Pattern reconfigurable metamaterial antenna for 5G base station network

Reconfiguration of an antenna’s radiation pattern in a predefined direction is very important for enhancing the performance of communication systems in terms of the quality of service, system security, avoiding interference, and economizing power. Metamaterials, on the other hand, are commonly used in antenna design to enhance the gain, bandwidth, and efficiency and recently to tilt the radiation beam. Nonetheless, few issues had been encountered especially when the frequency is pushed to higher range such as the inherent losses that restrict the variety of their applications. Hence, metamaterials structures with relatively low loss are in high demand. In this thesis, various metamaterial structures with low loss properties are proposed. Then these structures are reconfigured and integrated with the fifth-generation (5G) planar antennas at two different frequency bands i.e. millimetre-wave (MMW) band and sub-6 GHz band for beam deflection applications. The modified double square ring resonator (DSRR) and contiguous squares resonator (CSR) structures are investigated numerically and experimentally to provide low loss property at 76 GHz and around 28 GHz, respectively. DSRR and CSR achieve losses of 0.5 dB and 0.2 dB, respectively. Both structures are manufactured and measured to validate the results. Furthermore, the analytical model is introduced to predict the electromagnetic behaviour of the proposed metamaterial structures. Thereafter, the CSR, Bridge shaped resonator (BSR) and split square resonator (SSR) structures are electronically reconfigured to produce different refractive indices at MMW and sub-6 GHz spectrums, which are used for deflecting the radiation beam of the 5G planar antennas. An array of unreconfigurable adjacent square-shaped resonators (ASSRs) has been also used for tilting the radiation pattern of planar antenna at sub-6 GHz spectrum. These proposed structures are included in the substrate of the dipole antenna and bow-tie antenna for deflecting the radiation pattern in E-plane at two different 5G bands of 28 GHz and 3.5 GHz. The results of all designs at both bands show that the radiation beam of the antennas is deflected in both positive and negative directions with respect to y-direction of antenna. At 28 GHz, a high deflection angle of 34° is obtained using simple structure, BSR, with gain improvement up to 1.9 dB (26.7%). On the other hand, at 3.5 GHz, the beam deflection angle of ±39º is achieved with gain enhancement up to 2.4 dB (35.6%) using passive beam deflection antenna whereas the beam deflection of ±36º is obtained using an active beam deflection antenna. The reconfigurable metamaterial antennas are proposed to be used in 5G base station network with advantages of high deflection angles, gain enhancement, low profile structure, low cost, lightweight, and easy integration with other circuits for 5G beam deflection applications

Reconfigurable radiation pattern of planar antenna using metamaterial for 5G applications

In this research, a reconfigurable metamaterial (MM) structure was designed using a millimeter-wave (MMW) band with two configurations that exhibit di erent refractive indices. These two MM configurations are used to guide the antenna’s main beam in the desired direction in the 5th generation (5G) band of 28 GHz. The di erent refractive indices of the two MM configurations created phase change for the electromagnetic (EM) wave of the antenna, which deflected the main beam. A contiguous squares resonator (CSR) is proposed as an MM structure to operate at MMW band. The CSR is reconfigured using three switches to achieve two MM configurations with di erent refractive indices. The simulation results of the proposed antenna loaded by MM unit cells demonstrate that the radiation beam is deflected by angles of +30 an

Convertible Bandstop to Allpass Filter using Defected Ground Structure with Ideal Switch for Millimeter-Wave Band in 5G Application

According to this study, a defective ground structure (DGS) with an ideal switch can be used to create a bandstop to allpass filter for 5G applications. The redesigned Hairpin DGS's bandstop and allpass responses are mathematically investigated in this paper. Utilising an ideal switch via open circuit and short circuit conditions on DGS, the convertible filter is operated. Therefore, the filter's performance in terms of return loss, attenuation, and insertion loss is simulated. As a result, the filter operates at 25.875 GHz in open circuit condition with a narrowband (2.16 GHz) bandstop response at 10 dB and a maximum attenuation of 29.5 dB, and at 26 GHz with a wideband allpass response and return loss greater than 10 dB. As a result, the filter is appropriate for 5G applications that use millimeter-wave RF front-end systems   &nbsp

Convertible Bandstop to Allpass Filter using Defected Ground Structure with Ideal Switch for Millimeter-Wave Band in 5G Application

