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In this paper, an alternative approach for the design of open-ended waveguide array antennas is presented. The approach is based on microwave filter concepts. The exploitation of this alternative viewpoint has been made possible by the availability of a very efficient computer-aided design (CAD) tool which is based on a full-wave modal analysis technique. In this paper, we first outline the technique for the efficient analysis of open-ended waveguide array antennas. Using the software developed and following the alternative design approach, two different application examples are then shown, indicating how the alternative viewpoint introduced gives indeed significant additional degrees of freedom. Index Terms - Antenna arrays.

In this paper, we describe two multimode network representations for the analysis of radiating array of thick parallel plates. Due to periodicity and infinite extent, only one period of the structure needs to be studied. The key step is then the derivation of the equivalent network representation for the transition from a free-space region limited by phase-shift walls to a parallel plate waveguide. Two solutions to the problem are discussed. In the first solution, the relevant boundary value problem is cast into a network form that leads to an integral equation. The equation is then solved with the method of moments (MoM's). In the second solution, the elements of the multimode coupling matrix representing the grating are evaluated directly in terms of their network definition. The two solutions are then compared and the relative merits are discussed. The main feature of the approach presented in this paper, is that once the network representation of the key transition is obtained, it allows for the study of a wide class of scattering problems involving, for instance, corrugated surfaces and single or cascaded thick gratings. Comparison with published data are also presented, indicating that the two network representations developed are indeed very accurate. Index Terms - Electromagnetic scattering.

In this paper, a multimode equivalent network representation (MEN) is proposed for the scattering from a multistrip grating. Previously, rigorous analytical results were developed involving gratings with one or two strips in a period. In this paper, the MEN representation is extended to planar gratings with an arbitrary number of strips or apertures per unit cell. Both TE and TM incidence are described. The extension is obtained combining the MEN formulation with the Method of Moments solution (MoM) of the relevant integral equation. The code thus obtained retains the key feature of the MEN representation, namely the frequency independence of the characterization, and is much more flexible than the analytical solutions previously derived. The MoM solution procedure is described in detail and several application examples are discussed.

In this paper, an alternative approach for the design of angular bandpass filters composed of metal strip gratings is proposed. In the classic approach, frequency selective surfaces (gratings) are used as resonant elements and the spacing between them is adjusted to obtain the required electrical performance. Following this implementation, however, the electrical coupling to the individual resonators can not be fully controlled so that very limited design freedom is obtained. Following the approach that we propose, the resonant element is the spacing between surfaces while the individual grating geometries are adjusted to obtain the required inter-resonator couplings. With this arrangement the structure becomes effectively equivalent to a closed waveguide filter, all electrical parameters of interest can be individually controlled and considerably extended design freedom is achieved. In the paper the basic resonator performance is analyzed and complete filter design examples are discussed. Furthermore, it is shown that, following the approach that we propose, the frequency behavior of the structure is completely decoupled from its angular behavior in the design process thereby further extending the design freedom.