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This article presents an efficient and effective design approach of the phase distribution calculation across metasurface for significant radar cross section (RCS) reduction of a circular polarization (CP) and liner polarization (LP) radar waves. The RCS reduction using the proposed design approach is achieved by imposing a novel cusp phase mask (which is usually used to generate 3D self-accelerating and self-healing cusp beams) at each geometric phased anisotropic unit cell composing the proposed cusp phased metasurface. By solving the cusp phase formula using MATLAB, it is found that the cusp phase mask required to achieve more than 10 dB of RCS reduction over a wide frequency band can be calculated without the need of significant lengthy optimizations or huge computer resources. The ability of such cusp phase mask metasurfaces to achieve significant backward scattering and RCS reduction has been rigorously investigated by means of simulations and measurements. When illuminated by a far-field radar CP or LP plane wave, the proposed cusp phased metasurface realizes more than 10 dB of RCS reduction from 10.9 to 26 GHz, corresponding to a fractional bandwidth of FBW = 81.8%. The 10 dB RCS reduction bandwidth of the cusp metasurface is maintained under both normal and wide angular incidence up to 75o. The proposed cusp metasurfaces have potential applications to make objects stealthy where the incidence radar signal has an unknown frequency, polarization, or angle of incidence.

This article presents highly radio-frequency (RF) transparent phase gradient synthetic metasurfaces made of sub-wavelength-sized 3D printable meta-atoms with tailored permittivity that cannot be achieved with off-the-shelf, commercially available materials. The synthesized meta-atoms design uses one dielectric block of PREPERM ® ABS 1000 material with air and metallic inclusions to make low- and high-permittivity materials. The inclusions’ size and height are varied to achieve a complete phase range from 0 to 360°, while maintaining transmission magnitudes greater than −3.0 dB. A two-dimensional array of meta-atoms forms a metasurface, which can be used for phase-shifting structures. Such metasurfaces can manipulate RF waves by introducing progressive phase delay into array elements. The proposed meta-atoms are employed to create highly RF transparent phase-gradient metal-dielectric composite metasurfaces (MDCMs) operating at 11 GHz. These MDCMs can be implemented through 3D printed technology using low-cost thermoplastics or polymers with composite filaments and minimal human intervention. A pair of MDCMs are combined with an array of microstrip patches to demonstrate 2D beam steering functionality numerically. The antenna system provides a peak directivity of 19.9 dBi with a maximum conical scanning angle of 114° and a directivity variation of less than 3 dB.

Continuous health monitoring of vital signs of patients is a challenging issue, especially in emergency medical conditions. This paper designs a practical internet of medical things-based wireless body area network (IoMT-based WBAN), to address this issue. Accordingly, a two-fold test-bed design is proposed taking $i$ ) signaling and $ii$ ) antenna configuration into account to attain uninterruptible on/off-body communication links. Firstly, the Walsh-Hadamard coding technique is used in all bio-sensors to retain orthogonal simultaneous signaling for on-body links. Secondly, an antenna configuration of the hub is designed so that it prevents probable interruptions in off-body links which may be caused by some human postures. More accurately, a novel periodic leaky-wave antenna (LWA) with an elliptical belt shape is introduced which generates a quasi-omnidirectional pattern. The LWA is designed based on a multi-tone periodicity of a width-modulated microstrip line. At the design frequency of 5.8 GHz, the suggested conformal periodic LWA was simulated and then fabricated. Simulations and measurement results illustrate that the performance of on/off-body communication links is improved in comparison to conventional antennas. Furthermore, simulated and measured radiation patterns have a good agreement with theoretical calculations. Moreover, specific absorption rate (SAR) values of the proposed antenna are significantly below the SAR limits so that this technique can be highly recommended for WBAN applications.

A novel methodology is introduced for designing bespoke homogeneous and graded index lenses for enhancing the gain of travelling wave antenna arrays (TWAs). 3D-printed lenses in the literature are majorly explored with standing wave antennas (SWAs) such as a microstrip or a horn antenna for gain enhancement. As there is progressively less power radiated from each slot in a TWA, as well as the successive phase delay between slots, the existing lens design approaches used for SWAs is not optimal for TWAs. Accordingly, we present a new approach of introducing a curvature to the lens that is derived from studying the power radiation profile of each slot of the TWA. This new methodology is demonstrated on a dielectric filled waveguide (DFW) slot array antenna operating at 26 – 30 GHz band. An optimized dielectric graded lens and an optimized homogeneous lens have both been designed, fabricated, and measured with the DFW slot array. The new lens demonstrated a gain enhancement of more than 7 dB compared to less than 4 dB with conventional dielectric lenses. The proposed lens theory has been further verified with a bespoke optimized lens for a periodic stub-loaded microstrip leaky-wave antenna with a beam-scanning of 65°. Design rules are included that can be applied for any TWA.

