Communications: radio wave antennas – Antennas – Fractional – multiple – or full wave length linear type
Reexamination Certificate
2002-01-25
2003-07-08
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
Fractional, multiple, or full wave length linear type
C343S7000MS, C343S769000, C343S829000
Reexamination Certificate
active
06590545
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to antenna apparatuses and systems, and more particularly, to planar antennas with non-dispersive, ultra wide bandwidth (UWB) characteristics.
With respect to the antenna of radar and communications systems, there are five principle characteristics relative to the size of the antenna: the radiated pattern in space versus frequency, the efficiency versus frequency, the input impedance versus frequency, and the dispersion. Typically, antennas operate with only a few percent bandwidth, and bandwidth is defined to be a contiguous band of frequencies in which the VSWR (voltage standing wave ratio) is below 2:1. In contrast, ultra wide bandwidth (UWB) antennas provide significantly greater bandwidth than the few percent found in conventional antennas, and exhibit low dispersion. For example, as discussed in Lee (U.S. Pat. No. 5,428,364) and McCorkle (U.S. Pat. Nos. 5,880,699, 5,606,331, and 5,523,767), UWB antennas cover at least 5 or more octaves of bandwidth. A discussion of other UWB antennas is found in “Ultra-Wideband Short-Pulse Electromagnetics,” (ed. H. Bertoni, L. Carin, and L. Felsen), Plenum Press New York, 1993 (ISBN 0-306-44530-1).
As recognized by the present inventor, none of the above UWB antennas, however, provide high performance, non-dispersive characteristics in a cost-effective manner. That is, these antennas are expensive to manufacture and mass-produce. The present inventor also has recognized that such conventional antennas are not electrically small, and are not easily arrayed in both 1D (dimension) and 2D configurations on a single planar substrate. Additionally, these conventional antennas do not permit integration of radio transmitting and/or receiving circuitry (e.g., switches, amplifiers, mixers, etc.), thereby causing losses and system ringing (as further described below).
Ultra wide bandwidth is a term of art applied to systems that occupy a bandwidth that is approximately equal to their center frequency (e.g., greater than 50% at the −10 dB points). A non-dispersive antenna (or general circuit) has a transfer function such that the derivative of phase with respect to frequency is a constant (i.e., it does not change versus frequency). In practice, this means that an impulse remains an impulsive waveform, in contrast to a waveform that is spread in time because the phase of its Fourier components are allowed to be arbitrary (even though the power spectrum is maintained). Such antennas are useful in all radio frequency (RF) systems. Non-dispersive antennas have particular application in radio and radar systems that require high spatial resolution, and more particularly to those that cannot afford the costs associated with adding inverse filtering components to mitigate non-linear antenna phase distortion.
Another common problem as presently recognized by the inventor, is that most UWB antennas require balanced (i.e., differential) sources and loads, entailing additional manufacturing cost to overcome. For example, the symmetry of the radiation pattern (e.g., azimuthal symmetry on a horizontally polarized dipole antenna) associated with balanced antennas can be poor because of feed imbalances arising from imperfect baluns. Furthermore, the balun, instead of the antenna, can limit the antenna system bandwidth due to the limited response of ferrite materials used in the balun. Traditionally, inductive baluns are both expensive, and bandwidth limiting. Furthermore, other approaches used to deal with balanced antennas utilize active circuitry to build balanced (or differential) transmit/receive (TR) switches, differential transmitters, and differential receivers, in an effort to maximize the bandwidth at the highest possible frequencies. Such approaches, however, are more costly than simply starting with unbalanced antenna constructions.
Another problem with traditional UWB antennas is that it is difficult to control system ringing. Ringing is caused by energy flowing and bouncing back and forth in the transmission line that connects the antenna to the transmitter or receiver—like an echo. From a practical standpoint, this ringing problem is always present because the antenna impedance, and the transceiver impedance are never perfectly matched with the transmission line impedance. As a result, energy traveling either direction on the transmission line is partially reflected at the ends of the transmission line. The resulting back-and-forth echoes thereby degrade the performance of UWB systems. In other words, is, a clean pulse of received energy that would otherwise be clearly received can become distorted as the signal is buried in a myriad of echoes. Ringing is particularly problematic in time domain duplex communication systems and in radar systems because echoes from the high power transmitter obliterate the microwatt signals that must be received nearly immediately after the transmitter finishes sending a burst of energy. The duration of the ringing is proportional to the product of the length of the transmission line, the reflection coefficient at the antenna, and the reflection coefficient at the transceiver.
In addition to distortion caused by ringing, transmission lines attenuate higher frequencies more than lower frequencies, and sometimes delay higher frequency components more than lower frequency components (i.e. dispersion). Both of these phenomena cause distortion of the pulses flowing through the transmission line. Thus it is clear that techniques that allow shortening of the transmission line have many advantages—reducing loss, ringing, gain-tilt, and dispersion.
SUMMARY OF THE INVENTION
In view of the foregoing, there exists a need in the art for a simple UWB antenna that has an unbalanced feed, and can be arrayed in 1D and 2D on a single substrate (i.e., planar or conformal). Additionally, there is a need for a UWB antenna that is electrically small yet has low VSWR and allows the transmit and or receiving circuits to be integrated onto the same substrate to eliminate transmission line losses, dispersion, and ringing. Furthermore, there is a need for a UWB that can be mass-produced inexpensively.
Accordingly, an object of this invention is to provide a novel apparatus and system for providing an electrically small planar UWB antenna.
It is also an object of this invention to provide a novel apparatus and system for providing a UWB antenna that is inexpensive to mass-produce.
It is also an object of this invention to provide a novel apparatus and system for providing a UWB antenna that has a direct unbalanced feed that can interface to low-cost electronic circuits.
It is also an object of this invention to provide a novel apparatus and system for providing a UWB antenna that has a flat frequency response and flat phase response over ultra wide bandwidths.
It is also an object of this invention to provide a novel apparatus and system for providing a UWB antenna that exhibits a symmetric radiation pattern.
It is also an object of this invention to provide a novel apparatus and system for providing a UWB antenna that is efficient, yet electrically small.
It is also an object of this invention to provide a novel apparatus and system for providing a UWB antenna that integrates with the transmitter and receiver circuits on the same substrate.
It is also an object of this invention to provide a novel apparatus and system for providing a UWB antenna that is planer and conformal, so as to be capable of being easily attached to many objects.
It is also an object of this invention to provide a novel apparatus and system for providing a UWB antenna that does not require an active electronic means or passive means of generating and receiving balanced signals.
It is a further object of this invention to provide a novel apparatus and system for providing a UWB antenna that can be arrayed in both 1D and 2D, in which the array of UWB antennas are built on single substrate with the radiation directed in a broadside pattern perpendicular to the plane of the substrate.
These and other o
Phan Tho
Xtreme Spectrum, Inc.
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