Wave transmission lines and networks – Plural channel systems – Nonreciprocal gyromagnetic type
Reexamination Certificate
2000-05-23
2001-11-13
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Nonreciprocal gyromagnetic type
C333S024200
Reexamination Certificate
active
06317010
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a radio frequency circulator/isolator and components thereof. The circulator/isolator (called hereafter a “circulator” for brevity is a non-reciprocal device often used for discriminating and/or diverting oppositively directed signals transmitted through a network.
BACKGROUND OF THE INVENTION
Circulators generally contain two basic parts:
i/ a microwave circuit comprising an arrangement of conductors and ferrite blocks, and
ii/ a magnetic circuit providing a magnetic biasing field applied to the ferrite blocks that act as a non-reciprocal media for propagating radio frequency signals throughout the device.
An ideal three port circulator transmits power (as shown diagrammatically in
FIG. 1
) between any two ports in a forward direction only, i.e. from port
1
to port
2
, from port
2
to port
3
, from port
3
to port
1
. In the reverse direction (from port
1
to port
3
, from port
3
to port
2
and from port
2
to port
1
) no power can be transmitted (i.e. port
3
is isolated from port
1
, port
2
from port
3
, and port
1
from port
2
).
A circulator can be converted to an isolator by connecting a matched load to one of the ports. For example, if port
3
is terminated with a matched load, a drive signal is applied to input port
1
and an antenna is connected to output port
2
, then any power reflected from the antenna is directed to the terminated port
3
and dissipated in the load.
A typical prior art strip line lumped element circulator is shown in
FIGS. 2 and 3
. Conductors
4
connected to terminal ports are sandwiched between ferrite discs
5
and
6
which in turn are located in the gap between magnets
7
and
8
. Permanent magnets
7
and
8
are supposed to magnetise ferrite disks
5
and
6
and provide a dc biasing magnetic field in the ferrite disks
5
,
6
that is necessary for signal circulation between terminal ports. The direction of circulation is determined by the orientation of the applied dc magnetic field and may be reversed by reversing the polarity of the magnets
7
,
8
.
In such prior devices conductors
4
a
,
4
b
, and
4
c
form a multi-layered construction where individual strips are interwoven and their intersections are insulated during assembly. The conductor ends (
9
a
,
9
b
,
9
c
) are connected to terminal ports of the circulator and the other ends (
10
a
,
10
b
,
10
c
) are attached to a common ground plane.
The pattern of interwoven conductors
4
may be fabricated in two different ways. One approach is based on interweaving and joining separated insulated strip conductors. The other technique employs the technology of multi-layered metal and dielectric deposition on the surface of a ferrite disk. The former method is time consuming and the resulting conductor assemblies may have inconsistent topology. The latter procedure exploits thin film technology and is typically useful in fabrication of low power microwave integrated devices. Increasing power handling capacity may result in a substantial rise in manufacturing cost. Another problem encountered by both fabricating methods is the quality of the connections between conductor ends (
10
a
,
10
b
,
10
c
) and the common ground plane, the inconsistent joints causing increased losses and degradation of overall circulator performance.
Homogeneity of the biasing magnetic field inside the ferrite disks is normally desirable for optimum circulator performance. Non-uniformity of the biasing magnetic field associated with the shape of magnets and ferrite blocks may substantially degrade insertion losses and isolation between the circulator ports. The crucial problem of optimising distribution of the biasing magnetic field has been extensively explored and addressed in numerous publications and patents.
In particular, to generate a uniform magnetic field inside ferrite disks it has been proposed to attach ferrite semi-spheres either side of the ferrite discs (see E. F. Schloemann. “Circulators for Microwave and Millimeter-Wave Integrated Circuits”. Proceedings of IEEE, vol. 76, No. 2, February 1988, pp 188-200). Semi-spherical ferrite segments surrounding the ferrite disks neutralise the demagnetising effect of the disk-shaped ferrites on distribution of the internal biasing magnetic field. They help to preserve uniformity of the internal magnetic field when the system is exposed to a uniform external magnetic field. However, such an arrangement is bulky and only employs the central part of the magnetic system due to tight requirements of homogeneity in the external magnetic field. Ferrite semi-spherical segments are also expensive to produce and, due to the very poor thermal conductivity of ferrite, they impede heat transfer from the ferrite disks. The latter problem may result in substantial degradation of circulator performance with increasing power and/or varying temperature.
DE 2950632 discloses the use of frustoconical ferrites in a junction circulator. This is said to reduce noise and intermodulations by minimising the effect of irregularities in the biasing magnetic field nearby the edge of the ferrite. This, however, requires special fabrication techniques, thus increasing cost. This also increases the thickness of ferrite used, thus impeding heat transfer.
Further, in prior art circulators the ferrite was considered simply as part of the microwave circuit not affecting the DC magnetic circuit. This often resulted in difficulties of thermal stabilisation and the need for complex temperature controlling devices.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a circulator and components thereof which overcome or at least minimise the disadvantages mentioned above, or which at least provides the public with a useful choice.
According to a first aspect of the invention there is provided an integral conductor arrangement for a circulator comprising a plurality of overlying spaced apart crossing strips attached at one end to a base portion having an opening therein, and forming a first compartment adapted for receiving a ferrite block therein such that the ferrite block may be inserted into the first compartment with one face of the ferrite block located adjacent the strips while an opposite face of the ferrite block is exposed to allow direct contact with a circulator housing body.
There is further provided a method of forming a conductor arrangement for a circulator comprising the steps of:
i) forming an integral conductor arrangement consisting of a plurality of strips extending outwardly from a base portion having an opening therein;
ii) folding the arrangement to define a first compartment to accommodate a ferrite block; and
iii) folding the strips inwardly without a ferrite block being inserted into the first comartment to form an arrangement of spaced apart overlaying crossing strips.
Preferably, for axially symmetrical configurations of magnetic field, the lens consists of a disc-shaped section and a cone frustum section. The walls of the cone frustum section may be slighty convex or concave.
There is further provided a circulator comprising a conductor assembly and/or a lens and magnet assembly as hereinbefore described.
According to a further aspect of the invention there is provided a thermostable circulator including one or more permanent magnet and one or more ferrite block wherein the magnetic characteristics of the ferrite are correlated with the characteristics of the magnet, the combination of thermal characteristics of the permanent magnet and the ferrite being selected so that variations of the effective RF permeability of the ferrite are minimised over a specified temperature range. The permanent magnet would normally be saturated to ensure stability of the biasing magnetic field.
REFERENCES:
patent: 3030593 (1962-04-01), Von Aulock
patent: 3334318 (1967-08-01), Nakahara et al.
patent: 3716805 (1973-02-01), Knerr
patent: 3836874 (1974-09-01), Maeda et al.
patent: 4034377 (1977-07-01), Knox et al.
patent: 4174506 (1979-11-01), Ogawa
patent: 4246552 (1981-01-01), Fukas
Butland Roger John
Schuchinsky Alexander Grigorievich
Therkleson Gerald Leigh
Bettendorf Justin P.
Deltec Telesystems International Limited
Merchant & Gould P.C.
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