Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1999-05-07
2001-04-10
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S206000, C333S223000
Reexamination Certificate
active
06215376
ABSTRACT:
TECHNOLOGICAL FIELD
The invention relates in general to constructions of radio-frequency filters and oscillators. In particular the invention relates to a filter and oscillator construction which can be used in the frequency area of several gigahertz.
BACKGROUND OF THE INVENTION
FIG. 1
shows a longitudinal section of a known filter construction
100
used particularly in mobile phones in the 450-MHz frequency area. The construction comprises a low-loss printed circuit board
101
onto which finger-like projections
102
have been formed. Around each finger-like projection a cylindrical coil conductor, or helix,
103
has been wound to function as a resonator the electrical length of which is one quarter of the wavelength at the operating frequency. The lower ends, with respect to the position shown, of the helixes are grounded and the upper ends are open. The construction also includes a housing
104
that comprises outer walls and partition walls. Each helix is located inside a compartment of its own, separated from the next compartment by a partition wall. Partition walls may have holes of different sizes in various locations to realize electromagnetic coupling between adjacent helixes. In addition, inter-helix couplings can be realized through strip conductors
105
on the surface of the printed circuit board
101
.
FIG. 2
shows a longitudinal section of a known ceramic filter construction
200
used especially in mobile phones in the 900-MHz frequency area. The filter construction is based on a block
201
made of a dielectric ceramic material such that the outer surface of the block is for the greater part plated with an electrically conductive coating
202
and has got holes
203
in it that wholly or partly extend through the ceramic block. Also the inner surfaces of the holes
203
are plated using an electrically conductive material. The inner coating of a hole is at one end in galvanic contact with the coating on the outer walls of the block so that the coating of the hole constitutes a &lgr;/4 resonator in the same manner as the helix wire in the helix resonator described above. Coupling to the filter is realized through coupling strips
204
formed on the uncoated areas of the block
201
. Electromagnetic coupling between resonators is realized through the ceramic material and it can be controlled by varying the amount and pattern of the coating on the block.
FIG. 3
shows a coaxial resonator construction
300
for frequencies above 2 GHz, known from the Finnish patent application FI-970525. For illustrative purposes, part of the electrically conductive casing
301
around the filter is cut out in the drawing. Partition walls
302
divide the casing into compartments in the same manner as in helix resonators. There is one coaxial resonator
303
in each compartment of the filter.
FIG. 3
does not show the resonator in the middle compartment of the filter. In the lower parts of the partition walls
302
there are holes to realize electromagnetic couplings. The base plate
304
of the filter is a printed circuit board wherein electrically conductive areas of desired shape and size can be formed on both surfaces and all sides. On the top surface of the base plate there are conductive patterns
305
through which coupling to the resonators
303
is realized and which mediate in the electromagnetic coupling between resonators. On the bottom surface of the base plate there is a substantially continuous electrically conductive coating (not shown) that constitutes a ground plane and is in connection with the metal plating
306
on the edges of the base plate. There are gaps
307
in said metal plating that separate the continuous plating from ports strips
308
and
309
. Port strips are narrow conductive areas at the edge of the printed circuit board that have connections to certain conductive patterns on the top surface of the printed circuit board and thereby to certain resonators. At each port strip there is a gap (not shown) in the electrically conductive coating on the bottom surface of the printed circuit board and on the side of the casing to prevent a short circuit between a port strip and the ground plane.
For the attachment of resonators
303
the printed circuit board
304
according to
FIG. 3
has at each resonator a hole such that on the inner surface of the hole there is a metal plating or other electrically conductive coating connected to the electrically conductive coating, or ground plane, on the bottom surface of the printed circuit board. The inner surface of the hole need not be metal plated if electric coupling to the resonator can be made reliable enough in some other way. To ensure the best possible electric contact and to realize accurate electromagnetic dimensioning each hole may be encircled by a ring of conductive coating also on the top surface of the printed circuit board. The resonators can be soldered to their places or attached using electrically conductive glue, for example. In the filter according to
FIG. 3
there is at the upper end of each resonator a bulge the function of which is to produce a so-called impedance step, i.e. impedance change point in the direction of the longitudinal axis of the resonator. The resonators may also be manufactured without said bulge.
The prior-art filter constructions described above have the problem that they are only applicable to frequencies ranging from a few hundred megahertz to a few gigahertz at the most. In communications systems utilizing new radio technology, such as the wireless local loop (WLL) and wireless local area network (WLAN), there is a visible tendency towards 10 to 20-GHz frequencies which, when realized, would render quarter-wave resonator constructions so small that their mass manufacture with sufficiently precise mechanical tolerances would be impossible, at least at a reasonable cost level.
For frequencies of tens of gigahertz and for optical frequencies filters have been manufactured using waveguides which usually are structures with a rectangular cross section wherein a dielectric core is surrounded by a coating which is reflective at the operating frequency. On both sides of a waveguide in the middle waveguides can be placed that have gaps at regular intervals in their coatings. With suitable location and dimensions of the gaps the waveguides will be coupled only at precisely predetermined frequencies so that the construction can be used as a filter. The manufacturing costs of such a construction are relatively high and repeatability in mass production is poor. In addition, the construction is rather big in size.
SUMMARY OF THE INVENTION
An object of the invention is to provide a filter construction applicable in frequencies of up to about 20 GHz. A particular object of the invention is that the filter construction according to the invention is suitable for large-scale series production such that the unit costs are reasonable and repeatability is good. Another object of the invention is that the mechanical strength of the filter construction is good and temperature compensation can be realized in the filter. A further object of the invention is to provide an oscillator construction applicable in frequencies of up to about 20 GHz.
The objects of the invention are achieved by a filter construction having a plurality of adjacent coaxial resonators the dimensions of which are based on half of the wavelength at the operating frequency. As regards oscillators, the objects of the invention are achieved by a construction having a coaxial resonator the dimensions of which are based on half of the wavelength at the operating frequency,
The filter construction according to the invention is characterized in that a first end of each inner conductor is connected to the ground plane and a second end is connected to an electrically conductive casing so that the resonators comprised of the inner conductors, ground plane and casing function as half-wave resonators.
The oscillator construction according to the invention is characterized in that a first end of the inner conductor is connect
Hagstrom Panu
Pelkonen Jari
Darby & Darby
Lee Benny
LK-Products OY
Nguyen Patricia T.
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