Patent Description:
Passive, cavity-backed, sinuous and log-periodic antennas typically have a ~ <NUM>:<NUM> bandwidth and require larger sizes to go to lower frequencies. These incorporate baluns and impedance matching networks to arrive to <NUM> Ohm terminal impedance for connection to coax cables. An existing product that is on the market today is sold, for example, by L3 Randtron of Menlo Park, California. The impedance match bandwidth may be extended to lower frequencies by adding loss, which rapidly degrades sensitivity.

Feedback LNAs are known in the art but are typically matched to <NUM> Ohms and are not integrated into these types of antennas. Rather, they are separated by a transmission line that requires a <NUM> Ohm match from the antenna to avoid standing waves and their associated ripple in the frequency response.

The presently disclosed technology relates to a wideband receive antenna that operates both in a "traditional band" of operation, where the size is >= ½ wavelength (λ) at the minimum frequency in that band, and also in a low-frequency "extension band," where the antenna size is < λ/<NUM>. A boundary frequency fc is defined as that frequency which defines a boundary between the "traditional band" of operation and the "extension band" of operation. The presently disclosed antenna is a wideband antenna (preferably a cavity-backed sinuous antenna, but it also encompasses log-periodic and other types of antennas having N arms, N feed terminals, and an array of N buffer amplifiers integrated directly into or at the feedpoint of the antenna. N is greater than <NUM> and typical values of N may be <NUM> or <NUM>, for example. Other values of N (><NUM>) are also possible. "Directly into the feed or feedpoint" means that any transmission line used to connect the radiating arms of the antenna to a transistor input element of the buffer amplifiers (or example, the gate of a FET amplifier) is much shorter than a wavelength at any frequency in the extension band (preferably less than <NUM> wavelength at any frequency in the extension band) and at least less than <NUM>/<NUM> wavelength at any frequency in the traditional band. The buffer amplifiers are preferably configured to possess high gain and a low noise figure when noise-matched to an antenna impedance Za (typically different than <NUM> Ohms). Za is chosen as the input impedance of the antenna arms in the traditional band. The buffer amplifiers are tied to a common ground node that is floating relative to the antenna arms. These buffers preferably comprise CaN FET transistors and are preferably implemented on a single semiconductor the or module. The buffer outputs are preferably impedance matched to an interface impedance (typically <NUM>, <NUM> or <NUM> Ohms) and may be further coupled to either a combining network or to N receivers. As will be disclosed, the receive antenna may also be used as a transmit antenna, even though the present disclosure is primarily directed to its receive functionality.

A purpose of the presently disclosed technology is to make receive antennas have a wider bandwidth than is possible with state of the art antennas without increasing their size. Traditional wideband cavity-backed antennas operate over a <NUM>:<NUM> bandwidth and are between <NUM>. 5λ and 1λ in size at their operational minimum frequency. For example, an antenna operating from <NUM> - <NUM> is ~ <NUM> inches or more in size. Increasing the bandwidth requirement to <NUM> - <NUM> would mean increasing the size to ~<NUM> inches (and would introduce additional design challenges to maintain the impedance match), or would force the user to accept severely degraded receive sensitivity (i.e. minimum detectable signal) over the <NUM> - <NUM> extension band. This invention may allow operation over <NUM> - <NUM> with a <NUM> inch size without severely degrading the sensitivity.

Prior art devices do not exist, to our knowledge, which anticipate this invention. Prior art antennas have been combined with Low Noise Amplifiers (LNAs), but that prior art does not achieve this bandwidth extension found with the present invention.

The presently disclosed technology addresses a long-felt need for wide bandwidth in a small antenna. In addition, this invention runs counter to textbook teaching on antenna and low--noise amplifier design.

<CIT> discloses a wideband antenna that comprises an inverted cone, at least one sinuous arm coupled to the cone, and a ground plane behind the apex of the cone. The sinuous arm comprises at least two active resonators.

<CIT> discloses a subarray of elements integrated with an amplifier and other beam forming components. A separate amplifier and filter are disposed immediately adjacent and connected to each of the antenna elements or a subarray of antenna elements and a separate combiner/divider is connected to each of the amplifiers. The antenna elements, amplifier and filter are disposed on a common support. A base station is connected by the feed cables and is remote from each amplifier. A first group of the antenna elements with low power amplifiers forms a transmitting antenna system and/or a second group of the active antenna elements with low noise amplifiers forms a receiving antenna system. A variable attenuator and a variable phase shift circuit can be integrated with each amplifier and can be used for beam shaping and electronic beam pointing. For diversity combining, spatially separated or polarization diverse active antennas are used. For polarization diverse active antennas, implementation involves a shared column or two colocated orthogonally polarized columns.

