Abstract:
This invention uses the structures of the finite-sized conductor-backed coplanar waveguides for designing broadband switchable and tunable signal filters. The design methods construct a plurality of configurations, which including waveguides, via holes, metallic posts, and conductor planes in the structures, for selecting, coupling, converting, and dissipating of the signals with specific electromagnetic modes and frequencies propagating through the structures. The dominant electromagnetic modes of the signals include Coplanar Waveguide Modes and Microstrip-Like Modes. The design methods thereby produce a plurality of filter types, such as bandstop filters, bandpass filters, multiband filters, etc. The design methods can apply to the structures with single and multi-layer dielectric and metallic materials, such as Integrated Circuits, Thin-film transistor Circuits, Low Temperature/High Temperature Co-fired Ceramics (LTCC/HTCC), PCB, and others. In addition, the design methods add switches to perform electrically controllable functions including frequency band selection and filter type selection. The design methods can also perform impedance matching of broadband signals by electrically tuning the values of inductance and capacitance in conjunction with the structures.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    This invention relates to the field of waveguides, filters, resonators and more specifically to switchable and tunable finite-width conductor-backed coplanar waveguide resonators and filters in conjunction with via holes and switches. 
       BACKGROUND OF INVENTION 
       [0002]    The fast development of telecommunication services, such as Cellular phones, WiFi, WiMAX, RFID, Digital TV etc., faces different standards, spectrum allocations, and regulations. The portable products for these services move toward highly integrated forms as the technologies progress. To select a desirable signal or service on these products, we have been observing an increasing need exists for switchable and tunable filters for both broadband and multiband systems that are small in size, inexpensive, and easy to manufacture. 
         [0003]    Highly integrated portable telecommunication products demand system miniaturization. The design of filters evolves with the miniaturization efforts of System On Package (SOP) and System On Circuit (SOC) technologies accordingly. From the SOP perspective, new generation of filters are assembled with other active and passive RF components, such as integrated circuits and antennas in Low Temperature Co-fired Ceramics (LTCC) packages. From the SOC perspective, active filters make steady progress as the high Q value on-chip inductors improve performance (Kuhn, et al “Dynamic Range Performance of On-Chip RF Bandpass Filter”, IEEE Trans. On Circuits and Systems, Vol. 50, No. 10, October 2003, pp. 685-694). Recently, one of the efforts proposed Photonic Band Gap (PBG) or Electromagnetic Band Gap (EBG) structures on the substrates for the design of bandpass or bandstop filters or for the suppression of high-order harmonics (Y Qian, V. Radisic, and T. Itoh, “Simulation and experiment of photonic band-gap structures for microstrip circuits”, Asia-Pacific Microwave Conf., Hong Kong, December 1997, pp. 585-588). Other efforts adopted Defected Ground Structure (DSG) to create resonators on the ground plane. This approach resulted in that part of energy with frequencies at DSG resonators&#39; frequencies is coupled to the ground plane and dissipated and constructed bandstop filters. 
         [0004]    However, miniaturization does not directly meet the need for switchable and tunable filters for both broadband and multiband applications. Hereby, this invention follows the miniaturization trend and develops switchable and tunable filters based on some of prior arts:
   (1) Finite-sized conductor-backed coplanar waveguides   (2) Vias or Via holes including connecting posts   (3) Switches (such as PIN diodes, FET transistors, Thin Film Transistors, MEMS etc.)   
 
         [0008]    Coplanar waveguides was initially proposed by C. P. Wen in 1969 and has been under intensively investigation since this structure can be used for signal transmission and feeding, such as in Microwave Monolithic Integrated Circuits (MMICs) and antennas. For example, the inventor of this invention proposed of using coplanar waveguide for feeding high frequency patch antenna (D. Ni, et al, “Millimeter-Wave Generation and Characterization of a GaAs FET by Optical Mixing”, IEEE Trans. On Microwave Theory and Techniques, Vol. 38, No. 5, May, 1990, pp. 608-614). Since the IC chips are generally attached onto finite-sized packages constructed by metallic and dielectric materials, finite-sized conductor-backed coplanar waveguides have also been studied extensively as shown in the following publications: 
         [0009]    M. Riaziat, I. Feng, R. Majidi-Ahy, and B. Auld, “Single-Mode Operation of Coplanar Waveguides”, Electronic Letters, Nov. 19, 1987, Vol. 23, No. 24, pp. 1281-1283; 
         [0010]    C- C. Tien, C-K. C. Tzuang, S. T. Peng, and C-C. Chang, “Transmission Characteristics of Finite-Width Conductor-Backed Coplanar Waveguide”, IEEE Trans. On Microwave Theory and Techniques, Vol. 41, No. 9, September 1993, pp. 1616-1624. 
