WO2005013413A2 - Combined ultra wideband vivaldi notch/meander line loaded antenna - Google Patents

Abstract

A combination of aVivaldi slot (46) and a meander line loaded antenna (30) which exhibits an ultra wideband characteristic with de Vivaldi notch expanding the high end and with the meander line loaded antenna portion reducing the low frequency cut-off. When these antennas are arrayed, this array exhibits a single lobe and an ultra wide 100: l bandwidth. The Vivaldi notch portion of the antenna accommodates the higher frequencies, whereas the meander line loaded antenna portion of the antenna accommodates the lower frequencies, there being a smooth transition region between the Vivaldi and meander line portions of the antenna and no discontinuity. A polarity switchable embodiment (Figure 6A) and a concatenated embodiment (Figure 12) are also disclosed.

Description

COMBINED ULTRA WIDEBAND VIVALDI NOTCH/MEANDER LINE LOADED ANTENNA

CROSS REFERENCE TO RELATED APPLICATIONS This application claims rights from U.S. Patent Applications Serial No. 10/629,454; 10/629,500; and 10/629,659, all filed July 29, 2003. BACKGROUND OF INVENTION

1. Field of the Invention This invention relates to ultra wideband antennas, and more particularly to the utilization of a combined Vivaldi notch and meander line loaded antenna.

2. Brief Description of Prior Developments There has long been a requirement for a very wide band array antenna to cover, for instance, a band of 100:1 or even 300:1. The purpose of such an antenna is for any ultra wideband application in which one seeks to have a single lobe from the antenna array uncorrupted by so called grating lobes which are the spurious lobes which are the result of standing waves in the elements and element spacings greater than 0.5 wavelength. An array of bow tie elements suffers from grating lobes introduced by the many periods of oscillation in the element itself, and by the resulting large spacing of the elements. In order to eliminate the generation of multiple lobes, one would need some sort of traveling wave antenna with a width less than 0.5 wavelength at the highest frequency. One such traveling wave antenna is a Vivaldi notch antenna. The Vivaldi notch antennas are those which have exponentially tapered notches which open outwardly from a feed at the throat of the notch. Typically, in such a Vivaldi notch antenna there is a cavity behind the feed point which prevents energy from flowing back away from the feed point to the back end of the Vivaldi notch. As a result, in these antennas, one obtains radiation in the forward direction, and obtains a single lobe beam over a 10:1 frequency range. One can obtain a VSWR less than 3:1 with the beams staying fairly constant at about 80° or 90° beam widths. As can be seen, the Vivaldi notch antennas are single lobe antennas which have a very wide bandwidth and are unidirectional in that the beam remains relatively constant as a single lobe over a 10:1 bandwidth both in elevation and in azimuth. Note that a constant beam width is maintained because at high frequencies at the throat of the notch only a small area radiates. As one goes lower and lower in frequency, the wider parts of the notch are responsible for the radiating. As a result, the beam width tends to remain constant and presents itself as a single lobe. The Vivaldi notch antennas were first described in a monograph entitled The Vivaldi Aerial by P.G. Gibson of the Phillips Research Laboratories, Redhill, Surrey, England in 1978 and by Ramakrishna Janaswamy and Daniel H. Schaubert in IEEE Transactions on Antennas and Propagation, vol. AP-35, no.l, September 1987. The above article describes the Vivaldi aerial as a new member of the class of aperiodic continuously scaled antenna structures which has a theoretically unlimited instantaneous frequency bandwidth. This antenna was said to have significant gain and linear polarization that can be made to conform to constant gain versus frequency performance. One reported Gibson design had been made with approximately 10 dB gain and a minus -20 dB side lobe level over an instantaneous frequency bandwidth extending from below 2 GHz to about 40 GHz. One Vivaldi notch antenna is described in U.S. Patent 4, 853, 704 issued August 1, 1989 to Leopold J. Diaz, Daniel B. McKenna, and Todd A. Pett. The Vivaldi notch has been utilized in micro strip antennas for some time and is utilized primarily in the high end of the electromagnetic spectrum as a wide bandwidth antenna element. The problem with Vivaldi notch antennas is that at low frequencies, the notch becomes a short circuit. If one attempts to feed a short circuit at low frequencies, one obtains no output. There is therefore a necessity for providing an array antenna element which has the favorable characteristics of the Vivaldi notch antennas, yet is able to me made to operate at much lower frequencies. The problem, however, with making these antennas operate at much lower frequencies, is that as one goes lower in frequency, the antenna elements themselves become larger. When one attempts to array these elements, since the array elements are larger, their separation often exceeds a 0.5 wavelength. Separations over a 0.5 wavelength result in unwanted multiple lobes called grating lobes. It has been found that if one wants to avoid grating lobes, then the spacing between the antenna elements must be less than a 0.5 wavelength. It is therefore important to be able to fabricate an antenna with exceedingly small antenna elements so as to avoid the unwanted grating lobes while offering wideband performance.

