Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
2000-01-19
2001-08-14
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S203000, C333S204000, C333S206000, C333S212000
Reexamination Certificate
active
06275124
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to delay line filters, and more particularly to filters with one symmetrical cross-coupled pair of filter elements.
BACKGROUND OF THE INVENTION
Filters with stringent amplitude and group delay requirements over a passband region are widely used in modern communications systems.
FIG. 1
a
shows a top view of a conventional nine element linear phase filter
10
comprised of a housing
11
having rod-shaped filter elements
12
,
13
,
14
,
15
,
16
,
17
,
18
,
19
, and
20
, and metal walls
21
,
22
,
23
,
24
and
25
. Filter
10
has three cross couplings, namely between the pairs of elements
13
and
19
,
14
and
18
, and
15
and
17
. Walls
23
,
24
and
25
form a gap
26
to allow the cross coupling between filter elements
15
and
17
, by allowing the coupling between the pairs of the elements
15
and
16
and
16
and
17
.
In symmetrical filters, the first element to filter a signal, e.g. element
12
, and the last element to filter the signal, e.g., element
20
, are identical and the spacing between each of these respective elements and the elements adjacent to them are also identical. Similarly, in symmetrical filters the second and next to last filter elements. e.g., elements
13
and
19
, respectively, are identical, the third and second to last filter elements, e.g., elements
14
and
18
, respectively, are identical, and so on. Symmetrical filters are easier and thus less expensive to fabricate, align and tune than non-symmetrical filters since each filter half in the symmetrical filter is identical.
In filters of the type shown in
FIG. 1
a,
energy is transferred between coupled filter elements, e.g., between physically adjacent elements. For example, in filter
10
shown in
FIG. 1
a,
element
15
is coupled to element
16
which is coupled to element
17
. A pair of filter elements are cross-coupled when each element is coupled to the other in addition to at least two other filter elements. For example, in filter
10
shown in
FIG. 1
a,
element
15
is cross-coupled to element
17
because elements
15
and
17
are coupled to each other and coupled to at least two additional filter elements, for example element
15
is coupled to elements
14
,
16
and
17
and element
17
is coupled to elements
15
,
16
and
18
. Filters having cross-coupled elements have better operating characteristics than filters having only serially coupled elements. Specifically, whereas filters having only serially coupled elements can attain either a desired amplitude flatness or a desired gain flatness but not both, filters having cross-coupled elements can attain both a desired amplitude flatness and a desired gain flatness.
FIG. 1
b
shows a top view of conventional non-symmetrical nine element linear phase filter
27
comprised of a housing
28
having rod-shaped filter elements
29
,
30
,
31
,
32
,
33
,
34
,
35
,
36
and
37
, and metal walls
38
and
39
. A single cross coupling is produced between the element pair
32
and
35
. As mentioned above, non-symmetrical filters are more difficult to fabricate and tune than symmetrical filters. Filter
27
has a single cross coupling which is easier to implement than a filter having multiple cross couplings. However, the single cross coupling does not overcome the aforementioned drawbacks of non-symmetrical filters. Filters having a single cross coupling are easier and thus less expensive to fabricate, align and tune than filters having multiple cross couplings.
Conventional filters of the type just described suffer from significant drawbacks. Specifically, filter
10
requires three cross couplings. Filters with multiple cross couplings are difficult to tune and are not appropriate for some applications. Filter
27
requires the use of non-adjacent element coupling and is not symmetrical.
SUMMARY
A method and apparatus for implementing a delay line filter with a single cross-coupled pair of filter elements. In a first exemplary embodiment of the present invention, the filter is comprised of a plurality of symmetrically configured filter elements, wherein only two of the filter elements are cross-coupled. In a second exemplary embodiment of the present invention, the filter is comprised of a plurality of filter elements, wherein a first element is coupled to a second element, and the first and second elements are each coupled to at least two other elements and at least one of the at least two other elements for each of the first and second elements are the same.
REFERENCES:
patent: 2984802 (1961-05-01), Dyer et al.
patent: 3737816 (1973-06-01), Honicke
patent: 3882434 (1975-05-01), Levy
patent: 4246555 (1981-01-01), Williams
patent: 4423396 (1983-12-01), Makimoto et al.
patent: 4890078 (1989-12-01), Radcliffe
patent: 5262742 (1993-11-01), Bentivenga
patent: 5608363 (1997-03-01), Cameron et al.
patent: 5801605 (1998-09-01), Filakovsky
patent: 5896073 (1999-04-01), Miyazaki et al.
patent: 2056528 B2 (1978-09-01), None
Lee Benny
Lucent Technologies - Inc.
Summons Barbara
Zimmerman Jean-Marc
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