WO2012113026A1 - Wideband radiating elements - Google Patents

Wideband radiating elements Download PDF

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Publication number
WO2012113026A1
WO2012113026A1 PCT/AU2012/000174 AU2012000174W WO2012113026A1 WO 2012113026 A1 WO2012113026 A1 WO 2012113026A1 AU 2012000174 W AU2012000174 W AU 2012000174W WO 2012113026 A1 WO2012113026 A1 WO 2012113026A1
Authority
WO
WIPO (PCT)
Prior art keywords
waveguide
dipole antenna
waveguide section
radiating element
section
Prior art date
Application number
PCT/AU2012/000174
Other languages
French (fr)
Inventor
Peter John Liversidge
Ozgur Isik
Original Assignee
Andrew Llc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AU2011900647A external-priority patent/AU2011900647A0/en
Application filed by Andrew Llc filed Critical Andrew Llc
Publication of WO2012113026A1 publication Critical patent/WO2012113026A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
    • H01Q9/04—Resonant antennas
    • H01Q9/0407—Substantially flat resonant element parallel to ground plane, e.g. patch antenna
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
    • H01Q13/06—Waveguide mouths
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q21/00—Antenna arrays or systems
    • H01Q21/24—Combinations of antenna units polarised in different directions for transmitting or receiving circularly and elliptically polarised waves or waves linearly polarised in any direction
    • H01Q21/26—Turnstile or like antennas comprising arrangements of three or more elongated elements disposed radially and symmetrically in a horizontal plane about a common centre
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q5/00—Arrangements for simultaneous operation of antennas on two or more different wavebands, e.g. dual-band or multi-band arrangements
    • H01Q5/30—Arrangements for providing operation on different wavebands
    • H01Q5/307—Individual or coupled radiating elements, each element being fed in an unspecified way
    • H01Q5/342—Individual or coupled radiating elements, each element being fed in an unspecified way for different propagation modes
    • H01Q5/357—Individual or coupled radiating elements, each element being fed in an unspecified way for different propagation modes using a single feed point
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
    • H01Q9/04—Resonant antennas
    • H01Q9/0407—Substantially flat resonant element parallel to ground plane, e.g. patch antenna
    • H01Q9/045—Substantially flat resonant element parallel to ground plane, e.g. patch antenna with particular feeding means

Definitions

  • the present invention relates generally to antennas and in particular to wideband antennas and in particular for such antennas for use base station in wireless telecommunications.
  • a patch antenna comprises a ground plane, a patch radiator, and a feed.
  • the patch radiator is suspended above the ground plane and fed by a central symmetrical loop or by two loops symmetrically disposed about the centre of the patch in a plane normal to the patch between the patch and the groundplane.
  • the feed excites opposite sides of the patch radiator in antiphase.
  • the radiofrequency spectrum being made available for wireless voice and data services served by basestation antennas is continually increasing.
  • a wideband radiating element comprising: a section of waveguide having a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength, the waveguide section being short circuited at one end and open circuited at the other end to provide a waveguide aperture; at least one dipole antenna element disposed within the waveguide section as a feed for the waveguide section; and at least one tuned circuit coupled to each respective dipole antenna element as a feed for the dipole antenna element, the tuned circuit comprising at least one transmission line feed and a shunt resonator formed from a segment of transmission line.
  • the width of the waveguide section may be between about 0.7 wavelengths and about 1 wavelength.
  • the dipole antenna element may be located at a height of 0.25 wavelengths or about 0.25 wavelengths above the short-circuited end of the waveguide section.
  • the waveguide section may have a cross-section along the longitudinal extent of the waveguide section that is square, rectangular, or circular in form.
  • the wideband radiating element may further comprise an additional tuning element.
  • the additional tuning element may comprise a dielectric sheet coupled to the waveguide section.
  • the dielectric sheet may be disposed across at least a portion of the waveguide aperture of the waveguide section.
  • the dielectric sheet may be disposed within the waveguide section.
  • the waveguide section, the dipole antenna element, and the at least one tuned circuit may be configured to radiate over a fifty percent (50%) bandwidth with return loss in excess of 1 dB.
  • the waveguide section, the dipole antenna element, and the at least one tuned circuit may be coupled together provide an equal ripple band-pass filter.
  • the wideband radiating element may comprise one tuned circuit configured to feed a single polarized dipole antenna element, or two tuned circuits orthogonally configured as dual polarization feeds to feed orthogonally polarized dipole antenna elements.
  • the wideband radiating element may further comprise at least one printed circuit board, a tuned circuit formed on each printed circuit board.
  • Each tuned circuit may comprise at least one network of metallised components.
  • the wideband radiating element may comprise: two dipole antenna elements configured orthogonally relative to each other and disposed within the waveguide section as a feed for the waveguide section to radiate orthogonal polarizations; and two tuned circuits each coupled to a respective dipole antenna element as a feed for the respective dipole antenna element, each tuned circuit comprising at least one transmission line feed and a shunt resonator formed from a segment of transmission line.
  • a stand- alone antenna comprising a wideband radiating element in accordance with the foregoing aspect.
  • an array antenna comprising a plurality of wideband radiating elements, each radiating element in accordance with the foregoing aspect.
  • the array antenna may be configured as a wideband, cellular base-station antenna array.
  • a method of transmitting a signal using a wideband radiating element The signal is coupled from at least one tuned circuit to at least one dipole antenna as a feed for the dipole antenna element.
  • the tuned circuit comprises at least one transmission line feed and a shunt resonator formed from a segment of transmission line.
  • the signal is radiated from each dipole antenna element disposed within a waveguide section as a feed for the waveguide section.
