Patent Publication Number: US-6337609-B1

Title: Delay compensation device, delay line component and manufacturing method of the delay line component

Description:
TECHNICAL FIELD 
     The present invention relates to a delay compensation device and a delay line component for a radio frequency low distortion power amplifier used in a radio base station of portable phone communication systems and to a manufacturing method of the delay line component. 
     BACKGROUND ART 
     In a radio base station of potable phone communication system, the final stage of a radio frequency power amplifier is required to simultaneously amplify a number of different radio frequency signals which are amplitude modulated or frequency modulated for communication. In such a high power radio frequency amplifier used in the radio base station, the signals are usually affected by non-linear operation characteristics of used active components like transistors. Once the signals are affected by such non-linear characteristics, third harmonic inter modulation distortion (hereinafter called as “IMD ”) is caused and unnecessary radiation interference is resulted. To suppress such interference, some linearisation processing is necessary in radio frequency power amplification. To prevent IMD, an amplifier by feed-forward method (hereinafter called as “FF”) is used as shown in FIG. 1 (Japanese Unexamined Patent Publication No.6-224650). 
     In the figure, the reference number  10  is an input terminal of radio frequency signals for amplification,  11  is the first directional coupler connected with the input terminal  10 ,  12  is a main amplifier connected with the coupling port of the first directional coupler  11 ,  13  is a first delay compensation device connected with the primary output port of the first directional coupler  11 ,  14  is a second directional coupler connected with the output of the main amplifier  12 ,  15  is a third directional coupler connected with the output of the first delay compensation device  13  and with the coupling port of the second directional coupler  14 ,  16  is an error amplifier connected with the primary output port of the third directional coupler  15 ,  17  is a second delay compensation device connected with the primary output port of the third directional coupler  14 ,  18  is a fourth directional coupler connected with the output of second delay compensation device  17  and with the output of the error amplifier  16 , and  19  is an output terminal of amplified radio frequency signals connected with the primary output port of the directional coupler  18 . 
     As will be apparent from FIG. 1, an input radio frequency signal via the input terminal  10  is divided into two signals by the first directional coupler  11 , and one of the divided signal is amplified by the main amplifier  12  which generates IMD components (distortion signals) resulted from its non-linearity characteristics in addition to the main signals. The other of the divided signal propagates the first delay compensation device  13  which has a similar delay characteristic as the main amplifier  12 . By the directional coupler  15 , the output of the delay compensation device  13  is inversely added with the signal, which is adjusted by signal level and phase controllers not shown in the FIG. 1, from the coupling port of the directional coupler  14 . As a result, the two main signal components are canceled each other, and only IMD component (distortion signals) is left. The IMD component is amplified at the error amplifier  16  up to the level that is needed to cancel the IMD component generated in the main amplifier  12 . 
     The output signal of the main amplifier  12  propagates the second delay compensation device  17  which has a similar delay characteristic as the error amplifier  16 . And the output signal of the second delay line device  17  is inversely added with the IMD component from the error amplifier  16  by the fourth directional coupler  18 . Consequently, the two components of IMD are canceled each other and only the amplified radio frequency signal via the input terminal  10  is output via the output terminal  19 . By this configuration, a radio frequency amplifier system with good distortion characteristics can be built. 
     However, this kind of FF type amplifier has problems shown below. 
     (1) The typical requirement of delay time of the delay compensation device for such amplifier is tens of nanoseconds. If a coaxial cable type of delay line is used for the delay compensation device, the delay time of tens of nanoseconds requires a few meters length of the coaxial cable. That results in very large physical size. And definite propagation loss is resulted when small diameter coaxial cable is applied for physical size reduction. 
     (2) If a filter by combined resonators is applied for the delay compensation device, more than 10 stages of the resonators are required to achieve tens of nanoseconds. This results in large propagation loss, increased work load of assembling and difficulty in parameter adjusting. 
     (3) If a micro strip line structure is used as shown in Japanese Unexamined Patent Publication No.2-24120, the propagation loss becomes very large because of electromagnetic energy concentration at the side edges of strip line conductor. 
