The present invention relates generally to communication systems, and more specifically, to a communication system utilizing a circular polarization antenna.
An antenna is a transducer that converts radio frequency electric energy to electromagnetic waves that are then radiated into space. The electric field determines the polarization or orientation of the radio wave. The polarization of an antenna in a given direction is the polarization of the wave radiated by the antenna. Most antennas are oriented to produce linear polarization (e.g., horizontal or vertical polarization). A linear polarized antenna radiates only in one plane containing the direction of propagation. If one station transmits a vertically polarized signal and a receiving station is using a horizontally polarized antenna, this will result in a weak signal at the receiver. Circular polarization allows an antenna to receive and transmit horizontal and vertical polarizations as well as every angle between horizontal and vertical. In circular polarization the electric field vector rotates with circular motion about the direction of propagation, making one full turn for each RF cycle. Thus, no matter what polarization the receiving station is using, the signal will come in at the same intensity.
Circular polarization provides improved signal to noise ratio since most noise sources are linearly polarized. Also, multipath interference is reduced as reflections of circularly polarized transmissions reverse polarization and are not received. Only multipath reflections with an even number of reflections are restored to the correct polarization and received.
Conventional antennas for wireless communications systems typically use vertical linear polarization as the reference or basis polarization characteristic of both transmit and receive base station antennas and wireless phone antennas. These antennas have drawbacks since linear polarization systems are susceptible to relatively poor performance due to multipath fading and other factors. Furthermore, vertical polarization often causes significant problems with hand-held antenna tilt. The vertical polarized signal received by the hand-held device is rarely vertical due to normal transmission fluctuations. The amount of tilt of the device varies with the particular operator and the conditions and environment. Losses due to antenna position and the received signal polarization angle mismatch can be significant in conventional hand-held wireless devices. These and other problems can result in distortion, cancellation, and loss of signal strength.
A further drawback of conventional circular polarization antennas is that they are typically designed to transmit narrow band signals. The antennas thus cannot be used in spread spectrum transmissions which use broader bandwidths. Other drawbacks include the size and weight of conventional antennas which make them unattractive for consumer handheld devices. Furthermore, conventional circular polarized transmitters typically use single ended unbalanced outputs that are matched to drive single ended balanced antennas, which results in power and transmission inefficiencies.
An antenna system for a wireless communication system is disclosed. The system generally comprises an antenna configured to receive and transmit circular polarized transmissions and a drive system. The drive system is operable to produce at least two outputs having generally the same amplitude. Each output is coupled to a different portion of the antenna. A phase difference is created between the outputs that is approximately matched to the antenna so as to create a desired polarity.
The antenna may comprise, for example, one or more patch antennas, dipole antennas, monopole antennas, helical antennas, horn antennas, slot antennas, fractal antennas, or spiral antennas. The system may further include a controller operable to switch the outputs between clockwise and counterclockwise transmissions to allow for simultaneous operation of two subsystems.
The drive system may have two or more outputs that are phase related to produce, in combination with the antenna, the desired polarization effect. The drive system may include two outputs having approximately ninety degrees of relative phase difference, for example.
In another aspect of the invention, a wireless communication device generally comprises an antenna configured to receive and transmit circular polarized transmissions in a spread spectrum system and a drive system. The drive system is operable to produce at least two outputs having generally the same amplitude and a phase difference relative to one another. Each output is coupled to a different portion of the antenna.
In yet another aspect of the invention, an antenna system for a wireless system generally comprises an antenna configured to receive and transmit circular polarized transmissions and a drive system. The antenna includes dual balanced feedpoints. The drive system is operable to produce a dual balanced output to drive the dual balanced feedpoints of the antenna.
The above is a brief description of some deficiencies in the prior art and advantages of the present invention. Other features, advantages, and embodiments of the invention will be apparent to those skilled in the art from the following description, drawings, and claims.