SUMMARY OF THE INVENTION In order to obtain an ultra wideband antenna element for use in an array, in the subject invention, the Vivaldi notch antenna is combined with a meander line loaded antenna structure, such that for the higher frequencies, the Vivaldi notch dominates, whereas for the lower frequencies, the meander line loaded antenna functioning as a dipole provides a wide bandwidth low end for the antenna element. Because the meander line loaded structure reduces element size, this combination can be arrayed without producing grating lobes. In order to form the dipole necessary for the meander line loaded antenna, the Vivaldi notch antenna rather than being provided with a closed end cavity, is provided with the end cavity opened up with a rearward slot so that at the lower frequency range, the antenna element starts to look like a dipole. Since the feed point is no longer shorted out at the lower frequencies, the result is that one has a fairly fat dipole. The problem with such an arrangement is how to make the dipole work over a 10:1 frequency range of its own accord. In order to do so, one utilizes the meander line loaded antenna structure to make the dipole work over a wide bandwidth by canceling out reactances at the low end of the frequency range. Such operation is described in U.S. Patent Application Serial No. 10/123,787 filed April 16, 2002 by John T. Apostolos entitled "Method and Apparatus for Reducing the Low Frequency Cut-off of a Meander Line Loaded Antenna", assigned to the assignee hereof and incorporated herein by reference. In one embodiment, the antenna is provided with a Vivaldi notch in an upper plate which is bifurcated down its length. Two side plates vertically depending downwardly from respective top plates and are spaced from the top plates at either edge. The side plates are coupled to the top plate through a meander line structure, the purpose of which is to cancel reactances. The result is an overall ultra wideband structure that is small. When this structure is arrayed, the resulting structure does not violate the restriction that the spacing between the elements not be greater than a 0.5 wavelength at the highest frequency. This means that the arrayed antenna elements will exhibit no grating lobes across the entire ultra wideband range, and results in an ultra wideband single lobe antenna array. It has been found that by combining the two technologies, namely the Vivaldi notch antenna and the meander line technology, that at the high frequency the Vivaldi notch is the active radiator, which doesn't see the meander line at all. At the higher frequencies, the gap on the top plate is not seen, and the Vivaldi notch works as it would work normally at the higher frequencies. As the operating frequency gets lower and lower, the dipole begins to come into play, and the Vivaldi notch becomes less prominent. There is a transition region in which the notch and the dipole are now equally radiating. However, as one goes lower in frequency, the notch is not seen, and one simply is left with the dipole augmented with the meander line structure. The meander line structure is utilized to give the dipole the increased bandwidth by canceling out the reactances at the low end of the frequency band. This gives an exceptionally good match down to the very low frequencies. As part of this invention, it has been found that the transition region between the Vivaldi notch and the meander line loaded antenna is smooth, and that there is no discontinuity. The result is that one can provide that the antenna work over a 50:1 frequency range. When one seeks to put these elements in an array, the separation of the elements is not more than a 0.5 wavelength at the highest frequency, thus eliminating the possibility of creating grating lobes. If the spacing were for instance to become more on the order of a wavelength, one would obtain the undesirable multi-lobe pattern. It has been found that the subject antenna when arrayed can work over a range of 50 MHz and 1500 MHz. Note that the spacing of the elements is less than a 0.5 wavelength at the highest frequency. As one goes down to 1/50* of the highest frequency, then the 0.5 wavelength divided by 50 is .01 wavelengths at the low end of the frequency spectrum for the element. Thus for low frequencies, the spacing requirement is overly met, whereas at the highest frequencies the spacing requirement is just met. It will be appreciated that for an effective radiator, it is the volume of the structure which counts. Even though the element at the lowest frequency is very narrow, one nonetheless obtains volume in the longitudinal direction or axis of the antenna element. When the antenna elements are arrayed, one also obtains height and depth so that the total volume is such that it is still efficient at the low end of the frequency spectrum, even though its lateral dimension is .01 wavelengths in width. It will be appreciated that that the utilization of the Vivaldi notch along with the meander line loaded antenna configuration means that the elements are so small in the width direction that when the elements are arrayed, grating lobes are prevented from being generated. If one were going to use some other technology in order to work over a frequency range of 100:1, one could presumably use bow tie structures. However, at the lowest frequency of operation of a bow tie, one would have at least l/10^th of a wavelength which means that if one wanted to go up to 100:1 in frequency, then the structure at the high frequency would be 10 wavelengths long, resulting in a severe multi-lobe pattern. It has been found that the only other antenna element that could work is the meander line itself, but the meander line itself only works over a frequency range of approximately 5-7:1. It does not achieve the 100:1 frequency range that is required. Absent combining with a Vivaldi notch nearly using meander line structures will not yield an ultra wideband result. Providing a single lobe ultra wideband antenna is useful in ultra wideband authorization for wireless as well as other applications. In these applications, one does not want to have spurious side lobes or multiple lobes. Ultra wideband applications such as for instance covert communications, high data rate communications, burst communications, through-the-wall communications, ground-penetrating