## No full-text available

To read the full-text of this research,

you can request a copy directly from the authors.

IntroductionThe ProblemElectrically Small SurfacesElectrically Large SurfacesTwo ExamplesA Comparison of Analysis Methods
Appendix 4A—Interpretation of the ray theoryReferences

To read the full-text of this research,

you can request a copy directly from the authors.

... A conformal antenna array is an array with its antennas conformed to its bearing surface. Due to this flexibility, conformal arrays have found great applications in many modern defense and wireless communication systems [1,2]. Unfortunately, the existing beamforming and direction-of-arrival (DOA) estimation algorithms which have been developed for conventional planar arrays cannot be directly applied to conformal arrays since these algorithms assume elements with identical patterns which is not valid in conformal arrays. ...

... Due to the curvature of the bearing surface, each element in a conformal array has a far-field contribution in the direction of the incident signals which is different from the contributions of other elements. This means that, unlike conventional planar arrays, one cannot separate the element pattern from the array factor in the analysis of a conformal array [1]. To use high resolution DOA estimation algorithms such as MUSIC [3] or ESPRIT [4] for arrays with arbitrary geometries, interpolation techniques have been employed by some authors5678910111213. ...

... We suggest several geometries, including planar and volume geometries, to be used as a part of DF equipment used in ESM applications. Circular array geometries are of especial interest by virtue of their uniform performance over the azimuth range, and being not a saturated geometry, which means they could be easily extended to a new geometry by adding elements to the structure or by changing the whole geometry into a new circular-base geometry such as a cylindrical or a spherical geometry [13]. The organization of the paper is as follows. ...

... The second geometry, which be called the pyramid geometry, consists of the same UCA and an extra element at the center and a half of wavelength in height. The use of the extra element is beneficial to improving the elevation estimation accuracy in that it adds some kind of vertical aperture to the geometry [13]. Likewise, the third and the forth geometries, hereafter referred to as spiral-circular geometry and slanted-circular geometry, are enjoying the benefit of vertical aperture, whereas nine elements are used. ...

— In this paper, a comparison between several array geometries, including planar arrays and volume arrays, for two-dimensional Direction of Arrival (DOA) estimation using Multiple Signal Classification (MUSIC) is presented. For each geometry, various criteria is taken into consideration and a comparative study of the performance of geometries is carried out. The geometries together with their ultimate direction finding performance are compared based on Root Mean Square Error (RMSE), the ambiguity functions, and Cramer-Rao Bounds (CRB). Furthermore, the effects of phase and amplitude variations of the array element radiation pattern, namely Vivaldi and Monopole antenna, on DOA estimation performance are studied. The advantages and drawbacks of each geometry vis-à-vis the employed DOA estimation technique are shown through a numerical comparison.

... Based on the phase mode theory [28], a uniform circular current source leads to omnidirectional radiation with little gain ripples. The preliminary idea is to approach a circular uniform distribution using a four-element Vivaldi antenna array and the To extend the lower frequency bandwidth, the exponential radiated slots are prolonged in HP omnidirectional Antenna Ⅱ in Fig. 3(b). ...

A novel hybrid antenna for simultaneous RF energy harvesting (RF-EH) and dedicated wireless power transfer (WPT) is proposed. The hybrid antenna consists of a multiband dual-polarized omnidirectional antenna element (covering GSM-1800, UMTS-2100, ISM-2400/5800, 5G-3500 and WLAN bands) and a 2.4-GHz dual-polarized high-gain directional patch array element. In the WPT band (ISM-2400), directional beams locates at the null of omnidirectional beams, and a pair of spatially complementary beams is obtained. The omnidirectional beams are capable of capturing the ambient RF energy from low-elevation space for low-power circuits, while the directional beams receive the power from a dedicated source to activate high-power modules. Also the spatially complementary feature contributes low mutual couplings between ports that support the independent operation of WPT and RF-EH. For validation, an outdoor RF-EH test and an indoor WPT test are conducted. The measured results agree with the simulated ones.

... As an important application of array antennas, conformal arrays have been widely used in such platform which can be some part of an airplane, train or other vehicle. The design that the conformal arrays become integrated with the platform causes fewer disturbances such as extra drag, and the electrical advantages of conformal array are typically wide angle scanning capabilities [4]. As the important case of conformal arrays, conformal arrays on cylindrical surface have been widely used in radar and communication systems. ...

... The modules are usually fabricated on multilayered printed circuit boards (PCBs) [30, 31]. Adopting conformal design for arrayed antenna also allows being hosted on the fuselage of an aircraft or the superstructure of yacht [32, 33]. Another feature is the scalability because of its modular nature [34]. ...

Getting connected whenever and wherever you travel is not kind of luxury any more. Satellite communication researchers are making it a reality to bring you data, video, and voice services when you are away from home, out of office, or on a long journey. Satellite communication antenna mounted on mobile ground terminals is an essential prerequisite of successful connectivity. In this paper, we review the evolution of this kind of antenna in its historical context and outline the major research achievements on ground mobile terminals. Many striking demonstrations and prototypes are revisited to understand the emerging technologies and assess their potential towards practical implementations. The future trends and challenges are also discussed.

... Parameter estimation based on conformal antenna array has been a hot topic for a number of years. In particular, conformal array antennas potentially meet the needs of a variety of airborne radar and other defense applications [18, 19]. The benefits include reduction of aerodynamic drag, wide angle coverage, space savings, potential increase in available aperture [20]. ...

