1. A RF coaxial connector, comprising a socket (1) and an adapter (2), wherein the socket (1) comprises an outer conductor (11) and a center conductor (12), the adapter (2) comprises a plug (20) capable of being inserted into the socket (1), the adapter (2) further comprises an outer conductor (21) and a center conductor (22) that are configured to be respectively in contact with the outer conductor (11) and the center conductor (12) of the socket, the connector being characterized by the fact that: a dumbbell-shaped first insulating body (4) is disposed inside the plug (20) of the adapter and filled between the outer conductor (21) and the center conductor (22) of the adapter, the first insulating body (4) comprising two end portions (41a, 41b) and a middle portion (42) narrower than the two end portions (41a, 41b), thereby forming an annular gap (5) between the middle portion (42) of the first insulating body and the outer conductor (21) of the adapter, the first end portion (41a) of the first insulating body (4) facing the socket (1) when the plug (20) is inserted into the socket (1) having an impedance value less than 50Q.

2. The connector of claim 1, wherein a shoulder portion (13) is disposed inside the inner hole of the outer conductor (11) of the socket and extending towards the center of the inner hole.

3. The connector of claim 2, wherein a second insulating body (3) is disposed to the rear end of the socket (1) and filled between the outer conductor (11) and the center conductor (12) of the socket, the front end surface of the second insulating body being flush with the front end surface of the shoulder portion (13).

4. The connector of claim 2, wherein the diameter B of the inner hole of the outer conductor of the socket is 3.65-4.05mm, the depth I of the inner hole of the outer conductor of the socket is 2.3-3.3mm, the diameter G of the inner hole of the shoulder portion is 2.3-2.7mm, the width E of the shoulder portion is 0.2-0.6mm, the diameter A of the center conductor of the socket is 0.66-1.06mm, the inner diameter D of the outer conductor of the adapter is 3.0-3.4mm, the outer diameter C of the inner conductor of the adapter is 1.07-1.47mm, the width F of the end portions of the first insulating body is 0.6-1.0mm, and the outer diameter J of the middle portion of the first insulating body is 1.6-2.0mm.

5. The connector of claim 2, wherein the diameter B of the inner hole of the outer conductor of the socket is 3.85mm, the depth I of the inner hole of the outer conductor of the socket is 2.8mm, the diameter G of the inner hole of the shoulder portion is 2.5mm, the width E of the shoulder portion is 0.4mm, the diameter A of the center conductor of the socket is 0.86mm, the inner diameter D of the outer conductor of the adapter is 3.2mm, the outer diameter C of the inner conductor of the adapter is 1.27mm, the width F of the end portions of the first insulating body is 0.8mm, and the outer diameter J of the middle portion of the first insulating body is 1.8mm.

6. The connector of any preceding claim, wherein the first insulating body extends along a longitudinal axis and has a midplane perpendicular to said longitudinal axis.

7. The connector of any preceding claim, wherein each end portion of the first insulating body extends over a substantially equal length along the longitudinal axis of the first insulating body.

8. The connector of any preceding claim, wherein the ratio between the length of the middle portion of the first insulating body and the length of an end portion of said first insulating body lies between 2 to 10, in particular 3 to 7.

9. The connector of any preceding claim, wherein the first end portion and the middle portion of the first insulating body have the same inner diameter.

10. The connector of any preceding claim, wherein the second end portion of the first insulating body away from the socket when the plug is inserted into the socket has an inner diameter smaller than the inner diameter of the middle portion.

11. The connector of any preceding claim, wherein the first insulating body does not extend axially beyond the outer conductor of the plug.

12. The connector of any preceding claim, wherein the second end portion of the first insulating body is entirely within the outer conductor of the plug.

13. The connector of any preceding claim, wherein the center conductor of the plug extends along both of the end portions of the first insulating body and along the middle portion of said first insulating body.

14. The connector of any preceding claim, wherein the impedance value of the middle portion of the first insulating body is substantially equal to 50Q.

