GB2495093A - Dipole antenna with a composite right and left handed transmission line - Google Patents

Abstract

An antenna system, or a method of forming such a system, comprises of a dipole element with first and second half elements 1409, 1412 which are fed via respective feed cables passing through a conductive tube 1407 which is electrically connected to a plurality of outer plates 1405 by inner plates 1406 to form a composite right/left handed (CRLH) transmission line. The antenna system may be a wideband collinear antenna array 1401 that comprises linearly stacked dipole structures 1485, 1486, 1487. The inner plates 1406 may provide an inductive connection between the outer plates 1405 and the metal tube 1407. Various additional capacitive and/or inductive formations may be used in the transmission lines. Dipoles and CRLH transmission lines may be arranged radially around a metal tube 1407. The CRLH transmission lines are used to prevent anti-phase currents from being induced in the structure carrying the feed lines.

Description

OMNIDIRECTIONAL WIDEBAND COLUNEAR ANTENNA ARRAY

1. THE FIELD OF THE INVENTION

This invention relates generally to antennas making use of composite right / left hand (CRLH) transmission lines and more particularly to parallel-fed broadband antenna arrays making use of CRLH transmission lines.

2. BACKGROUND OF THE INVENTION

With new frequency bands being made available by regulating authorities, the requirement for antenna adaptable, wideband antennas increases. One example of such new bands being made available is in the frequencies allocated for White Space, another example is Long Term Evolution (LTE). A typical frequency range to be covered in White Space is from 470MHz to 790MHz, which is almost a 2:1 ratio. Because of the requirement to minimise interference with existing users of the same frequency spectrum, it would be advantageous if the polarisation of the antennas to be used with White Space equipment could be orthogonal to the polarisation used by the existing users of the spectrum. Specifically, a vertically polarised antenna for White Space equipment would minimise interference to current users, who predominantly use horizontal polarisation.

The optimal antenna for a base station requires that the radiation is omni-directional in azimuth and that it is high gain in elevation, preferably in a direction parallel to the ground surface, or pointing slightly downward. This ensures that the transmitted energy is directed at remote installations, and is not wasted in directions in free space where there are no terminal installations. Similarly, it ensures that the maximum signal is captured from the direction in which there are terminal installations, and that a minimum of noise is received from free space where there are no terminal installations. Omni-directionality in azimuth ensures that terminal installations at all horizontal angles are covered, without the need to rotate the antenna, either physically or electrically. A collinear antenna is an array of parallel dipole antenna elements stacked along a common axis. It is normal for collinear antenna arrays to be stacked vertically, so as to have a radiation pattern that is uniform in azimuth, while providing extra gain above what can be obtained from a single dipole, in elevation.

In terrestrial applications, as distinct to the free space case, the path travelled by a signal between a transmitter and a receiver will always comprise of a direct path and a multitude of reflected paths, the waves of which will be constructively and destructively interfering. Under certain conditions the reflected signal may be of a signal strength comparable to the direct path signal. In such cases it is advantageous if the radiation pattern of the antenna could be dynamically changed, for example by splitting the main lobe into two or more lobes, so that the path loss between the transmitter and the receiver is minimised. In certain cases it may also be desirable to statically or dynamically direct the antenna in azimuth. Appropriately weighted parallel multiple stacks allow directivity in azimuth. This, for example, allows a direct, dedicated link between a base station and a remote user. In general, this allows MIMO (multiple-input and multiple-output), SIMO (single-input and multiple-output) and MISO (multiple-input and single-output) operation in addition to 5150 (single-input and single-output) operation.

Many radio networks are asymmetric, in the sense that different equipment is used at the base station and the terminal. Typically, the equipment used at the base station can be more complex than the equipment at the terminal. The base station could be at a fixed installation, such as permanently attached to a building or tower, or it could be mounted on a vehicle, such as a bus, train or automobile.

3. THE BACKROUND ART It is well established in the field of antennas that a vertical stack of linear array of antennas provides a radiation pattern that is of uniform field strength in azimuth, while providing gain in elevation. Furthermore, wide bandwidth operation can be achieved through suitable design of the radiating elements. Such antennas are commonly used in fixed installations, such as radio base stations. Unfortunately, the feed lines interact in an undesirable way with the antenna in such a way that either the field pattern gets distorted, that the driving point impedance is affected, or that both the impedance and radiation pattern are affected. This happens because currents are induced in conductive objects close to radiating elements. In the case where the radiating elements are substantially parallel to the feed structure, or support structure, the image currents induced in the feed or support structure are out of phase with the currents in the radiating elements.

In such a case most of the power is reflected towards the generator, as opposed to being radiated, resulting in a poor voltage standing wave ratio (VSWR).

Fig. 1A shows a common solution to the wide bandwidth requirement, which is to thicken the radiating elements of a dipole, and to taper the thickness or width of the radiating elements, as in bi-conical antennas, butterfly antennas or caged dipole antennas 155. These dipoles are then commonly stacked vertically to achieve gain in elevation. To simultaneously achieve a uniform radiation pattern in azimuth, it is common to feed each dipole element through a horizontal feed line 154 that is arranged perpendicular to the dipole elements. In the case of a vertical linear (collinear) stack the feed ends are bent through 90 degrees and attached to either the inside or outside of a mast structure 153. For the radiation to be substantially omni-directional in azimuth, this requires that the antenna elements are spaced very far from the mast structure.

Fig. lB shows how, alternatively, multiple collinear arrays formed from dipole elements 155 are arranged around the mast 153, typically at 120 degree intervals, resulting in three antenna arrays around the mast, fed through horizontal feed lines 154. These solutions make the installations large, susceptible to wind loading, and visually unattractive.

