Portia is an intelligent woman trapped in a man's world.
Yes, Portia is smart, observant, clever and strong-willed. She is from a noble family, has married into a noble family and is well educated in the spheres of the domestic and the political.
Portia is an unusual Shakespeare female character in that she does not perfectly fit the mould of the typical tragic female who is often characterized as being overly-romantic, unable to form her own opinions, and hysterical due to her inability to control her emotions.
Portia is different because she is the polar opposite of a typical tragic female character. However, she must still conform to the patriarchal world in which she finds herself which is why she can never truly be Brutus' equal. In the end, when Portia kills herself by swallowing hot coals, she is totally alone, having been abandoned by her father, Caesar and her husband. Without a male figure to attach herself to in order to justify her existence in the play, Portia is no longer useful and so subscribes to the hysterical female character trait and kills herself in a gory final act.