Volume 76, Issue 3-4

This paper presents a new Doherty power amplifier (DPA) with harmonics suppression. A Wilkinson power divider (WPD) with open-ended and short-ended stubs is designed to suppress unwanted signals. To design the power divider in the circuit of the DPA, even and odd mode analyses are utilized. The proposed design operates at range of 1.2–1.6 GHz. The linearity of the suggested DPA is increased about 6 dBm, in comparison with the main amplifier. The designed Doherty amplifier has a power added efficiency (PAE), drain efficiency (DE) and Gain about 60, 61% and 19 dB, respectively. The designed WPD suppresses 2nd up to 14th harmonics with more than 20 dB suppression level, which is useful for suppressing unwanted harmonics in DPA design. ATF-34143 transistors (pHEMT technology) are used for this DPA amplifier design. The main amplifier has class-F topology and class-F inverse topology is used for auxiliary amplifier.

The quality of agricultural products can be remotely sensed and enhanced by determining the dielectric properties. This paper studies the dielectric properties of banana leaf and banana peel over the frequency range 1–20 GHz using the open-ended coaxial probe (OCP) method. A new curve fitting model is proposed to characterize the dielectric properties of banana leaf and banana peel. The different moisture content (MC) levels are considered for both banana leaf and banana peel samples and, their dielectric properties are characterized. Further, the banana leaf and banana peel’s measurement data are compared with the data obtained using the proposed model. In addition, Root Mean Square Error (RMSE) and R-squared ( R 2 ) are calculated to validate the performance of the proposed model. In case of banana leaf at 68.26% MC, the dielectric constant achieves the value of R 2 and RMSE of 0.98 and 0.0648, respectively. Similarly, dielectric loss achieves the value of R 2 and RMSE of 0.88 and 0.0795, respectively. Further, for banana peel at 80.89% MC, the dielectric constant achieves the value of R 2 and RMSE of 0.99 and 0.2989, respectively. Similarly, dielectric loss achieves the value of R 2 and RMSE of 0.96 and 0.6132, respectively.

Nowadays, the development of optical telecommunication systems requires more efficient all-optical elements appreciation to their high data transmission speeds and reduced electromagnetic interferences. In this work, our objective is to attest by simulation a design of an optical switch using 2D photonic crystals from polystyrene, an organic polymeric material with high Kerr non-linearity. This excellent ultra-fast switching leads us to the exploited in the construction of two new structures of all-optical AND/NAND and OR/NOR logic gates. These structures based on non-linear ring resonator NRR of different radius in order to operate a telecom wavelength of 1550.3 µm using RSoft (Full-Wave) software. The average contrast intensity is between 15.52 and 23.42 dB and low delay time varied from 20 fs to 5.0 ps. Hence, resulting a very high output signal for ON-switching (82–130% of P in ) and a weak signal for OFF-switching (0.2–7% of P in ) through a minimum threshold power around of 1.2 mW/μm 2 .

In this paper, we propose a concept of switchable electromagnetic shield based on seawater. The shield is designed to be a multilayer structure consisting of one chamber layer filled with free space or seawater and three dielectric layers to match with the communication wave signal. At low-power signal for communication purpose, the shield with the chamber layer filled with free space can make the wave signal transparently propagate through. At high-power interference microwave signal impinging onto the shield, the structure with the chamber layer filled with seawater can reflect and absorb the microwave energy. Transparency state for communication signal is designed based on the theory of transmission line, where a key indicator for communication signal transmission is the input impedance of the shield. Shielding state is theoretically calculated under different seawater parameters in a wide frequency band. Both the transparency and shielding states are validated by full-wave numerical calculations, and the results are in good agreement.

