Raveendranath U. Nair

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.

A Novel EM Analysis of Double-Layered Thick FSS Based on MM-GSM Technique for Radome Applications

The EM analysis of double-layered thick FSS structure with low-loss dielectric medium between the FSS layers has been carried out using MM-GSM technique. In this analysis, both evanescent and propagating modes are included that enhances the accuracy of the computation. This method provides less computational complexity in the formulation of FSS structures as compared to other numerical techniques. The cascaded FSS structure shows bandpass response (> 95% transmission) over a frequency range from 8.84 GHz to 10.74 GHz. It is found that this FSS structure shows very good in-band transmission characteristics and excellent roll characteristics outside the band. Further, the dependence of transmission characteristics on the spacing between the FSS layers is also investigated. The optimum bandpass response is achieved for 0.3

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.

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.

Broadband EM Performance Characteristics of Single Square Loop FSS Embedded Monolithic Radome

A monolithic half-wave radome panel, centrally loaded with aperture-type single square loop frequency selective surface (SSL-FSS), is proposed here for broadband airborne radome applications. Equivalent transmission line method in conjunction with equivalent circuit model (ECM) is used for modeling the SSL-FSS embedded monolithic half-wave radome panel and evaluating radome performance parameters. The design parameters of the SSL-FSS are optimized at different angles of incidence such that the new radome wall configuration offers superior EM performance from L-band to X-band as compared to the conventional monolithic half-wave slab of identical material and thickness. The superior EM performance of SSL-FSS embedded monolithic radome wall makes it suitable for the design of normal incidence and streamlined airborne radomes.

Temperature-Dependent Electromagnetic Performance Predictions of a Hypersonic Streamlined Radome

Nosecone radomes of hypersonic flight vehicles show degradation of electromagnetic (EM) performance characteristics due to variations in the dielectric parameters (dielectric constant and electric loss tangent) of the radome wall resulting from heating due to extreme aerodynamic drag. It is indicated that the EM performance predictions based on conventional monolithic half-wave wall based on average dielectric parameters corresponding to temperature ranges in hypersonic conditions may not be accurate. This necessitates the radome wall under hypersonic conditions to be modeled as an inhomogeneous dielectric structure for accurate EM performance predictions. In the present work, the hypersonic radome is considered as an inhomogeneous dielectric radome such that the cross-section of the radome wall in each EM window region is considered as an inhomogeneous planar layer (IPL) model with stacked layers of varying dielectric parameters. The material considered is RBSN Ceralloy 147-010F (an alloy of silicon nitride), which has excellent thermal shock resistance, dielectric and mechanical properties required for hypersonic radome applications. The EM modeling of a section of the radome wall in hypersonic conditions (i.e., IPL structure) is based on Equivalent Transmission Line Method. A comparative study of basic EM performance parameters of the radome wall (power transmission, power reflection, and insertion phase delay) for both the IPL model and conventional monolithic half-wave model are carried out over a range of incidence angles corresponding to the antenna scan ranges in each EM window region of the radome. Further the study is extended to compute the EM performance parameters of an actual tangent ogive nosecone radome (made of RBSN Ceralloy 147-010F) enclosing an X-band slotted waveguide planar array antenna, in a hypersonic environment. The antenna-radome interaction studies are based on 3-D Ray tracing in conjunction with Aperture Integration Method .I t is observed that the EM performance analysis based on conventional monolithic radome wall design cannot accurately predict the radome performance parameters in actual operating conditions during hypersonic flight operations. The current work establishes the efficacy of Inhomogeneous Dielectric Radome model for better EM performance predictions of streamlined airborne radomes in hypersonic environments.

EM performance analysis of novel double-layer MNG-ENG metamaterial FSS for radome applications

The EM performance analysis of double-layer MNG-ENG metamaterial FSS is presented in this paper using TLTM method. The transmittance and reflectance characteristics are studied for TE polarization at normal incidence. It is found that the proposed metamaterial structure exhibits superior bandpass characteristics over a wide frequency range 1.9-6.6 GHz and band rejection at 9.9 GHz. Further, the tuning of bandpass and band-reject responses are studied by varying the gap between the rings of SRR.

Electromagnetic Performance Analysis of Graded Dielectric Inhomogeneous Streamlined Airborne Radome

Streamlined nosecone radomes for airborne applications have to cater to high-end electromagnetic (EM) performance requirements of fire control radar antenna system. In this regard, the EM performance analysis of an ogival radome based on novel graded dielectric inhomogeneous wall structure is presented. The radome wall considered here consists of seven dielectric layers cascaded in such a way that the middle layer has maximum dielectric parameters (dielectric constant and electric loss tangent) and on either side, dielectric parameters of the layers decrease in a graded (or stepwise) manner. Further, the outer surface of the radome wall is coated with an antistatic and antierosion radome paint. The EM performance parameters of the radome enclosing an X-band slotted waveguide planar array antenna (center frequency: 10 GHz; bandwidth: 1 GHz) are computed based on 3-D ray tracing in conjunction with aperture integration method. The study shows that the proposed graded dielectric inhomogeneous streamlined radome is an excellent choice for airborne applications as compared to airborne radomes based on conventional constant thickness radome designs and variable thickness radome (VTR) designs. Further, it circumvents the constraints on fabrication that occur in streamlined VTR designs.

Metamaterial based K band substrate integrated waveguide filter for advanced communication systems

The next generation communication system demands for high data rate transfer leading towards exploring a higher level of frequency spectrum. In view of this demand, design of substrate integrated waveguide filters has been presented here in conjunction with metamaterial technology to increase the performance. A metamaterial based substrate integrated waveguide filter operating in the K band (18 – 26.5 GHz) has been demonstrated in this paper with the insertion loss of −0.57 dB in passband and provides a rejection band of 4.1 GHz.

A novel Jerusalem cross FSS embedded A-sandwich radome for aerospace applications

The application of Jerusalem cross frequency selective surface (FSS) for the enhancement of electromagnetic performance of A-sandwich radome is presented. The performance parameters of the Jerusalem cross FSS embedded radome panel are computed based on equivalent transmission line method in conjunction with equivalent circuit method (ECM). The EM analysis shows that the Jerusalem cross FSS embedded A-sandwich radome wall configuration has superior EM performance as compared to the A-sandwich wall alone configuration.