JP2007013368A - Bandpass filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an improved type bandpass filter suitable for a 60GHz band using low-temperature co-fire ceramic. <P>SOLUTION: This bandpass filter comprises a base which is made of low-temperature co-fire ceramic and has one or more holes, and a coplanar waveguide which is patterned on the base and covers one or more holes. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

    The present invention relates to a band-pass filter, and more particularly to a band-pass filter suitable for the 60 GHz band and designed based on LTCC (low temperature co-fired ceramic).

Various techniques have been proposed for designing low-pass filters and band-pass filters. For example, techniques for designing these filters are described in the following non-patent documents.
M. Kim, B. Lee “New L-shaped DGS for Coplanar Waveguide” 2003, Asia-Pacific Microwave Conference, Vol. 3, pp. 1454-1457 JS Lim, CS Kim, YT Lee, D. Ahn, S. Nam “Helical defect ground structure for coplanar waveguide” IEEE microwave and Wireless Components Letters, Vol. 12, No. 9, pp. 330-332, 2002 September TY Yun, K. Chang “Resonator with one-plane one-dimensional optical bandgap structure” IEEE Trans. Microwave Theory Tech. 49, 549-533, March 2001 YQ Fu., GH Zhang, NC Yuan "New PBG Coplanar Waveguide" IEEE microwave and Wireless Components Letters, Vol. 11, No. 9, pp. 447-449, November 2001 SW Wang, CL Wang, RB Wu “New Uniplanar Bandpass Filter with Coplanar Waveguide-Fed Step Perturbed Throttling Resonator” 2003 Asia-Pacific Microwave Conference, Volume 3, pages 669-672 Rainee N. Simons "Coplanar Waveguide Circuits, Elements, Systems" John Wiley & Sons, Inc, 2001

  As a useful method, a defective ground structure (DGS) [Non-Patent Document 1] [Non-Patent Document 2] has been proposed for designing a low-pass filter and a band-pass filter. Since a small number of DGSs may be used to construct the filter, the DGS is simpler than the optical bandgap (PBG) structure [Non-Patent Document 3] [Non-Patent Document 4].

  However, many PBGs must be used to design a filter using PBGs. In addition, since it is possible to approximate a simple RLC (resistance, inductance, capacitance) circuit to DGS, DGS can easily adjust and design its operating frequency range, especially according to the microstrip line structure. it can.

  The conventional DGS unit can cause the cutoff frequency and the attenuation pole to appear at a certain frequency without arranging the DGS in a periodic array.

  Traditionally, DGS or PBG has been used to design microstrip filters. Many papers on DGS applications have been published and various DGS structures are used in FIG.

  However, few papers have been published on the design of coplanar filters [Non-Patent Document 1] and [Non-Patent Document 2] using DGS. The coplanar waveguide (CPW) is an important element for planar circuit design, as is the microstrip line and slot line. There are various CPW structures [Non-Patent Document 6].

  The basic structure of CPW is composed of three coplanar striplines. As shown in FIG. 2 (a), the double-sided stripline has an infinite width. This structure is actually used only for theoretical and analytical work.

  Specifically, in a microwave integrated circuit (MIC), the CPW must be connected to a microstrip structure or have a conductor back ground. The two side grounds are connected to the conductor back ground by wiring or vias to form one ground (ie, can operate at equal voltage levels).

  Another problem is that the width of the side ground is finite in an actual circuit. Of course, in some cases, as long as the width is sufficiently large, this structure can be regarded as a conventional CPW [Non-Patent Document 6].

  The object of the present invention is to propose an improved bandpass filter suitable for the 60 GHz band, in particular based on LTCC.

  The object of the present invention and the problems solved by the present invention are achieved by the following technical solutions.

  The bandpass filter is made of a low temperature co-fired ceramic and has a base having one or more holes, a coplanar waveguide that is patterned on the base and covers the one or more holes, Is provided.

As the first and second embodiments, a new filter based on DGS and CPW is proposed.

1. First embodiment-based on DGS and CPW

1.1 Conventional DGS based on CPW for stopband filters

  Prior art of using DGS based on CPW is disclosed in [Non-patent Document 1] [Non-Patent Document 2]. Based on these papers, we will design a DGS-CPW filter that can operate at 60 GHz by changing DGS and CPW parameters.

Three examples of basic DGS based on CPW are used in FIGS. 2 (a), 3 (a), and 4 (a). These S parameters are Ansoft HFSS9.0
And are shown in FIGS. 2 (b), 3 (b) and 4 (b), respectively.

