Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
2002-06-06
2004-09-14
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Spiral or helical type
C343S749000, C343S881000
Reexamination Certificate
active
06791508
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to antennas, and more particularly to conical spiral antennas for use in high frequency, high bandwidth, skywave non-line-of-sight communications in connection with mobile and stationary systems.
BACKGROUND OF THE INVENTION
High Frequency (HF), high data rate radios typically require wide bandwidth antennas to provide communication. In order to achieve this broadband communication, known antennas are constructed very large to provide efficiency over the wide frequency range, but as a result, are inconvenient for use when mobility is needed (e.g., communications in remote areas). Small antennas are also known to provide HF communication when mobility is important. However, these antennas suffer from transmission inefficiencies, particularly at lower frequencies in the HF bandwidth (i.e., 2 Megahertz (MHz) to 6 MHz).
In general, antennas operate based on resonance and are constructed to provide communication at a fairly narrow frequency bandwidth. In order to communicate on a specific frequency bandwidth for use in communication via a particular radio system, an antenna must be properly tuned to provide acceptable signal transmission levels at those frequencies. Typically, depending upon the frequency bandwidth on which transmissions will occur or are desired, the physical length of wire for conducting (i.e., radiating signals) is adjusted and properly tuned (e.g., loaded) to be resonant on the selected frequency. Additionally, the overall impedance of the system must be matched (i.e., antenna and feed line matched).
In the HF frequency range, in order to provide an antenna resonant at one full wavelength at the lower end of the range (e.g., 3 MHz), the conducting wires would be about the length of a football field. In most situations providing this length is not possible (e.g., in a backyard) or practical, and in cases when it is possible (e.g., in an open field), it is usually inconvenient, as the antenna needs to be capable of easy setup and portability. As a result, antennas have been developed that operate using a length of wire that is a portion of the full wavelength (e.g., ¼ or ½). This is typically accomplished by loading the antenna to affect its electrical characteristics, thereby making the antenna appear longer (i.e., electrically longer) in order to communicate at the lower frequencies.
Further, in certain circumstances, such as, for example, in providing military tactical communications, non-line-of-sight (NLOS) transmissions are needed. In these circumstances, spiral conical antennas providing circular polarization are used to overcome obstacles between, for example, a base station and a receiver on a mobile unit (e.g., helicopter). In particular, propagation of a signal with a very high radiation angle (i.e., Near Vertical Incidence Skywave (NVIS)) to establish tactical communication (i.e., 0-300 kilometers) is desirable. However, such antenna systems for use in mobile situations typically have very limited effective bandwidth range for operation, and generally suffer from transmission inefficiencies at lower frequencies in the HF range. Present linear polarization systems have significant null zones when the transmit and receiving antennas are incorrectly aligned.
Known spiral antennas for providing communication with high frequency, high data rate radios are not effective to provide reliable communications due to antenna problems, particularly in NVIS applications. Thus, these antennas fail to provide effective NLOS communications for use in supporting, for example, military tactical communications with helicopters, cargo planes or fighter planes. Existing spiral antennas are larger in size in order to accommodate the lower frequencies and wide bandwidths particularly in NVIS communications. Further, in aircraft applications, present HF aircraft antennas must be linearly polarized due to aerodynamic considerations.
Thus, there exists a need for a spiral antenna capable of providing HF communications with high bandwidth, circular polarization, and a gain pattern optimized for NVIS communications. Such an antenna must be adapted for easy portability (i.e., small in size) and set-up, while providing efficient and reliable communication at all frequencies in the HF range without the need for constant adjustments for different frequency transmissions.
SUMMARY OF THE INVENTION
The present invention provides an antenna and method of providing the same that is smaller in size while allowing efficient NLOS communication over the HF transmission range. For example, the invention reduces the size and weight needed for a ground station antenna to support military tactical communications (i.e., NLOS communications) with helicopters, cargo planes or fighter planes. With circular polarization of the ground station and the extra gain provided by the antenna of the present invention, alignment of the aircraft antenna with respect to the ground antenna is not required. Thus, the radio can be used anytime and at any aircraft heading and is more efficient in NVIS applications regardless of the signal bandwidth.
The present invention provides an antenna for use in communication systems operating in frequency bands traditionally occupied by narrowband radios, including high frequency (HF), very high frequency (VHF), and ultrahigh frequency (UHF) bands, as well as systems operating in frequencies extending into the millimeter wave region. The antenna allows for these systems to support broad-based and highly mobile communications “on-the-move” and performs in environments of impressive diversity, from dense foliage to dense urban obstructions, and unintentional and intentional jamming. Thus, increased performance and decreased size of the antenna operating in the HF, VHF, UHF, and microwave frequency bands is provided.
Generally, an antenna of the present invention provides NVIS communication that uses circular polarization to eliminate fading as the polarity of the antenna is rotated in the horizontal plane, such as, for example, while on a mobile unit. By reducing the ground wave or horizontally directed energy, greater frequency reuse is obtained over a smaller geographical area (i.e., tactical communications range). With control of transmitted power, the received signal can have a greatly improved bit-error rate. Further, signals transmitted by the antenna are virtually undetectable (i.e., low probability of intercept) on a spectrum analyzer at any bandwidth at the receive end after the signal bounces off the ionosphere.
The antenna is capable of quick (e.g., less than two hours) and easy set-up using less resources (e.g., less people and heavy equipment). In connection with a properly configured HF radio/modem, the present invention provides efficient NLOS voice or data transmission (i.e., high speed data and voice transmission and reception) without regard to receiver (e.g., aircraft receiver) azimuth position over the HF range. For example, wideband video and data may be transmitted and received in a tactical NLOS environment from a helicopter to a Tactical Operations Center (TOC) without a satellite and with low probability of intercept or jamming (e.g., if used with a digital direct-sequence spread spectrum (DSSS) or other waveform transmitter). In operation, by the time a signal comes down from the ionosphere, the signal is often below the ambient noise for non-digital-signal-processing radios. Further, the antenna is adapted to restore communication links when the receiver is not line-of-sight.
Specifically, the present invention provides a conical spiral antenna having a horizontal member at the base of the antenna for terminating a conductor (e.g., wires for conducting and radiating signals) of the antenna, and a load provided at the center of the horizontal member, which allows for more efficient communication over the entire HF range. The conical spiral antenna has improved efficiency and smaller size, and provides the conductor, which preferably includes first and second elements electrical
Berry Sonja A.
Gilbert James R.
Harness & Dickey & Pierce P.L.C.
Ho Tan
The Boeing Company
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