Omni directional broadband coplanar antenna element

Abstract

The present invention provides an omni-directional antenna element configuration having a compensated radiation pattern. Broadband antenna elements are coplanarly disposed on a suitable planar dielectric material. A single element or antenna comprises a pair of balanced fed radiating microstrip elements symmetrically disposed about the centerline of a balanced signal feed network. Additionally, a pair of pattern augmentation rods positioned on each side of and proximate to the planar dielectric material running longitudinally to the centerline axis of a balanced feed network. Disposed proximate to each radiating element are partially coplanar, frequency bandwidth expanding microstrip lines. The combination of radiating elements together with pattern augmentation rods provides a broad bandwidth omni-directional radiating element suitable for use in multi-element antenna arrays.

Claims

1. An antenna structure comprising: a planar substrate comprising a dipole antenna; a first parasitic element separated from, and extending parallel to, a first side of the substrate by a first distance, and a second parasitic element separated from, and extending parallel to, from the first side of the substrate by a second distance; and a third parasitic element separated from, and extending parallel to, a second side of the substrate by a third distance, and a fourth parasitic element separated from, and extending parallel to, the second side of the substrate by a fourth distance, wherein the dipole antenna and the parasitic elements are configured for omni-directional radiation, and wherein the first parasitic element and the fourth parasitic element are symmetrically arranged opposite each other relative to the substrate, and wherein the second parasitic element and the third parasitic element are symmetrically arranged opposite each other relative to the substrate.

2. The antenna structure of claim 1 wherein the dipole antenna is printed on the substrate.

3. The antenna structure of claim 1 wherein the first and second distances and the third and fourth distances are selected for omnidirectional radiation.

4. The antenna structure of claim 1 wherein the first and fourth parasitic elements are substantially the same length and the second and third parasitic elements are substantially the same length.

5. The antenna structure of claim 2 wherein the first distance is less than the second distance and the fourth distance is less than the third distance.

6. The antenna structure of claim 1 wherein the dipole antenna comprises a first radiating element arranged on the first side of the substrate and a second radiating element arranged on the second side of the substrate.

7. The antenna structure of claim 1 wherein the four parasitic elements are arranged at the same height relative to the dipole antenna.

8. The antenna structure of claim 1 wherein an antenna operational frequency is within the frequency band of approximately 3.30 GHz to 3.80 GHz.

9. The antenna structure of claim 1 wherein the first parasitic element and the fourth parasitic element are symmetrically arranged directly opposite each other relative to the substrate, wherein the second parasitic element and the third parasitic element are symmetrically arranged directly opposite each other relative to the substrate.

10. A radio frequency base station comprising: a substrate comprising at least one antenna; a first parasitic element separated from, and extending parallel to, a first side of the substrate by a first distance, and a second parasitic element separated from, and extending parallel to, the first side of the substrate by a second distance; and a third parasitic element separated from, and extending parallel to, a second side of the substrate by a third distance, and a fourth parasitic element separated from, and extending parallel to, the second side of the substrate by a fourth distance, wherein the at least one antenna and the parasitic elements are configured for omni-directional radiation, and wherein the first parasitic element and the fourth parasitic element are symmetrically arranged opposite each other relative to the substrate, wherein the second parasitic element and the third parasitic element are symmetrically arranged opposite each other relative to the substrate, wherein the second and third parasitic elements are each spaced substantially the same distance from the substrate, and wherein the first and fourth parasitic elements are each spaced substantially the same distance from the substrate.

11. The radio frequency base station of claim 10 wherein the at least one antenna is at least one dipole antenna printed on the substrate.

12. The radio frequency base station of claim 10 wherein the first and second distances and the third and fourth distances are selected for omnidirectional radiation.

13. The radio frequency base station of claim 10 wherein the first distance is less than the second distance and the fourth distance is less than the third distance.

14. The radio frequency base station of claim 10 wherein the first parasitic element and the fourth parasitic element are located at the same height relative to the antenna.

15. The radio frequency base station of claim 10 wherein the second parasitic element and the third parasitic element are located at the same height relative to the antenna.

16. The radio frequency base station of claim 11 wherein the at least one dipole antenna comprises a first radiating element arranged on the first side of the substrate and a second radiating element arranged on the second side of the substrate.

17. The radio frequency base station of claim 10 wherein an antenna operational frequency is within the frequency band of approximately 3.30 GHz to 3.80 GHz.

