The coupling coefficient of the directional coupler using small coupling holes for the gyrotron of 100 GHz band is very small to monitor fields. To obtain large coupling coefficient, this paper presents the structure of the rectangular waveguide connected to the overmoded circular waveguide. We analyse it as a boundary value problem, and also present an approximate method. In conclusion of this analysis, we get enough large coupling coefficient and enough small reflective coefficient from this structure.

Excellent characteristics of a single-layered radial line slot antenna composed of a copper clad laminates are reported. The use of a thick substrate contributes to reduction of conductor loss. The efficiency of 71% and the gain of 33.2dBi is realized for a 44cmφ prototype antenna.

In the design of a large slotted waveguide array, evaluation of mutual couplings between the slots is time consuming. This paper proposes an effective approximation analysis of the external mutual couplings using periodic boundary condition. Simple design procedure is verified for two-dimensional slot array.

A numerical design of a coaxial-to-radial line adaptor is presented for the use as a feed in a radial line slot antenna. To realize stable performances in mass production, the reflection from a probe type adaptor in which only the outer conductor of a coaxial line is in contact with the waveguide, is analyzed and suppressed. The tolerance for the change and the errors in the height of the waveguide as well as the bandwidth is highlighted; the advantages of the conical probe over the conventional shorting post and the coax-gap adaptor are emphasized.

A new type of wide beamwidth antenna is proposed for mobile satellite communication systems. The microstrip crossed slot antenna consisting of four shorted quarter wave elements is one of the antenna elements of wide beamwidth. To widen the beamwidth still further, the antenna installed on a pyramidal ground plane is presented in this letter. The radiation pattern of this antenna is also measured and discussed.

One of the key technologies in the RF heating is the design of vacuum windows. This paper presents the theory of a pill-box shaped vacuum window connected with circular waveguides. We solved it regarded as a typical boundary value problem of microwave circuits, and evaluated its reflection coefficient and field distributions inside the window.

The radiation patterns of a circularly polarized GPS microstrip disk antenna mounted on the roof of a car are analyzed using UTD. Based upon the excellent agreements between the calculated and the measured results in all the observation directions, the effects of the antenna location upon radiation patterns are discussed in detail. As the distance between the antenna and the edge decreases, the gain in the low elevation angle on the same side as the edge considerably decreases. The effects of the earth are also extracted. They cause the fine ripples in the low elevation angle, though they are negligible in macroscopical view. Furthermore, the validity of the simple design neglecting the earth and the plates other than roof is investigated. The errors are localized at low elevation angle. The results obtained in this paper are useful in the design of the general antennas for mobile communication.

This paper deals with a problem of maximizing directivity of a uniformly spaced broadside array under constraints on the specified sidelobe level. For this purpose, we use a quadratic programming in order to clarify the properties of the radiation pattern with high directivity and low sidelobe level. In resulting radiation patterns, the first sidelobes are suppressed to the specified level and other sidelobes decrease gradually in magnitude similarly to a Taylor pattern. The number of sidelobes in equal magnitude is determined by the specified sidelobe level. These properties are still held for both isotropic and parallel dipole elements.

A numerical design of a matching spiral is proposed for the use as termination in a single-layered redial line slot antenna. The boundary element method is adopted for the analysis of unbounded radiation problems. Satisfactory performance of reflection less than 15 dB is predicted and is verified by experiments.

A radial line slot antenna (RLSA) is a high gain and high efficiency planar array. A single-layered RLSA is much simple in structure but the slot length must be varied to synthesize uniform aperture illumination. These are now commercialized for 12GHz band DBS reception. In RLSAs, considerable power is dissipated in the termination as is common to other traveling wave antennas; the uniform aperture illumination is not the optimum condition for high gain in RLSAs. Authors proposed a theoretical method reducing the termination loss for further efficiency enhancement. This paper presents the measured performances of the SL-RLSAs of this design with non-uniform aperture illumination. The efficiency enhancement of about 10% is observed; the measured gain of 36.7dBi (87%) and 32.9dBi (81%) for a 0.6mφ and 0.4mφ antennas respectively verify this technique.