  • the section of waveguide has a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength.
  • the waveguide section is short circuited at one end and open circuited at the other end to provide a waveguide aperture.
  • a method of receiving a signal using a wideband radiating element The signal is received at at least one dipole antenna element disposed within a waveguide section.
  • the section of waveguide has a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength.
  • the waveguide section is short circuited at one end and open circuited at the other end to provide a waveguide aperture.
  • the signal is coupled at at least one tuned circuit coupled to the dipole antenna element, the tuned circuit comprising at least one transmission line feed and a shunt resonator formed from a segment of transmission line.
  • the waveguide section may have a cross-section along the longitudinal extent of the waveguide section that is square, rectangular, or circular in form.
  • the width of the waveguide section may be between about 0.7 wavelengths and about 1 wavelength.
  • the dipole antenna element may be located at a height of 0.2S wavelengths or about 0.25 wavelengths above the short-circuited end of the waveguide section.
  • Fig. 1 is a perspective view of a wideband radiating element, i.e., a wideband dipole-fed cavity radiator, shown with one of the two polarization feeds removed for clarity, in accordance with an embodiment of the invention;
  • Fig. 2 is a perspective view of another wideband radiating element, i.e., a wideband dipole-fed cavity radiator, comprising an isolated dipole antenna element and a waveguide section with the matching feed network omitted for ease of illustration;
  • a wideband dipole-fed cavity radiator comprising an isolated dipole antenna element and a waveguide section with the matching feed network omitted for ease of illustration;
  • Fig. 3 is an S-parameter polar plot showing the optimised impedance match of the dipole waveguide combination of Fig. 2 (1710MHz-2690MHz) from 3D electromagnetic analysis;
  • Fig. 4 is a perspective view of an example of a waveguide/dipole/feed network combination to achieve wideband impedance matching and stable radiation pattern with frequency (single polarisation only shown);
  • Figs. 5 A and 5B are polar and rectangular plots of optimized impedance match using a transmission line and shunt resonator to feed the dipole/waveguide combination, as shown in Figs. 2 and 3.
  • Wideband radiating elements methods of transmitting and receiving signals using a wideband radiating element, standalone antennas, and array antennas are described hereinafter. More particularly the wideband radiating element is a wideband dipole-fed cavity radiator.
  • numerous specific details including frequency ranges, cables, dielectric materials, conductive materials, waveguide cross-sectional shapes, and the like are set forth. However, from this disclosure, it will be apparent to those skilled in the art that modifications and or substitutions may be made without departing from the scope and spirit of the invention. In other circumstances, specific details may be omitted so as not to obscure the invention.
  • the wideband radiating element is a wideband dipole-fed cavity radiator comprising: a section of waveguide, one or more dipole antenna elements, and one or more tuned circuits.
  • the waveguide section has a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength.
  • the waveguide section is short circuited at one end and open circuited at the other end to provide a waveguide aperture.
  • Each dipole antenna element is disposed within the waveguide section as a feed for the waveguide section.
  • Each tuned circuit is coupled to a respective dipole antenna element as a feed for the dipole antenna element.
  • the tuned circuit comprises at least one transmission line feed and a shunt resonator formed from a segment of transmission line.
  • the wideband radiating element can be used to transmit and/or receive signals.
  • the signal can be fed to the tuned circuit and radiated from the dipole antenna element.
  • the dipole antenna element is a feed for the waveguide section, which radiates the signal from the wideband radiating element to transmit the signal.
  • a signal can be received by the wideband radiating element.
  • the wideband dipole-fed cavity radiator can radiate single or dual linear polarization and is a suitable radiating element for wideband, cellular base-station antenna arrays.
  • Dipole antenna elements are commonly used as radiating elements in cellular base station antennas.
  • Arrays covering DCS 1800, UMTS and WiMax/LTE bands (1710-2690 MHz.) may use these wideband radiating elements, but the embodiments of the invention are not limited in application to these particular bands.
  • the resulting radiating element, i.e. the wideband dipole-fed cavity radiator is capable of operating over a fifty percent (50%) bandwidth with return loss in excess of 15 dB.
  • the variation in radiation pattern across this band is relatively small.
  • a cellular base-station panel antenna designed to have a 65° horizontal beamwidth varies in 3 dB beamwidth by less than ⁇ 7° over a 57% bandwidth.
  • the configuration of the wideband radiating element becomes a three resonator filter that can be designed to match the impedance of the input transmission line of a feed to the impedance at the open waveguide radiator.
  • the width of the waveguide section may be between about 0.7 wavelengths and about 1 wavelength.
  • the dipole antenna element may be located at a height of 0.25 wavelengths or about 0.25 wavelengths above the short-circuited end of the waveguide section.
  • the waveguide section may have a cross-section along the longitudinal extent of the waveguide section that is square, rectangular, or circular in form. The bandwidth of the resulting radiating element is significantly increased by the waveguide section.
  • the waveguide suitably dimensioned, also stabilises the radiation pattern, so that there is minimal variation in radiation pattern across the impedance bandwidth.
  • a dielectric body of suitable thickness, physical characteristics, and dielectric constant can be located within the waveguide as a tuning element to provide adjustment of the Q of the open waveguide radiator and can be used to optimise the impedance characteristics across the band of operation.
  • the wideband radiating element may further comprise an additional tuning element.
  • the additional tuning element may comprise a dielectric sheet coupled to the waveguide section. The dielectric sheet may be disposed across at least a portion of the waveguide aperture of the waveguide section. The dielectric sheet may be disposed within the waveguide section.
  • Dual linear polarization can be achieved by means of two orthogonal crossed dipole antenna elements.
