Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
  • H01Q3/26—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture
  • H01Q3/30—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture varying the relative phase between the radiating elements of an array
  • H01Q3/34—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture varying the relative phase between the radiating elements of an array by electrical means
  • H01Q3/36—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture varying the relative phase between the radiating elements of an array by electrical means with variable phase-shifters
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/18—Phase-shifters
  • H01P1/182—Waveguide phase-shifters
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/18—Phase-shifters
  • H01P1/184—Strip line phase-shifters

Definitions

• This invention relates to a technique for creating a variable phase shift in a transmission line and to the use of such a technique in an antenna array.
• Phase shifters are well known and come in a variety of different types. Ferrite phase shifters use plates, rods and other shapes of ferromagnetic material inside a waveguide or transmission line. The magnetic permeability of the material defines the propagation constant of such lines which can be controlled by an external magnetic field. Ferrite phase shifters can be operated at high speed (in the order of milliseconds for a 360° phase shift) and can be integrated into the feeding network of antennas . However, ferrite phase shifters are too expensive for low cost applications such as base station antenna technology, and personal mobile satellite based systems. In addition, ferrite phase shifters require a relatively high level of DC power for operation and introduce typical losses of around ldB per 360° phase shift. Bandwidth is also limited for these devices to 5-10%.
• Mechanical phase shifters are based on the mechanical displacement of a structure inside a transmission line or waveguide in order to change the propagation constant.
• the mechanical displacement may be achieved, for example, by using piezoelectric, electrostatic or electrical motor devices. They are potentially low cost, broadband devices, with low DC power consumption and are well suited to mass production. However, these devices have some practical limitations.
• the invention consists in a phase shifting element comprising: a transmission line segment adapted to support the propagation of an electromagnetic wave and including a ground plane or wall having at least one aperture, an electrically conductive plate adjacent the ground plane or wall, and displacement means connected to the electrically conductive plate and adapted to adjustably alter the distance between the electrically conductive plate and the ground plane or wall thereby adjusting the amount of phase shift introduced to the electromagnetic wave as it passes through the transmission line segment.
• a plurality of apertures are arranged periodically in the ground plane or wall in a series.
• the shape, pitch and/or size of individual ones of the periodically arranged aperture series are varied in order to improve the impedance match between the transmission line segment and a connected transmission line.
• the apertures are rectangular and the lengths of the apertures at either end of the periodically arranged series are reduced as compared to the length of the apertures in the middle of the aperture series .
• the transmission line segment is a microstrip line or stripline segment on a printed circuit board and the series of apertures are provided in the ground plane, directly beneath and aligned with the microstrip line or stripline.
• the transmission line segment is a segment of ridge, rectangular or circular waveguide and the apertures are provided in one of the walls of the waveguide.
• the width of the apertures in a direction parallel to the transmission line is less than or equal to about ⁇ /10, where ⁇ is the wavelength of the electromagnetic wave at the operating frequency.
• the electrically conducting plate is covered with a dielectric or ferrite layer on the surface of the ground plane or wall of the transmission line segment .
• the transmission line segment and series of apertures follow the same, meandering path.
• the meandering path comprises a plurality of straight paths series connected at angles to one another.
• the invention consists in a control system for an antenna array including a phase shifting element according to the first aspect.
• control system incorporates a plurality of phase shifting elements connected together and share a common electrically conductive plate.
• Figure 1A is a plan view from above of a phase shifting element in accordance with a first embodiment of the present invention
• Figure IB is a cross-sectional side elevation of the phase shifting element of Figure 1A though B-B;
• Figure 2 is a plan view of an alternative embodiment of the phase shifting element of Figures 1A and IB in which an integrated impedance matching structure is provided;
• Figure 3 is a cross-sectional view through a planar phase shifter incorporating the phase shifting element of Figures 1A and IB;
• Figure 4 is a plan elevation of a series of the phase shifting elements of Figures 1A and IB coupled together in series;
• Figure 5 is a plan elevation of an alternative embodiment of phase shifting element according to the present invention in which the transmission line follows a meandering path.
• phase shifting element 10 consists of a transmission line segment
• the apertures 3 are periodically distributed parallel to the direction of propagation of the wave.
• An electromagnetic wave is launched from one end of the transmission line 1 and received at the other end with a certain amount of phase shift.
• the apertures may be rectangular slots on the ground plane of a printed circuit board 6, however other aperture shapes can be used, such as circular or square holes.
• the ground plane may be a solid metal plate or may be a mesh.
• the apertures ⁇ 3 are preferably much smaller than the wavelength of the electromagnetic wave at the operating frequencies (for example, having a width of less than or equal to about ⁇ /10 where ⁇ is the wavelength of the electromagnetic wave at the operating frequency) to avoid leakage of energy by radiation.
• the apertures should be able to store a considerable amount of electromagnetic energy. This is achieved by locating the apertures in regions where the electric and/or magnetic fields have maximum strength. For the microstrip line, maximum field strength occurs just beneath the line conductor 1.
• a tuning electrically conductive plate 4 for example a metal plate, is placed adjacent and close to the apertures 3 to control the propagation constant of the line.
• the propagation constant is identical to the propagation constant of the un-slotted transmission line segment.
• the propagation constant changes gradually towards the propagation constant of the line loaded by the apertures.
• the phase of the electromagnetic wave at the end of the transmission line segment is controlled by the movement of the tuning plate.
