This paper presents a flexible microstrip low-pass filter (LPF) fabricated on a polyimide film substrate. The proposed flexible microstrip LPF with ten cascaded asymmetrical Pi-shaped defected ground structure (DGS) resonators are designed, simulated, manufactured, and measured. The simulation and experiment results demonstrate that the designed flexible microstrip LPF has a very sharp transition band, an ultra-wide stop-band (SB) and high rejection in SB performance compared with the existed microstrip LPFs with symmetrical and asymmetrical DGS. The proposed flexible LPF with ten cascaded resonators is with a compact size of 100 mm × 2.6 mm × 0.254 mm, a very low insertion loss of less than 1.9 dB under 2.2 GHz, and a wide SB from 2.7 to 12 GHz with the rejection of larger than 50 dB. The proposed flexible LPF has the potential to be used in wireless terminals to replace the traditional RF coaxial cable because it is very thin and has good transmission and filtering functions.INDEX TERMS Defected ground structure (DGS), flexible printed circuit board (FPCB), low-pass filter (LPF), pi-shaped DGS, wireless communication.

The design and implementation of a spiral-folded printed quadrifilar helical antenna (FPQHA) is presented for a global positioning system (GPS) L1-/L2-band application. The proposed FPQHA can be miniaturized by inserting dielectric loading inside the helix, covering the radiation elements by the dielectric sealant and turning the radiation elements into the form of parallelogram spirals. The manufactured antenna's radiation elements are printed on a hollow rod ceramic substrate with a diameter of 12 mm and a height of 24.7 mm. The measurement results of the proposed FPQHA mounting on unmanned platform fit very well with the simulations, which validates the design methods and suggests that the proposed FPQHA is suitable for GPS L1-/L2-band applications. INDEX TERMS Circular polarization, dual-band antenna, GPS antenna, printed quadrifilar helical antenna.

The design and implementation of printed helical spiral antenna (PHSA) and helical printed inverted-F antenna (IFA) are presented for unmanned aerial vehicle (UAV) with global positioning system (GPS) L1 band (1.57 GHz) and telemetry communication frequency band (2.33 GHz) applications. The proposed antenna is miniaturized by co-winding the radiation elements on the same ceramic rod, surface covering by dielectric sealant, inserting a high permittivity dielectric load into the helical structure, turning and meandering the radiation element of PHSA into a spiral parallelogram structure. The PHSA and helical IFA antenna radiation elements are manufactured by silver pasted on the same hollow ceramic cylinder with a diameter of 12 mm and a height of 24.7 mm. The experimental and simulation results show that the proposed PHSA and IFA can achieve the gain of 0.05dB and 1.97 dB respectively and be suitable for GPS L1 band and telemetry communication frequency band (2.33 GHz) applications separately. INDEX TERMS Circular polarization, GPS antenna, helical inverted-F antenna, printed spiral helical antenna, unmanned aerial vehicle.

The deformation control effect of loess tunnel composite foundation plays an important role in optimization design and reinforcement effect evaluation. Systematically evaluate the adaptability of the composite foundation of jet grouting pile in shallow collapsible loess tunnel. Taking the shallow buried section of Fujiyao Tunnel with a buried depth of 20 m as an example, using MIDAS finite element numerical simulation software, the foundation deformation control during construction and settlement control after construction are systematically studied, the differential deformation control is analyzed, and the reinforcement effect of the tunnel bottom is evaluated. The results show that the uplift displacement can be controlled by changing the pile length and increasing the replacement ratio. The combination of long and short piles can significantly reduce the uneven settlement and plastic zone of the foundation. The uneven settlement of 9 mm can be used as the evaluation index of the composite foundation reinforcement effect in a shallow buried section of the loess tunnel.

MoP@C nanocomposite, combined three-dimensional (3D) honeycomb carbon matrix with molybdenum phosphide, was synthesized through a simple hard template method followed by high-temperature phosphating treatment. The MoP@C has shown excellent sodium and potassium-ion storage properties applied as anode materials for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). The MoP@C composite maintains a high reversible specific capacity of 250 mAh g À 1 in SIBs after 100 cycles at 0.5 A g À 1 . Furthermore, even at a high current density of 5 A g À 1 , it still delivers a specific capacity of 200.5 mAh g À 1 . Additionally, the nanocomposite holds 147.2 mAh g À 1 at a high current density of 1 A g À 1 in PIBs. The excellent electrochemical performance benefits from the synergistic effect of the hierarchical MoP@C nanostructure. The exquisite porous nano-frame with higher conductivity and larger specific surface area, the active substance is fully infiltrated in the electrolyte, and successfully shortens the diffusion distance of electrons and ions. Moreover, the cavity in the heterostructure effectively inhibits the instinctive aggregation of MoP and simultaneously alleviates the volume expan-sion during the intercalation and deintercalation of ions in the charge and discharge process, enabling the excellent rate performance and long cycle life of the MoP@C electrode. The designed MoP@C composite shows excellent electrochemical cycle performance and rate performance as anode materials for sodium/potassium-ion batteries. The MoP@C composite maintained a high reversible specific capacity of 250 mAh g À 1 in sodium-ion batteries after 100 cycles at the current density of 0.5 A g À 1 . Furthermore, even at a high current density of 5 A g À 1 , it still delivered a specific capacity of 200.5 mAh g À 1 . Moreover, MoP@C composite materials also show excellent performance as anode material of potassium-ion batteries, with a specific capacity of 147.2 mAh g À 1 at the high current density of 1 A g À 1 . In summary, the excellent electrochemical performance of MoP@C composite materials fully proves that they can greatly improve the stability of the structure and reversibility as electrode materials, and lays a foundation for the further application of electrochemical energy storage devices in largescale applications.