Abstract:
An omni-directional antenna operable absent ground radials and providing at least 3 dB gain at a chosen wavelength relative to a dipole includes first and second like-oriented J-pole antennas and, coupled intermediate said J-pole antennas, a quarter-wavelength non-radiating delay line. Each J-pole antenna includes a half-wave radiating element, and a quarter-wavelength non-radiating section. The quarter-wavelength non-radiating delay line together with the quarter-wavelength non-radiation section of the second J-pole provide a half-wave non-radiating delay line. The result is that RF energy radiated by the first and second half-wave radiating elements are in proper phase, whereby gain is achieved. RF energy is coupled to the first J-pole antenna a distance Δ above the zero impedance end of that antenna.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to antennas that radiate and receive radio frequencies (RF), and preferably for such antennas designed for use in the very high frequency (VHF) range or ultra high frequency range (UHF) that do not require radials or connection to absolute ground. Preferably such antennas should be mechanically robust over extremes of temperature and wind conditions, and should be relatively inexpensive to mass produce and transport, and should be maintenance free. Further, such antennas should exhibit gain. 
       BACKGROUND OF THE INVENTION 
       [0002]    Radio frequency (RF antennas are used to receive and/or radiate RF signals. An effective antenna for use in transmission will exhibit an acceptably low standing wave ratio (SWR) at the frequencies of interest, and will present a reasonably good impedance match to the output of the transmitter, typically 50Ω to 75Ω. While some antenna designs such as beams exhibit directionality, i.e., more antenna gain in one direction compared to another, in many applications it is desired that the pattern of radiation from the antenna be omni-directional. Further it is often desired that the antenna not require ground radials, as radials undesirably increase antenna wind load, as well as the manufacturing cost. Further, radials diminish robustness of the antenna design, especially in inclement weather. 
         [0003]    Many innovations in antenna design have come from the amateur radio community. Pioneer work in the area of so-called fractal antenna has been accomplished by Nathan Cohen (W1IR, W1YW) of Belmont, Mass., e.g., U.S. Pat. Nos. 6,104,349, 6,127,977, 6,140,975, 6,445,352, 7,019,695, and 7,701,396, among others. 
         [0004]    Another innovation in antenna design is depicted in  FIGS. 1A and 1B , namely the so-called Don Johnson screwdriver antenna, named after its late inventor Don Johnson (W6AAQ) of Esparta, Calif. Overall antenna  10  includes a whip portion  20 , typically 3′ to perhaps 8′ in length, mounted to make electrical connection with the upper end of an inductor  30 . Inductor  30  typically is formed about a non-conductive cylinder of perhaps 2″ diameter and perhaps 12″ length. The upper portion of housing  40  includes conductive finger stock that presses against inductor  30 , effectively grounding to housing  40  all portions of inductor  40  that are within the housing. Inductor  30  and the cylinder it is formed upon can be urged vertically upward and downward within a metal cylinder housing  40  to alter magnitude of the effective inductance protruding from housing  40 . A threaded rotatable shaft  80  is connected between the lower end of the inductor  30  cylinder and the rotatable shaft of a small DC motor  70 . Motor  70  is typically a motor from an electric screwdriver, hence the “screwdriver” name for the antenna. Two wires from motor  70  can be applied to a plus or a minus polarity DC voltage, to cause motor  70  to rotate clockwise or counterclockwise, causing more or less of inductor  30  to lie within housing  40 , which is to say to decrease or increase magnitude of the effective inductance protruding from the housing. A matching inductor  50  is formed at the base of the antenna and a length of typically 50Ω coaxial cable  60  is connected as shown. The other end of coaxial cable  60  will typically go to a transceiver, or transmitter, or receiver. Tuning antenna  10  simply involves applying plus or minus DC voltage to motor  70  to mechanically resonate the antenna to a desired frequency range. Antenna  10  can be tuned by first setting the transceiver (or receiver) to a desired frequency and then adjusting the effective length of inductor  30  by rotating motor  70  in the proper direction (by applying plus or minus voltage to motor  70 ) to resonate the antenna, as evidenced by a peak in amplitude of received signals. 
         [0005]    In  FIG. 1A , DC voltage has been applied to motor  70  to rotate nearly all of inductor  30  into housing  40 . The effect at RF frequencies is that only the portion of inductor  30  protruding from housing  40  functions as an inductor. The antenna operates as a center loaded device whose resonance is determined primarily by the effective inductance  30  and the whip  20 . In  FIG. 1B , DC voltage was applied to motor  70  to rotate threaded shaft  80  such that more of inductor  30  can now resonant with whip  20 . Clearly the additional effective inductance used in  FIG. 1B  will lower the resonant frequency of the overall antenna. Advantageously the antenna can operate continuously within a very wide range of frequencies, merely by applying DC voltage to motor  70  to cause more or less inductance to be used. In practice, many thousands of Don Johnson screwdriver antennas have been used worldwide with great success over frequencies ranging from as low as about 3.5 MHz to as high as perhaps 144 MHz. 
