Input/output coupling structure for dielectric waveguide

Dielectric waveguide comprising a circular input/output electrode on its bottom surface and surrounded by an exposed dielectric portion thereof around which a conductor film is disposed. A short stub crosses through the exposed dielectric portion to couple the electrode and film together. The printed circuit board has a front surface formed with a generally-circular island-shaped electrode surrounded by a front surface-side ground pattern in a spaced-apart relation thereto, and a back surface formed with a strip line surrounded by a back surface-side ground pattern in spaced-apart relation thereto. An approximate center of the island-shaped electrode and one end of the strip line are coupled together, and the front surface-side ground pattern and the back surface-side pattern are coupled together. The input/output electrode of the dielectric waveguide and the island-shaped electrode of the printed circuit board are coupled together.

TECHNICAL FIELD

The present invention relates to an input/output coupling structure between a dielectric waveguide and a printed circuit board on which the dielectric waveguide is to be mounted, and, more particularly, to a bandwidth widening technique for the input/output coupling structure.

BACKGROUND ART

In late years, mobile communications devices have become widespread, and frequency bands up to about 2 GHz band have come to be used in mobile communications. In a base station for communications in such frequency bands, a dielectric waveguide filter has been used which comprises a combination of a plurality of resonators each composed of a dielectric waveguide.

The dielectric waveguide filter is capable of facilitating downsizing and weight reduction based on a wavelength shortening effect of dielectric, and thereby can be directly mounted on a printed circuit board.

However, the dielectric waveguide, and a strip line used in the printed circuit board, are different from each other in terms of a transmission mode of electromagnetic wave. Thus, as a prerequisite to using the dielectric waveguide filter while being directly mounted on the printed circuit board, it is necessary to provide, between the strip line and the dielectric waveguide, an input/output coupling structure for performing mode conversion.

LIST OF PRIOR ART DOCUMENTS

Patent Documents

SUMMARY OF THE INVENTION

Problem To Be Solved By the Invention

FIG. 6(a) is an exploded perspective view illustrating one example of a conventional dielectric waveguide input/output coupling structure.

As illustrated inFIG. 6(a), a dielectric waveguide60comprises a dielectric block composed of a rectangular parallelepiped-shaped dielectric, and a conductor film62covering an exterior of the dielectric block, wherein the dielectric waveguide60has a bottom surface having an island-shaped input/output electrode61made of a conductor and surrounded by an exposed dielectric portion, i.e., an exposed portion of the dielectric. On the other hand, a printed circuit board70has a front surface having: a generally-circular island-shaped electrode71made of a conductor; and a front surface-side ground pattern74made of a conductor and insulated from the island-shaped electrode71, while surrounding periphery of the island-shaped electrode71in spaced-apart relation to the island-shaped electrode71.

The printed circuit board70has a back surface having a strip line72, wherein the island-shaped electrode71and a distal end of the strip line72are coupled together via a through-hole73.

The dielectric waveguide60is mounted on the printed circuit board70to allow the input/output electrode61to be disposed in face-to-face relation to the island-shaped electrode71.

This dielectric waveguide input/output coupling structure has a problem that a range of an applicable relative bandwidth is narrow.

As a solution for the above problem, a dielectric waveguide input/output coupling structure illustrated inFIG. 6(b) has been developed.FIG. 6(b) is an exploded perspective view illustrating another example of the conventional dielectric waveguide input/output coupling structure.

As illustrated inFIG. 6(b), a dielectric waveguide80comprises a dielectric block composed of a rectangular parallelepiped-shaped dielectric, and a conductor film82covering an exterior of the dielectric block, wherein the dielectric waveguide80has a bottom surface having a generally quadrangular input/output electrode81made of a conductor and surrounded by an exposed dielectric portion, i.e., an exposed portion of the dielectric.

On the other hand, a printed circuit board100has a front surface having: a strip line102; a generally-quadrangular island-shaped electrode101located at a distal end of the strip line102; and a front surface-side ground pattern104made of a conductor and insulated from the island-shaped electrode101, while surrounding periphery of the island-shaped electrode101in spaced-apart relation to the island-shaped electrode101.

The dielectric waveguide80is mounted on the printed circuit board100while interposing therebetween a spacer90having an outer surface made of a conductor, to allow the input/output electrode81to be disposed in spaced-apart, face-to-face relation to the island-shaped electrode101.

