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In this communication, a dual-band shared-aperture reflectarray (RA) with a phased array is proposed for intersatellite links (ISLs). The Ka-band RA is integrated with an X-band phased array by a sharing mushroom patch structure. The high-frequency ratio allows the high-frequency RA and the low-frequency broadband phased array to operate independently to support high-speed communication of the geostationary orbit (GEO) relay nodes in the intersatellite network. To verify this concept, a prototype of the antenna is designed and fabricated, and its electrical performance is measured. The RA presents a peak gain of 30.1 dBi (28 GHz) and a 3 dB gain bandwidth of 11.4% (26.4–29.6 GHz). The phased array presents the peak gain of 21.7 dBi (9 GHz), and the relative bandwidth can reach 45.3% in the boresight direction. The scanning range can cover ±45°, and the H/E planes scan gain losses are less than 2.34 and 4.33 dB, respectively. [ABSTRACT FROM AUTHOR]

In this study, we propose a generalized algorithm for far-field radar cross section determination by using 3-D synthetic aperture imaging with arbitrary antenna-scanning surfaces. This method belongs to a class of techniques called image-based near-field-to-far-field transformation. The previous image-based approaches have been formulated based on a specific antenna-scanning trajectory or surface, such as a line, plane, circle, cylinder, and sphere; the majority of these approaches consider 2-D radar images to determine the azimuth radar cross section. We generalize the conventional image-based technique to accommodate an arbitrary antenna-scanning surface and consider a 3-D radar image for radar cross section prediction in both the azimuth and zenith directions. We validate the proposed algorithm by performing numerical simulations and anechoic chamber measurements. [ABSTRACT FROM AUTHOR]

A new approach is proposed to develop aperture-shared dual-band antennas using partially reflecting surfaces (PRSs). A fully aperture-shared dual-band antenna consisting of a low-band antenna (LBA) and a high-band antenna (HBA) right below the LBA is first investigated. The aperture sharing has little influence on the LBA but causes a severe shielding effect on the HBA. To alleviate the shielding effect, a low-pass PRS is inserted between the LBA and HBA, forming an air-filled quasi-Fabry–Perot cavity, which can make compensation for the radiation from the HBA but with little influence on the LBA. The second PRS is introduced above the LBA to enhance the bandwidth (BW) for HBA. It is shown that the fully aperture-shared dual-band antenna achieves an impedance BW ($\vert \text{S}11\vert < -15$ dB) of ~43.7% (0.68–1.07 GHz) for the LBA and ~45% (1.7–2.7 GHz) for the HBA with an average gain of ~8 dBi and stable radiation patterns. Based on the PRSs, an aperture-shared dual-band antenna subarray is finally developed for base-station applications, which covers the frequency bands of 0.68–0.96 and 1.7–2.7 GHz for 2G/3G/4G mobile communications. [ABSTRACT FROM AUTHOR]

This communication presents a freehand imaging system, which takes full advantage of a compact multiple-input multiple-output (MIMO) radar to provide the real-time results by means of freehand movements. The system is based on a commercial radar-on-chip, equipped with four receivers and two transmitters, and an optical tracking system (i.e., motion capture system) for retrieving its position and attitude. The reduced size of the radar enables its handheld operation, making possible to create a synthetic aperture by moving the scanner over the area of interest. Due to the new degrees of freedom with respect to previous implementations based on quasi-monostatic topologies, a novel calibration strategy for the system is required in order to mitigate positioning errors. After calibration, the simulations and measurements are accomplished revealing that the novel freehand multistatic setup significantly outperforms the monostatic setup in terms of scanning speed and image quality. Multimedia material is provided to illustrate this performance. [ABSTRACT FROM AUTHOR]

A novel hybrid approach to the power synthesis of mask-constrained shaped beams by means of concentric-ring isophoric arrays is presented. The basis of this procedure is to use the complex aperture distribution obtained by Elliott–Stern method as a starting point of an innovative algorithm that combines a classical density tapering method with a simulated annealing one. The proposed technique allows to outperform the previous procedures. [ABSTRACT FROM AUTHOR]