         [0006]    In other applications, especially higher frequency applications, a less mechanical antenna may be desired, especially for considerations of cost and ease of construction. One common type of antenna, especially for VHF (2 m range wavelengths) and/or UHF (70 cm range wavelengths), is the so-called collinear antenna. A collinear antenna is an array of at least two dipole antennas, configured such that every element of each dipole is an extension, relative to a longitudinal antenna axis, of the other dipoles in the array. Collinear antennas can exhibit gain over an isotropic radiator. 
         [0007]      FIG. 2A  depicts a collinear antenna  90  comprising collinear elements  100 ,  110 ,  120 , used with preferably at least four quarter-wavelength radials  130  mounted at the antenna base. Radials  130  function as a ground plane. Preferably coaxial cable  60  is coupled to antenna  90 , with the other end of coaxial cable  60  coupled to a transceiver, a transmitter, or a receiver (not shown). Lowermost element  100  in  FIG. 2A  is a quarter-wavelength at the nominal frequency of interest. Intermediate element  110  is coupled to act as a half-wave delay element, and uppermost radiating element  120  preferably has a length equal to a half-wave. The various elements  100 ,  110 ,  120  can be fabricated from lengths of coaxial cable, whose center conductor is indicated by phantom lines, and whose outer shield conductor is indicated by solid lines on either side of the center conductor. Note that the collinear arrangement alternates electrical connection between the center conductor of an element and the outer conductor. 
         [0008]    In  FIG. 2A , if one tried to use quarter-wavelength element  100  with an extension half-wavelength (i.e., center-conductor to center-conductor, shield-to-shield), no additional gain would result due to phase cancellation of radiation in the quarter-wave and half-wave elements.  FIG. 2B  depicts voltage amplitude versus phase for the various elements of antenna  90 . As confirmed by  FIG. 2B , non-radiating half-wave delay element  110  provides the desired ground reference function. This results from coupling the shielded outer conductor of element  100  to the inner conductor of element  110 , which inner conductor acts as a ground reference. Note at the base of antenna  90  that radials  130  are also coupled to this ground reference via the center conductor of element  100 . As shown in  FIG. 2A , after a quarter-wavelength at the junction of elements  100  and  110 , the shield and inner conductor are swapped. At its upper end, element  110  is coupled to the lower end of half-wave coaxial element  120 , again by swapping of center conductor and shield outer conductor. As the radiated radio frequency energy exits the upper end of element  120  it is back in phase with quarter-wavelength radiating element  100 . If desired additional elements, i.e., another triplet of elements  100 ,  120 ,  120  could be added atop present uppermost element  120  in collinear fashion. However a point of diminishing returns effectively occurs at about four elements in that marginal further increase in gain does not warrant the cost of the additional elements. 
         [0009]    Disadvantageously, antenna  90  requires several, typically at least four, quarter-wavelength radials  130 , preferably bent downward at an angle of perhaps 45° to establish an RF ground. As noted, an RF ground reference node exists at the junction of radials  130  and the outer shield of coaxial cable  60 . Radials often require machining to properly make good electrical connection at the base of antenna  90 . In practice stainless steel radials are preferred for reasons of strength and electrical contact over less expensive aluminum radials. The presence of radials impacts the robustness of the antenna design. Radials can easily break off in the presence of strong winds, or by birds perching on the radials. If the radials are on the ground, they may be damaged from being walked upon. Further, the electrical conductivity between the radials and the shield of coaxial cable  60  will inevitably deteriorate over time. 
         [0010]      FIG. 3  depicts an attempt in the prior art to eliminate radials by using a quarter-wave sleeve. Referring to  FIG. 3 , antenna  140  has at its base a quarter-wave element  100 , then a half-wave delay element  110 , above which is disposed an upper half-wave radiating element  120 . These collinear elements  100 ,  110 ,  120  in antenna  140  are configured similarly to the same elements in antenna  90  in  FIG. 2A , and are made from segments of coaxial cable. However rather than employ radials (as in  FIG. 2A ), antenna  90  employs a conductive quarter-wavelength sleeve  150  to implement an effective quarter-wavelength foldback and RF ground reference. The term “foldback” is used in that sleeve  150  covers a portion of the connecting coaxial cable  60 . Sleeve  150  is commonly made of conductive brass or copper pipe, and the connection to coaxial cable  60  is typically made within the sleeve. This configuration advantageously gains robustness by eliminating radials, and exhibits a slightly lower angle of radiation that can add to transmitting range of the antenna. However the sleeve configuration can make it difficult to achieve desired low SWR due to inherent coupling between the outer shield conductor of coaxial cable  60  and the wall of sleeve  150 . 
