Abstract
An omni-directional triband antenna operates without ground radials with gain commensurate with a half wavelength vertical on each band. The triband antenna includes a dual-band twinlead J-pole providing half wavelength radiators for UHF and VHF, and an impedance transformer defining feedpoints to which a length Lc of coaxial cable is attached. The Lc lower end is the triband antenna connector port. Intermediate band radiators are first and second wire elements that collectively are a half-wavelength at the intermediate band. The first element is wound helically about the impedance transformer, with upper end floating and lower end connected to a first feedpoint. The second element is wound helically about the Lc upper portion of coaxial cable, with upper end connected to the remaining feedpoint, and lower end of the element floating. The helical windings radiate vertically and there is no cross-interference between antenna radiation in any of the three bands.
Claims
1. An omni-directional triband antenna operable absent ground radials in at least one band selected from VHF band, UHF band, and intermediate VHF-UHF band, with performance of a half wavelength vertical dipole on each band, comprising: a dual-band (VHF-UHF) J-pole antenna of length L1 formed from a first lead of wire spaced-apart and parallel to a second lead of wire, and includes: a half wavelength vertically disposed VHF radiator; a half wavelength vertically disposed UHF radiator; and a passive impedance transformer having length l1 of said total length L1, disposed between a bottommost region of said UHF radiator and a bottommost region of said J-pole antenna whereat said first lead and said second lead are connected together to form a 0 bottom end of said J-pole antenna such that a distance above said 0 bottom end there exists a first feedpoint in said first lead and a second feedpoint in said second lead; a length Lc of coaxial cable having a center conductor with a first end coupled to one of said first feedpoint and said second feedpoint, and having a second end defining a center conductor connection port for said triband antenna, and having a braid shield with a first end coupled to whichever of said first feedpoint and said feedpoint is unconnected to said first end of said length Lc of coaxial cable, and having a second end defining a braid shield connection port for said triband antenna; wherein said center conductor connection port and said braid shield connection port at said second end of said length Lc of coaxial cable define an antenna connection port for said triband antenna, to which antenna connection port a device operable in at least one said band can be coupled via an external length of coaxial cable a vertically disposed half wavelength intermediate band antenna that includes: a first helix comprising a first length of wire, having an upper end and a lower end and a quarter wavelength at said intermediate band therebetween, wrapped helically concentrically in a first direction about said passive impedance transformer section of said J-pole antenna with a helix length of Lx1<l1, said upper end of said first length of wire allowed to float, and said lower end of said first length of wire connected to one of said first feedpoint and said second feedpoint; and a second helix comprising a second length of wire, having an upper end and a lower end and a quarter wavelength at said intermediate band therebetween, wrapped helically concentrically in said first direction about an upper portion of length Lx2<Lc of said length Lc of coaxial cable, said upper end of said second wire connected to whichever one of said first feedpoint and said second feedpoint is unconnected to said first helix, and said lower end of said second wire allowed to float; whereby a diameter of each said helix is substantially less than a wavelength at said intermediate band such that said half wave intermediate band antenna is substantially vertically disposed; and whereby cross-band interference with said J-pole antenna from said half wavelength intermediate band antenna is substantially eliminated as said first helix and said second helix are each formed about a passive region of said triband antenna.
2. The triband antenna of claim 1, wherein said triband antenna has at least one characteristic selected from a group consisting of (i) an impedance between said first feedpoint and said second feedpoint of about 50, and (ii) an impedance at said antenna connection port of about 50.
3. The triband antenna of claim 1, wherein at least a portion of said length L1 is twinlead comprising said lead 1 and said lead 2, said twinlead having an impedance of about 300.
4. The triband antenna of claim 1, wherein said passive impedance transformer acts as a quarter wavelength at VHF and is three-quarter wavelength at UHF.
5. The triband antenna of claim 1, further including means for decoupling said UHF radiator from at least a portion of said VHF radiator.
6. The triband antenna of claim 5, wherein said means for decoupling includes a length l4 of coaxial cable having an upper end with center conductor and braid shield coupled together and to a lower end of at least a portion of said VHF radiator, and having a lower end whereat said braid shield floats and said center conductor of length l4 is connected to an upper end of said UHF radiator; wherein l4 is a quarter wavelength at said UHF band.
7. The triband antenna of claim 1, wherein with respect to each said helix, said first direction is selected from a group consisting of (i) clockwise relative to a longitudinal axis of said triband antenna, and (ii) counterclockwise clockwise relative to a longitudinal axis of said triband antenna.