This paper presents the first demonstrator of a portable, multiview, high-resolution, 3-D, and real-time microwave imaging system. The system is based on a recently developed real-time 3-D microwave camera, which performs quasi-monostatic acquisitions, equipped with an optical depth camera, providing target surface profile information. In addition, the entire system can be arbitrarily moved along the target performing microwave and depth camera synchronized acquisitions from different views with a twofold purpose, namely: 1) enabling a coverage area much larger than that possible with a static imaging system and b) allowing for incorporation of several tilt angles (or views) to enhance capturing specular reflection imaging data to improve the overall image quality. At each scanning position, the imaging data from the microwave camera are processed to build a local 3-D microwave image. The information is then merged, using recently proposed techniques for multiview synthetic aperture imaging, to compose the global image. The synchronized optical camera depth acquisitions enable tracking the entire imager movements so that the position and attitude are known. Moreover, the data acquired by the depth camera are also use to build a complementary 3-D outer surface profile model of the target, producing a combined and realistic image of the internal and external geometries of the target. Finally, the performance of the combined system is evaluated using several examples related to hidden contraband covered by clothing (i.e., people screening). [ABSTRACT FROM AUTHOR]

This paper deals with the design of tensorial modulated metasurfaces able to implement a general radiating aperture field distribution. A new aperture synthesis approach is introduced, based on local holography and variable impedance modulation. In particular, it is shown that tensorial metasurfaces can be used to generate general radiating distribution (phase and amplitude). In addition, a step-by-step algorithm is presented. In order to validate the method, several solutions are presented at 20 GHz which implement aperture distributions able to radiate different beams with general polarization. [ABSTRACT FROM AUTHOR]

In this paper, the superluminal behavior of a radiated pulse in the near-field of an ideal dipole and an ultrawideband antenna is explained and demonstrated through simulations and measurements. The deformation of the radiated pulse in the near-field is illustrated using the ideal dipole antenna radiation as well as by a Vivaldi antenna through full-wave simulations and measurements. The apparent superluminal pulse velocity is due to the pulse reshaping of the radiated pulse in the near-field of the antenna. The pulse velocity is measured by tracking pulse peak, pulse envelope peak, and also calculating the pulse centrovelocity. The superluminal pulse peak velocity of the radiated pulse from a miniaturized Vivaldi antenna is confirmed through measurements in face-to-face and quasi-monostatic radar configurations. The effect of different values of pulse velocities on the quality of reconstructed images using synthetic aperture radar processing is demonstrated as well. [ABSTRACT FROM PUBLISHER]

In this paper, a procedure to design a fuzzy classifier to classify shell-shaped targets is proposed. The proposed procedure utilizes the radar cross section (RCS) of a shell-shaped target considering the relative orientation angle and polarization dependences in various flight scenarios based on real situations. In addition, particle swarm optimization (PSO) is applied to the fuzzy classifier to maximize its classification capability. Numerical results using three different shell-shaped targets are presented to assess the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A single-layer dual-band circularly polarized reflectarray antenna has been designed, fabricated, and tested for Ka-band satellite communications. The reflectarray antenna phasing element is composed of a concentric split-ring, in combination with a modified Malta Cross, where the technique of varying rotation angle and element size has been utilized to compensate the phase delay at 20 and 30 GHz, respectively. All the element configurations have been optimized to reduce cross-polar reflection. The aperture field method has been used to predict the reflectarray radiation performance, such as gain, radiation pattern, and cross-polarization level. A reflectarray with a circular aperture of 420 mm in diameter has been designed, manufactured, and tested for verification. A planar near-field measurement setup has been utilized to measure the reflectarray radiation characteristics. The measured results demonstrate that this dual-band reflectarray has achieved aperture efficiency of 66.5% at 20 GHz and 50% at 30 GHz, respectively. [ABSTRACT FROM PUBLISHER]

A particle swarm optimization technique is applied to maintain a constant beamwidth of a large phased-array when its major lobe is pointing away from the broadside direction. The first side-lobe is suppressed to a minimum possible level, at the expense of raising the other side-lobes. Tapering of excitation amplitude across the aperture is also exercised to help suppressing the side-lobe level. [ABSTRACT FROM AUTHOR]

Most of existing through-the-wall radar imaging (TWRI) algorithms deal with a single layer homogeneous wall in two-dimensional scenario. In this communication we present a generalized three-dimensional (3-D) beamforming algorithm for the focused imaging of targets behind multilayered building walls. The far field layered medium Green's function is incorporated in the 3-D beamformer for the compensation of the wall effect. 3-D polarimetric imaging is exploited in TWRI for enhanced target identification and feature extraction as well as wall effect mitigation. Numerical results show that the proposed 3-D beamformer provides high quality focused images in various wall-target scenarios. [ABSTRACT FROM AUTHOR]

