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.

This paper presents an analysis of a multi-hole directional coupler attached to an overmoded circular waveguide. The directional coupler is analized as a boundary value problem, and is solved numerically by a virtual cavity method. The approximate analysis of a small hole coupling coefficient is verified by this analysis. Numerical results indicate that the mutual coupling between holes is not negligible for calculating the directivity of the directional coupler.

A radial line slot antenna (RLSA) is a slotted waveguide planar array for the direct broadcast from satellite (DBS) subscriber antennas. A single-layered RLSA (SL-RLSA) is excited by a radially outward traveling wave. The antenna efficiency of more than 85% has already been realized. These antennas are designed on the assumption of perfectly rotationally symmetrical traveling wave excitation; the slot design is based upon the analysis of a slot pair on the rectangular waveguide model with periodic boundary walls. However, the slots perturb the inner field and the actual antenna operation is not perfectly symmetrical. This causes the efficiency reduction especially for very small size antenna. This paper presents a fundamental analysis of the inner field of the radial waveguide. It is impossible to analyze all the slot pairs in the aperture as it is and only the slots in the inner few turns are considered since these provide dominant perturbation. The calculated results are verified by the experiments and reasonable agreement is demonstrated. Some design policies are suggested for enhancing the rotational symmetry.

This paper presents a hole coupling theory for the directional coupler to monitor the output of Gyrotron. The theory gives an expression for a hole coupling coefficient including the wall thickness effect.

The authors design a simple feed system for a planar slotted waveguide array. A waveguide π-junction with negligible reflection is cascaded to compose a multiple-way power divider. The frequency characteristics of the power divided to each port and the reflection at the feed point are discussed and high performances are predicted. The maximum number of cascaded junctions in this system can be determined in terms of a desired frequency bandwidth and allowable deviation in divided power.

The reflection characteristics of large alternating-phase fed single-layer waveguide arrays with center-feeds are investigated to identify the mechanism for bandwidth narrowing effects. Firstly, the overall reflection for the whole array is analyzed by FEM and fine agreement with measurements is demonstrated. It is deviating from the conventional prediction based upon a simple sum of reflections from components in the array, such as the multiple-way power divider, the slot waveguides and the aperture at the antenna input. Careful diagnosis reveals that the mutual coupling between the alternating phase waveguides via external half-space is the key factor in reflection accumulation. Amongst all, the slot with strong excitation whose position depends upon the aperture illumination design produces the dominant contribution in the mutual coupling.

This paper presents an antenna for the UHF-TV reception consisting of skeleton slot array installed on a reflector. We propose a dipole model of the skeleton-slot elements to calculate its radiation pattern. The prototype antenna has 13 dBi antenna gain, 30% frequency band width and a function of beam tilting, which are sufficient characteristics for the UHF-TV reception.

The authors propose a waveguide π-junction with an inductive wall. Galerkin's method of moments is applied to analyze it and small reflection and desired power division ratio is realized. Good agreement between the calculated result and the measured one verifies the design of a unit π-junction. The characteristics of aπ-junction with a wall are almost the same as those of a conventional π-junction with a post. Important advantage of the new π-junction with a wall is that it can be manufactured in the die-cast process of the waveguide while a post in the conventional one must be attached in an additional process. A 16-way power divider consisting of 8 π-junctions is designed at 11.85 GHz and the characteristics are predicted.

A radial line slot antenna (RLSA) is a high efficiency and high gain planar antenna. The efficiency of RLSA becomes lower as the aperture size reduces due to rotational asymmetry of the illumination. A concentric array RLSA (CA-RLSA) was proposed to overcome this difficulty. It adopted three new techniques; (1) not spirally but concentrically arrayed slots, (2) a rotating mode feed circuit, (3) matching slot pairs eliminating termination loss. This paper proposes the basic slot design for (1) and (2) of CA-RLSA. Excellent characteristics of very small CA-RLSAs based upon this design are confirmed by measurements.

A flat diversity antenna, consisting of a disk loaded monopole antenna and four notch antennas composed in the same disk, was proposed as a vehicular antenna to reduce a fading effect of urban mobile telephone. The disk loaded monopole antenna is fed by a center probe and has four matching posts to realize the same pattern as that of a monopole antenna over a wide frequency range. This paper presents a new feed circuit for the flat diversity antenna, and measurement results of its input characteristics and radiation pattern when it is mounted on a vehicle. To verify the diversity effect of this antenna, we measured urban propagation characteristics at 900MHz, and compared the results with those of a space diversity antenna. We obtained almost the same characteristics with the flat diversity antenna as with the space diversity antenna.

A full-wave analysis of antennas with polarization grids is performed. Radiation patterns of antennas for two types of grids (straight strip and curved strip) are presented, where effects of the grid position and the grid paramenters are discussed.

The center-feed in a single-layer slotted waveguide array[1]-[3] is one of the key components in polarization division duplex (PDD) wireless systems. Two center-feed arrays with orthogonal polarization and boresight beams are orthogonally arranged side-by-side for transmission and reception, simultaneously. Each antenna has extremely high XPD (almost 50 dB in measurement) and a very high isolation (over 80 dB in measurement) between two arrays is observed provided the symmetry of slot arrangement is preserved [4]. Unfortunately, the area blocked by the center feed causes high sidelobe levels. This paper proposes the ridged cross-junction multiple-way power divider for realizing blockage reduction and symmetrical slot arrangement at the same time.

A radial line slot antenna (RLSA) is a high gain and high efficiency planar antenna proposed for DBS subscribers. Spirally arrayed slots are excited by a cylindrical wave with the rotational symmetry. In a small sized antenna where large slot coupling is adopted, aperture efficiency reduction due to rotational asymmetry associated with a spiral arrangement of the slots becomes notable. Authors proposed a RLSA with a concentric slot arrangement excited by a rotating mode in order to enhance the rotational symmetry. This is the first report of the normal operation of a rotating mode RLSA fed by a cavity resonator. The experiments confirm the basic operation of this novel antenna; the gain of 27.8dBi and the efficiency of 68% is measured at 11.85GHz for the RLSA with 0.24mφ.