Volume 79, Issue 1-2

A reconfigurable frequency selective surface (FSS) based absorber structure has been designed using a novel, cost-effective, simple to operate and easy to fabricate 3D printed interlocking blocks. Four different topologies have been investigated and validated through simulation and experimental studies. The basic geometry comprises a 3D printed mounting board, on which different blocks can be attached using interlocking studs. The frequency reconfigurability has been obtained by mechanically changing various resonating blocks on the board, which results in four distinct absorption frequencies at 4.89 GHz, 4.02 GHz, 2.92 GHz and 2.25 GHz achieving the absorptivities of 98.92 %, 96.52 %, 99.3 % and 99.5 % respectively in S and C bands. The absorption characteristics are further justified by evaluating the surface current distribution and impedance responses. The prototypes have been fabricated and tested, and they have attained a good agreement with the simulated responses. The absorption characteristics and operational frequencies remain the same, for all four cases during variations in the polarization angle for oblique incidence for both TE and TM polarizations up to 45°, as studied in the simulation. These have been experimentally verified up to 30° for TE polarization, thereby demonstrating the polarization-independent and angularly stable responses.

A beam-steering fed array antenna has been proposed for radar and mm-Wave applications operating from 22.6 to 26.89 GHz and 30–45 GHz with B.W % of 17.34 % and 40 % respectively having size of 12.11 × 25.58 × 0.8 mm 3 (0.96 λ o × 2.01 λ o × 0.06 λ o). For radar, this antenna covers 24.15 GHz as police radar, 24.25–25.25 GHz & 31.8–33.4 GHz as navigation radar, and 33.4–36 GHz as high-resolution radar for airport surveillance. This antenna also covers mm-wave bands for different countries (Brazil-40 GHz, China- 34–42.5 GHz, Mexico- 33 GHz and 37 GHz, and USA- 24 GHz, 37 & 39 GHz). At initial stage, a monopole antenna with DGS has been designed with an operating band of 20.2–31.2 GHz and 36.6–42.2 GHz. Proposed antenna shifts the beam pattern at 90° with each other after exciting each port in alternative order with a scanning angle of ±45°, ±75° & ±180°. Peak gain for 1st band ranges from 7.1 to 9 dBi and for the 2nd band ranges from 8.8 to 10.2 dBi and has a radiation efficiency of 88 %. Other diversity parameters such as ECC, DG, MEG, and isolation get analysed to observe the coupling effects. Design, development, and analysis of all antenna parameters is done by using HFSS 19 platform.

RF energy harvesting technology has garnered significant attention from researchers in recent years. This paper presents a high-efficiency quad-band RF energy harvesting (RFEH) system. It introduces an improved cross-coupled differential-drive rectifier designed for ambient wireless powering, capable of harnessing power from four distinct ambient RF sources: FM-100, DTV-600, GSM-1800, and WiFi-2400 frequency bands. The proposed RFEH system demonstrates notable advancements, achieving a high RF to DC conversion efficiency of over 80 % within an input power range of −5 dB m to +13 dB m, with a 5 kΩ resistance load. This power output is deemed sufficient for energizing low-power micro-devices autonomously, without reliance on external power sources. Notably, the DC output voltage of the proposed RFEH system exhibits a high level of stability against variations in input power, a characteristic not adequately addressed in existing systems.

This paper proposes a compact microstrip filtering power divider (FPD) with high selectivity and equal power division ratios based on the composite right/left-handed (CRLH) concept. The proposed equal microstrip FPD is designed by cascading two CRLH unit cells and a grounded via hole. The proposed CRLH unit cell is realized by an interdigital capacitor loaded between two transmission lines (TL) on the upper metal layer and the fractal/meander complementary split-ring resonator (FMCSRR) on the ground plane. The grounded via hole has been used to improve frequency selectivity and out-of-band rejection of the proposed microstrip FPD. The equivalent circuit model compared with full-wave simulation results of the proposed microstrip FPD has been provided. The proposed microstrip FPD has been fabricated and measured, and a good agreement has been found between the simulation and measurement results. The proposed microstrip FPD has a passband covering 2.38–2.45 GHz, and its measured 3 dB fractional bandwidth is about 2.9 %. The total size of the proposed microstrip FPD is 0.17 λ g  × 0.07 λ g . Compared with other reported FPDs, the presented microstrip FPD has many advantages like compact size, low loss, easy fabrication, extremely sharp rejection skirts around the desired passband and high selectivity.

A high-selectivity wideband bandpass filter (BPF) based on a quintuple-mode stub-loaded resonator and defected ground structures (DGSs) is presented. Thanks to the symmetrical topology, the even/odd theory is adopted for analyses. By properly adjusting the stub dimensions, the resonant frequencies of the transmission poles and zeros can be controlled to obtain wide passband and sharp out-of-band rejection performances. The bandwidth of the upper stopband is further extended by introducing a pair of DGSs under the interdigital coupled line feeding structures, and the spurious response rejection is improved by 18.9 dB. A BPF prototype that operates at 6 GHz with a fractional bandwidth (RBW) of 70 % is manufactured for validation. The measured insertion loss and return loss are 1.3 and 17 dB, respectively. The measured out-of-band rejection over DC-2 GHz and 8.8–21 GHz are better than −30 dB.