In this paper, after a brief review on the working principles of synthetic aperture radiometers exploiting interferometry and mechanical rotation of the antenna, analytical expressions are provided which allow to easily compute the receiving performance of the interferometer starting from given locations of its sensors. Then, an innovative and general approach is developed and discussed for the optimal synthesis of the locations of the array sensors in order to fulfill requirements of crucial interest. Moreover, an innovative approach is also developed for the synthesis of the optimal weighting of the different collected signals. Finally, the performances of the developed synthesis approaches are discussed with reference to the GEO Atmospheric Sounder (GAS) array instrument. [ABSTRACT FROM AUTHOR]

A method of estimating spatial degrees of freedom (DoF) from measured multipath propagation channels in the multiple-input single-output regime is presented. The DoF of the multipath channels on the transmit (Tx) side is derived by means of the spherical-wave expansion of electromagnetic fields radiated from a Tx antenna array having a certain aperture size. The DoF estimates are independent of particular realization of antenna elements on the Tx aperture. For a given aperture size, the DoF provides the number of the Tx antenna elements for efficient improvement of the system performance by utilizing the spatial diversity. Having confirmed the soundness of our DoF estimation method by channel measurements in an anechoic chamber, the DoF of indoor multipath channels is analyzed. The DoF on the Tx side of the considered multipath channels reveals larger values when the antenna aperture size is increased at a fixed frequency, and when the frequency increases for a fixed antenna aperture size. For a fixed frequency, increasing the antenna aperture size is more effective in observing extra DoF in the obstructed and non-line-of-sight channels than in the line-of-sight channels. Furthermore, for a fixed antenna aperture size, the use of the higher frequency brings larger DoFs in many propagation scenarios. The results also show that electrically smaller antennas are more efficient in observing the DoF. Finally, the solid angle of multipath is derived as a Tx antenna-independent metric of the multipath richness. It is defined as an angular range of dominant multipath clusters subtended on a unit sphere. Our analysis method is extendable to the multiple-input multiple-output regime in a straightforward manner. [ABSTRACT FROM PUBLISHER]

A new configuration of the dual-band and dual-polarized antenna is presented, which is fed by aperture coupling for the existing mobile communication systems working over 870–960 MHz (GSM) and 1710–2180 MHz (DCS/UMTS) frequency band. XX-Polar antenna stands for an antenna with dual-band and dual linear slant polarization. In this paper DU band stands for DCS/UMTS band. Measurement results show that the proposed antenna yields good broadside radiation characteristics including symmetric radiation patterns, low cross-polarization level (<-14 dB), low backlobe level (F/B>20\ dB) and high isolation (>30 dB) at both bands. The designed antenna has an impedance bandwidth of 20.4% (790–970 MHz) for VSWR<1.5 in the lower band and 29.3% for VSWR<1.6 (1630–2190 MHz) in the upper band. The measured average gains are about 9.3–10.2 and 8.6–10 dBi in the lower and upper band, respectively. It is also promising for array antenna in various wireless systems. [ABSTRACT FROM PUBLISHER]

A new directive ultra-wideband antenna based on rectangular waveguide aperture antennas is presented. Conventional rectangular aperture antennas are limited by the single mode operation of the waveguide as well as relatively long and narrowband resonant feeds. To overcome these limitations, we developed a new rectangular waveguide antenna feeding structure that can establish an aperture field distribution very similar to that of the fundamental waveguide mode with a relatively short waveguide section and over two octaves of bandwidth. The overall antenna size is 0.55 \lambdam \times 0.27\lambda m \times 0.18 \lambdam where \lambdam is wavelength at the minimum operating frequency. Due to the planar aperture of the antenna, a polarizer could be added to the antenna to ensure good cross-polarization performance with fabrication tolerances. The proposed feed requires a balun structure, and thus an integrated balun design is presented. It is found that a standard balun would interact with the antenna structure and thus a modified design was implemented. The antenna was fabricated and measured. The antenna had VSWR < 2.5 from 1.08 to 4.9 GHz and the measured gain showed almost constant aperture gain which increases from 5.3 dBi at the low frequency end to 11 dBi at the high frequency edge. [ABSTRACT FROM PUBLISHER]