  In these three designs, DGS shows good stopband characteristics at each resonance frequency. A paper discussing the approximation of DGS using microstrip by RLC circuit has been published. Based on the RLC circuit, the resonant frequency can be easily adjusted and the stopband DGS structure can be designed quickly.

  In fact, the DGS structure is a resonant structure. An appropriate DGS structure can be selected according to the resonance frequency required by us.

  In some cases, DGS may have a helical structure. If it is desired to design the DGS structure in a small size, a spiral having a larger number of cycles may be used.

  The largest volume structure of DGS is a rectangular waveguide.

DGS must be designed based on frequency and manufacturing requirements. 2 to 4, the double-sided conductor has an infinite width. A conductor back ground is not required.

1.2 DGS design based on BGCPW for bandpass filters

  Our goal is to design and improve a filter based on DGS and CPW with an operating frequency of about 60 GHz and a bandwidth of 1 GHz.

Considering MMIC, package, and dimensional requirements, it is desirable to design the filter using conductor backside CPW (CBCPW) technology and low temperature co-fired ceramic (LTCC) technology.

In the design shown below, the substrate parameters are er = 8.7, mr = 1, tand = 0.0015, and the thickness is 0.2 mm.

1.2.1 Case 1

  First, consider etching two DGSs into CBCPW.

The structure is shown in FIG. Its structural parameter (mm) is
sg = 0.4
s = 0.0925
w = 0.075
dgs1 = 0.2
dgs2 = 0.15
dgs3 = 0.1
dgs4 = 0.225
Via hole R = 0.1
t1 = 0.1
t2 = 0.1
viaholed = 0.3
It is.

  Based on this structure, t1 is fixed, tabdw = 0.075mm, tabdw1 = 0.26mm, and the S parameter when t2 is moved (just to select a different tabdl) is shown in FIG.

  From this figure, it can be seen that as tabdl decreases, the results become better, but the bandwidth increases. In order to connect the side ground and the conductor back ground in Fig. 7 (a), considering that the field at the edge of the DGS spreads radially when the via hole is not used to connect the two grounds of the DGS part. Two groups of via holes were added near DGS. To analyze the effects of tabdw, select different tabdw values, such as 0.2, 0.3, and 0.46, respectively. In this case, tabdw1 = 0.46 mm and tabdl = 0.1 mm.

  FIG. 7B shows a comparison result of these tabdw values for the S parameter.

  From this figure, it can be seen that as the tabdw is increased, the S parameter is improved, but the bandwidth is increased. Therefore, in the future, an appropriate tabdw must be selected that achieves both bandwidth and S-parameters.

In summary, in this design, this design is not successful because either S-parameters or bandwidth do not meet the design requirements.

1.2.2 Case 2

Consider other possibilities. In this design, as shown in FIG. 8A, two slots of the DGS are connected by a strip line. The configuration of this design is shown in FIG. The parameters of this design are
sg = 0.4
s = 0.095
w = 0.075
dgs1 = 0.22
dgs2 = 0.15
dgs3 = 0.1
dgs4 = 0.225
tabdw = ...
c1 = ...
t1 = 0.1
cw = ...
viaholed = 0.15
sviaholed = 0.28
sviaholel = 0.18
It is.

  First, let us consider the effect of the DGS placement position when cl = 0.1 and cw = 0.075. The DGS placement position is moved symmetrically along the x direction (referred to as tabdw). FIG. 9 shows that the S parameter improves as tabdw increases. However, the intermediate operating frequency is reduced and the bandwidth is increased.

  The major contribution of this design to our future design is that it was found that good S-parameters can be obtained by moving the DGS placement position and adjusting the intermediate operating frequency within a small range. . Next, the discontinuity of the central strip line is analyzed. FIG. 8 shows the structure and parameter configuration. All parameters in this example are set in Table 2, and tabdw = 0.56 mm.

  FIG. 10 shows changes in S parameters when cw is changed variously at cl = 0.5 mm.

  From this figure, it can be seen that the S parameter improves as cl decreases. Although bandwidth is narrowed, the change is not significant. Therefore, to obtain better results, cl should be selected as the minimum trace width according to the manufacturer's design rules.

  Similarly, FIG. 11 shows a change in S parameter when cw is changed at cl = 0.26 mm.

  From this figure, it can be seen that better results are obtained as cw decreases. In exchange, the bandwidth is somewhat reduced. Therefore, to obtain good S-parameters and narrow bandwidth, cw should be the minimum trace width according to manufacturing requirements.

  Therefore, to get good results, cl and cw should be narrowed as soon as possible. To do so, it is an easy choice to select the minimum trace width based on the manufacturer's requirements. Due to manufacturing limitations, this design does not have sufficient tuning parameters to tune the result of narrowing bandwidth.

