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.

Abstract-Three hexagonal patch antennas are designed for circular polarization and experimentally validated. These antennas are labeled; simple hexagonal patch, hexagonal patch with slotted ground and hexagonal patch with parasitic element. The measured impedance bandwidths of the three antennas are 2% for the simple patch, 5.2% for the patch with slotted ground and 6.35% for the antenna with parasitic element. The axial ratio (measured) obtained is 4.73% for the patch with slotted ground and 3.33% for the hexagonal patch antenna with parasitic element. The measured radiation patterns of these antennas are found to be in good agreement with the simulated radiation patterns. The average gain of all the three antennas is also evaluated. A frequency selective surface (FSS) is proposed with dimensions smaller than that of a conventional FSS structure. The measured gain improvement with the proposed FSS is around 3 dB in the operating band.

A CPW‐feed prototype slot antenna for ultra‐wideband applications is proposed. The slot is made by etching on the ground plane, the union of two elliptical structures placed at right angles. The fractal shape antenna is excited by two stepped CPW feed. To enhance the gain, a compact ultra‐wideband frequency selective surface (FSS) structure is designed and implemented. The measured impedance bandwidth of antenna with and without FSS is nearly same and equal to 9.0 GHz from 3.6 to 12.6 GHz. The measured peak gain varies from 3 to 5 dB without FSS and from 5 to 12.5 dB with FSS. Measured results are found in good agreement with the simulated results. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1498–1502, 2014

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