Title: Two-port isolator and communication device
Abstract: A two-port isolator includes a metal case including an upper metal case and a lower metal case, a permanent magnet, a central electrode assembly made of a ferrite and central electrodes, and a laminated substrate. In the central electrode assembly, the first and second central electrodes are disposed on the top surface of the disk-shaped microwave ferrite such that the first and second central electrodes intersect each other at right angles with an insulating layer therebetween. The electrode width of the first central electrode is different from the electrode width of the second central electrode. Thus, the inductance of the first central electrode and the inductance of the second central electrode are different from each other.
Patent Number: 6,900,704 Issued on 05/31/2005 to Hasegawa
| Inventors:
|
Hasegawa; Takashi (Mattou, JP)
|
| Assignee:
|
Murata Manufacturing Co., Ltd. (Kyoto, JP)
|
| Appl. No.:
|
607300 |
| Filed:
|
June 27, 2003 |
Foreign Application Priority Data
| Jun 27, 2002[JP] | 2002-188516 |
| Current U.S. Class: |
333/24.2; 333/1.1 |
| Intern'l Class: |
H01P 001/36 |
| Field of Search: |
333/242,11
|
References Cited [Referenced By]
U.S. Patent Documents
| 3010085 | Nov., 1961 | Seidel.
| |
| Foreign Patent Documents |
| 9-232818 | Sep., 1997 | JP.
| |
| 2001/-185912 | Jul., 2001 | JP.
| |
| 2001203507 | Jul., 2001 | JP.
| |
| 2001/-237613 | Aug., 2001 | JP.
| |
Primary Examiner: Jones; Stephen E.
Attorney, Agent or Firm: Keating & Bennett, LLP
Claims
1. A two-port isolator comprising:
a permanent magnet;
a ferrite to which a DC magnetic field is applied by the permanent magnet;
a first central electrode disposed on a main surface of the ferrite or inside
the ferrite, one end of the first central electrode being electrically connected
to a first input-output port, and the other end of the first central electrode
being electrically connected to a second input-output port;
a second central electrode disposed on the main surface of the ferrite or inside
the ferrite so as to intersect the first central electrode with electrical insulation
disposed therebetween, one end of the second central electrode being electrically
connected to the second input-output port, and the other end of the second central
electrode being electrically connected to a third port;
a first matching capacitor electrically connected between the first input-output
port and the second input-output port;
a resistor electrically connected between the first input-output port and the
second input-output port; and
a second matching capacitor electrically connected between the second input-output
port and the third port;
wherein
the third port is electrically connected to a ground and the inductance L
1
of the first central electrode is different from the inductance L
2 of the
second central electrode.
2. A two-port isolator as claimed in claim 1, wherein the first central electrode
has a different shape from that of the second central electrode.
3. A two-port isolator as claimed in claim 1, wherein the electrode width W
1
of the first central electrode is different from the electrode width W
2
of the second central electrode.
4. A two-port isolator as claimed in claim 1, wherein the electrode thickness
t
1 of the first central electrode is different from the electrode thickness
t
2 of the second central electrode.
5. A two-port isolator as claimed in claim 1, wherein the electrode length l
1
of the first central electrode is different from the electrode length l
2
of the second central electrode.
6. A two-port isolator as claimed in claim 1, wherein the number of electrodes
in the first central electrode is different from the number of electrodes in the
second central electrode.
7. A two-port isolator as claimed in claim 1, wherein each of the first central
electrode and the second central electrode includes a plurality of electrodes and
the spacing S
1 between electrodes in the first central electrode is different
from the spacing S
2 between electrodes in the second central electrode.
8. A two-port isolator as claimed in claim 1, wherein the capacitance C
1
of the first matching capacitor and the capacitance C
2 of the second matching
capacitor satisfy the expression 0.5≦C
1/C
2≦0.9.
9. A two-port isolator as claimed in claim 1, wherein the capacitance C
1
of the first matching capacitor and the capacitance C
2 of the second matching
capacitor satisfy the expression 1.1≦C
1/C
2≦3.0.
10. A two-port isolator as claimed in claim 1, further comprising a metal case
which encloses the permanent magnet, the ferrite, and the first and second central
electrodes, wherein the metal case includes a top surface portion, a bottom surface
portion, and a pair of opposing side surface portions which join the top surface
portion and the bottom surface portion;
one of the first central electrode and the second central electrode is disposed
so as to be substantially perpendicular to the side surface portions; and
the other of the first central electrode and the second central electrode is
disposed so as to be substantially parallel to the side surface portions.
11. A two-port isolator as claimed in claim 1, wherein the first external input-output
electrode electrically connected to the first input-output port and the second
external input-output electrode electrically connected to the second input-output
port are provided in the middle of a pair of opposing side surfaces of the two-port
isolator, respectively.
12. A two-port isolator as claimed in claim 1, wherein the ferrite is substantially
rectangular when viewed from above, and the first central electrode is disposed
so as to be substantially parallel to one side of the substantially rectangular
ferrite and the second central electrode is disposed so as to be substantially
parallel to a side at a right angle to the one side.