8. The triband antenna of claim 1, wherein overall length of said antenna is about 64.
9. The triband antenna of claim 1, where said VHF band includes a frequency range from about 140 MHz to about 170 MHz.
10. The triband antenna of claim 1, wherein in said VHF band, SWR1.5 over a frequency range of about 144 MHz to about 148 MHz.
11. The triband antenna of claim 1, wherein said UHF band includes a frequency range from about 420 MHz to about 470 MHz.
12. The triband antenna of claim 1, wherein in said UHF band, SWR1.7 over a frequency range of about 440 MHz to about 450 MHz.
13. The triband antenna of claim 1, wherein said intermediate band includes a frequency range from about 220 MHz to about 225 MHz.
14. The triband antenna of claim 1, wherein in said intermediate band, SWR1.5 over a frequency range of about 220 MHz to about 225 MHz.
15. The triband antenna of claim 1, further including a protective sheath of PVC tubing sized to encase said triband antenna.
16. A triband antenna having an upper, high impedance, end and a lower end defining a low impedance antenna connection port, and operable as a half wave vertical antenna absent ground radials in at least one band selected from VHF, UHF, and intermediate VHF-UHF, comprising: an uppermost length l5 of twinlead, whose uppermost end is said upper high impedance end of said triband antenna and whose lower end is also high impedance, said twinlead comprising a first lead spaced apart from a parallel second lead; said length l5 forming a portion of a half wave VHF radiator for said triband antenna; means for decoupling UHF, having an upper end coupled to said second lead of said lower end of said length l5 of twinlead, and having a lower end, with a length l4 therebetween; wherein a length of said lead 1 opposite said means for decoupling UHF defines a cut extending said length l4; a length equal to (L1-l5-l4) of twinlead extending downward from said lower end of said means for decoupling and at a lower end defining a 0 region of said triband antenna; an uppermost region of length l3 of said length equal to (L1-l5-l4) forming a quarter wavelength vertically disposed UHF radiator for said triband antenna, said second lead of said length l3 coupled to said lower end of said means for decoupling, and said first lead of said length l3 floating at each end; wherein at VHF band operation, said length l3 operates with said length l5 and said length l4 to form a half wave vertically disposed VHF radiator of said triband; a short length l2 of twinlead coupled to a lower end of said length l3, said second lead of said length l2 coupled to a lower end of said second lead of a bottommost region of said length l3, and said first lead of said length l2 defining a cut extending said length l2: a passive impedance transformer having length (l1+) of twinlead having an upper end coupled to a lower end of said length l2, and having a lower end defining a 0 region of said triband antenna, and defining a first low impedance feedpoint on said lead 1 and defining a second low impedance feedpoint in said lead 2 at a distance above said 0 region; a length Lc of coaxial cable having a center conductor and a braid shield, said center conductor at an upper end of said length Lc coupled to one of said first low impedance feedpoint and said second low impedance feedpoint, and said braid shield at said upper end of said length Lc coupled to which low impedance feedpoint is unconnected to said upper end of said center conductor; wherein said center conductor connection port and said braid shield connection port at said second end of said length Lc of coaxial cable define a connection port for said triband antenna, to which antenna connection port a device operable in at least one said band can be coupled via an external length of coaxial cable, a first helix comprising a first length of wire, having an upper end and a lower end and a quarter wavelength at said intermediate band therebetween, wrapped helically concentrically in a first direction about said passive impedance transformer a helix length of Lx1<l1, said upper end of said first length of wire allowed to float, and said lower end of said first length of wire connected to one of said first low impedance feedpoint and said second low impedance feedpoint; and a second helix comprising a second length of wire, having an upper end and a lower end and a quarter wavelength at said intermediate band therebetween, wrapped helically concentrically in said first direction about an upper portion of length Lx2<Lc of said length Lc of coaxial cable, said upper end of said second wire connected to whichever one of said first low impedance feedpoint and said second low impedance feedpoint is unconnected to said first helix, and said lower end of said second wire allowed to float; whereby a diameter of each said helix is substantially less than a wavelength at said intermediate band such that said first helix and said second helix together form a vertically disposed half wave intermediate band antenna; and whereby cross-band interference from said half wavelength intermediate band antenna is substantially eliminated as said first helix and said second helix are each formed about a passive region of said triband antenna.