Fig. 1C shows yet another prior art solution in which the feed lines 157 are placed inside a concentric mast tube 153, inside the dipole elements 155, which are made hollow. In this case the radiation in azimuth is omni-directional. However, because of the induction of current in the feed line the return loss to the antenna feed is high. One common solution to this problem is to add electronically tuneable adjustable tuning elements 156, to each dipole element. These tuning elements are then set to different values for different frequencies. This has a number of disadvantages: the system becomes complex, if the quality factor of the impedance transformation is large the losses in the tuning networks can become excessive.

Another prior art solution to the induced currents adversely affecting the return loss is shown in Fig. 1D, where the feed lines 157 are placed inside a tube 153 and upon exit at each dipole feed point is fed through chokes 159 placed between dipole sections and routed through baluns ( balanced to unbalanced transformer) 158 to dipole elements 155. The chokes 159 are typically formed of ferrite sleeves, or of bundles of feed lines wound in spirals. If these chokes 159 contain ferrite cores and are small enough not to affect the radiation pattern, the losses in the chokes 159 can become very high. Typically, ferrite chokes are only reflective below about 100MHz, above which ferrite materials become absorbtive, reducing the efficiency of the antenna array. In the case where the chokes are formed through spirally winding feed lines over an air core, the choke is physically and electrically large, and the radiation pattern, bandwidth, or both are normally adversely affected.

Another solution is to use a series feed, as opposed to the parallel feed described, above. Phase reversals are required between dipole elements, and these can only be realised over very restricted bandwidths, limiting the application to single-frequency or narrow-band usage.

4. SUMMARY OF THE INVENTION

The present invention advantageously provides a parallel fed collinear array antenna for receiving and broadcasting signals comprising a single or multitude of wavelengths. The phase of the induced current in the feed line assembly is the main reason for the unsatisfactory operation of prior art solutions. Therefore, the present invention presents a feed line in which the phase of the currents induced in the feed structure are in phase with the currents in the feed elements.

Materials commonly found in nature, and used in radio engineering, are designated right-handed (RH) materials. For these materials the permittivity and permeability are both positive. Another type of material, designated left-handed (LH) material, was proposed by Veselago (Veselago, V, "The electrodynamics of

S

substances with simultaneously negative values of e and i',' Soviet Physics Uspekhi, vol. 10, no. 4, pp. 509-514, 1968). Practical implementation of pure LH material is problematic, and in practice all LH materials will have some RH properties. Indeed, LH and RH material can both be considered special cases of the more general composite right /left-handed (CRLH) materials.

lithe diameter of the feed line assembly in a collinear antenna is a small fraction of a wavelength, it behaves as a linear, or one-dimensional (10) structure.

Currents induced will be aligned along the length of the structure, with negligible currents induced across the width of the feed line assembly. The present invention makes use of this property, and the working can be described in terms of transmission line theory.

One embodiment of the system, among other, can be implemented as follows.

The feed lines to the dipole elements are enclosed inside a metal tube, of which the outer surface serves as the return path of a CRLH transmission line. In this embodiment, the CRLH elements are formed by metal outer plates suspended over the metal tube. Adjacent outer plates are capacitively coupled through the fringe capacitance between the outer plates. Each outer plate is connected to the metal tube with a metal inner plate which serves as an inductive post. The linear length of each outer plate is much smaller than the wavelength of the lowest frequency of operation. At the resonance frequency of the parallel LC circuit formed by the outer plate, the fringing capacitance, the inductance of the inductive post and the RH transmission line formed by the outer plates over the metal tube, and over a limited frequency range around the resonance frequency, the impedance of the outer boundary of the structure becomes very large. Over a limited bandwidth around the resonant frequency both TE and TM surface waves are suppressed. When the phase of the reflected wave is between -90° and +90°, the reflective wave is in phase with the incident wave. In this embodiment, a dipole placed over the outer plates at a distance very small compared to a wavelength, and in parallel to the metal tube, induces in-phase currents in the metal tube over the limited bandwidth. In a second embodiment of the system, two dipoles are placed diametrically opposite each other. In a third embodiment of the system, four dipoles are placed 90° apart. For all three embodiments, antennas so defined, can be stacked end-on-end, so as to form linear arrays.

Other embodiments, using different numbers, both even and odd numbers, of dipoles spaced around the metal tube, are possible, and form part of the current invention.

Additional features and advantages of the invention will be or become apparent to one with skill in the art upon examination of the accompanying drawings and detailed description, which together illustrate by way of example, the features of the invention.

S. BRILF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a view of a collinear antenna fed orthogonally, in accordance with prior art.

FIG. lB is a view of a collinear antenna with elements spaced at 120°, in

accordance with prior art.

FIG. 1C is a view of a collinear antenna with a coaxial feed line and active tuning

elements, in accordance with prior art.

FIG. 1D is a view of a collinear antenna with a coaxial feed line and separation

choke elements, in accordance with prior art.

FIG. 2A shows the construction of the CRLH transmission line and two dipole half-elements.

FIG. ZB shows the equivalent electrical model of the CRLH transmission line, with two dipole half-elements.

FIG. ZC shows the simplified equivalent electrical model of the CRLH transmission line, with two dipole half-elements.

FIG. ZD shows the equivalent electrical model for a unit cell of a CRLH line.

FIG. ZE shows the equivalent electrical model for a CRLH line made of 8 unit cells.

FIG. 3 shows the transmission properties of a CRLH line.

FIG. 4 is a perspective view of a single dipole assembly, according to a first exemplary embodiment of the invention.

FIG. 5 is a perspective view of a single dipole assembly, according to a second exemplary embodiment of the invention.

FIG. 6 is a perspective view of a single dipole assembly, according to a third exemplary embodiment of the invention.

FIG. 7 is a perspective view of the electrical connections to a single dipole assembly, according to a first exemplary embodiment of the invention.

FIG. 8 is a perspective view of the electrical connections to a single dipole assembly, according to a second exemplary embodiment of the invention.

FIG, 9 is a perspective view of the electrical connections to a single dipole assembly, according to a third exemplary embodiment of the invention.