13. A communication device comprising a two-port isolator as claimed in claim 1.
14. A two-port isolator comprising:
a permanent magnet;
a ferrite to which a DC magnetic field is applied by the permanent magnet;
a first central electrode disposed on a main surface of the ferrite or inside
the ferrite, one end of the first central electrode being electrically connected
to a first input-output port, and the other end of the first central electrode
being electrically connected to a second input-output port;
a second central electrode disposed on the main surface of the ferrite or inside
the ferrite so as to intersect the first central electrode with electrical insulation
disposed therebetween, one end of the second central electrode being electrically
connected to the second input-output port, and the other end of the second central
electrode being electrically connected to a third port;
a first matching capacitor electrically connected between the first input-output
port and the second input-output port;
a second matching capacitor electrically connected between the second input-output
port and the third port,
a resistor electrically connected between the third port and a ground; wherein
the inductance L
1 of the first central electrode is different from the
inductance L
2 of the second central electrode.
15. A two-port isolator as claimed in claim 14, wherein the first central electrode
has a different shape than the second central electrode.
16. A two-port isolator as claimed in claim 14, wherein the electrode width W
1
of the first central electrode is different from the electrode width W
2
of the second central electrode.
17. A two-port isolator as claimed in claim 14, wherein the electrode thickness
t
1 of the first central electrode is different from the electrode thickness
t
2 of the second central electrode.
18. A two-port isolator as claimed in claim 14, wherein the electrode length
l
1 of the first central electrode is different from the electrode length
l
2 of the second central electrode.
19. A two-port isolator as claimed in claim 14, wherein the number of electrodes
in the first central electrode is different from the number of electrodes in the
second central electrode.
20. A two-port isolator as claimed in claim 14, wherein each of the first central
electrode and the second central electrode includes a plurality of electrodes and
the spacing S
1 between electrodes in the first central electrode is different
from the spacing S
2 between electrodes in the second central electrode.
21. A two-port isolator as claimed in claim 14, wherein the capacitance C
1
of the first matching capacitor and the capacitance C
2 of the second matching
capacitor satisfy the expression 0.5≦C
1/C
2≦0.9.
22. A two-port isolator as claimed in claim 14, wherein the capacitance C
1
of the first matching capacitor and the capacitance C
2 of the second matching
capacitor satisfy the expression 1.1≦C
1/C
2≦3.0.
23. A two-port isolator as claimed in claim 14, wherein the capacitance C
1
of the first matching capacitor and the capacitance C
2 of the second matching
capacitor satisfy the expression 1≦C
1/C
2≦2.0.
24. A two-port isolator as claimed in claim 14, further comprising a metal case
which encloses the permanent magnet, the ferrite, and the first and second central
electrodes, wherein the metal case includes a top surface portion, a bottom surface
portion, and a pair of opposing side surface portions which join the top surface
portion and the bottom surface portion;
one of the first central electrode and the second central electrode is arranged
so as to be substantially perpendicular to the side surface portions; and
the other of the first central electrode and the second central electrode is
arranged so as to be substantially parallel to the side surface portions.
25. A two-port isolator as claimed in claim 14, wherein the first external input-output
electrode electrically connected to the first input-output port and the second
external input-output electrode electrically connected to the second input-output
port are provided in the middle of a pair of opposing side surfaces of the two-port
isolator, respectively.
26. A two-port isolator as claimed in claim 14, wherein the ferrite is substantially
rectangular when viewed from above, and wherein the first central electrode is
disposed so as to be substantially parallel to one side of the substantially rectangular
ferrite and the second central electrode is disposed so as to be substantially
parallel to a side at a right angle to the one side.
27. A communication device comprising a two-port isolator as claimed in claim 14.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a two-port isolator, and more particularly,
to a two-port isolator preferably for use in microwave frequency bands, and to
communication device.
2. Description of the Related Art
Generally, an isolator allows a signal to pass only in one transmission
direction and stops a signal in the other transmission direction, and is used in
the transmission circuits of mobile communication equipment, such as automobile
telephones and portable telephones.
A two-port isolator (e.g., an isolator having two central electrodes) has been
commonly used for such isolators. This two-port isolator includes a permanent magnet,
a ferrite, a first central electrode and a second central electrode disposed on
a main surface of the ferrite, two matching capacitors, and a resistor mounted
in a metal case including a lower metal case and an upper metal case, which are
joined together. Normally, the first central electrode and the second central electrode
have the same shape and the two matching capacitors have the same capacitance.
The insertion loss and isolation characteristics of such a two-port isolator
used in mobile communication equipment are set according to the communication system
used. Accordingly, when the insertion loss and isolation characteristics of a typical
two-port isolator are compared with the requirements of a communication system,
even if the isolation characteristics satisfy the requirements, the insertion loss
characteristics may not fully meet the requirements. On the contrary, even if the
insertion loss characteristics satisfy the requirements, there are cases where
the isolation characteristics do not fully meet the requirements.
On the other hand, in mobile communication equipment, there is a strong demand
for reducing the insertion loss in order to suppress the power dissipation in the
transmission circuit portion and increase continuous talk time, even if the isolation
characteristics are deteriorated. However, the required insertion and isolation
characteristics of two-port isolators have not previous been achieved.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present
invention provide a two-port isolator and communication device in which the insertion
loss and isolation characteristics can be effectively adjusted.