17. The triband antenna of claim 16, wherein said means for decoupling is a quarter wavelength UHF stub.
18. The triband antenna of claim 16, wherein said means for decoupling includes a length l4 of coaxial cable having an upper end with center conductor and braid shield coupled together and to a lower end of at least a portion of said VHF radiator, and having a lower end whereat said braid shield floats and said center conductor of length l4 is connected to an upper end of said UHF radiator; wherein l4 is a quarter wavelength at said intermediate band.
19. The triband antenna of claim 16, wherein: said antenna exhibits an SWR1.5 over a frequency range of about 144 MHz to about 148 MHz; said antenna exhibits an SWR1.7 over a frequency range of about 440 MHz to about 450 MHz; and said antenna exhibits an SWR1.5 over a frequency range of about 220 MHz to about 225 MHz.
20. The triband antenna of claim 16, wherein said twinlead is approximately 300 impedance, and said antenna connection port has an impedance of about 50.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIGS. 1A and 1B depict a wide-frequency range, omni-directional Don Johnson type screwdriver antenna, according to the prior art;
(2) FIG. 2A depicts an omni-directional collinear antenna that requires radials, according to the prior art;
(3) FIG. 2B depicts voltage amplitude versus phase for various elements of the collinear antenna of FIG. 2A, according to the prior art;
(4) FIG. 3 depicts an omni-directional collinear antenna that uses a quarter-wave sleeve rather than radials, according to the prior art;
(5) 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;
(6) FIG. 5 depicts a mono-band omni-directional J-pole antenna with slight gain that operates without radials, according to the prior art;
(7) FIG. 6A depicts a DBJ-1 (WB6IQN) dual-band J-pole antenna that operates without radials, according to the prior art;
(8) FIG. 6B depicts the irregular radiation pattern that would result if the DBJ-1 antenna of FIG. 6A omitted a UHF decoupling stub, according to the prior art;
(9) FIG. 7 depicts a triband J-pole comprising three parallel coupled J-poles fabricated from copper tubing, according to the prior art;
(10) FIG. 8 depicts a triband antenna comprising a DBJ-1 dual-band (VHF-UHF) J-pole antenna coupled at the low impedance feedpoint region to a 220 MHz copper pipe J-pole antenna, according to a first experimental prototype of the present invention;
(11) FIG. 9 depicts a triband antenna comprising a DBJ-1 dual-band (VHF-UHF) J-pole antenna coupled at the low impedance feedpoint to a 220 MHz horizontal dipole, according to a second experimental prototype of the present invention;
(12) FIG. 10 depicts a triband antenna comprising a DBJ-1 dual-band (VHF-UHF) twinlead J-pole antenna coupled at the low impedance feedpoints to a 220 MHz horizontally disposed segmented hoop element concentric about the antenna length, according to a third experimental prototype of the present invention;
(13) FIG. 11A depicts a triband antenna comprising a DBJ-1 dual-band (VHF-UHF) twinlead J-pole antenna coupled at the low impedance feedpoints to a first 220 MHz quarter wavelength length of wire coaxially disposed around the passive non-radiating impedance matching region of the J-pole antenna, and a second 220 MHz quarter wavelength length of wire coaxially disposed around the upper region of the coaxial cable connected to the triband antenna, according to preferred embodiments of the present invention;
(14) FIG. 11B depicts the triband antenna of FIG. 11A mounted within a protective length of end-capped PVC pipe, according to preferred embodiments of the present inventions;
(15) FIG. 12A, FIG. 12B, FIG. 12C depict respective acceptably good SWR vs. frequency characteristics for the 2 m, 1.25 m, and 70 cm frequency ranges of the triband antenna of FIG. 11A, according to preferred embodiments of the present invention; and
(16) FIG. 13 depicts exemplary deployment of embodiments of the triband antenna of FIG. 11A, according to preferred embodiments of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
(17) FIG. 8 depicts applicant's initial attempt to design a triband antenna. Antenna 280 comprises a DBJ-1 (WB6IQN) dual-band VHF-UHF stacked J-pole twinlead antenna portion 260 (similar to antenna 260 in FIG. 6A), comprising sections 262, 264, 266, and 268. However at the bottom of the passive non-radiating impedance transform section 262 of VHF-UHF J-pole 260 there is coupled a 220 MHz 0.5 diam. copper J-pole antenna portion 288 with copper quarter-wavelength stub 284 (similar to the 220 MHz portion 284 of antenna 280 in prior art FIG. 7). Two lengths of coaxial cable, e.g., RG174A or the like, are disposed within copper antenna portion 288. The center conductor of one coaxial cable is coupled to lead 2 of the above-lying stacked J-pole assembly, and the center conductor of the other coaxial cable exits via an entry hole from member 288 and is soldered to the shell of copper stub member 286. The ground shield of this second coaxial cable is soldered the copper housing 288 near the exit hole. At the bottom of the overall antenna, the two center conductors are joined together to the feed coaxial cable 60 center conductor. The shield of cable 60 is soldered to copper member 288 as shown.