         [0011]    Recently, SOP efforts have integrated several active and passive components into millimeter-sized multi-layer LTCC packages, therein coplanar waveguides and the related waveguides once again under intensive modeling and simulation efforts. 
         [0012]    Via holes have been playing a crucial roles in MMIC technology. Recently, via holes are also extensively used in multi-layer LTCC packages for connecting signal paths and ground planes across multi-layers. There are studies and measurements on the parasitic parameters, such as inductance and capacitance, as well as interference phenomena. The following publications describe some of these efforts: 
         [0013]    K. L. Finch and N. G. Alexopoulos, “Shunt Posts in Microstrip Transmission Lines”, IEEE Trans. On Microwave Theory and Techniques, Vol. 38, No. 11, November 1990, pp. 1585-1594; 
         [0014]    M. E. Goldfarb and R. A. Pucel, “Modeling Via Hole Grounds in Microstrip”, IEEE Microwave and Guided Wave Letters, Vol. 1, No. 6, June 1991, pp. 135-137; 
         [0015]    E. Laermans, J. D. Geest, D. Zutter, F. Olyslager, S. Sercu, and D. Morlion, “Modeling Differential Via Holes”, IEEE Trans. On Advanced Packaging, Vol. 24, No. 3, August 2001; 
         [0016]    In the studies listed above, Finch and Alexopoulos used via holes in conjunction with microstrip lines to construct bandpass filter at specific frequencies. Along with the development of multi-layer packages, such as LTCC, via holes are used in various areas:
   (1) Isolation of signal waveguides from interference;   (2) Formation of walls of resonating cavities;   (3) Formation of connections for grounding;   (4) Use of via holes&#39; parameters, such as length and radius, to adjust inductance and capacitance for the purpose of impedance matching.   
 
         [0021]    The following publications and U.S. patents illustrate these usages of via holes: J. A. Ruiz-Cruz, Y. Zhang, K. A. Zaki, A. J. Piloto, and J. Tallo, “Ultra-Wideband LTCC Ridge Waveguide Filters”, and U.S. Patent Documents: U.S. Pat. Nos. 5,689,216, 6,137,383, 7,053,729 B2, 7,113,060 B2, 7,142,074 B2, 7,170,373 B2. 
         [0022]    Switchable and tunable filters take advantage of switching devices (such as PIN diodes, FET transistors, Thin film transistors, MEMS etc.) for connecting modules with different resonating frequencies. In the prior arts, designs of switchable and tunable coplanar filters used PIN diodes and MEMS for selecting or connecting several configurations of cavities or waveguide. Due to the fixed sizes and patterns of these configurations, the switchable types and tunable frequency range are limited. Others used magnetic of ferromagnetic materials, such as Barium Strontium Titanate Oxide (BSTO), for changing impedance and subsequently for tuning the frequencies. However, there are also limitations in frequency response due to the material characterization and manufacture cost. The following publications disclosed these prior arts: US Patent documents: U.S. Pat. Nos. 5,142,255, 5,693,429, 6,606,017, and 7,148,770. 
       SUMMARY OF INVENTION 
       [0023]    The primary object of the present invention is to provide design methods for designing broadband filters by using finite-width conductor-backed coplanar waveguide structures which including configurations of signal waveguides, grounding waveguides, conductor-backed planes (or back conductors), and via holes with metallic posts so arranged that the selected coplanar waveguide modes are coupled and converted to the related electromagnetic modes, such as Microstrip-Like modes (MSL) and then dissipated to the ground through the configured structures; thereby the filtering functions, such as bandstop, bandpass, multibands, etc. are established. 
         [0024]    A further object of the invention is to provide design methods for designing broadband filters by using finite-width conductor-backed coplanar waveguide structures, which can be implemented in various structures with single layer or a plurality of layers of metallic and dielectric materials, such as those used for building integrated circuits, thin film transistors, low temperature co-fired ceramics (LTCC), high temperature co fired ceramics (HTCC), printed circuit boards (PCB), etc. 
         [0025]    A specific object of the invention is to provide design methods for designing broadband switchable and tunable filters by using finite-width conductor-backed coplanar waveguide structures, which including configurations of signal waveguides, grounding waveguides, conductor-backed planes (or back conductors), and via holes with metallic posts; and further including additional switches between the ground waveguides and the conductor-back planes for electrically selecting the configuration of a specific filter type. 