A two-port isolator according to preferred embodiments of the present invention
includes a permanent magnet, a ferrite to which a DC magnetic field is applied
by the permanent magnet, a first central electrode which is disposed on a main
surface of the ferrite or inside the ferrite, one end of which is electrically
connected to a first input-output port, and the other end of which is electrically
connected to a second input-output port, a second central electrode which is disposed
on the main surface of the ferrite or inside the ferrite so as to intersect the
first central electrode with electrical insulation therebetween, one end of which
is electrically connected to the second input-output port, and the other end of
which is electrically connected to a third port, a first matching capacitor electrically
connected between the first input-output port and the second input-output port,
a resistor electrically connected between the first input-output port and the second
input-output port, and a second matching capacitor electrically connected between
the second input-output port and the third port.
The third port is preferably electrically connected to a ground and the inductance
L1 of the first central electrode is different from the inductance L2
of the second central electrode.
Furthermore, a two-port isolator according to another preferred embodiment
of the present invention includes a permanent magnet, a ferrite to which a DC magnetic
field is applied by the permanent magnet, a first central electrode which is disposed
on a main surface of the ferrite or inside the ferrite, one end of which is electrically
connected to a first input-output port, and the other end of which is electrically
connected to a second input-output port, a second central electrode which is disposed
on the main surface of the ferrite or inside the ferrite so as to intersect the
first central electrode with electrical insulation therebetween, one end of which
is electrically connected to the second input-output port, and the other end of
which is electrically connected to a third port, a first matching capacitor electrically
connected between the first input-output port and the second input-output port,
a second matching capacitor electrically connected between the second input-output
port and the third port, a resistor electrically connected between the third port
and a ground.
In this two-port isolator, the inductance L1 of the first central electrode
is preferably different from the inductance L2 of the second central electrode.
In order for the inductance L1 of the first central electrode to be different
from the inductance L2 of the second central electrode, for example, the
electrode width, the electrode thickness, the electrode length, the number of electrodes,
and the spacing between electrodes, of both electrodes may be made different. Furthermore,
the ferrite may be substantially rectangular or substantially circular when viewed
from above. Moreover, the capacitances C1 and C2 of the first and
second matching capacitors are preferably set so as to be optimized with and correspond
to the inductances L1 and L2 of the first and second central electrodes, respectively.
Because of the above-described unique construction, when the inductance L1
of the first central electrode is less than the inductance L2 of the second
central electrode (in the case of L1<L2), as the difference
between L1 and L2 increases, the isolation bandwidth decreases and
the insertion loss bandwidth increases. On the contrary, when the inductance L1
of the first central electrode is greater than the inductance L2 of the
second central electrode (in the case of L1>L2), as the difference
between L1 and L2 increases, the isolation bandwidth increases and
the insertion loss bandwidth decreases.
Furthermore, in a two-port isolator of preferred embodiments of the
present invention, a metal case which encloses the permanent magnet, the ferrite,
and the first and second central electrodes is provided. The metal case includes
a top surface portion, a bottom surface portion, and a pair of opposing side surface
portions joining the top surface portion and bottom surface portion, one of the
first central electrode and second central electrode is disposed so as to be substantially
perpendicular to the side surface portions, and the other central electrode is
arranged so as to be substantially parallel to the side surface portions.
Because of the above-described construction, in the central electrode arranged
so as to be substantially perpendicular to the side surface portions which join
the top surface portion and bottom surface portion of the metal case, a grounding
current easily flows to the top and bottom surface portions, and, in the central
electrode arranged so as to be substantially parallel to the side surface portions,
no substantial grounding current flows to the top and bottom surface portions.
Therefore, even if the first central electrode and second central electrode have
the same shape, the two inductances L1 and L2 can be made different
from one another.
Moreover, the first external input-output electrode which is electrically
connected to the first input-output port and the second external input-output electrode
which is electrically connected to the second input-output port may be provided
in the middle of a pair of opposing side surfaces of the two-port isolator. In
this way, when a two-port isolator is mounted on a printed-circuit board in portable
telephones, for example, when the two-port isolator is turned around by 180 degrees,
it is possible to mount the two-port isolator on a printed-circuit board in which
a signal input line and a signal output line are opposite to each other on the
right side and left side. Accordingly, it is unnecessary to provide two-port isolators
having different configurations in accordance with the direction of the signal
input line and signal output line on the printed-circuit board.
Furthermore, a communication device according to another preferred embodiment
of the present invention, in which the above-described two-port isolator is provided,
exhibits greatly improved characteristics as compared with communication device
which include conventional two-port isolators.
Other features, elements, characteristics and advantages of the present invention
will become more apparent from the following detailed description of preferred
embodiments of the present invention with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded perspective view showing a preferred embodiment of a two-port
isolator of the present invention.
FIG. 2 is a top view of the central electrode assembly shown in FIG. 1.
FIG. 3 is an exploded perspective view of the laminated substrate shown in FIG. 1.
FIG. 4 is an outer perspective view of the two-port isolator shown in FIG. 1.
FIG. 5 is an electrical equivalent circuit diagram of the two-port isolator
shown in FIG. 1.
FIG. 6 is a graph showing isolation characteristics.
FIG. 7 is a graph showing insertion loss characteristics.
FIG. 8 is a graph showing input reflection loss characteristics.
FIG. 9 is a graph showing output reflection loss characteristics.
FIG. 10 is a graph showing the relationship between the ratio C1/C2
and isolation.
