Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P7/00—Resonators of the waveguide type
  • H01P7/10—Dielectric resonators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/20—Frequency-selective devices, e.g. filters
  • H01P1/207—Hollow waveguide filters
  • H01P1/208—Cascaded cavities; Cascaded resonators inside a hollow waveguide structure
  • H01P1/2084—Cascaded cavities; Cascaded resonators inside a hollow waveguide structure with dielectric resonators

Definitions

• the present invention relates generally to the field of fil'ters and, in particular, to a dielectric resonator for use in, for example, a cavity filter.
• a typical wireless system includes a plurality of base stations that are connected to the public switched telephone network (PSTN) via a mobile switching center (MSC). Each base station includes a number of radio transceivers that are typically associated with a transmission tower. Each base station is located so as to cover a geographic region known colloquially as a "cell.” Each base station communicates with wireless terminals, e.g. cellular telephones, pagers, and other wireless units, located in its geographic region or cell.
• a wireless base station includes a number of modules that work together to process RF signals.
• modules typically include, by way of example, mixers, amplifiers, filters, transmission lines, antennas and other appropriate circuits.
• One type of filter that finds increased use in wireless base stations is known as a microwave cavity filter.
• a new type of resonator for a microwave cavity filter was proposed by Chi
• Embodiments of the present invention provide a resonator rod for the cavity filter that includes a base portion that allows the resonator rod to be attached to the inside of the cavity without substantial adverse effects on the insertion loss of the filter.
• a dielectric resonator in one embodiment, includes a rod having first and second ends and an exterior surface that extends between the first and second ends.
• the resonator also includes a base, coupled to the first end of the rod, the base being adapted to attach to an interior surface of a housing.
• the rod and the base comprise a dielectric material.
• Figure 1 is a perspective view that represents an embodiment of a dielectric resonator according to the teachings of the present invention.
• Figure 2 is a perspective view that represents another embodiment of a dielectric resonator according to the teachings of the present invention.
• Figure 3 is graph that depicts an example of electric fields in a Y-Z plane for an embodiment of a dielectric resonator according to the teachings of the present invention.
• Figures 4, 5, 6, 7, 8, and 9 are cross sectional views that illustrate various alternative embodiments of an attachment mechanism for attaching a dielectric rod within a housing according to the teachings of the present invention.
• Figures 10, 11, and 12 are perspective views of additional embodiments of a dielectric resonator according to the teachings of the present invention.
• Figure 13 is a perspective view of a filter including a plurality of dielectric resonators according to the present invention.
• FIG. 1 is a perspective view that represents an embodiment of a dielectric resonator, indicated generally at 100, according to the teachings of the present invention.
• Dielectric resonator 100 includes rod 102 and base 104.
• Rod 102 and base 104 are each constructed of a dielectric material.
• rod 102 and base ⁇ 04 are separately formed of ceramic material.
• rod 102 and base 104 are formed simultaneously using an appropriate pressing tool.
• Rod 102 has first and second opposite ends 106 and 108 and an exterior surface 110 that extends between the first and second ends 106 and 108.
• rod 102 comprises a cylindrical rod, as shown. In other embodiments, rod 102 comprises other appropriate shapes.
• Base 104 is attached to first end 106 of rod 102.
• base 104 is sintered to rod 102.
• base 104 and rod 102 are formed at the same time in a single pressing process.
• FIG. 2 illustrates another embodiment of a dielectric resonator, indicated generally at 200.
• Dielectric resonator 200 includes rod 202 and base 204.
• rod 202 and base 204 are formed in a single pressing motion in the direction of arrow 212.
• rod 202 and base 204 are formed separately and then sintered together.
