Electrical Connector

Abstract

An electrical connector for transferring electromagnetic energy between a coaxial cable and a microstrip transmission system, each having a characteristic impedance of 50 ohms, with a minimal power loss due to a reflective discontinuity during the transfer. The electrical connector includes a central conductor and an outer conductor enclosing the central conductor, and has first, second, and transition sections each of which is designed to have a characteristics impedance of 50 ohms. The first and second sections are designed like sections of a coaxial cable to have a characteristic impedance of 50 ohms by the proper selection of the ratio of the diameters of the central and outer conductors. The central conductor of the first section has a small diameter, and the diameter of the outer conductor is a selected multiple of the small diameter to yield a characteristic impedance of 50 ohms. The second section has a large diameter central conductor, and the diameter of the outer conductor is the same selected multiple of the large diameter to yield a characteristic impedance of 50 ohms. The central conductor has an abrupt shoulder like transition between the small ad large diameters of the first and second sections. Similarly, the outer conductor has an abrupt shoulder like transition between the small and large diameters of the first and second sections. The transition section of the connector joins the first and second sections, and is constructed to have a short length of the small diameter of the central conductor enclosed within a short length of the large diameter of the outer conductor. The abrupt shoulder like transitions of the central and outer conductors define a large surface area between the central and outer conductors over a short conductive path. This large surface area introduces a significant capacitive reactance which is compensated for by positioning the short length of the small diameter central conductor in the large diameter outer conductor. This relative positioning introduces a significant inductive reactance into the transition section to compensate for the significant capacitive reactance introduced by the large surface area, and results in a characteristic impedance of 50 ohms in the transition section.

Description

BACKGROUND OF THE INVENTION

The present invention relates generally to an electromagnetic transmission means, and more particularly pertains to a new and improved connector for transferring microwave electromagnetic energy between a coaxial mode of energy propagation and a strip mode of energy propagation with a relatively small power loss due to a reflective discontinuity at the transition between the two modes of energy propagation.

When electromagnetic energy is transferred between coaxial and strip modes of propagation, power losses due to reflective discontinuities at the transition should be minimized. In general, a reflective discontinuity is formed by a mismatched impedance at the transition. In the prior art, these power losses have been minimized by utilizing the following structure at the transition. The end section of the inner conductor of the coaxial cable is flattened, and the edges of this flattened section are chamfered to reduce the width of the inner section to the width of the strip transmission line. The chamfered end of the inner conductor is soldered to the input or output lead of the strip conductor. Although this approach reduces the power loss at the transition to a degree, there is still a reflective discontinuity which causes a partial loss of power during the energy transfer.

SUMMARY OF AN EMBODIMENT OF THE INVENTION

In accordance with a preferred embodiment, an electrical connector is disclosed wherein electromagnetic energy is efficiently transferred between coaxial and strip modes of propagation with a minimal amount of power loss due to reflective discontinuities at the transition. The disclosed embodiment presents a constant impedance to electromagnetic energy while changing the mode of propagation of the energy from coaxial to strip or vice versa. Electromagnetic energy has been transferred efficiently with the disclosed embodiment over the frequency range of from DC to 12.5 Ghz.

In one embodiment, an electrical connector is disclosed for transferring electromagnetic energy between a coaxial cable and a strip transmission line with a minimal power loss due to an impedance mismatch at the transfer. The electrical connector includes a central conductor and an outer conductor enclosing the central conductor and has first, second, and transition sections. The first and second sections are designed like sections of a coaxial cable according to art known techniques to have desired characteristic impedances. The central conductor has a relatively thin first portion positioned in the first connector section, and a relatively thick second portion positioned in the second section of the connector. The outer connector has a first portion with a relatively small aperture which encloses the first thin portion of the central conductor in the first connector section and a second portion with a relatively large aperture which encloses the second thick portion of the central conductor in the second section of the electrical connector. The transition section of the connector joins the first and second sections, and is constructed to have short length of the relatively thin first portion of the inner conductor enclosed within the relatively large aperture of the outer conductor. The transitions between the first and second portions of each of the central and outer conductors define a large surface area between the central and outer conductor over a short conductive path. This large surface area introduces a significant capacitive reactance which is compensated for by positioning the short length of the thin central conductor in the large aperture of the outer conductor. This relative positioning introduces a significant inductive reactance into the transition section to combine with the significant capacitive reactance introduced by the large surface area, and results in a desired characteristic impedance in the transition section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a microstrip circuit.

FIG. 2 is a perspective view of a housing for enclosing the microstrip circuit.

FIG. 3 is a partially sectioned view of an electrical connector utilized in the housing for transferring electrical energy between coaxial and strip modes of propagation.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 illustrates a microstrip circuit 10 which is formed on a ceramic substrate 11. The circuit has an input lead 12 and an output lead 14. The particular circuit illustrated in FIG. 1 is a band pass interdigital filter circuit, although this particular circuit is shown merely for illustrative purposes, and any microstrip circuit could be utilized with this invention.