We present a method to generate three-dimensional (3D) inverse synthetic aperture radar (ISAR) images of a target at arbitrary aspect angles using the shooting and bouncing ray (SBR) method. We have derived a 3D-image-domain ray-tube integration formula based on the SBR technique. The imaging formula is in a form of convolution, then a nonuniform fast Fourier transform (NUFFT) is induced to achieve the convolution, which can be used to generate 3D ISAR images rapidly. Compared to the conventional algorithm where the ISAR images are obtained by inverse Fourier transforming the computed scattered fields over a range of frequencies and a range of aspect angles, the new formula needs only one-time ray tracing and physical optics (PO) integration over a small angle span. Hence the computational time is decreased tremendously. The ISAR images of a missile target and an armored car for several aspect angles are presented to demonstrate the efficiency and accuracy of the proposed method. [ABSTRACT FROM PUBLISHER]

New configurations of small-size shielded metallic Fabry–Perot (FP) antennas with improved performance over a large frequency band are presented in S-band for space missions. The bandwidth enlargement is obtained by stacking two FP cavities of different size, each of them presenting a low quality factor. Their radiating apertures measure around \lambda0 and 2\,\times\lambda0, respectively. Concentric corrugations are also introduced between both cavities to control the higher-order modes that are excited systematically in shielded small-size FP antennas due to lateral resonances. The obtained results are compared to those of a single-stage FP cavity antenna with the same aperture size. Several prototypes have been fabricated and measured. An aperture efficiency higher than 70%, a reflection coefficient smaller than - 15 dB, and sidelobe levels lower than - 20 dB have been obtained experimentally, over a wide frequency band (2.4–2.66 GHz). These characteristics make stacked FP cavity antennas very attractive to replace global coverage horn antennas, or to be used in feed clusters of multiple-beam antennas, especially in C- and S-bands, where they lead to more compact and less bulky solutions compared to classical feed horns. [ABSTRACT FROM PUBLISHER]

Antenna array configurations have significant influence on the radiometric sensitivity of aperture synthesis microwave radiometers. In this paper, we propose a minimum degradation array (MDA) for optimum sensitivity. First, the degradation factor (DF) is defined to characterize the effect of redundant spatial frequency samples formed by an array on the sensitivity. Aiming at minimizing DF, a simulated annealing (SA) based method is proposed to search for an MDA, which, combining with a concept of augmented maximum baseline (CAMB), can effectively locate the true global minimum of DF. Numerical results validate the effectiveness of the proposed method as well as CAMB in optimizing DF. Further, the lower bound of DF is discussed. Finally, simulation and experiment results demonstrate that the proposed method as well as CAMB is of significance in achieving optimum sensitivity. [ABSTRACT FROM AUTHOR]

The phase retrieval problem has gained considerable attention since the wave phase is lost or impractical to measure in several applications in Electromagnetic Engineering. Quite a few approaches have been proposed recently for the extraction of phase from amplitude-only data; however few of them investigate the uniqueness of the problem prior to the solution. In this communication, the problem of the uniqueness of the phase retrieval problem from far field amplitude-only data is examined in detail. It is shown that uniqueness is guaranteed if two experiments can be performed that differ by a quadratic term in the phase. Conversely, experiments creating only linear phase differences in the data do not guarantee uniqueness. This result is demonstrated by considering the problems of a scattering target illuminated in two experiments differing by a quadratic phase shift, corresponding to two different values of defocusing of the incident wave. [ABSTRACT FROM AUTHOR]

The circular symmetry of concentric ring arrays becomes an advantage for situations where the radiation patterns are symmetric in the azimuthal direction. For planar arrays with elements in an equispaced grid, the fast Fourier transform can be applied in the calculations involved between the array factor and the source distribution. However, for circular arrays the elements are in a non-equispaced grid, making the application of fast computation algorithms difficult. Therefore, two techniques are proposed to synthesize circular arrays. The first one provides the control of the pattern by sampling the array factor. In this case, the fast Fourier transform can be applied. The windows technique is also utilized to control the sidelobe levels and the ripple structure of the shaped beam. The second technique considers the symmetric nature of concentric circular arrays and the control of the array factor is performed imposing some specific points of the pattern. [ABSTRACT FROM AUTHOR]

