Plane filter

A plane filter includes a dielectric substrate, a filter part provided on the dielectric substrate, and an input/output line connected to the filter part on the dielectric substrate. The filter part and the input/output line are provided on a front surface of the dielectric substrate. The dielectric substrate includes first and second regions. The filter part is provided in the first region, and the input/output line is provided in the second region. The first region having a first thickness in a first direction toward the front surface from a back surface at a side opposite to the front surface. The second region having a second thickness in the first direction, the second thickness being less than the first thickness. The back surface includes a step corresponding to a difference between the first thickness and the second thickness.

CROSS-REFERENCE TO RELATED APPLICATION

This is a National Phase entry of International Application No. PCT/JP2021/010521, filed Mar. 16, 2021, which claims the benefit of Japanese Application No. 2020-046515, filed Mar. 17, 2020, the contents of each of which are incorporated herein by reference in their entireties.

TECHNICAL FIELD

An embodiment relates to a plane filter.

BACKGROUND ART

The plane filter that is provided on a dielectric substrate is used in a high-frequency band of not less than several GHz and includes, for example, a combination of distributed constant lines. Therefore, downsizing of the plane filter is limited.

PRIOR ART DOCUMENTS

Patent Literature

SUMMARY OF INVENTION

Technical Problem

Embodiments provide a downsized plane filter.

Solution to Problem

A plane filter according to an embodiment includes a dielectric substrate, a filter part provided on the dielectric substrate, and an input/output line connected to the filter part on the dielectric substrate. The filter part and the input/output line are provided on a front surface of the dielectric substrate. The dielectric substrate includes a first region and a second region. The filter part is provided in the first region, and the input/output line is provided on the second region. The first region has a first thickness in a first direction. The second region has a second thickness in the first direction that is less than the first thickness. The first direction is directed toward the front surface from a back surface at a side opposite to the front surface. The backside surface has a step corresponding to a difference between the first thickness and the second thickness.

DESCRIPTION OF EMBODIMENTS

Embodiments will now be described with reference to the drawings. The same portions in the drawings are marked with the same numbers; a detailed description is omitted as appropriate; and different portions are described. The drawings are schematic or conceptual; and the relationships between the thickness and width of portions, the proportions of sizes among portions, etc., are not necessarily the same as the actual values. Also, the dimensions and proportions may be illustrated differently among drawings, even when the same portion is illustrated.

Furthermore, the arrangements and configurations of the portions are described using an X-axis, a Y-axis, and a Z-axis shown in the drawings. The X-axis, the Y-axis, and the Z-axis are orthogonal to each other and respectively represent an X-direction, a Y-direction, and a Z-direction. Also, there are cases where the Z-direction is described as up, and the opposite direction is described as down.

FIGS.1A and1Bare schematic views showing a plane filter1according to an embodiment.

FIG.1Ais a plan view showing the front surface of a dielectric substrate DS.FIG.1Bis a cross-sectional view along line A-A shown inFIG.1A.

As shown inFIG.1A, the plane filter1includes the dielectric substrate DS, a filter part FLP, an input/output line IOL1, and an input/output line IOL2. The plane filter1includes multiple distributed constant lines provided on the front surface of the dielectric substrate DS.

The dielectric substrate DS includes a first region TR1and a second region TR2. The filter part FLP is provided on the first region TR1. The input/output lines IOL1and IOL2are provided on the second region TR2. The dielectric substrate DS is, for example, a PPE resin substrate.

The filter part FLP is located between the input/output line IOL1and the input/output line IOL2. The input/output line IOL1, the filter part FLP, and the input/output line IOL2are arranged in a direction (e.g., the X-direction) along the front surface of the dielectric substrate DS. The input/output line IOL1and the input/output line IOL2each extend in the X-direction and are connected to the filter part FLP. The input/output line IOL1and the input/output line IOL2each have a line width W0in a direction (e.g., the Y-direction) along the front surface of the dielectric substrate DS.