  • An equi-ripple impedance response can be achieved by suitably adjusting the resonant frequencies and couplings between the three resonators, namely the tuned circuit, the dipole antenna element and the waveguide section.
  • the wideband radiating element(s) can be used to implement a stand-alone antenna, or an array antenna comprising a number (e.g., 10) of wideband radiating elements as a cellular base-station antenna array.
  • the wideband radiating element provides a relatively constant beamwidth and wide bandwidth.
  • a wideband radiator 100 comprises a short section 130 of waveguide, short circuited at one end and open circuited at the other end where radiation occurs.
  • the waveguide section 130 is fed by one or more dipole antenna elements 120 disposed within the waveguide section 130; in this embodiment there are two dipole antenna elements 120 configured in an orthogonal arrangement.
  • the dipole antenna elements 120 are in turn fed by one or more transmission line sections 110 and one or more shunt resonators 140.
  • Such a radiating element 100 is capable of operating over a 50% bandwidth with return loss in excess of 15 dB, can radiate single or dual linear polarization, and forms a satisfactory radiating element for wideband cellular basestation antenna arrays. The variation in radiation pattern across this band is acceptable for cellular basestation applications.
  • the dipole antenna elements 120 are suspended above the shorted section of waveguide 130 on a printed circuit board 150 mounted between the dipole antenna elements 120 and the waveguide section 130.
  • the transmission line sections 110 are implemented on the printed circuit board 150.
  • the shunt resonator 140 is coupled to the transmission line section 110 in Fig. 1 adjacent the shorted section of waveguide 130.
  • a single transmission line section 110 on a printed circuit board 150 with a shunt resonator 140 is shown. This feeds a single dipole antenna element 120.
  • a further transmission line section on another printed circuit board with a shunt resonator is omitted to simplify the diagram.
  • the waveguide section 130, the one or more dipole antenna element 120, and one or more tuned circuit 110 may be configured to radiate over a fifty percent (50%) bandwidth with return loss in excess of 15 dB.
  • the waveguide section 130, the dipole antenna element 120 and the at least one tuned circuit 110 may be coupled together providing an equal ripple band-pass filter.
  • the wideband radiating element 100 may comprise one tuned circuit configured to feed a single polarization dipole antenna element 120, or the wideband radiating element 100 may comprise two tuned circuits orthogonally configured as dual polarization feeds to feed orthogonally polarized dipole antenna elements 120, as shown in Fig. 1. Accordingly, the wideband radiating element 100 may comprise at least one printed circuit board, with a tuned circuit formed on each printed circuit board. Each tuned circuit may comprise one or more sections of transmission line and a single shunt resonator. Alternatively, each wideband radiating element 100 may comprise at least one tuned circuit feed, with each tuned circuit feed comprising a network of any conductive parts suitably arranged to form one or more transmission line sections and a shunt resonator
  • the wideband radiating element 100 comprises: two dipole antenna elements
  • Each tuned circuit 11 comprises at least one transmission line feed 110 and a shunt resonator 140 formed from a segment of transmission line on a printed circuit board 150.
  • the waveguide section 130 of Fig. 1 has a square cross-section, however, other shapes may be practiced without departing from the scope of the invention.
  • the method of wideband impedance matching is implemented as follows. Firstly, consider a single-polarization dipole antenna element 220, centrally located within a suitably dimensioned waveguide section 230, as depicted in Figure 2.
  • the width of the waveguide 230 is normally between 0.7 wavelengths and 1 wavelength, and the length of the waveguide section 230 is normally close to a quarter guide wavelength.
  • the dipole antenna element 220 displays a single resonance in its impedance response with frequency.
  • the variation of the impedance with frequency of this isolated dipole antenna element 220 is too large to permit operation over a bandwidth useful for wideband cellular basestation antennas.
  • the impedance variation can be greatly reduced, allowing an impedance match over a much wider frequency range to be achieved.
  • the waveguide 230 also stabilizes the pattern so that there is minimal variation in radiation pattern across the impedance bandwidth. Again, the waveguide section 230 is short circuited at one end and open circuited at the other end.
  • Fig. 3 shows a polar reflection coefficient plot of the dipole waveguide combination 220, 230 of Fig. 2 after the dipole antenna element 220 and the waveguide section 230 are optimized as described hereinbefore.
  • the plot shows the reflection coefficient for 1.71 GHz to 2.69 GHz.
  • the dual-resonance, wideband nature of the frequency response is evident.
  • a dipole's frequency response displays a wide arc over a 57% bandwidth. It is difficult to design a compact matching network to transform an arc such as this to the terminating impedance and provide a 15dB return loss. Instead of this, the polar plot in Fig.
  • FIG. 3 shows a dual-resonance response where the single-resonance arc has been transformed into a compact loop, with a much reduced spread of impedance with frequency.
  • 230 to match this combination 220, 230 to the required terminating impedance (typically 50 ohms) and to provide maximum bandwidth, one or more sections of transmission line (not shown in Fig. 2) in combination with a shunt resonator (not shown in Fig. 2) can be used at the feed point of the dipole antenna element 220.
  • the shunt resonator can also perform the function of a balun, which transforms an unbalanced transmission line feed into a balanced feed as required by the dipole antenna element 220.
  • the transmission line sections act as impedance transformers to bring the impedance of the dipole antenna element 220 to the required terminating impedance.
  • the shunt resonator acts to further reduce the impedance variation with frequency.
  • Fig. 4 shows a typical example of such a waveguide/dipole/feed network combination 400, where the feed-network transmission lines 410 and shunt resonator 440 are realized with microstrip tracks on a printed circuit board 450.