This dielectric waveguide input/output coupling structure has one problem that the relative bandwidth can be widened only at a frequency of 5 GHz or more, and another problem that downsizing and weight reduction of the input/output coupling structure will be hindered due to an increase in the number of components of the input/output coupling structure, an increase in size of the dielectric waveguide required for electromagnetic coupling, etc., and the input/output coupling structure will become complicated.

It is an object of the present invention to provide a dielectric waveguide input/output coupling structure capable of facilitating aligning of a dielectric waveguide with respect to a printed circuit board, and exhibiting low-loss and wideband characteristics even at a frequency of less than 5 GHz, with a simple configuration.

Means For Solving the Problem

In order to achieve the above object, according to one aspect of the present invention, there is provided a dielectric waveguide input/output coupling structure for coupling an input/output electrode of a dielectric waveguide and a strip line on a printed circuit board together, wherein the dielectric waveguide comprises: a generally circular input/output electrode provided on a bottom surface of the dielectric waveguide and surrounded by an exposed dielectric portion of the dielectric waveguide around which a conductor film is disposed; and a short stub crossing through the exposed dielectric portion to couple the input/output electrode and the conductor film together.

According to another aspect of the present invention, in addition to the above feature, the printed circuit board has a front surface having a generally-circular island-shaped electrode and a front surface-side ground pattern surrounding the island-shaped electrode in spaced-apart relation to the island-shaped electrode, and a back surface having a strip line and a back surface-side ground pattern surrounding the strip line in spaced-apart relation to the strip line, wherein an approximately central portion of the island-shaped electrode and one end of the strip line are coupled together, and the front surface-side ground pattern and the back surface-side ground pattern are coupled together, and wherein the input/output electrode of the dielectric waveguide and the island-shaped electrode of the printed circuit board are coupled together.

Effect of the Invention

The dielectric waveguide input/output coupling structure of the present invention can exhibit wideband and low-loss characteristics without causing an increase in the number of components.

DESCRIPTION OF EMBODIMENTS

FIG. 1is an exploded perspective view illustrating a dielectric waveguide input/output coupling structure according to one embodiment of the present invention.

As illustrated inFIG. 1, a dielectric waveguide10comprises a dielectric block composed of a rectangular parallelepiped-shaped dielectric, and a conductor film12covering an exterior of the dielectric block, wherein the dielectric waveguide10has a bottom surface having a generally circular input/output electrode11made of a conductor and surrounded by an exposed dielectric portion (i.e., an exposed portion of the dielectric) of the dielectric waveguide10. The input/output electrode11and the conductor film12are coupled together via a short (short-circuiting) stub13made of a conductor and formed to cross through the exposed dielectric portion.

On the other hand, a printed circuit board20has a front surface having: a generally-circular island-shaped electrode21made of a conductor; and a front surface-side ground pattern24made of a conductor and insulated from the island-shaped electrode21, while surrounding periphery of the island-shaped electrode21in spaced-apart relation to the island-shaped electrode21.

The printed circuit board20has a back surface having: a strip line22for connection to an external circuit; and a back surface-side ground pattern25made of a conductor and formed to surround the strip line22in spaced-apart relation to the strip line22.

The island-shaped electrode21and the strip line22are coupled together via a through-hole23provided at an approximately central portion of the island-shaped electrode21, and the front surface-side ground pattern24and the back surface-side ground pattern25are coupled together via a through-hole group26consisting of a plurality of through-holes provided to surround periphery of the island-shaped electrode21.

The dielectric waveguide10is disposed on the printed circuit board20to allow the input/output electrode11and the island-shaped electrode21to be coupled together.

FIGS. 2(a) and2(b) are schematic diagrams illustrating the input/output electrode of the dielectric waveguide and the island-shaped electrode of the printed circuit board inFIG. 1, whereinFIG. 2(a) is a bottom view of the dielectric waveguide, andFIG. 2(b) is a top view of the printed circuit board.

As illustrated inFIG. 2(a), the input/output electrode11has a diameter d1, and the short stub13crossing through the exposed dielectric portion to couple the input/output electrode11and the conductor film12together has a width w. The width w of the short stub13crossing through the exposed dielectric portion is set to be less than the diameter d1.

As illustrated inFIG. 2(b), the island-shaped electrode21has a diameter d2.

The diameter d2of the island-shaped electrode21is set to be less than the diameter d1of the input/output electrode11, so that a required level of mounting position accuracy can be lowered to facilitate aligning of the dielectric waveguide.

FIG. 3illustrates one example of a dielectric waveguide filter using a dielectric waveguide input/output coupling structure according to the present invention.