radar, and others, involve the sweeping of a frequency of, for instance, between 1.5 GHz and 100 GHz. Using the subject invention, one is now able with the combined Vivaldi notch and meander line structure to achieve an ultra wideband result. When arrayed, these antenna elements can be made to have a single lobe characteristic. One can therefore provide an antenna array whose elements are compact and whose spacing between the elements is less than a 0.5 wavelength. In summary, the combination of a Vivaldi slot and a meander line loaded antenna is provided which exhibits an ultra wideband characteristic with the Vivaldi notch expanding the high end and with the meander line loaded antenna portion reducing the low frequency cut-off. When these antennas are arrayed, this array exhibits a single lobe and an ultra wide 100:1 bandwidth. The Vivaldi notch portion of the antenna accommodates the higher frequencies, whereas the meander line loaded antenna portion of the antenna accommodates the lower frequencies, there being a smooth transition region between the Vivaldi and meander line portions of the antenna and no discontinuity. In one embodiment, the antenna is made to work between 50 MHz and 1500 MHz with a VSWR less than 3:1. The Vivaldi notch meander line combination assures that for an array one does not have a separation of the elements more than a 0.5 wavelength at the highest frequency, thus to eliminate the possibility of creating grating lobes. As one goes down in frequency to 1/50 of the highest frequency, the 0.5 wavelength is divided by 50. This means that antenna element spacing is .01 wavelength at the low frequency end, clearly below that separation which would cause grating lobes. In short, the generation of grating lobes at the high end is prevented because the antenna element spacing is less than a 0.5 wavelength, with the situation improving as one goes down in frequency. BRIEF DESCRIPTION OF THE DRAWINGS These and other features of the subject invention will be better understood in connection with the Detailed Description in conjunction with the Drawings, of which: Figure 1 is a top view of a Vivaldi notch antenna illustrating the feed point at the throat of the notch and a cavity to make the antenna unidirectional; Figure 2 is a diagrammatic representation of the subject combined Vivaldi notch, meander line loaded antenna configuration, illustrating that the width of the antenna is minimized due to the meander line loaded antenna portion thereof; Figure 3 is a graph of VSWR for the combined Vivaldi/MLA ultra wideband antenna, illustrating a VSWR less than 3:1; Figure 4 is a diagrammatic illustration of a prior art meander line loaded antenna illustrating triangular shaped top plates connected to side plates via a meander line; Figure 5 is a diagrammatic illustration of the reconfiguring of the top plates of the meander line loaded antenna of Figure 4, illustrating dual Vivaldi notches with the feed point being at the closest approximation of the Vivaldi notches, thus to provide a combined Vivaldi notch and meander line loaded antenna configuration which is bidirectional; Figure 6A is a diagrammatic illustration of the modification of the combined Vivaldi notch and meander line loaded antenna of Figure 2 to permit switching between dual polarizations through the selective application of different feeds to the feed points thereof, indicating a square horn configuration; Figure 6B is a block diagram of the processing unit of Figure 3A showing the generation of the various polarizations; Figure 7 is a mode table indicating the signals applied to the various feed points of the antenna of Figure 6A, indicating the ability to switch from vertical polarization, to horizontal polarization, to right hand circular polarization, and to left hand circular polarization; Figures 8A, 8B and 8C are front, top and side views of the dual polarity antenna of Figure 3, illustrating the placement of the meander lines internal to the horn structure; Figure 9 is a graph of horizontal/vertical polarization port isolation from 50 MHz to 2500 MHz; Figure 10 is a graph illustrating the gain of the antenna of Figure 6A versus frequency; and Figure 11 is graph showing the cross polarization isolation for the antenna of Figure 6A. Figure 12 is diagrammatic representation of the concatenation of two side-by-side combined Vivaldi notch/meander line loaded antennas, illustrating the side-by-side position of the antennas such that the right hand side plate of one antenna is shared as the left hand side plate of the adjacent antenna; Figure 13 is a cross-sectional view of the concatenated antennas of Figure 5, illustrating a single sheet or plate used between the two antenna elements which are concatenated, also showing the utilization of meander lines to connect top plates to the shared side plate; Figure 14 is a top view of the concatenated antenna of Figure 13, illustrating the single shared side plate; Figure 15 is an exploded view of the concatenation of four antenna horns each having a top plate, opposed side plates, and a bottom plate, with the plates configured in a combined Vivaldi notch, meander line loaded antenna configuration; Figure 16 is a diagrammatic representation of the concatenation of the horn elements of Figure 8 into an array, with the array formed thereby coupled by a combiner; Figure 17 is a cross-sectional diagrammatic illustration of the array of Figure 16, illustrating the feed points for the various Vivaldi notch/MLA components of the array, denoting the feed points as 1H-6H and 1V-6V; Figure 18 is a diagrammatic illustration of the utilization of two six-way combiners and a 90° hybrid combiner to provide the array with a horizontal polarization, a vertical polarization, and both right hand and left hand circular polarizations; Figure 19 is a diagrammatic illustration of four of the elements in a 12 element array, illustrating the control of the elevation angle through appropriate phasing of the feeds to these elements; Figure 20 is a diagrammatic illustration of a four element concatenation, illustrating the meander lines between the elements, also indicating the size of the combined elements in one embodiment; and, Figure 21 is a series of antenna patterns measured for the array of Figure 20, showing X-Y plane patterns at 50 MHz, 100 MHz, 200 MHz, 400 MHz, 800 MHz, and 1600 MHz.

