Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Reexamination Certificate
2001-11-01
2003-12-09
Blum, Theodore M. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
C342S428000, C342S434000, C342S374000
Reexamination Certificate
active
06661378
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to antennas and, more particularly, to direction finding or radiolocation antennas and methods of radio direction finding as well as to radio tracking and radiolocation systems in general and to scanning for target signals within a band of frequencies.
Radio tracking, direction finding or radiolocation apparatus and technology are used for military and civilian uses, including for military and civilian rescue missions, military and security control and tracking and radiolocation missions, military and civilian police operations and for various other purposes where one desires to both quickly and precisely respond to targets or other sources of radio frequency (RF) and to pinpoint their location or their precise bearing relative to RF receiving apparatus.
Heretofore, there have been many antenna configurations and radio direction finding and radiolocation techniques and systems using specialized antennas. Chief among the requirements in the design of such devices and systems is that of accuracy in direction finding. In azimuthal direction finding, it is desired to identify with precision the azimuthal direction to a source of RF energy. When triangulation of RF sources is used for radiolocation of such sources, accuracy can be increased substantially. As used for emergency location, as in the radiolocation of downed aircraft, obtaining azimuth bearings to an RF source from different locations enhances the likelihood of successful location. But in combat situations, where a downed airman may be unable to transmit for long periods, whether by reason of avoiding detection by hostile forces or because of limited transmitting power reserve, or in high security operations including clandestine tracking missions where decreasing length of transmitting time reduces risk of detection by those engaged in possible criminal activities, so that the time of transmission necessarily must be limited and speed of responding by tracking, direction finding or radiolocation system must be rapid.
It will thus be evident that increasing the speed of detection of a tracking, direction finding or radiolocation finding antenna system allows marked reduction in the time of transmission required for transmitting.
In a context in which there must be tracking, direction finding or radiolocation of multiple targets, increasing the speed of detection of a direction finding antenna system opens the possibility to determining the direction and location of greater numbers of multiple targets.
In the United States, regulatory requirement for cellular telephone system user location for emergency purposes has been established. Regulations have been promulgated by licensing authority functions of government which, in effect, impose on operators of cellular telephone systems a requirement that cellular systems provide capability for location of cellular users making use of such cellular systems.
In such situations, it is desired to carry out radiolocation with extreme speed, yet without diminution in accuracy.
Heretofore, radio direction finding as been carried out by a multitude of techniques, including amplitude nulling, signal comparison, and by triangulation methods as well as by IFF (from the term, Identify Friend-Or-Foe) protocols, as have been employed for many decades, as secondary radar co-aligned with primary radar in air commerce and as also extensively long used in military applications, coupled with the use of transponders which return encoded and/or encrypted signals, and which may employ digital protocols, in response to transmitted interrogation signals.
Many antenna arrays and configurations such as Yagi-Uda arrays and log-periodic or quasi-log-periodic arrays are known which have useful forward gain and directivity can be employed for receiving or transmitting signals relative to a known direction but their use heretofore has typically involved the use of arrangements for rotating such arrays, whether used alone, or in stacked configuration, or in phased relation, so as to selectively physically orient the array or arrays as by beam or mast rotation. Such physical orientation of arrays is not conducive to high-speed radiolocation, radio direction finding or scanning.
It has also been known to use so-called curtain antennas, which may include phased elements with selectively switchable reflectors to allow beam alignment, but the physical limitations and lack of mobility of such curtain antennas conducive to economical, highly mobile, field-usable, broadband high-speed radiolocation, radio direction finding or scanning.
Phased arrays have also been used extensively for radar, being particularly useful for target acquisition and tracking in military and aircraft uses, particularly at gigahertz frequencies, but the complication, cost and control complexity of such arrangements are typically not well-suited for cost-effective, readily portable or mobile, field-usable, broadband high-speed radiolocation, radio direction finding and scanning and particularly in VHF bands and low UHF bands.
Log-periodic antenna configurations and theory are of particular interest for adaptation to the presently inventive array, as log-periodic (LP) antenna structures offer the promise of wide frequency range if not frequency-independent (FI) consideration over a wide range of frequencies. Log-periodic antenna (LPA) theory and design is well-treated in the literature, and the characteristics of LPA constructions and quasi-log-periodic (QLP)variations thereof are succinctly and elegantly treated in P. E. Mayes,
Proc. IEEE,
vol. 80, no. 1, January 1992 (“Mayes” herein). In this important paper, portions of which originally appeared in Y. T. Lo and S. W. Lee,
Antenna Handbook, Theory, Applications, and Design.
New York: Van Nostrand Reinhold, 1988, cited infra. Prof. Mayes cautions that the term frequency-independent (FI) is reserved for antennas that have no theoretical limitation on the bandwidth of operation. He observes that, practically, for such antennas performance cannot be even approximately constant for all frequencies for, as he points, out, there are physical bounds that limit the band over which the performance can be held almost constant. He observes that between the band limits the performance varies in a manner periodic with the logarithm of the frequency, so that these antennas are often called logarithmically periodic or log-periodic (LP) antennas. To be considered FI, Dr. Mayes instructs that for such antenna structures variation with frequency of all pertinent measures of electrical performance must be negligible between band limits that can be very widely spaced, even 100:1 or more. However, he points out that useful performance over a narrower, although very broad, band may be achieved after relaxing some structural requirements related to true frequency independence, adding that in some cases the resulting antennas perform the same as true FI antennas, but only over a limited bandwidth that cannot be easily extended. In other cases, he observes that performance may be noticeably affected by changing frequency over the operating band. These changes may not be deleterious, he allows, noting that they may even be advantageous in certain applications. Antennas with minor departures from the geometric requirements for FI performance are denoted by Mayes as being sometimes called quasi-log-periodic (QLP).
In the presently disclosed system, novel log-periodic antenna printed circuit structures are employed for forming an active high density multi-element antenna system of the invention, wherein elements formed in the array may be considered to be in sets of elements within the array, and where the elements specifically in dipolar form oriented for vertical polarization, but insofar as the number of elements, geometry, spacing, and relation to other elements within the array as well as in relation to electrical isolation elements within the array, constitute deliberate departures from true FI configuration, being suited for operation o
Blum Theodore M.
Gilster Peter S.
Greensfelder Hemker & Gale, P.C.
Locus Technologies, Inc.
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