Kazuhiro Hirasawa

Analysis of a cavity-backed annular slot antenna with one point shorted

Analysis of a cavity-backed annular slot antenna with one point shorted is performed experimentally and theoretically. Resonance frequencies, bandwidths, and radiation patterns are studied with respect to slot width, cavity depth, and slot shorting position. In the theoretical analysis, the method of moments is applied to find the magnet current on the slot, and the Greens function for the field inside the cavity has been newly derived. By selecting a slot shorting position, circular polarization, and a bandwidth of more than 10%, the voltage standing-wave ratio (VSWR) >

Circularly polarized rectangularly bent slot antennas backed by a rectangular cavity

Rectangularly bent slot antennas backed by a rectangular cavity for circular polarization are proposed. Characteristics of three types of cavity-backed rectangularly bent slot antennas for circular polarization-the single square loop slot, the two-element square loop slot, and the two-arm square spiral slot antenna-are analyzed numerically. The generalized network formulation based on the equivalence principle is given in terms of the method of moments. The magnetic currents on the thin rectangularly bent slots in the presence of the backing cavity are obtained and used to calculate the input impedance, radiation pattern, and axial ratio. Experimental results on the input impedance, radiation pattern, and axial ratio are in good agreement with calculated data.

Two rectangular loops fed in series for broadband circular polarization and impedance matching

Two rectangular wire loops above an infinite ground plane are investigated for broadband circular polarization and impedance matching. Each rectangular loop is connected to each end of a short dipole fed by a coaxial cable through the ground plane. One gap on each loop is introduced to get circular polarization and the gap position controls the sense of circular polarization. The position of the gap, the length of the short dipole, the height of the loop above the ground plane and the shape of the rectangle are very important to get a good axial ratio (AR) and voltage standing-wave ratio (VSWR). The AR bandwidth (/spl les/3 dB) and the VSWR bandwidth (/spl les/2) are 18% and 22%, respectively. The measured and computed results are in good agreement.

The application of a biquadratic programming method to phase only optimization of antenna arrays

Antenna array optimization by a biquadratic programming method is formulated with variable-phase (analog and digital) and constant amplitude excitation. The method can optimize an antenna performance index expressible as a ratio of Hermitian quadratic forms. Power gain optimization and least-squares pattern synthesis with a specified gain are illustrated. Linear, planar, and circular arrays with dipole or circular loop elements are optimized, taking mutual coupling effects between antenna elements into account. The method shows much more rapid convergence characteristics than the Rosenbrock (1960) and Fletcher-Power (1963) methods. >

The mutual coupling and diffraction effects on the performance of a CMA adaptive array

The performance of the constant modulus algorithm (CMA) with the steepest descent method used in an adaptive array of monopole antennas mounted on a rectangular conducting plate was investigated. The mutual coupling (MC) effect among the array elements and the diffraction effect caused by the conducting plate were taken into account in the calculation by a hybrid method of moment method (MM) and geometrical theory of diffraction (GTD). Simulations showed that the CMA adaptive array performs differently when the MC and the diffraction effects are taken into account. In some cases, the speed of convergence is slower with MC, and in other cases it is faster. Also, in multipath scenarios the array sometimes converges on a weaker delayed ray rather than the direct ray when MC is included. The capture property is explained by the fact that the CMA algorithm is sensitive to initial conditions and the initial array pattern is directional due to MC-not omnidirectional as in the ideal case. The performance of the array on a finite ground plane is different from that on an infinite ground plane due to diffraction effects.

A dual-band inverted-L-folded-antenna with a parasitic wire

Low-profile antennas, such as inverted-L and F antennas, are widely used in mobile communications. With the introduction of two parasitic wires, a horizontal dipole antenna and an inverted-F antenna over a large ground plane show wideband impedance characteristics (King, H.E. and Wong, J.L., 1972; Nakano, H. et al., 1998). A dipole antenna with a parasitic wire has two resonant frequencies (Ebine, Y. and Kagoshima, K., 1988). However, an inverted-L antenna with a parasitic wire over a large ground plane shows neither wideband nor dual-band characteristics, because the input resistance is low at the fundamental resonant frequency. An inverted-L-folded antenna with only one parasitic wire over an infinite ground plane is introduced to realize dual-band characteristics. A folded-monopole antenna has higher input resistance than that of a monopole antenna at the fundamental resonant frequency. Therefore an inverted-L-folded antenna over an infinite ground plane may be matched to a 50 /spl Omega/ feed cable at the fundamental resonance. To get dual-band operation, one parasitic inverted-L wire is placed at the side of the inverted-L-folded antenna. It is found that the fundamental and the second resonant frequencies strongly depend on the lengths of the inverted-L-folded antenna and the parasitic wire, respectively.

A new inverted F antenna with a ring dielectric resonator

A new antenna combining the use of a ring dielectric resonator (DR) and an inverted F antenna (IFA) is proposed and investigated experimentally. In this application, the DR not only fills the role of a dielectric coating, but also serves the function of a radiator. The measurements of input impedance, return loss, and radiation pattern for both the IFA with the DR (IFA-DR) and the wire IFA (WIFA) are conducted at the S band. The measured data demonstrate that the IFA-DR operates in multiple resonance modes unlike a WIFA. Compared with the WIFA, the one proposed here incorporating a ring DR and an IFA is more attractive in having a smaller size and a larger impedance bandwidth.

A novel top-sleeve monopole in two parallel plates

A novel top-sleeve monopole antenna in two parallel plates is presented, which is developed to enhance its impedance bandwidth in a significant manner. By the introduction of a sleeve into a common SMA connector with a thin dielectric jacket, a noticeably broad bandwidth on the order of up to 70% is achieved for the proposed antenna. An eigenmode expansion technique is used to simulate the impedance characteristics of the top-sleeve monopole. The effects of geometric parameters of the structure, such as the sleeve length, monopole length, and the plate spacing on its impedance characteristics, are investigated. On the basis of our theoretical studies, an experimental prototype with bandwidth of 50% is designed and its characteristics are confirmed experimentally.

Experimental results with mobile antennas having cross-polarization components in urban and rural areas

The receiving performance of mobile antenna systems that have vertical and horizontal elements at the 920-MHz band has been investigated by measurements in both rural and urban areas in Japan. Three types of inverted-F antennas for a car and three types of antenna elements, a monopole, a bent-slot and an inverted-F antenna, for portable equipment were used in the experiments. The average received power and its probability density function are obtained as the parameter to evaluate the performance of antenna systems. The performances of the bent-slot antenna system for portable equipment and the inverted-F antenna system mounted on a car are compared with those of the monopole or dipole antenna systems used as reference antennas. A notable increase in the average received power has been observed in operation in an urban area where the field distributes randomly and consists of cross-polarized components. >

UHF bent-slot antenna system for portable equipment—I

A newly developed bent-slot antenna for UHF portable communication equipment is introduced. The bent-slot antenna, modified from a half-wave slot element, is designed to have both vertical and horizontal elements and is intended to achieve the improvement of the receiving performance in the urban area. The antenna system characteristics such as current distribution, radiation pattern, gain, and input impedance are investigated both theoretically and experimentally for such parameters as the slot location, the feed point and the width and height of the equipment box. In the calculation, the equipment box is assumed as a rectangular conducting box, and the surface of the box and the slot are modeled by wire grids. The method of moments is applied to find both the electric and magnetic current distributions on wires.