A novel direction of arrival (DOA) and polarization estimation method with sparse conical conformal array consisting of concentred loop and dipole (CLD) pairs along the z-axis direction is proposed in this paper. In the algorithm, the DOA and polarization information of incident signals are decoupled through transformation to array steering vectors. According to the array manifold vector relationship between electric dipoles and magnetic loops, the signal polarization parameters are given. The phase differences between reference element and elements on upper circular ring are acquired from the steering vectors of upper circular ring, it can be used to give rough but unambiguous estimates of DOA. The phase differences are also used as coarse references to disambiguate the cyclic phase ambiguities in phase differences between two array elements on lower circular ring. Without spectral peak searching and parameter matching, this method has the advantage of small amount of calculation. Finally, simulation results verify the effectiveness of the algorithm.

... For practical applications, such an array must provide a minimum attenuation level between two predefined directions, representing an interlocutor and a jammer (Fig. 1a). This kind of applications can be found in [2]. Note that the jammer could be a similar system already deployed, in this case, a high level of attenuation is requested to reduce interferences between both systems and must not depend on the projectile spin. ...

... Conformal antennas are especially difficult to characterize, since the polarizations of their elements are usually not aligned among themselves, a feature that considerably increases the design complexity. In spite of the fact that they nowadays constitute a well-studied subject, as seen in Josefsson (2006), surprisingly it is not easy to find any freely-distributed software tool capable of representing visual information about the spatial distributions of both their physical configuration and their electromagnetic radiation. The currently available tools correspond to either commercial electromagnetic simulators that make use of well-known numerical techniques, such as Finite Difference Time Domain (FDTD), Method of Moments (MM), etc., see Davidson (2010), or a recent MATLAB® toolbox called " Phased Array System Toolbox " -The Matlab Group (2011)-, neither of them freely available. ...

Electromagnetic laboratory teaching activities greatly benefit from utilizing Information and Communication Technologies (ICTs), due to the fact that the understanding of concepts that are difficult to be communicated using traditional approaches becomes easier. We have developed a graphical interface, designed with MATLAB®, that represents a very useful tool to convey concepts related to configuration and radiation of conformal antennas to students that are not experts in that particular field.

... Conformal antenna array, that is, array antennas with antenna elements arranged conformally on a curved surface, is widely used in a variety of airborne radar and other defense systems. The benefits include reduction of aerodynamic drag, wide angle coverage, space savings, and potential increase in available apertures282930. Cylindrical conformal array is a typical conformal array. ...

This paper proposes a quaternion-ESPRIT algorithm for closed-form estimation of direction of arrival (DOA) and polarization, using a cylindrical conformal array configuration. First, the array steering vector and the elevation are estimated using a quaternion eigenvalue decomposition of the data covariance matrix. Second, the azimuth is estimated. Finally, the polarization parameters are estimated using the relationships between the dipoles and the loops. These estimates are automatically matched. Simulation results show that the performance of quaternion method is obviously better than that of the long-vector method.

... To model the hybrid structure, one needs to determine the shaping parameters of the structure. The parametric equation of a GPOR is given by [11] í µí±¥ = í µí±í µí±¢ cos í µí¼, í µí±¦ = í µí±í µí±¢ sin í µí¼, í µí± § = −í µí±¢ 2 , (2) where í µí¼ is now the azimuth angle of GPOR varying from 0 to 360 ∘ , í µí±¢ is the GPOR basis parameter, and í µí± is the shaping parameter that represents the sharpness/flatness of the GPOR. ...

The radio-frequency (RF) field mapping and its analysis inside a space vehicle cabin, although of immense importance, represent a complex problem due to their inherent concavity. Further hybrid surface modeling required for such concave enclosures leads to ray proliferation, thereby making the problem computationally intractable. In this paper, space vehicle is modeled as a double-curvatured general paraboloid of revolution (GPOR) frustum, whose aft section is matched to an end-capped right circular cylinder. A 3D ray-tracing package is developed which involves a uniform ray-launching scheme, an intelligent scheme for ray bunching, and an adaptive reception algorithm for obtaining ray-path details inside the concave space vehicle. Due to nonavailability of image method for concave curvatured surfaces, the proposed ray-tracing method is validated with respect to the RF field build-up inside a closed lossy cuboid using image method. The RF field build-up within the space vehicle is determined using the details of ray paths and the material parameters. The results for RF field build-up inside a metal-backed dielectric space vehicle are compared with those of highly metallic one for parallel and perpendicular polarizations. The convergence of RF field within the vehicle is analyzed with respect to the propagation time and the number of bounces a ray undergoes before reaching the receiving point.

... Conformal antenna array, i.e., array antennas with antenna elements arranged conformal on a curved surface, will find its potential and promising applications in a variety of fields ranging from spaceborne , airborne, ship-borne, and missile-borne radar, space vehicles, wireless communication to sonar[1,2]. Its advantages include dramatic reduction of aerodynamic drag and the weight of arrays, wide angle coverage of 360 @BULLET , space-saving, reduction of radar cross-section, as well as potential increase in available aperture. ...