The near-field radiation of several electrically large apertures has been computed based on the aperture field convolution method, including a square aperture, a circular aperture, and a serrated edge aperture. The frequency range is 8.0-12.0 GHz. The aperture diameters are limited to 5.00 m and the corresponding electrical size is 133-200 wavelengths. The time domain spectrum has been obtained by chirp z-transform with a Hamming window and the mechanism for the generation of the aperture near-field radiation in time domain is analyzed. The calculation results demonstrate that the near-field radiation of the aperture can be approximately seen as the synthesis of a plane wave from the aperture, cylindrical waves from the edges, and spherical waves from the corners. By this method, the direction, position, and magnitude of incoming waves in the near-field region can be estimated, and the aperture design can be modified to meet the requirements of the near-field radiation. The near field of the three apertures mentioned above has been compared, and it is shown that the serrated edge aperture has more uniform direct wave and lower diffraction waves, making it a candidate for compact range (CR) aperture design. [ABSTRACT FROM AUTHOR]

A new free-space measurement approach is presented to characterize radio frequency (RF) materials and metamaterials over a wide frequency range. In contrast to the traditional spot-focused horn pair system, the proposed technique generates a Gaussian beam with a tight spot, focused on a sample under test via a synthesis using individually measured responses. Therefore, difficulties in fabricating lenses for the conventional spot-focused horn pair are avoided altogether. In this paper, we validate the proposed technique by extracting the permittivity of a known dielectric slab, and subsequently proceed to characterize the transmission properties of metamaterial assembly. The proposed technique can be adapted for measurements in EM facilities using spherical or planar scanning capability. [ABSTRACT FROM AUTHOR]

Floquet wave and element-by-element summation representations are implemented to investigate the radiation from a periodic, rectangular array of linearly phased/sequentially pulsed dipoles in the frequency- and time-domains. A synthetic aperture type formulation for Floquet wave representation and an asymptotic formulation for the element-by-element summation representation are developed. Numerical results are presented to demonstrate the efficiency of the Floquet wave representation in terms of radiating, non-radiating and diffracted wave constituents and then validated via comparison with direct summation over the contributions of individual dipole radiations. [ABSTRACT FROM AUTHOR]

Design aspects of high efficiency profiled circular horns with thin walls as feeds for multibeam reflector antennas for satellite applications are presented in this paper. The modal content at the circular aperture of the horn necessary to closely approximate a unipolarized uniform distribution is first established. Slope discontinuities along the length of the horn are then used to generate the necessary aperture modes with the appropriate amplitudes and phases. The performance of the horn is calculated using the mode matching technique. Significant improvement in the horn aperture efficiency and reduction in the cross-polar level over a straight conical horn can be achieved over a single band or two bands that are widely separated in frequency. This conclusion is supported by the good agreement between predictions and measurements of a high efficiency dual-band horn. [ABSTRACT FROM AUTHOR]

The rigorous numerical-analytical approach has been developed and used for study of the periodic aperture arrays containing multiple dissimilar apertures of complex shapes in stratified medium. The analysis method is based on the solution of the system of integro-differential equations by Galerkin method with the entire domain basis functions explicitly accounting for the field singularities at the edges of the whole aperture except corners. An analytical treatment of the Green's function convolutions with the basis and test functions provides an efficient regularization and rapid uniform convergence of the solutions. Thickness of conducting screen has been taken into account with the aid of the approximation for effective aperture dimensions. The characteristics of the quasioptical slot arrays simulated by the developed method are in excellent agreement with the results of measurements and alternative simulations. An extensive parametric study of several aperture array configurations has been performed to explore properties of the single layer array arrangements with multiple apertures of complex shapes in a unit cell and stacked layered arrays. Effect of the aperture shape on the array performance and the physical mechanisms underlying the transverse magnetic wave resonances and Luebbers' anomaly in the two-layer arrays are discussed in detail. [ABSTRACT FROM AUTHOR]

