This paper presents a compact high-isolation dual-polarized dipole antenna with an artificial magnetic conductor (AMC) reflector. The proposed antenna is composed of a radiating element, two short pins and a 7 × 7 AMC array. By introducing two short pins, the port isolation is lower than −33 dB in the whole band on two ports. With the ring and AMC reflector, the dimension of the proposed antenna is only 0.36λ 0 × 0.36λ 0 × 0.16λ 0 at 2.2 GHz. The antenna also achieves a 10-dB return loss bandwidth from 1.6 to 2.78 GHz (54%) for both ports. The gain of the proposed antenna is around 8 dBi, and the cross-polarization is about 30 dB. Due to these properties, the proposed antenna can be applied to 2G/3G/long term evolution (LTE) base station and WLAN/WiMAX applications.
It is well known that ultrafine grained and nanocrystalline materials show enhanced strength, while they are susceptible to thermally induced grain coarsening. The present work aims to enhance the thermal stability of ultrafine Al grains produced by equal channel angular pressing (ECAP) via dynamically precipitation. Detailed characterization by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) has been carried out to reveal the microstructural evolution during both ECAP and post-ECAP annealing. After five passes of ECAP, both Al-8Zn and Al-6Bi-8Zn alloys show an ultrafine grain structure together with dynamic precipitated nanoscale Zn particles along grain boundaries. Upon annealing at 200 °C, ultrafine grains in the Al-8Zn and Al-6Bi-8Zn alloys show a remarkable thermal stability compared to the Al-8Bi alloy, which is mainly due to the presence of nanoscale Zn precipitates along grain boundaries. The present work reveals that nanoscale Zn particles have a positive effect on preserving the ultrafine grains during annealing, which is useful for the design of UFG Al alloys with improved thermal stability.
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