DETAILED DESCRIPTION Referring to Figure 1, a Vivaldi notch waveguide antenna 10 is illustrated as having an aperture 12 which is formed by exponentially shaped edges 14 in a plate 16. The antenna has a pair of feed points 18 which are adjacent the region of closest approximation of edges 14. Behind the feed point is a cavity 20, the purpose of which is to reflect back any rearwardly projecting radiation out through the notch which is defined by edges 14. The notch is therefore established by these edges as notch 22. Note that the E-field for the Vivaldi notch antenna Figure is as illustrated by arrow 24. As mentioned hereinbefore, it is a feature of the Vivaldi notch antenna that its upper frequency cut-off is virtually unlimited. Thus it is typical for the Vivaldi notch antennas to operate from for instance from 100 MHz up to 10-20 GHz. While this wide bandwidth operation is desirable, in some instance, the low frequency cut-off of such a Vivaldi notch antenna is restricted due to the fact that as one descends lower and lower in frequency, the feed is looking into a dead short. The result is no effective radiated energy below 100 MHz. As part of the subject invention, and in an effort to decrease the low frequency cutoff of the antenna Figure 1, referring now to Figure 2, a combined Vivaldi notch/meander line loaded antenna structure 30 is illustrated as having bifurcated top plates 32 and 34, with the top plates having exponentially shaped edges respectively at 36 and 38. The feed points 40 and 42 are at the points of closest approximation of edges 36 and 38, with a cavity 44 formed behind the feed points. In an effort to lower the low frequency cut-off of the Vivaldi notch antenna, the top plate is bifurcated as illustrated so as to leave a slot 46 between the plates aft of cavity 44. What this does is to provide the opportunity for forming a dipole antenna having a low frequency cut-off much lower than that associated with the Vivaldi notch portion of the antenna. In order to complete the meander line loaded proportion of the antenna, downwardly depending side plates 50 and 52 are coupled to associated top plates 32 and 34 through meander lines 54 and 56 respectively. Each of the meander lines has an upstanding portion 58, a laterally projecting portion 60, a downwardly depending portion 62, and a folded back portion 64 attached at its distal end to an edge of plate 34, with the folded back portion being electrically insulated from the respective plate by an insulating layer 66. Note that in one embodiment for a 50 MHz to 1500 MHz antenna the width 70 of the combination is 4 inches and the width 71 of the side plates is 4 inches. It is the purpose of the meander line loaded structure to reduce the overall physical size of the dipole section of this antenna while at the same time decreasing the low frequency cut-off of this section by effectively canceling the reactance. Thus, as the operating frequency of the antenna decreases, the reactance cancellation results in a VSWR of less than 3:1 down to, for instance in one embodiment, 50 MHz, and in some instances, down to 30 MHz. It is the finding of the subject invention that the operation of the Vivaldi notch is not affected by the dipole portion of the antenna and as such the top or high frequency cutoff is unaltered by the meander line structure. On the other hand, it has been found that low frequency cut-off of the combined structure is that associated with the meander line loaded antenna portion. Additionally, it has been found that the transition between low frequency and high frequency is smooth, and that there are no discontinuities in operation as one goes from a lower frequency to a higher frequency. At the higher frequencies, it is the Vivaldi notch portion of the antenna which is active, whereas at the lower frequencies, it is the meander line loaded antenna dipole which is active. Moreover, the width of the antenna as illustrated by double ended arrow 70 is indeed minimized by virtue of the meander line loaded antenna structure, it being noted that the meander line loaded structure is in general utilized to provide miniaturization for antennas by reducing the overall size of the antennas involved. In terms of the antenna pattern from the antenna of Figure 2, it is desirable to have a single lobe uncorrupted by multiple lobes when the antennas are arrayed. As mentioned hereinbefore, it is important that at the highest frequency of operation, the width 70 be no greater than 0.5 wavelengths. The width reduction due to the meander line loading antenna portion satisfies this requirement up to and including 1.5 GHz. As can be seen from Figure 3, the VSWR of a combined Vivaldi/MLA ultra wideband antenna is less than 3:1 from a low frequency of 30 MHz up to a high frequency of 1.5 GHz. From a theoretical point of view, and referring now to Figure 4, a meander line loaded antenna in the past has been comprised of two triangular plates 80 and 82 and two corresponding side plates 84 and 86, joined to the top plates by meander lines 88 and 90. The E-field is noted by arrow 92. As described in the afore-mentioned patent application, this structure has achieved a 10: 1 bandwidth and can be made to have a low frequency cut-off as low as 30 MHz. In considering how to design a combined Vivaldi notch and meander line loaded antenna structure, and referring now to Figure 5, top plates 80' and 82' are configured with edges 102 and 104 which have the Vivaldi notch structure, namely that the edges have an exponential curve. In this case, meander lines 88 and 90 are the same as those shown in Figure 4, with the feed points 106 and 108 being closest approximation of the two curves 102 and 104. This type of antenna structure has an ultra wideband characteristic that rather than being unidirectional, is bidirectional. While this antenna is useful for some bidirectional purposes, in order to achieve the end firing unidirectional single lobe of that described in accordance with Figure 2, the rearward portion of the Vivaldi notch is eliminated in favor of slot 46 of Figure 2, with the antenna of Figure 5 being provided the cavity of 44 of Figure 2 to generate the end firing characteristic desired. In this manner, the meander line