Volume 78, Issue 11-12

The design and response of a triple-band linear-to-circular polarization converter (LTCPC) in the terahertz frequency regime using a graphene-based transmission-type metasurface have been studied numerically and analytically. The unit cell of the converter is constructed using lossy silicon dioxide (SiO 2 ) with a relative permittivity of 3.9 as the substrate. And two similar layers of graphene-based sub-wavelength structures are used at the top and bottom of it. Multiband linear to circular polarization conversion is achieved from 0.74 THz to 0.98 THz, 1.70 THz to 2.33 THz, and 4.06 THz to 5.19 THz, i.e., about 28 %, 31 %, and 24 % fractional bandwidths, respectively. As the same metasurface configuration is used at the top and bottom layers of the transmission-type unit cell, it can be used as a bidirectional polarization converter with identical responses from both sides. The geometrical optimization of the unit cell is done, and an equivalent lumped parameter circuit model is also proposed for the same, considering analogous responses. Tunability over the operating frequency is achieved by varying the chemical potential and relaxation time of graphene. Moreover, due to the ultrathin width and special types of identical configuration of the metasurfaces, the response of the system remains excellent over a wide range of incident angle variations up to 80° angle of incidence.

A framework of a metasurface (MTS) – based wideband circularly polarized (CP) reconfigurable antenna for fifth generation (5G) wireless systems operating in the sub-6 GHz mid-frequency range is presented in this article. The proposed structure contains a simple patch antenna, which serves as the primary source, a shorting pin, two ring slots, and a metasurface superstrate. The shorting pin and two ring slots produce perturbation resulting in circular polarization with a narrow axial ratio (AR) bandwidth. A metasurface (MTS) superstrate composed of 4 × 4 rectangular patches stacked over the primary source antenna generates additional resonances that significantly improve the −10 dB impedance and 3 dB axial ratio (AR) bandwidth. Two PIN diodes are employed to alter the circular polarization between left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). The prototype is made using an FR-4 epoxy substrate and has an overall size of 50 mm × 35 mm × 4.2 mm. The antenna has a −10 dB bandwidth of 44 % (4.0–6.2) and a 3 dB axial ratio bandwidth of 28 % (4.2–5.6). It also has a 3 dB beam width of 74° and 85° in the E and H planes, a gain of 7.1 dBi, cross-polar isolation of more than 15 dB, and a unidirectional radiation pattern. The simulated and measured results confirm that the implemented antenna is promising for sub-6 GHz 5G communication systems, particularly cognitive radio, wireless body area networks (WBAN), and satellite communication systems.

In this paper wide angle wide band polarization insensitive Metamaterial absorber (MA) has been proposed. The proposed unit cell structure consists of hexagonal concentric ring along with hexagonal packing. The structure is fabricated on FR4 substrate. The advantage of hexagonal packing is that it covers less area as compared to square packing. The unit cell structure is scaled w.r.t hexagonal ring and resistance of the substrate. The absorptivity achieved range from 6.54 to 14.85 GHz having Bandwidth (BW) of 8.31 GHz. The metamaterial behaviour of the structure is proven by plotting real and imaginary pat of permittivity and permeability. Absorption mechanism is shown by plotting surface current distribution at the top and bottom of the surface. The proposed MA structure is analysed for normal and oblique incidence. From the normal incidence it was found that structure has wide angle polarization insensitive. The absorptivity of the fabricated structure is measured inside the anechoic chamber. The simulated and measured plot is compared and found that both the results are very close to each other. At last, the proposed and already reported MAs are compared and from the observation it was found that proposed unit cell have larger BW compact in size, polarization insensitive and have hexagonal packing. The proposed MA covers partial C band, full X band and partial Ku band. The Proposed MA found practical applications for satellite communication, Wi-Fi devices, cordless telephone, military, air traffic control, defence tracking, vehicle speed detection.

The design of balanced filters based on composite right/left hand (CRLH) structure is well developed. Among those, few designs exist which although they provide some good responses, suffer from narrow stopbands and interdependent passbands. This paper proposes a new technique for improving the characteristics of dual-band balanced bandpass filters (B-BPFs) based on planar CRLH. Using unequal inductive stubs (UISs) attached to the interdigital capacitor (IDC) unit cell, we were able to achieve outstanding harmonic suppression and passband controllability. This structure offers higher degrees of freedom compared to conventional designs and provides better control over the filter specifications. Mathematical modeling, analysis, simulation, fabrication, and performance measurement of the proposed technique in a dual-band B-BPF are also provided. Our work resulted in an independent and controllable dual-band B-BPF with ultra-wide upper differential-mode (DM) stopband of 5.9 f 1 and common-mode (CM) suppression of 40.4 and 32.6 dB for the first and second bands, respectively.

A wideband bandpass filter (BPF) using capacitor-loaded coupled lines is proposed with super-compact circuit size and very simple structure. By loading three lumped capacitors in parallel to three same pairs of coupled lines, three transmission poles and four transmission zeros can be achieved and they can be calculated by input admittance derivation. To verify the design, a wideband BPF prototype with center frequency at 1.34 GHz is fabricated, whose measured 3-dB fractional bandwidth is 98.5 % (0.68–2 GHz), in-band insertion loss is less than 0.5 dB, return loss is greater than 17.5 dB, and circuit size is only 0.24 λ g  × 0.02 λ g ( λ g : guided wavelength at the center frequency).

