H. Miyashita

Electromagnetically coupled coaxial dipole array antenna

A new type of collinear antenna called electromagnetically coupled coaxial dipole array antenna is proposed. The antenna has an advantage of structural simplicity due to a novel use of an electromagnetically coupled feed structure for the radiating element. An analysis of the radiating element is presented and compared with experimental results. Fabrication and measurement of a prototype array antenna are also presented.

Radial line planar monopulse antenna

In recent years, mobile satellite communications have been growing rapidly. Monopulse tracking operations for beam pointing to the satellite are often employed for those systems which, in general, require rather severe EIRP and G/T specifications. Thus, the development of a monopulse antenna with a good antenna efficiency is of great interest. A radial line planar monopulse antenna is proposed. An analysis of the probes in a radial line has been carried out which gives an understanding of why the monopulse patterns can be synthesized, and a simple and effective theory is presented about a realization of uniform-aperture field distribution. The antenna has been fabricated and the radiation characteristics have been measured which supports the theory as well as verifies the capability of the antenna for the monopulse tracking operation.

Extended S-Parameter Method Including Radiation Pattern Measurements of an Antenna

Coaxial cables connected to the antenna frequently affect the characteristics of the antenna. Although the S-parameter method is one of the most effective methods of reducing the influence of the coaxial cables, it has so far only been applied to impedance measurements. We propose an extended S-parameter method that can also be applied to radiation pattern measurements of amplitude and phase. In this method, two cables are connected to an antenna, and the excitation coefficients of the two cables are obtained from the S-parameters under the condition where the unbalanced current of the coaxial cables is reduced. From array patterns generated with these excitation coefficients, we can obtain the radiation patterns with a reduced unbalanced current of the coaxial cables. We apply this method to dipole antennas and a helical antenna on a small housing. Our simulated and measured results demonstrate the validity of the proposed method and 20 dB reduction of the influence of the coaxial cables.

Optimal radome design with particle swarm optimization

In this paper, we presented the optimal radome design using optimization algorithm. The radome performance is optimized by adjusting the thickness of the radome layer and the shape of the radome. The numerical results and observations indicated that MPSO, which adopts a concept of ldquomutationrdquo in GA, is capable of performing better and more stably than the conventional PSO and GA with respect to searching the global optima without any burden such as tuning the parameters of the algorithms in an actual design procedure. We also confirmed that the transmission coefficients attained by the optimal radome synthesis is well above -2dB for the entire frequency bandwidth evaluated.

An analysis of antenna coupling between arrays on a polyhedron structure

Antenna coupling between arrays on a polyhedron structure is investigated. First of all, a high-frequency asymptotic closed-form formula is derived for the mutual admittance between two linearly polarized circular microstrip antennas located on the different faces of a perfectly conducting wedge. The microstrip antennas are modeled by the cavity model, and the mutual coupling caused by the wedge-diffracted field is analyzed by the EMF method using Kellers GTD diffraction coefficients for the diffracted field. Next, the antenna coupling between arrays is calculated and compared with an experimental result. Good agreement between them supports the theory. Finally, the properties of the antenna coupling are described by some numerical simulations. >

Decoupling networks composed of lumped elements for diversity/MIMO antennas

We show design equations for decoupling networks composed of lumped elements. These equations are valid for arbitrary two-element antenna arrays and plane-symmetrical three-element antenna arrays. The decoupling networks consist of series susceptances and shunt susceptances. We design small two-element and three-element antenna arrays with the decoupling networks, and verify the design equations by performing measurements and simulations. The sizes of the two-element and three-element antenna arrays including the ground planes are 0.12λ_c × 0.18λ_c and 0.25λ_c × 0.21λ_c, respectively. We confirm high isolation is achieved by the decoupling networks.

Capacitor antenna in a parallel plate waveguide

Time-consuming soldering process is required for waveguide-fed planar antennas with probe excitation of radiating elements. It is desirable to implement a sophisticated process for mass production. One of the candidates is a capacitor antenna in the waveguide etched under the radiating element as shown. In this study, input admittance of the circular capacitor antenna in a parallel plate waveguide is analyzed. The mode matching method is applied as a waveguide bifurcation problem in cylindrical coordinates. To construct analytical solution of edge admittance through the direct inversion or residue calculus method, the effect of disk curvature on the reflection coefficient is asymptotically neglected. The resultant expression of infinite products finally reduces to a simple closed form through appropriate approximations and sum formulas. Matching posts manufacturable by via-hole process are added inside the capacitor and the effect is calculated by the radial line equivalent circuit. Experimental verification is given.

Design and Fabrication of Wideband and Dual Polarized Open-Ended Waveguide

We propose a wideband and dual polarization open-ended waveguide that makes it easy to construct array antennas. The proposed device stacks feeding circuits for both polarizations on different substrates. In order to equalize the distances from the excitation probe of each polarization to the electrical ground, we propose to place metal slits on the antenna ground. This offsets the characteristic difference between polarizations. Additionally, since multiple elements are fed by using the branched strip lines on the feeding circuits, array antennas are easily formed. We have designed the antenna element, and fabricated a prototype for validation. The calculated and measured results agree well; both polarizations exhibit low reflection levels and similar gains.

Wave analysis of aperture field distribution for probe-fed radial line planar antennas

Probe-fed radial line planar antennas (RLPAs) have high efficiency, because the excitation probes of the radiating elements can be fed by a standing wave in the radial line with a short-circuited termination of its end. We propose a method for the wave analysis of a probe-fed RLPA. Good correspondence has been confirmed between measured and calculated values on the aperture field distribution. By observing the parameter dependence of the feeding network, a method is proposed to achieve a uniform aperture field distribution. The method is efficient for general geometries of probe-fed RLPAs.

Broadening beamwidth of E-plane radiation pattern of a dipole antenna with loaded monopole elements

Dipole antennas are widely used as the radiating elements of phased array antennas for communications and radar systems. The E-plane radiation pattern of a dipole antenna placed above a ground plane generally has a narrower beamwidth than that of the H-plane. Therefore, it is strongly desired to broaden the E-plane radiation pattern to achieve wide-scanning while keeping gain. A method to broaden the E-plane radiation pattern of a single dipole antenna over a ground plane is proposed, where two parasitic monopole elements with reactive impedance loads are placed in the vicinity of the driving dipole element. Numerical simulations using the EMF method and the method of moments (MoM) are shown to obtain an appropriate value of the reactance and the parameters of the antenna geometry for a broad beamwidth. Experimental results are also shown to demonstrate the broad beamwidth.