         [0011]      FIG. 4  depicts yet another attempt in the prior art to implement an omni-directional antenna without radials. As shown in  FIG. 4 , a portion of this antenna looks like the letter “J”, and this configuration is sometimes referred to as a “Super-J” antenna. A full description of antenna  160  may be found in QST magazine, September 1994, p. 61-62, J. Reynante (W6JRR) “An Easy Dual Band VHF/UHF Antenna.” Referring to  FIG. 4 , the lower end of antenna  160  is a quarter wavelength matching element, typically 300Ω twinlead  170 , whose two leads or wires are shorted together at the bottom  180 . The RF impedance at bottom  180  is of course 0Ω, but at a distance Δ above bottom  180 , the RF impedance will be close to the impedance of coaxial cable  60  to be a good match, e.g., 50Ω or so. The upper end of quarter-wavelength matching element  170  is coupled to a half-wave radiating element  190 , as the upper end of quarter-wavelength matching element  170 , and either end of half-wave radiating element  190  are both RF high impedances. 
         [0012]    Note that elements  170  and  190  are disposed vertically and will exhibit vertical radiation of RF energy. By contrast, the upper end of half-wave radiating element  190  is coupled to a horizontally disposed delay element  200 . Delay element  200  comprises two parallel quarter-wavelength element coupled in a horizontally-disposed “U”-shaped configuration. The horizontally polarized RF energy associated with the lower and with the upper elements of delay element  200  are 90° out-of-phase with respect to each other and thus cancel one another. Ideally the phase delay and radiation patterns associated with element  200  are perfectly out-of-phase, but in practice some phase error and associated antenna inefficiency will exist. “U”-shaped delay element  200  may be thought of as contributing an outgoing lower quarter-wavelength delay and an incoming quarter-wavelength delay. The net result is that these horizontally disposed elements represent an effective half-wave delay element  200 . The upper portion of “U”-shaped delay element  200  is connected to the lower end of a vertically disposed (and vertically radiating) half-wave radiating element  210 . In this fashion the antenna of  FIG. 4  implements the functional equivalent of the ready access to ground that was present in the antenna of  FIG. 2A . The desired overall half-wavelength delay with desired non-radiating characteristics for 180° of the phase waveform is achieved by “U”-shaped element  200 . 
         [0013]    Regrettably, antenna  160  is not robust in that delay element  200  projects out horizontally from the vertical antenna into the environment, and is difficult to reliably fasten between radiating elements  190  and  210 . Alternatively some designs also seek to achieve phase delay with inductor-capacitor (LC) components rather than with an element  200 . However such solutions are not optimum because losses and tolerance changes in the L and C components vary over time, which can reduce effectiveness of the desired delay function. 
         [0014]      FIG. 5  depicts a so-called conventional “J-pole” antenna that can be fabricated from a single length of 300Ω twin lead cable, comprising lead  1  and lead  2 , that has a gap or notch cut in one lead (lead  1 ), and whose bottom region has a short between the two leads. The lower portion of antenna  220  comprises a quarter-wavelength matching element  230 , sometimes referred to as a shorting stub element, whose lower end  180  has both leads shorted together to form a low impedance end of the J-pole antenna. A perhaps 0.25″ gap or notch  240  is formed in one side of the matching element (the left side in  FIG. 5 ), cutting through one of the two wires or leads. A half-wave radiating element  250  is connected to the upper portion of quarter-wavelength matching element  230 . As shown the upper end of J-pole antenna  220  is open, and is high impedance. 
         [0015]    Thus, as used herein, the term “J-pole” antenna is understood to refer to an antenna comprising spaced-apart first and second conductive wires, e.g., twinlead, shorted together at one end to form a zero impedance first end, and a quarter-wavelength away from this zero impedance first end, an open high impedance quarter-wavelength second end. The first conductive wire (lead  1 ) has a notch or gap cut through the wire approximately a quarter wavelength above the zero impedance first end, and the second conductive wire (lead  2 ) is approximately three-quarter wavelength at resonant frequency. An RF low impedance feedpoint exists a distance Δ in each lead above the zero impedance first end. The quarter wavelength section adjacent the zero impedance first end functions as a quarter-wavelength impedance matching element, and the half-wavelength of each lead measured from the high impedance second end forms a half-wavelength radiating element. 
         [0016]    In a conventional half-wave antenna, the antenna ends are high impedance and the antenna center is low impedance. But in a half-wave vertical dipole antenna such as antenna  220 , end matching must be done at a high impedance point. As noted above, this condition is satisfied using quarter-wave shorted stub matching element  230  at the lower end of antenna  220 , by having the upper end of half-wave radiating element  250  open, e.g., not shorted or connected to anything. Thus, J-pole antenna  220  exhibits high impedance at the upper end of half-wave radiator element  250 , and exhibits 0Ω impedance at shorted region  180 . However at a distance Δ above short  180  a good match to typically 50Ω coax feedline  60  may be found. As such, quarter-wavelength matching element  230  acts like an impedance matching transformer. Matching distance Δ is commonly on the order of perhaps 0.5″ or so for an antenna resonant in the 70 cm band. In practice, distance Δ may be determined experimentally using an antenna analyzer. Further details regarding the design of antenna  220  may be found at QST magazine, February 2003, pp 38-401, E. Fong (WB6IQN), “The DBJ-1: A VHF-UHF Dual-Band J-Pole”, and QST magazine, March 2007, E. Fong (WB6IQN), “The DBJ-2: A Portable VHF-UHF Roll-up J-pole Antenna for ARES”. 