15. The connector of any preceding claim, wherein the center conductor does not extend beyond the first insulating body toward the socket. The invention discloses a RF coaxial connector, which includes a socket and an adapter. The socket includes an outer conductor and a center conductor. The adapter includes a plug capable of being inserted into the socket. The adapter also includes an outer conductor and a center conductor that can be in contact with the outer conductor and the center conductor of the socket, respectively. A dumbbell-shaped first insulating body is disposed inside the plug of the adapter and filled between the outer conductor and the center conductor of the adapter. The first insulating body has a middle portion narrower than two end portions thereof such that an annular gap is formed between the middle portion of the first insulating body and the outer conductor of the adapter, thereby forming different impedance regions at the connection regions of the plug and the socket. Therefore, a high impedance region and a low impedance region can compensate each other so as to decrease the adverse effect of the high impedance region on the connector performance and improve electrical and RF performance of the product. Compared with the prior art, the connector of the present invention allows a larger axial offset.

BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to a RF coaxial connector.
2. Description of Related Art:
RF coaxial connectors are used for providing interconnection between circuit
boards, between RF modules, or between circuit boards and RF modules. In these
applications, the allowable tolerance between relative positions of two connected elements
tends to increase so as to facilitate fabrication of the elements and reduce the fabrication
cost.
Currently, there are several circuit board interconnection techniques that allow
axial and radial offsets between circuit boards. The oldest technique is based on standard
snap-on connectors, such as SMB and MCX connectors, which have sockets and plugs for
interconnecting the circuit boards. As shown in FIG. 1, in such a connector, inner
conductors and outer conductors thereof have a staggered pin and insertion hole
arrangement, which allows a limited axial offset. Since the elastic insertion holes of the
inner and outer conductors only can tolerate extremely small axial and radial offsets, the
number of the connectors disposed to a circuit board is not more than three pairs. In order to
overcome the drawback, a second circuit board interconnection technique uses an adapter
as an intermediate connection element, such as MMBX and SMP series on the market. The
adapter can have a small rotation relative to a socket fixed to a circuit board, thereby
allowing a radial offset of Lsin(a). Therein, L is the length of the adapter and a is the
rotational angle of the adapter. As shown in FIG. 2, the axial offset and the radial offset
angle of a SMP connector with the maximum board-to-board distance H are ±0.3mm and
±4°, respectively, and the axial offset and radial offset angle of a MMBX connector is
±0.70mm and ±4.5°, respectively. The RF electrical performance of the above-described
connectors depends on the degree of impedance match at the interconnection interface of

the connectors. An air gap at the connection interface leads to high impedance of the
region.
In addition, in order to ensure a sufficiently large offset angle in the case of a
minimum tolerance along the axial distance H, the joining distance between the pins and
insertion holes of the center conductors must be as small as possible such that over-stress
does not occur when the center conductors have an angle offset, which however limits the
increase of the axial offset of the connectors with the board-to-board distance H.
SUMMARY OF THE INVENTION
According to the above drawback, exemplary embodiments of the present
invention provide a RF coaxial connector that allows a larger axial offset and achieves
superior RF electrical performance.
Exemplary embodiments of the present invention provide a RF coaxial
connector, which comprises a socket and an adapter. The socket may comprise an outer
conductor and a center conductor. The adapter may comprise a plug capable of being
inserted into the socket. The adapter may further comprise an outer conductor and a center
conductor that are configured to be in contact with the outer conductor and the center
conductor of the socket, respectively. A dumbbell-shaped first insulating body may be
disposed inside the plug of the adapter and filled between the outer conductor and the
center conductor of the adapter, and the first insulating body may comprise two end
portions and a middle portion narrower than the two end portions, thereby forming an
annular gap between the middle portion of the first insulating body and the outer conductor
of the adapter.
Such a dumbbell-shaped first insulating portion may enable an impedance
compensation effect to be achieved when the air-gap at the connection interface varies, the
variation of the air-gap lying for instance between 0 and 2mm.