The enclosed claims define the invention. In one aspect the presently disclosed technology provides a wideband active antenna system comprising an antenna having N outputs, each of the N outputs being <CIT> directly coupled to an associated buffer amplifier, with a distance between the N balanced outputs and a first active stage of each associated buffer amplifier preferably being maintained as short as reasonably possible and at least no greater than <NUM>/<NUM> wavelength of any frequency the wideband of the antenna system.

In another aspect the invention provides a method for extending a useful frequency range of a passive antenna, the antenna having a plurality of arms which extend away from a central location, the method including: providing a chip with a plurality of buffer amplifiers embodied therein, each buffer amplifier having a signal input terminal, disposing the chip at said central location and arranging a layout of the buffer amplifiers embodied in said chip so that (i) the signal input terminal of each buffer amplifier in said chip is disposed immediately adjacent a proximate end of an associated one of said plurality of arms when said chip is disposed at said central location and (ii) the signal input terminal of each buffer amplifier in said chip is disposed immediately adjacent a control element of an active device of an associated one of said buffer amplifiers.

In another aspect the invention provides an apparatus for extending a useful frequency range of an otherwise passive antenna, the antenna having a plurality of arms which extend away from a central location, the apparatus including: a chip with a plurality of buffer amplifiers embodied therein, each buffer amplifier having a signal input terminal, the chip being disposed at said central location, and the chip having a layout of the buffer amplifiers embodied in said chip wherein (i) the signal input terminal of each buffer amplifier in said chip is disposed immediately adjacent a proximate end of an associated one of said plurality of arms of said antenna when said chip is disposed at said central location and (ii) the signal input terminal of each buffer amplifier in said chip is disposed immediately adjacent a control element of an active device of an associated one of said buffer amplifiers.

The presently disclosed technology permits a prior art, passive cavity-backed antenna designed to operate in some traditional band of operation (where the size of the receive or transmit elements are each >= ½ wavelength (λ) at the minimum frequency in that band) to operate over a much wider bandwidth that includes a low-frequency "extension band," where the size of the receive or transmit elements are < ½ wavelength (λ) at the minimum frequency that the antenna was otherwise designed to operate. A boundary frequency fc is defined as that frequency which defines a boundary between the "traditional band" of operation and the "extension band" of operation. The presently disclosed active antenna is a wideband antenna (preferably a cavity-backed, sinuous antenna, but it also encompasses log-periodic and other types of antennas having N arms, N feed terminals, and an array of N buffer amplifiers integrated directly into or at the feedpoint of the antenna, which permits an otherwise designed passive antenna to operate as an active antenna at lower frequencies than for which the passive antenna was designed.

While the presently disclosed technology can extend the bandwidth of a prior art passive antenna it is believed that it is can also be utilized to extend the bandwidth of future antenna designs of what would otherwise be a passive antenna having a comparatively narrower bandwidth.

The following description is presented to enable one of ordinary skill in the art to make and use the invention and to incorporate it in the context of particular applications. Various modifications, as well as a variety of uses in different applications will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to a wide range of embodiments. Thus, the present invention is not intended to be limited to the embodiments presented.

In the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without necessarily being limited to these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the present invention.

All the features disclosed in this specification, (including any accompanying claims, abstract, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.

<FIG> show a cavity-backed wideband antenna according to the prior art. This implementation is a dual-polarization sinuous antenna. Four arms extend outward from the central feed point on a top layer of the antenna. When a first pair of opposing arms are fed differentially, the antenna radiates linear polarization. When a second pair of opposing arms are fed differentially, the antenna radiates linear polarization orthogonal to the radiation from the first pair of feeds. A variation of this antenna is the single polarization sinuous antenna (not shown), in which only two arms are present. The radiating layer sits atop a cavity that is loaded with absorptive material in order to provide a wideband termination to the downward traveling waves. A typical size of the antenna is <NUM> inches in diameter for operation over <NUM> - <NUM>. The feedpoint is in the center of the radiating layer and comprises four terminals <NUM>. A typical feed configuration is to feed the two opposing sets of feed terminals in a balanced manner (i.e. with baluns). An alternative configuration is to use alternative mode formers to generate dual circular polarization. This behavior is similar to other antennas, for example log-periodic antennas.