FIG. 10 is a top view of the dielectric layers inside, and surrounding a single dipole assembly.

FIG. 11 shows an example of enhancement of the series inductance per unit length of the outer plates.

FIG.12 shows examples of enhancement of the coupling capacitance between the outer plates.

FIG. 13 shows examples of enhancement of the inductance of the inner plates.

FIG. 14 is a perspective view of an antenna array stacked from three dipole assemblies, according to a third exemplary embodiment of the invention.

FIG. 15 is a detail perspective view of a dipole assembly, according to a third exemplary embodiment of the invention.

FIG. 16A shows the orientation of the axes and the definition of angles used in the radiation patterns.

FIG. 16B shows an example azimuth radiation pattern obtained with dipole elements according to a first embodiment of the invention.

FIG. 16C shows an example azimuth radiation pattern obtained with dipole elements according to a second embodiment of the invention.

FIG. 16D shows an example azimuth radiation pattern obtained with dipole elements according to a third embodiment of the invention.

FIG. 16E shows an example elevation radiation pattern obtained with an array formed of a vertical stack of five dipole elements according to a second embodiment of the invention.

FIG. 16F shows an example elevation radiation pattern obtained with an array formed of a vertical stack of three dipole elements according to a third embodiment of the invention.

FIG. 17 shows the connections made to single dipole assemblies according to a first, second and third exemplary embodiment of the invention, the return loss for each case is shown in FIG. 17D.

FIG. 18A, FIG. lBS and FIG. 18C show exemplary front-end modules, as applied to a first embodiment of the invention.

FIG. 19A shows the use of a weighting network and vertical distance between dipole elements so as to change the radiation pattern in elevation.

FIG. 195, FIG. 19C and FIG. 19D show three examples of radiation patterns according to FIG. 19A.

FIG. ZOA shows a multiple array, formed of three arrays formed from a third exemplary embodiment of the invention, so as to obtain specific gain in azimuth in desired directions, and for MIMO applications.

FIG. 20B and FIG. 20C show two examples of radiation patterns according to FIG. ZOA.

FIG. 21 shows a weighting network applied to the terminals of a third exemplary embodiment of the invention, to achieve control over the gain in azimuth.

FIG. 22 shows multiple vertical stacks of arrays.

FIG. 23A and FIG. 23B show an exemplary construction of the CRLH structure.

6. DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2A shows the cross section through a dipole formed from a first downward dipole half element 208 and a second upward dipole half element 212, supplied with a first terminal connection 216 to the first dipole half element and second terminal connection 220 to the second dipole half element. The dipole is placed in close proximity to a metal tube 207, which could act as physical support and as conduit for feed lines. The feed lines and any control lines required are preferably fed from one end of the metal 207 tube and exit at an opening in the tube close to the terminal connections 216 and 220. A CRLH structure is formed by the metal tube 207 and outer plates 205 which are spaced from the metal tube and connected to it by inner plates 206. Inner plates 206 form an electrical connection between the outer plates and the metal tube. Between adjacent outer plates 205 there is a gap 252. For the purpose of the description the dipole is formed from two thin strips of metal having the same width throughout the length of each dipole element. As is well known, a dipole can also be constructed from conductive elements that have finite thickness, from meandering conductive elements and from dipoles formed of elements with non-uniform width, all of which are included in the scope of the invention.

The equivalent electrical network for the CRLH structure is shown in FIG. 2B. The outer plates of the CLRH structure are represented by sections of transmission line TLs and the gap between adjacent outer plates by series capacitance Cs. The inner plates act as inductive posts Lp, with which shunt capacitors Cp are associated. The return path of the CRLH transmission line is the metal tube, which is represented by TLg. The two dipole elements 208 and 212, with their terminations 220 and 216, are shown over the schematic representation of the CRLH transmission line.

A simplification of the equivalent electrical network is shown in FIG. 2C. The sections of transmission line TIs are represented by series inductors Ls, and the sections of transmission line TLg are represented by series inductors Lg. The gap between adjacent outer plates has series capacitance Cs. The inner plates are represented by inductive posts Lp. Shunt capacitors Cp is associated with the outer plates and the inner plates. The two dipole elements 203 and 212, with their terminations 220 and 216, are shown over the schematic representation of the CRLFI transmission line.

One element of the CLRH structure, defining a unit cell, is shown in FIG. 2D. The radiation from the line is represented by two resistors, Rr and Rs. The resistance of Rr is constant and the resistance of Rs is modelled to increase linearly with frequency.

FIG. 2E shows the circuit model for $ CRLH unit cells arranged to form a CRLH transmission line. The Partial Element Equivalent Circuit (PEEC) values for the lumped components can be calculated, using closed-form equations, or through finite element analysis, or through a combination of these methods.

The inductance of a sheet is given by IXR [ f21\ 1W Lsheet = 2ff [0.5)< In + with 1 the length of the sheet in metre, w the width of the sheet and R0 the permeability of free space.

The inductance of a cylinder with a circular cross-section is given by Ixt0 Ii I 12\ I 2 1 2 ln+1l+(_) )_41+() +i+ with I the length of the cylinder in metre, r the radius of the cylinder and 1o the permeability of free space.

The fringing capacitance between two plates is given by (13+12) _____ cosh I IT 19 with C the fringing capacitance, e the dielectric constant on one side of the plates, £2 the dielectric constant on the other side of the plates, w the width of the plates and g the gap between the plates.

In one example of a CRLH line the metal tube could have a circular cross section with a diameter 19mm, the length of each outer plate could be 76mm, the width of each outer plate could be 76mm, the spacing between plates could be 2.48mm, the inner plate could be 38mm long, the inner plate could have a width of 29.5mm at its widest section and 17mm at its narrowest section. The transfer characteristics for such a line are shown in FIG. 3, in which the finite element model for a line consisting of eight unit cells is compared with the lumped model.

The band gap, over which transmission is attenuated, is indicated.