         [0017]    J-pole antenna  220  is similar to a vertically oriented end-fed half-wave dipole, but with a radiation pattern closer to an ideal vertical dipole. The enhanced radiation pattern results because feedline  60  is in-line rather than perpendicular to the antenna. A well-designed J-pole antenna is a good half-wave radiator that provides about 2.1 dB gain over an isotropic radiator, but no gain relative to a half-wave antenna. 
         [0018]    It will be appreciated that J-pole antenna  220  is omni-directional, inexpensive to fabricate, and requires no radials. In practice the antenna can be inserted within a length of UV-resistant PCV pipe that is sealed at the top and bottom, to provide a robust configuration with relatively low wind resistance. In practice J-pole antenna  220  can achieve about a 1.5 dB gain improvement over a quarter-wave ground plane antenna because it is a true half-wave antenna. In a conventional ground plane antenna such as was described in  FIG. 2A , ground radials  130  were necessary to act a counter element (e.g., ground or earth). With radials bent downward from say 0° (i.e., horizontal) to about 45°, and disadvantageously a relatively high angle of radiation will result. By contrast, a J-pole such as antenna  220  has no radials and advantageously exhibits a lower angle of radiation, which results in a gain of about 1.5 dB in the horizontal plane relative to a conventional ground plane antenna. 
         [0019]    While the J-pole provides an interesting starting point for many antenna designs, further gain may be demanded of many applications. Thus there is a need for an inexpensive, robust antenna with low wind resistance and high reliability. Preferably such antenna should provide gain beyond what a conventional J-pole antenna can provide and indeed should provide gain over a half-wave antenna. Such antenna should be omni-directional, should not require radials or special collars, and should not require an absolute ground connection. 
         [0020]    The present invention provides such an antenna. 
       SUMMARY OF THE PRESENT INVENTION 
       [0021]    The present invention provides an omni-directional collinear gain antenna that operates without radials or an absolute ground. In a preferred embodiment, two J-pole antenna sections are joined together with a quarter-wavelength non-radiating delay line disposed between the two J-poles. A first J-pole section comprising spaced-apart parallel first and second conductive leads, preferably twinlead, has a zero impedance first end and a high impedance second end with a gap in the first lead approximately a quarter-wavelength above the zero impedance first end and about a half-wavelength below the high impedance second end. An RF low impedance feedpoint, e.g., 50Ω, is located a distance Δ above the 0Ω first end on each lead. This first J-pole antenna may thus be implemented with an approximately three-quarter wavelength piece of twinlead, e.g., 300Ω twinlead. The half-wave portion of the first J-pole acts as a radiating element, whereas the quarter-wavelength matching element does not radiate any substantial RF energy. 
         [0022]    The high impedance second end of this first J-pole is connected to the high impedance second end of a first quarter-wavelength non-radiating delay line, whose other, first, end has its first and second leads shorted together to form a low RF impedance, preferably 0Ω. This first quarter-wavelength non-radiating delay line may be a quarter-wavelength of twinlead, e.g., 300Ω twinlead, whose first lead has a notch cut into the high impedance end to remove perhaps 0.25″ of the first lead. In terms of the overall antenna to be implemented, this first quarter-wavelength delay line does not radiate any substantial RF energy. 
         [0023]    A second J-pole, substantially similar to the first J-pole antenna, has its low impedance first end coupled to the low impedance first end of the first quarter-wavelength non-radiating delay line. Similar to the first J-pole, there is a quarter-wavelength element between the low impedance first end and the region encompassing a gap or notch cut into the first lead, which quarter-wavelength element functions as a second quarter-wavelength non-radiating delay line. Thus, the first quarter wavelength non-radiating delay line and the second quarter-wavelength non-radiating delay line comprise a half-wavelength non-radiating delay line. The second J-pole has a half-wave radiating element that, like the half-wave radiating element associated with the first J-pole, radiates RF energy. Thanks to the half-wave delay present in the overall antenna, RF energy radiating into the two half-wave radiating elements is in proper phase with each other. The first and second J-pole antennas are configured with like orientation, which is to say both J-pole sections have their low impedance end facing in a first direction, e.g., down, and their high impedance end facing in an opposite second direction, e.g., up, although the up and down orientations for both J-pole sections could be reversed. 
         [0024]    The resultant antenna is omni-directional, is collinear, requires neither a ground plane nor radials, requires no an absolute RF ground, and exhibits gain relative to a half-wave dipole antenna. The antenna may be fabricated from an approximately 1.75 wavelength (at frequency of interest) piece of twinlead, with gaps or notches formed in the first lead at the appropriate locations. The antenna is readily mass producible at low cost, has low weight and is readily shippable, and is robust in that it is of integral one-piece construction. 