FIG. 11 is a graph showing the relationship between the ratio C1/C2
and insertion loss.
FIG. 12 is a graph showing the relationship between the ratio C1/C2
and output reflection loss.
FIG. 13 is an exploded perspective view showing another preferred embodiment
of a two-port isolator of the present invention.
FIG. 14 is an exploded perspective view of the laminated substrate shown in
FIG. 13.
FIG. 15 is an exploded perspective view showing another preferred embodiment
of a two-port isolator of the present invention.
FIG. 16 is an exploded perspective view of the laminated substrate shown in
FIG. 15.
FIG. 17 is an electrical equivalent circuit diagram of the two-port isolator
shown in FIG. 15.
FIG. 18 is a graph showing isolation characteristics.
FIG. 19 is a graph showing insertion loss characteristics.
FIG. 20 is a graph showing input reflection loss characteristics.
FIG. 21 is a graph showing output reflection loss characteristics.
FIG. 22 is a graph showing the relationship between the ratio C1/C2
and isolation.
FIG. 23 is a graph showing the relationship between the ratio C1/C2
and insertion loss.
FIG. 24 is a graph showing the relationship between the ratio C1/C2
and input reflection loss.
FIG. 25 is an electrical circuit block diagram of a communication device of
a preferred embodiment of the present invention.
FIG. 26 is a bottom view showing a modified example of the central electrode
assembly according to preferred embodiments of the present invention.
FIG. 27 is a bottom view showing another modified example of the central electrode
assembly according to preferred embodiments of the present invention.
FIG. 28 is a top view showing another modified example of the central electrode
assembly according to preferred embodiments of the present invention.
FIG. 29 is a top view showing another modified example of the central electrode
assembly according to preferred embodiments of the present invention.
FIG. 30 is a top view showing another modified example of the central electrode
assembly according to preferred embodiments of the present invention.
FIG. 31 is a top view showing another modified example of the central electrode
assembly according to preferred embodiments of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Hereinafter, preferred embodiments of a two-port isolator and communication
device according to the present invention will be described with reference to the
accompanying drawings.
First Preferred Embodiment
FIG. 1 shows an exploded perspective view of a first preferred embodiment of
a two-port isolator of the present invention. The two-port isolator
1 is
preferably a lumped-constant isolator. As shown in FIG. 1, the two-port isolator
1 includes a metal case including an upper metal case
4 and a lower
metal case
8, a permanent magnet
9, a central electrode assembly
13 made of a ferrite
20 and central electrodes
21 and
22,
and a laminated substrate
30.
The upper metal case
4 is substantially box-shaped including a top surface
portion
4a and four side surface portions
4b. The lower
metal case
8 includes a bottom surface portion
8a and left
and right side surface portions
8b. Since the upper metal case
4
and the lower metal case
8 define a magnetic circuit, they are made of a
ferromagnetic material such as, for example, soft iron, and surfaces thereof are
plated with silver or gold.
In the central electrode assembly
13, first and second central electrodes
21 and
22 are disposed on the top surface of the disk-shaped microwave
ferrite
20, such that the first and second central electrodes
21
and
22 intersect each other substantially at right angles with an insulating
layer (not illustrated) disposed therebetween. In the present preferred embodiment,
the central electrodes
21 and
22 are preferably configured as two
straight lines. Both end portions
21a and
21b, and
22a and
22b of the first central electrode
21
and the second central electrode
22 extend so as to reach the bottom surface
of the ferrite
20 and the end portions
21a to
22b
are separated from each other.
As shown in FIG. 2, the electrode width W
1 of the first central electrode
21 and the electrode width W
2 of the second central electrode
22
are different from each other. Thus, the inductance L
1 of the first central
electrode
21 is different from the inductance L
2 of the second central
electrode
22. In the present preferred embodiment, although the inductances
L
1 and L
2 are made different from each other by using the different
electrode widths W
1 and W
2, the method of differentiation is not
limited thereto. For example, the inductances L
1 and L
2 may be made
different from each other by making the electrode thickness t
1 of the first
central electrode
21 different from the electrode thickness t
2 of
the second central electrode
22, by making the electrode length l
1
of the first central electrode
21 different from the electrode length
12
of the second central electrode
22, by making the spacing S
1 between
electrodes of the first central electrode
21 different from the spacing
S
2 between electrodes of the second central electrode
22, or by a
combination thereof.
Here, as the electrode widths W
1 and W
2 of the central electrodes
21 and
22 decrease, the inductances L
1 and l
2 increases.
Furthermore, as the electrode thicknesses t
1 and t
2 decrease, the
inductances L
1 and l
2 increases. Moreover, as the electrode lengths
l
1 and L
2 increase, the inductances L
1 and l
2 increase.
Moreover, as the spacing S
1 and S
2 between the electrodes decreases,
the inductances L
1 and l
2 increases.
The central electrodes
21 and
22 may be wound around the ferrite
22 using a copper foil, or may be formed by printing silver paste on the
ferrite
20 or inside the ferrite
20. Or, the central electrodes
21
and
22 may be formed by using a laminated substrate, as described in Japanese
Unexamined Patent Application Publication No. 9-232818. However, since the printed
central electrodes
21 and
22 have a higher positional accuracy, the
connection to the laminated substrate
30 is greatly improved. In particular,
when the connection is made by using extremely small connection electrodes
51
to
54 for the central electrodes (to be described later), the central electrodes
21 and
22 formed by printing are reliable and workable.