Abstract The paper presents a new practical design for a 4 × 1 planar switched array of dielectric filled waveguide antennas loaded with bow‐tie shaped slots operating at 26.5 to 29.5 GHz for 5G millimetre‐wave applications. The design is realized as a three‐layered architecture, with the top layer behaving as a radiator, the bottom layer as a feed network and a control circuit; and a common ground plane in the middle layer, offering a small form factor. The bow‐tie slots are used to achieve suitable bandwidth with a stable gain of ∼ 13 dBi. The proposed dielectric filled waveguide (DFW) is shown to offer a 5 deg/GHz freq.‐controlled beam‐sweep and a 70° fixed freq. beam‐steer. With only three switching ICs, it offers low power consumption and fast beam‐steering. Further, a combination of freq.‐controlled beam‐scanning and fixed‐freq. beam‐steering allows for a wide coverage of the antenna.

This article presents the design of 1-bit metasurfaces for radar cross section (RCS) reduction over wide frequency band from 60 GHz to 120 GHz. The proposed 1-bit metasurfaces can be designed without the need for any complicated optimization algorithms such as genetic algorithms (GA) or particle swarm algorithms (PSO), or time-consuming simulations to achieve the optimized phase distribution map. The phase distribution maps required for more than 10-dB RCS reduction of the proposed metasurfaces were generated using two-dimensional (2D) quick response (QR) 1-bit generator in MATLAB which are fast and efficient. After we carefully studied several metasurfaces with various 2D QR codes, it was found that the QR coded metasurfaces are very powerful in achieving more than 10-dB RCS reduction with low-level diffusive scattering patterns. Two metasurfaces with their unit cells phase distributions being exactly the same as the QR codes of the words “IEEE” and “Metasurface” were designed and their RCS reduction characteristics were investigated. For off-normal or oblique incidence, more than 10-dB RCS reduction is preserved up to incident angles of 60° over the entire frequency band. The simulation and measured results show the proposed QR coded metasurfaces reduce the backscattered energies and RCS by more than 10-dB for different polarizations over the frequency range from 60 GHz to 120 GHz yielding a fractional bandwidth of 66.7%. The proposed approach is powerful and fast and makes the realization of coding metasurface much easier.

Rapid advances in antennas, propagation, electromagnetics, and materials are opening new and unexplored opportunities in body area sensing and stimulation. Next-generation wearables and implants are seamlessly providing round-the-clock monitoring. In turn, numerous applications are brought forward with the potential to ultimately transform healthcare, sports, consumer electronics, and beyond. This review paper provides a comprehensive overview, discusses challenges and opportunities, and indicates future directions for: (a) enabling technologies needed to make body area sensing and stimulation a reality, and (b) emerging bioelectromagnetics applications that may readily benefit from such technologies.

The design of photonic devices is usually done through analytical modeling or variation in geometry and material parameters to obtain the required functionalities. Here, we report the use of topology optimization to obtain a bi-focal lens that concentrates the electromagnetic field at different spatial positions depending on the wavelength. Numerical inverse design is carried out to obtain the permittivity layout, satisfying this objective. The resulting device is then 3D printed using two low-loss dielectrics, and experimental field mapping at microwaves demonstrates the ability to enhance the field locally at distinct locations for two separate frequencies.

This paper describes a novel method of characterizing complex permittivity using a complementary frequency selective surface (CFSS). The CFSS provides a passband behavior and the change in the passband when a material under test (MUT) is placed adjacent to the CFSS has been used for retrieving of the complex permittivity of the MUT. The complex permittivity of the MUT are determined based on the measured bandpass resonant frequency and insertion loss of the CFSS with the MUT. This is an amplitude-only method where phase measurements are not required. This technique offers a convenient, fast, low-cost and nondestructive measurement that is not restricted by the sample size or shape.

Flexible heterogeneous substrates have been constructed, using three-dimensional printing in a single process, by introducing air-filled slots. These substrates have been used to substantially reduce the substrate losses for a flexible microstrip patch antenna causing an increase in its radiation efficiency. By combining transverse magnetic (TM)10 and TM01 modes the bandwidth of this antenna has also been increased.