We simulated the performance of a single polarization of a dual polarization antenna with a balanced feed (i.e. a lumped port) spanning the gap between two opposite arms <NUM> (see <FIG>) of antenna <NUM>. See <FIG> and <NUM>(e). This shows a good impedance match to <NUM> Ohms over <NUM> - <NUM>; it is assumed that <NUM> - <NUM> is also matched to <NUM> Ohms, but we did not simulate this because it does not help point out what is new in the embodiments disclosed herein. Below <NUM>, the antenna efficiency (i.e. the ratio of gain to directivity) falls off rapidly. Note that the efficiency reduction is primarily due to impedance mismatch.

<FIG> present a basic embodiment of the presently disclosed technology wherein an array of N buffer amplifiers is connected to N antenna terminals located at the proximate ends of the arms <NUM> of antenna <NUM>. The buffer amplifiers <NUM> preferably share a common ground terminal <NUM>G that is floating with respect to the antenna <NUM>. Each buffer amplifier <NUM> has an RF output port <NUM> that is preferably impedance matched to a reference or system impedance Z0. Building on the embodiment of <FIG>, the N buffer amplifiers <NUM> may be further coupled to N transmission lines <NUM><NUM>-N and then to a combining network <NUM> that combines the outputs to generate beams at ports A and B (e.g. horizontal and vertical or RHCP and LHCP) as is shown for the embodiment of <FIG> where N=<NUM>.

<FIG> are schematic views of one embodiment of the presently disclosed technology. The antenna <NUM> in these views is a dual-polarization, cavity-backed, sinuous antenna. Each of the feed terminals <NUM>, <NUM>, <NUM> & <NUM> are disposed at or adjacent the proximate ends of the arms <NUM> of antenna <NUM> and each is directly coupled (see transmission lines <NUM><NUM> - <NUM><NUM>) to a separate low noise buffer amplifier <NUM><NUM> - <NUM><NUM>. Note that there is no balun or other matching network between the four terminals <NUM>, <NUM>, <NUM> & <NUM> and the inputs (typically FET gates) of the four buffer amplifiers <NUM><NUM>-<NUM><NUM>. In this embodiment and the other disclosed embodiments, the transmission lines <NUM><NUM> - <NUM><NUM> between the antenna terminals <NUM>, <NUM>, <NUM> & <NUM> and the buffers <NUM><NUM>-<NUM><NUM> are made as short as possible by disposing one or more chips <NUM> containing the four buffer amplifiers <NUM><NUM>-<NUM><NUM> immediately adjacent the proximate ends of arms <NUM> of antenna <NUM> which in turn may be supp5rted by a substrate <NUM>. See in particular <FIG> where a single chip <NUM> embodying four buffer amplifiers <NUM><NUM>-<NUM><NUM> is directly coupled (and preferably bonded to) metallic arms <NUM> (individually labeled <NUM><NUM> - <NUM><NUM> in some views) of the antenna <NUM> where they approach a center of the antenna <NUM>. In other embodiments, chip <NUM> may be replaced with multiple chips <NUM>. Moreover, the antenna terminals may be coupled to one or more chip(s) <NUM> via waveguiding structures that realize the modal impedances equal to Za, the impedance of the antenna in the traditional band, or to other circuit board bearing chips <NUM> (see the embodiment of <FIG> discussed below). For example, for a single polarized antenna, its two terminals could be coupled to a balanced transmission line <NUM> with a characteristic impedance = Za. For a dual-polarization antenna, there are four transmission lines <NUM><NUM>-<NUM><NUM> where the modes corresponding to the two linear polarizations have a characteristic impedance = Za ~ <NUM> Ohms. The length of this guiding structure should preferably be minimized.

<FIG> depict an embodiment the cavity <NUM> of a cavity-backed antenna with cavity <NUM> wherein instead of bonding the chip <NUM> directly to the arms <NUM> of the antenna, each of the buffer amplifiers <NUM><NUM>-<NUM>N is embodied in a separate chip <NUM><NUM>-<NUM>N. Each chip is preferably mounted of a separate printed circuit board <NUM><NUM>-<NUM>N. Only two chips <NUM><NUM> and <NUM><NUM> and their corresponding circuit boards <NUM><NUM> and <NUM><NUM> are shown for clarity of representation in <FIG>, while four circuit boards are shown in <FIG> (but the corresponding chips <NUM> are omitted from <FIG> for clarity of representation). The printed circuit board <NUM><NUM>-<NUM>N are preferably mounted at a right angle to a printed circuit board or other dielectric substrate <NUM> bearing arms <NUM> of the cavity-backed antenna <NUM> as is described in greater detail below. The printed circuit board <NUM><NUM>-<NUM>N may be disposed at right angles to a neighboring board <NUM> as is depicted by Fig. <NUM>(g).

