WO2003107474A2

WO2003107474A2 - Shared element array antenna

Info

Publication number: WO2003107474A2
Application number: PCT/US2003/016717
Authority: WO
Inventors: David Theobold
Original assignee: Cisco Technology, Inc.
Priority date: 2002-06-14
Filing date: 2003-05-28
Publication date: 2003-12-24
Also published as: AU2003234668A8; WO2003107474A3; AU2003234668A1

Abstract

An antenna array is disclosed which a plurality of sub-arrays are provided, each including a respective plurality of antenna elements associated therewith. One or more shared antenna elements are shared by some or all of the antenna sub-arrays. The shared antenna elements are common elements of the respective pluralities of antenna elements in the sub-arrays that shared elements.

Description

SHARED ELEMENT ARRAY ANTENNA Background of the Invention

The present invention is directed to antenna systems, particularly antenna array systems including a number of sub-arrays for obtaining a desired topology.

Antenna systems are commonly used to cover a desired service area for a wireless local area network (WLAN). Users of the WLAN can move about the service area and access the network with a wireless client without the requirement of a hard-wired network connection. The wireless client includes radio components that enable communication with a wireless access point (AP) having similar radio components plus a hard-wired network connection.

In a relatively small WLAN, a number of clients can simultaneously communicate with one or more AP's using different frequency bands and time slices. However, as the number of clients in a WLAN increases, bandwidth and service time become limited and it is desirable for several clients to operate simultaneously on the same shared frequency bands. As demand increases in this manner, the WLAN can no longer manage frequency and time without decreasing throughput, and it becomes necessary to manage space.

Space can be managed in a WLAN by using one or more directional antenna patterns that can be selectively steered in the direction of clients to allow communication between the clients and the network. The directional antenna will only communicate with the client to which it is directed, even if multiple clients are operating within a spatial region within the same frequency bandwidth. The directional antenna alternatively steers toward each associated client in turn, enabling isolated communication with the network. Likewise, the antenna can be designed to place pattern nulls in the direction of interference, thereby mitigating potential degradation to the signals being received from desired directions. A common type of directional antenna is an antenna array system. A plurality of nearly omni-directional antenna elements are deployed in an array. The separation of each antenna is selected so as to provide phase differences between the antenna elements such that peak and null patterns are established for transmitting and receiving signals from the clients. By selectively varying the phase differences of the signals at each antenna element, the maximum and minimum points can be varied, allowing the antenna array to be "steered" as is known in the art. The arrangement of the antenna elements can be defined in a desired topology to provide the necessary coverage for a specific service area. For example, the antenna elements can be laid out in a one-dimensional array, along a line. The elements can also be laid out in a two-dimensional array, over an area, or in the three-dimensional array, within a volume.

Arrayed antenna systems are thus designed to provide fixed or variable gain pattern functions. A process of pattern synthesis is employed to select a proper topology for the antenna elements. In the process of pattern synthesis, a variety of mathematical and heuristic techniques can be employed to arrive at a required number of elements, in a specific topology, and with a suitable combining approach, in an effort to optimize performance and efficiency for specific network coverage. Thus, a given antenna topology requires appropriate algorithms to determine weighting factors for each antenna. However, as a practical consideration, it is necessary to limit the design of an antenna array to remain within reasonable manufacturing and cost limits. This may place limits on the number of antenna elements that can be employed, and also the physical size of the array, along with cabling complexity, electronic combining complexity, and other such parameters.

It can happen that disparate, conflicting requirements may arise within the antenna design process. For example, a specific synthesized topology may require an odd number of antenna elements, but the electronic combining of these elements may be best implemented by an even number of elements. In previous array systems, these problems have been addressed by "array thinning," where one or more antenna elements are eliminated, and by "random spacing" where variable spacing between antenna elements is employed to control the array extent. Such techniques can offer adequate pattern synthesis while meeting other practical design requirements. However, such techniques require physically extended topologies, and thereby may not offer the most efficient method of implementing an antenna array, especially when size is a constraint.

Summary of the Invention The difficulties and drawbacks of the previous antenna systems are addressed by the antenna array of the present invention. A plurality of sub-arrays are provided, each including a respective plurality of antenna elements associated therewith. Some or all of the antenna sub- arrays share one or more antenna elements. The shared antenna elements are common elements of the respective pluralities of antenna elements in the sub-arrays that share elements. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative and not restrictive.

Brief Description of the Drawings

Fig. 1 is a diagrammatic depiction of the steps for producing an antenna topology with overlapping sub-arrays, in accordance with the present invention.

Fig. 2 shows an antenna element amplifier arrangement in accordance with the present invention. Detailed Description of the Invention

With the present invention, an antenna array 10 is indicated as being composed of a plurality of identical sub-arrays 12, where each sub-array 12 includes a plurality of antenna elements 14 associated with each sub-array 12. The exemplary embodiment of Fig. 1 shows an array defined by a group of three sub-arrays 12A, 12B, 12C, arranged across a two-dimensional area. Each sub-array includes three antenna elements 14, and the three sub-arrays 12 A, 12B, 12C are used to synthesize a desired array antenna topology requiring nine elements. In order to reduce the physical requirements of an array using an odd number of antenna elements 14, a topology is subsequently synthesized in which at least two sub-arrays overlap such that the positions of one or more antenna elements 14 from each sub-array coincide. In this way, the coincidental antenna elements 14 can be replaced by a shared antenna element 16, shared by the respective antenna sub-arrays. In this way, the respective antenna elements 14 are actively combined into a single shared element 16 that is a common antenna element to the respective sub-arrays, so as to be equivalent to two antenna elements occupying the same physical space. The shared antenna element 16 will provide two respective signals for associated sub-array 12 processing, as will be explained in greater detail below.