This paper describes the general properties of power dividers, in particular matching and isolation. This original works relates to three different divider structures based on the circular-shaped resonator. These prototypes resemble the Wilkinson power divider due to their geometric configuration. These power dividers provide very good isolation between their output ports of −51.26 dB. In fact, the originality of these new structures stems from the idea of minimizing the size of this classic power divider. The required design parameters for the three proposed dividers came from a simulation study using the Ansoft HFSS tool in addition to a design theory. The experimental prototypes are well presented and operate at 2.4 GHz. They demonstrate excellent performance in adaptation, which refers to impedance matching, ensuring consistent impedance at the component terminations. Additionally, they exhibit low insertion losses and high isolation at 2.4 GHz. The measurement results agree well with those of the simulation. The benefits demonstrated by this study are significant, justifying the preference for these components.

This manuscript introduces an innovative 1-to-4 modified Wilkinson power divider designed to operate at a frequency of 3.5 GHz. The configuration of the proposed divider is fabricated on Rogers RT/Duroid 5,880, featuring a relative permittivity of 2.2 and a thickness of 0.565 mm, respectively. The circular shape employed in the design minimises size and enhances power handling capability. To achieve a 4-way power division with equal power distribution at each output port, a 1:2 power divider at 3.5 GHz is cascaded. Furthermore, we present and analyse a 1:4 WPD implemented on a microstrip line utilised as a power supply for measuring a four-port MIMO antenna. This divider exhibits excellent impedance matching at all ports and consistent phase and amplitude characteristics between the output ports. The performance metrics of the presented divider, as detailed in both experimental and simulated results, include a return loss of 27.92 dB (1:2) and 29 dB (1:4), isolation of 33.046 dB (1:2) and 35.56 dB (1:4) and insertion loss of 3.17 dB (1:2) and 6.6 dB (1:4) respectively. These proposed power dividers hold potential applications in microwave and communication systems, mainly where power division is imperative with minimal signal loss and robust impedance matching.

In this article, an integrated radiation and scattering performance array conformed with the cylinder is presented. Wideband RCS reduction can be achieved and the radiating performance is maintained without loading any other structures. Two different antenna units with similar radiation performances and different reflection phases are designed to form a 6 × 6 conformal array. To verify the simulation results, a prototype of a 6 × 6 units integrated conformal array was fabricated and measured. The experimental results show that the proposed conformal array has better scanning performance above ±40° in the range of 8.2–11.3 GHz. In addition, the monostatic RCS reduction of the proposed array is more than 5 dB covering the working band of the array antenna with a maximum reduction value of 24.2 dB. The measured results agree well with the simulation results.

In this letter, a wideband folded reflectarray antenna with a novel circularly polarized converter is presented. The main reflectarray is composed of dual-polarized units, which can achieve good polarization and phase characteristics with a smaller size. Based on 3-D printing technology, the proposed dielectric unit can be used to design the low-cost linear-to-circular polarization converter (LCPC) with wider bandwidth. In order to validate the performance of the proposed circularly polarized folded reflectarray antenna (CPFRA), a prototype is manufactured and measured. The maximum gain of 25.3 dBic and the maximum aperture efficiency of 38 % are obtained. The measured 3 dB gain bandwidth is 32.7 % and the measured 3 dB AR bandwidth is 31.7 %, respectively. The simulated and measured results show great agreement.

The paper presents an UWB antenna for on-body application with advancements in EBG backed reflector incorporating the compatibility and flexibility in structure. The ultra-wideband (UWB) frequency range supported by the designed antenna is between 2.78 GHz and 18 GHz. The antenna is designed with jeans textile substrate for the compatibility in on-body applications, which has appealing qualities such as flexibility and low dielectric properties, while the antenna radiator patch and ground plane are made of copper. The designed antenna is applicable on human body, meticulously designed EBG surface that could minimize antenna frequency detuning, with specific absorption rate (SAR). This allows for a great deal of flexibility in terms of the antenna design, allowing it to realize a high gain, enhanced bandwidth and directional radiation pattern. The antenna gain is increased by 99.8 % once EBG is applied and the SAR is decreased from 22.03 W/kg to 0.104 W/kg.

This research introduces a compact Ultra-Wideband (UWB) antipodal Vivaldi antenna with a U-slot tailored for biomedical applications. Utilizing an elliptical tapered patch variation on a 50*32 mm 2 substrate achieves its compact design. Parameter optimization, employing the Multi-Layer Stacked Shallow Attention Neural Network (MLSSANN) with Adaptive Gannet Optimization Algorithm (AGOA), ensures accurate predictions and efficient exploration of the design space. Performance analysis includes metrics like gain, directivity, reflection coefficients, return loss and radiation efficiency. The U-slot variant exhibits higher gain peaking at 24.5 GHz (10 dB) compared to the standard variant peaking near 37 GHz (13.7 dB). The U-slot antenna also shows improved directivity and return loss, with a 13.89 % enhancement in return loss at 3.7 GHz. Moreover, the addition of the slot shifts the lower cut-off frequency from 1,580 MHz to 740 MHz, reducing the antenna size by 41 % while maintaining acceptable radiation characteristics.

Radio Frequency Identification (RFID) is considered a key element of the Internet of Things (IoT). It enables objects to be identified and tracked using radio waves. In RFID systems, several tags may be present within the range of the reader, leading to collisions and interference between signals that reduce system performance. Several anti-collision solutions have been proposed to solve this problem based on TDMA (Time-Division Multiple Access) technique, such as the ALOHA, Slotted ALOHA and Dynamic Framed Slotted ALOHA (DFSA) protocols. In this paper, we propose to improve TDMA anti-collision protocols based on the Cell Averaging Constant False Alarm Rate (CA-CFAR) scheme. The CA-CFAR technique is introduced to estimate the number of tags in the physical layer so that the reader can adjust its transmission parameters accordingly and avoid collisions. The obtained results show that this technique achieves good results in terms of system efficiency and the number of required slots to identify all the tags of the system.