FIG. 4 is a perspective view of a single dipole assembly 400, according to a first exemplary embodiment of the invention. The feed line to the dipole assembly is routed through a metal tube 407. The CRLH transmission line construction is as follows. Outer plates 405 are suspended over the metal tube 407 in such a way that a capacitive gap 452 is formed between adjacent outer plates 405. One exemplary construction for the outer plates 405 is shown, where the plates are bent inward at an angle of 300. In other exemplary constructions, a plate with circular or flat section could be used. One end of an inner plate 406 is attached to the middle of each outer plate 405, with the other end of the an inner plate 406 attached to the metal tube 407. The first downward dipole half element 408 and the first upward dipole half element 412 are suspended over the outer plates 405 and fed through gaps 432 in the outer plate 405 from lower terminal connection 416 and from upper terminal connection 420. For the purposes of the description the metal tube is shown as having a circular cross section. The present invention includes metal tubes of different cross section, including but not limited to circular, square, rectangular or octagonal cross sections.

FIG. 5 is a perspective view of a single dipole assembly 500$ according to a second exemplary embodiment of the invention. The feed line to the dipole assembly is routed through a metal tube 507. Two CRLH transmission lines are constructed as follows. Double sets of outer plates 505 arranged on opposite sides of the metal tube 507 are suspended over the metal tube 507 in such a way that a capacitive gap 552 is formed between adjacent outer plates 505. One exemplary construction for the outer plates 505 is shown, where the plates are bent inward at an angle of 30°. In another exemplary construction, a plate with circular section could be used. In another exemplary construction, the outer plates 505 are flat, and suspended over a metal tube 507 of rectangular cross section. One end of an inner plate 506 is attached to the middle of each outer plate 505, with the other end of the inner plate 506 attached to the metal tube 507. The first downward dipole half element 508, the first upward dipole half element 512, the third downward dipole half element 510 and the third upward dipole half element 514 are suspended over the outer plates 505 and fed through gaps 532 in the outer plate 505 to lower terminal connection 516 and to upper terminal connection 520. Similar feed connections are made to the other two dipole elements, 510 and 514.

FIG. 6 is a perspective view of a single dipole assembly 600, according to a third exemplary embodiment of the invention. The feed line to the dipole assembly is routed through a metal tube 607. Four CRLH transmission lines are constructed as follows. Quadruple sets of outer plates 605 arranged on four quadrant sides of the metal tube 607 are suspended over the metal tube 607 in such a way that a capacitive gap 652 is formed between adjacent outer plates 605. One exemplary construction for the outer plates 605 is shown, where the plates are bent inward at an angle of 300. In another exemplary construction, a plate with circular section could be used. In another exemplary construction, the outer plates 605 are flat, and suspended over a metal tube 607 of square cross section. One end of an inner plate 606 is attached to the middle of each outer plate 605, with the other end of the inner plate 606 attached to the metal tube 607. Four dipoles are placed over four quadrants of the metal tube 607. Shown are the first downward dipole half element 608, the first upward dipole half element 612, the fourth downward dipole half element 611 and the fourth upward dipole half element 615 suspended over the outer plates 605 and fed through gaps 632 in the outer plate 605.

FIG. 7 is a perspective view of details of the electrical connections to a single dipole assembly, according to a first exemplary embodiment of the invention. A first downward dipole half element 708 and a first upward dipole half element 712 are shown. The lower terminal connection 716 to the first dipole half element and the upper terminal connection 720 to the first dipole half element of the dipole so formed are connected through a lower stripline 744 and an upper stripline 745 to the two balanced terminals of a balun 746. The signal connection to the antenna feed point 704 is through a coaxial cable 743.

FIG. 8 is a perspective view of details of the electrical connections to a single dipole assembly, according to a second exemplary embodiment of the invention.

A first downward dipole half element 808, a first upward dipole half element 812, a third downward dipole half element 810 and a third upward dipole half element 814 are shown. The lower terminal connection 816 to the first dipole half element, the upper terminal connection 820 to the first dipole half element, the lower terminal connection 818 to the third dipole half element and the upper terminal connection 822 to the third dipole half element of the dipole so formed are connected through a lower stripline 844 and an upper stripline 845 to the two balanced terminals of a balun 846. The signal connection to the antenna feed point 804 is through a coaxial cable 843.

FIG. 9 is a perspective view of details of the electrical connections to a single dipole assembly, according to a third exemplary embodiment of the invention. A first downward dipole half element 908, a first upward dipoie half element 912, a second downward dipole half element 909, a second upward dipole half element 913, a third downward dipole half element 910,3 third upward half dipole element 914, a fourth downward dipole half element 911 and a fourth upward dipole half element 915 are shown. The connections to the first of the four dipoles so formed is fed through a balun 933 and an impedance matching inductor 937 to the upper terminals of a coaxial cable 941. The connections to the second of the four dipoles so formed are fed through a balun 934 and an impedance matching inductor 938 to the upper terminals of a coaxial cable 941.

The connections to the third of the four dipoles so formed are fed through a balun 935 and an impedance matching inductor 939 to the upper terminals of a coaxial cable 942. The connections to the fourth of the four dipoles so formed is fed through a balun 936 and an impedance matching inductor 940 to the upper terminals of a coaxial cable 942. The two coaxial cables 941 and 942 could be routed down the inside of the metal tube to the bottom of the antenna assembly, or to a position in-between the dipole feed point and the bottom of the assembly, where the two coaxial cables are connected in shunt. An impedance transforming transformer 947 could be used to transform the impedance of the antenna to a desired impedance, typically 500. The signal connection to the antenna feed point 904 is through a coaxial cable 943.