(18) Referring still to FIG. 8, the resultant antenna 280 did perform well as a triband antenna in the 2 m, the 1.25 m, and the 70 cm frequency ranges. The dual-band J-pole portion 260 of antenna 280 may be sized similarly to antenna 260 shown in FIG. 6A: l5 was about 17, UHF decoupling stub 266 was a length l4 of about 4.25 length l2 of RG174A coaxial cable, the l3 portion of 264 was about 11.25, gap 240 was length l2 of about 0.25, length l1 of portion 262 was about 16, and distance was about 1.25. (These dimensions assume that the dual-band J-pole antenna portion 260 will be encased in PVC tubing.) However the overall vertical size of antenna 280 was too large: L1 was about 49, and L2 was about 36 for a total vertical size of about 85 or about 2.2 m. The antenna vertical size and the presence of the soldered copper pipe region 286, 288 caused applicant to reject this initial design.
(19) The configuration of FIG. 9 was next investigated by applicant, wherein a DBJ-1 (WB6IQN) dual-band VHF-UHF twinlead antenna portion 260 (similar to antenna 260 in FIG. 6A) includes a horizontally disposed 220 MHz dipole comprising elements 290, each element 290 being a quarter wavelength at 220 MHz (about 12 in length). The 220 MHz dipole elements 290 are coupled preferably at the dual-band J-pole antenna low impedance feedpoints, whereat coaxial cable 60 is connected. Dimensions l1, l2 (gap), l3, l4 and l5 are similar to what has been given with respect to the dual-band J-pole antenna configuration portions shown in FIG. 6A and FIG. 8. Triband antenna 280 had overall height L1 about 49. While antenna 280 exhibited triband functionality in the 2 m, 1.25 cm, and 70 cm bands, unfortunately the horizontally disposed radial-like 220 MHz dipole 290 radiated RF horizontally, whereas the vertically disposed 2 m and 70 cm portions of the antenna radiated RF vertically, as is generally preferred. Further horizontally extending 220 MHz dipole elements 290 reduced robustness of overall antenna triband antenna 280.
(20) Applicant next experimented with the triband antenna configuration shown in FIG. 10. The upper portion of triband antenna 290 comprises a DBJ-1 (WB6IQN) dual-band stacked J-pole VHF-UHF twinlead antenna portion 260 (similar to antenna 260 in FIG. 6A, and antenna portions 260 in FIG. 8, FIG. 9, and FIG. 10), coupled preferably at the low impedance coaxial cable 60 feedpoints to a horizontally disposed 220 MHz segmented circular hoop element 300 made of wire and having a circumference of about 24, e.g., a half wavelength at 220 MHz. Element 300 is two semi-circles. One end of each semi-circle terminates at one of the two low impedance feedpoints, and the other end of each semi-circle is separated from the other end of the other semicircle by a small insulation piece, shown in phantom in FIG. 10. The vertical axis of antenna 290 lies through the center of the twinlead and passes through the center of the plane of circular hoop element 300, which extends outward from the vertical axis with a radius of about 3.8. To minimize interaction with the main J-pole configuration, circular hoop element 300 wants to stand off and away from the J-pole at the feedpoints by at least 1.
(21) Understandably having to secure segmented circular half wavelength element 300 to J-pole 260 decreases robustness of the overall antenna. In FIG. 10, dimensions l1, l2, l3, l4, l5 are similar to that given with respect to antennas shown in FIG. 6A and FIG. 8, with overall height L1 being about 49. While antenna 290 functioned as a working triband antenna, horizontally disposed hoop element 300 radiated RF at 220 MHz substantially horizontally rather than the more preferred vertical radiation. However in the embodiment of FIG. 10 it was realized that disposing the 220 MHz element 300 coaxially about the length of J-pole antenna 260 advantageously kept 220 MHz RF radiation from substantially interfering with RF radiation in the 140 MHz band or the 440 MHz band, and vice versa. All in all the configurations of FIG. 9 and FIG. 10 encouraged applicant that his experiments were leading in a proper direction, and that a practical triband antenna design might be attainable notwithstanding that the desired third (intermediate) band was not harmonically related to either the VHF or UHF bands.