FIG. 2 illustrates a housing 20 which encloses the microstrip circuit, and protects the circuit from physical damage and electrical noise. The housing has a main body 22 with a central aperture 28 formed therein. Central aperture 28 has a peripheral ledge 30 upon which the circuit is positioned. The housing has input and output contacts 32 which transfer electrical energy to the input and output leads of the microstrip circuit. Housing 22 has threaded connectors 24 and 26 for connection with input and output coaxial cables. The microstrip circuit is placed within the central aperture 28 of the housing, and cover 34 is placed on the housing and secured by screws 36. An elastic conductive sheet 38 is positioned below the cover 34 to compliantly hold the circuit 10 within the housing 20. The sheet 32 forms an electrical contact with the circuit and holds the circuit within the housing without physically stressing the ceramic substrate. This arrangement lessens the possibility of cracking the ceramic substrate when cover 34 is secured in place with screws 36.

FIG. 3 illustrates a partially sectioned view of one embodiment of an electrical connector which is utilized in the housing to transfer electrical energy between coaxial and strip modes of propagation. Conductor 40 of connector 26 is threaded at 42 to receive a coaxial cable in a conventional manner while making an electrical contact with the outer conductor of the coaxial cable. The inner lead of the coaxial cable makes an electrical contact with a central conductor 44 of the electrical connector which leads to a contact of the microstrip circuit.

Conductor 40 is electrically grounded to housing 22 to form two sections of an outer conductor of the electrical connector. There is an abrupt shoulder like transition 45 between the inner diameter 41 of conductor 40 and the inner diameter 48 of aperture 47 in housing 22. The significance of this structure will be explained later.

Central conductor 44 has a first smaller cylindrically shaped section 54 and a second larger cylindrically shaped section 58. There is an abrupt shoulder like transition 55 between section 54, which has a relatively small diameter 56, and cylindrical section 58, which has a relatively large diameter 60. The significance of this structure will be explained later. Central connector 44 has a cantilevered tab portion 32 at one end for making an electrical contact with the microstrip circuit. Tab 32 is bent slightly relative to the central conductor to form a tensioned cantilever-type contact with the microstrip circuit in the housing. The section 58 has a hole 64 formed axially therein for receipt of the central conductor of the coaxial cable. Two slits 66, are cut along and on opposite sides of hole 64. The end section 58 is crimped as illustrated along each of the slits 66. This crimping allows the central conductor of the coaxial cable to be resiliently force fitted into hole 64.

Dielectric 46 insulates and relatively positions the central and outer conductors of the electrical connector. Dielectric 46 has a first smaller cylindrically shaped section 68 and a second larger cylindrically shaped section 72. A first cylindrically shaped aperture 70 is formed axially along the entire length of first section 68 and partially into second section 72 for a distance 49. A second cylindrically shaped aperture 74 is formed axially along the remainder of the length of second section 72.

An aperture 50 is illustrated which extends widthwise across the assembly of outer conductor 42, dielectric member 46, and central conductor 44. This aperture has been provided so that it may be filled with a potting or glue material to permanently attach the components into one unitary assembly.

The significance of the dimensions which were mentioned previously will now be explained. In a typical microstrip circuit the characteristic impedance of the circuit is 50 ohms. The characteristic impedance of a coaxial cable carrying electrical energy to and from the microstrip circuit is also normally selected to be 50 ohms. The dimensions of the electrical connector are selected to transfer electrical energy between coaxial and strip modes of propagation with a characteristic impedance of 50 ohms. A different impedance would result in a reflective discontinuity to electrical energy at the connector.

The dimensions for the electrical connector are selected as follows. The width of the input and output leads 12 and 14 of the microstrip circuit are designed to give the microstrip circuit a characteristic impedance of 50 ohms. That designed width determines the desired width of the cantilevered tab 32 which makes a direct contact with the microstrip circuit. The width of tab 32 is the same as the width of the first section 54 of the central conductor. In a coaxial type of conductor, as is formed between first section 54 of the central conductor and cylindrically shaped aperture 47 of the housing 22, the characteristic impedance varies according to the ratio of the diameters of the inner and outer conductors. Therefore, the inner diameter 48 of aperture 47 is selected to be a given multiple of the diameter of first section 54 to produce a characteristic impedance in this section of 50 ohms.

In the second section of the electrical connector, the diameter of the second section 58 of the center conductor and the inner diameter 52 of the outer conductor 40 are also selected to yield a characteristic impedance of 50 ohms. It should be noted that the ratio of these two diameters, for reasons explained above, is the same as the ratio of the two diameters in the first section of the connector.

The first and second sections of the connector must also be joined with a characteristic impedance of 50 ohms. This joinder is accomplished across the transition section 49 wherein a short length of the smaller diameter central conductor is located within a short length the larger diameter outer conductor. This section of the connector operates as follows. As is well known in the art, characteristic impedance is a combination of capacitive and inductive reactance. The abrupt shoulder like transitions 45 and 55 of the inner and outer conductors, between each of the two sections thereof, define a large surface area between the conductors over a short conductive path. This large surface area introduces a significant capacitive reactance between the inner and outer conductors. This significant capacitive reactance is compensated for by positioning a short length of the smaller diameter central conductor within a short length of the larger diameter outer conductor. This combination introduces a significant inductive reactance. This significant inductive reactance compensates for the significant capacitive reactance introduced by the large surface area, and results in a characteristic impedance of 50 ohms in section 49. An optimum length of the transition section may be determined imperically by testing different lengths of the transition section for power transfer or power reflectance. One instrument that might be used to make such a measurement is a time domain reflectometer.

