Patent Application
20140342581
This description relates generally to electrical connectors and more specifically to high frequency connectors.
Vertical mounted printed circuit board (“PCB”) or equivalently printed wiring board (“PWB”) connectors appeared in microwave connector catalogs shortly after printed circuits came into use. A vertical mount SMA connector for stripline has been available since 1963 with adequate performance at the lower microwave frequencies. As improved substrates became available for use at higher microwave frequencies above 10 GHz, edge mounted connectors were often used and vertical mounted connectors saw little use. More recently printed circuits have become more complex and digital circuits have reaches speeds equivalent to the high microwave frequencies (40 GHz or more). Both analog and digital circuit designers need more flexibility in the positioning high frequency coaxial inputs, outputs and test ports. A need now exists for a vertical mounted connector with performance at least equal to the best edge mounted connector.
Vertical mounted connectors presently offered consist of basic four leg flange outer conductor and a center conductor that can be trimmed to fit by the customer. Circuit board modifications to improve the impedance match are also left to the customer.
Printed circuit board parameters will change with electrical and mechanical performance criteria; therefore one connector design will not accommodate all board sizes or materials. Given specific board parameters optimized for high microwave frequencies, a connector can be designed for excellent performance with specified board geometry. This will provide the customer with an economic advantage of a one trial design of a coaxial port to his planar circuit.
The following presents a simplified summary of the disclosure in order to provide a basic understanding to the reader. This summary is not an extensive overview of the disclosure and it does not identify key/critical elements of the invention or delineate the scope of the invention. Its sole purpose is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later.
The present example of a vertical mount PCB connector provides a connector having a matched transition of a vertical mounted coaxial connector to a microstrip or coplanar waveguide transmission line on a printed circuit board.
The examples provide a vertical mounted connector with improved electrical performance to transmit a microwave signal to or from a coaxial port to planar printed circuitry. The vertical mount PCB connector includes a threaded housing with a four post flange for attachment to the PCB, a center conductor and a dielectric bead to support the center conductor.
The bottom of the flange has a uniquely contoured cavity to provide air space for the electromagnetic field above the planar transmission line. Four posts at the corners of the flange serve as the ground connection from the connector to the substrate ground planes. The open or large cavity under the flange is designed to provide high values of inductive reactance at the high end of the microwave band and typically requires changing the planar geometry to achieve even a narrow band impedance match. This examples described have a reduced diameter cavity around the center conductor which, along with properly positioned via's on the PCB, tend to limit the inductive reactance and provide a broad band impedance match. This connector design can accommodate both stripline and grounded coplanar waveguide (GCPW).
A major factor in achieving improved performance at higher frequencies is the contoured cavity cut into the flange. The reduced size allows the vias that short the top and bottom ground planes to make direct contact to the bottom of the connector flange tending to improve performance.
Many of the attendant features will be more readily appreciated as the same becomes better understood by reference to the following detailed description considered in connection with the accompanying drawings.
The present description will be better understood from the following detailed description read in light of the accompanying drawings, wherein:
Like reference numerals are used to designate like parts in the accompanying drawings.
The detailed description provided below in connection with the appended drawings is intended as a description of the present examples and is not intended to represent the only forms in which the present example may be constructed or utilized. The description sets forth the functions of the example and the sequence of steps for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples.
The present example provides a connector having a matched impedance transition of a vertical mounted coaxial connector to a microstrip or coplanar waveguide transmission line on a printed circuit board.
The connectors described herein are often applied to circuitry operating at high frequencies, which may be termed radio frequency (“RF”) or microwave frequencies. It is understood that these are general terms not meant to limit the design to a specific band of frequencies (for example Ku band, X band, millimeter wave, or the like) unless specifically stated to do so, but rather merely indicative of the suitability of the examples described herein to use at higher frequencies.
As used herein microstrip transmission lines or simply “microstrip” is understood to mean a single signal conductor above a single ground plane, typically supported by a dielectric material that defines the characteristic impedance of the microstrip transmission lines calculated from parameters including the signal conductor width, height from the center conductor to the ground plane, and the dielectric constant of the dielectric material as is known to those skilled in the art.