A dielectric waveguide filter30is a 5-stage filter using five dielectric waveguide resonators. Each of the five dielectric waveguide resonators is composed of a rectangular parallelepiped-shaped dielectric waveguide (31to35) comprising a dielectric block and a conductor film covering the dielectric block.

The dielectric waveguides31to35are arranged side-by-side in a line, and adjacent ones of the dielectric waveguides31to35are coupled together via coupling windows40each provided on a respective one of opposed side surfaces thereof to expose a portion of a dielectric thereof. Each of the two dielectric waveguides31,35located at opposite ends of the dielectric waveguide filter30has a bottom surface having a generally circular input/output electrode (41,42) made of a conductor and surrounded by an exposed dielectric portion thereof, wherein the input/output electrode (41,42) and the conductor film are coupled together via a short stub (43,43).

On the other hand, a printed circuit board50has a front surface having: two generally-circular island-shaped electrodes51,52; and two front surface-side ground patterns54surrounding periphery of respective ones of the island-shaped electrodes51,52. Each of the island-shaped electrodes51,52is insulated from a corresponding one of the front surface-side ground patterns54.

The printed circuit board50has a back surface having non-illustrated two strip lines, and non-illustrated two back surface-side ground patterns surrounding periphery of respective ones of the strip lines. Each of the strip lines is insulated from a corresponding one of the back surface-side ground patterns.

The dielectric waveguide filter30is disposed on the printed circuit board50to allow the input/output electrode41and the island-shaped electrode51to be coupled together and allow the input/output electrode42and the island-shaped electrode52to be coupled together.

FIG. 4is a graph illustrating a relative bandwidth measured when the width w of the short stub and the diameter d1of the input/output electrode are changed in the dielectric waveguide filter using the dielectric waveguide input/output coupling structure according to the present invention as illustrated inFIG. 3.

InFIG. 4, the horizontal axis represents the diameter d1[mm] of the input/output electrode, and the vertical axis represents the relative bandwidth. The characteristic curve2and the characteristic curve1were obtained when the width w of the short stub is set, respectively, to 2.0 [mm] and 1.0 [mm], and the characteristic curve3was obtained in a dielectric waveguide filter devoid of the short stub.

The relative bandwidth was calculated under the following conditions: a center frequency f=2.6 [GHz]; a return loss RL=20 [dB]; and the number n of dielectric waveguide resonators=5.

FIG. 5is a graph illustrating a transmission characteristic of the dielectric waveguide filter mounted on the printed circuit board50as illustrated inFIG. 3, under the following conditions: the center frequency f=2.6 [GHz]; the width w of the short stub=1.0 [mm]; and the diameter d1of the input/output electrode=4.6 [mm]. InFIG. 5, the horizontal axis represents the relative bandwidth, and the vertical axis represents the transmission characteristic [dB], wherein the solid line indicates a transmission characteristic curve obtained in the dielectric waveguide filter using the dielectric waveguide input/output coupling structure according to the present invention, and the dotted line indicates a transmission characteristic curve obtained in a comparative dielectric waveguide filter devoid of the short stub.

The results inFIGS. 4 and 5show that a bandwidth of the transmission characteristic can be widened by providing the short stub and setting each of the width of the short stub and the diameter of the input/output electrode to a desired value.

As described above, the dielectric waveguide input/output coupling structure of the present invention can be used to facilitate aligning and coupling between the input/output electrode of the dielectric waveguide and the island-shaped electrode of the printed circuit board, and minimize adverse effects on characteristics even if some degree of misalignment occurs, without causing an increase in the number of components. Thus, it becomes possible to provide a dielectric waveguide input/output coupling structure capable of facilitating aligning and coupling between the dielectric waveguide and the printed circuit board, and exhibiting wideband and low-loss characteristics, with a simple configuration.

In the above embodiment, the through-hole group26provided around the island-shaped electrode21can suppress unwanted radiation of electromagnetic wave in an input/output coupling region, and enhance isolation between adjacent input/output coupling regions, to provide further enhanced efficiency of the input/output coupling structure.

In cases where the printed circuit board20is a multilayer board having a plurality of wiring layers, the strip line22may be provided on an inner layer. Further, the short stub may be formed at any suitable position. The strip line22is not indispensable. For example, the strip line22may be omitted by providing a connector directly on the back surface of the printed circuit board, and directly coupling the connector to the through-hole.

REFERENCE NUMERALS