         [0026]    Another specific object of the invention is to provide design methods for designing broadband switchable and tunable filters by using finite-width conductor-backed coplanar waveguide structures, which including configurations of signal waveguides, grounding waveguides, conductor-backed planes (or back conductors), and via holes with metallic posts; and further including additional switches between the ground waveguides and the conductor-back planes for electrically selecting the configuration of a specific central frequency of a configured filter. 
         [0027]    Another specific object of the invention is to provide methods for designing broadband switchable and tunable filters by using finite-width conductor-backed coplanar waveguide structures, which including configurations of signal waveguides, grounding waveguides, conductor-backed planes (or back conductors), and via holes with metallic posts; and further including additional switches between the ground waveguides and the conductor-back planes for electrically selecting the configuration for impedance matching of broadband signals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  illustrates a Finite-Width Conductor-Backed coplanar waveguide structures in this invention; 
           [0029]      FIG. 2  is the top view of  FIG. 1  and shows via holes; 
           [0030]      FIG. 3  is the cross sectional view of  FIG. 1  and shows single layer of dielectric material, via holes including metallic connecting posts between metallic ground waveguides and metallic back conductor; 
           [0031]      FIG. 4  is the equivalent circuit of the Finite-Width Conductor-Backed coplanar waveguide structure shown in  FIG. 3 ; 
           [0032]      FIG. 5  is the equivalent circuit shown in  FIG. 4  with additional switches connecting via holes including metallic connecting posts and metallic ground waveguides; 
           [0033]      FIG. 6  is the Scattering parameters: S 21 , S 11 , and S 22  of GaAs finite-width conductor-backed coplanar waveguide without via holes; 
           [0034]      FIG. 7  is the Scattering parameters: S 21 , S 11 , and S 22  of GaAs bandstop filter based on finite-width conductor-backed coplanar waveguide structures as shown in  FIG. 2 ; 
           [0035]      FIG. 8  shows the frequency response of GaAs tunable bandstop filter. Each data point represents a specific configuration; 
           [0036]      FIG. 9  shows cross sectional view of an alternative Finite-Width Conductor-Backed coplanar waveguide structure with the via holes including metallic connecting posts, which are not connected to the metallic back conductor; 
           [0037]      FIG. 10  shows cross sectional view of another alternative Finite-Width Conductor-Backed coplanar waveguide structure with two dielectric layers and the via holes including metallic connecting posts, which are not connected to the metallic back conductor; 
           [0038]      FIG. 11  is the equivalent circuit of the Finite-Width Conductor-Backed coplanar waveguide structure shown in  FIG. 9 ; 
           [0039]      FIG. 12  shows cross sectional view of another alternative Finite-Width Conductor-Backed coplanar waveguide structure with the via holes including metallic connecting posts comprising multi-sectional and separated columns, which do not connect directly to the metallic ground waveguides and the metallic back conductor. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0040]      FIG. 1  illustrates a finite-width conductor-backed coplanar waveguide structures of this invention,  FIG. 2  is the top view of  FIG. 1 ;  FIG. 3  is the cross sectional view of  FIG. 1 ; herein  101  represents the metallic signal waveguide of the coplanar waveguide;  102  and  103  represent the metallic ground waveguides individually;  104  represents the metallic back conductor;  105  and  106  represent via holes including the metallic conducting posts between metallic ground waveguides  102 , 103  and the metallic back conductor  104 ;  107  represents the dielectric material;  108  and  109  represent individually the surfaces of the dielectric material without covering by metallic materials;  110  and  111  represent individually the surfaces of dielectric material  107  between metallic signal waveguide  101  and metallic ground waveguides  102  and  103 ;  FIG. 1  shows the structures that comprising single layer dielectric material  107 , and via holes including the metallic conducting posts  105  and  106 , which connected directly to the metallic ground waveguides  102  and  103  and the metallic back conductor  104 . The via holes including the metallic conducting posts  105  and  106  can be connected directly to the metallic ground waveguides  102  and  103  and the metallic back conductor  104  as shown in  FIG. 3 ; or do not directly connect to the metallic back conductor  104  as shown in  FIG. 9  and  FIG. 10 ; or the via holes including the metallic conducting posts  105  and  106  comprising multi-sectional and separated columns, which do not connect directly to the metallic ground waveguides  102  and  103  and the metallic back conductor  104  as shown in  FIG. 12 . The metallic back conductor  104  can be a single layer of conductor or a plurality of layers of connected conductors. 
