GB2354885A

GB2354885A - Microwave circulators and isolators

Info

Publication number: GB2354885A
Application number: GB0031718A
Authority: GB
Inventors: William Terence Nisbet
Original assignee: Racal MESL Ltd
Current assignee: Garrett Motion UK Ltd
Priority date: 1996-12-09
Filing date: 1996-12-09
Publication date: 2001-04-04
Anticipated expiration: 2016-12-09
Also published as: GB2320138B; GB9625568D0; GB0031718D0; GB2354885B; GB2320138A

Abstract

A microwave circulator / isolator comprises a centre conductor 12 sandwiched between a pair of ferrite disc resonators 11 with a plurality of magnets (30, see figure 2) spaced about the circumference of the centre conductor. The magnets are arranged so that the N-S pole axis of each magnet is perpendicular to the plane of the centre conductor, and may be housed in holes (31, see figure 2) in the extruded metal housing 20.

Description

2354885 MICROWAVE CIRCULATOR AND ISOLATORS This invention relates to

microwave circulators and isolators.

Microwave circulators and microwave isolators have the same basic structure, however, an isolator has at least one port which is terminated.

Microwave circulators are widely used in applications requiring a duplexing function. Microwave isolators, on the other hand, are often used in wireless communications systems to isolate unwanted signals which might otherwise give rise to system interference; for example, microwave isolators are used in base station combiners to reduce reflected signals carrying intermodulation products.

Since the production volume of these devices is generally large there is a need to reduce production costs without, of course, compromising the required electrical and mechanical specification.

Figure 1 of the accompanying drawings shows a longitudinal sectional view through a known microwave circulator/isolator.

2 This construction comprises a resonant structure 1 sandwiched between machined aluminium ground planes 2,2'. The resonant structure I has a strip-line centre conductor 3 and a pair of ferrite disc resonators 4,41 mounted on opposite sides of the centre conductor 3.

The centre conductor 3 has three symmetrically configured legs (of which only two are shown in Figure 1), each for connection to a respective input/output port via a flanged connector 5 attached to the ground planes 2,21 by fixing screws. Each leg of the centre conductor 3 may include an impedence matching quarter-wave transformer.

The resonant structure 1 is magnetically biassed by two permanent magnets 6,61 located in recesses formed in the ground planes 2,21, and the entire assembly is housed within a pressed sheet metal casing 7 made from a magnetic alloy which provides both mechanical protection and r.f. and magnetic shielding.

This known construction has several disadvantages. It has a large number of component parts and this adds to the overall production costs and increases the assembly time. Also, there 3 is a tendency for microwave radiation to leak through gaps between the sheet metal casing 7 and the flanged connectors 5. Therefore, additional shielding is required, and this is usually in the form of an electrically conductive material such as a silver-based epoxy applied around the edges of the casing. Again, this adds to production costs.

Machined aluminium ground plates are particularly expensive components. In the case of large-scale production, die cast ground planes could alternatively be used; however, the necessary tooling is both costly and time consuming.

According to one aspect of the invention there is provided a microwave circulator/ isolator comprising a strip-line centre conductor, a pair of ferrite resonators arranged on opposite sides of the centre conductor and magnetic means for magnetically biassing the ferrite resonators, wherein the centre conductor, said pair of ferrite resonators and the magnetic means are all mounted in a common housing in the form of an extrusion.

According to another aspect of the invention there is provided a microwave circulator/isolator comprising a strip-line centre 4 conductor, a pair of ferrite resonators arranged on opposite sides of the centre conductor and magnetic means for magnetically biassing the ferrite resonators, wherein the magnetic means comprises a plurality of magnets arranged around said ferrite resonators with the poles of each magnet lying on opposite sides of the centre conductor.

A microwave circulator/ isolator according to the invention is now described, by way of example only, with reference to the accompanying drawings, in which Figure 1 is a longitudinal sectional view through a known microwave circulator/ isolator, and Figures 2 and 3 show transverse and longitudinal sectional views respectively of a microwave circulator/isolator according to the invention.

Referring to Figures 2 and 3, the microwave circulator/ isolator has a 3way resonant structure 10 mounted in a central cavity C of a housing 20. The housing is in the form of an aluminium extrusion, and the cavity C extends from one end face 21 of the extrusion to the opposite end face 211.

In this embodiment, the resonant structure 10 is of conventional form, comprising a pair of ferrite disc resonators 11,111 mounted on opposite sides of a 3 -way stripline centre conductor 12. The ferrite disc resonators may be formed from any suitable ferrite material including ferrimagnetic spinels such as nickel iron oxide (NiFe2ol) and garnets such as yttrium iron garnet (Y3Fe5O12). In the case of a centre conductor including impedance matching transformation regions, the disc resonators 11,111 may have a composite structure including non-magnetic dielectric material as well as ferrite material.