As shown in FIG. 3, the laminated substrate
30 includes the connection
electrodes
51 to
54 for the central electrodes, a dielectric sheet
41 on the bottom surface of which capacitor electrodes
55 and
56
and a resistor
27 are provided, a dielectric sheet
42 on the bottom
surface of which a capacitor electrode
57 is provided, a dielectric sheet
43 on the bottom surface of which a grounding electrode
58 is provided,
and a dielectric sheet
45 on the surface of which an external input electrode
14, an external output electrode
15, and an external grounding electrode
16 are provided. The connection electrode
51 for the central electrodes
defines an input port P
1, the connection electrodes
53 and
54
for the central electrodes define an output port P
2, and the connection
electrode
52 for the central electrodes defines a third port P
3.
The laminated substrate
30 is preferably produced as follows. Dielectric
sheets
41 to
45 are preferably made of low-temperature sintered material
including Al
2O
3 as a main component and one or a plurality
of SiO
2, SrO, CaO, PbO, Na
2O, K
2O, MgO, BaO, CeO
2,
and B
2O
3 as secondary components.
Furthermore, shrinkage-suppressing sheets
46 and
47 that
are not fired at firing conditions for the laminated substrate
30, particularly
at a temperature of about 1000° C. or less and suppress firing shrinkage in
the planar direction (the X-Y direction) are provided. The shrinkage-suppressing
sheets
46 and
47 are preferably made of a mixture of alumina powder
and stabilized zirconia powder. The thickness of the sheets
41 to
47
is preferably, for example, about 10 μm to about 200 μm.
The electrodes
51 to
58 are formed on the bottom surface of the
sheets
41 to
43 and
46 by a method of pattern printing, or
other suitable method. The electrodes
51 to
58, are made of a material,
for example, Ag, Cu, Ag—Pd, having a low resistivity, which can be simultaneously
fired with the dielectric sheets
51 to
58. The thickness of the electrodes
51 to
58 is preferably, for example, about 2 μm to about 20
μm. Normally, the thickness of the electrodes
51 to
58, is
at least about two times the skin depth.
The resistor
27 is formed on the bottom surface of the dielectric sheet
41 preferably by a method of pattern printing. As a material for the resistor,
cermet, carbon, ruthenium, or other suitable materials are preferably used. The
resistor
27 may be formed by printing on the top surface of the laminated
substrate
30, or may be formed as a chip resistor.
Via holes
60 and
65 on the side surface, and external electrodes
14 to
16 are formed such that, after via holes have been formed in
the dielectric sheets
41 to
45 via laser machining, punching, or
other suitable method, conductive paste is filled in the via holes.
The capacitor electrode
57, which is opposed to the capacitor electrode
55 so as to sandwich the dielectric sheet
42, defines a matching
capacitor
25. Furthermore, the capacitor electrode
57, which is opposed
to the capacitor electrode
56 and the grounding electrode
58 so as
to sandwich the dielectric sheets
42 and
43, defines a matching capacitor
26. These matching capacitors
25 and
26 and the resistor
27
together with the electrodes
51 to
54, the external electrodes
14
to
16, and the via holes
60 and
65 define an electric circuit
inside the laminated substrate
30.
The dielectric sheets
41 to
45 are laminated, and, after the laminated
dielectric sheets
41 to
45 are sandwiched from the top and bottom
sides by the shrinkage-suppressed sheets
46 and
47, the dielectric
sheets
41 to
45 are fired. In this manner, a fired body is obtained,
and, after any shrinkage-suppressing material which is not fired has been removed
by ultrasonic cleaning and wet honing, the laminated substrate
30 shown
in FIG. 1 is produced.
On both end portions of the laminated substrate
30, the external input
electrode
14, external output electrode
15, and external grounding
electrode
16 are formed. The external input electrode
14 is electrically
connected to the capacitor electrode
55, and the external output electrode
15 is electrically connected to the capacitor electrode
57. The external
grounding electrodes
16 are electrically connected to the grounding electrode
58. After that, gold plating is applied on a nickel plating to define a
ground. The nickel plating increases the fixing strength of the silver and gold
plating of the electrodes. The gold plating improves the solder wettability and,
since the gold plating has outstanding conductivity, the isolator
1 has
reduced loss.
Moreover, this laminated substrate
30 is usually made as a mother
board. Half-cut grooves having a fixed pitch are formed on the mother board and
a laminated substrate
30 having a desired size is obtained by breaking the
mother board along the half-cut groove. Or a laminated substrate
30 having
a desired size may be cut out by breaking the mother board with a dicer, laser,
or other suitable device.
The laminated substrate
30 obtained in this manner includes the matching
capacitors
25 and
26 and the resistor
27 inside the laminated
substrate
30. The matching capacitors
25 and
26 are formed
so as to have capacitances of a required accuracy. However, if required, trimming
of the laminated substrate
30 takes place before the matching capacitors
25 and
26 and the central electrodes
21 and
22 are
connected. That is, in the laminated substrate
30, the inner capacitor electrodes
55 and
56 (in the second layer) are trimmed together with the dielectric
body in the surface layer. For example, a cutting machine and YAG laser machine
using the fundamental wave, frequency-doubled wave, and frequency-triple wave are
used. When a laser is used, the processing is quickly and precisely performed.