The pattern of each element in conformal array has a different direction for the curvature of conformal carrier, which results in polarization diversity of conformal array antenna. Polarization parameters of incident signals are considered in snapshot data model in order to describe the polarization diversity of conformal array antenna. It is required that the polarization parameters and direction of arrival (DOA) of incident signals are estimated together. An integrated frequency and DOA estimation method is proposed in this paper for cylindrical conformal array antenna. The frequency estimation of signal source is obtained by constructing state-space matrix. Through well-designed configuration of elements on cylindrical carriers along with estimation of signal parameters via propagator method (PM), the decoupling scheme for DOA and polarization parameters is implemented. A novel parameter pairing method for frequency and DOA of multiple sources utilizing the interpolation technique is given, based on which the fast frequency-DOA estimation algorithm is developed. Effectiveness of the proposed method is demonstrated by simulation experimental results.

... Circularly polarised (CP) microstrip patch antenna (MPA) is widely used in wireless communication and radar system due to its advantages of lightweight, low profile, ease of manufacturing, and conformation to the platform [1, 2]. However, it is difficult for the conventional MPA to realize ultrawide beam coverage which usually has more applications [3]. ...

A novel right-hand circularly polarized (RHCP) UHF microstrip antenna with 3 dB beamwidth of more than 150° is presented in this paper. The 3 dB RHCP beamwidth can be broadened by utilizing a combined ground structure with a hollow truncated cone ground plane and a metallic rectangular plate. Optimizing the half-angle θc of cone and the cone height hcone, a 3dB RHCP beamwidth ofmore than 200° can be acquired, which is about 120° greater than its corresponding regular RHCP microstrip antenna. There is a good agreement between the measured results and simulated results for the proposed antenna operating in UHF band.

... However, the algorithm suffers from tremendous computational complexity . Conformal array is the array mounted on the curvature carrier [18]. It has many advantages such as reduction of aerodynamic drag, reduction of the weight of array, space saving, and reduction of radar cross-section (RCS) [19]. ...

Most conventional direction-of-arrival (DOA) estimation algorithms are affected by the effect of mutual coupling, which make the performance of DOA estimation degrade. In this paper, a novel DOA estimation algorithm for conformal array in the presence of unknown mutual coupling is proposed. The special mutual coupling matrix (MCM) is applied to eliminate the effect of mutual
coupling. With suitable array design, the decoupling between polarization parameter and angle information is accomplished. The
two-demission DOA (2D-DOA) estimation is finally achieved based on estimation of signal parameters via rotational invariance
techniques (ESPRIT). The proposed algorithm can be extended to conical conformal array as well. Two parameter pairing methods
are illustrated for cylindrical and conical conformal array, respectively. The computer simulation verifies the effectiveness of the
proposed algorithm.

... [5], the circular has a potential of 360° coverage; and this only by adjusting phase excitations. Until our days, the common solution is to employ three separate antennas, each covering a 120° sector. [6]. The idea of our work is based on Taguchi Optimization Method using CST Microwave for simulation. ...

This paper presents a new approach to synthesize conformal cylindrical antenna arrays by controlling the phase excitation, to create a directive lobe usingtaguchìs method. The aim of our proposed method consists on the minimization of the fitness function between obtained and desired results. The results found, with the application of this method to synthesize conformal cylindrical arc antenna arrays, are validated with simulation by CST Microwave. We have used CST Microwave to simulate an 8-element conformal cylindrical arc antenna; witch has been tested in variable types of beam configurations.

... The conformal microstrip antennas have received significant attention for their advantages of simple structure, easy manufacture, low cost, convenient integration with other microwave components and fabrication of their feeding network together with antennas. Many researchers have been studying these antennas for years12345, and developed a structure conformal to the surface of missiles and satellites. However, conformal microstrip antennas still have disadvantages of lower efficiency and narrow band width due to the effects of surface waves, feeder loss and dielectric loss. ...

An antenna and an array with photonic bandgap (PBG) structures, which are cylindrical conformal microstrip antennas, both operating in X-band (10.2 GHz) are proposed. As shown in the simulation, PBG structures could suppress the surface wave propagating on substrate and balance the influence of cylindrical curvature at resonance frequency on antennas. The simulation results indicate that they have a higher gain and better directivity over the conventional antenna without PBG structure. Both of the antenna and the array are designed and manufactured, and the measurement results agree well with the simulations.

... Recently, enhancement of impedance and pattern bandwidth for slotted arrays by adding a wide-band matching element at the impedance transformation plan [3]. Activities where motivation was to find the relationship between the slot offset and the length with slot active conductance at the slot plan [4]. The microstrip antennas are known by their narrow frequency band and disability to operate at high power levels of waveguide, coaxial line or even stripline. ...

In this paper, a wide-band and high-gain microstrip antenna with mullti-layer microstrip patch and an aperture-coupled
feeding is proposed. The antenna has a condensed structure where the dimension is about 8.5mm by 7.5mm by 4.662mm
leading to good bandwidths covering 8.05 GHz to 12.01 GHz (39.48%), and the gain is up to 5.23dB. The low expenses
of this profile and its simple configuration allows for an its easy fabrication, with appropriation with wireless and satellite
communication.

... To overcome this problem, a simple solution is orientating the dipoles vertical axis (polar or polarization reference axis) to coincide with the cone axis. Otherwise, a polarization control device using a variable power divider VPD as inFigure 3 should be used for each element [18]. There are many possible element designs: crossed dipoles, crossed slots, and crossed notch elements .Orthogonal feeds can be used in many radiators such as patches, square and circular wave guides, and so on. ...

