Apparatus and methods related to ferrite based circulators

Abstract

Apparatus and methods related to ferrite based circulators are disclosed. A ferrite disk used in a circulator can be configured to reduce intermodulation distortion when routing radio-frequency signals having closely spaced frequencies. Such a reduction in intermodulation distortion can be achieved by adjusting magnetization at the edge portion of the ferrite disk. By way of an example, a ferrite disk with a reduced saturation magnetization (4PiMs) edge portion can reduce intermodulation distortion. Example configurations with such a reduced 4PiMs edge portions are disclosed.

1 . (canceled) 
     
     
         2 . A passive circulator, comprising:
 a ferrite plate that extends laterally along a first plane and has a center portion and an edge portion, the center portion having a first saturation magnetization value and the edge portion having a second saturation magnetization value that is lower than the first saturation magnetization value;   a magnet that extends along a second plane parallel to the first plane, the magnet disposed relative to the ferrite plate to provide a static magnetic field to the ferrite plate to magnetize the ferrite plate, the magnetization configured to facilitate transmission of a radio-frequency signal between a first location and a second location along a perimeter of the ferrite plate based on a standing wave pattern formed in the ferrite plate due to the magnetization; and   a housing that surrounds the magnet and the ferrite plate and which provides a return path for the static magnetic field, the housing comprising a hollow portion with an inner dimension that is larger than a lateral dimension of the magnet and a lateral dimension of the ferrite plate, and a plate portion that extends along a third plane parallel to the second plane so that the magnet is disposed between the plate portion and the ferrite plate, the plate portion attached to the hollow portion to seal an end of the hollow portion.   
     
     
         3 . The circulator of  claim 2  further comprising a flux conductor disposed relative to the ferrite plate so that the ferrite plate is disposed between the flux conductor and the magnet, the flux conductor configured to provide resonator and matching network functionalities. 
     
     
         4 . The circulator of  claim 2  further comprising a dielectric structure disposed along an outer perimeter of the ferrite plate, the dielectric structure configured to facilitate impedance matching between a first electrical conductor and a second electrical conductor. 
     
     
         5 . The circulator of  claim 2  wherein the ferrite plate is a ferrite disk with a circular outer perimeter. 
     
     
         6 . The circulator of  claim 5  wherein the edge portion of the ferrite disk is defined by a ring disposed about a center disk that defines the center portion of the ferrite disk. 
     
     
         7 . The circulator of  claim 6  further comprising a dielectric ring disposed about the ring. 
     
     
         8 . The circulator of  claim 2  wherein the ferrite plate is a single piece disk. 
     
     
         9 . A method for reducing intermodulation distortion, the method comprising:
 providing a ferrite plate having a center portion having a first saturation magnetization to allow passage of a transmit signal between a first location and a second location of the ferrite plate and passage of a receive signal between the second location and a third location of the ferrite plate;   providing an edge portion of the ferrite plate having a second saturation magnetization that is lower than the first saturation magnetization to reduce intermodulation distortion occurring at the edge portion of the ferrite plate;   applying a static magnetic field to the ferrite plate with a magnet, the magnet disposed relative to the ferrite plate so that the magnet extends along a parallel plane to the ferrite plate; and   providing a return path for the magnetic field with a housing that surrounds the magnet and the ferrite plate, the housing comprising a hollow portion with an inner dimension that is larger than a lateral dimension of the magnet and a lateral dimension of the ferrite plate, and a plate portion that extends along a third plane parallel to the magnet so that the magnet is disposed between the plate portion and the ferrite plate, the plate portion attached to the hollow portion to seal an end of the hollow portion.   
     
     
         10 . The method of  claim 9  wherein the second saturation magnetization of the edge portion reduces a third order product of fundamentals of the transmit and receive signals to a level of at least about −85 dBc. 
     
     
         11 . The method of  claim 10  wherein the reduction of the third order product is to a level of at least about −90 dBc. 
     
     
         12 . The method of  claim 9  further comprising disposing a dielectric structure along an outer perimeter of the ferrite plate to facilitate impedance matching between a first electrical conductor and a second electrical conductor. 
     
     
         13 . A passive circulator module for isolating transmit and receive RF signals from each other, the module comprising:
 a ferrite plate that extends laterally along a first plane and has a center portion and an edge portion, the center portion having a first saturation magnetization value and the edge portion having a second saturation magnetization value that is lower than the first saturation magnetization value;   a magnet configured to provide a static magnetic field to the ferrite plate to magnetize the ferrite plate to facilitate transmission of a radio-frequency signal between a first location and a second location along a perimeter of the ferrite plate based on a standing wave pattern formed in the ferrite plate due to the magnetization, the magnet extending along a second plane parallel to the first plane;   a housing that surrounds the magnet and the ferrite plate to provide a return path for the static magnetic field, the housing comprising a hollow portion with an inner dimension that is larger than a lateral dimension of the magnet and a lateral dimension of the ferrite plate, and a plate portion that extends along a third plane parallel to the second plane so that the magnet is disposed between the plate portion and the ferrite plate, the plate portion attached to the hollow portion to seal an end of the hollow portion; and   signal ports coupled to a transmit radio-frequency signal, a receive radio-frequency signal, and an antenna.   
     
     
         14 . The module of  claim 13  wherein the hollow portion and the plate portion are separate pieces. 
     
     
         15 . The module of  claim 13  further comprising a dielectric structure disposed along an outer perimeter of the ferrite plate. 
     
     
         16 . The module of  claim 13  wherein the ferrite plate is a single piece disk. 
     
     
         17 . The module of  claim 13  wherein the ferrite plate is a ferrite disk with a circular outer perimeter. 
     
     
         18 . The module of  claim 17  wherein the edge portion of the ferrite disk is defined by a ring disposed about a center disk that defines the center portion of the ferrite disk, the ring having an inner diameter greater than or equal to an outer diameter of the center disk. 
     
     
         19 . The module of  claim 18  further comprising a dielectric ring disposed about the ring. 
     
     
         20 . A wireless device, comprising:
 a transmitter circuit;   a receiver circuit;   an antenna configured to transmit signals from the transmitter circuit and to receive signals for the receiver circuit; and   a passive circulator for isolating transmit and receive signals between the transmitter and receiver circuits, including (a) a ferrite plate that extends laterally along a first plane and has a center portion and an edge portion, the center portion having a first saturation magnetization value and the edge portion having a second saturation magnetization value that is lower than the first saturation magnetization value; (b) a magnet extending along a second plane parallel to the first plane and disposed relative to the ferrite plate to provide a static magnetic field to the ferrite plate to magnetize the ferrite plate to facilitate transmission of a radio-frequency signal between a first location and a second location along a perimeter of the ferrite plate based on a standing wave pattern formed in the ferrite plate due to the magnetization; (c) a magnetic circuit configured to provide a return path for the magnetic field, the magnetic circuit at least partially defined by a housing that surrounds the magnet and the ferrite plate, the housing comprising a hollow portion with an inner dimension that is larger than a lateral dimension of the magnet and a lateral dimension of the ferrite plate, and a plate portion that extends along a third plane parallel to the second plane so that the magnet is disposed between the plate portion and the ferrite plate, the plate portion attached to the hollow portion to seal an end of the hollow portion; and (d) signal ports coupled to the transmitter circuit, the receiver circuit, and the antenna.   
     
     
         21 . The wireless device of  claim 20  wherein the wireless device includes a base station.