(22) FIG. 11A depicts a triband antenna 310, according to embodiments of the present invention that satisfies the initially stated design criteria. The upper portion of triband antenna 310 includes a DBJ-1 dual band J-pole 260 as has been described with respect to FIG. 6A, and the upper portions of the antenna structures shown in FIGS. 8, 9, and 10. Thus looking at antenna 310 from the top down, uppermost is a portion of the VHF RF radiator 268 of length l5 (about 17), below which in LEAD 2 appears UHF decoupling stub 266, preferably a length l4 (about 4.25) of RG74A coaxial cable With the outer shield connected at the top to the coaxial cable center conductor, but open at the bottom end of the decoupling stub. As noted the short at the top of decoupling stub 266 translates at a quarter wavelength of UHF to an open circuit at the bottom of the stub. Continuing downward with antenna 310, beneath UHF decoupling stub 266 occurs UHF radiator 264 of length l3 (about 11.25), a half wavelength at UHF. At UHF frequencies, decoupling stub 266 appears somewhat like an open circuit and decouples the portions of the antenna higher than element 264, which allows element 264+l2 to operate as a half wave UHF RF radiator. However at VHF frequencies, decoupling stub 266 acts somewhat like a short circuit, allowing a half wave VHF RF radiator to be formed from the series-connected combination of antenna portions l2+264, 266, and 268.
(23) Continuing further downward, a gap 240 is cut in LEAD 1 with gap height l2 of about 0.25 to isolate UHF radiating element 264 from lower sections of the antenna. Below gap 240 is found the passive non-RF radiating impedance transforming section 262, having length l1 of about 16. As noted, section 262 acts as a quarter wavelength impedance stub at VHF and acts as a three-quarter wavelength stub at UHF, as the UHF band is an odd harmonic (third harmonic) of the VHF band. The bottommost region of DBJ-1 dual-band J-pole 260 is shorted together at 180, and at a distance (about 1.25) above the short there is found a low impedance region (about 50) whereat first and second feedpoints are present. A length Lc, typically about 14, of coaxial cable 60, e.g., RG174A, has its upper end connected to the two feedpoints. For example the center conductor of cable 60 may be connected to the first feedpoint on LEAD 1 and the braid shield of cable 60 may be connected to the second feedpoint on LEAD 2, or vice versa. As shown in FIG. 11A, the center conductor of coaxial cable 60 (typically RG174A) connects to one feedpoint, while the braid shield of the coaxial cable 60 connects to the other feedpoint. The bottommost portion of length Lc of coaxial cable 60 is the antenna port for triband antenna 260, the region whereat an external length of coaxial cable (who other end is connectable to a transceiver or the like) may be connected to the triband antenna.
(24) Thus far antenna 310 as described implements performance on the VHF band and the UHF band. Triband antenna performance at intermediate band (about 220 MHz-225 MHz) as provided in preferred embodiments of the present invention will now be described. Intermediate band functionality is created by providing near the bottom portion of antenna 310 a half wave RF radiator at intermediate band frequencies, comprising a first quarter wavelength of wire 340-1 and a second quarter wavelength of wire 340-2. Each wire 340-1, 340-2 if stretched out would be a quarter wavelength at the intermediate band, about 12 length. Adequate stiffness is provided by single 16 gauge wire for 340-1, 340-2. As noted from applicant's earlier experiments with the triband antenna configurations of FIG. 9 and FIG. 10, the intermediate band elements should have minimal adverse magnetic coupling effects that could distort good patterns of RF radiation on each of the three bands. It is further desired to maintain a compact and robust form factor for antenna 310. Thus the first quarter wavelength of wire 340-1 is wrapped helically about at least a portion of the passive non-RF radiating impedance transforming section 262 of the antenna, namely a helix top-to-bottom length Lx1 of the length l1 of section 262. The bottom end of wire 340-1 is attached to one of the two low impedance feedpoints, and the upper end of wire 340-1 is left floating. Length 11 of impedance transforming section 262 is about 16, and the wound top-to-bottom helix length for wire 340-1 Lx1, about 7. The second quarter wavelength of wire 340-2 is wrapped around a length Lc, preferably about 14) of the upper approximately half of coaxial cable 60 and will have a wound top-to-bottom helix length Lx2, which occupies about half of length Lc. Length Lx1 and length Lx2 may but need not be equal and will be in the range of 6 to about 8. Length Lc could be much longer than 14, e.g., many feet, but an approximate 14 length is convenient for mounting the antenna, which includes length Lc, within PVC tubing of reasonable height.
