located symmetrically with respect to the coordinate origin, and each is made of a circularly polarized (CP) metaline that shows a negative propagation phase constant at the design frequency (2.45 GHz). The antenna height is extremely small: approximately 0.03 wavelength. By changing the feed...
We have proposed a metal disc-shaped terahertz surface wave splitter with a center hole and radially placed gratings. Unfortunately, appreciable reflected waves have been observed from the input port of the center hole. To reduce the reflected waves, we insert a metal rod with a tapered end into the center hole of the disc-shaped splitter operating at two frequencies. It is found that the reflected...
A circularly polarized (CP) antenna is proposed, where four metalines are used as radiation elements. This CP antenna supports a negative phase constant current, leading to a small antenna height of approximately 1/100 wavelength. The same antenna characteristics are reproduced even when the feed point position is changed for beam-steering in the azimuth plane, because the metalines are arrayed symmetrically...
At THz frequencies, indium antimonide (InSb) exhibits a negative permittivity, leading to the excitation of a surface plasmon resonance (SPR) [1]. In this work, we investigate the transmission characteristics of THz filters with the localized SPR excited around InSb square patches using the three-dimensional finite-difference time-domain method. First, we use an FR4 substrate with a thickness of 500...
The frequency-dependent finite-difference time-domain (FDTD) method has widely been used to treat dispersive materials, e.g., metal at optical frequencies, semiconductors at THz frequencies, water at microwave frequencies, and so on. Unfortunately, the time step size is restricted by the Courant-Friedrichs-Lewy (CFL) condition even for the frequency-dependent FDTD method. To remove this restriction,...
The radiation from a conventional metamaterial loop antenna (metaloop) is circularly polarized within two frequency bands. This paper reveals that the radiation from a novel metaloop, where stubs are added to the loop arm, is circularly polarized within three frequency bands specified by the Nion frequency, Hion frequency, and upper band-edge frequency for a fast wave. The antenna characteristics,...
A low-profile body of revolution (BOR) with a shorted parasitic ring (SPR) antenna realizes a wideband VSWR characteristic (approximately 148%). The radiation pattern is omnidirectional around the antenna axis for base station applications. It is found that a modification of the SPR by removing four areas contributes to a reduction in the cross-polarized radiation field in the azimuth plane. It is...
This paper discusses an antenna system composed of a fed metaspiral element and two dielectric slabs above the spiral. Analysis reveals that the slabs lead to an increase in the gain, in accordance with the formation of a narrow radiation beam. A gain of 6.5 dBi is obtained, which is 6.5 dB higher than the gain in the absence of the slabs.
An inverted LFFL card antenna (InvLFFL) is designed as a quadband antenna, where target frequency bands are 1.7 GHz, 2.45 GHz, 3.5 GHz, and 5.2 GHz bands. The InvLFFL is composed of a modified inverted L element, two inverted F elements, and a parasitic inverted L element. The design is performed based on one-quarter wavelength resonance at each band. The InvLFFL has a 4.6% bandwidth around 1.7 GHz,...
An antenna composed of a fed metaloop and a parasitic metaloop is presented. The antenna characteristics for this double metaloop, including the radiation pattern, axial ratio, gain, and VSWR, are compared with those for a single metaloop where the parasitic metaloop is removed. The double metaloop antenna has a smaller cross-polarized radiation component than the single metaloop, leading to a wider...
The prototype of a crossed-plate antenna operates across a frequency range of 2.26 GHz to 15 GHz (148% VSWR bandwidth). To suppress interference signals from nearby devices, slots are introduced to the crossed plates of the prototype antenna. The parameter study reveals that the slot length determines the stop-band center frequency and the slot width affects the stop bandwidth for a VSWR = 10 criterion...
This article presents several topics regarding the FDTD analysis of terahertz (THz) devices. First, the treatment of metal is discussed with attention to the use of the perfect electric conductor approximation and the Drude model that takes metal dispersion into account. Next, two ways to support THz waves are explained on the basis of the propagation characteristics of surface plasmon polaritons...
Optical nanodipole antennas using surface plasmon polaritons are numerically investigated with the three-dimensional finite-difference time-domain method. The length of the dipole arm is determined using the effective index of the metal rod calculated from the eigenmode analysis. A stub structure is introduced to match the impedance between the nanodipole antenna and the feeding wave-guide. The radiation...
A metaloop antenna that has a negative propagation phase constant for the current on its closed arm is proposed and investigated. A linearly polarized (LP) broadside radiation pattern is obtained at different frequencies below and above frequency fT, where the propagation phase constant is zero. In addition, it is revealed that the metaloop forms an LP dual-peak radiation pattern at different frequencies...
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