As shown in the exemplary embodiment of Fig. 1 , the sub-arrays 12A, 12B include a shared element 16AB that cooperates respectively with both sets of antenna elements 14 A, 14B associated with each sub-array 12A, 12B. It should, of course, be appreciated that the present invention is not limited to this exemplary embodiment. The present process may be generalized to any topology using M sub-arrays, with N elements in each sub-array, in a linear, two dimensional, or three-dimensional array. If a topology is required that uses M sub-arrays, the synthesis process may be performed to produce one overlap (utilizing MxN-1 elements), two overlaps (MxN-2 elements) or any number of overlaps k (MxN-k) such that suitable performance can be maintained. In this way, the present method allows the construction of arrays having the equivalent of odd-numbered element topologies but enabling the use of commercially available antenna packages having two or four devices per package. As shown in Fig. 2, each of the antenna elements 14 in a sub-array 12 cooperates with a respective plurality of amplifier elements 20. In the preferred embodiments, the amplifier elements 20 are low noise amplifiers (LNA). A shared antenna element 16 is configured to further cooperate with a respective plurality of amplifier elements 22 corresponding to the respective antenna sub-arrays 12 between which the element 16 is shared. For example, Fig. 2 shows the amplifier arrangement that would correspond to the nine-element array shown in Fig. 1. The shared element 16AB in common with the sub-arrays 12 A, 12B communicates with a low noise amplifier 20 having adequate gain to effectively set the noise floors of the respective array channels just after the amplifier 20. Respective intermediate amplifiers 22A, 22B are positioned after the LNA 20 to enable processing on each array channel without affecting the other channels. The outputs of the amplified elements 14A, 16AB, 14B, 14C associated with each sub-array, are received by a processing means 24, for subsequent signal processing. The present invention can be used so that one or more sub-array is an adaptive directional array. Other realizations could be contemplated without departing from the invention.

With the present invention, a synthesized array topology can be made to conform to packaging and manufacturing constraints. Also, the total number of front-end RF electronic packages is reduced, thereby lowering cost, complexity, size and weight. In this way, the invention simplifies the electronics while maintaining the benefits of sub-array processing. The invention provides a straightforward array synthesis methodology and simplifies many beam- forming processing designs by providing a simple translational topology for the sub-arrays. Translational topologies are particularly attractive to the beamforming processes requiring subspace matrix mathematical approaches.

As described hereinabove, the present invention solves many problems associated with previous array systems. However, it will be appreciated that various changes in the details, materials and arrangements of part which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the area within the principle and scope of the invention will be expressed in the appended claims.

Claims

We Claim:

1. An antenna array comprising: a plurality of antenna sub-arrays each including a respective plurality of antenna elements associated therewith; at least one shared antenna element shared by at least a portion of the antenna sub-arrays such that at least one shared antenna element is a common element of each of the respective pluralities of antenna elements associated with at least a portion of the antenna sub- arrays.

2. The antenna array of claim 1 wherein each of the respective plurality of antenna elements in each antenna sub-array cooperate with a respective plurality of amplifier elements.

3. The antenna array of claim 2 further comprising processing means for receiving the output of the plurality of amplifier elements associated with each sub-array.

4. The antenna array of claim 2 wherein at least one shared antenna element cooperates with a respective plurality of amplifier elements corresponding to at least a portion of the antenna sub-arrays.

5. The antenna array of claim 4 wherein at least a portion of the antenna sub-arrays comprise first and second antenna sub-arrays and wherein at least one shared antenna element cooperates with respective first and second amplifier elements.

6. The antenna array of claim 1 wherein at least one of the plurality of antenna sub- arrays comprise an adaptive directional antenna array.

7. An antenna array comprising: a first antenna sub-array including a first plurality of antenna elements; a second antenna sub-array including a second plurality of antenna elements; wherein the first antenna sub-array and the second antenna sub-array comprise at least one shared antenna element.

8. The antenna array of claim 7 wherein at least one shared antenna element is a common element of the first plurality of antenna elements and also the second plurality of antenna elements.

9. The antenna array of claim 7 wherein each of the respective plurality of antenna elements in each antenna sub-array cooperate with a respective plurality of amplifier elements.

10. The antenna array of claim 9 further comprising processing means for receiving the output of the plurality of amplifier elements associated with each sub-array.

11. The antenna array of claim 9 wherein at least one shared antenna element cooperates with a respective plurality of amplifier elements corresponding to the first and second antenna sub-arrays.

12. The antenna array of claim 1 wherein at least one of the first and second antenna sub-arrays comprise an adaptive directional antenna array.

13. A method of designing an antenna array topology comprising: providing a plurality of antenna sub-arrays each including a respective plurality of antenna elements associated therewith; positioning at least a portion of the antenna sub-arrays such that at least one antenna element is respectively shared between the respective sub-arrays, so as to provide a shared antenna element common to each of the respective pluralities of antenna elements associated with at least a portion of the antenna sub-arrays.