Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2001-02-16
2002-10-08
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S770000, C343S818000
Reexamination Certificate
active
06462710
ABSTRACT:
TECHNICAL FIELD
The present invention is generally directed to an antenna for communicating electromagnetic signals, and relates more particularly to a planar array antenna having patch radiators exhibiting dual polarization states and producing substantially rotationally symmetric radiation patterns with controlled beamwidths.
BACKGROUND OF THE INVENTION
Diversity techniques at the receiving end of a wireless communication link can improve signal reception without additional interference. One such diversity technique is generating dual simultaneous polarization states. The term “dual simultaneous polarization states” typically means that an antenna has at least two different radiators, where each radiator simultaneously generates or receives RF energy according to a separate and unique polarization relative to an opposing active radiator. Therefore, unlike circular polarization which employs phasing between respective radiators, dual simultaneous polarization states requires respective radiators to be fed in phase. Those skilled in the art recognize that an antenna's polarization is defined to be that of its electric field, in the direction where field strength is maximum.
Dual polarization states can increase performance of a base station antenna that is designed to communicate with portable communications units having mobile antennas. The effectiveness of dual polarization for a base station antenna relies on the premise that transmit polarization of a typically linearly polarized mobile or portable communications unit will not always be aligned with a vertical linear polarization for the antenna at a base station site nor will it necessarily be in a linearly polarized state. Further, depolarization, which is the conversion of power from a reference polarization into the cross polarization, can occur along the multi-path propagation between the mobile user and a base station.
In order to compensate for the effects of depolarization, dual polarization can be employed at a base station antenna in order to communicate with mobile or portable communication units. However, dual polarization or polarization diversity typically requires a significant amount of hardware that can be rather complex to manufacture. Further, conventional dual polarized antennas typically cannot provide symmetrical radiation patterns where respective electric field (E) and magnetic field (H) plane beamwidths are substantially equal. Additionally, conventional antenna systems usually cannot provide for a wide range of magnetic field (H) plane beamwidths from a compact antenna system. In other words, the conventional art typically requires costly and bulky hardware in order to provide for a wide range of operational beamwidths, where beamwidth is measured from the half-power points (−3 dB to −3 dB) of a respective RF beam.
Another draw back of the conventional art relates to the manufacturing of an antenna system and the potential for passive intermodulation (PIM) that can result because of the material used in conventional manufacturing techniques. More specifically, with conventional antenna systems, dissimilar materials, ferrous materials, metal-to-metal contacts, and deformed or soldered junctions are used in order to assemble a respective antenna system. Such manufacturing techniques can make an antenna system more susceptible to PIM and therefore, performance of a conventional antenna system can be substantially reduced.
A further problem in the conventional art is the ability to effectively control the beamwidth of the resulting radiation patterns of a dual polarized antenna system. The conventional art typically does not provide for any simple techniques for controlling beamwidth of a dual polarized antenna system.
Unrelated to the problems discussed above, antenna designers are often forced to design antennas in a backward fashion. For example, because of the increasing public concern over aesthetics and the “environment”, antenna designers are typically required to build an antenna in accordance with a radome that has been approved by the general public, land owners, government organizations, or neighborhood associations that will reside in close proximity to the antenna. Radomes are typically enclosures that protect antennas from environmental conditions such as rain, sleet, snow, dirt, wind, etc. Requiring antenna designers to build an antenna to fit within a radome as opposed to designing or sizing a radome after an antenna is constructed creates many problems for antenna designers. Stated differently, the antenna designer must build an antenna with enhanced functionality within spatial limits that define an antenna volume within a radome. Such a requirement is counterproductive to antenna design since antenna designers recognize that the size of antennas are typically a function of their operating frequency. Therefore, antenna designers need to develop high performance antennas that must fit within volumes that cut against the ability to size antenna structures relative to their operating frequency.
Accordingly, there is a need in the art for a substantially compact antenna system that can fit within a predefined volume and that can exhibit dual polarization states while also providing for adjustable beamwidths. There is a further need in the art for a compact dual polarization antenna system that can provide radiation fields having substantially rotationally symmetric radiation patterns. There is also a need in the art for a compact antenna system that can generate RF radiation patterns where the beamwidth of respective RF fields for respective radiating elements are substantially equal and are relatively large despite the compact, physical size of the antenna system. There is a further need in the art for a compact antenna system exhibiting dual polarization states that can also provide for adjustable beamwidths in a fairly simple manner. Further, there is another need in the art for a compact antenna system that can be manufactured with ease and that can utilize manufacturing techniques which substantially reduce passive intermodulation. There is an additional need in the art for a substantially compact antenna system that can handle the power characteristics of conventional antenna systems without degrading the performance of the antenna system.
SUMMARY OF THE INVENTION
The present invention solves the aforementioned problems with an antenna system that can generate RF radiation fields having dual simultaneous polarization states and having substantially rotationally symmetric radiation patterns. The term “rotationally symmetric” typically means that radiation patterns of respective radiators having different polarizations are substantially symmetrical and substantially equal. In other words, the present invention can generate RF radiation patterns where the beamwidths of respective RF fields for respective radiating elements are substantially equal and are relatively large despite the compact, physical size of the antenna system. For example, the present invention can produce radiation patterns where each RF polarization produced by an individual radiating element is substantially equal to a corresponding orthogonal RF polarization produced by another individual radiating element. For example, the beamwidths produced by each radiating element can be adjusted from widths of approximately sixty-five (65) to ninety (90) degrees, where beamwidth is measured from the half-power points (−3 dB to −3 db) of a respective RF beam. Other beamwidths are not beyond the scope of the present invention.
This enhanced functionality can be achieved with a compact antenna system, where the antenna system (without a radome) can typically have a height of approximately less than one seventh ({fraction (1/7)}) of a wavelength and a width that is less than or equal to six-tenths (0.6) of a wavelength. With a radome, the antenna system can have a height of approximately one-fifth (⅕) of a wavelength. The antenna system can comprise one or more patch radiators and a non-reso
Carson James C.
Phillips Sara
EMS Technologies Inc.
Ho Tan
King & Spalding
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