Assuming, for example, a hairpin filter, a microwave signal is input to the input/output line IOL1and output from the input/output line IOL2via the filter part FLP. Also, the microwave signal may be input to the input/output line IOL2and output from the input/output line IOL1via the filter part FLP.

The filter part FLP includes, for example, a resonator HR1, a resonator HR2, a resonator HR3, a first coupling line CL1, a second coupling line CL2, a connecting line IOLA, and a connecting line IOLB. The resonators HR1to HR3are apart from each other and arranged in, for example, the X-direction. The resonator HR2is provided between the resonator HR1and the resonator HR3.

The first coupling line CL1is provided between the connecting line IOLA and the resonator HR1. The first coupling line CL1is connected to the connecting line IOLA. Also, the first coupling line CL1is apart from the resonator HR1.

The second coupling line CL2is provided between the connecting line IOLB and the resonator HR3. The second coupling line CL2is connected to the connecting line IOLB. Also, the second coupling line CL2is apart from the resonator HR3.

The input/output line IOLA is provided between the first coupling line CL1and the input/output line IOL1. The input/output line IOLA is connected to the input/output line IOL1at the boundary between the first region TR1and the second region TR2. Also, the input/output line IOLA is connected to the first coupling line CL1on the first region TR1. For example, the input/output line IOLA has a width W0Ain the Y-direction. The width W0Ais less than a width W0in the Y-direction of the input/output line IOL1.

By providing the input/output line IOLA, the impedance discontinuity of the line is reduced, and the reflection of the microwave can be reduced between the input/output line IOL1and the first coupling line CL1.

The input/output line IOLB is provided between the second coupling line CL2and the input/output line IOL2. The input/output line IOLB is connected to the input/output line IOL2at the boundary between the first region TR1and the second region TR2. Also, the input/output line IOLB is connected to the second coupling line CL2on the first region TR1. For example, the input/output line IOLB has a width W0Bin the Y-direction. The width W0Bis less than the width W0in the Y-direction of the input/output line IOL2.

By providing the input/output line IOLB, the impedance discontinuity of the line is reduced, and the reflection of the microwave can be reduced between the input/output line IOL2and the second coupling line CL2.

The input/output line IOL1, the input/output line IOL2, the resonators HR1to HR3, the first coupling line CL1, and the second coupling line CL2each are metal layers provided on the dielectric substrate DS and include, for example, copper (Cu).

As shown inFIG.1B, the dielectric substrate DS has a first thickness ST1and a second thickness ST2in the direction (e.g., the Z-direction) from a back surface BS toward a front surface FS of the dielectric substrate DS. The first thickness ST1is less than the second thickness ST2. The dielectric substrate DS has the first thickness ST1in the first region TR1, and has the second thickness ST2in the second region TR2. Moreover, the dielectric substrate DS includes, for example, a step at the back surface BS side thereof. The step is provided at the boundary between the first region TR1and the second region TR2, and corresponds to a difference ΔT between the first thickness ST1and the second thickness ST2.

The dielectric substrate DS includes a metal layer10covering the back surface BS of the dielectric substrate DS. The metal layer10includes, for example, copper (Cu). The metal layer10also covers the step at the back surface BS side of dielectric substrate DS.

FIG.2is a partial plan view schematically showing the plane filter1according to the embodiment.FIG.2is a schematic view showing the filter part FLP.

As shown inFIG.2, the first resonator HR1includes a first line13, a second line15, and a third line17. The first line13and the second line15each extend in a direction (e.g., the Y-direction) along the front surface FS of the dielectric substrate DS. The first line13and the second line15are apart from each other and faces each other.

The first line13includes a first end13aand a second end13barranged in this order in the Y-direction. The second line15includes a first end15aand a second end15barranged in this order in the Y-direction. For example, the third line17extends in the X-direction and is connected to the second end13bof the first line13and the second end15bof the second line15.