(25) In FIG. 11A, wire 340-1 and wire 340-2 should each be wound in the same direction, e.g., both wound clockwise or both wound counter-clockwise, to avoid distortions in the generated RF pattern. In the embodiment shown in FIG. 11A, the upper end of wire 340-2 is connected to the remaining low impedance feedpoint, while the lower end of this wire is left floating, e.g., is not connected to anything. If desired the helix winding connections to the two feedpoints could be reversed. Better intermediate band RF radiation occurs if helical windings 340-1, 340-2 are stretched out with a smaller turns/inch pitch (without overlying an active portion of the antenna), rather than wound very closely together. In practice a winding pitch of about one turn/inch works out well. If diameter Dx of the two helical windings were too large, magnetic effects could distort RF radiation at intermediate band frequencies, which is not desired. Note that winding 340-2 preferably is not allowed to simply fall vertically, as it would then be parallel to coaxial cable 60, and its magnetic field would distort the RF radiation pattern, and adversely affect the impedance matching, or SWR. In practice Dx preferably is small such that triband antenna 310 can fit within a length of 0.75 O.D. 200 PSI PVC pipe, e.g., Dx< 0.75. Such PVC pipe or tubing provides protection for the antenna within against inclement weather, UV radiation that can weaken the twinlead, and facilitates robust outdoor mounting. FIG. 11B depicts such installation.
(26) It is noted in FIG. 11A, that both quarter-wavelength windings 340-1, 340-2 are wound helically advantageously about passive, non-RF radiating regions of triband antenna 310. As noted region 262, about a portion of which is wound first helix 340-1, is simply an impedance transformer and radiates no RF at any band. Further, coaxial cable 60 has, by definition, a surrounding braid shield and is also passive, and radiates no RF at any band. Thus, second helix 340-2 is thus also wound about a passive, non-RF radiating element. This coaxial helical disposition of the vertically disposed intermediate band RF radiating elements 340-1, 340-2 relative to the longitudinal axis of triband antenna 310, and the relatively small helix diameter Dx, e.g., < 0.75, relative to 220 MHz quarter wavelengths (about 6) minimizes adverse magnetic coupling effects. Advantageously this results in maintaining a low SWR in each of the three bands, and also promotes a substantially undistorted intermediate band RF propagation pattern. The radiating elements for VHF, UHF are each half wavelength end-fed vertical dipoles, and the radiating element for intermediate band operation is a half wavelength center-fed vertical dipole. Consequently there is substantial elimination of cross-band radiation interference between VHF, intermediate band, and UHF operation, and no substantial degradation of triband antenna performance.
(27) As noted, dimensions given for antenna 310 are approximate within a few percent, and assume the finished antenna will be mounted within PVC tubing, as in FIG. 11B. Were such not the case, the various dimensions would be increased by about 4%-5%. Dimensions may also vary, for example, if twinlead having a different velocity factor is used to make antenna 310. In general, overall length Lx of triband antenna 310 will be about 64 or about 1.6 m. (If antenna 310 is deployed within protective PVC tubing, the tubing length with endcaps may be about 1.7 m.) Note too in FIG. 11A that coaxial cable 60 is connected to and drops down vertically and substantially parallel to the longitudinal axis of the remainder of triband antenna 310. This disposition advantageously reduces the potential for this length Lc of coaxial cable 60 to physically interfere with radiated RF at any of the three bands.
(28) In practice an antenna 310 is cut and assembled and is then inserted into a length of appropriate PVC tubing such as 320 in FIG. 11B. Antenna characteristics are then measured at UHF, at intermediate band, and at VHF frequencies, using a network analyzer (e.g., an Agilent 8753D) or an antenna analyzer (e.g., an MFJ-269 Pro). Instruments such as these can measure the complex impedance of triband antenna 310 at frequencies in each band, and can measure the standing wave ratio (SWR) at different frequencies in each band. Ideally impedance should be about 50 with no substantial complex component, and ideally SWR is 1:1. Adjustments to the characteristics of antenna 310 can generally be made at UHF by changing slightly the magnitude of l2, usually by cutting away slightly more material from the bottom of the gap. Next antenna 310 is characterized at VHF, with adjustments made to the upper end of l5. Finally the antenna is characterized at the intermediate band by slightly compressing or extending both helixes 340-1, 340-2, preferably equally. Advantageously the topology of the preferred embodiments allow these adjustments to be made without disrupting adjustments already made on the other bands. Once an individual triband antenna 310 has been fine-tuned per the above procedure or equivalent, the antenna can be permanently inserted into PVC tubing as shown in FIG. 11B, and described below.
