An antenna solution for broadband communication satellite applications is presented. The proposed antenna design provides a full dual-band (Tx/Rx) four-color multibeam coverage of Europe in K/Ka-band while utilizing only a single main reflector aperture. This solution is especially relevant for smaller platforms and secondary payloads. The antenna system consists of an offset Cassegrain antenna combining two multiple-feed-per-beam (MFB) feed clusters and a doubly curved modulated modulated frequency surface (FSS) sub-reflector, which is the key enabling technology validated in this work. By utilizing a modulated FSS design, the antenna system fulfills all radio frequency (RF) requirements that were specified on the antenna coverage parameters. An engineering model (EM) of the doubly curved FSS sub-reflector has been designed and fabricated. Its RF performance was characterized experimentally, and good agreement has been observed between simulations and measurements, thus validating the proposed concept.

This Roadmap overviews present challenges and opportunities for the development of antenna measurement techniques and technologies to support the all-pervasive and ever-increasing demand for radio-frequency wireless systems in modern society. The Roadmap comprises 19 inspiring contributions by 34 leading experts in antenna measurements.

Reflectarrays are widely considered prime candidates for high-gain antennas on micro-and nanosatellite platforms, such as CubeSats. For such platforms, the fact that reflectarrays can be constructed using planar surfaces means that they are much easier to stow in the limited launch envelope than traditional reflector antennas, that require curved surfaces to produce high gain. Furthermore, the missions flown on nanosatellite platforms typically require less bandwidth than missions on medium and large satellites which means that the limitations in bandwidth, that are the major drawback of reflectarrays compared to traditional reflector antennas, are less important. TICRA has for the last decade been involved in several projects related to developing reflectarrays for CubeSats. These include projects related both to the development of software for design of reflectarrays and in the development of reflectarray antenna systems, including in a number of projects for the European Space Agency (ESA). In this work, the work carried out at TICRA in the area of Reflectarrays in general and on reflectarrays for CubeSats in particular, will be presented.

In this work, a method for diagnostics of large reflector antennas for space applications is presented. By using a Calderón projection together with a Higher-Order (HO) Method of Moments (MoM) discretization, the inverse electromagnetic scattering problem is solved in an efficient manner, allowing for diagnostics based on the equivalent currents. This method is referred to as the Calderón method and is shown to be well suited for use in antenna diagnostics applications. Two reflector antenna cases have been analysed and significant reductions in computation time and memory allocation requirements are observed in comparison to other state-of-the-art solvers.

In this paper, we present a computational model of the DTU-ESA Standard Validation antenna VAST12, and investigate the impact of how different features on the antenna impact the radiation pattern. It is shown that the termination of the central tube, used to mount the antenna, has a significant impact on the sidelobe level of the antenna.

We present a fast source reconstruction method suitable for antenna diagnostic applications of radiating structures on electrically large platforms. The method is based on a novel implementation of a recent reformulation of the inverse electromagnetic scattering problem, and is solved using a Higher Order Method of Moments (MoM) discretization. The novel implementation achieves asymptotically better scaling the previously possible, and in particular the memory use is substantially lower than was previously possible. Results from two example cases are presented where the new method is compared to the current commercial state-of-the-art solver in DIATOOL 1.1, and significant improvements are observed in terms of computation times and memory requirements.

We present antenna system using a circular polarization selective surface (CPSS) to realize a circular polarization (CP) equivalent to the widely used linear polarization (LP) gridded or dual-gridded reflector (DGR). The CPSS is realized by a multilayer stack of nonresonant anisotropic meander line surfaces, achieving a very wide bandwidth. The CPSS reflection and transmission dyadics are computed using full-wave simulations for all angles of incidence and design frequencies applicable, and the doubly curved reflector surface shapes are optimized in the TICRA POS software. The data are input to the TICRA tools software framework for antenna-system level radio frequency (RF) simulations. A planar CPSS sample was first manufactured and tested to demonstrate the adequacy of the selected multilayer design. A doubly curved reflector demonstrator based on the same technology and with a projected aperture of 750 mm was then designed, manufactured, and tested at Ku-band. While promising, the experimental results emphasize the difficulty of producing an electrically large multilayer doubly curved surface with RF performance equivalent to the original flat design and recommendations are provided to improve further the implementation of the proposed design.