• displacement of the tuning plate will be between 0 to 2mm from the ground plane 2.
• the tuning plate 4 is suspended parallel to the slotted ground plane 2 and does not require any electrical connection to the transmission line.
• the geometry of the phase shifting element is identical to a conventional transmission line or waveguide, ensuring simple interfacing to other transmission lines.
• the apertures 3 on the ground plane 2 are tunable impedance loads on the transmission line 1. If the apertures are periodically distributed (as shown in Figures la and lb) , the line can be seen as periodically loaded. Typically, the pitch between the apertures is smaller than about a quarter wavelength. In this case, the loaded line behaves as a new transmission line, with a new effective characteristic impedance and propagation constant . The amount of impedance loading is modified by the proximity of the ground plane 2.
• the effect of the apertures in the transmission line segment may alternatively be explained using the concept of artificial dielectric.
• Small apertures in a metallic wall have an associated magnetic dipolar moment. If the apertures are much smaller than the wavelength (typically around ⁇ /10) they produce an average magnetic moment per surface unit that contributes to the effective magnetic polarisability of the substrate 2 in a similar way to the magnetic dipolar moment from atoms and molecules of the substrate. As a result, the apparent magnetic permeability of the substrate 2 is increased by the magnetic field induced into the apertures .
• the metallic tuning plate 4 is placed close to the apertures 3 on the transmission line. The tuning plate 4 alters the induced magnetic dipolar moment of the apertures and therefore the propagation constant of the transmission line segment. If the distance between the tuning plate 4 and the apertures
• the phase shifting element 10 may be provided with an integrated impedance matching structure wherein the size, pitch and/or shape of the apertures can be varied to match the aperture-loaded line to the connected input/output standard lines.
• a gradual change of the aperture sizes can provide a good broadband impedance match, provided that the phase shifting element is at least one wavelength long.
• tapered apertures 5 having varying, shorter lengths are provided at either end of a series of uniform length apertures .
• a particular advantage of this integrated matching structure is that the return loss is low for all displacements of the tuning plate 4 (and therefore all phase shift settings within the range of the device) . This happens because when the ground plane is at zero distance from the apertures the transmission line appears unloaded and the return loss is extremely low. As the tuning plate
• phase shifting element 10 is matched in an adaptable way. This flexible behaviour saves space and increases performance in comparison to rigid matching structures designed to cope with a broad range of propagation constant .
• the taper of the apertures can, for example, be linear (as shown in Figure 2) , parabolic or any other custom profile to obtain the lowest reflection.
• the taper will be optimised for the maximum separation of the tuning plate 4 from the apertures 3 since very low reflection is expected for the minimum (zero) separation.
• the apertures can form blocks of different sizes rather than a continuous taper. These blocks are typically ⁇ /4 sections that can match the device over a narrowband.
• a planar phase shifter may be implemented using simple manufacturing procedures, typically in a physically planar form (for example microstrip line) .
• An example is shown in Figure 3 which is suitable for mass production of low cost phase shifting devices.
• the sensitivity of the device with respect to displacements of the tuning plate is very high (typically enabling phase shifts of up to 250° per mm of displacement in the microstrip implementation) depending upon design.
• piezoelectric and electrostatic or other low cost displacement mechanisms 7 can be employed to produce accurate vertical displacement of the tuning plate 7, keeping a low profile and low power consumption.
• conventional electrical motors can also be used as a low cost displacement mechanism in some cases.
• the apertures 3 may be etched or mould cut in the ground plane 2 (or a flat electrically conductive wall of the transmission line or waveguide in alternative implementations) .
• the amount of phase shift achieved per unit of length can be enhanced by coating the tuning plate 4 with a dielectric of ferrite material.
• a single control compact scanning array antenna is possible by coupling together a plurality of phase shifting elements according to the present invention.
• FIG. 4 shows an example layout of four series coupled phase shifting elements, each of which share a single tuning plate 4 and which combine to form a microstrip array. Because each of the phase shifting elements 10 share a common tuning plate 4, all of the phase shifting elements are electromagnetically coupled. This arrangement can be used to implement a scanning array that requires a single control for all of the phase shifters of a corporate or series feeding network having multiple input/output ports 8.
• the tuning plate 4 can be slightly inclined or shaped (for example curved) to produce an initial phase distribution in the array, which may then be varied globally as the plate displacement is altered.
• the array can be configured to scan a beam of a linear, planar or conformal array for example, in a single plane and, if appropriately configured, in arbitrary scan directions.
• Figure 5 shows a further embodiment of a phase shifting element 10 wherein the microstrip line 1 follows a meandering path over selected apertures 3 in a ground plane 2.
• the apertures shown in Figure 5 are square shaped and include tapered apertures 5 having gradually reduced sizes to achieve the above described impedance matching benefits.
• This embodiment allows a relatively long length of transmission line segment to be used in a reduced space and therefore improves the compactness of the device incorporating the phase shifter.
• the apertures could of course be other shapes, such as rectangular or circular, and the microstrip line 1 could be replaced with other transmission line types such as waveguide structures.

Landscapes

• Waveguide Switches, Polarizers, And Phase Shifters (AREA)
• Variable-Direction Aerials And Aerial Arrays (AREA)
• Networks Using Active Elements (AREA)

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Cited By (19)

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• 2001
  • 2001-02-14 EP EP01301238A patent/EP1235296A1/de not_active Withdrawn
• 2002
  • 2002-02-12 EP EP02726106A patent/EP1371108B1/de not_active Expired - Lifetime
  • 2002-02-12 DE DE60204672T patent/DE60204672T2/de not_active Expired - Fee Related
  • 2002-02-12 WO PCT/EP2002/001428 patent/WO2002073733A1/en not_active Application Discontinuation
  • 2002-02-12 AT AT02726106T patent/ATE298134T1/de not_active IP Right Cessation

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