  • This figure corresponds to that shown in Fig. 1 except that an extra dipole antenna element 420 is omitted.
  • Fig. 5 shows a possible match of the dipole/waveguide represented in Figs. 2 and 3, achieved after optimization of a feed network comprising a single length of transmission line of approximately 1 ⁇ 4 wavelength long in combination with an approximately 1 ⁇ 4 wavelength long shunt resonator.
  • a theoretical impedance match of greater than 20dB return loss can be achieved over a 50% bandwidth with such a matching network.
  • the plots in Figs. 5A and 5B display the wideband triple-tuned response achieved with this configuration.
  • a broadband radiating element comprising a section of waveguide of square, circular, or other cross section, which is approximately a quarter of a guide wavelength in length and is fed by a dipole antenna element.
  • the dipole antenna element is in turn fed by one or more sections of transmission line that are resonated with a shunt section of transmission line.
  • These radiating elements may be used in an array antenna on a ground plane or as a stand-alone antenna.
  • Additional tuning elements such as a dielectric sheet placed across the waveguide aperture or elsewhere in the waveguide may be practiced.
  • wideband radiating elements with dual polarization feeding may be practiced in the form of orthogonal dipoles so as to radiate orthogonal polarizations.
  • the coupling of 3 or more resonant elements may be selected in such a way as to approximate an equal ripple band-pass filter.
  • a method of transmitting a signal using the foregoing wideband radiating element is coupled from at least one tuned circuit to at least one dipole antenna as a feed for the dipole antenna element.
  • the tuned circuit comprises at least one transmission line feed and a shunt resonator formed from a segment of transmission line.
  • the signal is radiated from each dipole antenna element disposed within a waveguide section as a feed for the waveguide section.
  • the section of waveguide has a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength.
  • the waveguide section is short circuited at one end and open circuited at the other end to provide a waveguide aperture.
  • a method of receiving a signal using a wideband radiating element The signal is received at at least one dipole antenna element disposed within a waveguide section.
  • the section of waveguide has a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength.
  • the waveguide section is short circuited at one end and open circuited at the other end to provide a waveguide aperture.
  • the signal is coupled at at least one tuned circuit coupled to the dipole antenna element.
  • the tuned circuit comprises at least one transmission line feed and a shunt resonator formed from a segment of transmission line.
  • the waveguide section has a cross-section along the longitudinal extent of the waveguide section that is square, rectangular, or circular in form.
  • the width of the waveguide section is between about 0.7 wavelengths and about 1 wavelength.
  • the dipole antenna element is located at a height of 0.25 wavelengths or about 0.25 wavelengths above the short-circuited end of the waveguide section.
  • Wideband radiating elements methods of transmitting and receiving signals using a wideband radiating element, standalone antennas, and array antennas have been described.
  • modifications and/or substitutions may be made without departing from the scope and spirit of the invention.

Abstract

A wideband radiating element (100, 400), an antenna, and methods of transmitting and receiving signals are provided. The wideband radiating element (100, 400) comprises: a section of waveguide (130, 430), at least one dipole antenna element (120, 420), and at least one tuned circuit. The section (130, 430) of waveguide has a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength and is short circuited at one end and open circuited at the other end to provide a waveguide aperture. Each dipole antenna element (120, 420) is disposed within the waveguide section (130, 430) as a feed for the waveguide section (130, 430). Each tuned circuit is coupled to a respective dipole antenna element (120, 420) as a feed for the dipole antenna element (120, 420). The tuned circuit comprises at least one transmission line feed (110, 410) and a shunt resonator (140, 440) formed from a segment of transmission line.

Description

WIDEBAND RADIATING ELEMENTS
RELATED APPLICATION
The present application claims the benefit of the earlier filing date, including under 35 USC §119 in the United States, of Australian Provisional Patent
Application No. 2011900647, which is incorporated by reference herein in its entirety, filed on 24 February 2011 in the name of Argus Technologies (Australia) Pty Ltd et al.
TECHNICAL FIELD
The present invention relates generally to antennas and in particular to wideband antennas and in particular for such antennas for use base station in wireless telecommunications. BACKGROUND
International (PCT) Patent Publication No. WO 2006/135956 published on 28 December 2006 (International Patent Application No. PCT/AU2006/000814 filed on 15 June 2006 filed in the name of Argus Technologies (Australia) Pty Ltd et al) discloses dual-polarized patch antennas having reduced beamwidths. Such a patch antenna comprises a ground plane, a patch radiator, and a feed. The patch radiator is suspended above the ground plane and fed by a central symmetrical loop or by two loops symmetrically disposed about the centre of the patch in a plane normal to the patch between the patch and the groundplane. The feed excites opposite sides of the patch radiator in antiphase.
International (PCT) Patent Publication No. WO 2010/042976 published on 22
April 2010 (International Patent Application No. PCT/AU2009/001343 filed on 12 October 2009 filed in the name of Argus Technologies (Australia) Pty Ltd et al) describes wideband radiating elements that have a wide bandwidth for a relatively constant beamwidth and comprises a section of waveguide, a patch radiator, and one or more tuned loops. The waveguide section is a quarter of a guide wavelength long or thereabouts, short circuited at one end, and open circuited at the other end. The patch radiator is disposed within the waveguide section. The tuned loops are coupled to the patch radiator as a feed for the patch radiator in a plane normal to the patch radiator. The width of the waveguide section is between about 0.7 wavelengths and about 1.3 wavelengths and the patch radiator is located at a height of 0.125 wavelengths or thereabouts above the short-circuited end of the waveguide section.