A low loss dual circularly polarized feed antenna for a high gain deployable K-band reflectarray antenna on a CubeSat platform is designed. The feed consists of an elliptical horn antenna and its feed network, which will be optimized alongside with the reflectarray to match the desired performance goals of the antenna system. The antenna system reaches a peak gain of 38.5 dBi in the 19.7-20.2 GHz band. The gain variation is less than 0.2 dB and the feed reflection coefficient is less than -23.4 dB throughout the bandwidth.

This paper presents a study of transmission through arrays of periodic sub-wavelength apertures. Fundamental limitations for this phenomenon are formulated as a sum rule, relating the transmission coefficient over a bandwidth to the static polarizability. The sum rule is rigorously derived for arbitrary periodic apertures in thin screens. By this sum rule we establish a physical bound on the transmission bandwidth which is verified numerically for a number of aperture array designs. We utilize the sum rule to design and optimize sub-wavelength frequency selective surfaces with a bandwidth close to the physically attainable. Finally, we verify the sum rule and simulations by measurements of an array of horseshoe-shaped slots milled in aluminum foil.

In recent years, there have been significant interest in reflectarray antennas and the latest research have shown that reflectarrays can be used to provide solutions which are otherwise not possible using existing solutions. In this paper, we present a general design framework for the design of advanced reflectarrays and show how it can be used to design reflectarrays for applications for future antenna systems.

There has been significant interest in reflectarray antennas in recent years. The latest research have shown that reflectarrays can be used to provide solutions which are not possible using conventional technologies. In this paper, we present a general design framework for the design of advanced reflectarrays and show how it can be used to design antenna systems for future space-borne applications.

This paper presents a study of extraordinary transmission (EoT) through arrays of sub-wavelength apertures. Fundamental limitations for this phenomenon are formulated as a sum rule, relating the transmission coefficient over a bandwidth to the static polarizability. The sum rule is rigorously derived for arbitrary periodic apertures in thin screens. By this sum rule we establish a physical bound on the bandwidth of EoT which is verified numerically for a number of aperture array designs. We utilize the sum rule to design and optimize subwavelength frequency selective surfaces with a bandwidth close to the physically attainable. Finally, we verify the sum rule and simulations by measurements of an array of horseshoe-shaped slots milled in aluminum foil.

We present a non-resonant, dual band circular polarization selective structure (CPSS) for satellite communication applications in the K- and Ka-band. The structure consists of multiple layers of cascaded anisotropic sheets, with printed meander lines, separated by low permittivity spacers. It reflects right hand circular polarization and transmits left hand circular polarization in the lower frequency band. In the upper frequency band the opposite polarization selectivity is achieved. The theory of dual band circular polarization selectivity from cascaded anisotropic sheets is presented, and it is concluded that the separation between the frequency bands of operation is governed by the relative rotation between subsequent layers. An optimization routine for synthesizing dual band CPSSs from predefined design requirements is introduced, where a number of different optimization algorithms are utilized. A simulated design is presented which fulfills the strict design requirements of insertion loss and return loss less than 0.5dB, and axial ratio less than 0.78dB, in the frequency bands 17.7–20.2GHz and 27.5–30.0GHz. A prototype of the optimized design has been fabricated and characterized experimentally, both in transmissionandreflection,andgoodagreementisobservedbetweensimulated and experimental results. This type of structure is a potential candidate for implementation in dual band multiple spot beam systems utilizing frequency and polarization reuse schemes. (Less)

This paper presents imaging results from measurements of an industrial planar composite panel, utilizing two introduced algorithms for data postprocessing. The system employs a planar near-field scanning set-up for characterizing defects in industrial planar composite panels in the 50–67GHz band, and can be considered as a complementary diagnostic tool for non-destructive testing purposes. The introduced algorithms are based on the reconstruction of the illuminating source at the transmitter, enabling a separation of the sampled signal with respect to the location of its potential sources; the scatterers within the device under test or the transmitter respectively. The algorithm is extended to a L1-minimization problem formulation exploiting the sparsity of the defects, which allows for compressive sensing techniques to be adapted for image retrieval. The algorithms are benchmarked against a more conventional imaging technique, based on the Fourier Transform, and it is seen that the complete imaging system provides increased dynamic range, improved resolution and reduced measurement time by removal of a reference measurement. Moreover, the system provides stable image quality over a range of frequencies.