Moreover, trimming of the laminated substrate
30 in the mother board may
be performed effectively.
Thus, since the capacitor electrodes
55 and
56 located close
to the top surface of the laminated substrate
30 are trimmed, the thickness
of the dielectric layer to be removed during trimming is minimized. Moreover, since
the number of electrodes, which hinders trimming, is minimized (only the connection
electrodes
51 to
54 in the present preferred embodiment), the area
of capacitor electrodes which can be trimmed is increased, and accordingly, the
range of adjustment of the capacitance is greatly increased.
Furthermore, since the resistor
27 is also included in the laminated
substrate
30, the resistance value R of the resistor
27 can also
be adjusted by trimming the resistor
27 together with the dielectric body
on the surface in the same manner as the matching capacitors
25 and
26.
In the resistor
27, as the width is reduced even at one location, the resistance
value R increases, and accordingly, the width is cut at most halfway.
As shown in FIG. 1, the permanent magnet
9 is attached to the ceiling
of
the upper metal case
4 via adhesive. The central electrode assembly
13
is mounted on the laminated substrate
30 such that the terminal portions
21a to
22b of the central electrodes
21 and
22 are electrically connected to the connection electrodes
51 to
54 for the central electrodes, which are formed on the surface of the laminated
substrate
30. Moreover, soldering of the connection electrodes
51
to
54 to the central electrodes
21 and
22 is effectively performed
while the laminated substrate
30 is still a portion of the mother board,
or not cut out from the mother board.
The laminated substrate
30 is mounted on the bottom surface
8a
of the lower metal case
8 and the grounding electrode
58 provided
on the lower surface of the laminated substrate
30 is connected and fixed
to the bottom surface
8a by soldering
80. Thus, the grounding
port
16 is easily electrically connected to the bottom surface
8a.
Then, the lower metal case
8 and the upper metal case
4 define
a metal case when the side portions
8b and
4b are joined
by soldering and function as a yoke. That is, this metal case forms a magnetic
path surrounding the permanent magnet
9, the central electrode assembly
13, and the laminated substrate
30. Furthermore, the permanent magnet
9 applies a DC magnetic field to the ferrite
20.
In this manner, the two-port isolator shown in FIG. 4 is obtained. FIG. 5 is
an
electrical equivalent circuit diagram of the isolator
1. One end portion
21a of the first central electrode
21 is electrically connected
to the external input electrode
14 through the input port P
1 (connection
electrode
51 for the central electrodes). The other end portion
21b
of the first central electrode
21 is electrically connected to the external
output electrode
15 via the output port P
2 (connection electrode
54 for the central electrodes). One end portion
22a of the
second central electrode
22 is electrically connected to the external output
electrode
15 via the output port P
2 (connection electrode
53
for the central electrodes). The other end portion
22b of the second
central electrode
22 is electrically connected to the external grounding
electrode
16 through the third port P
3 (connection electrode
52
for the central electrodes). A parallel RC circuit including the matching capacitor
25 and the resistor
27 is electrically connected between the input
port P
1 and the output port P
2. The matching capacitor
26
is electrically connected between the output port P
2 and the third port
P
3. The third port P
3 is electrically connected to ground.
In the two-port isolator having the above-described configuration, the inductance
L
1 of the first central electrode
21 and the inductance L
2
of the second central electrode
22 are different from each other, and, in
the case of L
1<L
2, when the difference between L
1 and
L
2 is increased, the isolation bandwidth decreases and the insertion loss
bandwidth increases. On the contrary, in the case of L
1>L
2,
when the difference between L
1 and L
2 is increased, the bandwidth
for isolation increases and the bandwidth of insertion loss decreases. That is,
the isolation bandwidth and the insertion loss bandwidth can be adjusted to conform
with the requirements of the communication system by adjusting the values of L
1
and L
2.
On the other hand, when the inductance values L
1 and L
2 of the
central
electrodes
21 and
22 are different from each other, the capacitances
C
1 and C
2 of the matching capacitors
25 and
26 must
be different from each other (to set optimal capacitances C
1 and C
2).
That is, the parallel resonance circuit including L
1 and C
1 and the
parallel resonance circuit including L
2 and C
2 must have the same
resonance frequency. Therefore, in preferred embodiments of the present invention,
the matching capacitors
25 and
26 are provided by using the electrodes
55 to
58 provided inside the laminated substrate
30. Thus,
the capacitances C
1 and C
2 of the matching capacitors
25 and
26 are easily made different from each other by making the opposing areas,
spacings, etc., of the electrodes
55 to
58 different.
FIGS. 6 to
9 show the isolation characteristics, insertion loss characteristics,
input reflection loss characteristics, and output reflection loss characteristics,
respectively, when the inductances L
1 and L
2 of the first and second
central electrodes
21 and
22 and the capacitances C
1 and C
2
of the matching capacitors
25 and
26 of the two-port isolator
1
are changed as shown in Table 1-1.
