Tunable microstrip patch antenna and control system therefor

• US 6,061,025 A
• Filed: 11/12/1997
• Issued: 05/09/2000
• Est. Priority Date: 12/07/1995
• Status: Expired due to Fees

• Current Assignee: Titan Aerospace Electronics Division
• Original Assignee: Atlantic Aerospace Electronics Corp. (Titan Corporation)
• Inventors: Jackson, Trent M., McKinzie, William E. III, Humen, Andrew Jr., Lilly, James D.
• Primary Examiner(s): Vu, David H.
• Assistant Examiner(s): PHAN, THO GIA
• Application Number:
  US08/968,216
• Time in Patent Office: 909 Days
• Field of Search: 343/700 MS, 343/745, 343/815, 343/816, 343/817, 343/818, 343/846
• US Class Current: 343/700.0MS
• CPC Class Codes: H01Q 1/38 formed by a conductive layer on an insulating support patch antennas H01Q9/0407; microstrip dipole antennas H01Q9/065; microstrip slot antennas H01Q13/106; transmission line microstrip antennas H01Q13/206; manufacturing reflecting surfaces using insulating material for supporting the reflecting surface H01Q15/142
• CPC Class Codes: H01Q 19/005 Patch antenna using one or more coplanar parasitic elements
• CPC Class Codes: H01Q 9/0421 with a shorting wall or a shorting pin at one end of the element H01Q9/0414 takes precedence
• CPC Class Codes: H01Q 9/0442 with particular tuning means
• CPC Class Codes: H01Q 9/045 with particular feeding means for circular polarisation H01Q9/0428
• CPC Class Codes: H01Q 9/0478 with means for suppressing spurious modes, e.g. cross polarisation

Abstract

A patch antenna is provided with one or more tuning strips spaced therefrom and RF switches to connect or block RF currents therebetween. When a control system for the antenna selectively connects and isolates RF currents between certain of the tuning strips and the patch, the tuning strips change the effective length of the patch and thus the antenna'"'"'s resonant frequency, thereby frequency tuning the antenna electrically over a relatively broad band of frequencies. The control system includes circuitry for rapidly switching the antenna to a desired frequency with minimal delay and with superior isolation from the antenna, making it suitable for use in DAMA, TDMA, and other frequency hopping applications.

Claims

1. An antenna including:

a ground plane that is electrically conductive having a first side surface;

a first patch that is electrically conductive having;

at least one edge; and

a first side surface;

a dielectric layer positioned between said first patch and said ground plane, said dielectric layer including;

a first side surface in contact with said first side surface of said first patch; and

a second side surface in contact with said first side surface of said ground plane;

at least one tuning strip that is electrically conductive spaced from said at least one edge of said first patch and spaced from said ground plane by said dielectric layer;

an RF feed connected to said first patch;

switch means to electrically connect and disconnect RF energy between said at least one tuning strip and said first patch; and

a control system coupled to said switch means that applies predetermined DC biases to cause said switch means to electrically connect and disconnect RF energy between said at least one tuning strip and said first patch.

2. An antenna as defined in claim 1, wherein said control system includes:

a bias control circuit that applies said predetermined DC biases to said switch means via a bias line; and

a programmable control circuit that controls the operation of said bias control circuit to apply said predetermined DC biases in accordance with a desired frequency.

3. The antenna as defined in claim 2, wherein said bias control circuit is coupled between said bias line and first and second predetermined bias voltages, said programmable control circuit controlling the operation of said bias control circuit such that only one of said first and second predetermined bias voltages is applied to said bias line.

4. The antenna as defined in claim 3, wherein said programmable control circuit causes said bias control circuit to apply said first predetermined bias voltage to said bias line in accordance with a first desired frequency, and causes said bias control circuit to apply said second predetermined bias voltage to said bias line in accordance with a second desired frequency different than said first desired frequency.

5. The antenna as defined in claim 2, wherein said bias control circuit includes first and second photovoltaic relays respectively coupled between said bias line and first and second predetermined bias voltages, said first and second photovoltaic relays being controlled such that only one of said first and second predetermined bias voltages is applied to said bias line.