• Base 104 provides an attachment surface 114 for attaching rod 102 to interior surface 113 in cavity 115 of housing or enclosure 116.
• base 104 is smaller than interior surface 113 of housing 116.
• rod 102 and base 104 are secured in place by an attachment mechanism coupled to base 104 that reduces losses caused by conventional attachment mechanism associated with the end of a dielectric rod.
• Example embodiments of attachment mechanisms that can be used to secure base 104 in cavity 115 are illustrated in Figures 4-9, which Figures are described in detail below.
• lossy fixing materials e.g., epoxy
• these materials can considerably reduce the Q-value of the resonator when applied to the end of the rod where the electric fields are typically quite strong.
• embodiments of this invention advantageously reduce the affect of the fixing material on the Q-value of the resonator by moving the lossy fixing materials away from the rod where electric fields are weaker.
• Figure 4 is a simulation generated with Ansoft HFSS Version 7.0.04 that illustrates the relative strength of electrical fields in the Y-Z plane in base 104 and rod 102. The strength of the electric fields in region 400 of base 104 are lower than the fields in rod 102.
• the affect of the lossy fixing materials on the Q-value of the resonator is substantially reduced.
• Base 104 is wider than rod 102.
• base 104 and rod 102 comprise concentric structures with the width of base 104 exceeding the width of rod 102.
• the base does not extend around the entire perimeter of the rod.
• base 204 extends in a direction (N) normal to surface 110 on opposite sides of rod 202.
• each base 104, 204 provides an attachment surface 114, 214 that lie outside a planar projection of rod 102, 202 on the interior surface 113, 213 of the housing 116, 216. It is understood that other shapes for the base may be substituted that allow the lossy attachment mechanism to be moved out away from the end of the rod.
• spurious properties means the affect of signals at frequencies in unused modes that affect frequency response properties outside the passband of a filter incorporating the resonator.
• Figures 4, 5, 6, 7, 8, and 9 are cross sectional views that illustrate various alternative embodiments of an attachment mechanism for attaching a dielectric rod within a housing according to the teachings of the present invention. Each of the embodiments is described in turn.
• rod 402 and base 404 are coupled to surface 413 using an adhesive 420 such as an epoxy resin.
• adhesive 420 comprises, in other embodiments, other appropriate substances, compounds and glues with a low dissipation factor that are capable of affixing a ceramic material to a metal surface.
• adhesive 420 is applied to attachment surface 414 along its perimeter 422.
• attachment mechanism 520 includes at least two screws 524 and collar 526.
• Collar 526 includes surface 528 that engages base 504 between collar 526 and surface 513. Screws 524 pass through collar 526 and into surface 513.
• collar 526 encompasses the entire perimeter of base 504. In other embodiments, collar 526 comprises multiple collars with each collar engaging only a portion of the perimeter of base 504. In one embodiment, collar 526 and screws 524 comprise a plastic material. In other embodiments, collar 526 and screws 524 comprise a dielectric material.
• attachment mechanism 620 includes a plurality of screws through base 604 into surface 613.
• the screws of attachment mechanism 620 comprise plastic screws.
• attachment mechanism 620 comprises screws of any other appropriate material for use in a resonator housing, e.g., any appropriate dielectric material.
• rod 702 and base 704 are coupled to surface 713 using any of the attachment mechanisms of Figures 5, 6, 8, and 9.
• air cavity 720 is provided under base 704. It is noted that the presence of the air cavity shifts the resonant frequency of the resonator, but does not substantially affect the Q value of the resonator.
• Figure 7 illustrates that base 704 provides the advantages of reduced insertion loss even though base 104 is attached to an uneven surface.
• attachment mechanism 820 includes dielectric a plurality of supports 822. In one embodiment, two or more supports 822 are dispersed around the perimeter of base 804. Supports 822 are affixed to surface 813 using, for example, an adhesive. It is noted that the resonator performance is improved with the use of attachment mechanism 820 even though the bottom of resonator rod 802 is separated by a distance from surface 813.