The second resonator HR2includes a fourth line23, a fifth line25, and a sixth line27. The fourth line23and the fifth line25each extend in the Y-direction. The fourth line23and the fifth line25are apart from each other and faces each other.

The fourth line23includes a first end23aand a second end23barranged in this order in the Y-direction. The fifth line25includes a first end25aand a second end25barranged in this order in the Y-direction. For example, the sixth line27extends in the X-direction and is connected to the first end23aof the fourth line23and the first end25aof the fifth line25.

A third resonator HR3includes a seventh line33, an eighth line35, and a ninth line37. The seventh line33and the eighth line35each extend in the Y-direction. The seventh line33and the eighth line35are apart from each other and faces each other.

The seventh line33includes a first end33aand a second end33barranged in this order in the Y-direction. The eighth line35includes a first end35aand a second end35barranged in this order in the Y-direction. For example, the ninth line37extends in the X-direction and is connected to the second end33bof the seventh line33and the second end35bof the eighth line35.

The first resonator HR1and the second resonator HR2are apart from each other and arranged in the X-direction; and the second line15of the first resonator HR1faces the fourth line23of the second resonator HR2. Also, the first end15aof the second line15faces the first end23aof the fourth line23; and the second end35bof the second line15faces the second end23bof the fourth line23.

The second resonator HR2and the third resonator HR3are apart from each other and arranged in the X-direction; and the fifth line25of the second resonator HR2faces the seventh line33of the third resonator HR3. Also, the first end25aof the fifth line25faces the first end33aof the seventh line33; and the second end25bof the fifth line25faces the second end33bof the seventh line33.

The first coupling line CL1extends in the Y-direction and faces the first line13of the first resonator HR1in the X-direction. The first coupling line CL1includes a first end CLa and a second end CLb arranged in this order in the Y-direction and is connected to the connecting line IOLA at the first end CLa. Also, the first end CLa of the first coupling line CL1faces the first end13aof the first line13; and the second end CLb of the first coupling line CL1faces the second end13bof the first line13.

The second coupling line CL2extends in the Y-direction and faces the eighth line35of the third resonator HR3in the X-direction. The second coupling line CL2includes the first end CLa and the second end CLb arranged in this order in the Y-direction and is connected to the connecting line IOLB at the first end CLa. Also, the first end CLa of the second coupling line CL2faces the first end35aof the eighth line35; and the second end CLb of the second coupling line CL2faces the second end35bof the eighth line35.

The first coupling line CL1is connected to the X-direction end of the connecting line IOLA. The first coupling line CL1is connected at a position such that the first end CLa is shifted ΔW in the Y-direction from one of the two corners at the end of the connecting line IOLA. For example, the first coupling line CL1is connected to the connecting line IOLA with a connection width of W0A−ΔW, where W0Ais the Y-direction width of the connecting line IOLA.

The second coupling line CL2is similarly connected to the X-direction end of the connecting line IOLB. In other words, the second coupling line CL2is connected at a position such that the first end CLa is shifted ΔW in the Y-direction from one of the two corners at the end of the connecting line IOLB. For example, the second coupling line CL2is connected to the connecting line IOLB with a connection width of W0B−ΔW, where W0Bis the Y-direction width of the connecting line IOLB.

A width W1in the X-direction of the first line13, a width W2in the X-direction of the second line15, a width W4in the X-direction of the fourth line23, a width W5in the X-direction of the fifth line25, a width W7in the X-direction of the seventh line33, and a width W8in the X-direction of the eighth line35are, for example, less than the width W0Ain the Y-direction of the connecting line IOLA and the width W0Bin the Y-direction of the connecting line IOLB. For example, the widths W1, W2, W4, W5, W7, and W8are substantially the same.