The radiofrequency spectrum being made available for wireless voice and data services served by basestation antennas is continually increasing. Currently, there is a requirement for up to 50% bandwidth to be achieved with an impedance match of 15dB. Therefore, a need exists for an improved antenna having wider bandwidth.
SUMMARY
In accordance with an aspect of the invention, there is provided a wideband radiating element, comprising: a section of waveguide having a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength, the waveguide section being short circuited at one end and open circuited at the other end to provide a waveguide aperture; at least one dipole antenna element disposed within the waveguide section as a feed for the waveguide section; and at least one tuned circuit coupled to each respective dipole antenna element as a feed for the dipole antenna element, the tuned circuit comprising at least one transmission line feed and a shunt resonator formed from a segment of transmission line.
The width of the waveguide section may be between about 0.7 wavelengths and about 1 wavelength.
The dipole antenna element may be located at a height of 0.25 wavelengths or about 0.25 wavelengths above the short-circuited end of the waveguide section.
The waveguide section may have a cross-section along the longitudinal extent of the waveguide section that is square, rectangular, or circular in form.
The wideband radiating element may further comprise an additional tuning element.
The additional tuning element may comprise a dielectric sheet coupled to the waveguide section. The dielectric sheet may be disposed across at least a portion of the waveguide aperture of the waveguide section.
The dielectric sheet may be disposed within the waveguide section.
The waveguide section, the dipole antenna element, and the at least one tuned circuit may be configured to radiate over a fifty percent (50%) bandwidth with return loss in excess of 1 dB.
The waveguide section, the dipole antenna element, and the at least one tuned circuit may be coupled together provide an equal ripple band-pass filter.
The wideband radiating element may comprise one tuned circuit configured to feed a single polarized dipole antenna element, or two tuned circuits orthogonally configured as dual polarization feeds to feed orthogonally polarized dipole antenna elements.
The wideband radiating element may further comprise at least one printed circuit board, a tuned circuit formed on each printed circuit board.
Each tuned circuit may comprise at least one network of metallised components.
The wideband radiating element may comprise: two dipole antenna elements configured orthogonally relative to each other and disposed within the waveguide section as a feed for the waveguide section to radiate orthogonal polarizations; and two tuned circuits each coupled to a respective dipole antenna element as a feed for the respective dipole antenna element, each tuned circuit comprising at least one transmission line feed and a shunt resonator formed from a segment of transmission line.
In accordance with another aspect of the invention, there is provided a stand- alone antenna, comprising a wideband radiating element in accordance with the foregoing aspect.
In accordance with still another aspect of the invention, there is provided an array antenna comprising a plurality of wideband radiating elements, each radiating element in accordance with the foregoing aspect.
The array antenna may be configured as a wideband, cellular base-station antenna array. In accordance with a further aspect of the invention, there is provided a method of transmitting a signal using a wideband radiating element. The signal is coupled from at least one tuned circuit to at least one dipole antenna as a feed for the dipole antenna element. The tuned circuit comprises at least one transmission line feed and a shunt resonator formed from a segment of transmission line. The signal is radiated from each dipole antenna element disposed within a waveguide section as a feed for the waveguide section. The section of waveguide has a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength. The waveguide section is short circuited at one end and open circuited at the other end to provide a waveguide aperture.
In accordance with a further aspect of the invention, there is provided a method of receiving a signal using a wideband radiating element. The signal is received at at least one dipole antenna element disposed within a waveguide section. The section of waveguide has a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength. The waveguide section is short circuited at one end and open circuited at the other end to provide a waveguide aperture. The signal is coupled at at least one tuned circuit coupled to the dipole antenna element, the tuned circuit comprising at least one transmission line feed and a shunt resonator formed from a segment of transmission line.
The waveguide section may have a cross-section along the longitudinal extent of the waveguide section that is square, rectangular, or circular in form.
The width of the waveguide section may be between about 0.7 wavelengths and about 1 wavelength.
The dipole antenna element may be located at a height of 0.2S wavelengths or about 0.25 wavelengths above the short-circuited end of the waveguide section.
These and other aspects of the invention are described in detail hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention are described hereinafter with reference to the drawings, in which: Fig. 1 is a perspective view of a wideband radiating element, i.e., a wideband dipole-fed cavity radiator, shown with one of the two polarization feeds removed for clarity, in accordance with an embodiment of the invention;
Fig. 2 is a perspective view of another wideband radiating element, i.e., a wideband dipole-fed cavity radiator, comprising an isolated dipole antenna element and a waveguide section with the matching feed network omitted for ease of illustration;
Fig. 3 is an S-parameter polar plot showing the optimised impedance match of the dipole waveguide combination of Fig. 2 (1710MHz-2690MHz) from 3D electromagnetic analysis;
Fig. 4 is a perspective view of an example of a waveguide/dipole/feed network combination to achieve wideband impedance matching and stable radiation pattern with frequency (single polarisation only shown); and
Figs. 5 A and 5B are polar and rectangular plots of optimized impedance match using a transmission line and shunt resonator to feed the dipole/waveguide combination, as shown in Figs. 2 and 3.
DETAILED DESCRIPTION
Wideband radiating elements, methods of transmitting and receiving signals using a wideband radiating element, standalone antennas, and array antennas are described hereinafter. More particularly the wideband radiating element is a wideband dipole-fed cavity radiator. In the following description, numerous specific details, including frequency ranges, cables, dielectric materials, conductive materials, waveguide cross-sectional shapes, and the like are set forth. However, from this disclosure, it will be apparent to those skilled in the art that modifications and or substitutions may be made without departing from the scope and spirit of the invention. In other circumstances, specific details may be omitted so as not to obscure the invention.