(29) As shown in FIG. 11A and FIG. 11B, triband antenna 310 comprises 300 twinlead with a small, typically 4.24 section of coaxial cable (UHF decoupling stub 266 two lengths of preferably 16 gauge wire (340-1, 340-2), and an approximately 14 length of coaxial cable 60. These components are relatively lightweight and inexpensive, and can be rolled up and mailed as a lightweight package to an end user. If the antenna was cut and dimensioned for use within PVC tubing, preferably the antenna, but not PVC tube 320 (see FIG. 11B), is mailed to the end user with instructions to obtain the specific type of PVC tubing 320 locally, e.g., 0.75 OD 200 PSI PVC, for which the antenna was designed, and to insert the antenna within and then cement on PVC end caps. If desired, PVC upper end cap 330 with nylon string or the like 332 glued to the inner cap surface to secure the upper end of antenna 310 through a hole in the uppermost portion of the plastic twinlead material (not shown to avoid cluttering the drawings), and lower end cap 344 with coaxial antenna connector 350 attached, may be mailed to the end user along with the rolled-up antenna and instructions.
(30) In some embodiments it may be desired to always deploy the antenna without protective PVC tubing. In such cases the antenna dimensions will typically be 4%-5% greater than those given for in-PVC tubing embodiments due to the change in velocity factor of PVC vs air, and characterization of the antenna will take place in open air, using the exemplary procedure noted above. As such, the rolled up antenna, without end caps, and with a coaxial or other connector attached to the bottom end of coaxial cable 60, or indeed with length Lc increased to several feet is lightweight and compact. The antenna can be kept in a vehicle glove compartment, in a desk drawer, or even in a shirt pocket, for deployment when needed, often with a handheld handi-talkie transceiver. In such applications the typically 6 dB-8 dB gain realized by a triband antenna according to embodiments of the present invention over the performance of a typical so-called rubber duck antenna used on such devices is very substantial. If Lc is several feet in length, antenna 310 may be suspended from a tree branch or a house door, to provide a bit of elevation.
(31) As noted earlier, portions of lead 1 in regions 268 and 264 are simply floating and do not radiate RF and these portions of lead 1 could be omitted. If desired, lead 2 in regions 268, 264, and 240 could simply be a single wire. As such, a triband antenna according to the present invention may be said to be fabricated at least in part from twinlead. In some embodiments, the twinlead runs the full length L1 of the dual-band J-pole antenna portion of the triband antenna, and in other embodiments twinlead may only be the length of +l1 or +l1+l2 (with gap 240 formed in lead 1). In such latter embodiments, there would be no lead 1 higher than gap 240, and lead 2 may be a single wire, but not necessarily wire in a portion of twinlead.
(32) FIG. 11B depicts triband antenna 310 as shown in FIG. 11A, mounted within a length Lt, typically about 65-66 (about 1.7 m), of preferably 0.75 O.D. 200 PSI PVC tubing 320. The top of antenna 310 can be suspended with a nylon string 332 or the like from the inner surface of PVC end cap 330, perhaps with glue. Antenna 310 then extends downward within tubing 320 and at the bottommost end, a coaxial or other bulkhead type receptacle 350 is attached to a bottom PVC end cap 340. This receptacle attaches to the lower end coaxial center conductor and braid shield of coaxial cable 60 is becomes the connection port triband antenna 310. Exemplary such receptacles include an SO-239 connector, N-type, or chassis mount screw type Amphenol 554-77 connector. The upper and lower PVC end caps may be permanently attached to PVC tube 320, i.e., with adhesive. In use, an external length of coaxial cable 60 (see FIG. 13) with a suitable mating plug simply attaches to the bottom of antenna 310 at connector 350. The bottom 7-8 of PVC 320 surrounds only the passive, non-radiating bottom portion of coaxial cable 60. This readily enables clamping the bottom portion of the tubing, and thus the antenna, to a metal vent pipe (see 355 in FIG. 13) or the like.
