We report the successful incorporation of bifunctional (acid/base) catalytic sites in the crystalline organocatalytic porous COF (2,3-DhaTph). Due to the presence of acidic (catachol) and basic (porphyrin) sites, 2,3-DhaTph shows significant selectivity, reusability, and excellent ability to perform the cascade reaction.

The design of a high-gain horizontally polarised antenna for ultrawideband (UWB) operation is presented and experimentally demonstrated. Gain enhancement is achieved by using a frequency selective surface (FSS) reflector. Both the antenna and the FSS have simple structures and are printed on a similar substrate. The antenna is a three-stepped narrow rectangular slot excited using a three-stepped microstrip feed line. By optimising the lengths and widths of the sections of the slot and the feed line, an ultra-wide impedance bandwidth (3.2-12 GHz, measured) has been achieved. The FSS is a two-layer structure where each layer is an array of rectangular patches printed on one side of the substrate. With the application of the FSS, the antenna gain is enhanced by 3-4 dBi over most of the band. The polarisation purity (in terms of the measured cross-polar difference) is also improved with the FSS. Such an antenna-FSS combination will be useful for high-gain UWB applications requiring horizontal polarisation.

In this paper, a dual polarized slot antenna for ultra wideband applications is proposed. The slot has an overall shape of a square ring whose four arms are identical and stepped rectangular. While two adjacent arms of the ring are microstrip fed and are responsible for the orthogonally polarized fields, the other two arms are introduced to make the structure symmetric and reduce the cross polarization. The impedance matching and isolation are controlled by properly shaping the slot arms and the feed section and by insertion of narrow metallic and slot stubs. The measured impedance bandwidth is 120% (3.0 GHz to 12.0 GHz). The isolation is better than 20 dB over most of the band. With the help of radiation patterns and aperture electric field distribution, the dual polarized nature of the antenna is justified. The antenna will be useful for UWB MIMO transmission, polarimetric radar and medical imaging applications.

Abstract-A compact, low profile, dual polarized, ultra wideband, frequency selective surface is proposed. It is designed by using two similar metallic array structures separated by dielectric material FR4. The simulated reflection bandwidth (with transmission < −20 dB) for TE incident wave is 8 GHz from 2.87 GHz to 10.87 GHz corresponds to 116%. The unit cell dimension and periodicity are of the order of 0.37λ at the centre frequency. The overall thickness of the proposed FSS is 1.8 mm.The proposed FSS has higher order of band-stop response and good angular stability. The measured transmission response of FSS is very close to simulated response. Design expressions for the resonance frequencies are proposed, and the calculated results are found to be in good agreement with the simulated ones. Finally, a parametric analysis of the proposed FSS is presented.