In this paper a new conformal array antenna of conical structure has been proposed. A conical phased array antenna can steer the radar beam electronically in both azimuth and elevation to cover a hemi-sphere mesh surrounding the radar antenna. Beam steering can be accomplished either continuously or discretely at definite directions. The proposed technique not only overcomes the limitations of mechanical steering systems and surveillance radar dead cone but also improves the radar tracking capability. Moreover, it is suitable to be used in MIMO radars and enemy deception systems. Element weights of the conical phased array antenna are used four famous window functions known as, Chebychev, Hamming, Hanning, and Kaiser window. The windowing process improves the beam pattern peak side lobe level (PSLL) while maintaining a narrow beam width. A high resolution phase shifter and adaptive attenuator have been used for each element to acquire both the desired phase and the weight for conical array beam pattern. Beam pattern is simulated and tested using a Matlab Program.

... As to the modes discussed in Refs.1213141516, they can be identified as creeping waves. The term " creeping wave " is used in the theory of diffraction [23, 24] for a refracted wave on conducting surfaces where an extra attenuation due to the curvature is present [17,2526272829. A creeping wave is characterized by a rapidly increased attenuation when the radius is decreased. This type of wave is unique for the curved surface and cannot be found in the planar case. ...

We derive a reduced wave equation for the surface waves on an air-metal interface with a given radius of curvature R. Using the Leontovich boundary condition with a small dimensionless surface impedance ξ we find solutions to this equation in terms of the Airy-Fock functions. A relation between the surface waves on a planar and cylindrical metal-air interfaces is elucidated and the dispersion relation of a planar surface wave is recovered as the limit of a sufficiently large curvature radius R.

... Conformal antennas have been of wide interest to scholars due to the purpose of integrating with the structures such as part of airplane, train, or other vehicles. The theory and design of conformal antennas are fully described in [1]. Different surfaces can be used in conformal antennas, such as a cylindrical shape, a conical shape, and a spherical shape. ...

A conical conformal leaky-wave antenna based on substrate integrated waveguide (SIW) technology is proposed and demonstrated in this paper. This antenna conforms to a conical shape surface with the angle of 40°. It has a narrow beam that scans from 80° to 97° with varying frequency (34 GHz37 GHz). Both conformal and nonconformal antennas are fabricated through the standard PCB process. Their performances are compared within the desired frequency.

... Nowdays, conformal phased array systems have developed considerably due to their capability of complying with the requirements for aerodynamic shape, low antenna radar cross section (RCS), wide scan range, etc [1][2]. And recent years have seen a spectacular increase in our capability to model, simulate, and design conformal arrays due to much progress has been made in enhancing the electromagnetic (EM) fullwave numerical techniques [3]. ...

The simplifying analysis for single symmetry conformal array with arbitrary excitation weights is proposed. By substituting the original array with a magnetic and an electronic symmetry array with calculated excitation weights, the original conformal array can be analyzed from the half geometry, which reduces memory requirement to half. Finally, a single symmetry sectoral cylinder microstrip array is employed to validate the proposed technique.

... The purpose is to build the antenna so that it becomes integrated with the structure and does not cause extra drag. The purpose can also be that the antenna integration makes the antenna less disturbing, less visible to the human eye; for instance, in an urban environment [1]. In electrodynamics, circular polarization of an electromagnetic wave is a polarization in which the electric field of the passing wave does not change strength but only changes direction in a rotary manner. ...

... In many applications, especially in avionics and aerospace designs where the aerodynamic drag considerations are inevitable, the mechanical requirements often dictate that the antennas should be conformed to a curved surface which leads many scientists to conduct research on this topic. In [2] and [3] the fundamental principles behind conformal antennas are presented, also as a special application of conformal structures, Vivaldi antennas are conformed to prescribed shapes for different application areas in [4]–[6]. When the frequency band is considered, there are several technical and operational reasons to justify X-band over other frequencies. ...

In this study, the design and simulation of a circularly-bended antenna array at X-band for satellite applications is presented. Antipodal Vivaldi Antenna (AVA) is selected as an array element due to its wideband and end-fire characteristics. The proposed antenna, operating in the 8-12 GHz frequency range, provides good VSWR and high gain without degradation of radiation pattern caused by conforming operation. The design is intended to be used to in both satellite and ground systems with beam scanning capability. Keywords— broadband antenna array; conformal microstrip antennas; satellite antennas; X-band applications

... Conformal arrays can be flexibility conformed to curved surface of platforms such as aerospace vehicles and ships [1]. This design lead to its advantages of excellent aerodynamic performance, low radar cross section (RCS), large surveillance coverage and volume saving. ...

... Overall in order to properly determine the system capacity, it is necessary to know the mutual coupling between the antenna elements. For complicated antenna geometries such as conformal arrays full wave analysis and rigorous electromagnetic analysis is indispensable [12]. Conformal antenna arrays are utilized in airborne and space vehicles and also find applications in situations where surface adaptation is required (e.g., environmentally friendly cellular base stations) or flexible substrates [13][14][15]. ...

