Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
2001-04-30
2003-08-12
Issing, Gregory C. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S435000, C343S753000, C343S818000, C343S833000
Reexamination Certificate
active
06606057
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to mobile or portable cellular communication systems and more particularly to an antenna apparatus for use with a mobile or portable subscriber unit that communicates with a base station, wherein the antenna apparatus offers improved beam-forming capabilities by increasing the antenna gain in both the azimuth and the elevation directions.
BACKGROUND OF THE INVENTION
Code division multiple access (CDMA) communication systems provide wireless communications between a base station and one or more mobile or portable subscriber units. The base station is typically a computer-controlled set of transceivers that are interconnected to a land-based public switched telephone network (PSTN). The base station further includes an antenna apparatus for sending forward link radio frequency signals to the mobile subscriber units and for receiving reverse link radio frequency signals transmitted from each mobile unit. Each mobile subscriber unit also contains an antenna apparatus for the reception of the forward link signals and for the transmission of the reverse link signals. A typical mobile subscriber unit is a digital cellular telephone handset or a personal computer coupled to a cellular modem. In such systems, multiple mobile subscriber units may transmit and receive signals on the same center frequency, but different modulation codes are used to distinguish the signals sent to or received from individual subscriber units.
In addition to CDMA, other wireless access techniques employed for communications between a base station and one or more portable or mobile units include those described by the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard and the so-called “Bluetooth” industry-developed standard. All such wireless communications techniques require the use of an antenna at both the receiving and transmitting end. It is well-known that increasing the antenna gain in any wireless communication system has beneficial effects on the wireless system performance.
The most common type of antenna for transmitting and receiving signals at a mobile subscriber unit is a monopole or omnidirectional antenna. This type of antenna consists of a single wire or antenna element that is coupled to a transceiver within the subscriber unit. The transceiver receives reverse link audio or data for transmission from the subscriber unit and modulates the signals onto a carrier signal at a specific frequency and modulation code (i.e., in a CDMA system) assigned to that subscriber unit. The modulated carrier signal is transmitted by the antenna. Forward link signals received by the antenna element at a specific frequency are demodulated by the transceiver and supplied to processing circuitry within the subscriber unit.
The signal transmitted from a monopole antenna is omnidirectional in nature. That is, the signal is sent with approximately the same signal strength in all directions in a generally horizontal plane. Reception of a signal with a monopole antenna element is likewise omnidirectional. A monopole antenna does not differentiate in its ability to detect a signal in one direction versus detection of the same or a different signal coming from another direction. Also, a monopole antenna does not produce significant radiation in the zenith direction. The antenna pattern is commonly referred to as a donut shape with the antenna element located at the center of the donut hole.
A second type of antenna that may be used by mobile subscriber units is described in U.S. Pat. No. 5,617,102. The system described therein provides a directional antenna comprising two antenna elements mounted on the outer case of a laptop computer, for example. The system includes a phase shifter attached to each element. The phase shifters impart a phase angle delay to the signal input thereto, thereby modifying the antenna pattern (which applies to both the receive and transmit modes) to provide a concentrated signal or beam in a selected direction. Concentrating the beam is referred to as an increase in antenna gain or directivity. The dual element antenna of the cited patent thereby directs the transmitted signal into predetermined sectors or directions to accommodate for changes in orientation of the subscriber unit relative to the base station, thereby minimizing signal losses due to the orientation change. In accordance with the antenna reciprocity theorem, the antenna receive characteristics are similarly effected by the use of the phase shifters.
CDMA cellular systems are recognized as interference limited systems. That is, as more mobile or portable subscriber units become active in a cell and in adjacent cells, frequency interference increases and thus bit error rates also increase. To maintain signal and system integrity in the face of increasing error rates, the system operator decreases the maximum data rate allowable for one or more users, or decreases the number of active subscriber units, which thereby clears the airwaves of potential interference. For instance, to increase the maximum available data rate by a factor of two, the number of active mobile subscriber units can be decreased by one half. However, this technique is not typically employed to increase data rates due to the lack of priority assignments for individual system users. Finally, it is also possible to avert excessive interference by using directive antennas at both (or either) the base station and the portable units.
Generally, a directive antenna beam pattern can be achieved through the use of a phased array antenna. The phased array is electronically scanned or steered to the desired direction by controlling the input signal phase to each of the phased array antenna elements. However, antennas constructed according to these techniques suffer decreased efficiency and gain as the element spacing becomes electrically small as compared to the wavelength of the transmitted or received signal. When such an antenna is used in conjunction with a portable or mobile subscriber unit, the antenna array spacing is relatively small and thus antenna performance is correspondingly compromised.
SUMMARY OF THE INVENTION
Problems of the Prior Art
Various problems are inherent in prior art antennas used on mobile subscriber units in wireless communications systems. One such problem is called multipath fading. In multipath fading, a radio frequency signal transmitted from a sender (either a base station or mobile subscriber unit) may encounter interference in route to the intended receiver. The signal may, for example, be reflected from objects, such as buildings, thereby directing a reflected version of the original signal to the receiver. In such instances, the receiver receives two versions of the same radio signal; the original version and a reflected version. Each received signal is at the same frequency, but the reflected signal may be out of phase with the original signal due to the reflection and consequent differential transmission path length to the receiver. As a result, the original and reflected signals may partially or completely cancel each other (destructive interference), resulting in fading or dropouts in the received signal, hence the term multipath fading.
Single element antennas are highly susceptible to multipath fading. A single element antenna has no way of determining the direction from which a transmitted signal is sent and therefore cannot be tuned to more accurately detect and receive a signal in any particular direction. Its directional pattern is fixed by the physical structure of the antenna. Only the antenna position or orientation can be changed in an effort to obviate the multipath fading effects.
The dual element antenna described in the aforementioned reference is also susceptible to multipath fading due to the symmetrical and opposing nature of the hemispherical lobes formed by the antenna pattern when the phase shifter is activated. Since the lobes created in the antenna pattern are more or less symmetrical and opposite from one another, a signal reflected tow
Chiang Bing
Gainey Kenneth M.
Gothard Griffin K.
Snyder Christopher A.
Beusse Brownlee Bowdoin & Wolter P.A.
DeAngelis Jr. John L.
Issing Gregory C.
Tantivy Communications Inc.
LandOfFree
High gain planar scanned antenna array does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High gain planar scanned antenna array, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High gain planar scanned antenna array will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3103531