Here, a ferrite
20, which has a diameter of about 2.0 mm and a thickness
of about 0.4 mm was used. The self-inductance was set to be about 0.7 nH by setting
the electrode width W of the central electrodes
21 and
22 to about
0.2 mm, the electrode spacing S to about 0.2 mm, and the electrode length l to
about 2 mm. Furthermore, the self-inductance was set to about 0.5 nH by setting
the electrode width W of the central electrodes
21 and
22 to about
0.5 mm, the electrode spacing S to about 0.2 mm, and the electrode length l to
about 2 mm. Moreover, the self-inductance was set to about 1.0 nH by setting the
electrode width W of the central electrodes
21 and
22 to about 0.1
mm, the electrode spacing S to about 0.1 mm, and the electrode length l to about
2 mm. The resistance value of the resistor
27 was set to about 60 Ω
in all cases. The inductances in Table 1-1 show the self-inductances of the central
electrodes
21 and
22 when the relative magnetic permeability was
assumed to be about 1, and the inductances L
1 and L
2 were obtained
when the inductances were multiplied by the effective permeability of the ferrite
20. Furthermore, the worst values in the band of 893 MHz to 960 MHz are
summarized in Table 1-2.
| TABLE 1-1 |
| |
| |
Self- |
Self- |
|
|
| |
inductance |
inductance |
Capacitance |
Capacitance |
| |
of first |
of second |
C1 of |
C2 of |
| |
central |
central |
matching |
matching |
| |
electrode |
electrode |
capacitor |
capacitor |
| |
21 |
22 |
25 |
26 |
| |
| Comparative |
0.7 nH |
0.7 nH |
22 pF |
22 pF |
| example 1 |
| Preferred |
0.5 nH |
1.0 nH |
32 pF |
15 pF |
| Embodiment 1 |
| Preferred |
1.0 nH |
0.5 nH |
15 pF |
32 pF |
| Embodiment 2 |
| |
| TABLE 1-2 |
| |
| |
Input |
|
|
Output |
| |
reflection |
Insertion |
Isolation |
reflection |
| |
loss (dB) |
loss (dB) |
(dB) |
loss (dB) |
| |
| Comparative |
22.4 |
0.75 |
12.2 |
11.8 |
| example 1 |
| Preferred |
23.0 |
0.47 |
9.5 |
14.8 |
| Embodiment 1 |
| Preferred |
22.6 |
1.18 |
15.5 |
9.6 |
| Embodiment 2 |
| |
From FIGS. 6 to
9 and Table 1-2, when the self-inductance of the first
central electrode
21 is less than the self-inductance of the second central
electrode
22, as in the first preferred embodiment, although the isolation
is deteriorated, the insertion loss and reflection loss are greatly improved.
On the contrary, as in preferred embodiment 2, when the self-inductance of the
first central electrode
21 is greater than the self-inductance of the second
central electrode
22, although the insertion loss and reflection loss are
deteriorated, the isolation is greatly improved.
In this way, when the self-inductance of the two central electrodes
21
and
22 are made different from each other, the insertion loss and isolation
can be optimized to provide an isolator
1 having excellent characteristics.
Normally, the insertion loss required in a two-port isolator used in the
mobile communication equipment is about 1.2 dB or less and the isolation is at
least about 8.0 dB. Then, two-port isolators
1 meeting these conditions
were investigated by changing the capacitance ratio C
1/C
2 of the
matching capacitors
25 and
26. Table 2 shows the results, and FIGS.
10 to
12 are graphs showing the isolation characteristic, insertion loss
characteristic, and output reflection characteristic, respectively.
| TABLE 2 |
| |
| |
Input |
|
|
Output |
| |
reflection |
Insertion |
Isolation |
reflection |
| C1/C2 |
loss (dB) |
loss (dB) |
(dB) |
loss (dB) |
| |
| |
| 0.33 |
22.70 |
1.60 |
17.20 |
7.70 |
| 0.50 |
22.60 |
1.18 |
15.50 |
9.60 |
| 0.66 |
22.00 |
0.97 |
13.50 |
10.30 |
| 0.90 |
22.10 |
0.80 |
12.70 |
11.40 |
| 1.00 |
22.40 |
0.75 |
12.20 |
11.80 |
| 1.10 |
22.10 |
0.70 |
11.80 |
12.10 |
| 1.50 |
22.20 |
0.60 |
10.60 |
12.90 |
| 2.00 |
23.00 |
0.47 |
9.50 |
14.80 |
| 3.00 |
23.20 |
0.38 |
8.00 |
16.20 |
| 3.50 |
24.00 |
0.35 |
7.10 |
16.90 |
| |
As shown in Table 2 and FIGS. 10 and 11, in the range where the insertion loss
is about 1.2 dB or less and the isolation is at least about 8.0 dB, when a two-port
isolator
1 having excellent isolation is required, it is desirable to design
it such that the value of C
1/C
2 satisfies the expression, 0.5≦C
1/C
2≦0.9.
This is because the isolation is improved by about 0.5 dB when C
1/C
2
is about 0.9 or less. However, when C
1/C
2 is less than about 0.5,
although the isolation is further improved, the insertion loss exceeds about 1.2
dB and the isolator cannot be used in practice.
Furthermore, in the range where the insertion loss is about 1.2 dB or
less and the isolation is at least about 8.0 dB, when a two-port isolator
1
having excellent isolation is required, it is desirable to design it such that
the value of C
1/C
2 satisfies the expression 1.1≦C
1/C
2≦3.0.