Printed wiring boards with microstrip conductors may also include large areas of ground conductor on the signal conductor side with plated feed-through holes (“vias”) to couple the ground plane. Typically these ground areas on the center conductor side provide shielding and grounds for circuitry on that side of the printed wiring board.
Although the present examples are described and illustrated herein as being implemented in a connector having a matched transition of a vertical mounted coaxial connector to a microstrip or coplanar waveguide transmission line on a printed circuit board, the system described is provided as an example and not a limitation. As those skilled in the art will appreciate, the present examples are suitable for application in a variety of different types of transmission line systems.
A conventional connector 102, may include an cable attachment portion 104 where an external connection (typically to a 50 or 75 ohm cable) through a mating connector (not shown) may be made. The connector 102 may include a printed circuit board (“PCB”) attachment section 106 that couples the connector to the electrical ground and signal traces of a PCB (or alternatively printed wiring board PWB) upon which the connector 102 is disposed. The printed wiring traces are typically designed to have a characteristic impedance of 50 or 75 ohms, although any desired characteristic impedance may be provided.
The connector typically has its exterior surface tied to, electrical ground. The center pin 112 carries the signal that may be coupled to a PCB trace (not shown). In making the transition from the pin 112 to the trace, care must be taken in the design to prevent shorting the signal to the PCB ground plane (not shown) that is typically present in good radio frequency (RF) and microwave designs. The hole pattern for mechanical mounting of connector 102 to the PWB 116 is shown. To prevent shorting a space 122 is often provided between the connector body and the PWB 116 to which the connector will be disposed.
A standoff 108 may be included on all four posts as a spacer to prevent shorting the PCB signal line 112 to ground (the connector body and posts 110). The four posts 110 are the ground connection to PCB however the space provided by the standoffs 108 is typically more than ¼ of a wavelength above 15 GHz which may cause signal leakage or the undesired launch a surface wave on the PCB. As can be seen in this design there is nothing particularly done in the way of impedance matching between the cable attachment portion 104 and the PCB attachment portion 106 to preserve signal characteristics at this discontinuity, or transition.
The poor impedance match is evident in the poor return loss numbers typically published above 25 GHz cited in the manufactures catalog for this type of connector. Both of these connector types described above 200, 102 (of
The vertical mount PCB connector includes a unique contoured cavity 301 cut into the flange 304. The contoured cavity 301 provides air space above the signal line when the vertical mount PCB connector 300 is attached to the top of a planar transmission line (not shown). The contoured shape shown of the cavity is exemplary. For equivalent electrical performance in impedance matching rectangular, square or trapezoidal shapes may be utilized. The rounded corners shown tends to aid is a machining convenience. The flange bottom surface 306 contacts the top ground plane of the PCB (not shown) and tends to contain the electromagnetic field within the enclosed structure.
The examples described herein provide a vertical mount PCB connector with improved electrical performance to transmit a microwave signal to or from a coaxial port to planar printed circuitry. The vertical mount connector includes a threaded housing 318 with a four post flange 304 for attachment to the PCB (not shown), a center conductor 310 and a dielectric bead to support the center conductor. The bottom of the flange has a contoured cavity 301 to provide air space for the electromagnetic field above the planar transmission line. The coaxial interface 318 illustrated in
Two alignment pads 308 will tend to improve the precision of the center conductor 310 alignment with a mating PCB conductor pad (not shown) that is disposed upon the PCB. Standard dimensional tolerances on the four mounting posts 312 may exceed the desired alignment for high microwave frequency performance. Accordingly, care must be taken in the layout and drilling of these mounting holes, and the construction of the posts 312. Four posts 312 at the corners of the flange serve as the ground connection from the connector to the substrate ground planes on the PWB (not shown).
A specially designed cavity structure 301 cut into the flange 304 tends to provide a somewhat broad band impedance match where the PWB trace (not shown) couples to a center pin or conductor 310 of the connector 300. The open or large cavity 314 on the bottom side of the flange 304 may lead to high values of inductive reactance at the high end of the microwave band and may require changing the planar geometry to achieve even a narrow band impedance match.