loaded antenna of Figure 4 is combined with the Vivaldi notch antenna of Figure 1 so as to arrive at the configuration shown in Figure 2 which delivers a single lobe forwardly firing ultra wide bandwidth antenna. Switchable Polarization Referring now to Figure 6A, what is now presented is the manner in which the antenna of Figure 2 can be modified in order to provide a structure which enables switching between linear and circular polarizations. Here a square cross-sectioned horn structure 80 has a top plate 82 which is identical to the plates 32 and 34 of Figure 2. However, the side plates, rather than being of the type illustrated at 50 and 52 in Figure 2, are configured themselves to carry a Vivaldi notch. Thus, side plate 84, which is duplicated on the other side at 86, is shown to have the same type of Vivaldi notch defined by edges 88 and 90 as are in top plate 82. Here these edges carry reference characters 88' and 90', with the edges in side plate 86 having an edge 88" and edge 90". Note that sides 84 and 86 are orthogonal to top plate 82 which, inter alia, has a cavity 92 and bifurcation slot 94 therein. This cavity and slot configuration is duplicated in the two side plates and in the bottom plate of the antenna now to be described. It is noted that a bottom plate 100 is utilized to complete the horn structure, with the Vivaldi notch therein defined by edges 88'" and 90'". For convenience, the feed points for side plate 86 are designated A, for top plate 82 are designated B, for side plate 84 are designated C, and for bottom plate 100 are designated D. It is these feed points, when appropriately connected to a processor 101 that provide for a vertical polarization, a horizontal polarization, a right hand circular polarization, or a left hand circular polarization. What will be apparent from looking at the square horn structure of Figure 6A is that a Vivaldi notch/MLA structure is substituted for the usual side plate in a linearly polarized Vivaldi notch MLA antenna. Moreover, what will be noticed is that meander line structures, here shown in dotted outline at 102, 104, and 208, couple the respective Vivaldi notch-bearing plates to their side plates. Note, the coupling between side plate 86 and bottom plate 100 is accomplished by meander line structure 106. Referring to Figure 6B, processor 101 of Figure 6A may include a linear combiner 103 having as inputs feed points B and D to provide a horizontal polarization for the antenna of Figure 6A. As to vertical polarization, a linear combiner 105 has inputs from feed points A and C of the antenna of Figure 6A, thus to give the antenna a vertical polarization characteristic. If one wants to provide the antenna with either a right hand circular polarized or a left hand circular polarized characteristic, then the outputs of combiners 103 and 105 are applied to a quadrature hybrid combiner 107 with the outputs thereof being right hand circularly polarized and left hand circularly polarized. The processing of Figure 6B is the processing for a receive mode, in which the antenna is given switchable polarization characteristics in accordance with the mode table of Figure 4 to be described hereinafter. Note, however, that processing 101 can be operated in reverse to provide a switchable polarization characteristic for transmission, with the combiners operating in a bidirectional fashion, given the connections illustrated in the mode table. Referring to Figure 7, in the case of transmission, what can been seen from the mode table is that if one wishes to give the antenna of Figure 6A a vertical polarization, then one couples combiner 101 to feed points A and C in-phase, and does not couple the combiner to points B and D at all. If one wishes to provide the antenna of Figure 3A with a horizontal polarization, then one couples combiner 101 to points B and D and drives points B and D with in-phase signals, leaving feed points A and C devoid of input signals. For a right hand circular polarized result, combiner 101 drives feed points A and C with in-phase signals, and drives feed points B and D with -90° out of phase signals, whereas for a left hand circular polarization result, one likewise drives feed points A and C with in-phase signals, but rather provides feed points B and D with +90° phase shifted input signals. Referring to Figures 8A, 8B, and 8C, what will be seen is that a cross-section of the antenna of Figure 8B along dotted line 5B, results in a cross-section clearly showing the placement of the meander line structures 102-108 interior of the horn. As will be appreciated, it is the purpose of the meander line structures to complete the dipole portion of the combined antenna. Moreover, it is been found that the particular placement of the meander lines is not particularly critical, although the symmetric pinwheel type arrangement shown in Figure 8B provides a preferred antenna configuration. Referring to Figure 9, a horizontal vertical port isolation graph indicates that from 50 MHz to 2500 MHz, the isolation is quite good. Referring to Figure 10, a gain graph is presented which shows that the gain for the ultra wideband antenna of Figure 6A over a ground plane, goes from about -7 dBI at 50 MHz, all the way up to a 15 dBI gain at 2500 MHz. Referring to Figure 11, a graph is shown of cross-polarization isolation, which is about half the port to port isolation and therefore represents the fact that there is minimal interference between the ports of the antenna of Figure 6A. Concatenation Referring to Figure 12, concatenation of two horizontally disposed adjacent elements is provided for the purpose of decreasing the low frequency cut-off of the array by increasing the size of the array at low frequencies. Here a left hand combined Vivaldi notch/MLA element 200 is to be concatenated with a right hand element 202 of like configuration. As will be seen, element 200 has a bifurcated top plate 203, side plates 204 and 206, and meander lines 208 and 210 which couple respectively side plates 206 and 204 to the bifurcated top plate. Each of the top plates includes exponentially shaped notch edges 212 and a cavity 214 at the throat of the notch, along with a slot 216 rearward of cavity 214. Element 202 is like configured, having