In this paper, an optically transparent metamaterial with broadband absorption is presented theoretically and demonstrated experimentally. The design comprises of structures made of resistive films of indium-tin-oxide and the metamaterial exhibits over 10 dB absorption in the frequency range of 6.06–14.66 GHz. The novelty of the structure lies in its large absorption bandwidth along with a reduced thickness and optical transparency compared to broadband absorbers reported earlier. Besides, the proposed design is polarization-insensitive and gives rise to angular independent absorption for both transverse electric and transverse magnetic polarizations. The absorption mechanism in the structure has been studied by deriving an equivalent circuit model as well as analyzing several design parameters. Finally, a prototype of the proposed structure has been fabricated and measured, which shows good agreement with the simulated results.

Design and implementation of a broadband polarization-insensitive multi-layered microwave absorber using resistive ink has been presented here. The proposed absorber is constructed using layers of resistive surface where each layer consists of periodic arrangement of resistive patterns printed on a low cost FR4 sheet using resistive ink. Due to multilayer in nature, the proposed absorber shows broadband absorption having simulated reflection co-efficient less than -10dB in the frequency range from 2.00 GHz to 18.50 GHz under normal incidence which covers the entire S, C, X and Ku bands with the smallest thickness of 0.082 $\lambda_L$ (at lowest operating frequency of the absorption band) as compared to the state-of the-art absorbers. In order to validate the proposed absorber, the equivalent circuit model has also been presented. The equivalent circuit model shows good match with the proposed absorber. The proposed absorber is experimentally verified and the experimental results shows good agreement with the simulated results.

A novel polarization rotator design is demonstrated theoretically as well as experimentally based on frequency selective surface (FSS). The polarization rotator selectively allows the linearly polarized incident wave to pass through the structure and rotates it by 90o in a given frequency band. The periodic element of the FSS design consists of orthogonally oriented Vshaped slots on two metal sheets with the dielectric substrate separating the sheets. The proposed structure exhibits a relative bandwidth of 8% (9.76 - 10.57 GHz) with a maximum insertion loss of 0.5 dB. Co-polarized reflection coefficient is less than -10 dB in the same frequency band. The novelties of the structure lie in its reduced thickness (0:053o) as well as compact design (0:28o) as compared to the existing polarization rotators. A prototype has also been fabricated and good agreement between the simulated and experimental results is observed.

In this letter, a single-layer compact copolarized shorted TM _1/2,0 mode microstrip patch antenna is presented for in-band full-duplex application. Two shorted TM _1/2,0 mode patch antennas, used for transmission and reception purposes, make the structure compact. The wideband behavior of the patch antenna is obtained by fusing the two resonances, one because of the shorted TM _1/2,0 mode radiating patch and the other because of the λ/4 line resonator. To enhance the isolation between the transmitter and receiver antenna, a novel defected ground structure is used. Slots are introduced into the ground plane to create a weak field region for the basic antenna element. The other antenna element (receiver) is located in the weak field region to enhance isolation. Further enhancement in isolation is achieved by introducing a T-shaped metallic strip into the slots. The structure is proposed with the credits of compactness, enhanced bandwidth, colinear polarization, very less fabrication complexity, low profile, and high isolation. The proposed structure is fabricated and measured. The structure experimentally exhibits a bandwidth (≤ −10 dB) of 2.42–2.52 GHz with the isolation of 25 dB, peak isolation of 36 dB, and an average realized gain of 4 dBi in the entire band.

An electromagnetic wave modulation technique using actively tuned frequency selective surfaces (FSS) to shift the frequency of electromagnetic (EM) waves reflected from the surface is presented. The reflected EM wave contains significant components at multiple sideband frequencies along with the original incident frequency. The time modulated complex-valued reflection coefficient can be appropriately designed to suppress the original incident frequency component highly and significantly boost the sidebands. Such a time modulated surface can help in evading Doppler Radar where the object velocity is detected from the Doppler shifted frequency of received signal. Presence of multiple frequency sidebands and suppression of the original frequency component can make Doppler Radar imaging very difficult or even impossible when the modulation frequencies are dynamically managed. Here the reflected electromagnetic wave from an FSS is modulated by applying a time-varying periodic biasing voltage across varactor diodes in the FSS. Variation in the bias voltage changes the reflection coefficient of the FSS, and thereby modulates the reflected EM wave. A prototype of the designed modulator surface is fabricated to verify the modulation performance experimentally. Here two modulation schemes, sinusoidal and saw-tooth biasing, have been demonstrated to show symmetrical and asymmetrical power distribution in the sidebands.

Designing and deploying a broadband microwave absorber that provides wide bandwidth radar cross section (RCS) reduction for planar and curved surfaces is challenging. We present a resistive ink-based multilayered wideband absorber using a low-priced FR4 substrate to cope with the challenge. The reflection coefficient response of the structure lies beneath −10 dB reference over the frequency span of 1.3–18.6 GHz for the normally incident electromagnetic waves. The multilayered structure incorporates the entire microwave radar frequency span with a relative fractional bandwidth of 173.86%. Moreover, to examine the applicability of the structure for a nonplanar geometrical surface, we further design the structure on a very thin FR4 substrate that can be bent easily. We performed an RCS analysis of the redesigned structure under monostatic and bistatic conditions. The structure thereby exhibits novelty in terms of wider stealth and electromagnetic compatibility applications and also a good counterbalance among different design attributes comprising thickness, bandwidth, and periodicity, unlike the earlier reported work. The proposed prototypes are fabricated and experimentally validated for planar and curved surfaces, respectively. The experimental results depict a good concurrence with the simulated results.