A width W3in the Y-direction of the third line17, a width W6in the Y-direction of the sixth line27, and a width W9in the Y-direction of the ninth line37are, for example, less than the width W0. For example, the widths W3, W6, and W9are substantially the same.

According to the embodiment, the first to ninth lines13-37, the first coupling line CL1, and the second coupling line CL2each have, for example, a characteristic impedance of 85Ω. Also, the first connecting line IOLA, the second connecting line IOLB, the input/output line IOL1, and the input/output line IOL2each have, for example, a characteristic impedance of 50Ω. Therefore, in the filter part FLP provided on the first region TR1, the widths W1to W9of the first to ninth lines13-37, a width WC1in the X-direction of the first coupling line CL1, and a width WC2in the X-direction of the second coupling line CL2are, for example, narrower than such widths when the filter part FLP is provided on a dielectric substrate that does not include the first region TR1. Furthermore, the distances between the lines next to each other in the X-direction can be reduced. Thereby, a width WF1in the X-direction of the filter part FLP is narrower compared to, for example, when provided on a dielectric substrate that does not include the first region TR1. As a result, the plane filter1is downsized compared to that provided on a dielectric substrate that does not include the first region TR1. A width WF2in the Y-direction of the filter part FLP is, for example, substantially the same as λ/4 (λ: microwave wavelength).

For example, the plane filter can be downsized by making the dielectric substrate thin. However, when the dielectric substrate is made thin, the substrate easily warps, and the mechanical strength of the substrate is reduced. According to the embodiment, by providing the first region TR1and the second region TR2, the plane filter1can be downsized while maintaining the mechanical strength of the dielectric substrate DS.

FIG.3is a graph showing characteristics of the plane filter1according to the embodiment. The horizontal axis is the microwave frequency (GHz), and the vertical axis is a transmission coefficient (dB) and a reflection coefficient (dB) of the microwave.

As shown inFIG.3, the plane filter1is a band-pass filter having a center frequency of 20 GHz. The pass characteristic is about negative 2.8 dB, and the passband width is about 1.5 GHz.

In the example, the dielectric substrate DS is a PPE resin substrate. The first thickness ST1of the first region TR1is 0.2 mm, and the second thickness ST2of the second region TR2is 0.4 mm. The width WF1in the X-direction of the filter part FLP is 2.95 mm, and the width WF2in the Y-direction is 2.25 mm.

For example, a plane filter4shown inFIG.6is provided on a dielectric substrate having a Z-direction thickness of 0.4 mm. The plane filter4is provided on a dielectric substrate having a uniform thickness and does not include the first region TR1. As shown inFIG.7, the plane filter4has a pass characteristic equivalent to that of the plane filter1; and the X-direction width of the filter part FLP of the plane filter4is 4.3 mm. In other words, in the plane filter1according to the embodiment, it is possible to reduce the surface area of the dielectric substrate about 35% without changing the pass characteristic.

FIG.4is a schematic view showing a plane filter2according to a first modification of the embodiment. The plane filter2includes the filter part FLP, the input/output line IOL1, and the input/output line IOL2provided on the front surface of the dielectric substrate DS. The filter part FLP is provided on the first region TR1. The input/output lines IOL1and IOL2are provided on the second region TR2.

In the example, the filter part FLP includes the resonator HR1, the resonator HR2, the first coupling line CL1, the second coupling line CL2, the connecting line IOLA, and the connecting line IOLB. The arrangement of the input/output line IOL1, the connecting line IOLA, the first coupling line CL1, and the resonator HR1is the same as that of the plane filter1.

The second coupling line CL2is provided between the resonator HR2and the connecting line IOLB and faces the fifth line25of the resonator HR2. The first end25aof the fifth line25faces the first end CLa of the second coupling line CL2. The second end25bof the fifth line25faces the second end CLb of the second coupling line CL2. The connecting line IOLB is connected to the second end CLb of the second coupling line CL2.

