Wide tuning range, frequency agile MIMO antenna for cognitive radio front ends

1. A frequency-reconfigurable, multiple-input-multiple-output antenna system for cognitive radio platforms, wherein the antenna system has a wide tuning range covering several wireless standards and that enables switching between operating bands in cognitive radio platforms, said antenna system comprising:

a board having a top layer substrate and a bottom layer ground plane, said bottom layer ground plane containing four antenna elements;

each said antenna element comprises a circular slot and an annular slot spaced outwardly of and extending circumferentially around the circular slot;

said top layer substrate overlying the bottom layer ground plane and contains a microstrip feed-line for each said antenna element; and

a varactor diode positioned on the top layer to span the width of each said annular slot in the bottom layer to tune the resonance frequency over a wide operation band.

2. The frequency-reconfigurable antenna system as claimed in claim 1 , wherein:

said top layer substrate has a relative permittivity (ε r ) of 3.48, a loss tangent of 0.0036 and a board thickness of 0.76 mm.

3. The frequency-reconfigurable antenna system as claimed in claim 2 , wherein:

the microstrip feed lines comprise SMA connectors.

4. The frequency-reconfigurable antenna system as claimed in claim 3 , wherein:

the board has a length dimension of 120 mm and a width dimension of 60 mm.

5. The frequency-reconfigurable antenna system as claimed in claim 4 , wherein:

the circular slots each have a radius of 8.5 mm; and

the annular slots each have a radius of 10.1 mm and a width of 0.5 mm.

6. The frequency-reconfigurable antenna system as claimed in claim 5 , wherein:

the varactor diodes each have terminals connected with a respective biasing circuit via two shorting posts on the bottom layer ground plane.

7. The frequency-reconfigurable antenna system as claimed in claim 6 , wherein:

the varactor diodes spanning the width of the annular slots load the antenna by reactive capacitance.

8. The frequency-reconfigurable antenna system as claimed in claim 7 , wherein:

the bottom layer ground plane acts as a co-planar reflector for the multiple-input-multiple-output antenna elements, enabling beam tiling and thus lowering the field coupling for better multiple-input-multiple-output performance.

9. The frequency-reconfigurable antenna system as claimed in claim 8 , wherein:

the multiple-input-multiple-output antenna is on a board having typical smart phone dimensions of 60 mm width, 120 mm length and 0.76 mm thickness.

10. The frequency-reconfigurable antenna system as claimed in claim 9 , wherein:

the antenna system covers a wide frequency band from 1800 MHz to 2450 MHz and supports several wireless standards bands, including GSM1800, LTE, UMTS and WLAN.

11. The frequency-reconfigurable antenna system as claimed in claim 10 , wherein:

the bottom layer ground plane and top layer substrate have substantially the same overall length and width dimensions.

12. The frequency-reconfigurable antenna system as claimed in claim 11 , wherein:

said biasing circuitry consists of two 1 μH RF chokes and two 2.1 kΩ resistors connected in parallel to two terminals of the varactor diodes, said varactor diodes being reverse biased by applying variable voltage.

13. The frequency-reconfigurable antenna system as claimed in claim 12 , wherein:

the varactor diodes used are SMV 1233.

14. The frequency-reconfigurable antenna system as claimed in claim 13 , wherein:

the varactor diode reverse bias voltage is varied between 0˜15 volts.

15. The frequency-reconfigurable antenna system as claimed in claim 14 , wherein:

resonating frequency is smoothly changed over the frequency band 1800˜2450 MHz.

16. The frequency-reconfigurable antenna system as claimed in claim 15 , wherein:

capacitance of said varactor diodes is varied from 0.7 pF to 6 pF.