The use of conformal antennas in a MIMO link scenario is investigated. Conformal slot antennas are considered both in the transmitter and the receiver. First, a new modified correlation coefficient is derived that goes beyond the Clarke coefficient and takes into account the element radiation pattern. Secondly, a hybrid formulation that accounts for the impact of the mutual coupling and the pattern dependent correlation on the capacity is presented. The mutual coupling for slots placed circumferentially on a paraboloid substrate is derived using a rigorous approach based on Uniform Theory of Diffraction (UTD). The capacity is evaluated for the case of Rayleigh fading channel considering the new pattern dependent correlation coefficient and the conformal antenna mutual coupling. The planar case is included as a limiting case. It is shown that for conformal antennas on a paraboloid the capacity degradation compared to the planar case is up to 0.5 bps/Hz due to coupling and correlation.

... These antennas are composed of some radiation elements etched on a surface and a feed antenna to illuminate radiation elements as shown in Fig. 1 . Conformal reflectarray antennas are the most important types of reflectarrays that are used in radars and communication systems [1]. However, there are some limitations for installation of these antennas on communication equipment. ...

In this paper the bandwidth performance of a reflectarray antenna to obtain fixed shaped-beam radiation pattern is studied. In order to achieve this purpose two parameters including the curvature of reflective surface and the phase distribution of reflective surface in the whole frequency band are simultaneously manipulated. Phase synthesis procedure is used to analyze the reflectarray. The particle swarm optimization is also used for obtaining the shaped-beam radiation pattern in the whole frequency band. It is shown that the bandwidth of a large reflectarray is considerably enhanced by decreasing the path length difference between phase center of the feed antenna and each point of the reflective surface. To verify this purpose, a shaped-beam reflectarray with concave reflective surface has been designed and simulated in the X-band with the commercial full-wave electromagnetic software, CST Microwave Studio and results to about 17% bandwidth for the stable cosecant square radiation pattern and pencil beam radiation pattern in E and H planes respectively.

... The purpose is to build the antenna so that it becomes integrated with the structure and does not cause extra drag. The purpose can also be that the antenna integration makes the antenna less disturbing, less visible to the human eye; for instance, in an urban environment [1]. In electrodynamics, circular polarization of an electromagnetic wave is a polarization in which the electric field of the passing wave does not change strength but only changes direction in a rotary manner. ...

The paper presents the design of a microstrip patch antenna having E and U shape slot which is back to back connected to each other mounted on the finite cylindrical surface that can operate on a triple band 2.057 GHz, 3.6102 GHz, and 6.2624 GHz. This conformal structure with truncated corner used for circular polarization. This antenna is simulated through CST microwave studio finite element package. All the simulated parameters like return loss, Directivity, Gain , Radiation pattern in 2D/3D for port one and port two are presented. Keywords— CST; microstrip patch antenna; conformal microstrip patch antenna;triple band

... A monopole antenna is the most antenna types that are commonly used for air vehicle communications [1]. Other than monopole antenna as well as its variations, there are more than 20 different antenna types suitable to be mounted on the body of air vehicle [2]. One of them which fit the special requirements is a traveling wave antenna [3]–[4]. ...

This paper deals with the development of wrap-around cylindrical printed traveling wave passive antenna based on interdigital capacitor structure for experimental-rocket communication. The proposed antenna is intended to be used for 2.35MHz communication between an experimental rocket and the ground station. The antenna which has the dimension of 238.64mm x 22mm consists of 7 blocks of interdigital capacitor structure as antenna radiators and deployed on a grounded Roger RT/Duroid®6010 dielectric substrate with the thickness of 0.127mm. The use of very thin dielectric substrate for antenna realization is aimed to have a conformable antenna which wraps-around the cylindrical body of experimental rocket communication. After obtaining the optimum performance design, the proposed passive antenna is then realized through wet etching technique for experimental characterization. From the characterization result, it shows that the realized passive antenna resonates at center frequency of 2.375GHz with gain of -18.763dBi. This is comparable with the design one which has resonant frequency of 2.35GHz and gain of -19.996dBi.

... The fringes observed beside the main lobe angles in all plots are actually the side lobes of the coding metasurface, which are common in the antenna arrays and have been well studied in many literatures. [33] The remaining scattering observed in the backscattering direction (0°) in all cases and the reflection lobes near 30° in Figure 2iare caused by the amplitude inequality of reflections between coding particles (see Figure 1f), which are clearly interpreted from the perspective of Fourier Transform in the Supporting Information Figure S4. For the second coding sequence S 2 , the efficiency at 0.78 THz is almost the same with the first case, while it decreases to 27.7% at 1.19 THz because the energy of normal incidence is divided equally into four beams (see Figure 2e). ...

A frequency-dependent dual-functional coding metasurface is proposed at terahertz frequencies using two layers of metamaterial structures, each of which is responsible for the independent control of reflection phases at two distinct frequencies. The zero interference between the functionalities at the lower and higher frequencies are promising for possible applications in multicolor holography for color displays or a frequency beam splitter.

Application of integral equation methods in compu-tational electromagnetics has been widely explored in problems with varying degrees of complexity. Central to the formulation of such integral equation methods is the appropriate Green's function that in most cases is an important contributor to the accuracy of the final solution. It is however well known that at high frequencies special analytical forms of the problem-matched Green's function reduces the computation resources and hence renders solutions to electrically large problems practicable. These special high-frequency representations are derived analytically by well-known asymptotic methods when the characteristic wavenumber |κ| → ∞. In this presentation a novel asymptotic method, known as hyperasymptotics, originally developed by Berry and Howls, is introduced. The main feature of the hyperasymptotic technique is that the numerical error in neglecting the remainder, obtained after optimal truncation of the asymptotic series, is of the order O(e −C|κ|), where C is a positive constant. Thus the error in the hyperasymptotic method decreases exponentially at high frequencies for |κ| → ∞, and hence this specific asymptotic technique appears numerically most suitable for development of hybrid methods for challenging problems in computational electromagnetics. The salient features of the hyperasymptotic method is illustrated here with reference to the Stokes phenomenon for the Airy function of complex argument, and, its potential applications to some problems in computational electromagnetics are identified.

