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A broadband gain enhancement endfire antenna is presented. The gain enhancement is achieved by loading with an I-shaped resonator (ISR) structure in the endfire direction. Broad bandwidth is realised by using a microstrip-to-coplanar balun and bowtie dipole elements, while gain enhancement is achieved by loading the ISR structure in the endfire direction. The measurements show that the ISR-loaded antenna presents a gain of about 4-8 dB in the whole working band (4.5-9.5 GHz), which is about 2 dB more than the unloaded one. The advantages of broad bandwidth and high gain make this antenna valuable in wireless communication systems.Introduction: In recent years, many metamaterials that exhibit unique properties have been widely applied in microwave component and antenna applications [1]. These artifical materials can be formed by periodic arrangements of many small inclusions; for example, electric resonators, such as complementary split-ring resonators [2] and electric LC resonators [3], or composite right-/left-handed transmission lines (CRLH TLs) [4] or magnetic resonators, such as split-ring resonators (SRRs) [5]. Great interest has been focused on meta-based antennas. Among them, low-/zero-index materials have features of controlling the direction of a microstrip patch antenna, and 1-2 dB gain improvement was obtained. However, this kind of structure makes the antenna heavy in weight and thick in profile. The SRR structure was introduced to achieve high gain along the endfire direction [6]. However, the bandwidth of this antenna was quite narrow. The dipoles are widely used for their simple structure and broad bandwidth [7]. However, the feature of low gain restrict their applications. In [7], a wideband endfire antenna with an impedance bandwidth of 70% and directional patterns was proposed based on the idea of a quasi-Yagi antenna. Nevertheless, its gain with an average of 4 dB was still low.In this Letter, we combine the advantages of the metamaterial structures and the wide bandwidth endfire antenna together to develop a broadband high-gain antenna as given in [8]. Instead, I-shaped resonators (ISRs) with a simpler structure are introduced in this design. Gain enhancement is achieved by loading with two rows of ISRs symmetrically in the endfire direction while maintaining the wideband performance of the periodic endfire antenna. The ISR-loaded antenna has a gain of about 4-8 dB in the whole working band (4.5-9.5 GHz), which is about 2 dB more than the unloaded one. HFSS software is used to optimise this antenna, and good agreement between the measured and simulated results is achieved.

Hydrogen generation by electrolysis of water in an alkaline solution is a promising technology for clean hydrogen energy. Amorphous materials show much better performance than their crystalline counterparts. However, it is still challenging to design amorphous metal materials. Here, a series of amorphous transition metal nanoparticles (NPs) is successfully synthesized using a twisted covalent organic network (CON) that can provide twisted carbon layers as well as asymmetrically distributed nitrogen. With the fixed monomer pore, a low loading amount of RuCl3 results in amorphous‐only Ru nanoclusters (NCs, 1.5 nm), while a high content of RuCl3 leads to crystalline dominant Ru NPs (3 nm). The mixed phased Ru‐CON catalyst for the hydrogen evolution reaction (HER) shows extremely low overpotential at 10 mA cm–2 (12.8 mV in 1.0 m KOH) and superior stability (after 100 h test, current loss 5.3% at 75 mA cm–2). More importantly, amorphous‐only Ru‐CON with smaller Ru NCs shows much better mass activity and considerable stability compared to mixed‐phase Ru‐CON materials since amorphous Ru NPs can provide more active sites than in their crystalline state. With this strategy, amorphous Fe NPs and Ir NPs are successfully prepared for extended applications, and the HER activities are reported.

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