A multimode horn with both a low cross-polarization component less than -30 dB and good VSWR characteristics has been realized at frequency bands 8.6-9.8 GHz and 10.75-11.15 GHz. The improved performance of the proposed horn is verified by comparing with the previous dual-band double-flared horn. The design method for such a horn is based on the mode-matching approach combined with the optimization procedure. This paper proposes an objective function taking account of a spill-over loss and a rotational symmetry in the radiated field instead of an ideal radiation pattern. The effectiveness of our horn is verified by comparison between experimental results in the X band and predicted ones.

This paper proposes a new rectangular horn with two orthogonal multiple-step taper sections for obtaining a dual-polarized elliptical-beam. One of the sections has a stepwise sectoral taper configuration on both sidewalls that starts with a square waveguide feed and then the other is a taper one on both top and bottom walls toward the rectangular aperture. The proposed taper configuration is useful enough to control higher-order modes required for an elliptical beam and is so simple to apply optimization design based on mode-matching approach. As a design example, we present a rectangular horn with -10 dB beamwidth of 33 90at 9.5-10.5 GHz. The effectiveness of the proposed horn is verified numerically and experimentally.

This paper develops planar circuit filters consisting of arbitrarily-shaped conductor patches and slots on a conductor-backed dielectric substrate, which are designed by an optimization technique based on the genetic algorithm. The developed filter has multiple resonators and their mutual couplings in the limited space by using both sides of the substrate, so that its compactness is realized. We first demonstrate the effectiveness of the present filter structure from some design samples numerically and experimentally. Then as a practical application, we design compact UWB filters, and their filter characteristics are verified from the measurements.

To obtain a broad circular-coverage beam with low sidelobe, this paper proposes optimization design based on the quadratic programming approach for circular horns. The desired excitation coefficients of higher-order modes are pre-determined and also evaluated by calculating universal radiation patterns. We show a design example of a multimode horn which has circular-coverage beam with low sidelobe level of about -30 dB. The effectiveness of the designed horn is discussed by evaluating VSWR and radiation characteristics in X-band numerically and experimentally.

We present a design procedure of a leaky-wave antenna with low sidelobes based on the stub-loaded ridge-rectangular waveguide. As a typical example, we desig the antenna with the Taylor distribution of -30 dB sidelobes and fabricated it. The agreement between the measured and the numerical results validate the proposed antenna.

In this paper, an eight-legged resonant element is proposed for a multiband and dual-polarized frequency selective surface (FSS). The FSS element has two resonant frequencies for constructing two reflection bands, of which the separation can be easily controlled by adjusting the shape of the element. The flexibility is demonstrated by the simulated results of transmission responses for various geometrical parameters. And it is shown that introducing resonant-grid and closely-packing techniques can improve the reflection bandwidth. Finally, the good agreement between the measured and the calculated results proves that the eight-legged element is useful for the design of a multiband FSS.

We propose here a composite right/left handed transmission line constructed by using conductor-backed coplanar strips. In this line, we can easily realize a shunt inductor without via because it has the electric-wall symmetry at the guide center. The left-handed nature is verified by both the finite difference time-domain (FDTD) and the equivalent-circuit calculations. Furthermore, we demonstrate the proposed line can easily satisfy the balanced condition for no band gap between the right-handed and the left-handed modes, and can be applied to a leaky-wave antenna, numerically and experimentally.

In this paper, we propose a novel feeding structure for a coaxial-excited compact waveguide filter, which is composed of planar resonators called frequency-selective surfaces (FSSs). In our proposed feeding structure, new FSSs located at the input and output ports are directly excited by the coaxial line. By using the FSSs, the transition from the TEM mode to the TE10 mode is realized by the resonance of the FSSs. Therefore, the backshort length from the coaxial probe to the shorted waveguide end can be made much shorter than one-quarter of the guided wavelength. Additionally, the coaxial-excited FSS provides one transmission zero at each stopband. As a design example, a three-stage bandpass filter with 4% bandwidth at the X band is demonstrated. The designed filter has a very compact size of one cavity and has high skirt selectivity with six transmission zeros. The effectiveness of the design is confirmed by the comparison of frequency characteristics obtained by the simulation and measurement.

A best-fit panel model in the radio holographic metrology taking into account locations and sizes of actual surface panels in a large reflector antenna is presented. A displacement and tilt of each panel can be estimated by introducing the best-fit panel model. It was confirmed by simulations that the distinction can be drawn between a continuous surface error and a discontinuous one. Errors due to truncation of the radiation pattern were calculated by simulations. It was found that a measurement of a 128128 map is optimum for the 45-m telescope. The reliability of the measurements using this model was examined by experiments with panel displacements. Panel adjustments using the best-fit panel model successfully improved the surface accuracy of the antenna from 138µm rms to 84µm rms (/D=210-6).

For achieving low cross-polarization component in addition to circular-coverage pattern in compact structure, this paper proposes a novel multimode horn with arbitrary coaxial-corrugation configuration which plays two roles of mode converters and chokes. The proposed horn can be designed by iteration of non-linear optimization procedure based on generalized scattering matrices pre-calculated by the mode-matching technique. We show a compact horn with four coaxial corrugations for shaping circular-coverage beam over frequency range of bandwidth 20%. The effectiveness of the designed horn is discussed by evaluating VSWR and radiation characteristics in X-band numerically and experimentally.

This paper proposes a genetic algorithm (GA) based design method for arbitrarily-shaped resonant elements that offer enhanced reflectarray antenna performance. All elements have the specified phase property over the range of 360°, and also have dual-polarization and low cross-polarization properties for better reflectarray performance. In addition, the proposal is suitable for linear-to-circular polarization conversion elements. Thus, polarizer reflectarray elements are also presented in this paper. The proposed elements are validated using both numerical simulations and experiments.

This paper proposes a new type of evanescent-mode waveguide filters consisting of two parallel cutoff waveguide paths, in which a number of swelled portions are provided as resonators. One of two paths (the subsidiary path), mechanically connected to the main path in parallel, achieves the negative coupling to exhibit an elliptic-like feature. This type of filters includes a number of complicated waveguide-junction discontinuities. They are analized accurately by the full-wave analytical method based on the mode-matching method. After deriving the generalized equivalent network, the main-path structure is designed to exhibit the specified passband response by using its approximated network. The specified overall characteristic is then synthesized by a computer-aided design method by using an equivalent network without approximations. Measurements on the filters modeled in both X- and U-bands show excellent agreement with the designed characteristics, and prove the feasibility of two-path cutoff-waveguides for filter applications in the microwave and millimeter-wave regions.