With the use of antenna arrays the directivity and gain are improved, however, side lobes appear in the
radiation pattern of the structure. The reduction of the secondary side lobe level is of particular importance,
because its represents radiation in unwanted directions, and normally it is represents as a ratio of power density of the given lobe level and the main lobe level. In this paper two linear arrays working at 2, 25 GHz of 4 and 8 elements with approximately -25 dB or side lobe level are presented, using microstrip aperture coupled antenna and a corporative (parallel) feeding network with non uniform power divider. The simulated results of booth arrays are displayed, observing with the increasing of element number (although a more complex feeding network is needed) an increasing of directivity and gain, and a reduction of the main lobe with. The individual element used it’s an aperture coupled microstrip antenna with inverted upper substrate, which it’s implemented and adjusted, achieving good results.

In this paper a microstrip patch antenna has been used for microwave frequency. The patch antenna is printed on RT/DUROID
5880. In addition a rectangular conducting plate of comparable dimensions was placed above the patch in order to enhance the
bandwidth. The package was used to analyze the effect of the top patch, in particular the variation of VSWR with two
parameters, namely the distance between the two patches and the size of the upper patch. Simulation and experiment result of a
constructed array of two multipatch microstrip antenna with resonance frequency at 5.2 GHz shows the return loss S11 of
about -29 dB, gain level of about 10.683 dB with 23.07% bandwidth improvement and after that we have designed an array of
three multipatch microstrip antenna and achieved a bandwidth about 29.61% with directivity about 11.47 dB and return loss -
29 dB at the frequency 5.74GHz.
Keywords: Multipatch Microstrip Antenna, Microstrip antennas (MSA), Resonant frequency, Advanced Design
System(ADS).

In this paper we discuss the effect of discretization on the azimuthal pattern of circular ring array. One of the characterizations of the circular ring is discretizing the array elements on the azimuthal plane. The discrete array excitation is a sampled version of the continuous case. The elements are feed with a linearly increasing phase which gives rise to a corresponding phase mode excitation. Although, in the discrete case we also obtain harmonics in addition to the fundamental phase mode. The phase mode excitations of the azimuthal plane are discussed for two different element separations. The higher-order Bessel functions decay rapidly with an increasing order and hence higher excitation phase modes radiate poorly. For a given diameter array; to minimize the impact of these distortion modes, small element separations are required. The program is written using python and the simulation results are discussed for an eight element circular array.

This paper discusses the singly curved phased reflector for reduced RCS pattern, which has minimized RCS level at boresight with a null by phase cancelation and the lowered RCS level of main beam by splitting the main beam into multi directions. Considering the reduced level of boresight and main beam compared to the same sized reference PEC, this proposed multi-beam reflector can be adopted in the mono-static radar and the bi-static radar environment. The proposed reflector is a multi-beam reflector, which has different phase distributions at each row for different steering angle. It is designed through an intermediate stage of a single and dual-beam reflector. The behaviors of the designed reflectors are verified through full-wave simulation and experiment. The reflectors are designed in the frequency of 10 GHz and it has a size () with the curvature k=3.3. From the measured results, the proposed reflectors reduce the reflected power by 17 dB at boresight.

This work presents the design, simulation and implementation of a linear array antenna with a fully constrained cosecant squared radiation pattern and a novel wideband feeding network. This antenna is constructed of wideband printed dipole antennas as the array elements in which the mutual coupling effect is properly compensated. For this purpose, a constrained particle swarm optimisation (PSO) algorithm is used as the synthesis method which is able to deal with multiple constraints in the desired radiation pattern. The excitations obtained from the PSO algorithm are applied to the design of a wideband feeding network which is able to deliver stable phase shifts and output powers to the array elements over the desired bandwidth. Finally, the simulation results are confirmed by the measurement results.

Smart antennas are important for satellite communications because they can increase the channel capacity, spectrum efficiency, and coverage range of the communication systems. This chapter reviews the technology for smart array antenna design with examples. Applications of smart antennas for satellite ground stations and direct broadcast satellite systems are also presented in this chapter. A detailed list of references is given in the end of this chapter. © Springer Science+Business Media Singapore 2016. All rights reserved.

Self-adapting conformal antennas for changing spherical surfaces are investigated in this work. More specifically, the theory on the relationship between the radius of the spherical surface, element spacing of the conformal array and required phase compensation is developed. Initially, for theoretical validation, a 4 × 4 phased array antenna is assembled with individual microstrip antennas used as the radiators at 2.47 GHz. Each antenna is connected to a commercially available voltage controlled phase shifter with identical SMA cables and then each phase shifter is connected to a port on a sixteen-way power divider. This phased-array antenna allows for convenient placement of individual patches on the spherical surface and precise phase control. For further validation, a second 4 × 4 phased-array antenna with embedded phase shifters and a sensing circuit is manufactured. The sensing circuit is used to measure the radius of curvature of the spherical surface and use this information to autonomously apply the appropriate phase compensation, based on the previous theoretical developments, to recover the radiation pattern of the array for different spherical surfaces at 2.47 GHz. Overall, good agreement between theory, simulation and experimental data is shown and that it is possible to recover the radiation pattern autonomously.