International (PCT) Patent Publication No. WO 2010/042976 published on 22 April 2010 (International Patent Application No. PCT/AU2009/001343 filed on 12 October 2009 filed in the name of Argus Technologies (Australia) Pty Ltd et al) is incorporated herein by reference.
In accordance with the embodiments of the invention, the wideband radiating element is a wideband dipole-fed cavity radiator comprising: a section of waveguide, one or more dipole antenna elements, and one or more tuned circuits. The waveguide section has a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength. The waveguide section is short circuited at one end and open circuited at the other end to provide a waveguide aperture. Each dipole antenna element is disposed within the waveguide section as a feed for the waveguide section. Each tuned circuit is coupled to a respective dipole antenna element as a feed for the dipole antenna element. The tuned circuit comprises at least one transmission line feed and a shunt resonator formed from a segment of transmission line. The wideband radiating element can be used to transmit and/or receive signals. The signal can be fed to the tuned circuit and radiated from the dipole antenna element. In turn, the dipole antenna element is a feed for the waveguide section, which radiates the signal from the wideband radiating element to transmit the signal.
Similarly, a signal can be received by the wideband radiating element.
The wideband dipole-fed cavity radiator can radiate single or dual linear polarization and is a suitable radiating element for wideband, cellular base-station antenna arrays. Dipole antenna elements are commonly used as radiating elements in cellular base station antennas. Arrays covering DCS 1800, UMTS and WiMax/LTE bands (1710-2690 MHz.) may use these wideband radiating elements, but the embodiments of the invention are not limited in application to these particular bands. The resulting radiating element, i.e. the wideband dipole-fed cavity radiator, is capable of operating over a fifty percent (50%) bandwidth with return loss in excess of 15 dB. The variation in radiation pattern across this band is relatively small. For example, a cellular base-station panel antenna designed to have a 65° horizontal beamwidth varies in 3 dB beamwidth by less than ±7° over a 57% bandwidth.
With optimum selection of dimensions, the configuration of the wideband radiating element becomes a three resonator filter that can be designed to match the impedance of the input transmission line of a feed to the impedance at the open waveguide radiator. The width of the waveguide section may be between about 0.7 wavelengths and about 1 wavelength. The dipole antenna element may be located at a height of 0.25 wavelengths or about 0.25 wavelengths above the short-circuited end of the waveguide section. The waveguide section may have a cross-section along the longitudinal extent of the waveguide section that is square, rectangular, or circular in form. The bandwidth of the resulting radiating element is significantly increased by the waveguide section. The waveguide, suitably dimensioned, also stabilises the radiation pattern, so that there is minimal variation in radiation pattern across the impedance bandwidth.
Optionally, a dielectric body of suitable thickness, physical characteristics, and dielectric constant can be located within the waveguide as a tuning element to provide adjustment of the Q of the open waveguide radiator and can be used to optimise the impedance characteristics across the band of operation. That is, the wideband radiating element may further comprise an additional tuning element. The additional tuning element may comprise a dielectric sheet coupled to the waveguide section. The dielectric sheet may be disposed across at least a portion of the waveguide aperture of the waveguide section. The dielectric sheet may be disposed within the waveguide section.
Dual linear polarization can be achieved by means of two orthogonal crossed dipole antenna elements. An equi-ripple impedance response can be achieved by suitably adjusting the resonant frequencies and couplings between the three resonators, namely the tuned circuit, the dipole antenna element and the waveguide section. The wideband radiating element(s) can be used to implement a stand-alone antenna, or an array antenna comprising a number (e.g., 10) of wideband radiating elements as a cellular base-station antenna array. The wideband radiating element provides a relatively constant beamwidth and wide bandwidth. These and other aspects are described hereinafter in greater detail with reference to the embodiments shown in Figs. 1 to 5.
As shown in Fig. 1, a wideband radiator 100 comprises a short section 130 of waveguide, short circuited at one end and open circuited at the other end where radiation occurs. The waveguide section 130 is fed by one or more dipole antenna elements 120 disposed within the waveguide section 130; in this embodiment there are two dipole antenna elements 120 configured in an orthogonal arrangement. The dipole antenna elements 120 are in turn fed by one or more transmission line sections 110 and one or more shunt resonators 140. Such a radiating element 100 is capable of operating over a 50% bandwidth with return loss in excess of 15 dB, can radiate single or dual linear polarization, and forms a satisfactory radiating element for wideband cellular basestation antenna arrays. The variation in radiation pattern across this band is acceptable for cellular basestation applications.
In the embodiment shown in Fig. 1, the dipole antenna elements 120 are suspended above the shorted section of waveguide 130 on a printed circuit board 150 mounted between the dipole antenna elements 120 and the waveguide section 130. The transmission line sections 110 are implemented on the printed circuit board 150. The shunt resonator 140 is coupled to the transmission line section 110 in Fig. 1 adjacent the shorted section of waveguide 130.