an identical top plate 203, a left side plate 220, and a right side plate 222. Side plate 220 is coupled to top plate 203 by a meander line 224, whereas side plate 222 is coupled to top plate 203 by meander line 226. As illustrated, the rest of the elements in top plate 203 are identical between elements 200 and 202. The feed point for element 200 is illustrated at 230, whereas the feed point for element 203 is illustrated at 232. In order to process the feed points either to address them or to couple them out, a combiner 240 is utilized. This combiner is a bidirectional combiner such that it may be used to provide a phasing of the array of these two elements either from a receive mode point of view or a transmit mode point of view. It is the purpose of the concatenation to provide, at least at the lower frequencies, a single antenna element having double the width of the single elements themselves. While it is possible merely to electrically attach side plate 206 to side plate 220, as shown in Figure 13 one may use or substitute a single plate 242 for plates 206 and 220 of Figure 12. The meander lines coupling together top plates 203 with adjacent side plates 204 and 220, are as illustrated, namely meander lines 210 and 224. Referring to Figure 14, as can be seen the top view of the concatenated two elements, like elements have like reference characters with respect to Figures 12 and 13. What will be appreciated is that plate 242 is shared by elements 200 and 202, such that the elements 200 and 202 are connected together. The connection together of the two side-by-side elements at the lower frequencies produces a single element having a width which is twice that of the elements acting independently. As mentioned hereinbefore, the elements act independently at the higher frequencies, but at the lower frequencies, act as one element. This means that the low frequency cut-off of the concatenated elements may be decreased by the amount of increase of the width due to the concatenation. Referring to Figure 15, an array of elements such as that illustrated in Figure 6A may be fabricated by concatenating the square horn shaped elements both in a horizontal and in a vertical direction. Here the upper left most element is designated 80', the upper right most element is designated 80", the lower left element is 80'", and the lower right 80"". The plates which are shared between the elements are plates 243 and 245 for elements 80' and 80", and plates 244 and 246 for elements 80'", and 80"" for the horizontal concatenations. For the vertical concatenations, plates 248 and 250 of elements 80' and 80'" are shared, whereas plates 252 and 254 are the shared plates between elements 80" and 80" " . The concatenation of the four hom antennas into a quad array provides four times the lineal length of antenna, and therefore even further decreases the low frequency cut-off of the array, to for instance, as little as 20 MHz, with the remainder array going up to 1.5 GHz without grating lobes, and beyond if grating lobes are tolerable. Referring to Figure 16, the array achieved by the concatenation of four Vivaldi notch/MLA horns, is illustrated in which the feed points of the various Vivaldi notch/meander line loaded antennas are coupled to a combiner 260, with combiner 260 combining the outputs of the twelve feed points involved. Referring to Figure 17 in cross-section, the feed points for the concatenated array of Figure 16 are labeled 1H, 2H, 3H, 4H, 5H, 6H, IV, 2V, 3V, 4V, 5V, and 6V. The shared plates for the concatenated antennas are illustrated at 270, 272, 274, and 276, with meander lines 280-312 being interposed between the respective plates of the various antenna elements. Referring Figure 18, combiner 260 may include a six-way horizontal polarity combiner 320, and a six-way vertical polarization combiner 322, the outputs of which are coupled to a 90° hybrid combiner 324. The output of the horizontal polarity combiner is illustrated as H, whereas the output of the vertical polarization combiner 322 is illustrated as V. These outputs may be utilized independently to give the antenna array a horizontal or vertical polarization. Alternatively, right hand circular polarization and left hand circular polarization is available at the output of combiner 324, it being understood that the combiners are bidirectional, such that in the transmit mode, the desired transient polarization may be achieved. Having described how the antenna may be phased, referring to Figure 19, the concatenated elements, here illustrated at 1, 2, 3, and 4 can be provided with a major lobe that exits at an elevation angle 340, with the four element concatenations of Figure 20 providing a single lobe given array dimensions of four inches by sixteen inches. It will be appreciated that one has a circular lobe in the X-Y plane. How this lobe varies with frequency is shown in Figure 21, in which the array patterns are respectively 352 at 50 MHz, 354 at 100 MHz, 356 at 200 MHz, 358 at 400 MHz, 360 at 800 MHz, and 362 at 1600 MHz. What can be seen is that in the X-Y horizontal azimuth plane for the array, the array pattern is close to circular at the lower frequencies, and has modified lobes in the end-fire direction illustrated by arrow 366, all the way up to through 1600 MHz. While the subject invention has described concatenation in terms of the arraying of four horns together to provide the array, it will be appreciated that the concatenated array elements can be multiplied as desired for an array of any desired size. Thus while the quad configuration represents the process of arraying four Vivaldi notch/meander line loaded antenna elements, arrays of hundreds of such elements is within the scope of the subject invention. Having now described a few embodiments of the invention, and some modifications and variations thereto, it should be apparent to those skilled in the art that the foregoing is merely illustrative and not limiting, having been presented by the way of example only. Numerous modifications and other embodiments are within the scope of one of ordinary skill in the art and are contemplated as falling within the scope of the invention as limited only by the appended claims and equivalents thereto.

