I have changed antennas for a TP-LINK wireless router before. You may check the following indoor Omni-directional Antennas in the link below http://www.tp-link.com/en/products/?categoryid=217

No, their utility is not Mac compliant.

Since my modem is a cable modem,i just did a MAC Clone, and now it works beautiful.

Thanks!!! The problem has bee solved by the change the MTU size. This is really good to me since I have working on it for a so long time.

I have already tried to do the MAC clone. But this did not help. I also tried ping. No matter it is ping www.yahoo.com or the numbers you gave me. Both can not reach. Is there something wrong with my...

I checked that with my ISP. When I connect to the modem only, all pages can open without problem. I am sure that the problem is TP-LINK router now.