The impedance match is further aided by the reduced diameter cavity 316 around the center conductor 310 which, along with properly positioned via holes between ground planes on the PCB, will tend to limit the inductive reactance at the discontinuity and provide a broad band impedance match over frequency. This connector design can accommodate both stripline and grounded coplanar waveguide (GCPW). The depth of the cavity cut into flange 304 in the example described below is nominally 0.0255 inches deep.
The feature that tends to allow improved performance at higher frequencies is the contoured cavity 301 cut into the flange. The reduced size 316 additionally allows the vias that short the top and bottom ground planes of the PWB (not shown) to make direct contact to the bottom of the connector flange 304. This structure optimally allows matching coaxial connectors to other transmission media by making the ground connections as short as possible. It is further worth noting that the matching structure 301 incorporated in the flange 304, may be incorporated into a variety of coaxial connector interfaces, as desired.
In this example the wide cavity 314 includes a first rectangular region 402 nominally 0.120 inches wide and 0.040 inches deep. Adjoining it, and centered about its width is a second rectangular region 404 0.070 inches wide and substantially 0.025 inches deep, and having two substantially quarter circle radiused areas 406 between the first rectangular region 402 and the second rectangular region 404, where the radiuses are nominally 0.025 Inches.
The reduced diameter cavity 316 includes a third rectangular region 408 0.070 inches wide centered about her first and second rectangular regions 402, 404. The third rectangular region 408 is adjacent a semicircular region 410 of substantially a radius of 0.035 inches. The distance from the edge of the third rectangular region adjacent to the semicircular region to the outside or distal edge of the first rectangular region is substantially 0.100 inches.
The 1.85 mm interface is useful through 67 GHz. Larger diameter connector interfaces may be step matched by conventional techniques into the 50 ohm line. This tends to limit high frequency performance, but may allow standardization of connectors with the PCB etch patterns and provide better low frequency performance.
This exemplary PWB may be made of, Rogers RO4003® having the following characteristics: substrate. RO4003 is a glass reinforced hydrocarbon/ceramic laminate, dielectric constant 3.38, a loss tangent of 0.0027, 0.0005 inch thick copper on both sides, and a total thickness of 0.008 inches.
This etch pattern tends to be an optimized PC top ground plane pattern for use with the connector (300 of
λc=(D+d)π/2
This is an approximation, accurate typically within 3% of a more accurate numerical solution and it shows there will be no higher modes supported below 80 GHz in the air filled connector 0.070 diameter cavity. The ring of vias has an exemplary diameter of 0.0790 and may be filled with exemplary RO4003 and dielectric constant of 3.38. This substantially forms a circular waveguide cavity where the TE11 mode cutoff wavelength is: λc=D/2√∈3.412 and λc=49 GHz and is within the frequency band of interest. A small hole or aperture etched or otherwise formed in the bottom ground plane centered under the center conductor (as shown in cross sectional view of
The factor in achieving improved performance at higher frequencies is the contoured cavity (301 of
Where a circuit module or “package” design utilizes stacked PC boards or a shielded enclosure, the ground plane hole may employ a thin layer of air space below the hole. The extra cost and complexity may be prohibitive and an alternate design is suggested. The center conductor of the connector can be tapered from the exemplary 24 mill diameter to 14 mil with the etched trace to match. This will tend to reduce the parallel plate capacitance and raise the inductive reactance of the air cavity. The top ground plane hole can now be optimized for 50 ohms or the lowest return loss for the transition.
The simulated results for the S parameters is
Those skilled in the art will realize that the process sequences described above may be equivalently performed in any order to achieve a desired result. Also, sub-processes may typically be omitted as desired without taking away from the overall functionality of the processes described above.
This application claims the benefit of U.S. Provisional Patent Application No. 61/783,841 filed Mar. 14, 2013, the contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61783841 | Mar 2013 | US |