However, with this design, the minimum value should be selected for cl and cw, and the bandwidth and S parameter can be changed by moving the DGS placement position (tabdw). The design experience about a kind of CPW-DGS filter design could be obtained.

1.2.3 Case 3

  The previous two designs also assumed that the central stripline was not short. In this example, it is assumed that the central strip line is cut and divided into two parts. This structure is shown in FIG. The S parameter of this structure is shown in FIG.

Obviously, according to our design requirements, S-parameters are unacceptable. This aspect will be omitted in the future.

1.2.4 Case 4

Based on Cases 1 and 2, the new design shown in FIG. 13 is proposed. The basic parameters of this design are
sg = 0.4
s = 0.095
w = 0.075
dgs1 = 0.225
dgs2 = 0.125
dgs3 = 0.125
dgs4 = 0.225
tabdw = 0.075
tabdl = ...
tabdw1 = ...
t1 = 0.075
t2 = ...
sviaholed = 0.28
viaholed = ...
sviaholew = 0.18
Via hole radius = 0.1
It is.

  It is clear that this design is a combination of the first and second designs.

  First, the characteristics of the moving DGS (referred to as tabdw1) are analyzed. FIG. 14 (b) shows a comparison of S-parameters when the CPW via hole arrangement and DGS parameters are variable. In FIG. 14B, viaholed = 0.15 mm, t2 = 0.15, tabdl = 0.1 mm, px = 0.18 mm, and py = 0.08 mm. In this figure, a result similar to that obtained in FIG. 9 is obtained.

  This characteristic can be used to change the bandwidth and intermediate operating frequency. In both FIG. 9 and FIG. 14, when the value of tabdw1 is changed, the turn point on the right side is almost unchanged.

  Discuss the effects of side via holes. FIG. 15 shows S parameters when the position of the center point of the via hole is changed. In FIG. 15, tabdw1 = 0.72 mm, t2 = 0.075, tabdl = 0.1 mm, px = 0.23 mm, and py = 0.03 mm.

  From this figure, it can be seen that when the via hole is moved away from the DGS (referred to as viaholed), the intermediate operating frequency decreases. It can also be seen that the bandwidth is almost constant. Finally, the DGS slot is analyzed at tabdw1 = 0.72 mm, t2 = 0.075, tabdl = 0.1 mm, px = 0.23 mm, py = 0.03 mm, and viaholed = 0.15 mm.

A comparison of S parameters is shown in FIG. From this figure, it can be seen that the bandwidth decreases as the slot width decreases.

1.3 Final design

Based on the background discussion above, the final design is shown in FIG. 17 by adjusting the via hole location, DGS location, and central stripline tab. The structural parameters of this design are
sg = 0.4
s = 0.0925
w = 0.075
dgs1 = 0.225
dgs2 = 0.125
dgs3 = 0.125
dgs4 = 0.225
tabdl = 0.1
tabdw = 0.075
tabdw1 = 0.26
t1 = 0.075
t2 = 0.12
sviaholed = 0.24
viaholed = 0.235 / 0.28
sviaholew = 0.2
px = 0
py = 0
py1 = 0
It is.

  The S parameters of the final CPW-DGS filter based on these design parameters are shown in FIGS. FIG. 18 shows a case where viaholed = 0.28 mm, and FIG. 19 shows a case where viaholed = 0.235 mm.

The detailed simulation parameters for this filter for 59.5 GHz are:
Pass bandwidth: 58.85 to 60.0 GHz (2%)
Return loss: <2dB
Insertion loss:> 18dB
Turn bandwidth: 4.5GHz (5%)
3dB bandwidth: ~ 0.5GHz

The parameters for 61.5 GHz are
Pass bandwidth: 61-62 GHz (1.7%)
Return loss: <2dB
Insertion loss:> 15dB
Turn bandwidth: 5.4GHz (5%)
3dB bandwidth: ~ 0.5GHz

2. Second embodiment-based on DGS

  In the first embodiment, the CPW-DGS filter was successfully designed, and the results were reasonable and acceptable. Next, consider another type of CPW-DGS filter structure.

The DGS structure is shown in FIG. Start with a basic DGS-CPW structure to create the final design.

2.1 Basic design borrowed from conventional DGS CPW design

  First, consider the structure shown in FIG. The S parameter of this structure is shown in FIG.

From this result, it can be seen that this filter has a stop band characteristic. The stop band range is 55 GHz to 60 GHz. However, the return loss was not significant in this bandwidth.

2.2 Modified design based on BGCPW for bandpass filters

Taking the idea of the first design, let's modify the basic design shown in FIG.

