that tracks and matches the variation of the input impedance of the microstrip antenna at various frequencies this way multi band active integrated antenna behavior is achieved with good efficiency and matching conditions since a mimo antenna system requires multiple antenna structures and since for wireless handheld devices space is limited especially in cellular phones and pocket sized handheld devices compact antenna structures are desirable however placing antennas close to each other increases coupling reduces efficiencies and degrades the mimo system performance though high channel correlations that is why the present invention also contemplates providing a new multi band mimo antenna structure based on a semi circular antenna array comprised of first semi ring antenna element 46 and connected second semi ring antenna element 48 printed on a top side 400 a of the substrate as shown in fig4 a the ground plane side is shown in fig4 b as shown in fig4 a two identical dual semi ring antennas 46 are disposed within a minimum distance s 40 of each other on a substantially rectangular shaped substrate 400 a having a predetermined length l 41 and a predetermined width w 42 for mimo operation the feed point 47 on the outer ring is tuned to provide the necessary input matching at one band while the inner semi ring 48 is used to tune the other band a shorting post 49 in radial alignment with the connection of the first semi ring antenna element to the second semi ring antenna element and extending from the antenna surface 400 a to the bottom ground plane 400 b.