Communication system and methods utilizing a reactively controlled directive array

• US 5,767,807 A
• Filed: 06/05/1996
• Issued: 06/16/1998
• Est. Priority Date: 06/05/1996
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Pritchett, Don Michael
• Primary Examiner(s): Hajec, Donald T.
• Assistant Examiner(s): PHAN, THO GIA
• Application Number:
  US08/658,327
• Time in Patent Office: 741 Days
• Field of Search: 343/700 MS, 343/790, 343/814, 343/815, 343/816, 343/817, 343/818, 343/819, 343/833, 343/834, 343/836, 343/837, 343/846, 343/853, 342/374, 342/433, 342/435
• US Class Current: 342/374
• CPC Class Codes: H01Q 19/32 the primary active element being end-fed and elongated
• CPC Class Codes: H01Q 3/24 varying the orientation by switching energy from one active radiating element to another, e.g. for beam switching
• CPC Class Codes: H01Q 3/446 the radiating element being at the centre of one or more rings of auxiliary elements

Abstract

A reactively controlled directive antenna array that has a single central monopole or dipole as a radiating element excited directly by a feed system. A plurality of parasitic elements surround the radiating element and through changing the state of the parasitic impedance causing the antenna to be in an omni directional or beam pointing mode according to whether the parasitic elements are open circuited or short circuited. A computer modem and memory including stored programs control the antenna array in an omnidirectional or directive mode to locate, identify and communicate with nodes in a wireless communication network. A stored table is created in the memory indicating the antenna direction for communicating with each node in the network. Using the stored table, the computer initiates a communication sequence with a selected node, the sequence having the advantages of improved signal sensitivity and angular discrimination for wireless communication systems.

Claims

1. In a communication network with a plurality of communicating nodes, a local communication node comprising:

(a) a radio antenna array including a central emitting element having a data input for transmitting a data bearing radio signal, the array also including a plurality of parasitic elements proximate to said emitting element, each parasitic element having a control input;

(b) a plurality of impedance switching circuits, each coupled to one of said plurality of parasitic elements for selectively changing the parasitic impedance of each parasitic element to said radio signal;

(c) said radio antenna array broadcasting an omni directional mode signal when all of said parasitic elements are in a high impedance state and said array broadcasting a directed mode radio signal in a selected direction when a selected sub-plurality of said parasitic elements are selectively placed in a lower impedance state in response to said switching circuits;

(d) a computer modem having a first data path coupled to said emitting element for sending and receiving data by said radio signal with other ones of said plurality of nodes in said network, and having a second data path coupled to said switching circuits for outputting signals representing said selected direction;

(e) a memory in said computer for storing program instructions and a table of antenna direction values representing directions between the local node and said other ones of said plurality of nodes; and

(f) said computer communicating with a selected one of said other ones of said plurality of nodes by accessing a selected direction value from said memory for said selected one node and outputting signals on said second data path to said switching circuits and exchanging communication signals with said emitting element over said first data path.

2. The communication node of claim 1 further comprising:

(i) receiving means in said computer for selecting said omni directional mode while receiving a broadcast from one of said other ones of said plurality of nodes that is not directed to said local node;

(ii) scanning means in said computer to sequentially output control signals to said switching circuits to sequentially change said selected direction of said antenna array;

(iii) comparison means in said computer to identify a preferred direction for said receive broadcast;

(iv) decode means in said computer for decoding an identity of said one other nodes; and

(v) said computer storing said identity and said preferred direction in said table in said memory.

3. The communication of claim 2 further comprising:

detection means in said computer detecting of broadcast from one of said other nodes that is directed to said local node and in response thereto selecting said directed mode; and

said computer accessing said preferred direction of said one other nodes from said memory using said identity and outputting on said second data path to switching circuits to enable exchanging directed mode radio signals with said one other nodes.

4. The communication node of claim 1 wherein said impedance switching circuits further comprise:

a substantially vertical conductor mounted above a substantially horizontal ground plane as a parasitic element;

a printed circuit transmission line with a first end connected to said conductor and second end connected through a low radio-frequency impedance to said ground plane, said transmission line having an electrical length substantially one quarter of a wavelength of said radio signal, forming a high impedance at said first end;

a switching device connected between said conductor and said ground plane having a low impedance when forward biased and a high impedance when not forward biased; and

a switch connected between said second end of said transmission line and a bias voltage source having a control input coupled to said second data path from said computer for selectively forward biasing said switching device and thereby reducing the parasitic impedance of said conductor to said radio signal.

5. A method for accessing and communicating with nodes in a local area network including a computer modem and memory, comprising the steps of:

selecting an omni directional mode for a directional antenna coupled to the computer modem;

receiving radio signals from existing traffic in the local area network which includes a plurality of nodes, each node including a directional antenna coupled to the computer modem;

identifying a node of the local area network using the directional antenna and computer modem;

determining a valid direction of a selected node of the network;

selecting a directional mode for the directional antenna and setting the antennas direction to the selected node;

transmitting an acquisition request to the selected node, using the directional antenna and selected direction;

receiving permission;

a time slot list for the respective nodes of the local area network;

identifying an antenna for each respective node of the network and storing the direction in a computer table in the memory;

setting the direction for said directional antenna to begin a communication sequence with the selected node of the local area network; and

transmitting and receiving radio communications with said selected node over said selected direction.

6. The method of claim 5 wherein each directional antenna comprises a central radiating element surrounded by a plurality of parasitic elements and the step of selecting an omni directional mode for directional antennas further comprises the step of:

placing the parasitic elements in an "open circuit" state for receiving radio signals by the directional antenna.

7. The method of claim 6 wherein the step of selecting a directional mode for the directional antenna further comprises the steps of:

placing selected parasitic elements in a "short circuit" state;

transmitting a radio beam from the central radiating element in a selected direction based upon the parasitic elements placed in the "short circuit" state.

8. The method of claim 7 further comprising the step of:

changing the "short circuit" state of the parasitic elements to form a beam steered radio signal.

9. The method of claim 8 wherein the memory comprises a plurality of stored program instructions and the step of identifying a node in the local area network further comprises the step of using a detection program stored in the memory to identify each node in the local area network.

10. The method of claim 9 further comprises the step of forming a table in the memory providing an antenna direction to each node in the local area network.

11. An electronic reconfigurable antenna comprising:

a supporting member having a top surface and a ground plane bottom surface and an opening;

A radiating element mounted in the opening;

a plurality of microstrip lines surrounding the opening with each microstrip forming an rf choke by virtue of their high characteristic impedance, substantially quarter-wavelength electrical length, and low rf impedance to ground termination at a bias feed point;

a plurality of antenna elements surrounding the radiating element, each antenna element attached to a different microstrip at the via;

A plurality of switching device, each switching device coupled at one end to a different antenna element through the via hole and at the other end to a said ground plane on a back surface of the supporting member;

a bias circuit coupled to each switching device whereby one state of the bias circuit places the switching device in a conducting condition to cause the attached antenna element to be in a low impedance state;

a second state of the bias circuit causing the switching device to be in a non-conducting condition causing the antenna element to be in high impedance state; and

means for causing the antenna to be in an omni-directional state when the antenna elements are in high impedance state and causing the antenna to be in a directional state when the antenna elements are in a low impedance state.