18. The radio frequency base station of claim 10 wherein the substrate, the first and second parasitic elements and the third and fourth parasitic elements are surrounded by a radome.

19. The radio frequency base station of claim 10 wherein the first parasitic element and the fourth parasitic element are symmetrically arranged directly opposite each other relative to the substrate, wherein the second parasitic element and the third parasitic element are symmetrically arranged directly opposite each other relative to the substrate.

20. A radio frequency device comprising: an antenna structure including a substrate having configured thereon an antenna; a first parasitic element separated from, and extending parallel to, a first side of the substrate by a first distance, and a second parasitic element separated from, and extending parallel to, the first side of the substrate by a second distance; and a third parasitic element separated from, and extending parallel to, the second side of the substrate by a third distance and a fourth parasitic element separated from, and extending parallel to, the second side of the substrate by a fourth distance, wherein the first parasitic element and the fourth parasitic element are symmetrically arranged opposite each other relative to the substrate, wherein the second parasitic element and the third parasitic element are symmetrically arranged opposite each other relative to the substrate, wherein the first distance is substantially equal to the fourth distance and the second distance is substantially equal to the third distance, wherein the second and third parasitic elements are each spaced substantially the same distance from the substrate, and wherein the first parasitic element and the fourth parasitic element are substantially the same shape.

21. The radio frequency device of claim 20 wherein the at least one antenna and the parasitic elements are configured for omni-directional radiation.

22. The radio frequency device of claim 20 wherein the first parasitic element and the fourth parasitic elements are arranged at substantially the same height with respect to the substrate.

23. The radio frequency device of claim 20 wherein the at least one antenna is at least one dipole antenna printed on the substrate.

24. The radio frequency device of claim 20 wherein the second parasitic element and the third parasitic element are arranged at substantially the same height with respect to the substrate.

25. The radio frequency device of claim 20 wherein the first parasitic element and the fourth parasitic element are symmetrically arranged directly opposite each other relative to the substrate, wherein the second parasitic element and the third parasitic element are symmetrically arranged directly opposite each other relative to the substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a top planar view and selected planar cross-sections of an omni-directional antenna element in accordance with the invention.

(2) FIG. 2 is an XY cross sectional view of an antenna element in accordance with the invention utilizing a dual tube configuration, mounted inside a radome tube.

(3) FIG. 2A is an XY cross sectional view of an antenna element in accordance with the invention utilizing a quad horizontal tube configuration, mounted inside a radome tube.

(4) FIG. 2B is an XY cross sectional view of an antenna element in accordance with the invention utilizing quad vertical tube configuration, mounted inside a radome tube.

(5) FIG. 3 is a left sided perspective view of an antenna element in accordance with the invention.

(6) FIG. 4 is a right sided perspective view of an antenna element in accordance with the invention.

(7) FIG. 4A is a vertically oriented perspective view of an antenna element in accordance with the invention.

(8) FIG. 5 is a graph showing input return loss for a dual 190 mil tube configuration, as a function of spacing (R1 range of 360 to 440 mil) from the dielectric plane surface.

(9) FIG. 6 is a graph showing input return loss for a dual tube configuration, as a function of tube diameter (160 to 250 mil) placed R1=440 mils from the surface of the dielectric plane.

(10) FIG. 7 is a graph showing azimuth gain ripple as a function of a dual (190 mil) tube placement (R1=360 to 560 mils) above the surface of the dielectric plane.

DETAILED DESCRIPTION OF THE INVENTION

(11) One object of the present invention is to provide dielectric based coplanar antenna elements which have broad frequency bandwidth and are easy to fabricate using conventional PCB processes. The present invention may preferably utilize a radiating element structure described in patent application Ser. No. 12/212,533 filed Sep. 17, 2008 and provisional patent application No. 60/994,557 filed Sep. 20, 2007, the disclosures of which are incorporated herein by reference in their entirety. In addition to coplanar radiating elements the present invention preferably takes advantage of pattern augmentation rods positioned in near proximity to the dielectric plane, equidistant to each surface side. To achieve an omni-directional radiation pattern a pair of symmetrically opposing radiating elements are preferably fed by a balanced feed network structure. The balanced feed structure provides equal signal division for each radiating element to achieve a symmetric radiation pattern. Additionally, a broad band balun is used to convert between a balanced feed network and an unbalanced, coaxial feed network.

(12) In carrying out these and other objectives, features, and advantages of the present invention, a broad bandwidth antenna element is provided for use in a wireless network system.