Thus, the electrical connector is formed of three sections, each of which is designed to have a characteristic impedance of 50 ohms. This design presents a relatively small reflective discontinuity to electrical energy flowing through the electrical connector.

One embodiment of the electrical connector was built according to the following specifications. The housing 22 and conductor 40 were constructed of gold plated stainless steel. The central conductor 44 was constructed of beryllium copper, with cantilevered tab 32 being gold plated. The dielectric 46 was formed from polytetrafluoroethylene plastic rod. The conductive sheet 38 was made from silicon rubber impregnated with silver. Binding hole 50 was potted with an epoxy type glue. The width of first section 54 of the central conductor 44 was 0.025 inches, and the inner diameter 48 of aperture 47 was 0.081 inches. The diameter of second section 58 of the central conductor 44 was 0.05 inches, and the inner diameter 41 of conductor 40 was 0.162 inches. It should be noted that the ratios of the diameters in the first and second sections of the connector are equal to yield a characteristic impedance of 50 ohms in each of these sections. The transition section 49 had a length of 0.01 inches.

The principle explained above of introducing inductive reactance to compensate for the large capacitive reactance introduced by the abrupt shoulder like changes may be extended as follows. If the change in diameter between the several sections of the connector is very large, the connector may be designed with several steps of an abrupt reduction in diameter with several introductions of compensating inductive reactance.

While several embodiments have been described, the teachings of this invention will suggest many other embodiments to those skilled in the art.

Claims

I claim:

1. Apparatus for transferring electromagnetic energy between a coaxial cable and a strip transmission line with a relatively small power loss due to a reflective discontinuity comprising:

a. said strip transmission line having first and second conductive elements;

b. said coaxial cable having a central conductor and an outer conductor;

c. a connector having a first conductor for connecting said central conductor of the coaxial cable with said first conductive element of the strip transmission line, said first conductor having a relatively thin first section, and a relatively thick second section adjoining said first section with the joinder of said first and second sections of said first conductor defining a large surface area over a short conductive path which introduces a capacitive reactance;

d. said connector having a second conductor for connecting said outer conductor of the coaxial cable with said second conductive element of the strip transmission line, said second conductor having a first section with a relatively small aperture and a second section, adjoining said first section, with a relatively large aperture with the joinder of said first and second sections of said second conductor defining a large surface area over a short conductive path which introduces a capacitive reactance; and

e. means for supporting said second section of said first conductor within said second section of said second conductor, and for supporting said first section of the first conductor within said first section of said second conductor and partially within said second section of said second conductor to introduce an inductive reactance to compensate for said capacitive reactances, whereby the relatively thin first section of said first conductor being partially positioned within the relatively large aperture of said second conductor results in a desired impedance to electromagnetic energy being transferred between said strip transmission line and said coaxial cable.

2. Apparatus as set forth in claim 1 wherein said first conductor has an abrupt, shoulder like transition between said relatively thin first section and said relatively thick second section, and said second conductor has an abrupt, shoulder like transition between said small and large apertures.

3. Apparatus as set forth in claim 1 wherein said first and second sections of said first conductor each have cylindrical shapes and said small and large apertures of said second conductor each have cylindrical shapes.

4. Apparatus as set forth in claim 1 wherein only a small portion of said first section of said first conductor is located within said second section of said second conductor.

5. Apparatus as set forth in claim 1 wherein the characteristic impedance of said coaxial cable is 50 ohms, the characteristic impedance of said strip transmission line is 50 ohms, and the characteristic impedance of said connector is 50 ohms.

6. Apparatus as set forth in claim 1 wherein said relatively thin first section of said first conductor includes a cantilevered section protruding from the end of said first section for making an electrical contact with the strip transmission line.

7. Apparatus as set forth in claim 1 wherein said strip transmission line is a microstrip slab, and is supported within a housing means.

8. Apparatus as set forth in claim 1 wherein:

a. said first and second sections of said first conductor each have cylindrical shapes, and said small and large apertures of said second conductor each have cylindrical shapes;

b. said first conductor has an abrupt, shoulder like transition between said relatively thin first cylindrical section and said relatively thick second cylindrical section; and

c. said second conductor has an abrupt shoulder like transition between said small and large cylindrical apertures.

9. Apparatus as set forth in claim 8 wherein the characteristic impedance of said coaxial cable is 50 ohms, the characteristic impedance of said strip transmission line is 50 ohms, and the characteristic impedance of said connector is 50 ohms.

10. Apparatus as set forth in claim 9 wherein said strip transmission line is a microstrip slab, and is supported within a housing means.