FIG. lOis a top view of the dielectric layers inside, and surrounding a single dipole assembly, according to a third exemplary embodiment of the invention. Four inner plates 1006 are shown joined close to the metal tube 1007. A first dielectric layer 1048 fills the space between the metal tube 1007 and a second dielectric layer 1049. A second dielectric layer 1049 fills the space between the first dielectric layer 1048 and a third dielectric layer 1050. A third dielectric layer 1050 fills the space between the second dielectric layer 1049 and a fourth dielectric layer 1051. First dipole elements 1012, second elements 1013, third elements 1014 and fourth elements 1015 are contained inside the third dielectric layer 1050. A fourth dielectric layer 1051 fills the space between the third dielectric layer 1050 and the free-space in which electromagnetic waves propagate. The fourth dielectric layer lOsicould result from the need to put a protective or structural cover over the antenna assembly, and could be made of an organic plastic polymer. The properties of each of the other dielectric layers could be chosen in such a way as to optimally reduce the size of the antenna assembly. As is well known to those skilled in the art, the velocity of propagation of an electromagnetic wave is slowed down inside a material with a relative dielectric constant greater than unity. By introducing such materials, the size of the antenna can be reduced, with a consequent reduction in bandwidth. Optimisation of parameters, using analytical and numerical field solving techniques, could be used to achieve the desired balance between size and bandwidth. In one specific exemplary embodiment, all the relative dielectric constants could be unity, in another all but the fourth dielectric layer 1051 could be unity, and in other embodiments all dielectric constants could assume unique values.

In many cases, it is advantageous to increase the per unit inductance of the CRLH transmission line without a corresponding increase in shunt capacitance. FIG. hA shows an example of how the series inductance per unit length of the outer plates 1105 could be increased through the introduction of a plurality of horizon cutout sections 1160. FIG. 118 shows how the inductance per unit length of the outer plates 1105 could be increased through the introduction of a meander section 1165. FIG. 11C shows how the inductance per unit length of the outer plates 1105 could be increased through the introduction of a planar spiral inductor 1166. FIG. 110 shows how the inductance per unit length of the outer plates 1105 could be increased through the introduction of a lumped inductor 1167.

In many cases, it is advantageous to increase the fringing capacitance between the outer plates. FIG. 12A shows an example of how the fringing capacitance between metal plates 1205 could be enhanced through the introduction of series lumped capacitors 1261. FIG. 12B shows an example of how the fringing capacitance between metal plates 1205 could be enhanced through the introduction of a perpendicularly bent section 1262. FIG. 12C shows an example of how the fringing capacitance between metal plates 1205 could be enhanced through the introduction of a parasitic capacitive coupling plate 1263. FIG. 12D shows an example of how the fringing capacitance between metal plates 1205 could be enhanced through the introduction of a meandering interdigital capacitive coupling section 1264.

In some cases, it is advantageous to increase the per unit inductance of the inner plates without an increase in the length of the inner plates. In FIG. 13k, FIG. 138 and FIG. 13C it is shown how the inductance of the inner plates 1306 could be increased without having to move the outer plates 1305 further away from the metal tube 1307. FIG. 13A shows an example of how the series inductance per unit length of the inner plates 1306 could be increased through the introduction of a meander line section 1365. FIG. 13B shows an example of how the series inductance per unit length of the inner plates 1306 could be increased through the introduction of a planar spiral inductor 1366. FIG. 13C shows an example of how the series inductance per unit length of the inner plates 1306 could be increased through the introduction of a lumped inductor 1367. Another way in which the inductance of the inner plates 1306 could be increased is by narrowing the width of the inner plates 1306, down to the limiting case in which the plate object becomes a single wire. The converse can also be achieved: widening the width of the inner plates 1306, or increasing the thickness of the wire obtained in the limiting case, decreases the inductance.

FIG. 14 shows a perspective view of an antenna array 1401 stacked from three dipole assemblies 1485, 1486 and 1487, according to a third exemplary embodiment of the invention. In FIG. 14 some of the outer plates 1405 are removed in order to more clearly show the construction example. Each dipole assembly is made from four vertical dipoles that are arranged at 900 intervals over a CRLH transmission line structure. The CRLH transmission line structure is formed by the metal tube 1407, the outer plates 1405 and inner plates 1406. For the top dipole assembly making up the array 1401 shown are a first downward dipole half element 1408, a second first downward dipole half element 1409, a fourth downward dipole half element 1411, a first upward dipole half element 1412, a second upward dipole half element 1413, a third upward dipole half element 1414 and a fourth upward dipole half element 1415. A first cable connecting the bottom dipole assembly 1487 to a first antenna feed point 1402, a second cable connecting the middle dipole assembly 1486 to a second antenna feed point 1403 and a third cable connecting the top dipole assembly 1485 to a third antenna feed point 1404 are all preferably cut to the same length, so that the signals at the individual dipole feed points are in phase. The excess cable length could be wound around the metal tube 1407.

FIG. 15 is a detail perspective view of a dipole assembly, according to a third exemplary embodiment of the invention. In FIG. 15 some of the outer plates 1505 and part of the metal tube 1507 are removed in order to more clearly show the construction example. Shown are a lower termination 1516 to a first dipole lower half element, a lower termination 1517 to a second dipole lower half element, a lower termination 1518 to a third dipole lower half element, a lower termination 1519 to a fourth dipole lower half element, an upper termination 1520 to a first dipole upper half element, an upper termination 1521 to a second dipole upper half element, an upper termination 1522 to a third dipole upper half element, an upper termination 1523 to a fourth dipole half element, a lower terminal plate 1524 to a first dipole lower half element, a lower terminal plate 1525 to a second dipole lower half element, a lower terminal plate 1526 to a third dipole lower half element, a lower terminal plate 1527 to a fourth dipole lower half element, an upper terminal plate 1528 to a first dipole upper half element, an upper terminal plate 1529 to a second dipole upper half element, an upper terminal plate 1530 to a third dipole upper half element and an upper terminal plate 1531 to a fourth dipole upper half element. Cut-outs 1532 are made in outer plates 1505 adjacent to dipole feed points, to prevent an electrical short circuit between dipole elements and the CRLH transmission line structure.