         [0041]    The design methods for designing switchable and tunable broadband filters using finite-width conductor-backed coplanar waveguide structures, referring to  FIGS. 1 ,  2 , and  3 , include the following steps:
   (1) Based on the requirements of center frequency of a specific frequency band, number of electromagnetic modes, mode matching, mode coupling, and conversion of modes, the design methods specify length (L), width (W), and thickness (H) of the dielectric material  107 , width (Ws) of the metallic signal waveguide  101 , width (Wg) of the metallic ground waveguides  102  and  103 , width (Wd) of the dielectric material without covering by the ground waveguides  108  and  109 , distance (G) between the signal waveguide  101  and the ground waveguides  102  and  103 , and relative dielectric constant (∈r) of the dielectric material for an optimal broadband operation.   (2) The design methods construct a configuration of a plurality of via holes including the radius or cross section and height of metallic connecting posts  105  and  106  at designated locations between the metallic ground waveguides  102  and  103 , and metallic back conductor  104  for selecting the coupling modes, optimizing mode coupling efficiency, and defining the filter types; herein the via holes including the metallic conducting posts  105  and  106  can be connected directly to the metallic ground waveguides  102  and  103  and the metallic back conductor  104  as shown in  FIG. 3 , or do not directly connect to the metallic back conductor  104  as shown in  FIG. 9  and  FIG. 10 ; or the via holes including the metallic conducting posts  105  and  106  comprising multi-sectional and separated columns, which do not connect directly to the metallic ground waveguides  102  and  103  and the metallic back conductor  104  as shown in  FIG. 12 ; in addition, the dielectric material between the metallic ground waveguides  102  and  103  and metallic back conductor  104  can be single layer dielectric material  107  as shown in  FIG. 3  and  FIG. 9 , or two layers dielectric materials  107  and  112  as shown in  FIG. 10 , or more than two layer of dielectric materials (FIG. is not shown); thereby these different configurations provide a plurality sets of parameters for the definition of a specific type of filters.   (3) The design methods install a plurality of switches between the metallic ground waveguides  102 ,  103  and a plurality of the via holes including the metallic conducting posts  105  and  106 ; or between metallic back conductor  104  and a plurality of the via holes including the metallic conducting posts  105  and  106  in order to change the configuration for constructing different filter types, such as bandpass, bandstop, multiband, lowpass, highpass etc.   (4) The design methods install a plurality of switches between the metallic ground waveguides  102 ,  103  and a plurality of via holes including the metallic conducting posts  105  and  106 ; or between metallic back conductor  104  and a plurality of via holes including the metallic conducting posts  105  and  106  in order to change the configuration for tuning the center frequency of the configured filter.   
 
         [0046]    The main differences of the invention from the prior arts of tunable and switchable filters are as follows:
   (1) The configuration of the metallic signal waveguide  101  maintains unchanged when the filter performs switchable or tunable functions. This feature enables the metallic signal waveguide  101  processing signals across broader bandwidth than the configurations in the prior arts.   (2) The metallic ground waveguides  102 ,  103 , metallic back conductor  104 , and a plurality of the via holes including the metallic conducting posts  105  and  106  between these two sets of the metallic conductors construct a filter configuration, which comprises a flexible set of parameters for specifying different types of switchable and/or tunable filters.   (3) Since there is no switch directly connected to the metallic signal waveguide, the design methods simplify the filter structures and avoid signal and/or bias isolation problems existed in the prior arts.   
 
         [0050]    The inductance introduced by the via holes including the metallic conducting posts  105 ,  106  can be calculated by the following formula: 
         [0000]        L =(μ 0 /2π){ H× 1 n [( H +( R   2   +H   2 ) 1/2 )/ R]+  3/2 [R −( R   2   +H   2 ) 1/2 ]} 
         [0000]    Here, L represents inductance, μ 0  represents permeability, H represents the height of via hole metallic conducting post, R is the radius or cross section of via holes. 
         [0051]      FIG. 4  shows the equivalent circuit of  FIG. 3 , wherein a plurality of the via holes including the metallic conducting posts  105 ,  106  are directly connected to the metallic ground waveguides  102 ,  103  and the metallic back conductor  104 . In  FIG. 4 ,  401  represents the equivalent circuit of the metallic signal waveguide ( 101 );  402  represents the equivalent circuit of the metallic ground waveguide ( 102 ,  103 );  403  represents the equivalent circuit of back conductor ( 104 ); the configuration in  FIG. 3  produces a plurality of resonating cavities, which are represented by LC circuits in  FIG. 4 . These cavities absorb part of the energy, which are coupled from the metallic signal waveguide based on the resonating frequencies of the cavities, and dissipate the energy to the metallic back conductor. As an illustration, the above configuration produces a bandstop filter. As another illustration, the design methods can also construct a different configurations, which combining two bandstop filters for forming a bandpass filter; further,  FIG. 11  shows the equivalent circuit of  FIG. 9  and  FIG. 10 , wherein the via holes including the metallic conducting posts  105  and  106  do not directly connect to the metallic ground waveguides  102 ,  103  and the metallic back conductor  104 . The capacitance introduced by the gaps between post columns and the back conductor can be calculated directly from the area of cross section and dielectric constant. 