(13) Next a preferred embodiment of the present invention will be described. Reference will be made to the accompanying drawings, which assist in illustrating the various pertinent features of the present invention. In certain instances herein chosen for illustrating the invention, certain terminology is used which will be recognized as being employed for convenience and having no limiting significance. For example, the terms horizontal, vertical, upper, lower, bottom and top refer to the illustrated embodiment in its normal position of use. Some of the components represented in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention.

(14) FIG. 1 shows a top (XY planar view) view of a coplanar omni directional antenna element, 100, according to an exemplary implementation, which utilizes a substantially planar dielectric material 12. Additional antenna elements exterior of dielectric plate 12 are omitted from this figure for clarity and will be described later. Two broad bandwidth radiating elements 10a and 10b are disposed symmetrically on each side of dielectric material 12 about the Y axis. Construction of such radiating elements 10a and 10b employs a method which prints or attaches thin metal conductors directly on top 12a and bottom 12b sides of a dielectric substrate 12, such as a PCB (printed circuit board). The square dielectric plate 12 is dimensioned to fit all necessary conductors in a manner which is not only compact but which provides a desired radiation pattern, frequency response and bandwidth over the desired frequency. In an exemplary embodiment the desired radio frequency (RF) is approximately 3.30 GHz to 3.80 GHz while coplanar omni-directional antenna element, 100 is constructed utilizing commercially available PCB material manufactured by Taconic, specifically Taconic RF-35, with .sub.r=3.5 and thickness=30 mills. Alternative dielectric substrates (PCB material) 12 are possible provided that properties of such substrate are chosen in a manner to be compatible with commonly available PCB processes; alternatively metal conductor attachment to the dielectric substrate can be achieved through various means known to the skilled in the art.

(15) As shown, omni-directional antenna element 100 is provided with an upper dielectric 12a (12b is a lower side of a dielectric) side RF unbalanced input-output port 106. Input RF signals are further coupled over balun 104 structure (details are omitted). A balun is an electromagnetic structure for interfacing balanced impedance device or circuit, such as an antenna, with an unbalanced impedance, such as coaxial cable or microstrip line. In its common use a balanced signal comprises a pair of symmetrical signals which are equal in magnitude and opposite in phase (180 degrees). In contrast, an unbalanced impedance may be characterized by a single conductor for supporting the propagation of unbalanced (i.e., asymmetrical) signals relative to a second conductor (i.e., ground). Numerous balun structures are known to those skilled in the art for converting the unbalanced to balanced signals and vice versa.

(16) Thereafter, balanced RF signals are coupled onto 50 Ohm balanced impedance transmission line 102 (bottom side transmission line 112 is not visible) which is connected to 50 to 25 Ohm balanced transformer comprising co-aligned bi-planar transmission lines 108, 118. Conventional implementation of a transformer can readily utilize 35.3 Ohm characteristic impedance microstrip lines. Radiating elements' 10a, 10b characteristic load impedance is not the same as a conventional (73 Ohms) dipole known in the art. Instead, load impedance function of several variables such as parasitic coupling element spacing (30, 28) and mutual overlap o1, pattern augmentation rods 206, 208 positioning and diameter as well as several other variables to a lesser degree. Utilizing commercially available computer software (HFSS), radiating element 10a and 10b are optimized as a unit to provide an omni-directional radiation pattern as well as suitable load impedance (50 Ohms). Having 50 ohm load impedance greatly simplifies the feeding (110a-120a and 110b-120b) structure for each radiating element 10a, 10b. In a preferred implementation 50 Ohm balanced microstrip line (110a-120a and 110b-120b) pairs are used to feed respective radiating elements (10a, 10b) from the end of the transformer 108, 118 from a common node (not labeled). The lengths of the 50 Ohm balanced microstrip line (110a-120a and 110b-120b) pairs also are, optimized to provide an omni-directional pattern among other parameters. Alternative feed implementations are possible that may provide additional benefits or circuit simplification.

(17) A detailed description of a preferred embodiment of radiating element 10 can be found in patent application Ser. No. 12/212,533 filed Sep. 17, 2008 and provisional patent application No. 60/994,557 filed Sep. 20, 2007 the disclosures of which are incorporated herein by reference in their entirety. This embodiment provides a broadband capability as described in the above applications. Alternative designs for radiating elements 10 can be employed, however, especially where broad bandwidth is not important and a variety of radiating element designs will be possible as known to those skilled in the art.