         [0025]    If desired, at least a second additional quarter-wavelength non-radiating delay line and an additional third J-pole could be connected to the high impedance second end of the second J-pole. However in practice, the somewhat marginal increase in gain that may result from adding additional quarter-wavelength non-radiating delay lines and associated J-poles seems unjustified by the additional overall antenna length and material requirements. 
         [0026]    Other features and advantages of the invention will appear from the following description in which the preferred embodiments have been set forth in detail, in conjunction with their accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIGS. 1A and 1B  depict a wide-frequency range, omni-directional Don Johnson type screwdriver antenna, according to the prior art; 
           [0028]      FIG. 2A  depicts an omni-directional collinear antenna that requires radials, according to the prior art; 
           [0029]      FIG. 2B  depicts voltage amplitude versus phase for various elements of the collinear antenna of  FIG. 2A , according to the prior art; 
           [0030]      FIG. 3A  depicts an omni-directional collinear antenna that uses a quarter-wave sleeve rather than radials, according to the prior art; 
           [0031]      FIG. 4  depicts a so-called “Super-J” omni-directional antenna with a half-wave delay element that operates without radials, according to the prior art; 
           [0032]      FIG. 5  depicts an omni-directional “J-pole” antenna with slight gain that operates without radials, according to the prior art; 
           [0033]      FIG. 6A  depicts formation of an omni-directional gain antenna operable without radials and without an absolute ground, comprising a series connection of a first J-pole antenna, an inverted second J-pole antenna, and a third J-pole antenna, according to embodiments of the present invention; 
           [0034]      FIG. 6B  depicts an exemplary omni-directional gain antenna that operates without radials and without an absolute ground, resulting from joining together of the exemplary J-pole elements depicted in  FIG. 6A , according to embodiments of the present invention; 
           [0035]      FIG. 6C  depicts voltage amplitude versus phase for various elements of the antenna of  FIG. 6B , according to embodiments of the present invention; and 
           [0036]      FIG. 7  depicts various deployments of embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0037]      FIG. 6A  depicts an exemplary antenna  270 , according to embodiments of the present invention. Antenna  270  comprises a first J-pole section denoted {circle around (A)}, a first quarter-wavelength non-radiating delay line section denoted {circle around (B)}, and a second J-pole section denoted {circle around (C)}. First J-pole section {circle around (A)} is similar to what has been described with respect to  FIG. 5 , and includes spaced-apart parallel first and second leads that form a quarter-wave matching element  230  whose first, lower, end has the two leads connected together by a short  180  to form an RF low impedance end, preferably 0Ω. The lead  2  side of element  230  extends about a quarter-wavelength at the nominal frequency of interest and has a high impedance second end. Lead  1  has a notch or gap  240  cut into the wire for a length of perhaps 0.25″. In  FIG. 6A , below the level of notch  240  is the quarter-wavelength matching element, and above the notch is a half-wavelength radiating element  250 . While short  180  defines a 0Ω RF impedance, a distance Δ can be determined experimentally above the short at which an impedance that matches coaxial cable  60  can be found, preferably about 50Ω. For a nominal wavelength in the 70 cm band, the distance Δ will be on the order of perhaps 0.5″. Those skilled in the art will realize that the distance Δ whereat a nominal 50Ω (or other matching RF impedance) exists can be found with the aid of an antenna analyzer. Thus first J-pole antenna section {circle around (A)} comprises a quarter-wavelength matching element  230  that does not radiate substantial RF energy, and a half-wavelength radiating element  250  that does radiate substantial RF energy. Although other materials may be used, first J-pole section {circle around (A)} may be formed from a length of twinlead, e.g., 300Ω twinlead. 
         [0038]    In  FIG. 6A , first quarter-wavelength non-radiating delay line section denoted {circle around (B)} comprises a quarter-wavelength  230 ′ of spaced-apart parallel first and second leads, preferably a length of twinlead, e.g., 300Ω twinlead. Assume for the moment that the small piece of electrical wire  255  is removed. As noted the upper or second end of J-pole antenna section {circle around (A)} is high impedance. Similarly the lower or second section of non-radiating delay line  230 ′ is also high impedance, being open at each lead. Note that lead  1  of this section defines a notch or gap  240 ′ similar to notch  240 . Since the lead  2  side of section {circle around (B)} is open and high impedance, it can be joined directly to the open, high impedance lead  2  side of J-pole section {circle around (A)}, e.g., with wire  255 . In  FIG. 6A , the upper or first end of section {circle around (B)} is low impedance by virtue of short  180 ′, which connects the first and second leads to each other. It will be appreciated that section {circle around (B)} may be implements from a quarter-wavelength section of twinlead, e.g., 300Ω twinlead, with a notch or gap  240 ′ cut in the first lead as noted. 
