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T-junction. Its CP operation is realized by the interaction from the T-shaped stub and the T-junction. Measured results show that the antenna has an impedance bandwidth of 58% and 3-dB bandwidth of axial ratio of 22.2%. ACKNOWLEDGMENTSThis work was supported in part by the National Natural Science Foundation of the People's Republic of China under grant no. 60471046 and Ministry of Education under grant no. NCET-04 -0519. On the other hand, very narrow gaps required for low impedance lines cause high current density at the edges and subsequent increase in the conductor loss. In addition, the total loss increases rapidly with frequency especially in high frequency range. Therefore, the conventional CPW has to be modified to achieve higher performance. So, many efforts have been devoted to improve structures [3][4][5]. Among them, introducing MEMS technology in the design and fabrication processes of CPW is particularly effective and interesting. When compared with conventional CPW, these structures have better performance in some aspects, such as reducing total loss or widening available impedance range. In radio frequency (RF) MEMS field, the miniature of microwave component is also demanded besides their performance. The structures mentioned earlier do not meet the needs very well in this aspect. In this letter, a new micromachinable interdigital CPW was designed and fabricated. This design can minimize the whole size of microwave components. In this design, the ground lines were thickened by micromachining techniques, which can reduce the interference between the adjacent parallel sections of center conductor and improve the distribution of current density. DESIGN AND SIMULATIONThe interdigital CPW is more compact in structure, but the interference between the adjacent parallel sections of signal line is a critical problem and has to be dealt with seriously. Using ground lines with high aspect ratio, this letter presents a design, which can reduce this interference through air, as shown in Figure 1. The transmission line is composed of meander signal line, slot, and the ground fingers, which are thick enough to reduce this interference.The performance of this design was estimated by means of electromagnetic simulation. For this purpose, we used CST Mi- crowave Studio, a commercial simulator for three-dimensional (3-D) electromagnetic analysis to simulate this structure. In the simulation models, special attentions were paid to the influence of the length of straight segment of interdigital CPW a and the ground finger width d while the center conductor width s and the slot width w were fixed to 40 and 90 m, respectively, and the thickness of signal line and ground line were 5 and 25 m in addition. The whole structure was mounted on ceramic wafer with a thickness of 500 m and a relative dielectric constant of 9.4. Figure 2 shows the simulated return loss as a function of frequency over the frequency range from 5 to 20 GHz. When compared with conventional CPW, the return loss of interdigital CPW has two minimal v...

(+)‐Physostigmine and (+)‐physovenine have been synthesized. The anti‐acetylcholinesterase activities of these two bases, which have been investigated in vitro using erythrocyte acetylcholinesterase, have been found to be much lower than the corresponding activities of the alkaloids (‐)‐physostigmine and (‐)‐physovenine. Possible reasons for these activity differences are discussed.