The manuscript contributes a novel triple band integrated reconfigurable filtering antenna for wideband and narrowband applications. First, a compact dual band reconfigurable filter is conferred composed of two folded half-wavelength high impedance T-shaped resonators. The lower half of the feed lines comprises T-shaped resonator to obtain a passband from 2.8 to 3.5 GHz in order to cater WiMax band. The resonator at the upper half of the feed lines generates a passband from 5.15 to 5.75 GHz for WLAN operations. A transmission line is inserted underneath the feeding line to establish additional transmission zeroes. Two uniform impedance resonators (UIRs) are incorporated to the proposed dual band filter so that it can discard a band from 5.35 to 5.45 GHz by creating a notch at 5.4 GHz. Presence of notch band separates the WLAN band into two sub-bands. Thus, the proposed dual band filter can be easily reconfigured to a triple band bandpass filter. Later, a broadband antenna is implemented using a ground ring and an inverted L-shaped resonator which is radiating from 2.6 to 6 GHz. In the end, the filter is integrated with the antenna structure to develop the suggested triple-band reconfigurable filtering antenna. The developed filtering antenna is fabricated that perceives a fine agreement between the measured and the simulated response.

A novel ultra-wideband end-shot antenna based on artificial surface-isolated excitations (SSPP) is designed. The antenna adopts a coplanar waveguide structure and introduces an SSPP transmission line consisting of a symmetric exponential Gaussian curve reference ground and an elliptical aperture-type cell, which effectively improves the bandwidth of the SSPP antenna and realizes the high-frequency operating characteristics of this antenna. In addition, the design combines the asymmetric structure of the SSPP transmission line and the guided branch structure to enhance the directivity of the antenna. The measured results of the antenna show that the antenna operates in the bandwidth range of 21.5–34.0 GHz, and the average gain of the antenna in the whole operating bandwidth range reaches 9.4 dBi, and the average radiation efficiency is 92.6 %, which can be better applied in the field of high-frequency communication.

In this study, the performance of two metamaterial-based antennas – transmit antennas with a double negative index (DNI) and receive antenna with an epsilon near zero (ENZ) material is described for image transfer application. These three-layered antennas are simulated and fabricated on Roger RO3003 substrate. The transmit antenna achieves a gain of 5.5 dBi and a bandwidth of 3.9 GHz, while the receive antenna reports a gain of 11.4 dBi with a 3-dB angular beam width of 32.5° at 5.8 GHz. These antennas are employed with a commercially available transmitter with a camera and receiver. Few images are captured at various distances and simultaneously transferred to the receiver. The images transferred wirelessly are found better in terms of the image quality score obtained using the Blind/Reference less Image Spatial Quality Evaluator (BRISQUE) method, compared to those transferred using the standard dipole antennas. So, the proposed metamaterial-based antennas are suitable for wireless image/video transfer applications.

This paper presents an ultra-miniaturized skin implantable Multiple Input Multiple Output (MIMO) antenna for biotelemetry in the Industrial, Scientific, and Medical (ISM) band (2.4–2.48 GHz). The two-element configuration exhibits a compact planar volume of 4.5 × 6.2 × 0.25 mm³, with an edge-to-edge distance of 0.8 mm and a 75.85 % size reduction. Fabricated on a 0.25 mm thick Roger 10.2LM high permittivity substrate, the antenna achieves a Fractional Bandwidth (FBW) of 9.27 % and a realized gain of −28.2 dBi, with over 24.3 dB isolation across the entire band. Experimental results in multilayer animal tissue aligned well with simulations. Specific Absorption Rate (SAR) analysis at 1 W input power showed values of 848 W/kg (1-g) and 88.46 W/kg (10-g), yielding allowable input powers of 3.77 mW and 45.2 mW, respectively, adhering to international safety guidelines. The 2 × 2 element antenna demonstrated efficient communication over 7 m with a data rate of 78 Mbps/s. Multiple Input Multiple Output channel analysis revealed a Channel Capacity of 10.8 bps/Hz at a 20 dB SNR, nearly double that of an ideal Single Input Single Output system, making it suitable for high data rate skin-implantable applications.

Implantable antenna is embedded in implantable medical devices to communicate with external world for continuous patient monitoring. The implantable antenna performance may vary with patients due to their different skin and fat thickness owing to their environment, location and concentration of collagen in skin, estrogen and testosterone concentration, age, diseases like obesity, Gottron syndrome etc. Estimation of IMA performance requires a proper description of its dependence on variable skin and fat thickness which is not studied extensively in previous related works. In this article, we have designed a muscle-implanted antenna at 2.45 GHz to examine its performance dependence on variable skin and fat thickness values. In this study, we have designed an artificial neural network (ANN) for prediction of antenna performance parameters at 2.45 GHz for wide range of skin and fat thickness variations. The designed ANN model can predict antenna performance with ∼0.99 % error. Here, accurate dependence analysis of radiation performance of implantable antenna in terms of S 11 , realized gain, bandwidth and operating frequency on skin and fat thickness variations is performed which has not been studied yet and use of ANN in this field for accurate prediction is also a novel approach.