2.2.1 Case 1

  First, connect the two slots of DGS with one slot line. FIG. 21A shows this structure, and FIG. 21B shows the S parameter of this structure.

From this figure, it can be seen that this design has good S-parameters at intermediate operating frequencies and good stopband characteristics at high frequencies. However, this design has too wide operating bandwidth and turn bandwidth.

2.2.2 Case 2

Consider two striplines connected to two groups of DGS shoulders. The structure and configuration parameters are shown in FIG. The basic parameters are
sg = 0.4
s = 0.095
w = 0.075
dgs1 = 0.25
dgs2 = 0.147
dgs3 = 0.15
dgs4 = 0.225
tabdx = ...
tabdy = ...
t1 = 0.075
t2 = 0.075
t3 = 0.095
sviaholex = 0.175
sviaholey = 0.28
sviaholew = 0.2
px = 0
py = 0
viaholed = ...
It is.

  In the following test, some parameters such as tabdw, tabdl, and dgs parameters are analyzed.

  First, consider changing the value of tabdy symmetrically at tabdx = 0.72mm.

  FIG. 23 shows the S parameter in this case. As tabdy increases, bandwidth decreases. At the same time, the S parameter changes. However, when the two tab lines are brought into contact with the CPW terminal, the right side turn point does not change, but the S parameter deteriorates.

  Therefore, tabdy should be reasonably variable according to manufacturing requirements.

  Next, adjust tabdx parameters symmetrically at tabdy = 0.225mm. FIG. 24 shows the S parameter in this case. Moving the two DGSs to the center stripline narrows the bandwidth, but the right side turn point is almost unchanged.

  From these two examples, it can be seen that tabdy and tabdx should be changed within a reasonable range in order to obtain narrowband characteristics. Tabdy and tabdx were also used to change the intermediate operating frequency. However, this is not a very good idea because changing the intermediate operating frequency also changes its bandwidth.

  Finally, change the DGS size. FIG. 25 shows the S parameters with different DGS configurations (dgs1, dgs2, dgs3, dgs4). From this figure, when the dgs configuration is changed, the S parameter, the intermediate operating frequency, and the turn point also change.

  It became clear that the DGS structure should be changed when it is desired to change from one intermediate operating frequency to another. However, due to manufacturing limitations, this idea cannot ultimately be used.

In practice, as the etched area of the DGS increases, the effective series inductance of the DGS increases, and the cutoff frequency decreases as the series inductance increases.

2.2.3 Case 3

In this section, the first and second test designs are combined to create a third test CPW-DGS filter. The structure and configuration are shown in FIG. To test this design, some parameters are set first.
sg = 0.4
s = 0.095
w = 0.075
dgs1 = 0.25
dgs2 = 0.097
dgs3 = 0.1
dgs4 = 0.225
tabdx = 0.52
tabdy = 0.3
t1 = 0.075
t2 = 0.075
t3 = 0.075
sviaholey = 0.28
sviaholex = 0.175
px = 0.13
py = 0.05

  First, the characteristics of t3 used to connect two slots of DGS are tested at viaholed = 0.13mm. FIG. 27 shows a comparison result when t3 is present and when t3 is absent.

In the same configuration, the S parameter without t3 transitions to a high frequency and has a good stopband characteristic at a high frequency. However, the bandwidth without t3 is wider than with t3. Next, we will discuss the stripline (SS) used to connect the two slots of DGS at viaholed = 0.13mm.
FIG. 28 shows the S parameter when the distance between the two DGSs is fixed, 0.72 mm (referred to as tabdx), and the SS length is changed.

  If the length of SS is less than 2s + w, the S parameter changes in reverse. However, when the SS length increases and becomes greater than 2s + w, the S parameter transitions to a higher frequency.

  Now consider the effect of via holes in CPW. FIG. 29 shows parameters when different via hole positions are selected. It is clear that the S parameter transitions to high frequency when the via hole approaches DGS.

  Finally, FIG. 30 shows S parameters when the two DGSs are moved symmetrically. Similar results were obtained with the second test filter. If the two DGSs are moved symmetrically apart, the S parameter transitions to a lower frequency.

2.3 Final design

Based on the background discussion above, the final structure parameters obtained by adjusting the via hole position, DGS position, and center strip line tab are:
sg = 0.4
s = 0.095
w = 0.075
dgs1 = 0.25
dgs2 = 0.097
dgs3 = 0.1
dgs4 = 0.225
tabdx = 0.52
tabdy = 0.3
t1 = 0.075
t2 = 0.075
t3 = 0.075
sviaholed = 0.28
viaholed = 0.112 / 0.14
px = 0.13
py = 0.05
It is.