FIG. 16A shows the orientation of the axes and the definition of angles used in the radiation patterns, simulated using finite element analysis.

FIG. 1GB shows an example azimuth radiation pattern obtained with dipole elements according to a first embodiment of the invention. The elevation angle 8 is 90°.

FIG. 16C shows an example azimuth radiation pattern obtained with dipole elements according to a second embodiment of the invention. The elevation angle B is 900.

FIG. 16D shows an example azimuth radiation pattern obtained with dipole elements according to a third embodiment of the invention. The elevation angle 8 is 90°.

FIG. 16E shows an example elevation radiation pattern obtained with an array formed cia vertical stack of five dipole elements according to a second embodiment of the invention. The azimuth angle 0 is 900.

FIG. 16F shows an example elevation radiation pattern obtained with an array formed of a vertical stack of three dipole elements according to a third embodiment of the invention. The azimuth angle 0 is 900.

FIG. 17A to FIG. 17C show test connections made to single dipole assemblies, in order to demonstrate the impedance match so obtained. For simulation purposes, the ideal transformers shown are used as baluns to convert balanced signals to unbalanced signals. FIG. 17A shows the connections made to a single dipole assembly according to a first exemplary embodiment of the invention. The two connections to the two dipole elements are shown as 1720 and 1720. FIG. 17B shows the connections made to single dipole assemblies according to a second exemplary embodiment of the invention, with the four connections to the dipole half elements indicated as 1720, 1716, 1722 and 1718. FIG. 17C shows the connections made to single dipole assemblies according to a third exemplary embodiment of the invention with the eight connections to the dipole half elements indicated as 1720, 1716, 1722, 1718, 1721, 1717, 1723 and 1719. The impedance match, simulated using finite element analysis and referenced to 500, for each case is shown in FIG. 17D, with Sli representing the return loss for the first exemplary embodiment, 522 representing the return loss for the second exemplary embodiment and S33 representing the return loss for the third exemplary embodiment.

Cable loss between a receiver and an antenna adds to the noise figure in the receiver. Also, cable loss between a transmitter and an antenna dissipates power in the cable, instead of transmitting all the available power. To overcome this limitation, front end modules (FEM) could be placed at the antenna, or as is shown here, inside the antenna. FIG. iSA to FIG. 18C show exemplary front-end modules, as applied to a first and second embodiment of the invention. FIG. 18A shows a completely passive implementation, where a balun 1846 is used to transform the balanced feed points 1820 and 1816 into an unbalanced signal that can be fed in a coaxial cable 1804, and where no attempt is made to amplify either the receive or transmit signals. FIG. 186 shows how a power amplifier PA is used to amplify the signal, when operating in transmit mode, to a desired output level. When in receive mode, the low-noise amplifier LNA is used to amplify the signal sufficiently to overcome cable losses. Switches S route the signals in transmit or receive mode appropriately through the PA and LNA. The switches S switch position is controlled by a line 1868, which for convenience is shown as a separate line, but which could also be one of the conductors in the coaxial line, which when used in a such a way, is appropriately decoupled with capacitors and inductors of suitable values. Common to many radio standards are the requirements for the limitation of spurious radiations. When transmit levels are sufficiently low, a single power amplifier PA as in FIG. 18B could adequately provide in this requirement. At higher power levels this becomes more difficult, because of inherent non-linearity in power amplifying devices. One solution to overcome this is to use larger output state active devices, which frequently leads to expensive systems. Another solution is to place one or more power amplifiers in parallel, using power combiners, or, as is shown in FIG. 18C, feeding each arm of a dipole half element with a separate power amplifier PA. While shown for use with dipole assembles containing single dipoles, the principle could be extended to cover dipole assemblies formed of multiple dipole elements.

Distance d in FIG. 19A is the distance between the lower dipole elements 1908 of one dipole assembly in a vertical array and the upper elements 1912 of the dipole assembly directly below it. The dipoles are placed over a CRLH transmission line 1869. Increasing the distance d increases the gain in elevation in the lower portion of the frequency band. Further increase in d leads to the formation of multiple beams and side-lobes, beginning in the upper part of the frequency band. Depending on the application, d can be optimised, using analytical methods or simulation. Also shown in FIG. 19A are weighting networks 1970 which could be placed at the dipole feed points, or inside the metal tube forming part of the CRLH transmission line 1869. Each weighting network 1970 contains a phase-retardation circuit and a gain section. The phase-retardation circuit could be made of fixed passive components, making for an array with a radiation pattern defined during manufacturing. The gain section inside each weighting network 1970 could consist of a fixed passive attenuator, or it could consist of as amplifier with fixed gain, making for an array with a radiation pattern defined during manufacturing. Preferably, the gain or phase, or both gain and phase in each weighting network 1970 could be made electronically-adjustable, making for an array with a radiation pattern that is dynamically adjustable. In such a case, each of the weighting networks 1970 could be supplied with control signal lines, which could conveniently be routed through the CRLH transmission line 1869. The signals to and from the weighting networks 1970 are combined in a power splitter/combiner 1971. In another embodiment of the weighting networks, the weighting networks 1970 could all be centralised away from the dipole feed points and co-located with the power splitter /combiner 1971. FIG. 19B to FIG. 19D shows vertical cuts through the radiation pattern in elevation for three cases.

In FIG. 19B the weighting is equal in both amplitude and phase for each of the dipole assemblies making up the array. In FIG. 19C the weighting is adjusted so that the radiation pattern is pointing downwards at an angle a, which is an advantageous direction for several base-station applications. FIG. 190 shows the case where the beam is purposely split into more than one section, through the use of the appropriate weighting, in order to receive both direct and reflected signals.