A terahertz metasurface absorber with actively switchable bandwidth enabled by vanadium dioxide (VO 2 ) is presented and investigated numerically. The VO 2 is a phase-change material and its conductivity in the terahertz range changes by several orders of magnitude upon phase-transition. The metasurface consists of an H-shaped fractal resonator placed on top of a polyimide spacer and a ground-plane of gold. The resonator is composed of an H-shaped level-1 fractal of gold and VO 2 strips that converts it to a level-2 fractal. At room temperatures, the VO 2 is in the insulator state and the resonator reduces to a level-1 fractal offering narrowband absorption at 8.08 THz reaching 0.98 absorption. At higher temperatures, the VO 2 is in the metallic state and the resonator is effectively a level-2 fractal with an absorption higher than 0.9 in a bandwidth of 6.63–9.89 THz.

Sub-terahertz (THz) technology is expected to deliver exceptional data rates for future sixth generation wireless communication systems especially for intelligent communication among devices falling under the Internet of Things (IoT) category. Moving from current 5G millimeter wave (mmW) technology towards THz spectrum will eventually provide unprecedented solutions that will guarantee higher transmission rates and channel capacity for any wireless communication system. With various electronic and wireless components working together to fulfill this promise, high gain antennas having compact profile is one such technology that will aid in achieving sub-THz communication while offering low path and power losses with reliable and fast data transfers. In this context, this work proposes a novel deformed patch antenna operating in the sub-THz spectrum i.e. at 300 GHz band. The proposed antenna is fed via a microstrip line following the proximity coupled feeding technique. Utilizing this technique provides a wide impedance bandwidth with a broadside radiation pattern having minimum side lobe levels of around −12 dB and a directivity of 10–15 dBi for the single and array elements respectively. The proposed design has a small footprint of 1.5 × 1.5 × 0.06 mm 3 for the single element while the array element has dimensions of 6 × 5 × 0.06 mm 3 . Both the designs have been simulated in Computer Simulation Technology-Microwave Studio (CST-MWS) and the results verified via high-frequency structure simulator (HFSS) simulator. The results confirm the viability of the proposed designs to be potential candidates for future sixth generation and IoT based applications.

Radio Frequency (RF) plays a vital role nowadays in harvesting RF Energy from the ambient source. An antenna is required to harvest RF energy and solve the spectrum underutilization problem for the Cognitive Radio (CR) system. This paper presents an optimization of a reconfigurable Coplanar Waveguide Antenna (CPW), which harvests RF energy and is also used for sensing and communication purposes. The performance metrics of the proposed antenna are gain, radiation efficiency, front-back ratio (FBR) and group delay. First, the optimized CPW antenna (sensing antenna) is designed and fabricated in the FR4 substrate for the wideband frequency range of (0.25–3 GHz) with the fractional bandwidth percentage of 175%. The gain of the proposed optimized CPW antenna for different frequency band is: DTV band (UHF-0.47 GHz)-3.327 dBi, GSM 900-2.39 dBi, GSM 1800-3.42 dBi, 3G-3.227 dBi, and Wi-Fi-3.21 dBi. The average gain of the optimized CPW antenna for the frequency range of (0.25–3 GHz) is 3.11 dBi, and the maximum radiation efficiency of the antenna is 91.05%. Next, the optimized CPW antenna is reconfigurable, and it can be reconfigured for a specific frequency band using a PIN diode switch. When the PIN diode switch is in ON state, the antenna acts as a reconfigurable antenna (communicating antenna), and it is operated for the specific frequency band of (0.47 GHz-DTV [UHF] band), (0.9, 1.8, and 2.1 GHz-mobile bands), and (2.4 GHz-Wi-Fi bands). The maximum gain of the optimized frequency reconfigurable CPW antenna is 3.61 dBi, and the radiation efficiency is 92.5%. In the OFF state, the antenna acts as a sensing antenna, and it operates at a wideband frequency range of (0.25–3 GHz). Finally, the prototype of a four-stage Villard voltage multiplier RF-dc conversion circuit using an adjustable impedance matching network is proposed for powering the cognitive radio applications.