According to this study, a defective ground structure (DGS) with an ideal switch can be used to create a bandstop to allpass filter for 5G applications. The redesigned Hairpin DGS's bandstop and allpass responses are mathematically investigated in this paper. Utilising an ideal switch via open circuit and short circuit conditions on DGS, the convertible filter is operated. Therefore, the filter's performance in terms of return loss, attenuation, and insertion loss is simulated. As a result, the filter operates at 25.875 GHz in open circuit condition with a narrowband (2.16 GHz) bandstop response at 10 dB and a maximum attenuation of 29.5 dB, and at 26 GHz with a wideband allpass response and return loss greater than 10 dB. As a result, the filter is appropriate for 5G applications that use millimeter-wave RF front-end systems   &nbsp

Refractive index reconfigurable metamaterial structure at 28 GHz frequency range

In this paper, a new refractive index reconfigurable metamaterial structure at millimeter wave (MMW) frequency range has been designed and simulated for beam switching in a future fifth-generation (5G) mobile network applications. The new proposed structure is composed of a Ladder shaped resonator (LSR) printed on the front face of a substrate layer and operates at 28 GHz. By proper arrangement of LSR unit cell, the proposed structure achieves a low loss and almost full transmission by -0.26 dB (0.97 in linear scale). To provide the refractive index reconfigurable feature, two PIN diodes are formed in the gaps of the structure. Thus, LSR can be switched between four states with a different refractive index values which are -60, -14, 0 and -12 at 28 GHz. In the simulation, the copper strip and measured S-parameters of the proposed PIN diode are used to achieve the reconfigurability. To demonstrate a reconfigurability of the new metamaterial structure, the return loss, insertion loss and real parts of the effective refractive index at each reconfigurable frequency are studies and investigated

Dual mode modified double square ring resonator structure at 76 GHz

Dual mode modified double square ring resonator (MDSRR) operating at 76 GHz millimeter-wave has been simulated, and experimentally verified. MDSRR structure operates in two modes, metamaterial (MTM) mode and frequency selective surface (FSS) mode, depending on the direction of the electric field. The MDSRR in the MTM mode performs well at the desired frequency region by providing the highest insertion loss, S21, as reported in the literature with a loss of −0.5 dB. The electromagnetically induced transparency principle is applied to explain the loss reduction mechanism. The low losses MTM structure has the potential to enhance the performance of the radiating elements of the automotive radar systems. Conversely, in the FSS mode, the FSS characteristics of the proposed structure are numerically simulated and verified experimentally by changing the direction of the electric field along the x-direction, in which the structure shows opposite behavior compared to the MTM performance. To demonstrate the validity of the FSS characteristics, the MDSRRs structure was tested using a waveguide measurement facility. The experiment results match well with that of the simulation, and wideband-stop characteristics are introduced in the range of 74 GHz to 80.3 GHz

Pancreatic surgery outcomes: multicentre prospective snapshot study in 67 countries

Background: Pancreatic surgery remains associated with high morbidity rates. Although postoperative mortality appears to have improved with specialization, the outcomes reported in the literature reflect the activity of highly specialized centres. The aim of this study was to evaluate the outcomes following pancreatic surgery worldwide.Methods: This was an international, prospective, multicentre, cross-sectional snapshot study of consecutive patients undergoing pancreatic operations worldwide in a 3-month interval in 2021. The primary outcome was postoperative mortality within 90 days of surgery. Multivariable logistic regression was used to explore relationships with Human Development Index (HDI) and other parameters.Results: A total of 4223 patients from 67 countries were analysed. A complication of any severity was detected in 68.7 percent of patients (2901 of 4223). Major complication rates (Clavien-Dindo grade at least IIIa) were 24, 18, and 27 percent, and mortality rates were 10, 5, and 5 per cent in low-to-middle-, high-, and very high-HDI countries respectively. The 90-day postoperative mortality rate was 5.4 per cent (229 of 4223) overall, but was significantly higher in the low-to-middle-HDI group (adjusted OR 2.88, 95 per cent c.i. 1.80 to 4.48). The overall failure-to-rescue rate was 21 percent; however, it was 41 per cent in low-to-middle-compared with 19 per cent in very high-HDI countries.Conclusion: Excess mortality in low-to-middle-HDI countries could be attributable to failure to rescue of patients from severe complications. The authors call for a collaborative response from international and regional associations of pancreatic surgeons to address management related to death from postoperative complications to tackle the global disparities in the outcomes of pancreatic surgery (NCT04652271; ISRCTN95140761)