The impedance associated with a first insulating body as provided by
exemplary embodiments of the invention may be much smaller than 50Ω.
The first insulating body may extend along a longitudinal axis and may
optionally have a midplane perpendicular to said longitudinal axis.
The first end portion of the first insulating body faces the socket when the plug
is inserted into the socket and may have an impedance value less than 50Ω, lying for
instance between 40Ω and 49Ω, in particular between 48Ω and 49Ω.
The impedance value of the middle portion of the first insulating body may be
substantially equal to 50Ω.
In an exemplary embodiment of the invention, the first end portion of the first
insulating body has an impedance value less than 50Ω, lying for instance between 48Ω and
49Ω, and the middle portion and the second end portion of the first insulating body that is
away from the socket when the plug is inserted in said socket have an impedance value of
around 50Ω. Said second end portion may have an impedance value varying slightly from
50Ω based on a function of the diameter of the outer and/or center conductor.
Each end portion of the first insulating body may optionally extend over
substantially equal lengths along the longitudinal axis of the first insulating body.
The ratio between the length of the middle portion of the first insulating body
and the length of an end portion of said first insulating body, for example the first end
portion, lies between 2 to 10, in particular 3 to 7.
The first end portion and the middle portion of the first insulating body may
have the same inner diameter.

The second end portion of the first insulating body may have an inner diameter
smaller than the inner diameter of the middle portion, which enables said second end
portion to receive the portion of the center conductor having a smaller outer diameter.
The first insulating body may not extend axially beyond the outer conductor of
the plug, which may prevent the first insulating body from abutting a surface of the socket,
thereby protecting the first insulating body.
The second end portion of the first insulating body may be entirely within the
outer conductor of the plug, enabling for instance protection of the center conductor against
excessive radial forces
The center conductor of the plug may extend along both of the end portions of
the first insulating body and along the middle portion of said first insulating body.
The center conductor may not extend beyond the first insulating body toward
the socket.
The outer conductor of the socket may comprise a tubular position defining an
inner hole. A shoulder portion may be disposed inside the inner hole of the outer conductor
of the socket and extending towards the center of the inner hole.
Further, a second insulating body may be disposed to the rear end of the socket
and filled between the outer conductor and the center conductor of the socket, wherein the
front end surface of the second insulating body may be flush with the front end surface of
the shoulder portion.
In exemplary embodiments of the invention, the diameter B of the inner hole of
the outer conductor of the socket is 3.65-4.05mm, the depth I of the inner hole of the outer
conductor of the socket is 2.3-3.3mm, the diameter G of the inner hole of the shoulder
portion is 2.3-2.7mm, the width E of the shoulder portion is 0.2-0.6mm, the diameter A of
the center conductor of the socket is 0.66-1.06mm, the inner diameter D of the outer

conductor of the adapter is 3.0-3.4mm, the outer diameter C of the inner conductor of the
adapter is 1.07-1.47mm, the width F of the end portions of the first insulating body is
0.6-1.0mm, and the outer diameter J of the middle portion of the first insulating body is
1.6-2.0mm.
In particular, the diameter B of the inner hole of the outer conductor of the
socket may be 3.85mm, the depth I of the inner hole of the outer conductor of the socket
may be 2.8mm, the diameter G of the inner hole of the shoulder portion may be 2.5mm, the
width E of the shoulder portion may be 0.4mm, the diameter A of the center conductor of
the socket may be 0.86mm, the inner diameter D of the outer conductor of the adapter may
be 3.2mm, the outer diameter C of the inner conductor of the adapter may be 1.27mm, the
width F of the end portions of the first insulating body may be 0.8mm, and the outer
diameter J of the middle portion of the first insulating body may be 1.8mm.
The present invention may achieve following advantageous effects. When the
dumbbell-shaped first insulating body is disposed inside the plug of the adapter, different
impedance regions may be formed at the connection regions of the plug and the socket. If a
large axial offset distance exists between the connecting elements, a large air gap may
appear at the connection interface, thereby forming a high impedance region. Meanwhile,
an end portion of the first insulating body may form a low impedance region and an annular
gap between the middle portion of the first insulating body and the outer conductor of the
adapter may form a normal impedance region. Because the high impedance region and the
low impedance region may compensate each other, the adverse effect of the high
impedance region to the connector performance may be decreased and the electrical and RF
performance of the product may be improved. Therefore, compared with the prior art, the
RF coaxial connector of the present invention may allow a larger axial offset (>lmm),
reduce the impedance mismatch caused by the air gap at the connection interface, and
achieve preferred RF electrical performance over a frequency range from 0 to 6GHz.
A low impedance region may also be formed at the shoulder portion region.
Thus, the low impedance regions may be formed at both sides of the high impedance region,
thereby enhancing the compensation effect.

BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows the structure of a conventional snap-on coaxial connector;
FIG. 2 shows the structure of a conventional coaxial connector with an adapter;
FIG. 3 shows the structure of a coaxial connector according to the present
invention;
FIG. 4 shows the structure of a first insulating body according to the present
invention;
FIG. 5 shows regional distribution of. different impedance in the coaxial
connector according to the present invention;
FIG. 6 shows a VSWR (voltage standing wave ratio) curve of a conventional
connector;
FIG. 7 shows a VSWR curve of the connector according to the present
invention (before parameter optimization); and
FIG. 8 shows a VSWR curve of the connector according to the present
invention (after parameter optimization).
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The following illustrative embodiments are provided to illustrate the disclosure of
the present invention, these and other advantages and effects may be apparent to those
skilled in the art after reading the disclosure of this specification.
As shown in FIG. 3, a RF coaxial connector according to exemplary embodiments
of the present invention comprises a socket 1 and an adapter 2. The socket 1 comprises an

outer conductor 11 and a center conductor 12. The adapter 2 comprises a plug 20 disposed
at one end thereof and capable of being inserted into the socket 1. The adapter 2 further
comprises an outer conductor 21 and a center conductor 22. When the plug 20 is inserted
into the socket 1, the outer conductor 21 and center conductor 22 of the adapter 2 are in
contact with the outer conductor 11 and center conductor 12 of the socket 1, respectively.
A dumbbell-shaped first insulating body 4 extending along a longitudinal axis X is
disposed inside the plug 20 of the adapter. As shown in FIG. 4, the first insulating body 4
comprises a first end portion 41a and a second end portion 41b and a middle portion 42
narrower than the two end portions 41a and 41b. The first insulating body 4 is filled
between the outer conductor 21 and the center conductor 22 of the socket such that an
annular gap 5 is formed between the middle portion of the first insulating body and the
outer conductor of the adapter, wherein the annular gap 5 forms a normal impedance region
(region V of FIG. 5).
A shoulder portion 13 is disposed inside the inner hole of the outer conductor 11 of
the socket and extending towards the center of the inner hole. When the plug 20 is inserted
into the socket 1, if the end surface of the outer conductor 21 is not closely attached to the
front end surface of the shoulder portion 13, an air gap is formed between the shoulder
portion 13 and the end surface of the plug (comprising the end surface of the first insulating
body 4), wherein the air gap forms a high impedance region (region T of FIG. 5) which
adversely affects the connector performance, while the region where an end portion of the
first insulating body is located forms a low impedance region (region U of FIG. 5). Since
the high impedance region T and the low impedance region U are adjacent to each other,
they may compensate each other so as to reduce impedance mismatch and improve
connection performance.
Further, a second insulating body 3 is disposed to the rear end of the socket and
filled between the outer conductor 11 and the center conductor 12 of the socket. Therein,
the front end surface of the second insulating body 3 is flush with the front end surface of
the shoulder portion 13. Thus, a normal impedance region (region R of FIG. 5) is formed at
the end portion of the socket between the outer conductor 11 and the center conductor 12,
and a low impedance region (region S of FIG 5) is formed between the inner hole of the