         [0039]    Second J-pole section {circle around (A)}′ in  FIG. 6A  is substantially the same as first J-pole section {circle around (A)}, although there is no need to make any coaxial cable feedline connection. Second J-pole section {circle around (A)}′ has like configuration with first J-pole section {circle around (A)} in that each section has its low impedance end facing in a first direction, e.g., down in  FIGS. 6A and 6B , and each has its high impedance end facing in an opposite direction, e.g., up in  FIGS. 6A and 6B . (In some installations the first direction could be up, and the second configuration could be down.) Second J-pole section {circle around (A)}′ includes at its lower end a non-radiating delay line  230 ″ whose lower first end is low impedance, e.g., 0Ω by virtue of short  180 ″, which connects the first and second leads together, and whose second end is high impedance. Lead  2  is about a quarter-wavelength long but a gap or notch  240 ″ is cut into lead  1  as indicated. Above the level of notch  240 ″ is formed half-wavelength radiating element  250 ″. It is understood that second J-pole antenna {circle around (A)}′ may be formed from an approximately three-quarter wavelength piece of twinlead, e.g., 300Ω twinlead. 
         [0040]      FIG. 6A  shows first and second connecting wires  185 ,  185 ′ coupling together respective ends of lead  1  and lead  2 , preferably at a distance Δ above or below the 0Ω low impedance end of section  230 ′ or  230 ″. For example if the RF impedance at the distance Δ is 50Ω, then wires  185 ,  185 ′ are merely coupling 50Ω to 50Ω. However it is easier to simply couple together the 0Ω impedances at  180 ″ and  180 ′. Such 0Ω coupling eliminates any need to determine the distance Δ for the two non-radiating delay line elements  230 ′,  230 ″. This in fact is what is shown in  FIG. 6B . 
         [0041]      FIG. 6B  depicts a preferred embodiment of antenna  270  in which wire  255  in  FIG. 6A  is eliminated and lead  2  is simply a continuum in the relevant region. Also, exemplary wires  185 ,  185 ′ in the embodiment of  FIG. 6A  are eliminated, and the junction between the low RF impedance, i.e., 0Ω, ends of elements {circle around (B)} and {circle around (A)}′ is made directly at short  180 ′, which shorts together lead  1  and lead  2  at that location. As has been noted, section {circle around (B)} functions as a first quarter wavelength non-radiating delay line  260 . As noted, the lower section  260  of second J-pole antenna {circle around (A)}′, denoted {circle around (B)}′ in  FIG. 6B , also functions as a second quarter-wavelength non-radiating delay line  260 ′. Thus collectively, quarter-wavelength sections {circle around (B)} and {circle around (B)}′ function as a half-wave non-radiating delay line. 
         [0042]    Compare now the radiating and non-radiating sections of antenna  270  in  FIG. 2B , and the corresponding phase-vs-voltage waveforms shown in  FIG. 6C . At the lower end of antenna  270 , section  230  functions as a quarter-wavelength matching element and do not radiate any substantial RF. Accordingly the associated portion of the phase waveform in  FIG. 6C  is drawn in phantom line to indicate no RF radiation. 
         [0043]    Continuing upward along antenna  270 , half-wavelength element  250  radiates RF energy, and its corresponding region of the phase waveform in  FIG. 6C  is drawn with solid line to indicate RF radiation. Next come the two quarter-wavelength non-radiating delay line sections, which radiate substantially no RF energy. This is indicated in FIG. C by the phantom line portion of the phase waveform. At the upper end of antenna  270 , half-wave element  250 ″ radiates RF energy, and its corresponding portion of the phase waveform in  FIG. 6C  is drawn with solid line. Note that the radiation from the two half-wavelength elements  250  and  250 ″ form a continuous phase, thanks to the half-wave cancellation function carried out by first and second quarter-wavelength non-radiating sections {circle around (B)} and {circle around (B)}′. Thus antenna  270  performs substantially as intended. 
         [0044]    Note that from top-to-bottom, antenna  270  may be implemented using a single approximately 1.75 wavelength piece of twinlead, e.g., 300Ω twinlead, with first notch  240 , second notice  240 ′ and third notch  240 ″ cut into lead  1  at the locations noted. Each notch removes perhaps 0.25″ of lead  1  wire when antenna  270  is designed for the 70 cm UHF band. Antenna  270  when designed for operation in the 70 cm UHF band exhibits 3 dB to 4 dB gain over a well made dipole, exhibits about 5.5 dB over a ground plane antenna, and exhibits about 7.1 dBi relative to an isotropic radiator. Tables 1 and 2, following, provide exemplary design data and performance data for antennas, according to embodiments of the present invention. 
         [0045]    A somewhat marginal increase in gain can be achieved by adding an additional section {circle around (B)} and an additional section {circle around (A)}′ atop the upper, high impedance end, of half-wave radiating element  250 ″ in  FIG. 6B . In practice, however, the additional three-quarter wavelength added to the height of antenna  270  seems unwarranted by the very marginal increase in gain. 
         [0046]    Table 1 below gives exemplary characteristics for antenna  270 , as depicted in  FIG. 6B , for 2 m and for 70 cm wavelengths, where the antenna was designed to be disposed within PVC pipe. As noted later herein, if the antenna is not to be disposed within PVC pipe, the dimensions given in Table 1 should be increased slightly by about 2% to 5%. It is understood that tolerances given for the various dimensions given are approximate to within perhaps ±3% or so. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                 240, 
                   