For ease of illustration only a single transmission line section 110 on a printed circuit board 150 with a shunt resonator 140 is shown. This feeds a single dipole antenna element 120. A further transmission line section on another printed circuit board with a shunt resonator is omitted to simplify the diagram. The waveguide section 130, the one or more dipole antenna element 120, and one or more tuned circuit 110 may be configured to radiate over a fifty percent (50%) bandwidth with return loss in excess of 15 dB. The waveguide section 130, the dipole antenna element 120 and the at least one tuned circuit 110 may be coupled together providing an equal ripple band-pass filter. The wideband radiating element 100 may comprise one tuned circuit configured to feed a single polarization dipole antenna element 120, or the wideband radiating element 100 may comprise two tuned circuits orthogonally configured as dual polarization feeds to feed orthogonally polarized dipole antenna elements 120, as shown in Fig. 1. Accordingly, the wideband radiating element 100 may comprise at least one printed circuit board, with a tuned circuit formed on each printed circuit board. Each tuned circuit may comprise one or more sections of transmission line and a single shunt resonator. Alternatively, each wideband radiating element 100 may comprise at least one tuned circuit feed, with each tuned circuit feed comprising a network of any conductive parts suitably arranged to form one or more transmission line sections and a shunt resonator
The wideband radiating element 100 comprises: two dipole antenna elements
120 configured orthogonally relative to each other and disposed within the waveguide section 130 as a feed for the waveguide section to radiate orthogonal polarizations; and two tuned circuits each coupled to a respective dipole antenna element 120 as a feed for the respective dipole antenna element 120. Each tuned circuit 11 comprises at least one transmission line feed 110 and a shunt resonator 140 formed from a segment of transmission line on a printed circuit board 150. The waveguide section 130 of Fig. 1 has a square cross-section, however, other shapes may be practiced without departing from the scope of the invention.
The possibility of using components other than a printed circuit board to realise the feed network exists. This could be done instead of using a printed circuit board
The method of wideband impedance matching is implemented as follows. Firstly, consider a single-polarization dipole antenna element 220, centrally located within a suitably dimensioned waveguide section 230, as depicted in Figure 2. The width of the waveguide 230 is normally between 0.7 wavelengths and 1 wavelength, and the length of the waveguide section 230 is normally close to a quarter guide wavelength. On its own without the waveguide component 230, the dipole antenna element 220 displays a single resonance in its impedance response with frequency. The variation of the impedance with frequency of this isolated dipole antenna element 220 is too large to permit operation over a bandwidth useful for wideband cellular basestation antennas. However, if the dipole antenna element 220 is located within the cavity of the waveguide section 230 and the dipole arms are optimized in length to obtain a resonance at the desired frequency, the impedance variation can be greatly reduced, allowing an impedance match over a much wider frequency range to be achieved. The waveguide 230 also stabilizes the pattern so that there is minimal variation in radiation pattern across the impedance bandwidth. Again, the waveguide section 230 is short circuited at one end and open circuited at the other end.
Fig. 3 shows a polar reflection coefficient plot of the dipole waveguide combination 220, 230 of Fig. 2 after the dipole antenna element 220 and the waveguide section 230 are optimized as described hereinbefore. The plot shows the reflection coefficient for 1.71 GHz to 2.69 GHz. The dual-resonance, wideband nature of the frequency response is evident. On a polar plot such as this, a dipole's frequency response displays a wide arc over a 57% bandwidth. It is difficult to design a compact matching network to transform an arc such as this to the terminating impedance and provide a 15dB return loss. Instead of this, the polar plot in Fig. 3 shows a dual-resonance response where the single-resonance arc has been transformed into a compact loop, with a much reduced spread of impedance with frequency. To match this combination 220, 230 to the required terminating impedance (typically 50 ohms) and to provide maximum bandwidth, one or more sections of transmission line (not shown in Fig. 2) in combination with a shunt resonator (not shown in Fig. 2) can be used at the feed point of the dipole antenna element 220.
The shunt resonator can also perform the function of a balun, which transforms an unbalanced transmission line feed into a balanced feed as required by the dipole antenna element 220. The transmission line sections act as impedance transformers to bring the impedance of the dipole antenna element 220 to the required terminating impedance. The shunt resonator acts to further reduce the impedance variation with frequency.
Fig. 4 shows a typical example of such a waveguide/dipole/feed network combination 400, where the feed-network transmission lines 410 and shunt resonator 440 are realized with microstrip tracks on a printed circuit board 450. This figure corresponds to that shown in Fig. 1 except that an extra dipole antenna element 420 is omitted.
Fig. 5 shows a possible match of the dipole/waveguide represented in Figs. 2 and 3, achieved after optimization of a feed network comprising a single length of transmission line of approximately ¼ wavelength long in combination with an approximately ¼ wavelength long shunt resonator. A theoretical impedance match of greater than 20dB return loss can be achieved over a 50% bandwidth with such a matching network. The plots in Figs. 5A and 5B display the wideband triple-tuned response achieved with this configuration.
Thus, a broadband radiating element has been described comprising a section of waveguide of square, circular, or other cross section, which is approximately a quarter of a guide wavelength in length and is fed by a dipole antenna element. The dipole antenna element is in turn fed by one or more sections of transmission line that are resonated with a shunt section of transmission line. These radiating elements may be used in an array antenna on a ground plane or as a stand-alone antenna.
Additional tuning elements such as a dielectric sheet placed across the waveguide aperture or elsewhere in the waveguide may be practiced. Further, wideband radiating elements with dual polarization feeding may be practiced in the form of orthogonal dipoles so as to radiate orthogonal polarizations. The coupling of 3 or more resonant elements may be selected in such a way as to approximate an equal ripple band-pass filter.
In one embodiment of the invention, there is provided a method of transmitting a signal using the foregoing wideband radiating element. The signal is coupled from at least one tuned circuit to at least one dipole antenna as a feed for the dipole antenna element. The tuned circuit comprises at least one transmission line feed and a shunt resonator formed from a segment of transmission line. The signal is radiated from each dipole antenna element disposed within a waveguide section as a feed for the waveguide section. The section of waveguide has a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength. The waveguide section is short circuited at one end and open circuited at the other end to provide a waveguide aperture.