  When viaholed is 0.14 mm, a DGS-CPW filter having an intermediate operating frequency in the vicinity of 59.5 GHz is obtained. FIG. 31 shows detailed S parameters.

  When viaholed is 0.112 mm, a DGS-CPW filter having an intermediate operating frequency in the vicinity of 61.5 GHz is obtained. FIG. 32 shows the S parameter.

The design performance of these two filters for 59.5 GHz is
Pass bandwidth: 59-59.9 GHz (1.5%)
Return loss: <2dB
Insertion loss:> 15dB
Turn bandwidth: 4.5GHz (7.5%)
3dB bandwidth: ~ 1GHz
It is.

The performance for 61.5GHz is
Pass bandwidth: 61-62 GHz (1.55%)
Return loss: <2dB
Insertion loss:> 15dB
Turn bandwidth: 5GHz (8%)
3dB bandwidth: ~ 0.8GHz
It is.

  In this application, an improved bandpass filter has been proposed. Various embodiments and modifications can be made without departing from the broad spirit and scope of the invention. The above-described embodiments are for explaining the present invention and do not limit the scope of the present invention.

  The scope of the present invention is defined by the appended claims rather than the embodiments. Various modifications made within the scope of the equivalents of the claims and the scope of the claims according to the present invention are considered to be included in the scope of the present invention.

FIG. 1 is a schematic diagram showing several types of DGS for microstrip use. FIG. 2 is a schematic diagram showing a conventional CPW DGS 1 with a stopband design. FIG. 3 is a schematic diagram showing a conventional CPW DGS2 with a stopband design. FIG. 4 is a schematic diagram showing a conventional CPW DGS 3 with a stopband design. FIG. 5 is a schematic diagram showing the configuration of a filter design that was first prototyped based on DGS. FIG. 6 is a schematic diagram comparing S parameters in different tabdls. FIG. 7 is a schematic diagram showing a CPW-DGS filter structure and its S parameters in different tabdw. FIG. 8 is a schematic diagram showing the configuration of a filter design that was second prototyped based on DGS. FIG. 9 is a schematic diagram illustrating the CPW-DGS filter structure and the characteristics of the DGS position. FIG. 10 is a schematic diagram for comparing S parameters when cl is changed. FIG. 11 is a schematic diagram for comparing S parameters when cw is changed. FIG. 12 is a schematic diagram showing the open characteristics of the central strip line of the third prototype CPW-DGS filter. FIG. 13 is a schematic diagram showing the configuration of a fourth prototype CPW-DGS filter. FIG. 14 is a schematic diagram for comparing S parameters when tabdw1 is changed. FIG. 15 is a schematic diagram comparing S parameters when the CPW via hole position is viaholed. FIG. 16 is a schematic diagram comparing S parameters at different slot widths t1. FIG. 17 is a schematic diagram showing the configuration of the final CPW-DGS filter. FIG. 18 is a schematic diagram showing S parameters of the final CPW-DGS filter at an intermediate operating frequency of 59.5 GHz. FIG. 19 is a schematic diagram showing S parameters of the final CPW-DGS filter at an intermediate operating frequency of 61.5 GHz. FIG. 20 is a schematic diagram showing a basic CPW-DGS structure and S parameters thereof. FIG. 21 is a schematic diagram showing the CPW-DGS structure that was first prototyped and its S parameter. FIG. 22 is a schematic diagram showing a second prototype CPW-DGS filter and its S parameter. FIG. 23 is a schematic diagram comparing S parameters with different tabdy. FIG. 24 is a schematic diagram comparing S parameters with different tabdx. FIG. 25 is a schematic diagram comparing S parameters with different DGS configurations. FIG. 26 is a schematic diagram showing a second prototype CPW-DGS filter and its configuration. FIG. 27 is a schematic diagram comparing the S parameters when t3 is present and when t3 is absent. FIG. 28 is a schematic diagram showing the effect of the central stripline used to connect the two slots of the DGS. FIG. 29 is a schematic diagram showing the effect of viaholed. FIG. 30 is a schematic diagram comparing S parameters when two DGSs are moved symmetrically by tabwd. FIG. 31 is a schematic diagram showing S parameters at an intermediate operating frequency of 59.5 GHz. FIG. 32 is a schematic diagram showing S parameters at an intermediate operating frequency of 61.5 GHz.

Claims (1)

A base made of low temperature co-fired ceramic and having one or more holes;
A coplanar waveguide patterned on the base and covering the one or more holes;
A band-pass filter comprising:

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