                   
                   
                   
                 Gain over 
               
               
                   
                   
                   
                 240′, 
                 250, 
                   
                 Gain over 
                 Gain over 
                 isotropic 
               
               
                 λ 
                 Δ 
                 230 
                 240″ 
                 250″ 
                 230′ 
                 dipole 
                 ground plane 
                 radiator 
               
               
                   
               
             
             
               
                 2 m 
                 1.5″ 
                 12″ 
                 0.25″ 
                 37.5″ 
                 15″ 
                 3 dB-4 dB 
                 5.5 dB 
                 7.1 dBi 
               
               
                 70 cm 
                 0.5″ 
                  4″ 
                 0.25″ 
                 12.5″ 
                  5″ 
                 3 dB-4 dB 
                 5.5 dB 
                 7.1 dBi 
               
               
                   
               
             
          
         
       
     
         [0047]    Table 2 below depicts the measured gain characteristics of one, two, and three elements of an antenna according to the present invention, relative to a ground plane antenna. Also shown is the antenna gain of a so-called “rubber duck” antenna, typically about 4″ in length and commonly used with hand-held transceivers relative to a ground plane antenna. The two element collinear configuration in Table 2 exhibits 5 dB gain relative to a ground plane antenna. As noted, going from a two element collinear configuration (e.g.,  FIG. 6B ) to a three element collinear configuration does not result in appreciable gain. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 ground 
                 rubber 
                 1 element 
                 2 element 
                 3 element 
               
               
                 plane 
                 duck 
                 collinear 
                 collinear 
                 collinear 
               
               
                   
               
             
             
               
                 0 dB 
                 −3 dB 
                 +1.5 dB 
                 +5 dB 
                 +5 dB 
               
               
                   
               
             
          
         
       
     