In <FIG> a dual-polarization cavity-backed antenna is embodied instead as a log periodic antenna. The top metal arms <NUM> (which appear in black in these views) replaces sinuous pattern of <FIG> but the cavity backing structure shown in <FIG> is retained. As such a method of making the passive portion of antenna <NUM> of this embodiment would be essentially the same as <FIG>. The difference between this embodiment and the prior art of <FIG> is the placement of a chip <NUM> (containing active elements, namely, buffer amplifiers <NUM><NUM> - <NUM><NUM>) directly on or immediately adjacent the antenna <NUM> thereby making the transmission lines <NUM><NUM> - <NUM><NUM> as short as possible and thus much less than a quarter wavelength in length (the wavelength corresponding to a highest frequency at which the antenna is nominally operable). <FIG> depicts the details at the center of embodiment of antenna <NUM> of <FIG>. Chip <NUM> is depicted both as a chip disposed at or near the proximate ends of arms <NUM> of the antenna along and schematically in terms of the buffer amplifiers.

In the embodiments of <FIG> four antenna terminals <NUM>, <NUM>, <NUM> & <NUM> are depicted for the antenna <NUM>. But there may be more or fewer terminals in a given antenna embodiment. So conceptually, an array of N buffer amplifiers <NUM><NUM>-<NUM>N is connected to N antenna terminals <NUM>-N where N = <NUM> in embodiment of antenna <NUM> depicted by <FIG> and <FIG> and N may equal <NUM> in other embodiments. These N buffers <NUM><NUM>-<NUM>N share a common ground terminal <NUM>G (see also <FIG>) that is floating with respect to the antenna terminals <NUM>-N. Each buffer <NUM> has an RF output port <NUM> that is preferably impedance matched to a reference impedance Z0. The outputs of the N buffers <NUM> may be further separately coupled to N transmission lines <NUM><NUM>-<NUM>N and then to a combining network <NUM> that combines the outputs to generate beams at ports A and B (preferably with, for example, horizontal and vertical polarization or RFICP and LHCP polarization).

The arms <NUM> of the cavity-backed antenna <NUM> may be defined by metal disposed on a printed circuit board or other dielectric substrate <NUM> as shown in <FIG>, with an integrated circuit chip or chips <NUM> being disposed directly on the substrate <NUM> or on circuit board(s) <NUM> disposed adjacent (and preferably at right angles to) printed circuit board or other dielectric substrate <NUM>, the integrated circuit chip(s) <NUM> having buffer amplifiers <NUM> that are preferably individually positioned on chip(s) <NUM> in order to make their connections (via transmission lines <NUM><NUM> - <NUM>N) to arms <NUM> as short as reasonably possible. The chip <NUM> includes N buffers <NUM> (with FET amplifiers preferably as depicted by <FIG>) whereby contacts 16c (see also <FIG>) on the chip(s) <NUM> are bonded directly to the ends of the arms <NUM> of the cavity-backed antenna <NUM> (in some embodiments thereof) and thus the ends of the arms <NUM> are very closely arranged with respect to the amplifiers in buffers <NUM> so that the conductors (transmission lines <NUM><NUM> - <NUM>N) between the ends of the arms <NUM> of the cavity-backed antenna <NUM> and the inputs (typically FET gates <NUM>) to the buffer amplifiers <NUM> are preferably maintained as short as reasonably possible by forming the gates <NUM> of the FET buffer amplifiers immediately adjacent the aforementioned chip contacts 16c. The object here is to keep the physical distance between a gate <NUM> of a buffer amplifier and the proximate end of an associated arm <NUM> of antenna <NUM> as short as reasonably possible. If the FET amplifiers have more than one stage, then it is the gates of the first stage of each buffer amplifier which are preferably arranged next to the aforementioned contacts. The chip <NUM> is preferably disposed on a side of the substrate <NUM> which supports the antenna arms <NUM> and thus faces the cavity <NUM> (see <FIG>). Since the embodiments of <FIG> and <FIG> have four arms <NUM> (and hence N = <NUM>), then there are four buffer amplifiers <NUM> preferably embodied in a single chip <NUM>. The cavity <NUM> is typically loaded with a carbon filled foam material.