(33) FIG. 12A, FIG. 12B, and FIG. 12C respectively depict standing wave ratio (SWR) vs. operating frequency for operation in the radio amateur VHF band, the intermediate VHF-UHF band, and the UHF band for triband antenna 310 as shown in FIG. 11A. In an ideal world with a perfect antenna the SWR would be 1:1 at all frequencies. However in practice an SWR1.5:1 or so is acceptable. As such, the data in FIG. 12A, FIG. 12B, and FIG. 12C demonstrate that a very acceptable SWR is present when using the triband antenna of FIG. 11A on any or all of the three bands for which it is designed. As noted, fine tuning antenna 310 to optimize performance on one of the three bands advantageously does not substantially affect performance on the remaining bands
(34) Turning now to FIG. 13 various deployments of triband antenna 310 as described in FIG. 11A are shown. For example at the upper left portion of FIG. 13 antenna 310 is depicted in phantom mounted to a vent pipe 355 on a house roof within a length of PVC pipe 320 having a top end cap 330 and a bottom end cap 340, with receptacle connector 350 at the bottom, similarly to what was described in FIG. 11B. After exiting the bottom of antenna 310, coaxial cable 60 enters the house adjacent a window and is shown coupled to the RF connector of an electronic device 360, e.g., a transceiver, receiver, or transmitter suitable for use at the wavelengths for which triband antenna 310 was designed. Typically electronic device 360 is a transceiver, which means it can transmit and can receive at the frequencies of interest. Often device 360 will communicate via a repeater 370, which can receive a relatively weak incoming signal, perhaps from device 360, 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 360 can also communicate directly with other equipment 360, without recourse to a repeater, e.g., in so-called simplex mode.
(35) At the upper right portion of FIG. 13, device 360 is a low power, typically 3 W to 5 W, handheld transceiver, show coupled to triband antenna 310 via coaxial cable 60. The upper end of antenna 310 is shown connected by a string or the like 360 to an overhead branch of a tree. In an emergency situation where the user of the handheld transceiver (or handi-talkie) must make radio communication to summon help, the 6 dB to 8 dB gain provided by antenna 310 over a rubber duck antenna can make the difference between successful communications and no communications. Advantageously, as noted if triband antenna 310 is designed for use, and used, without protective PVC tubing, the antenna can literally be rolled up and stuffed in a backpack or even a pocket. In practice triband antenna 310 can safely handle RF transmitted power in the range of about 75 W over the three bands for which the antenna was designed.
(36) At the lower right corner of FIG. 13, antenna 310 is again protected by PVC tubing 320 and is mounted at the rear of a vehicle in a mobile configuration. Coaxial cable 60 is brought into the vehicle and coupled to device 360, 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 360 and may be mounted by the driver's seat, with connection for a microphone, and with full control over the remotely located device.
(37) To summarize, the present invention provides a triband omni-directional collinear antenna that operates without radials or an absolute ground on any or all of the VHF, intermediate band, and UHF band frequencies. The resultant antenna is inexpensive to fabricate, e.g., using 300 twinlead or the like, some wire, some coaxial cable, and is light weight and thus readily and inexpensively shipped. The antenna can be designed and deployed within protective PVC pipe, or can be designed and use without pipe. In the latter case, the antenna can be rolled-up and kept in a backpack, or a glove compartment for use when needed, perhaps with a VHF, UHF, or intermediate band mobile transceiver. The antenna has the gain performance of a half wavelength dipole on each band, namely 2.1 dB gain over an isotropic radiation, and provides about 6 dB to about 8 dB gain over the rubber duck type antenna found on handheld VHF-UHF-intermediate band handheld transceivers. At UHF and at VHF operation the triband antenna provides an end-fed half-wavelength vertical dipole, and at intermediate band operation the triband antenna provides a center-fed half-wavelength vertical dipole. The antenna can be adjusted or fine-tuned to affect operation on one band without interfering with the performance of the antenna on the other two bands. Depending upon presence or absence of a protective PVC tubing sheath, antenna height is about 1.6 m-1.7 m. In short, all of the design goals set out by applicant have been met by embodiments of the present invention.
(38) While embodiments of the preferred invention have been described with respect to designing a triband antenna operable over VHF, UHF, and intermediate band frequencies, it will be appreciated that a triband antenna operating over a different selection of three bands could also be made. Further it will be appreciated that applicant's use of a helically wound half wave antenna formed over passive components of a J-pole antenna could be used even if that J-pole were a monoband antenna rather than a dual band antenna.
(39) 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.