FIG. 20A shows a multiple array, formed of three arrays formed from a third exemplary embodiment of the invention 2001, so as to obtain specific gain in azimuth in desired directions, and for MIMO applications. By appropriately phasing the arrays, the gain in azimuth can be controlled, as shown in FIG. 20B and FIG. 20C. Preferably this is done dynamically, which allows for the radiation pattern to be directed in a specific direction depending on particular conditions at the time the radio connection is established. One particular case, as an example, is for MIMO applications.

FIG. 21 shows a weighting network applied to the terminals of a third exemplary embodiment of the invention, to achieve control over the gain in azimuth. A first downward dipole half element 2108, a first upward dipole half element 2112, a second downward dipole half element 2109, a second upward dipole half element 2113, a third downward dipole half element 2110, a third upward dipole half element 2114, a fourth downward dipole half element 2111 and a fourth upward dipole half element 2115 are shown. The connections to the first of the four dipoles so formed is fed through a balun 2133 and an impedance matching inductor 2137 to a weighting network 2170. The connections to the second of the four dipoles so formed is fed through a balun 2134 and an impedance matching inductor 2138 to a weighting network 2170. The connections to the third of the four dipoles so formed is fed through a balun 2135 and an impedance matching inductor 2139 to a weighting network 2170. The connections to the fourth of the four dipoles so formed is fed through a balun 2136 and an impedance matching inductor 2140 to a weighting network 2170. The power to or from the four weighting networks 2170 are combined in a power splitter/combiner 2171. The gain or phase, or both gain and phase in each weighting network 2170 could preferably be made electronically-adjustable, making for a dipole assembly array with a radiation pattern that is dynamically adjustable in azimuth. In such a case, each of the weighting networks 2170 could be supplied with control signal tines.

An array formed of a vertical stack of five dipoles has a maximum gain of approximately 10dB. If more gain is required, more elements can be stacked.

Doubling the number of radiating elements results in approximately 3dB extra gain in azimuth. More elements would require longer lengths of feed line, the losses in which will eventually cancel out the benefit of adding any more elements to the array. FIG. 22 shows a multiple vertical stack of N arrays, in which the appropriate placement of active networks overcomes the problem of excess cable loss. The first array 2272, the second array 2273 and the Nth array 2274 are shown. Each array is formed of dipole half elements 2212 and 2208 placed over CRLH transmission line 2269. Weighting networks 2270 control the phase and amplitude to each individual dipole assembly. The signal connections to and from the weighting networks 2270 are combined in splitters/combiners 2271. To overcome the problem of cable loss, active gain stages, similar to the FEM networks shown in FIG. 18 are added in either the splitters/combiners 2271, or in the weighting networks 2270, Signal lines 2282 transport signals along the length of the array that are gain-buffered, and for this reason losses in signal lines 2282 are not dominant. When the correct amount of gain is used in the power amplifiers and low noise amplifiers in the front end modules, the signal lines 2282 can be made thin, allowing a large number N of signal lines 2282 to be housed in the CRLH structure, and to be combined in an N-way power splitter/combiner 2283.

There at-c several ways in which such a CRLH structure could be manufactured. It would be advantageous if a predominantly planar process could be used, so keeping manufacturing costs down. FIG. 23A and FIG. 23B show how the CRLH structure for a single dipole assembly, as per third exemplary embodiment of the invention, could be constructed. In FIG. 23A sections of a thin metal plate 2384 are fully etched away along solid lines 2378 and partially etched along the dashed lines 2376 and 2377. FIG. 238 shows thin connecting sections 2379 that are left behind after the completion of the etching process. These serve to keep all 16 outer plates 2305 so formed together, and properly spaced apart. The partially etched lines 2376 and 2377 form thin grooves in the metal sheet, and allow accurate bending to be done along the lines. Accordingly, sections of the inner plates 2306 so formed are bent through 90° along lines 2377 and the outer plate sections 2305 are bent through 30° along lines 2376. The narrow section of the inner plates 2306 is soldered, spot-welded or otherwise fixed to the metal tube.

Cover plates 2380, which are etched, using a similar process, are soldered, spot- welded or otherwise fixed along contact area 2381 to the outer plates 2305. Cut-out sections 2332 are etched away on the cover plates that are placed next to the dipole feed points. The thin connecting sections 2379 are cut, so electrically separating each outer plate 2305 from its neighbour. In another manufacturing method, sections in the metal placed are stamped out, instead of being chemically etched away. In yet another manufacturing method, the metal sheet is formed from a copper sheet laminated on a dielectric substrate, such as FR4, and then selectively etched away.

Acronyms One-dimensional Two-dimensional Balun Balanced to unbalanced transformer CRLH Composite right handed and left handed structure FEM Front End Module LNA Low Noise Amplifier MIMO Multiple-Input and Multiple-Output MISO Multiple-Input and Single-Output) PA Power Amplifier PEEC Partial Element Equivalent Circuit SISO Single-Input and Single-Output

TE Transverse Electric Field

TM Transverse Magnetic Field

It should be emphasised that while the above description contain many specifics, these are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the invention, and should not be construed as limitations on the scope of the invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the scope and spirit of the invention, and all such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.

Claims (1)