shoulder portion 13 and the center conductor 12. Since the low impedance region S is also
adjacent to the high impedance region T, they may compensate each other so as to improve
the connection performance. That is, if there exists a larger axial offset between the
interconnection elements, the high impedance region T formed by the air gap at the
connection interface may be compensated or offset by the low impedance regions S, U
adjacent thereto, thereby improving impedance match and connection performance of the
connector in the case of a larger axial offset. The above-described R, S, T, U, V denote axial
ranges of the different impedance regions. Radial ranges of the impedance regions are
located between the outer conductors and inner conductors.
In order to achieve a preferred impedance match performance, parameters such as
the outer diameter A of the center conductor of the socket, the diameter B of the inner hole
of the outer conductor of the socket, the outer diameter C of the insertion hole of the center
conductor of the adapter, the diameter D of the inner hole of the outer conductor of the
adapter, the width E of the shoulder portion, the width F of the end portions of the first
insulating body and the diameter G of the inner hole of the shoulder portion and width H
may be optimized. The impedance value of the high impedance region may be determined
once the diameter B of the inner hole of the outer conductor of the socket and the outer
diameter A of the inner conductor of the socket are determined, and the high impedance
region presents an inductive impedance. The optimized parameters are for example as
follows: the diameter B of the inner hole of the outer conductor of the socket is
3.65-4.05mm, the depth I of the inner hole of the outer conductor of the socket is
2.3-3.3 mm, the diameter G of the inner hole of the shoulder portion is 2.3-2.7mm, the width
E of the shoulder portion is 0.2-0.6mm, the diameter A of the center conductor of the socket
is 0.66-1.06mm, the inner diameter D of the outer conductor of the adapter is 3.0-3.4mm,
the outer diameter C of the inner conductor of the adapter is 1.07- 1.47mm, the width F of
the end portions of the first insulating body is 0.6-1.0mm, the outer diameter J of the middle
portion of the first insulating body is 1.6-2.0mm. When the high and low impedance
regions have different lengths and shapes and the two low impedance regions (which
present capacitive impedance) have different impedance values, the compensation of the
capacitive impedance and the inductive impedance of the three impedance regions as well
as delay compensation are calculated. Accordingly, when an optimum compensation is

reached, the optimized parameters may be obtained from the corresponding lengths and
shapes of the impedance regions.
After the parameter optimization, the performance of the connector may be
improved significantly. FIG. 6 shows a VSWR (voltage standing wave ratio) curve of a
conventional connector. As shown in FIG. 6, when the air gap at the connection interface
increases, the VSWRs of the connector also increase and the connection performance of the
connector decreases significantly. FIG. 7 shows a VSWR curve of the connector of the
present invention before the parameter optimization. As shown in FIG. 7, when the air gap
is zero, the VSWRs of the connector increase. FIG. 8 shows a VSWR curve of the
connector of the present invention after the parameter optimization, wherein the diameter B
of the inner hole of the outer conductor of the socket is for example 3.85mm, the depth I of
the inner hole of the outer conductor of the socket is for example 2.8mm, the diameter G of
the inner hole of the shoulder portion is for example 2.5mm, the width E of the shoulder
portion is for example 0.4mm, the diameter A of the center conductor of the socket is for
example 0.86mm, the inner diameter D of the outer conductor of the adapter is for example
3.2mm, the outer diameter C of the inner conductor of the adapter is for example 1.27mm,
the width F of the first insulating body is 0.8mm, the outer diameter J of the middle portion
of the first insulating body is for example 1.8mm. As shown in FIG. 8, the VSWRs of the
connector at same air gaps and frequencies may totally decrease (the connection
performance may increase). The VSWRs at two extreme positions (when the air gap is zero
and maximum) are close to each other and larger than the VSWRs at other positions, which
means a preferred connection performance may be achieved at most of the connection
states.
The above-described descriptions of the detailed embodiments are only to
illustrate the preferred implementation according to the present invention, and it is not to
limit the scope of the present invention, Accordingly, all modifications and variations
completed by those with ordinary skill in the art should fall within the scope of present
invention defined by the appended claims.

WE CLAIM :
1. A RF coaxial connector, comprising a socket (1) and an adapter (2),
wherein the socket (1) comprises an outer conductor (11) and a center conductor (12), the
adapter (2) comprises a plug (20) capable of being inserted into the socket (1), the adapter
(2) further comprises an outer conductor (21) and a center conductor (22) that are
configured to be respectively in contact with the outer conductor (11) and the center
conductor (12) of the socket,
the connector being characterized by the fact that:
a dumbbell-shaped first insulating body (4) is disposed inside the plug (20) of the adapter
and filled between the outer conductor (21) and the center conductor (22) of the adapter, the
first insulating body (4) comprising two end portions (41a, 41b) and a middle portion (42)
narrower than the two end portions (41a, 41b), thereby forming an annular gap (5) between
the middle portion (42) of the first insulating body and the outer conductor (21) of the
adapter, the first end portion (41a) of the first insulating body (4) facing the socket (1) when
the plug (20) is inserted into the socket (1) having an impedance value less than 50Q.
2. The connector of claim 1, wherein a shoulder portion (13) is disposed
inside the inner hole of the outer conductor (11) of the socket and extending towards the
center of the inner hole.
3. The connector of claim 2, wherein a second insulating body (3) is disposed
to the rear end of the socket (1) and filled between the outer conductor (11) and the center
conductor (12) of the socket, the front end surface of the second insulating body being flush
with the front end surface of the shoulder portion (13).
4. The connector of claim 2, wherein the diameter B of the inner hole of the
outer conductor of the socket is 3.65-4.05mm, the depth I of the inner hole of the outer
conductor of the socket is 2.3-3.3mm, the diameter G of the inner hole of the shoulder
portion is 2.3-2.7mm, the width E of the shoulder portion is 0.2-0.6mm, the diameter A of

