[0001] The present invention relates to a three-gate thin-film circulator with impedance
matching.
[0002] A three-gate thin-film circulator is a device which when inserted in a transmission
line makes the path nonreciprocal, i.e. not two-directional. If inserted in a microwave
branching system said device permits conveyance to a single antenna of the signals
of several transmitters or else distribution of signals from said antenna to appropriate
receivers. If one of the three matched gates is closed on a matching termination the
device ensures decoupling if placed between two microwave circuits or matching if
inserted upstream from the circuit in question.
[0003] A known three-gate circulator is made at present with a substrate of magnetizable
material formed of a garnet or ferrite disk entirely metallized on both sides and
inserted in a special hole made in a dielectric substrate. Access thereto is through
three transmission lines deposited on the dielectric substrate and arranged at 120°
to each other. If a magnetizable substrate in circular form is not available, one
of the sides of the magnetizable substrate is metallized with a circular geometry
of appropriate diameter the access to which is likewise obtained with three transmission
lines arranged at 120° on the magnetizable substrate.
[0004] Said known circulator has several shortcomings, specifically rather large space occupied
linked to the diameter of the magnetizable substrate, the need to use impedance transformers
to match output impedance to that of the circuit with which it is associated (with
the resulting further increase in size) and finally the greater insertion losses introduced
by the matching lines.
[0005] To overcome these shortcomings there has recently been accomplished another known
circulator in which metallization of the accessible face of the magnetizable substrate
is no longer uniformly circular but divided in three distinct areas by narrow radial
nonconducting segments 120° apart, the external edges of said areas constituting the
input and output gates.
[0006] This metallization geometry made it possible to reduce the diameter of the magnetizable
substrate and hence the space occupied by the device, transmission frequency being
equal, but didn't solve the problem of matching. The operation of the circulator was
also unsatisfactory.
[0007] The object of the present invention is accordingly to achieve a thin-film three-gate
circulator which would occupy little space and display selfmatching impedance characteristics
such that no external adapters would be needed.
[0008] In accordance with the invention said object has been achieved by a circulator comprising
a substrate of magnetizable material with one face provided with unbroken thin-film
metallization and another face provided with thin-film metallization having a geometry
such that it describes three transmission lines 120° apart converging at a common
centre from respective input and output gates characterized in that it comprises three
other line sections placed at intervals between said transmission lines and coming
together at said common centre to achieve impedance matching of said input and output
gates.
[0009] In other words the present invention takes as its starting point the known three-area
circulator, reducing the extent of said areas in favor of the intervals between said
areas, wherein there have been inserted respective line sections (stubs) having an
impedance matching function. The result is a circulator made up of three transmission
lines 120° apart provided with impedance matching units. The space occupied by the
circulator is thus further reduced and the insertion losses otherwise caused by the
external matching networks are eliminated.
[0010] Two practical examples of the accomplishment of the present invention are illustrated
for greater clarity in the annexed drawings wherein -
FIG. 1 shows a plan view of a circulator in accordance with the invention made in
circular form,
FIG. 2 shows a cross section along line II-II of FIG. 1 of said circular,
FIG. 3 shows a plan view of a circulator in accordance with the invention made in
triangular form.
[0011] The circulator illustrated in FIGS. 1 and 2 comprises a substrate of magnetizable
material 1 made in the form of a garnet or ferrite disc. One face thereof (the bottom
face shown in the drawings) is completely coated with circular thin-film metallization
2, also called "ground plane", while the other face thereof (the top face in the drawings)
has thin-film metallization of a more complex geometry describing the electrical circuit
of the circulator described below.
[0012] As shown in FIG. 1 the metallization of the top face of the substrate 1 comprises
three transmission lines 3 arranged 120° apart and converging at a common centre
4 from respective input and output gates 5 which pass through a circular non-metallized
periphery of the substrate 1 which is not necessary for the electrical operation of
the circulator and serves only to make clear the input and output gates 5 thereof.
[0013] Again as shown in FIG. 1 in the intervals between the transmission lines 3 are placed
three more line sections 6 which come together in the common centre 4 and operate
as impedance adaptors (stubs).
[0014] The conformation of the line sections 6, generally of uniform width up to a terminal
narrowing 7 before the common centre 4, is such that the transmission lines 3 have
in turn an innermost line portion 8 of uniform width (and hence impedance) and an
outermost line portion 9 of variable width (and hence impedance) in the direction
of propagation. The outermost portion 9 communicates with the corresponding input/output
gate 5.
[0015] The circulator of FIGS. 1 and 2 is designed to be inserted in a dielectric substrate
on which is made a microwave circuit and together therewith in a container in which
there is also housed a magnet capable of supplying a steady magnetic field. This design
is known in itself and is therefore not described and illustrated in detail here.
[0016] While it is essential that metallization of the top face (in the drawings) of the
substrate 1 have the geometry described with the three transmission lines 3 and three
matching line sections 6 it is not essential that said metallization and the circulator
in general have a circular conformation. Alternatively there can be provided a triangular
conformation like that shown in FIG. 3 where the same reference numbers as in FIGS.
1 and 2 are used to indicate corresponding parts.
[0017] Finally it should be noted that an alternative use of the circulator of FIGS. 1 and
2 or of the one shown in FIG. 3 can call for the deposit directly on the substrate
1 between a gate 5 and the ground plane 2 of a resistance having a value equal to
that of the characteristic impedance of the circuit. In this case the circulator functions
as a separator, offering low attenuation in one direction and high attenuation in
the other.
1. Thin-film circulator with three gates comprising a substrate of magnetizable material
(1) having one face provided with unbroken thin-film metallization (2) and another
face provided with thin-film metallization having a geometry such as to describe three
transmission lines (3) 120° apart converging at a common centre (4) from respective
input and output gates (5) characterized in that it comprises three other line sections
(6) placed in the intervals between said transmission lines (3) and coming together
at said common centre (4) to accomplish impedance matching of said input and output
gates (5).
2. Circulator in accordance with claim 1 characterized in that said matching line
sections (6) have essentially uniform width with narrowing ends (7) toward said common
centre (4) and said transmission lines (3) have an innermost portion (8) of constant
width and an outermost portion (9) of variable width in the direction of propagation.
3. Circulator in accordance with claim 1 characterized in that said metallization
(3-6) of the other face of the substrate (1) is circular in form.
4. Circulator in accordance with claim 1 characterized in that said metallization
(3-6) of the other face of the substrate (1) is of triangular form.
5. Circulator in accordance with claim 1 characterized in that it comprises a resistance
of a value equal to that of the characteristic impedance of the microwave circuit
with which it is associated placed on said substrate (1) between one of said gates
(5) and said face (2) provided with thin metallization in such a manner as to function
as a separator.