1. <claim-text>Claims What is claimed is: 1. An antenna system comprising: a) a first dipole half element; I,) a second dipole half element; c) a first connection to the first half dipole element; d) a second connection to the second half dipole element; b) a conductive tube in which the electrical connection wires and cables to the first connection to the first dipole half element and the second connection to the second dipole half element are enclosed; f) a composite right and left handed (CRLH) transmission line, placed in parallel to and at a distance much smaller than the wavelength of the lowest frequency at which the antenna is used from the dipole, comprising i) a plurality of outer plates, placed over ii) the conductive tube, and iii) a plurality of inner plates placed between the outer plates and the conductive tube and making an electrical connection between the conductive tube and the outer plates.wherein the CRLH transmission line is configured to have one or more left handed and one or more right handed resonance modes associated with the antenna signal frequencies, and to exhibit a stop band over the bandwidth of the antenna signal frequencies.</claim-text> <claim-text>2. The antenna in accordance with claim 1, wherein two right and left handed (CRLH) transmission lines each supporting a first dipole half element and a second dipole half element placed in parallel to and at a distance much smaller than the wavelength of the lowest frequency at which the antenna is used from the dipole half elements are placed at 180 degrees intervals around, and share a common conductive tube containing the electrical connection wires and cables.</claim-text> <claim-text>3. The antenna in accordance with claim 1, wherein four right and left handed (CRLH) transmission lines each supporting a first dipole half element and a second dipole half element placed in parallel to and at a distance much smaller than the wavelength of the lowest frequency at which the antenna is used from the dipole half elements are placed at 90 degrees intervals around, and share a common conductive tube containing the electrical connection wires and cables.</claim-text> <claim-text>4. The antenna in accordance with claim 1, wherein any number M right and left handed (CRLH) transmission lines each supporting a first dipole half element and a second dipole half element placed in parallel to and at a distance much smaller than the wavelength of the lowest frequency at which the antenna is used from the dipole half elements are placed at regular angular intervals around, and share a common conductive tube containing the electrical connection wires and cables, where the number M is larger than one, and where the number M could be even or uneven.</claim-text> <claim-text>5. The antenna in accordance with claim 1, claim 2, claim 3 and claim 4, configured in a collinear stack of antennas.</claim-text> <claim-text>6. The antenna in accordance with claim 1, claim 2, claim 3, claim 4 and claim 5, wherein the volume inside and outside the antenna is filled with a plurality of dielectric materials.</claim-text> <claim-text>7. The antenna in accordance with claim 1, claim 2, claim 3 claim 4, claim S and claim 6, wherein the inductance of the outer plates forming part of the (CRLH) transmission line is increased by cutting a plurality of elongated slots in the outer plates.</claim-text> <claim-text>8. The antenna in accordance with claim 1, claim 2, claim 3 claim 4, claim 5 and claim 6, wherein the inductance of the outer plates forming part of the (CRLH) transmission line is increased by inserting meander lines in the outer plates.</claim-text> <claim-text>9. The antenna in accordance with claim 1, claim 2, claim 3 claim 4, claim Sand claim 6, wherein the inductance of the outer plates forming part of the (CRLH) transmission line is increased by inserting planar spiral inductors in the outer plates.</claim-text> <claim-text>10. The antenna in accordance with claim 1, claim 2, claim 3 claim 4, claim 5 and claim 6, wherein the inductance of the outer plates forming part of the (CRLH) transmission line is increased by inserting lumped inductors in the outer plates.</claim-text> <claim-text>11. The antenna in accordance with claim 1, claim 2, claim 3 claim 4, claim 5 and claim 6, wherein the capacitance between outer plates forming part of the (CRLH) transmission line is increased by inserting lumped capacitors between outer plates.</claim-text> <claim-text>12. The antenna in accordance with claim 1, claim 2, claim 3 claim 4, claim 5 and claim 6, wherein the capacitance between outer plates forming part of the (CRLH) transmission line is increased by providing a perpendicularly bent section between outer plates.</claim-text> <claim-text>13. The antenna in accordance with claim 1, claim 2, claim 3 claim 4, claim S and claim 6, wherein the capacitance between outer plates forming part of the (CRLH) transmission line is increased by providing a parasitic capacitive coupling plate positioned over the gap between outer plates, and placed in a plane substantially parallel to the outer plates.</claim-text> <claim-text>14. The antenna in accordance with claim 1, claim 2, claim 3 claim 4, claim S and claim 6, wherein the fringe capacitance between outer plates forming part of the (CRLH) transmission line is increased by providing a meandering interdigital capacitive coupling between outer plates.</claim-text> <claim-text>15. The antenna in accordance with claim 1, claim 2, claim 3 claim 4, claim 5 and claim 6, wherein the inductance of the inner plates forming part of the (CRLH) transmission line is increased by inserting meander lines in the inner plates.</claim-text> <claim-text>16. The antenna in accordance with claim 1, claim 2, claim 3 claim 4, claim S and claim 6, wherein the inductance of the inner plates forming part of the (CRLH) transmission line is increased by inserting planar spiral inductors in the inner plates.</claim-text> <claim-text>17. The antenna in accordance with claim 1, claim 2, claim 3 claim 4, claim S and claim 6, wherein the inductance of the inner plates forming part of the (CRLH) transmission line is increased by inserting lumped inductors in the inner plates.</claim-text> <claim-text>18. The antenna in accordance with any preceding claim, whercin a front end module (FEM) containing a balun, one or more low noise amplifiers (INA), power amplifiers (PA) and switches is provided.</claim-text> <claim-text>19. The antenna in accordance with any preceding claim, wherein weighting networks that are effective at the feed points allow the beam to be steered in elevation.</claim-text> <claim-text>20. The antenna in accordance with any preceding claim, configured in horizontally spaced arrays wherein weighting networks allow the beam to be steered in azimuth.</claim-text> <claim-text>21. The antenna in accordance with any preceding claim, wherein weighting networks at the feed points allow the beam to be steered in azimuth.</claim-text> <claim-text>22. The antenna in accordance with any preceding claim, configured in multiple vertically stacked collinear stacks of antennas and supplied with active buffers 23. A method of assembling the antenna in accordance with any preceding claim, the method comprising the steps of: a) using a photo resistive etching process to form multiples of joined outer plates and inner plates, which farm part of the CRLH transmission lines; b) using a photo resistive etching process to form multiples of cover plates for the outer plates, which form part of the CRLH transmission lines; c) bending sections of the plates through 90 degrees sections and sections of the plated through angles between 0 degrees and 90 degrees to farm parallel CRLH transmission lines; d) soldering, spot-welding or otherwise fixing the narrow ends of the inner plates to the metal tube containing the wiring and cables; e) removing the connecting sections between outer plates; f) placing dipole elements on isolators over the CRLH transmission lines.</claim-text>