In an embodiment with N buffer amplifiers (one for each of the N arms <NUM> of the antenna <NUM>), each buffer amplifier has one RF output port <NUM>, which is preferably impedance matched to a specified characteristic impedance Z0 (e.g. <NUM>, <NUM> or <NUM> Ohms). N=<NUM> in the preferred dual-polarization embodiment shown in <FIG> and <NUM>(g), but N=<NUM> (a single polarized antenna <NUM>) is also a desirable embodiment (see, for example, the embodiment of <FIG>). The output ports <NUM> may then be connected to other components common in the art. In one embodiment, the N output ports <NUM> are coupled to N transmission lines <NUM><NUM> - <NUM>N, which are then coupled to N RF connectors. In other embodiments, the output ports <NUM> are coupled to N receivers for a digital beamforming system. In another embodiment (see <FIG> for example), the N output ports <NUM> are coupled to N transmission lines <NUM><NUM> - <NUM>N, which are then coupled to a combining or beamforming network <NUM>. The N transmission lines <NUM><NUM> - <NUM>N are preferably amplitude matched and phase matched. This combining network <NUM> may comprise hybrid couplers, baluns, etc. to form output beams. In one example, outputs from transmission lines <NUM><NUM> and <NUM><NUM> are combined differentially, as are the outputs from transmission lines <NUM><NUM> and <NUM><NUM> to form outputs A and B, which are two orthogonal linear polarizations. Alternative combining networks, as are known in the art, can produce dual-circular polarization.

The N buffer amplifiers <NUM> preferably all reside on a single integrated circuit die or chip <NUM> and preferably comprise CaN FET transistors in order to maintain good amplitude and phase match between the buffers <NUM> and allow the buffer amplifiers <NUM> to be packed into small physical dimensions at or immediately adjacent the feedpoints at the proximate ends of arms <NUM> of the antenna <NUM> and to achieve the highest levels of linearity and power handling known today. Alternative embodiments may use other transistors in order to take advantage of known or future device technology developments. Furthermore, the buffers <NUM> may be integrated into a hybrid module in accordance with the preferred feed method (i.e. no transmission line), or may be integrated with the antenna separately (like a brick architecture for an array antenna).

Each buffer amplifier <NUM> may comprise a common-source amplifier. A preferred embodiment employs resistive feedback (see, for example, <FIG>), noting that the capacitor C2 is a DC blocking capacitor in this preferred embodiment preferably with impedance lower than that of the resistor R2 over the both the traditional and extension bands). Alternative embodiments employ both resistive and inductive feedback, no feedback, or output matching features. Output matching may or may not be aided by resistive attenuation. The first stage <NUM>first of the buffer <NUM> of <FIG> may be augmented by a second stage <NUM>second, which may aid in tailoring the frequency response or increasing the gain of buffer <NUM> of that embodiment. Furthermore, the buffer amplifier <NUM> may be split into two bands (or more) using a single-pole double-throw (SPDT) or multiple throw (SPMT) switch <NUM> (see the embodiment of <FIG> for a SPDT embodiment). Since the embodiment of buffer amplifier <NUM> of <FIG> has two outputs <NUM>, then N buffers (according to that embodiment) would either provide <NUM>*N outputs or the two depicted outputs <NUM> in <FIG> could be combined with a second SPDT switch (not shown) in tandem with the first mentioned SPDT switch to provide a single output for the buffer of <FIG>. The output match of the buffers <NUM> can be improved by adding attenuation (not shown) after the buffers <NUM>. Due to the gain of the buffers, adding such attenuation has a minimal impact on the noise figure. Such attenuation is preferably less than <NUM> dB.

The antenna <NUM> may also be utilized, if desired, as a transmit antenna using a a single-pole double-throw (SPDT) switch <NUM> to switch the antenna terminal to either a buffer amplifier <NUM> or to a power amplifier <NUM> of a transmitting device as depicted by <FIG>. Without taking additional measures, the antenna <NUM> would perform well only in the traditional band as a transmitting antenna but would be useful in both the traditional band and the extended band as a receiving antenna by using a suitable switching arrangement (not shown).