6. The antenna as defined in claim 2, wherein said bias control circuit includes first and second photovoltaic relays coupled between said bias line and first and second predetermined bias voltages, said first and second photovoltaic relays being controlled such that only one of said first and second predetermined bias voltages is applied to said bias line, said first and second photovoltaic relays also being controlled such that only one of first and second predetermined bias currents is applied to said bias line.

7. The antenna as defined in claim 6, wherein said programmable control circuit causes said bias control circuit to apply said first predetermined bias current to said bias line in accordance with a first radiation efficiency, and causes said bias control circuit to apply said second predetermined bias current to said bias line in accordance with a second radiation efficiency different than said first radiation efficiency.

8. The antenna as defined in claim 6, wherein said bias control circuit applies said first and second predetermined bias voltages and said first and second predetermined bias currents in response to logic signals having logic states that are determined by said programmable control circuit, said bias control circuit further including a logic buffer that logically combines said logic signals and outputs said logically combined logic signals to said first and second photovoltaic relays.

9. The antenna as defined in claim 8, further including a jumper disposed between said logic buffer and said first and second photovoltaic relays that permits manual override of said logically combined logic signals so that only one of said first and second predetermined bias currents is applied to said bias line regardless of said logic states of said logic signals.

10. The antenna as defined in claim 2, further including a temperature sensor disposed at a predetermined position relative to said first patch, and wherein said programmable control circuit controls the operation of said bias control circuit in accordance with a detected temperature received from said temperature sensor.

11. The antenna as defined in claim 1, wherein said switch means includes first and second diodes connected in parallel between said at least one tuning strip and said first patch, said first and second diodes each having their cathode sides connected to said first patch.

12. The antenna as defined in claim 11, wherein said switch means further includes:

a first series connection of a capacitor and an inductor connected between an anode terminal of said first diode and said first patch, said capacitor being connected to said first patch and said inductor being connected to said anode terminal of said first diode;

a second series connection of a capacitor and an inductor connected between an anode terminal of said second diode and said first patch, said capacitor being connected to said first patch and said inductor being connected to said anode terminal of said second diode, said predetermined DC biases being applied at a connection point between said capacitor and said inductor.

13. The antenna as defined in claim 11, wherein said switch means further includes:

a first series connection of a capacitor and an inductor connected between an anode terminal of said first diode and said first patch, said capacitor being connected to said first patch and said inductor being connected to said anode terminal of said first diode;

a second series connection of a capacitor and an inductor connected between an anode terminal of said second diode and said first patch, said capacitor being connected to said first patch and said inductor being connected to said anode terminal of said second diode;

a third series connection of a capacitor and an inductor connected between a connection point between said capacitor and said inductor of said second series connection and said first patch, said capacitor being connected to said first patch and said inductor being connected to said connection point, said predetermined DC biases being applied at a connection point between said capacitor and said inductor of said third series connection.

14. An antenna system including:

an antenna having;

a first patch that is electrically conductive and is dimensioned such that it has a resonant frequency when RF energy is fed thereto,

a tuning strip that, when RF energy is electrically connected between said tuning strip and said first patch, changes said resonant frequency of said first patch, and

a switch that electrically connects and disconnects RF energy between said first patch and said tuning strip;

an RF feed that feeds RF energy to said first patch; and

a control system coupled to said switch that applies predetermined DC biases to cause said switch to electrically connect and disconnect RF energy between said tuning strip and said first patch.

15. An antenna as defined in claim 14, wherein said control system includes:

a bias control circuit that applies said predetermined DC biases to said switch via a bias line; and

a programmable control circuit that controls the operation of said bias control circuit to apply said predetermined DC biases in accordance with a desired frequency so that said resonant frequency of said first patch approaches said desired frequency.

16. The antenna as defined in claim 15, wherein said bias control circuit is coupled between said bias line and first and second predetermined bias voltages, said programmable control circuit controlling the operation of said bias control circuit such that only one of said first and second predetermined bias voltages is applied to said bias line.