In this paper, a circular antenna with a 3-D printed substrate is introduced to achieve a multiband behavior. The circular antenna is matched using a key-shaped stub located on the perimeter of the designed antenna. The 3-DP circular antenna adopted the apollonian gasket technique to perform the multi-circular cuttings in the Polylactic Acid (PLA) substrate as an innovative technique to obtain quintuple bands. The proposed antenna is designed to operate for Bluetooth, WLAN, WiMAX, and other wireless applications in S-band and C-band. The designed antenna has a compact size of 61.1 × 43.6 × 1 mm 3 . The prototype of the suggested 3-D printed antenna is fabricated and measured to confirm the simulation results. A good agreement is evident between simulation and experimental results which validates the design concept.

A simple and compact circularly polarized broadband circular slot antenna is proposed for WLAN/WiMAX/DBS applications. The main objective of this work is to design a microstrip line fed broadband circularly polarized antenna that is achieved by introducing an asymmetric perturbation over the circular slot onto the ground plane. A broad axial ratio bandwidth is achieved by using a small circular segment cut into the circular slotted ground and by adding a short stub on the feedline. To achieve a broad impedance bandwidth, a horizontal strip onto the slotted ground is placed just above the feed line on the opposite side. The proposed antenna is fabricated with an overall dimension of 20 × 20 × 1.6 mm 3 (0.34 λ o  × 0.34 λ o  × 0.03 λ o , where λ o represents the free-space wavelength at the center operating frequency). It is found that the impedance bandwidth of 75.82% ranges from 3.21 to 7.13 GHz and the 3 dB axial ratio (AR) bandwidth reaches 54.27% from 3.8 to 6.6 GHz. Throughout this paper, the improvement and validation process of the proposed antenna outcomes to accomplish desired characteristics are discussed.

The design and experimental verification of miniaturized cavity-backed self-triplexing antenna (STA) with high-isolation employing half-mode substrate integrated waveguide (HMSIW) are presented in this work. The proposed STA is constructed by using HMSIW, an Y-shaped slot and three 50Ω feed lines. Three unequal radiating patches are generated by engraving an Y-shaped slot on the top surface of the HMSIW cavity to operate at 3.7/5.0/5.8 GHz for WiMAX/WLAN applications. The proposed STA allows to realize one of the operating band independently by keeping other operating band unaltered and vice-versa. The circuit area of STA is highly miniaturized due to the use of HMSIW cavity and loading of Y-shaped slot. The isolations between three ports are greater than 31 dB. The fabricated STA provides 5.5, 5.92 and 5.93 dBi peak gains at 3.7, 5.0 and 5.8 GHz, respectively. The efficiency of the STA is greater than 92% at all the frequency bands. The constructed STA has a front-to-back ratio of more than 23 dB and a separation of more than 21 dB between co-to-cross polarization levels. Fabrication and measurement are used to validate the intended STA.

A compact, circularly polarized, CPW-fed antenna is proposed for wearable applications in ISM Band (5.8 GHz). The antenna is based on DGS, where the ground plane is responsible for impedance matching. The 10 dB impedance of the proposed antenna varies from 5.39 GHz to 5.94 GHz. The circular stub introduced in the ground plane mitigates the surface current and enriches the 3 dB axial ratio from 5.73 GHz to 5.92 GHz. Proposed antenna exhibits the LHCP and RHCP pattern of circular polarization, the antenna can effectively work for biomedical and wearable applications. The antenna is analyzed on the skin phantom model and the SAR value obtained is 1.218 W/kg, which is below the maximum permissible level. The proposed antenna is also used for the detection of breast tumors.

In this paper, a miniaturized bandstop frequency selective surface (FSS) with high angular stability is presented. Each FSS element consists of four sets each consisting eight octagonal concentric interconnected loops. The four sets are connected with each other through outermost octagonal loop. The unit size is miniaturized to 0.066 λ 0 at the resonant frequency of 1.79 GHz. The proposed configuration achieves excellent angular stability (only 0.025 GHz resonant frequency deviation is observed upto 83° oblique angles). The working mechanism of FSS is explained with the help of equivalent circuit model (ECM), electric field distribution, and corresponding surface current distribution. A prototype of the designed bandstop FSS is fabricated to verify the simulated frequency response. The experimental results are consistent with the simulation results. Simple geometry, low profile, high angular stability, and compact cell size are prominent features of the proposed structure.