In another embodiment of the invention, there is provided a method of receiving a signal using a wideband radiating element. The signal is received at at least one dipole antenna element disposed within a waveguide section. The section of waveguide has a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength. The waveguide section is short circuited at one end and open circuited at the other end to provide a waveguide aperture. The signal is coupled at at least one tuned circuit coupled to the dipole antenna element. The tuned circuit comprises at least one transmission line feed and a shunt resonator formed from a segment of transmission line.
The waveguide section has a cross-section along the longitudinal extent of the waveguide section that is square, rectangular, or circular in form.
The width of the waveguide section is between about 0.7 wavelengths and about 1 wavelength.
The dipole antenna element is located at a height of 0.25 wavelengths or about 0.25 wavelengths above the short-circuited end of the waveguide section.
Wideband radiating elements, methods of transmitting and receiving signals using a wideband radiating element,, standalone antennas, and array antennas have been described. In view of this disclosure, it will be apparent to one skilled in the art that modifications and/or substitutions may be made without departing from the scope and spirit of the invention.

Claims

1. A wideband radiating element, comprising:
a section of waveguide having a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength, said waveguide section being short circuited at one end and open circuited at the other end to provide a waveguide aperture;
at least one dipole antenna element disposed within said waveguide section as a feed for said waveguide section; and
at least one tuned circuit coupled to each respective dipole antenna element as a feed for said dipole antenna element, said tuned circuit comprising at least one transmission line feed and a shunt resonator formed from a segment of transmission line.
2. The wideband radiating element as claimed in claim 1, wherein the width of said waveguide section is between about 0.7 wavelengths and about 1 wavelength.
3. The wideband radiating element as claimed in claim 1 or 2, wherein said dipole antenna element is located at a height of 0.25 wavelengths or about 0.25 wavelengths above said short-circuited end of said waveguide section.
4. The wideband radiating element as claimed in any one of claims 1 to
3, wherein said waveguide section has a cross-section along the longitudinal extent of the waveguide section that is square, rectangular, or circular in form.
5. The wideband radiating element as claimed in any one of the preceding claims, further comprising an additional tuning element.
6. The wideband radiating element as claimed in claim 5, wherein said additional tuning element comprises a dielectric sheet coupled to said waveguide section.
7. The wideband radiating element as claimed in claim 6, wherein said dielectric sheet is disposed across at least a portion of the waveguide aperture of said waveguide section.
8. The wideband radiating element as claimed in claim 6, wherein said dielectric sheet is disposed within said waveguide section.
9. The wideband radiating element as claimed in any one of the preceding claims, wherein said waveguide section, said dipole antenna element, and said at least one tuned circuit are configured to radiate over a fifty percent (50%) bandwidth with return loss in excess of 15 dB.
10. The wideband radiating element as claimed in any one of the preceding claims, wherein said waveguide section, said dipole antenna element, and said at least one tuned circuit coupled together provide an equal ripple band-pass filter.
11. The wideband radiating element as claimed in any one of the preceding claims, comprising one tuned circuit configured to feed a single polarized dipole antenna element.
12. The wideband radiating element as claimed in any one of claims 1 to 10, comprising two tuned circuits orthogonally configured as dual polarization feeds to feed orthogonally polarized dipole antenna elements.
13. The wideband radiating element as claimed in any one of the preceding claims, further comprising at least one printed circuit board, a tuned circuit formed on each printed circuit board.
14. The wideband radiating element as claimed in any one of the preceding claims, wherein each tuned circuit comprises at least one network of metallised components.
15. The wideband radiating element as claimed in any one of the preceding claims, comprising:
two dipole antenna elements configured orthogonally relative to each other and disposed within said waveguide section as a feed for said waveguide section to radiate orthogonal polarizations; and
two tuned circuits each coupled to a respective dipole antenna element as a feed for the respective dipole antenna element, each tuned circuit comprising at least one transmission line feed and a shunt resonator formed from a segment of transmission line.
16. A stand-alone antenna, comprising a wideband radiating element as claimed in any one of claims 1 to IS.
17. An array antenna comprising a plurality of wideband radiating elements, each radiating element as claimed in any one of claims 1 to 15.
8. The array antenna as claimed in claim 17 configured as a wideband, cellular base-station antenna array.
19. A method of transmitting a signal using a wideband radiating element, said method comprising the steps of:
coupling said signal from at least one tuned circuit to at least one dipole antenna as a feed for said dipole antenna element, said tuned circuit comprising at least one transmission line feed and a shunt resonator formed from a segment of transmission line; and
radiating said signal from each dipole antenna element disposed within a waveguide section as a feed for said waveguide section, said section of waveguide having a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength, said waveguide section being short circuited at one end and open circuited at the other end to provide a waveguide aperture.
20. A method of receiving a signal using a wideband radiating element, said method comprising the steps of:
receiving said signal at at least one dipole antenna element disposed within a waveguide section, said section of waveguide having a length that is a quarter of a guide wavelength or about a quarter of the guide wavelength, said waveguide section being short circuited at one end and open circuited at the other end to provide a waveguide aperture; and
coupling said signal at at least one tuned circuit coupled to the dipole antenna element, said tuned circuit comprising at least one transmission line feed and a shunt resonator formed from a segment of transmission line.
21. The method as claimed in claim 19 or 20, wherein said waveguide section has a cross-section along the longitudinal extent of the waveguide section that is square, rectangular, or circular in form.
22. The method as claimed in claim 19 or 20, wherein the width of said waveguide section is between about 0.7 wavelengths and about 1 wavelength.
23. The method as claimed in claim 19 or 20, wherein said dipole antenna element is located at a height of 0.25 wavelengths or about 0.25 wavelengths above said short-circuited end of said waveguide section.
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