Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
1999-09-07
2001-05-08
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C455S277100
Reexamination Certificate
active
06229486
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to electronically scanned radio frequency (RF) antennas, specifically to such antennas used in fixed and mobile subscriber terminals of wireless radio frequency communication systems.
2. Description of the Related Art
The explosive growth in demand for wireless radio frequency communications necessitates increased efficiency in use of the radio frequency spectrum. In response to the problem extensive efforts have been applied to the development of antenna systems that use some form of scanning technique to improve network performance. Multiple techniques have been demonstrated such as space-diversity combining switched/multiple-beam arrays, RF scanning arrays, and digital beam forming. U.S. Pat. No. 5,903,826 to Nowak, for example, describes a wireless communication system which uses adaptive narrow beam antennas at the subscriber end of the communication link. The technique described in Nowak however is relatively complex and expensive to produce because it requires antennas having multiple polarizations. Further, the technique described in Nowak is geared to fixed access systems, and no claims are made relative to mobile subscriber units. U.S. Pat. No. 5,303,240 to Borras et al describes a similar system but it is limited to Time Domain Multiple Access (TDMA) protocols. The system described in U.S. Pat. No. 5,430,769 to Pasiokas, et al is also similar but limited to transmission and reception of digital data because it depends on the measurement of bit transition times. Each of the described techniques is based on the premise that a more directive beam scanned over a wide angle will result in reduced mutual interference thereby improving system performance for both coverage and capacity. These systems are generally referred to as smart or adaptive antennas that change radiation pattern in response to a changing signal environment.
Implementation of smart antennas at the base station of wireless systems provides narrow beams to be generated for each subscriber or group of subscribers. Consequently, the smart antenna reduces interference by forming nulls in the direction of other sources, thereby improving system capacity and coverage. See, for example, U.S. Pat. No. 5,907,816 to Edward M. Newman et al. The techniques described in Newman's patent also involve forming several narrow antenna beams to improve coverage of the base station. However, the techniques described are not applied at subscriber units. Despite all efforts to date, no subscriber based smart antenna system has been widely accepted primarily because of a failure to produce a cost effective device capable of supporting the large number of fixed and mobile subscribers found within a typical cellsite coverage area. While smart antennas have been applied at base stations, their use is limited due to high cost.
One alternative solution to improve system performance by reducing interference is to provide a stationary highly directive antenna with each subscriber unit. Such a solution has its obvious limitations for mobile subscriber applications stemming from the fact that mobility of the subscriber unit would frequently result in the antenna beam being directed away from the base station transmitting the optimal signal. However, this technique has been implemented in fixed wireless applications in which the subscriber unit is stationary. The solution utilizes a highly directive antenna such as a Yagi-Uda mounted on a roof top for each subscriber unit. The antenna is mounted with the main beam directed at the base station with the strongest signal. Mounting of the antenna requires specialized labor making this a costly solution. Furthermore, this solution is not adaptive to a growing wireless network where increased capacity requires addition of cellsites resulting in fixed subscriber antennas that are no longer directed toward the optimal base station.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a scanning antenna system suitable for use in all wireless communication applications both analog and digital irrespective of the protocol employed.
It is yet another object of the present invention to provide a scanning antenna system for use with each subscriber unit providing a simple and therefore cost effective means to lower system interference in wireless communications applications.
It is yet another object of the present invention to provide an electronic scanning multi-element antenna system for use with each subscriber unit that cost effectively lowers system interference without the added cost of installation labor in both mobile and fixed wireless applications.
It is yet another object of the present invention to provide a cost effective electronic scanning multi-element antenna system for use with each subscriber unit that is self adjusting in order to avoid the need to manually adjust beam direction in response to a change in optimal base station position or movement of the subscriber antenna system itself.
According to the invention a cost effective electronic scanning multi-element self adjusting antenna system is provided. This antenna system will be utilized as a smart antenna with each subscriber unit in both fixed and mobile wireless applications. Cost effectiveness of the wireless communication system is improved because more subscribers can share a single base station owing to the fact that the smart antenna minimizes mutual interference. Furthermore, implementation of the subscriber based smart antenna is simple and therefore inexpensive. The smart antenna consists of multiple antenna elements arranged on multiple sides of the unit with individual beams independently covering sections of free space such that collectively, complete coverage of the desired free space is accomplished. Each individual antenna element or element array is connected to an electronic switch which has its common port connected to the subscriber unit antenna port. The switch is driven by a controller that intelligently determines which antenna element or elements should be used to obtain the optimal signal. This configuration of the antenna system with its various antenna elements is designated the “optimum configuration”. Scanning for the optimum signal is controlled using various algorithms or a combination of algorithms such as periodic scanning, scanning when the signal drops below an absolute threshold, scanning when the signal drops below a relative threshold, and statistically based scanning that compensates for the constantly changing signal environment by utilizing both the directional and space diversity nature of the smart antenna.
REFERENCES:
patent: 5552798 (1996-09-01), Dietrich et al.
patent: 5701583 (1997-12-01), Harbin et al.
patent: 5708679 (1998-01-01), Fernandes et al.
patent: 5812933 (1998-09-01), Niki
patent: 5832389 (1998-11-01), Dent
patent: 5903826 (1999-05-01), Nowak
patent: 5977914 (1999-11-01), Harano
Tran Chuc
Wong Don
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