This paper presents a procedure to reduce the computational effort for the full-wave analysis of corrugated or stepped rectangular horns/cavities, open-ended oil an infinite ground plane. This procedure, framed in the method of moments (MoM), is based on the construction of appropriate basis functions generated by solving the problem of one element in isolation. These functions are termed "synthetic aperture functions" (SAF); being numerical solutions of a physical problem, they have the adequate contents of high-order waveguide modes which allow the proper storage of local reactive energy. They also include a good approximation of the correct edge behavior. The technique reveals a significant reduction of computational resources compared to an ordinary MoM solution, especially for a large number of radiating elements. [ABSTRACT FROM AUTHOR]

The classic aperture synthesis widely used in radio astronomy, synthetic aperture radar, and remote sensing is based on the measurement of the degree of spatial coherence in the diffraction pattern of a radio emission source. All these applications imply correlation with a coherent reference signal. The possibility of obtaining the same information from the autocorrelation of a signal recorded on a single, mobile antenna is considered. Comparison of the output of an ordinary cross-correlation two-element radio interferometer and the autocorrelation output of a mobile antenna shows a similarity that allows extraction of information about the radio source spatial coherence in the latter case. The limitations of this method of aperture synthesis are considered. [ABSTRACT FROM AUTHOR]

The problem of a slot loaded by a hemispherical dielectric and/or a hemispherical backing cavity is solved using the method of moments (MoM). A novel recurrence formula is presented for fast calculations of the MoM admittance integrals associated with the spherical homogeneous solutions. The method enables the admittance integrals to be calculated without the need for any numerical integration. Measurements were carried out and good agreement between theory and experiment is obtained. [ABSTRACT FROM AUTHOR]

In this first part of a two-paper sequence, we develop a Gabor-based Gaussian beam (GB) method for the representation of three-dimensional (3-D) time-harmonic vector electromagnetic fields excited by two-dimensional (2-D) truncated arbitrarily polarized planar aperture field distributions. The biorthogonal Gabor basis is tied to a lattice in the discretized four-dimensional (4-D) [configuration (space)]-[spectrum (wavenumber)] phase space which spans the 2-D aperture plane. This study generalizes previous investigations of the simpler corresponding procedure for 2-D fields excited by one-dimensional (1-D) apertures [1]. By subsequent specialization, in the 1-D aperture case, to narrow-waisted 2-D ray-like GBs, we have shown that tracking such beams through interactions with complex environments and recombining them to synthesize the total 2-D field produces robust, efficient and accurate algorithms that are useful for a variety of forward and inverse scattering scenarios [2]-[6]. Extension to the time domain via narrow-waisted pulsed GBs has likewise been considered [6], [7]. These potential applications have motivated the extension here to general 3-D EM fields excited by time-harmonic 2-D truncated apertures. The presentation relates each step in the analytic development to a corresponding step in the 1-D aperture case [1], thereby highlighting the complications (in the parameterizing phase space) associated with the 2-D aperture problem. The outcome is the formal exact solution of the problem under consideration. In Part II [8], this formal solution is reduced by high-frequency asymptotics to yield physics-based explicit efficiently computable expressions for implementation. For the reasons noted above, also treated is the specialization to 3-D narrow-waisted ray-like GBs and the calibration of the resulting algorithms through a series of numerical tests. [ABSTRACT FROM AUTHOR]

In this second part of the two-part sequence dealing with Gabor-based Gaussian beam (GB) representations for the excitation of time-harmonic three-dimensional (3-D) vector electromagnetic fields excited by two-dimensional (2-D) arbitrarily polarized truncated planar aperture distributions (set in a discretized [configuration (space)]-[spectrum (wavenumber)] phase space), we employ high-frequency asymptotic approximations to reduce the formal solutions developed in Part I [1] to efficient algorithms for implementation. The resulting explicit expressions for the 3-D GB propagators are applied to the species of narrow-waisted GBs, which possess ray-like features without the failures of ray fields in ray-optical transition regions. The potential utility, of such GBs in the synthesis of wave interactions with complex environments has been discussed in [1]. The narrow-waisted GB algorithms for the aperture and radiated near-to-far zone fields are calibrated for robustness, accuracy and efficiency by comparison with numerically generated reference solutions in a series of tests involving coordinate-separable rectangular aperture distributions with cosine amplitude tapers. [ABSTRACT FROM AUTHOR]

Provides information on a study which presented a generalized study of classical axially symmetric dual-reflector antennas. Geometric aspects; Design equations; Calculation of antenna radiation characteristics through geometrical optics aperture field distribution; Conclusion.