The centre conductor 12 has three legs 12a,12b,12c which radiate outwardly from, and are arranged symmetrically around the longitudinal axis X-X of the central cavity C of the extrusion. Each leg 12a,12b,12c is electrically connected to a respective port Pj,P2,P3 of the microwave circulator/ isolator. To this end, each leg is connected to a serrated electrical connector 13a,13b,13c which is a push-fit in an associated hole 14a,14b,14c in the extrusion wall.

The resonant structure 10 is magnetically biassed by a group of three permanent magnets 30a,30b,30c disposed symmetrically 6 around the longitudinal axis X-X of the central cavity C. The magnets 30a, 30b,30c are mounted in longitudinally extending holes 31a,31b,31c formed in the extrusion around the central cavity C and are positioned such that their North and South poles lie on opposite sides of the centre conductor 12. The magnets produce magnetic flux lines F which orthogonally intersect the end faces of the disc resonators 11, 11 1.

Pressed, magnetic alloy end plates 32,321 are fixed to the end faces 21, 211 of the extrusion by self-tapping screws, and each end plate is sealed to the respective end face by a suitable gasket 33,331. The end plates 32, 32, form ground planes, and the outwardly facing surfaces of the disc resonators may be metallised to establish a reliable electrical contact to the adjacent ground plane.

Use of an extruded aluminium housing substantially reduces tooling costs and gives a structure having fewer component parts than do conventional structures of the kind described with reference to Figure 1. Furthermore, the extrusion facilitates the use of push-fit electrical connectors thereby obviating the need for fixing screws and tapped holes. Also, pushfit connectors can be manufactured more cheaply than the 7 conventionally used f langed connectors.

As has been described, the permanent magnets 30a,30b,30c are disposed around the central cavity C of the extrusion. Again, this configuration is advantageous, giving a structure which is considerably more compact than conventional structures in which the magnets are disposed to either side of the resonator.

In view of the above, microwave circulators/ isolators can be manufactured at considerably reduced cost and require shorter assembly time.

8

Claims

1 A microwave circulator/ isolator comprising a strip-line centre conductor, a pair of ferrite resonators arranged on opposite sides of the centre conductor and magnetic means for magnetically biassing the ferrite resonators, wherein the magnetic means comprises a plurality of magnets arranged around said ferrite resonators with the poles of each magnet lying on opposite sides of the centre conductor.

2. A microwave circulator/isolator as claimed in claim 1, wherein the centre conductor, said pair of ferrite resonators, and the magnetic means, are all mounted in a common housing.

3. A microwave circulator/isolator as claimed in claim 2, wherein said common housing is an extrusion.

4. A microwave circulator/isolator as claimed in claim 3, wherein the extrusion is an aluminium extrusion.

S. A microwave circulator/isolator as claimed in claim 3 or claim 4, wherein said centre conductor and said pair of ferrite resonators are mounted in a central cavity of said extrusion, and said magnets are mounted in holes formed in the 9 extrusion around the central cavity.

6. A microwave circulator/ isolator as claimed in any one of claims 3 to 5, wherein said centre conductor has a plurality of legs arranged symmetrically about the longitudinal axis of the central cavity, and electrical connection is made to each leg via a respective hole formed in the extrusion.

7. A microwave circulator/isolator as claimed in claim 6, wherein the electrical connection to each said leg is formed by an electrical connector which is a push-fit in the respective hole.

8. A microwave circulator/ isolator as claimed in claim 7, wherein said electrical connectors are serrated.

9. A microwave circulator/ isolator as claimed in any one of claims 5 to 8, wherein said central cavity extends from one end face of the extrusion to the opposite end face of the extrusion and a respective end plate is attached to each said end face.

10. A microwave circulator/ isolator as claimed in claim 9, wherein each said end plate forms a ground plane.

11. A microwave circulator/ isolator as claimed in claim 9 or claim 10, wherein each said end plate is sealed to the respective end face by a gasket.

12. A microwave circulator/ isolator as claimed in any one of claims 9 to 11, wherein said end plates are pressed magnetic alloy end plates.

13. A microwave circulator/ isolator as claimed in any one of claims 10 to 12, wherein an end face of each said ferrite resonator is metallised to provide electrical contact with a respective said ground plane.

14. A microwave circulator/ isolator as claimed in any one of claims 9 to 13, wherein said end plates are attached to the extrusion by self-tapping screws.