Claims

WHAT IS CLAIMED IS:

1. An ultra wideband antenna comprising: a combined Vivaldi notch antenna and a meander line loaded antenna.

2. The antenna of Claim 1, wherein the Vivaldi notch antenna dominates for a high frequency range of said antenna and wherein the meander line loaded antenna dominates for a continuous low frequency range of said antenna, the change over between high and low frequencies being smooth and without discontinuities.

3. The antenna of Claim 2, wherein said antenna includes a top plate having a Vivaldi notch at one end thereof, said Vivaldi notch having a throat, a cavity behind said throat, a slot behind said cavity, and side plates to either side of said top plate, said side plates each including a meander line for coupling the side plate to a portion of said top plate to a side of said slot.

4. The antenna of Claim 3, wherein the physical size of said antenna is minimized by said meander lines, thus to permit arraying of said antennas without producing grating lobes.

5. The antenna of Claim 4, wherein the width of said top plate is less than 0.5 wavelengths at the highest frequency at which said antenna is to operate.

6. The antenna of Claim 1, wherein said antenna is linearly polarized.

7. The antenna of Claim 3, wherein said meander lines are coupled to exterior surfaces of said plates.

8. A method of extending the operating frequency range of a Vivaldi notch antenna, coupling the steps of: providing the Vivaldi notch antenna with a rearwardly extending slot from the throat thereof, and providing a meander line loaded antenna having at least one side plate coupled to said Vivaldi notch antenna by the meander line thereof, whereby a combined Vivaldi notch and meander line loaded antenna is formed with the Vivaldi notch extending the high frequency cut-off of the antenna and with the meander line loaded antenna extending the low frequency cut-off of this antenna, thus to provide an ultra wide bandwidth antenna.

9. The method of Claim 1, and further including the step of providing a cavity between the throat of the Vivaldi notch and the slot, thus to provide an end fire antenna.

10. The method of Claim 9, wherein the Vivaldi notch is provided in a plate having a width less than 0.5 wavelengths at the high frequency cut-off of the antenna, thus to preclude the generation of grating lobes when said antenna is arrayed with other Vivaldi notch/meander line loaded antennas.