The connecting line IOLB is connected to the input/output line IOL2at the boundary between the first region TR1and the second region TR2. The input/output line IOL2extends in the X-direction along the front surface of the dielectric substrate DS.

Thus, the resonators HR1to HR2are appropriately arranged between the first coupling line CL1and the second coupling line CL2to obtain the desired filter characteristics. The number of resonators is not limited to these examples; for example, three or more resonators may be provided between the first coupling line CL1and the second coupling line CL2.

FIGS.5A and5Bare schematic views showing a plane filter3according to a third modification of the embodiment.FIG.5Ais a plan view showing the front surface of the dielectric substrate DS.FIG.5Bis a cross-sectional view along line B-B shown inFIG.5A.

The plane filter3includes the filter part FLP, the input/output line IOL1, and the input/output line IOL2provided on the front surface of the dielectric substrate DS. The filter part FLP is provided on the first region TR1. The input/output lines IOL1and IOL2are provided on the second region TR2.

As shown inFIG.5A, the dielectric substrate DS further includes a third region TR3. The third region TR3is provided between the first region TR1and the second region TR2. The plane filter3further includes the connecting line IOLA and the connecting line IOLB extending over the first region TR1and the third region TR3.

The connecting line IOLA is provided between the first coupling line CL1and the input/output line IOL1. The connecting line IOLA is connected to the input/output line IOL1at the boundary between the second region TR2and the third region TR3. Also, the connecting line IOLA is connected to the first coupling line CL1in the first region TR1.

For example, the connecting line IOLA has the width W0in the Y-direction at the boundary between the second region TR2and the third region TR3. Also, the connecting line IOLA has the width W0Ain the Y-direction on a first region TR. The connecting line IOLA has the width W0Ain the Y-direction at the boundary between the first region TR1and the third region TR3. The width W0Ais less than the width W0. The Y-direction width of the connecting line IOLA becomes narrower from the boundary of the second region TR2and the third region TR3toward the boundary of the first region TR1and the third region TR3.

The connecting line IOLB is provided between the second coupling line CL2and the input/output line IOL2. The connecting line IOLB is connected to the input/output line IOL2at the boundary of the second region TR2and the third region TR3. Also, the connecting line IOLB is connected to the second coupling line CL2in the first region TR1.

For example, the connecting line IOLB has the width W0in the Y-direction at the boundary of the second region TR2and the third region TR3. Also, the connecting line IOLB has the width W0Bin the Y-direction on the first region TR1. Also, the connecting line IOLB has the width W0Bin the Y-direction at the boundary of the first region TR1and the third region TR3. The width W0Bis less than the width W0. The Y-direction width of the connecting line IOLB becomes narrower from the boundary of the second region TR2and the third region TR3toward the boundary of the first region TR1and the third region TR3.

As shown inFIG.5B, for example, the dielectric substrate DS has the second thickness ST2at the boundary of the second region TR2and the third region TR3. Also, the dielectric substrate DS has the first thickness ST1at the boundary of the first region TR1and the third region TR3. In other words, a third thickness ST3of the third region TR3becomes thin toward the first region TR1.

For example, the dielectric substrate DS has a third thickness ST3Aat a first position P1in the third region TR3, and has a third thickness ST3Bat a second position P2. The first position P1is positioned between the first region TR1and the second position P2; and the third thickness ST3Ais less than the third thickness ST3B.

By the configuration described above, for example, the connecting line IOLA and the connecting line IOLB are provided to each have a characteristic impedance of 50Ω.

In the example, the reflection of the microwave can be further reduced between the input/output line IOL1and the first coupling line CL1and between the input/output line IOL2and the second coupling line CL2.

While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. These novel embodiments may be embodied in a variety of other forms; and various omissions, substitutions, and changes may be made without departing from the spirit of the inventions. Such embodiments and their modifications are within the scope and spirit of the inventions, and are within the scope of the inventions described in the claims and their equivalents.