         [0048]      FIG. 7  depicts various deployments for antenna  270 , as indicated in  FIG. 6B . For example at the upper left of  FIG. 7 , antenna  270  is mounted outdoors on a roof, and is protected against the environment by a length of PVC pipe  280 , which has an upper cap  290  and a lower cap  295 . Those skilled in the art will appreciate that one cannot simply construct antenna  270  as shown in  FIG. 6B  designed for use in open air, and then insert the antenna into pipe  280  without experiencing antenna detuning due differences in velocity factors between air and PVC pipe. In practice 0.75″ diameter 200 PSI PVC pipe has been found very suitable as a protective sheath material, if such is desired, for an antenna according to the present invention. In practice one can arrive at appropriate dimensions for an antenna that will be disposed within PCV pipe as follows. Initially two independently working J-pole sections {circle around (A)} and {circle around (A)}′ are fabricated. RF is coupled to one of these J-pole sections, e.g., section {circle around (A)} via coaxial cable  60 , and quarter-wavelength matching element  230  is adjusted in length until there is no appreciable change in standing wave ratio (SWR) when the J-pole is inserted into a length of PVC pipe. 
         [0049]    Generally if the quarter-wavelength matching section is too long, resonant frequency will be lower than desired, and if this section is too short in length, the resonant frequency will be higher than desired. However trial and error will result in dimensions for quarter-wavelength matching section  230 , such as shown in Table 2 above. Once the quarter-wavelength section dimension is arrived at, the precise length of the half-wave radiating element  250  can be adjusted, e.g., by cutting off quarter-inch increments from the upper high impedance end, until there is no substantial detuning of the J-pole section when inserted into the length of PVC pipe. The dimensions arrived at for the first J-pole section {circle around (A)} may be used to fabricate the second J-pole section {circle around (A)}′. Section {circle around (B)} is tuned for lowest SWR at resonant frequency, similar to what has been described for section {circle around (A)}. With care, precise dimensions for the various sections {circle around (A)}, {circle around (B)} and {circle around (A)}′ comprising antenna  270  in  FIG. 6B  can be arrived at such that the antenna characteristics when inserted within a length of PVC pipe will be as desired. 
         [0050]    Within the PVC pipe one may suspend antenna  270  from the upper cap, although in practice if one uses conventional 300Ω twinlead to construct the antenna, the twinlead itself is sufficiently rigid to require no suspension at all. Preferably the lower region of the PVC pipe will extend 10″ or so beyond the lower region  180  of antenna  270 . This is to provide 10″ of PVC pipe mast for mounting, such that mounting will not detune the quarter-wavelength matching element  230 . Thus perhaps 10″ of coaxial cable  60 , e.g., RG-174, will be within the PVC. A suitable coaxial type connector, e.g., SO-239 or N-type, may be mounted to the lower end cap. The distal end of the 10″ or so length of coaxial cable within the PVC tubing will be connected to this connector. External to the end cap, coaxial cable  60  will terminate in an appropriate mating connector. 
         [0051]    The completed antenna may be slid into a suitable length of PVC tubing  280 , see  FIG. 7 . It is not necessary to anchor the antenna within the PVC tubing as the 300Ω twin lead and lengths of RG-174A are sufficiently rigid. A suitable connector, e.g., SO-239 connector, N-type, or chassis mount screw type Amphenol® 554-77 connector may be attached at the bottom of lower end cap  295 . Within the PVC pipe, a 10″ so length of coaxial cable will coupled between the connector and the Δ impedance-matching regions of quarter-wavelength matching element  230 . It is preferred that the overall length of the PVC pipe be about 10″ longer than the antenna length. This will permit about 10″ of space below the lower end of the antenna within the PVC such that mounting the PVC to a mast, e.g.,  300  with clamps  310  or other mechanism will not detune the sensitive lower quarter-wavelength matching section  230 . It is preferred that the antenna be clamped (for mounting) only at the bottommost 10″ of PVC length to assure optimum performance of the antenna within minimal detuning effects from the adjacent environment, such as a mounting mast. 
         [0052]      FIG. 7  depicts different embodiments of the present invention used in a mobile configuration, in a handheld transceiver configuration, and in a base station configuration. Thus in the deployment shown at the upper left of  FIG. 7 , a roof-mounted antenna  270  is protected within a PVC pipe  280 . The feedline coaxial cable  60  is shown entering the building adjacent a window and is coupled to the RF connector of an electronic device  310 , e.g., a transceiver, receiver, or transmitter suitable for use at the wavelengths for which antenna  270  was designed. Typically electronic device  310  is a transceiver, which means it can transmit and can receive at the frequencies of interest. Often device  310  will communicate via a repeater  320 , which can receive a relatively weak incoming signal, perhaps from device  310 , and rebroadcast it, typically on a different frequency or band, often using an antenna disposed in a favorable location, perhaps atop a tall tower. Of course device  310  can also communicate directly with other equipment  310 , without recourse to a repeater, e.g., in so-called simplex mode. 
         [0053]    At the upper right corner of  FIG. 7 , device  310  is a low power, typically 3 W to 5 W, handheld transceiver, show coupled to antenna  270  via coaxial cable  60 . The upper end of antenna  270  is shown connected by a string or the like  330  to an overhead branch of a tree. In an emergency situation where the user of the handheld transceiver must make radio communication to summon help, the several dB gain provided by antenna  270  can well make the difference between successful communications and no communications. Advantageously it will be appreciated that antenna  270  can literally be rolled up and stuffed in a backpack or even a pocket, while camping. In practice antenna  270  can safely handle RF transmitted power in the range of about 50 W. 
         [0054]    At the lower right corner of  FIG. 7 , antenna  270  is again protected by PCV tubing and is mounted at the rear of a vehicle in a mobile configuration. Cable  60  is brought into the vehicle and coupled to device  310 , which is often hidden in the trunk or other out-of-sight location to minimize theft. In such installations a remote head connects electrically to device  310  and may be mounted by the driver&#39;s seat, with connection for a microphone, and with full control over the remotely located device. 
         [0055]    To summarize, the present invention provides an omni-directional collinear gain antenna that can be fabricated from a single length of twinlead, and that operates without radials or an absolute ground. The resultant antenna is inexpensive to fabricate, is light weight and thus readily and inexpensively shipped, and can be folded-up and kept in a backpack, or a glove compartment for use when needed. The 5 dB gain provided by such an antenna is substantial, especially when compared to the performance of the commonly used “rubber-duck” antennas found on handheld VHF and/or UHF low power transceivers. 
         [0056]    Modifications and variations may be made to the disclosed embodiments without departing from the subject and spirit of the invention as defined by the following claims.