the center conductor of the socket is 0.66-1.06mm, the inner diameter D of the outer
conductor of the adapter is 3.0-3.4mm, the outer diameter C of the inner conductor of the
adapter is 1.07-1.47mm, the width F of the end portions of the first insulating body is
0.6-1.0mm, and the outer diameter J of the middle portion of the first insulating body is
1.6-2.0mm.
5. The connector of claim 2, wherein the diameter B of the inner hole of the
outer conductor of the socket is 3.85mm, the depth I of the inner hole of the outer conductor
of the socket is 2.8mm, the diameter G of the inner hole of the shoulder portion is 2.5mm,
the width E of the shoulder portion is 0.4mm, the diameter A of the center conductor of the
socket is 0.86mm, the inner diameter D of the outer conductor of the adapter is 3.2mm, the
outer diameter C of the inner conductor of the adapter is 1.27mm, the width F of the end
portions of the first insulating body is 0.8mm, and the outer diameter J of the middle
portion of the first insulating body is 1.8mm.
6. The connector of any preceding claim, wherein the first insulating body
extends along a longitudinal axis and has a midplane perpendicular to said longitudinal
axis.
7. The connector of any preceding claim, wherein each end portion of the first
insulating body extends over a substantially equal length along the longitudinal axis of the
first insulating body.
8. The connector of any preceding claim, wherein the ratio between the
length of the middle portion of the first insulating body and the length of an end portion of
said first insulating body lies between 2 to 10, in particular 3 to 7.
9. The connector of any preceding claim, wherein the first end portion and the
middle portion of the first insulating body have the same inner diameter.
10. The connector of any preceding claim, wherein the second end portion of
the first insulating body away from the socket when the plug is inserted into the socket has
an inner diameter smaller than the inner diameter of the middle portion.

11. The connector of any preceding claim, wherein the first insulating body
does not extend axially beyond the outer conductor of the plug.
12. The connector of any preceding claim, wherein the second end portion of
the first insulating body is entirely within the outer conductor of the plug.
13. The connector of any preceding claim, wherein the center conductor of the
plug extends along both of the end portions of the first insulating body and along the middle
portion of said first insulating body.
14. The connector of any preceding claim, wherein the impedance value of the
middle portion of the first insulating body is substantially equal to 50Q.
15. The connector of any preceding claim, wherein the center conductor does
not extend beyond the first insulating body toward the socket.

The invention discloses a RF coaxial connector, which includes a socket and an
adapter. The socket includes an outer conductor and a center conductor. The adapter
includes a plug capable of being inserted into the socket. The adapter also includes an outer
conductor and a center conductor that can be in contact with the outer conductor and the
center conductor of the socket, respectively. A dumbbell-shaped first insulating body is
disposed inside the plug of the adapter and filled between the outer conductor and the
center conductor of the adapter. The first insulating body has a middle portion narrower
than two end portions thereof such that an annular gap is formed between the middle
portion of the first insulating body and the outer conductor of the adapter, thereby forming
different impedance regions at the connection regions of the plug and the socket. Therefore,
a high impedance region and a low impedance region can compensate each other so as to
decrease the adverse effect of the high impedance region on the connector performance and
improve electrical and RF performance of the product. Compared with the prior art, the
connector of the present invention allows a larger axial offset.