11. A polarity switchable combined Vivaldi notch/meander line loaded antenna, comprising: a top plate having a Vivaldi notch antenna therein; a pair of side plates each having a Vivaldi notch therein; a bottom plate having a Vivaldi notch therein, each of said Vivaldi notches having a throat and a feed point at said throat; meander lines electrically connecting adjacent plates together and; a processor coupled to selected feed points for selectively providing said antenna with a horizontal polarization, a vertical polarization, a right hand circular polarization or a left hand circular polarization.

12. The antenna of Claim 11, wherein each of said plates has a slot extending rearwardly of said Vivaldi notch.

13. The antenna of Claim 12, wherein adjacent edges of said plates are spaced apart.

14. The antenna of Claim 13, wherein said meander lines bridge respective spaced apart plates.

15. The antenna of Claim 12, and further for each plate including a cavity interposed between the throat of a Vivaldi notch and the associated slot, thus to provide an end-fire antenna.

16. The antenna of Claim 11, wherein said processor includes a linear combiner and a quadrature hybrid combiner coupled thereto.

17. The antenna of Claim 16, wherein the feed for said top plate is denoted B, wherein the feeds for the side plates are respectively denoted A and C, and wherein the feed for the bottom plate is denoted D and wherein the mode of operation of said antenna as determined by said processor is:

18. The antenna of Claim 11, wherein said plates form a retilinear horn, and wherein said meander lines are carried internal to said plates.

19. The antenna of Claim 18, wherein said meander lines are arrayed in a symmetric pattern.

20. The antenna of Claim 19, wherein said symmetric pattern includes a pedal pattern.

21. The antenna of Claim 20, wherein said meander lines point around a cross- sectioned horn periphery in the same direction.

22. Apparatus for decreasing the low frequency cut-off of a combined Vivaldi notch/meander line loaded antenna, comprising: an array of concatenated Vivaldi notch meander line loaded antenna elements, each of said elements having at least one plate coupled to an adjacent plate by a meander line, adjacent elements having adjacent plates electrically coupled together, whereby at low frequencies the adjacent antenna elements function as one larger element having a low cutoff frequency lower than that associated with the adjacent elements separately.

23. The apparatus of Claim 22, wherein said adjacent plates have a single plate substituted therefor.

24. The apparatus of Claim 22, wherein each of said plates includes therein a Vivaldi notch having a throat and a slot to the rear of said throat.

25. The apparatus of Claim 24, wherein each of said plates has a cavity interposed between the throat and the slot therein.

26. The apparatus of Claim 22, wherein two of said elements are concatenated, thus to decrease said low frequency cut-off by the increased size of the array over a single one of said elements.

27. The apparatus of Claim 22, wherein four of said elements are concatenated.

28. The apparatus of Claim 27, wherein the low frequency cut-off of said array is below 20 MHz.

29. The apparatus of Claim 22, wherein each of said elements have an ultra wide bandwidth.

30. The apparatus of Claim 29, wherein said array exhibits a single lobe end-fire pattern.

31. The apparatus of Claim 30, wherein the high frequency cut-off of said array is in excess of 1.5 GHz.

32. The apparatus of Claim 30, wherein the high frequency cut-off is below that frequency at which grating lobes are unacceptable.

33. The apparatus of Claim 30, wherein the high frequency cut-off is below that frequency at which grating lobes exist.

34. A method for reducing the low frequency cut-off of a combined Vivaldi notch/meander line loaded antenna comprising the step of: concatenating a number of adjacent Vivaldi notch/meander line loaded antenna elements such that at low frequencies the elements act as one element.

35. The method of Claim 34, wherein said concatenated elements form an array.

36. The method of Claim 34, wherein the elements have plates and wherein the concatenation step includes providing that adjacent elements share a plate.

37. The method of Claim 34, wherein the elements have plates and wherein the concatenation step includes the step of electrically connecting plates of adjacent elements.

38. The method of Claim 34, wherein the elements have plates and wherein selected ones of said plates have therein a Vivaldi notch having a throat and a slot communicating with the notch and running aft of the notch.

39. The method of Claim 38 and further including a cavity interposed between the notch and the slot.

40. The method of Claim 38, wherein each of the plates have therein the Vivaldi notch and the slot.

41. The method of Claim 34, wherein the low frequency cut-off is below 20 MHz.

42. The method of Claim 34 and further including the steps of providing the concatenated elements with a selectable polarity characteristic.

42. The method of Claim 34, wherein the polarity characteristic is selected from the group consisting of horizontal, vertical, left hand circularly polarized and right hand circularly polarized polarities.

44. The method of Claim 35, wherein the array is steerable.

45. The method of Claim 34, wherein at the higher frequencies each of the concatenated elements operates independently.

46. The method of Claim 43, wherein at the higher frequencies there is significant isolation between horizontal and vertical polarization.