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Mutual Coupling in Phased Arrays: A Review

The mutual coupling between antenna elements affects the antenna parameters like terminal impedances, reflection coefficients and hence the antenna array performance in terms of radiation characteristics, output signal-to-interference noise ratio (SINR), and radar cross section (RCS). This coupling effect is also known to directly or indirectly influence the steady state and transient response, the resolution capability, interference rejection, and direction-of-arrival (DOA) estimation competence of the array. Researchers have proposed several techniques and designs for optimal performance of phased array in a given signal environment, counteracting the coupling effect. This paper presents a comprehensive review of the methods that model and mitigate the mutual coupling effect for different types of arrays. The parameters that get affected due to the presence of coupling thereby degrading the array performance are discussed. The techniques for optimization of the antenna characteristics in the presence of coupling are also included.

Novel Inhomogeneous Planar Layer Radome Design for Airborne Applications

In airborne radome applications, monolithic half-wave wall configuration is generally used to provide superior electromagnetic (EM) performance at the design frequency. However, the application of a monolithic half-wave wall is limited due to its very narrow bandwidth. In order to circumvent this problem, inhomogeneous planar layer (IPL) with exponential variation of complex permittivity is proposed here for the design of a radome wall. As compared to the conventional monolithic half-wave radome of identical thickness, the IPL-based radome wall offers superior EM performance both at the normal and high incidence angles. The EM performance analysis shows that the IPL wall configuration is a better choice for designing both the normal-incidence and the highly streamlined airborne nosecone radomes.

Trends in Adaptive Array Processing

Enormous progress has been made during the past five decades in the area of adaptive array processing. Increased computational power has resulted in many practical applications of optimum algorithms. The present paper deals with many facets of array signal processing and adaptive beam forming. It provides a comprehensive description of various beam-forming schemes, adaptive algorithms to adjust the required weighting on antenna elements, direction-of-arrival estimation methods, including their performance comparison. The effects of various types of errors on the performance of an array system are illustrated along with their remedial measures. Since array signal processing has widespread applications, the study is carried out across various disciplines.

Electromagnetic Design and Performance Analysis of Airborne Radomes: Trends and Perspectives [Antenna Applications Corner]

The spectacular advancements in antenna technologies for control, guidance, surveillance, and communication applications for airborne platforms have resulted in the realization of novel conformal antenna arrays, embedded antenna systems on the body of the fuselage, and structurally integrated radiating systems. Such antenna systems/ radiating structures facilitate superior functional capabilities with reduced payloads, desirable for airborne applications. They demand novel airborne radome structures with superior electromagnetic (EM) performance characteristics. Furthermore, rapid progress in the fields of frequency-selective surfaces (FSS) and metamaterials has had significant impact on the development of radome technology. Since conventional EM design techniques, based on transmission-line models, may not be sufficient for such applications, new techniques, based on numerical methods, have been developed. In order to circumvent the limitations of conventional low-frequency/high-frequency methods in analyzing antenna-radome interaction phenomena, hybrid methods, in conjunction with novel algorithms, are currently used. Considering the significant growth in EM technologies for airborne radome applications, the objective of this paper is to provide a glimpse of the techniques/methods for the EM design and analysis of airborne radomes. Some of the challenging EM issues/problems pertaining to airborne radome development are also discussed, which may be of interest to the radome community in the aerospace sectors.

Electromagnetic Techniques and Design Strategies for FSS Structure Applications [Antenna Applications Corner]

Frequency-selective surfaces (FSSs) have a wide spectrum of applications in airborne platforms, wireless communication systems, medical imaging instruments, and high-power microwave systems. To employ finite, electrically large, and conformal FSSs for such applications, the development of an efficient electromagnetic (EM) design and analysis technique is essential, which is a challenging task in terms of computational complexity and requirements of highend computing platforms. In view of assessing the efficacies of various EM techniques for the design and analysis of FSS structures employed for planar and conformal surfaces, a brief review is presented here. Furthermore, the design strategies of novel FSS structures including metamaterial (MTM)-element FSSs are discussed for specific applications such as highperformance radomes, radar absorbing structures (RASs), and antennas. The complex issues associated with the EM design and analysis of FSS structures are also outlined for radomes, RAS, and antennas.