17. The antenna as defined in claim 16, wherein said programmable control circuit causes said bias control circuit to apply said first predetermined bias voltage to said bias line in accordance with a first desired frequency, and causes said bias control circuit to apply said second predetermined bias voltage to said bias line in accordance with a second desired frequency different than said first desired frequency.

18. The antenna as defined in claim 15, wherein said bias control circuit includes first and second photovoltaic relays respectively coupled between said bias line and first and second predetermined bias voltages, said first and second photovoltaic relays being controlled such that only one of said first and second predetermined bias voltages is applied to said bias line.

19. The antenna as defined in claim 15, wherein said bias control circuit includes first and second photovoltaic relays coupled between said bias line and first and second predetermined bias voltages, said first and second photovoltaic relays being controlled such that only one of said first and second predetermined bias voltages is applied to said bias line, said first and second photovoltaic relays also being controlled such that only one of first and second predetermined bias currents is applied to said bias line.

20. The antenna as defined in claim 19, wherein said programmable control circuit causes said bias control circuit to apply said first predetermined bias current to said bias line in accordance with a first radiation efficiency, and causes said bias control circuit to apply said second predetermined bias current to said bias line in accordance with a second radiation efficiency different than said first radiation efficiency.

21. A method of controlling an antenna having a first patch that is electrically conductive and is dimensioned such that said first patch has a resonant frequency when RF energy is fed thereto, and a plurality of tuning strips, each of said tuning strips, when RF energy is electrically connected between said each tuning strip and said first patch, changes said resonant frequency of said first patch, said method comprising:

connecting RF energy between certain of said tuning strips and said first patch while isolating other of said tuning strips from said first patch in accordance with a desired frequency so that said resonant frequency of said first patch approaches said desired frequency;

preparing a table for respectively associating a plurality of predetermined combinations of said tuning strips with a plurality of predetermined resonant frequencies;

receiving said desired frequency;

looking up one of said predetermined resonant frequencies closest to said desired frequency in said table; and

controlling the connection of RF energy between said first patch and one of said predetermined combinations of said tuning strips associated with said one of said predetermined resonant frequencies.

22. The method as defined in claim 21, further comprising:

detecting a temperature of said antenna; and

adjusting the connection of RF energy between certain of said tuning strips and said first patch in accordance with said detected temperature and said desired frequency.

23. The method as defined in claim 21, wherein said step of connecting RF energy between certain of said tuning strips and said first patch while isolating other of said tuning strips from said first patch includes controlling application of a first predetermined bias voltage to switch elements coupled between said certain of said tuning strips and said first patch while controlling application of a second predetermined bias voltage to switch elements coupled between said other of said tuning strips and said first patch.

24. An antenna including:

a ground plane that is electrically conductive having a first side surface;

a superstrate having a first side surface and a second side surface opposite said first side surface;

a first patch on said first side surface of said superstrate, said first patch being electrically conductive and having at least one edge;

a dielectric layer positioned between said superstrate and said ground plane, said dielectric layer including;

a first side surface in contact with said first side surface of said superstrate; and

a second side surface in contact with said first side surface of said ground plane;

at least one tuning strip on said second side surface of said superstrate that is electrically conductive, said tuning strip being spaced from said at least one edge of said first patch and spaced from said ground plane by said dielectric layer and said superstrate;

an RF feed connected to said first patch;

a switch, responsive to an applied DC bias, that electrically connects and disconnects RF energy between said at least one tuning strip and said first patch.

25. The antenna as defined in claim 24, further comprising:

a plated through center hole through said first patch, said superstrate, said dielectric layer and said ground plane.

26. The antenna as defined in claim 25, wherein said center hole is thermally and electrically conductive.

27. The antenna as defined in claim 26, wherein said center hole is a hollow copper bolt.

28. The antenna as defined in claim 26, wherein said center hole is comprised of copper having a minimum cross-sectional area of about 0.10 in².

29. The antenna as defined in claim 25, further comprising:

a lead line for supplying said applied DC bias to said switch that is fed through said center hole.