Many direction-of-arrival (DOA) estimation algorithms have been proposed recently. However, the effect of mutual coupling among antenna elements has not been taken into consideration. In this paper, a novel DOA and mutual coupling coefficient estimation algorithm is proposed in intelligent transportation systems (ITS) via conformal array. By constructing the spectial mutual coupling matrix (MCM), the effect of mutual coupling can be eliminated via instrumental element method. Then the DOA of incident signals can be estimated based on parallel factor (PARAFAC) theory. The PARAFAC model is constructed in cumulant domain using covariance matrices. The mutual coupling coefficients are estimated based on the former DOA estimation and the matrix transformation between MCM and the steering vector. Finally, due to the drawback of the parameter pairing method in Wan et al., 2014, a novel method is given to improve the performance of parameter pairing. The computer simulation verifies the effectiveness of the proposed algorithm.

In this paper, we study the characteristics of a 12-and 18-element array integrated on a projectile fuse of conical shape. The latter are investigated in terms of gain, bandwidth and capabilities of the array to scan its main beam so as to maintain radiation in a given direction for any location and position (spin) of the projectile along its trajectory.

Multiple-Input Multiple-Output (MIMO) radar is an emerging radar system that is of great interest to military and academic organizations due to its advantages and extensive applications. The main purpose of Space-Time Adaptive Processing (STAP) is to suppress ground clutter and realize Ground Moving Target Indication (GMTI). Nowadays, STAP technology has been extended to MIMO radar systems, and MIMO radar STAP has quickly become a hot research topic in international radar fields. This paper provides a detailed description of the extension and significant meaning of MIMO-STAP, and gives an overview of the current research status of clutter modeling, analysis of clutter Degree Of Freedom (DOF), reduced-dimension (reduced-rank) processing, simultaneous suppression of clutter plus jamming, non-homogeneous environment processing, and so on. The future perspective for the development of MIMO-STAP technology is also discussed.

In this paper, a real-time voltage control platform, based-on genetic algorithm (GA) program, is built to optimize a 32-element high gain beam-forming antenna. After 500 generations, S21 has been significantly improved. The gain of the antenna has promoted to 8.95dBi, and the beam-width of the antenna has narrowed down to 30°.

In practical mobile communication engineering applications, surfaces of antenna array deployment regions are usually uneven. Therefore, massive multi-input-multi-output (MIMO) communication systems usually transmit wireless signals by irregular antenna arrays. To evaluate the performance of irregular antenna arrays, the matrix correlation coefficient and ergodic received gain are defined for massive MIMO communication systems with mutual coupling effects. Furthermore, the lower bound of the ergodic achievable rate, symbol error rate (SER) and average outage probability are firstly derived for multi-user massive MIMO communication systems using irregular antenna arrays. Asymptotic results are also derived when the number of antennas approaches infinity. Numerical results indicate that there exists a maximum achievable rate when the number of antennas keeps increasing in massive MIMO communication systems using irregular antenna arrays. Moreover, the irregular antenna array outperforms the regular antenna array in the achievable rate of massive MIMO communication systems when the number of antennas is larger than or equal to a given threshold.

A fully printable and conformal antenna array on a flexible substrate with a new Left-Handed Transmission Line (LHTL) phase shifter based on a tunable Barium Strontium Titanate (BST)/polymer composite is proposed and computationally studied for radiation pattern correction and beam steering applications. First, the subject 1 × 4 rectangular patch antenna array is configured as a curved conformal antenna, with both convex and concave bending profiles, and the effects of bending on the performance are analyzed. The maximum gain of the simulated array is reduced from the flat case level by 34.4% and 34.5% for convex and concave bending, respectively. A phase compensation technique utilizing the LHTL phase shifters with a coplanar design is used to improve the degraded radiation patterns of the conformal antennas. Simulations indicate that the gain of the bent antenna array can be improved by 63.8% and 68% for convex and concave bending, respectively. For the beam steering application, the proposed phase shifters with a microstrip design are used to steer the radiation beam of the antenna array, in planar configuration, to both negative and positive scan angles, thus realizing a phased array antenna.

Based on conical conformal array with crossed dipole elements, the quaternion array signal model is built and quaternion multiple signal classification (MUSIC algorithm is proposed in this paper. This algorithm realizes de-coupling polarization and direction of arrival (DOA) information through resetting the elements with the same polarizations of sub-arrays and principle of rank-loss, then it obtains the estimation of 2D DOA and polarization parameter of incident signals. The computational complexity of joint polarization-DOA estimation is reduced significantly. Finally, the effectiveness of the method has been verified by computer simulation.

This geometry can offer certain characteristics that can't be achieve by planner antenna. Antenna is design to function in 2.4 GHz wireless radio band. This work present performance of 4-element conformal antenna array for cylindrical surface and observe effect of mutual coupling between patch. In this, angle is preserved to conform the shape to reduce extra drag. The radius of cylinder is considered to be atleast one quarter wavelength or slightly more. The simulated results shows its resonant frequency is not affected with change in curvature however the radiation patterns are significantly affected more in elevation direction and less in azimuth. Simulations has been carried on CST software.