This paper presents imaging results from measurements of an industrially manufactured composite test panel, utilizing two introduced algorithms for data postprocessing. The system employs a planar near-field scanning setup for characterizing defects in composite panels in the 50-67-GHz band, and can be considered as a complementary diagnostic tool for nondestructive testing purposes. The introduced algorithms are based on the reconstruction of the illuminating source at the transmitter, enabling a separation of the sampled signal with respect to the location of its potential sources, the scatterers within the device under test or the transmitter. For the second algorithm, an L-1-minimization problem formulation is introduced that enables compressive sensing techniques to be adapted for image retrieval. The algorithms are benchmarked against a more conventional imaging technique, based on the Fourier transform, and it is seen that the complete imaging system provides increased dynamic range, improved resolution, and reduced measurement time by removal of a reference measurement. Moreover, the system provides stable image quality over a range of frequencies.

Two approximation methods are presented for fast calculations of the monostatic scattering from axially symmetric scatterers coated with electromagnetic absorbers. The methods are designed for plane wave illumination parallel to the axis of rotation of the scatterer. The first method is based on simulating the scattering of a perfect electric conductor (PEC) enclosing the absorber coated scatterer, and multiplying the result with the squared magnitude of the absorber reflection coefficient in a planar scenario. The second method is based on simulating the scattering scenario in a physical optics (PO) solver, where the electromagnetic absorber is treated as reflection dyadic at the outer surface of the scatterer. Both methods result in a significant acceleration in computation speed in comparison to full wave methods, where the PO method carries out the computations in a number of seconds. The monostatic scattering from different geometries have been investigated, and parametric sweeps were carried out to test the limits where the methods yield accurate results. For specular reflections, the approximation methods yield very accurate results compared to full wave simulations when the radius of curvature is on the order of half a wavelength or larger of the incident signal. It is also concluded that the accuracy of the two methods varies depending on what type of absorber is applied to the scatterer, and that absorbers based on volume losses such as a carbon doped foam absorber and a thin magnetic absorber yield better results than absorbers based on resistive sheets, such as a Salisbury absorber. (Less)

We present a nonresonant circular polarization selective structure (CPSS) based on multiple layers of stacked meander line sheets arranged closely after each other. The structure has a total thickness of 13.5 mm (0.68 wavelengths at center frequency 15 GHz) and is realized by cascading printed circuit boards interspaced with a low-permittivity foam material, and the different layers are bonded together with thin layers of adhesive spray. A design procedure is presented that can be used to optimize the proposed structure based on its target band of operation. Based on this method, an optimized design has been simulated, and the structure shows a return loss and an insertion loss better than 0.5 dB, and axial ratio in transmission and reflection better than 0.78 dB, over a fractional bandwidth of 45.8% at normal incidence, fully covering the K-u-band 12-18 GHz. The functionality of the structure has been verified experimentally through measurements, both in reflection and transmission, with a total bandwidth of 42.0%, covering 86.7% of the K-u band. The simulated performance at oblique angles of incidence shows significant improvements when compared to classical resonant CPSSs.

We present a technique for performing high-accuracy measurements of the transmission and reflection properties in circular polarizations (CPs) of a test panel. Using linearly polarized antennas and measuring at four different antenna orientations, all with a relative rotation of 45°, an efficient normalization of each scattering component can be utilized. This method achieves a high signal-to-noise ratio in all normalized linear polarization components used to synthesize the CP scattering. Furthermore, a postprocessing scheme is introduced to compensate for measurement uncertainties due to antenna misalignments. The novel measurement and postprocessing techniques are utilized to characterize a manufactured wideband CP selective structure, both in transmission and reflection, and the measurement results are in excellent agreement with simulation results from commercial software. The repeatability of the measurement results is investigated, and the results are in the expected range in comparison with estimated measurement uncertainties.

This paper discusses the design and analysis of a reflector antenna system combining two doubly-curved Circular Polarization Selective Surfaces to provide a functionality equivalent to that of a dual gridded reflector but in circular polarization. The key feature of this design is to use a non-resonant CPSS design to avoid the bandwidth limitation of most CPSS designs previously discussed in the literature. A specific design at Ku-band is investigated and promising results are demonstrated, providing a cross-polarization discrimination higher than 25 dB over the full band.

We present a study of the performance degradation of electromagnetic absorbers when applied to doubly curved surfaces. The scattering from a perfectly conducting sphere coated with different types of single- and multilayer absorbers has been evaluated using analytic recursion expressions. A comparison of the effect of curvature on the absorber performance is presented for structures based on homogeneous resistive sheets and low permittivity spacers, circuit analog absorbers, bulk material absorbers, and ultra thin magnetic absorbers. A conclusion from this study is that bulk absorbers, based on lossy materials, are less sensitive to curvature than absorbers consisting of multiple layers of low permittivity spacers and resistive sheets.