Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
2001-10-23
2002-11-26
Ham, Seungsook (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S212000
Reexamination Certificate
active
06486753
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a filter in a millimeter wave band, and more particularly to a millimeter wave band filter to which the technology of a non-radiative dielectric waveguide (“NRD guide”) is applied.
2. Description of Prior Art
An NRD guide circuit has attracted attention as a transmission line for a micro wave band, particularly a millimeter wave band above 30 GHz, due to its small transmission loss in comparison with a microstrip line and due to its easiness in manufacturing the transmission line in comparison with prior waveguides.
The structure of a general prior NRD guide circuit is illustrated in FIG.
1
. The NRD guide circuit has a structure that a dielectric line
10
through which an electromagnetic wave is transmitted is sandwiched between two parallel conductive plates
12
a,
12
b
made from conductive metal. A space h of the two parallel plates
12
a,
12
b
is less than half a free space wavelength of a using frequency. Accordingly, the electromagnetic wave is blocked in places other than the dielectric line
10
and its radiation is restricted, so that the NRD guide circuit can transmit the electromagnetic wave along the dielectric line
10
at a small loss. Paying attention to such transmission superiority of the NRD guide circuit, there have been proposed NRD guide filters of the 35 GHz and 50 GHz bands.
FIGS. 2 and 3
illustrate the structure of a prior air gap coupled filter using an NRD guide. The prior air gap coupled filter has a structure that multi-staged dielectric blocks are sandwiched between the parallel conductive plates
12
a,
12
b.
One dielectric line is cut into multiple dielectric blocks with proper lengths. The dielectric blocks
14
a
~
14
e
are straight aligned, with maintaining certain gaps therebetween, in the direction to which a signal proceeds and is air gap coupled with dielectric lines
10
a,
10
b
on input and output sides, respectively. Each of the dielectric blocks operates as a dielectric resonator at each stage of the filter. The number of the dielectric resonator blocks is proportional to an order number of the filter. The air gap coupled filter shown in
FIG. 2
is the fifth order filter because it has five dielectric resonator blocks
14
a
~
14
e.
The typical raw material for the dielectric line of the NRD guide which is applicable to millimeter waves is teflon. Teflon has an advantage that transmission loss is small whereas it has such disadvantages arising from its material characteristic that its processing is difficult due to its weakness and that its assembly is difficult because it does not easily adhere to other materials like metal. These disadvantages are the reason why the NRD guide has not been commercially used since the first introduction by Professor Yoneyama in the early 1980's.
Since the using frequency is as high as the millimeter wave band, a wavelength of the electromagnetic wave transmitted along the dielectric resonator blocks in the waveguide, i.e., within the parallel conductive plates, is very short. The characteristic of the filter, in this case, is sensitively changed in accordance with the physical dimensions of structural bodies and fixtures for setting the resonator. Thus, it is necessary not only that a length of each of the dielectric resonator blocks
14
a
~
14
e
should be so accurately calculated as to be resonated at a certain frequency within a passing band, but also that each of the dielectric resonator blocks should be made as precisely as a predetermined length to obtain a wanted characteristic of the filter.
Further, each of the multi-staged dielectric resonator blocks
14
a
~
14
e
should be spaced to maintain a proper gap apart from its adjacent dielectric resonator blocks. This gap should be determined to obtain an optimal impedance matching between the two adjacent resonator blocks. That is, in order to obtain a good characteristic of a designed filter, there should be a precision of several microns not only in the length of each of the dielectric resonator blocks
14
a
~
14
e
but also in the distance between the resonators.
However, in manufacturing the prior air gap coupled filter using the NRD guide, it is difficult to make the dielectric resonator blocks
14
a
~
14
e
have such a precision. And also, with maintaining the precision of several microns, it is difficult to align the dielectric resonator blocks
14
a
~
14
e
which have different lengths in a straight line in the direction that a wave proceeds. In doing so, a lot of time and labor are required. Due to these reasons, the prior air gap coupled filter is a disadvantageous structure in terms of making, assembly and production, and is not suitable for a commercial model which is applicable to a high frequency in the millimeter wave band.
That is, in the case of the prior NRD guide air gap coupled filter, the resonator of each stage exists as a single independent block having a different length from one another, and has a structure that an impedance of each stage is controlled by adjusting a distance between each resonator. In this kind of structure, it is difficult to precisely make the dielectric resonators and to align the independent block of each stage in the right position within the filter housing with maintaining a predetermined distance.
SUMMARY OF THE INVENTION
In order to improve the above problems, an object of the present invention is to provide a metal post filter assembly, using an NRD guide, which is designed for an easy making and a good productivity resulting from a convenient and accurate assembly and is capable of stably having filter characteristics to a wanted degree.
To accomplish the object of the present invention, there is provided a metal post filter assembly using a non-radiative dielectric waveguide, comprising: a filter housing which includes parallel conductive plates facing each other; and a filter, disposed between said parallel conductive plates, for filtering a certain frequency band of a traveling electromagnetic wave, said filter including, a single body type dielectric line, made from a non-radiative dielectric, whose side surface is formed with a plurality of inserting holes running parallel to said parallel conductive plates, said dielectric line being segmented into multi-stages by one or more sets of said inserting holes which are spaced apart by a predetermined distance along a length direction of said dielectric line, and the number of the sets corresponding to a filtering order of said filter assembly, and a plurality of metal posts, each of which having a diameter to be fittingly inserted in each of said inserting holes.
The filter is formed with multi-staged dielectric resonators cascaded as a single body and segmented by said metal posts, said multi-staged dielectric resonators providing a filtering function which selectively allows only the certain frequency band of the traveling electromagnetic wave to pass therethrough by a predetermined impedance coupling relationship. It is particularly preferable that an impedance of said multi-staged dielectric resonators is largest in a middle stage and becomes gradually and symmetrically smaller to both end stages. Further, it is preferable that a length of said multi-staged dielectric resonators is longest in a middle stage and becomes gradually and symmetrically shorter to both end stages.
According to one preferred embodiment of the filter, one inserting hole is formed per each stage on the side surface of said dielectric line, said inserting hole in each stage having a diameter which is largest in the middle stage and becomes gradually and symmetrically smaller to both end stages and being disposed along an approximately half-height of said side surface in line.
According to another preferred embodiment of the filter, two inserting holes whose diameters are identical are disposed, per each stage, above and below an approximately half-height point of said side surface of said dielectric line and a vertical distance of said two inserting holes in each sta
Cole Thomas W.
Ham Seungsook
Nixon & Peabody LLP
NRD Co. Ltd.
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