Rf field mapping inside a large passenger-aircraft cabin using a refined ray-tracing algorithm

Radio-frequency (RF) field mapping and its analysis inside a large passenger aircraft is a complex EM analysis problem, owing to its inherent concavity. The further hybrid surface modeling required for such concave enclosures leads to ray proliferation, thereby making the problem computationally intractable. In this paper, a large passenger-aircraft cabin is modeled as a single curved elliptical cylindrical cavity having a floorboard and windows. Unlike the available ray-tracing packages that use extensive numerical search methods, a quasi-analytical ray-propagation model is proposed here. This involves uniform ray launching, an intelligent scheme for ray bunching, and an adaptive reception algorithm to obtain the ray-path details inside the concave cabin. Although the image method yields precise point-to-point solutions, it cannot be used for curved concave environments. The developed method is therefore validated with respect to the RF field inside a cuboid. The RF field at the receiver within the cabin is determined using the ray-path descriptions and the constitutive EM parameters of the aircrafts cabin materials. The convergence analysis of the RF field buildup is carried out with respect to the propagation time and the number of bounces.

EM performance analysis of double square loop FSS embedded C-sandwich radome

Double square loop frequency selective surface (DSL-FSS) for the broadbanding of C-sandwich radome is presented. Equivalent transmission line method in conjunction with equivalent circuit model is used for the EM performance analysis of aperture type double square loop embedded C-sandwich radome. EM analysis shows that the DSL-FSS embedded C-sandwich radome panel has superior performance parameters as compared to C-sandwich alone.

Plasma-based Radar Cross Section Reduction

The concealment of aircraft from radar sources or stealth is achieved either through shaping, or radar absorbing coatings, or engineered materials, or plasma, etc. Plasma-based stealth is a radar cross-section (RCS) reduction technique associated with the reflection and absorption of incident electromagnetic (EM) wave by the plasma layer surrounding the structure. Plasma cloud covering the aircraft may give rise to other signatures such as thermal, acoustic, infrared, or visual. Thus it is a matter of concern that the RCS reduction by plasma enhances its detectability due to other signatures. This needs a careful approach toward the plasma generation and its EM wave interaction. This book presents a comprehensive review of the plasma-based stealth, covering the basics, methods, parametric analysis, and challenges toward the realization of the idea. The book starts with the basics of EM wave interactions with plasma, briefly discusses the methods used to analyze the propagation characteristics of plasma, and its generation. It presents the parametric analysis of propagation behavior of plasma, and the challenges in the implementation of plasma-based stealth technology. This review serves as a starting point for graduate and research students, scientists, and engineers working in the area of low-observables and stealth technology.

Particle Swarm Optimization for Multiband Metamaterial Fractal Antenna

The property of self-similarity, recursive irregularity, and space filling capability of fractal antennas makes it useful for various applications in wireless communication, including multiband miniaturized antenna designs. In this paper, an effort has been made to use the metamaterial structures in conjunction with the fractal patch antenna, which resonates at six different frequencies covering both C and X band. Two different types of square SRR are loaded on the fractal antenna for this purpose. Particle swarm optimization (PSO) is used for optimization of these metamaterial structures. The optimized metamaterial structures, after loading upon, show significant increase in performance parameters such as bandwidth, gain, and directivity.

RF leakage radiation from microwave oven for aircraft interior applications

The EM analysis of RF leakage radiation from microwave oven has been carried out using FDTD method in this paper. Here the microwave oven structure is modeled as rectangular cavity. The leakage through the gap between the door and the oven cavity, which is the most probable path of leakage of radiation, is determined using FDTD method. Further, the far-field radiation pattern of microwave oven is computed by the far-field transformation of Huygens equivalent sources using Greens function. It is found that the RF leakage from microwave oven has a characteristic interference far-field pattern.