Filter element and fabrication thereof

Details Filter element and fabrication thereof Filter element and fabrication thereof

1999-08-16

2002-11-19

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Coupling networks

Wave filters including long line elements

C333S246000, C333S238000

Reexamination Certificate

active

06483403

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a filter element, and more particularly relates to a distributed constant filter.
2. Description of Related Art
Cellular telephones, radio-Local Area Networks (radio-LAN), and other high frequency communication devices that use a microwave band or milliwave band carrier typically have filter elements, such as low pass filter (LPF) and band pass filter (BPF). The filter elements may be designed using a distributed constant filter formed with a conventional microstrip transmission line. Unlike filter elements that have a composite component consisting of an inductor (L) and a capacitor (C) that are combined to form an L-C circuit having a concentrated or lumped constant L-C parameter, a conventional microstrip transmission line has serially distributed L and C parts formed on a substrate as shown in
FIGS. 1 and 2
.
FIG. 1
is a plan view illustrating the structure of a conventional filter element
10
formed with a microstrip transmission line. The conventional filter element
10
includes a dielectric (or insulating) substrate
12
such as a ceramic substrate or a printed substrate (e.g., a dielectric, such as silicon dioxide or silicon nitride, is deposited on a substrate and then masked using known fabrication techniques to form a printed dielectric pattern on the substrate). The conventional filter element
10
also includes a strip conductor pattern
14
formed on the dielectric substrate
12
, and I/O electrodes
16
and
18
that are electrically connected to the strip conductor pattern
14
. The strip conductor pattern
14
includes a first group of segments
20
,
22
,
24
, and
26
that function as inductors and a second group of segments
28
,
30
, and
32
that function as capacitors. Each inductor segment
20
,
22
,
24
and
26
has a width (e.g., width
23
of inductor segment
20
as shown in
FIG. 1
) of about 0.1 millimeters (mm) and a length (e.g., length
21
of inductor segment
20
) of about 0.3 mm. Each capacitor segment
28
,
30
, and
32
has a width (e.g., width
29
of capacitor segment
28
as shown in FIG.
1
)of about 5 mm and a length (e.g., length
27
of capacitor segment
28
)of about 3 mm. The conventional filter element
10
shown in
FIG. 1
is a microstrip line LPF that has an impedance which is varied alternately as a result of forming the strip conductor pattern
14
on the dielectric substrate
12
. By forming the strip conductor pattern
14
to have inductor segments and capacitor segments that are optimally sized, a signal in a bandwidth higher than a desired frequency can be attenuated.
An equivalent electrical circuit representation
50
of the conventional filter element
10
is shown in FIG.
2
. The inductor segments
20
,
22
,
24
, and
26
correspond to the inductors
52
,
54
,
56
, and
58
, respectively. The capacitor segments
28
,
30
, and
32
correspond to the capacitors
60
,
62
, and
64
, respectively. Because the inductor segments and the capacitor segments in the conventional filter element
10
have a flat structure, the filter element
10
can be formed simultaneously in a process for forming a wiring pattern on a mounting substrate using known printing or lithography techniques.
However, in forming the conventional filter element
10
as described above, a problem arises where the inductance effect (e.g., ability to oppose any change to a electrical current flowing through the filter element) of the equivalent electrical circuit
50
shown in
FIG. 9
is reduced due to a parasitic capacitance of the portion of the dielectric between the substrate
12
and the strip conductor pattern
14
that occurs when a signal in the frequency range of microwave and milliwave is transmitted through the filter element
10
. Parasitic capacitance, for example, may be the capacitance or collection of charge between a conduction layer, such as the strip conductor pattern
14
and a base, such as the substrate
12
. Parasitic capacitance, which degrades the performance of a circuit on a substrate or chip, is not intentionally designed into the chip or circuit but is rather a consequence of the layout of the circuit on the chip. This problem of parasitic capacitance is particularly prevalent when the transmitted signal through the conventional filter element
10
is in the frequency range exceeding 5 GHz.
To prevent the reduction in the inductance effect of the equivalent electrical circuit
50
and to obtain the desired filter performance, the inductance in the conventional filter element
10
is increased by thinning the width of the inductor segments
20
,
22
,
24
and
26
in the strip conductor pattern
14
shown in FIG.
1
. Further, to reduce the passband loss of the filter element
10
, the length of each inductor segment
20
,
22
,
24
, and
26
is reduced substantially. Passband loss, defined in decibels (dB), describes the absolute loss across a band of frequencies the conventional filter element
10
is supposed to pass.
By substantially reducing the width and the length of the inductor segments
20
,
22
,
24
, and
26
within the strip conductor pattern
14
, the resulting conventional filter element
10
has the following other problems:
1) The inductor segments
20
,
22
,
24
, and
26
may require micrometer (&mgr;m) order accuracy in fabrication, making it difficult to obtain a high production yield for the conventional filter element
10
.
2) The significantly reduced length of the inductor segments
20
,
22
,
24
, and
26
results in an unintentional strong electromagnetic coupling between respective adjacent capacitor segments
28
,
30
, and
32
, which impacts the desired performance of the filter element
10
.
3) The difference in line width between the inductor segments
20
,
22
,
24
, and
26
and the capacitor segments
28
,
30
, and
32
is significantly large. The line width of one capacitor segment (i.e.,
28
,
30
, or
32
in
FIG. 1
) may be 10 times that of the one inductor segment (i.e.,
20
,
22
,
24
, and
26
in FIG.
1
). The large difference in line width causes a large stress at the contact or connection between the inductor segments
20
,
22
,
24
, and
26
and the capacitor segments
28
,
30
, and
32
as a result of temperature cycling during operation of the conventional filter element
10
. The large stress may cause a disconnection between a respective inductor segment and capacitor segment in the strip conductor pattern
14
. Thus, the conventional filter element
10
has poor reliability due to this disconnection problem.
4) If a device which generates heat during operation, such as a power amplifier, is mounted on the substrate
12
on which the filter element
10
has been formed, heat from the power amplifier may burn or melt one of the thin inductor segments
20
,
22
,
24
, and
26
, causing a disconnection in the strip conductor pattern
14
.
Thus, a filter element that is formed with a conventional microstrip line has several significant problems, such as low production yields due to the difference in size in line width of the inductor segments and capacitor segments formed in the conventional microstrip line, and disconnections in the conventional microstrip line due to the stress caused between connections of inductor segments and capacitor segments during temperature cycles of the conventional microstrip line.
The present invention works toward providing an improved filter element that is formed with a microstrip line that has uniform line width to effectively improve the production yield and reliability of the improved filter element. The present invention also works toward providing a fabrication method for producing the improved filter element at high production yield.
SUMMARY OF THE INVENTION
The present invention provides a filter element fabricated by forming a strip conductive pattern on a dielectric substrate that has a surface and a cavity with an aperture disposed on the surface of the dielectric substrate, wherein the strip conductive pattern is formed

Affiliated with

Also associated with

Rating

Filter element and fabrication thereof does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Filter element and fabrication thereof, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Filter element and fabrication thereof will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2964691