Preliminary simulations of the invention have been completed using full-wave simulations of the cavity--backed sinuous antenna and non--linear models extracted for HRL T3 GaN transistor devices available from HRL Laboratories, LLC, of Malibu, California, having a size of, for example, <NUM> × <NUM> µm. These models do have a limitation in that they do not account for <NUM>/f noise, which could limit the fidelity of the results at the lowest frequencies. The first step in the simulation was to convert the simulated radiation pattern and impedance of the radiator and to generate a <NUM>-port model of the antenna (see <FIG>). In this model, S21 is the total antenna efficiency (including impedance match and radiation efficiency), and S22 is the passive antenna reflection coefficient. S21 and the noise figure were evaluated both with and without a buffer. In order to evaluate the impact on the sensitivity, a <NUM> dB attenuator was inserted to account for receiver noise. The input third-order intercept point (IIP3) was also simulated using harmonic balance. The reference plane is the incident wave. In this simulation, the model for one of the two polarizations was converted to its differential half circuit. Therefore, this model applies to a linear polarization formed by combining the outputs of arms <NUM> and <NUM> or <NUM> and <NUM> differentially.

Turning to <FIG>, the buffer amplifier <NUM> improves the gain by ~<NUM> dB over the band relative to the passive antenna <NUM>. The improvement in Noise Figure (NF) is approximately <NUM> dB over the extension band and <NUM> dB over the traditional band. Over the traditional band, this improvement is explained by the gain of the buffer amplifier, which swamps out the receiver noise figure. This is a textbook result and is not surprising. In the extension band, the increased benefit is explained by the fact that the T3 devices available from HRL Laboratories have excellent noise parameters. Specifically, the degradation in NF with impedance mismatch is determined by the noise parameters and noise circles. For this buffer, the minimum NF is < <NUM> dB and the noise resistance is ~ <NUM> Ohms. This means that the impact of mismatch on the active NF is less than the impact on the passive antenna gain.

The comparison in <FIG> does not constrain the antenna <NUM> to be impedance matched to the system impedance Z0. This mismatch is unacceptable for many receivers. <FIG> shows a comparison when both the buffered and passive antennas were matched using attenuators, <NUM> and <NUM> dB, respectively, in order to achieve a -<NUM> dB reflection coefficient over the entire band. In this figure, the receiver is modeled by a <NUM> dB attenuator. Due to the buffer gain, adding a <NUM> dB attenuator at the output has little impact on the NF. For the passive antenna, however, adding a <NUM> dB attenuator at its terminals degrades the NF by another <NUM> dB. Therefore, the buffer amplifier is advantageous by an additional <NUM> dB.

The disclosed embodiments permit a prior art passive cavity-backed antenna designed to operate in some traditional band of operation (where the size of the receive or transmit elements are each >= ½ wavelength (λ) at the minimum frequency in that band) to operate over a much wider bandwidth that includes a low-frequency "extension band," where the size of the receive or transmit elements are < ½ wavelength (λ) at the minimum frequency that the antenna was otherwise designed to operate. A boundary frequency fc is defined as that frequency which defines a boundary between the "traditional band" of operation and the "extension band" of operation. The presently disclosed active antenna is a wideband antenna (preferably a cavity-backed sinuous antenna, but it also encompasses log-periodic and other type antennas having N arms, N feed terminals, and an array of N buffer amplifiers integrated directly into or at the feedpoint of the antenna, which permits an otherwise designed passive antenna to operate as an active antenna at lower frequencies than for which the passive antenna was designed.

The term band or frequency band when used herein is intended to refer to a frequency band having a nominal bandwidth where a rolloff at the edges of the band correspond to a point when the gain (or attenuation) has decreased by some amount, typically - <NUM> dB, compared to a frequency center of the band. So the terms "traditional" band and "extension band" have gain rolloffs at the edges of those bands which are down by some amount, for example -<NUM> dB, compared to a center frequency of those bands. The gain rolloffs occur where the gain at frequencies beyond the band edges continue to decrease from that amount (typically - <NUM> dB).

Claim 1:
A wideband active antenna system comprising a passive antenna; said passive antenna having a nominal bandwidth with a minimum frequency; said passive antenna comprising receive or transmit elements with a size larger than or equal to half the wavelength of said minimum frequency, and said passive antenna (<NUM>) having a number N of outputs (<NUM>, <NUM>, <NUM>, <NUM>), with N > <NUM>, each of the N outputs (<NUM>, <NUM>, <NUM>, <NUM>) being directly coupled to an associated buffer amplifier (<NUM>; <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM>), with a physical distance between the N outputs (<NUM>, <NUM>, <NUM>, <NUM>) and a first active stage of each associated buffer amplifier (<NUM>; <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM>) being no greater than <NUM>/<NUM> wavelength of any transmission and/or receiving frequency of the wideband active antenna system , such that the wideband active antenna system has a greater nominal bandwidth, additionally comprising lower frequencies than said nominal bandwidth of said passive antenna.