• attachment mechanism 920 includes a plurality of protuberances or posts 924 that are selectively spaced around region 930 of surface 913 for receiving base 904.
• the plurality of posts comprises four posts spaced apart around base 904. In other embodiments, any appropriate number of posts 924 are used that allow base 904 to be securely held in place on surface 913. Base 904 is secured in place by adhesive 922 between base 904 and posts 924. In one embodiment, posts 924 comprise a single ridge that encircles the perimeter of base 904.
• Figures 10, 11, and 12 are perspective views of additional embodiments of a dielectric resonator according to the teachings of the present invention.
• the structures of these resonators are designed to allow the resonator to be shortened to allow use with a smaller cavity.
• metal plate 1040 is attached to second end 1008 opposite base 1004 attached to first end 1006 of rod 1002.
• ceramic body 1140 is attached to second end 1108 opposite base 1104 attached to first end 1106 of rod 1102:.
• ceramic body 1240 is attached to second end 1208 opposite base 1204 attached to first end 1206 of rod 1202. IV.
• Filter Figure 13 is a partially exploded perspective view of a filter, indicated generally at 1300, including a plurality of dielectric resonators 1350-a, 1350-b, and 1350-c according to the present invention.
• each of resonators 1350-a, 1350-b, and 1350-c includes a base of the type described above with respect to Figures 1 and 2 that allows the resonators to be affixed in cavities 1352-a, 1352-b, and 1352-c with reduced losses caused by conventional attachment mechanism associated with the end of a dielectric rod.
• resonators 1350-a, 1350-b, and 1350-c are each affixed to surface 1354 in housing 1356 using, for example, one or more of the attachment mechanisms of Figures 4-9.
• Filter 1300 also includes lid 1358 that is selectively attached to housing 1356.
• Lid 1358 includes tuning screws 1360-a, 1360-b, and 1360-c that are associated with resonators 1350-a, 1350-b, and 1350-c, respectively. Tuning screws 1360-a, 1360-b, and 1360-c are used to adjust the passband of filter 1300.
• Lid 1358 further includes tuning screws 1362-a and 1362-b that adjust the coupling between cavities 1352-a, 1352-b and 1352-b, 1352-c, respectively.
• Filter 1300 also includes input 1364 and output 1366.
• Input 1364 receives an input signal for filtering by filter 1300.
• the filtered output of filter 1300 is provided at output 1366.
• the resonators of the various embodiments include rods, bases and other components that are formed of dielectric materials, such as ceramic materials.
• the dielectric materials comprise materials with a dielectric constant, ⁇ r , of about 45, for example, with low dielectric losses. It is understood that materials with other dielectric constants can also be used.
• the various dielectric elements are produced with commercially available ceramic materials such as 4500 series ceramic material from Trans-Tech, Inc., Adamstown, MD or K4500 ceramic material from EDO Electro-Ceramics, Salt Lake City, UT.
• the embodiments provide a dielectric resonator with a base for attaching the resonator rod within a housing.
• the base is designed such that the attachment mechanism reduced losses caused by conventional attachment mechanism associated with the end of a dielectric rod.
• the base in one embodiment has a diameter that is greater than the diameter of an end of the resonator rod.
• Other embodiments are also provided that provide a base with an attachment surface that is outside the planar projection of the rod on the surface of the housing.
• the dielectric material used for the base and the rod can be varied.
• the base can be used with any appropriate resonator structure for single mode or multimode resonators.

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Cited By (4)

Citations (8)

• 2001
  • 2001-11-13 DE DE10196900T patent/DE10196900T1/de not_active Withdrawn
  • 2001-11-13 WO PCT/US2001/047117 patent/WO2002039535A1/en not_active Application Discontinuation
  • 2001-11-13 AU AU2002228876A patent/AU2002228876A1/en not_active Abandoned
  • 2001-11-13 GB GB0310222A patent/GB2386258A/en not_active Withdrawn

Patent Citations (8)

Non-Patent Citations (4)

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