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Abstract. A hybrid uniform geometrical theory of diffraction (UTD)-moment method (MOM) approach is introduced to provide an efficient analysis of the electromagnetic radiation/scattering from electrically large, finite, planar periodic arrays. This study is motivated by the fact that conventional numerical methods become rapidly inefficient and even intractable for the analysis of electrically large arrays containing many antenna or frequency-selective surface (FSS) elements. In the present hybrid UTD-MOM approach, the number of unknowns to be solved is drastically reduced as compared to that which is required in the conventional MOM approach. This substantial reduction in the MOM unknowns is essentially made possible by introducing relatively few, special ray-type (or UTD) basis functions to efficiently describe the unknown array currents. The utility of the present hybrid approach is demonstrated here for the simple case of a large rectangular phased array of short and thin metallic dipoles in air, which are excited with a uniform amplitude and linear phase distribution. Some numerical results are presented to illustrate the efficiency and accuracy of this hybrid method.

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Poisson sum formulas have been previously presented and utilized in the literature [1]-[8] for converting a finite element-by-element array field summation into an alternative representation that exhibits improved convergence properties with a view toward more efficiently analyzing wave radiation/scattering from electrically large finite periodic arrays. However, different authors [1]-[6] appear to use two different versions of the Poisson sum formula; one of these explicitly shows the end-point discontinuity effects due to array truncation, whereas the other contains such effects only implicitly. It is shown here, via the sifting property of the Dirac delta function, that first of all, these two versions of the Poisson sum formula are equivalent. Second, the version containing implicit end point contributions has often been applied in an incomplete fashion in the literature to solve finite-array problems;it is also demonstrated here that the latter can lead to some errors in finite-array field computations.Index Terms-Array antennas, Poisson sum formula.

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In this paper, the use of reflecting microstrip arrays as stable target points, called PS as described above, is investigated for SAR interferometry applications. The reflecting surface of a reflectarray can be designed to scatter most of the incident radiation back in the direction of incidence. This goal is achieved by imposing a phase distribution (n) of the kind [5]:where n is the element position, d gives the spacing between elements, is the wavelength, and i the angle of incidence (Fig. 1). The phase contribution of each element must be chosen not only to satisfy the final distribution given by Eq. (1), but also to compensate for the phase delay ⌬ n ϭ (2/)⌬r n in the different path lengths of the incident field (Fig. 1).The overall design of microstrip reflectarray entails the use of a specified phase design curve. The phase tuning technique based on elements of different size is adopted in this work. The number of radiating elements is used to control reflectarray RCS level, which is directly related to the size of the reflecting surface. When imposing the required RCS values, the proposed planar reflector is obviously advantageous with respect to a tridimensional CR having the same face size. The use of microstrip technology gives itself significant improvements such as low cost, less weight, and easy installation. NUMERICAL RESULTSThe validity of the proposed method has been tested by realizing a reflectarray prototype with a maximum backscattering in the direction i ϭ 23Њ (typically, an incidence angle of ERS-1/2 SAR). At present, a test facility of limited size is available for far-field measurements, so that a 10-GHz array of 7 ϫ 7 elements 0.6 spaced has been designed. Figure 2 shows a photo of the reflectarray, printed on a Diclad870 substrate with r ϭ 2.33 and thickness t ϭ 0.762 mm. Square radiating elements of dimensions spanning from 5.556 mm to 10.186 mm have been chosen from the phase design curve reported in Figure 3. RCS measurements have been performed in the anechoic chamber at the Microwave Laboratory of the University of Calabria. Two X-band pyramidal horns have been used as transmitting and receiving antennas for the monostatic configuration illustrated in Figure 4. A good agreement between simulations and experimental results can be observed in Figure 5, where a maximum backscattering value exists at the required incidence angle i ϭ 23Њ. CONCLUSIONPrinted reflectarrays were proposed in this work as artificial PS for SAR applications. A maximum backscattering in a prescribed direction of incidence was obtained as in standard CR, but using a very thin and flat structure. The new planar reflector avoids the storage of unwanted materials, which usually compromises CR electromagnetic response, thus much more stability is obtained together with less cost and easier installation. The proposed method was tested on a 10-GHz reflectarray prototype. Both numerical and experimental validations show a RCS peak at i ϭ 23Њ, which is the typical ERS1/2 SAR angle of incidence. , where N tot is the to...