A high-isolation, ultra-wideband simultaneous transmit and receive (STAR) antenna with monopole-like radiation characteristics is presented. The proposed STAR antenna consists of a center-located monocone and a circular array of bent loops. The monocone and the array of loops are located in the near fields of each other and serve respectively as the transmit (TX) and receive (RX) antennas. To achieve omnidirectional, vertically-polarized radiation patterns, the array factor of the bent loops is first examined. A circular top loading and four T-shaped parasitic elements are exploited to decrease the lowest frequency of operation of the antenna without increasing its occupied volume. Finally, based upon the analysis of the array factor, four directors are strategically mounted over the ground plane to enhance the omni-directionality of the antenna in the azimuth plane. A prototype of the antenna operating in the UHF band is fabricated and measured. Experimental results demonstrate that the proposed STAR antenna achieves an isolation greater than 40 dB from 0.6 GHz to 1.75 GHz (2.9:1 bandwidth). Furthermore, the STAR antenna is capable of maintaining consistent monopole-like radiation patterns and vertical polarization for both the TX and the RX channels across the entire band of operation.

Physical geometry and optical properties of objects are correlated: cylinders
focus light to a line, spheres to a point, and arbitrarily shaped objects
introduce optical aberrations. Multi-functional components with decoupled
geometrical form and optical function are needed when specific optical
functionalities must be provided while the shapes are dictated by other
considerations like ergonomics, aerodynamics, or esthetics. Here we demonstrate
an approach for decoupling optical properties of objects from their physical
shape using thin and highly transparent flexible dielectric metasurfaces which
conform to objects' surface and change their optical properties. The conformal
metasurfaces are composed of silicon nano-posts embedded in a polymer substrate
that locally modify optical wavefronts. As proof of concept, we show that
cylindrical lenses covered with metasurfaces can be transformed to function as
aspherical lenses focusing light to a point. The conformal metasurface concept
introduces a novel paradigm for developing arbitrarily shaped multi-functional
optical devices.

The design and experimentation of conformal printed traveling wave antenna composed of interdigital capacitor structures is presented. The antenna which is designed to work around center frequency of 2.35MHz for experimental-rocket communication with the ground station is deployed on a 0.127mm thick of RT/Duroid R® 6010LM dielectric substrate. The use of very thin dielectric substrate for antenna realization intends to be conformable with the cylindrical body of experimental-rocket. Prior hardware realization, the parameters of antenna including reflection coefficient, gain, and radiation pattern are investigated to obtain the optimum performance design. From experimental characterization, it shows that the realized proposed antenna which consists of 7 blocks of interdigital capacitor structure with total dimension of 238.64mm (length) × 22mm (width) and fits 76mm diameter of experimental-rocket body resonates at frequency of 2.375GHz with gain and -10dB working bandwidth of -18.763dB and 13MHz, respectively.

The use of radars in detecting low flying, small targets is being explored for several decades now. However radar with counter-stealth abilities namely the passive, multistatic, low frequency radars are in the focus recently. Passive radar that uses Digital Video Broadcast Terrestrial (DVB-T) signals as illuminator of opportunity is a major contender in this area. A DVB-T based passive radar requires the development of an antenna array that performs satisfactorily over the entire DVB-T band. At Fraunhofer FHR, there is currently a need for an array antenna to be designed for operation over the 450-900 MHz range with wideband beamforming and null steering capabilities. This would add to the ability of the passive radar in detecting covert targets and would improve the performance of the system. The array should require no mechanical adjustments to inter-element spacing to correspond to the DVB-T carrier frequency used for any particular measurement. Such an array would have an increased flexibility of operation in different environment or locations.
The design of such an array antenna and the applied techniques for wideband beamforming and null steering are presented in the thesis. The interaction between the inter-element spacing, the grating lobes and the mutual couplings had to be carefully studied and an optimal solution was to be reached at that meets all the specifications of the antenna array for wideband applications. Directional beams, nulls along interference directions, low sidelobe levels, polarization aspects and operation along a wide bandwidth of 450-900 MHz were some of the key considerations.

This paper presents a polarization reconfigurable printed loop antenna which could alter its polarization states electronically to right-hand circular polarization (RHCP), left-hand circular polarization (LHCP) or linear polarization (LP). By inserting four PIN diodes into the symmetric gaps of a dual-loop planar antenna, the proposed antenna can switch its polarization status by controlling the on-off state of PIN diodes electronically. Meanwhile, a coplanar stripline (CPS) has been employed as an impedance transformer for this antenna. It is shown that the antenna can achieve a 5.4% 3-dB AR bandwidth with a wider impedance bandwidth of 12.5% for both RHCP and LHCP and a 7.1% impedance bandwidth for LP. The proposed antenna has a uni-directional radiation pattern with a peak gain of 9.8 dBi under all polarization status. The presented antenna can achieve polarization reconfigurability and a high gain, while having a low profile and low cost. It is promising for applications in satellite communications and terrestrial wireless communication systems.

Smart antennas are important for satellite communications because they can increase the channel capacity, spectrum efficiency, and coverage range of the communication systems. This chapter reviews the technology for smart array antenna design with examples. Applications of smart antennas for satellite ground stations and direct broadcast satellite systems are also presented in this chapter. A detailed list of references is given in the end of this chapter.

ResearchGate has not been able to resolve any references for this publication.