A slotted waveguide planar array using a single-layer feed circuit is applied to high frequency and high gain use. The remarkable efficiency of 75.6% is realized for the gain of 35.9 dBi in 22 GHz band and 64% is realized for 35.1 dBi in 60 GHz band. Each antenna consists of only two components; a slotted plate and a groove base plate, and are highly mass produceable.

The authors propose a novel waveguide two-way power divider, named as τ-junction, in a feed waveguide of a single-layer slotted waveguide array antenna. This junction occupies only a small space and is placed in the middle of a cascade of several power dividers. It suppresses the long line effect and widens the bandwidth of the feed waveguide. The junction has two inductive walls; one is for suppressing the reflection and the other is for controlling the ratio of divided power to the two output ports. Analysis using Galerkin's method of moments is verified by experiments of a 4 GHz-band model. We install the junctions in a 12 GHz-band single-layer slotted waveguide array. The gain reduction at the band-edge is suppressed.

This letter presents an approximate analysis for coupling coefficients of a multi-slotted directional coupler to diagnose propagating modes in an output waveguide of a gyrotron. The coupling coefficients are calculated approximately and verified by a rigorous analysis.

In practical applications of the artificial boundary surfaces, such as corrugation and strips on a grounded dielectric slab, the surfaces have finite sizes. The diffraction fields from anisotropic surface of this kind can not be calculated using conventional diffraction coefficients. In this paper, uniform diffraction coefficients for the strips on a grounded dielectric slab are given in the sense of physical optics, as functions of incident angle, polarization and structural parameters of the surface. Firstly, the incident plane wave is decomposed into the two special polarization directions. Then uniform diffraction coefficients originally derived for isotropic surfaces with arbitrary impedance can be applied for each polarization component. Finally, expressions for the diffraction coefficients from the anisotropic surface are given as the sum of those for two polarization components. The validity of the diffraction coefficients is verified theoretically and experimentally.

This paper presents a mathing circuit of a T-shaped ridge waveguide by means of loaded probes. The reactance of the loaded probes for the matching between the ridged waveguide and the coaxial-cable is calculated by the impedance matrix of a source and loaded probes.

In a two-layer self-diplexing antenna fed at two ports, theoretical analysis has already shown that the isolation characteristics can be improved by adjusting the angle between the feed locations of the transmitting and receiving antennas. In this letter, we experimentally investigate the isolation characteristics of the self-diplexing array antenna. First, calculated and experimental results for each feed location of the element antenna are compared and good agreement is found. Second, experimental results with a 19-element planar array indicate that a self-diplexing antenna with suitably chosen feed configuration is effective in improving the isolation in a phased array antenna.

A low-loss polarization-selective grating with a symmetrical double structure is proposed for wider frequency band use. Theoretical transmission loss is smaller than 0.025 dB in the frequency band of 0.6551.185 which is twice as wide as the previously reported one.

The authors propose a waveguide π-junction with an inductive post for the element of a multiple-way power divider in a single-layered slotted waveguide array. This π-junction splits part of the power into two branch waveguides through one coupling window, and can excite densely arrayed waveguides at equal phase and amplitude. The power dividing characteristics are analyzed by Galerkin's method of moments and are confirmed experimentally. Reflection from the π-junction is suppressed to the level below 30 dB over 5.4% bandwidth by attaching an inductive post.

A Radial Line Slot Antenna (RLSA) is a high gain planar antenna for receiving DBS (satellite TV) in 12 GHz band. To suppress grating lobes from the array, a slow wave structure is installed in the upper waveguide of RLSA. This letter proposes a novel slow wave structure filled up with expanded polyethylene. The basic design and the performances of the antenna are summarized. The measured gain of 36.3 dBi and efficiency of 75% at 12 GHz confirms the potential of this slow wave structure.