(18) With reference to FIG. 2 a radome 200 with rod support(s) 210 is presented in addition to (along Y Axis) ZX planar view of dielectric plate 12. Rod support(s) 210 may be a suitable lightweight nonconductive material, for example such as Teflon or an RF transparent plastic. Supports 210 may have a planar shape as shown or other suitable shape to fit within radome 200. Proximate to, and running along longitudinal axis of the dielectric plate 12 are radiation pattern augmentation rods 206 and 208, positioned above and below top 12a and bottom 12b surface of dielectric plate 12 and attached to supports 210. The two radiation pattern augmentation rods 206 and 208 are symmetrical about the x-axis, and disposed equidistantly R1 from the surface of the dielectric. Preferably, the two radiation pattern augmentation rods 206 and 208 are constructed using conductive material, such as aluminum and the like. For additional weight and cost savings plastic rods with metallic surface treatment can be utilized, while metal based rods can utilize a thin wall metal tube or an extrusion instead of solid metal rod material. Therefore, the term rod as used herein covers all such variations and is not limited to a solid or a precisely cylindrical shape.

(19) It will be appreciated by those skilled in the art that the conductive rods 206, 208 parasitically couple to the electromagnetic field of radiating elements 10a, 10b and have currents induced on their surface thereby becoming parasitic radiating elements. This provides an augmentation of the beam pattern from that of the elements 10 alone. More specifically, absent the radiation pattern augmentation rods 206 and 208 the beam pattern of radiating elements 10a, 10b would be bidirectional in nature, directed along the +/x direction of FIG. 2. With the addition of the radiation pattern augmentation rods 206 and 208 the beam pattern becomes substantially omni-directional. Since the radiation pattern augmentation rods 206 and 208 operate as parasitic elements no feed network is required to supply the rods. Also, a ground plane is not:necessary. As a result the omni-directional antenna can be light weight and inexpensive relative to other omni-directional antenna designs.

(20) Performance of the omni-directional antenna 100 element equipped with a pair of radiation pattern augmentation rods 206 and 208 can be further modified which may provide improved performance in some applications. A single rod, can be replaced with pair of similarly constructed rods on each side of dielectric plate 12 to form a quad rod implementation. Quad rod implementations can be oriented horizontally (FIG. 2A) or vertically (FIG. 2B). It is also possible to replace a single pairing of rods (206a, b and 208a, b) with a single piece extrusion or the like and variations in shape may be provided from the rod or tube illustrated.

(21) Preferred dimensions for a 3.30 GHz to 3.80 GHz embodiment with 50 impedance source 106 impedance are as follows.

(22) TABLE-US-00001 Element Dimension Min (mills) Max (mills) Typical (mills) 24, 26 W1 86 90 88 24, 26 L1 66 67 66.4 28, 30 W2 105 120 112 28, 30 L2 570 580 576 30 <> 26 s1 90 94 92 28 <>30 O1 252 264 258 110, 120 W3 86 90 88 110, 120 L3 540 550 544 108, 118 W4 135 139 137 108, 118 L4 475 485 480 206, 208 R1 400 540 440 206, 208 d1 150 200 190 206a-b, 208a-b R2 460 560 520 206a-b, 208a-b H1 190 240 200 206a-b, 208a-b d2 150 200 190 206a-b, 208a-b R3 340 400 360 206a-b, 208a-b V1 80 140 100 206a-b, 208a-b d3 60 120 100

(23) Results employing exemplary parameters were obtained. FIG. 5 is a graph showing input return loss for a dual 190 mil tube configuration, as a function of spacing (R1 range 360 to 440 mil) from the dielectric plane surface. FIG. 6 is a graph showing input return loss for a dual tube configuration, as a function of tube diameter (160 to 25 mil) placed R1=440 mils from the surface of the dielectric plane. FIG. 7 is a graph showing azimuth gain ripple as a function of a dual (190 mil) tube placement (R1=360 to 560 mils) above the surface of the dielectric plane.

(24) The present invention has been described primarily in solving the aforementioned problems relating to expanding useful frequency bandwidth of a coplanar antenna element while providing a nearly uniform omni-directional radiation pattern. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Accordingly, variants and modifications consistent with the following teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described herein are further intended to explain modes known for practicing the invention disclosed herewith and to enable others skilled in the art to utilize the invention in equivalent, or alternative embodiments and with various modifications considered necessary by the particular application(s) or use(s) of the present invention.