         [0052]      FIG. 5  shows the equivalent circuit of  FIG. 4  with additional switches;  401  represents the equivalent circuit of metallic signal waveguide ( 101 );  402  represents the equivalent circuit of metallic ground waveguide ( 102 ,  103 );  403  represents the equivalent circuit of the back conductor ( 104 );  404  represents a plurality of switches. Under normal operation, the switching devices have parasitic inductance and capacitance; in addition, they need biases, i.e., external voltage and current supplies, in order to change and to maintain connecting or disconnecting status. The configurations in the prior arts of switchable and tunable filters connect directly the switches onto the signal transmission conductors (referred as metallic signal waveguide  401  in this invention). The direct connection will result in characteristic drift of the filters and due to signal isolation problems, which increase the cost of manufacture. The design methods of this invention connect a plurality of switches to the metallic ground waveguides  102 ,  103 , and therefore avoid the induced problems and cut down significant part of manufacture cost. 
         [0053]    Based on  FIG. 2 , the design methods illustrate hereby an embodiment of designing a GaAs MMIC broadband bandstop filter. The design methods specify the ratios of length (L), width (W), and thickness (H) of dielectric material  107 , the width (Ws) of metallic signal conductor  101 , the width (Wg) of metallic ground conductors  102  and  103 , the width (Wd) of dielectric material without covering by ground conductors  108  and  109 , the distance (G) between signal conductor  101  and ground conductors  102  and  103 , and relative dielectric constant (∈r) as follows:
       L: 10   W: 15   H: 10   Ws: 1   Wg: 3   Wd: 3   G: 3   ∈r: 12.9       
 
         [0062]      FIG. 6  shows the scattering parameters: S 21 , S 11 , and S 22  of the GaAs coplanar waveguide without via holes. The FIG. shows a single electromagnetic mode propagating through the finite-width conductor-backed coplanar waveguide, and the signal strength S 21  indicates very low attenuation.  FIG. 7  shows the scattering parameters: S 21 , S 11 , and S 22  after a plurality of the via holes including the metallic conducting posts  105  and  106  connected directly to the metallic ground waveguides  102  and  103  and the metallic back conductor  104 . The FIG. shows a bandstop filter with center frequency attenuated more than 20 dB.  FIG. 6  can be viewed as the switches connecting via holes including the metallic conducting posts  105  and  106  are open or disconnected from the metallic ground waveguides  102  and  103 ;  FIG. 7  can be viewed as the switches connecting via holes including the metallic conducting posts  105  and  106  are closed or connected to the metallic ground waveguides  102  and  103 .  FIG. 8  shows the tuning range and attenuation of the center frequencies for a plurality of the configurations. The tunable range exceeds 30 GHz.  FIG. 7  and  FIG. 8  illustrates the broadband characteristics of this invention.  FIG. 8  can be viewed as the frequency response of a tunable filter as the configuration changed from one to another by electrically controlling a plurality of switches. 
         [0063]    In summary, the design methods of the invention includes the following steps: the design methods take the conditions of the center frequency of the designated frequency band, number of electromagnetic modes, mode matching, mode coupling, and conversion of modes for determining the ratios of length (L), width (W), and thickness (H) of the dielectric material, width (Ws) of metallic signal waveguide, width (Wg) of metallic ground waveguides, width (Wd) of dielectric material without covering by metallic ground waveguides, distance (G) between metallic signal waveguide and metallic ground waveguides; then construct a specific configuration, which are formed by the metallic ground waveguides, the metallic back conductor, and a plurality of the via holes including the metallic conducting posts, for building the filter with desirable characteristics, such as center frequency, type, bandwidth etc.; further, the design methods install a plurality of switches between the metallic ground waveguides and a plurality of the via holes including the metallic conducting posts to facilitate switchable and tunable capabilities of these filters. 
         [0064]    Although the present invention has been described in the detailed embodiment, a myriad of changes, variations, alterations, transformations and modifications may be suggested to one skilled in the art, and it is intended that the present invention encompass such changes, variations, alternations, transformations and modifications that fall within the spirit and scope of appended claims.