This is because the insertion loss is improved by about 0.05 dB when C
1/C
2
is at least about 1.1. However, when C
1/C
2 exceeds about 3.0, although
the insertion loss is further improved, the isolation exceeds about 8.0 dB and
the isolator cannot be used in practice.
Moreover, in the case of three-port isolators (isolators having three central
electrodes), as described in Japanese Unexamined Patent Application Publication
No. 2001-185914, Japanese Unexamined Patent Application Publication No. 2001-203507,
and Japanese Unexamined Patent Application Publication No. 2001-203508, the configuration
in which the inductances of the central electrodes are made different from each
other is well-known. However, in these three-port isolators, the asymmetrical configuration
is adjusted by changing the electrode widths, etc.
In contrast, in preferred embodiments of the present invention, an asymmetrical
configuration is used and the isolation and insertion loss are set so as to have
the desired characteristics. In the three-port isolators, even if the thicknesses
of the central electrodes are different from one another, the isolation bandwidth
and the insertion loss bandwidth cannot be adjusted to offset each other. Only
a two-port isolator according to preferred embodiments of the present invention
in which the input-output ports P
1 and P
2 are connected to both end
portions
21a and
21b of the central electrode
21
achieves such an effect.
Second Preferred Embodiment
A two-port isolator
1A shown in FIG. 13 preferably has the same configuration
as the two-port isolator according to the first preferred embodiment except for
a central electrode assembly
13A and a laminated substrate
30A.
In the central electrode assembly
13A, first and second central electrodes
21 and
22 are disposed on the top surface of the ferrite
20
so as to intersect each other with an insulation layer disposed (not illustrated)
therebetween. The first and second central electrodes
21 and
22 preferably
have the same shape (electrode width, electrode thickness, electrode length, and
spacing between electrodes).
As shown in FIG. 14, the laminated substrate
30A includes connection electrodes
51 to
54 for the central electrodes, a dielectric sheet
41
on the bottom surface of which a capacitor electrode
55 and a resistor
25
are provided, a dielectric sheet
42 on the bottom surface of which a capacitor
electrode
57 is provided, a dielectric sheet
43 on the bottom surface
of which a grounding electrode
58 is provided, a dielectric sheet
45
on which an external input electrode
14, an external output electrode
15,
and an external grounding electrode
16 are provided, and others. This laminated
substrate
30A is preferably produced in the same way as the laminated substrate
30 of the first preferred embodiment of the present invention.
The capacitor electrode
57, facing the capacitor electrode
55 with
the dielectric sheet
42 therebetween, constitutes a matching capacitor
25.
Furthermore, the capacitor electrode
57, facing the grounding electrode
58 with the dielectric sheet
43 therebetween, constitutes a matching
capacitor
26.
The connection electrodes
51 to
54 for the central electrodes are
disposed in the vicinity of the middle of the four sides of the laminated substrate
30A. Furthermore, the external input electrode
14 and the external
output electrode
15 are also disposed in the middle of the two opposing
sides of the laminated substrate
30A. The connection electrode
51
for the central electrodes defines an input port P
1, the connection electrodes
53 and
54 for the central electrodes define output ports P
2,
and the connection electrode
52 for the central electrodes defines a third
port P
3.
The central electrode assembly
13A having the above-described configuration
is mounted on the laminated substrate
30A such that either of the two central
electrodes
21 and
22 is substantially perpendicular to the side surface
portion
8b of the lower metal case
8 joined to the upper metal
case
4. In the central electrode
22 disposed to be substantially
perpendicular to the side surface portion
8b, a grounding current
easily flows to the top surface portion
4a and the bottom surface
portion
8a, and, in the central electrode
21 disposed so as
to be substantially parallel to the side face portion
8b, virtually
no grounding current flows to the top surface portion
4a and bottom
surface portion
8a of the metal case. Therefore, even if the central
electrodes
21 and
22 have the same shape, the inductances L
1
and L
2 thereof are different from one another.
Accordingly, the two-port isolator
1A exhibits the same advantages
as the isolator
1 of the first preferred embodiment of the present invention.
Moreover, a grounding current is generated in an electric power unit (not illustrated)
connected to the external input and output electrodes
14 and
15 and
flows through various paths in the isolator
1A. For example, a grounding
current flows in a path defined by the external input electrode
14, the
central electrode
21, the central electrode
22, and the external
grounding electrode
16, and flows in a path defined by the external input
electrode
14, the central electrode
21, the matching capacitor C
2
(displacement current), and the external grounding electrode
16.
Furthermore, in the second preferred embodiment, the external input
electrode
14 and the external output electrode
15 are provided in
the middle of a pair of opposing side surfaces of the isolator
1A. Accordingly,
when the isolator
1A is mounted on a printed circuit board in, for example,
portable telephones, it is possible to mount the isolator
1A on the printed
circuit board, in which a signal input line and a signal output line are provided
opposite to each other on the right and left, by turning around the isolator
1A
by 180 degrees. Therefore, it is unnecessary to provide two kinds of isolators
1A which are adapted to the directions of the signal input line and signal
output line on the printed circuit board. As a result, the cost of the isolator
1A is greatly reduced.
In particular, in this two-port isolator
1A, the reflection loss versus
frequency characteristics vary greatly between the cases