     (4) In an actual power amplifier system, the main amplifier and the error amplifier have independent and different frequency transfer characteristics. And in order to completely remove IMD components, the frequency transfer characteristics of the two different amplifiers must be adjusted to be matched each other in a certain frequency range. This requires very complicated and careful tests and adjustments of the main amplifier and the error amplifier after the build of the power amplifier system. The work load of manufacturing is remarkably increased. 
     DISCLOSURE OF INVENTION 
     It is therefore an object of the present invention to solve the problems in the conventional art, and to provide a delay compensation device, a delay line component and manufacturing method of the delay line component that can contribute to realize small propagation loss in a radio frequency and a very small physical bodied device. 
     Another object of the invention Is to provide a delay compensation device, whereby two frequency transfer characteristics of a main amplifier and an error amplifier can be easily adjusted and matched each other. 
     The present invention provides a delay line component with coaxial cable structure, including a center conductor, a dielectric which surrounds the center conductor and an outer conductor which is formed outside the dielectric. The dielectric is made of a ceramic dielectric with a large dielectric constant. 
     In order to get for example 35 nanoseconds of delay time, 10.5 meters length of a line in vacuum environment is needed. An usually widely used coaxial cable uses dielectric insulator with the dielectric constant of ∈r=2-3, and around 7 meters of such cable is necessary for 35 nanoseconds delay. In the present invention, a large dielectric constant ceramic insulator is used for the coaxial cable dielectric material, and consequently the cable length can be greatly reduced. If the used ceramic insulator&#39;s dielectric constant is ∈r=92, the propagation velocity factor expressed by root square of ∈r becomes about 9.6. The necessary length by such coaxial cable for 35 nanoseconds delay is only about 1.1 meters. 
     It is preferred that the ceramic dielectric in the coaxial cable structure is made of sintered ceramic materials or a dielectric with a resin in which ceramic particles are included. 
     It is preferred that at least the center conductor is made of a metal conductor with no grain boundary 
     It is also preferred that the center conductor is formed by a metal conductor melted and sintered in a center hole of the ceramic dielectric, by a pipe-shaped metal conductor inserted and rolled in a center hole of the ceramic dielectric, or by a wire-shaped solid metal conductor inserted into a center hole of the ceramic dielectric. 
     If the center conductor is formed by a pipe-shaped metal conductor rolled in the center hole of the ceramic dielectric, preferably, this center conductor is formed by a metal conductor which is expanded by static inside pressure or by explosive gaseous pressure and closely contacted to an inner surface of the center hole. 
     It is very preferred that the ceramic dielectric is formed by a plurality of independent ceramic dielectric blocks with a predetermined axis length. The electromagnetic mode in a coaxial cable is basically TEM (Transverse Electro-Magnetic Mode), and there is no electric and magnetic field component toward the direction of propagation. The ceramic dielectric is not necessary to be consecutive along the direction of wave propagation in a coaxial cable. This permits to link or stack a plurality of short and proper length ceramic dielectric blocks along the direction of coaxial cable. 
     Each of the ceramic dielectric blocks may be formed by a cylindrical shaped or polygonal tube shaped block with a center hole. 
     It is preferred that the outer conductor is formed by a metal film sintered on an outer surface of the ceramic dielectric, or by a pipe-shaped metal conductor which covers in contact the outer surface of the ceramic dielectric. 
     It is also preferred that the ceramic dielectric located in at least one end portion of the delay line component has a dielectric constant which is different from that of the ceramic dielectric located in another portion of the delay line component. 
     It is also preferred that the ceramic dielectric located in at least one end portion of the delay line component has a ratio of inner/outer diameters which is different from that of the ceramic dielectric located in another portion of the delay line component. 
     It is also preferred that the ceramic dielectric located in at least one end portion of the delay line component has an outer diameter which is different from that of the ceramic dielectric located in another portion of the delay line component. 
     It is preferred that a main delay line portion of the delay line component consists of only a straight coaxial cable line, or includes a plurality of straight coaxial cable lines, and a plurality of curved coaxial cable lines which connect the straight coaxial cable lines with each other. 
     In the latter case, the dielectric of the curved coaxial cable lines is made of a dielectric with ceramic particles mixed in a soft resin, or made of a plurality of independent ceramic dielectric blocks. 
     Also, the present invention provides a delay compensation device having a coaxial cable type delay line component with a center conductor, a dielectric which surrounds the center conductor and an outer conductor which is formed outside the dielectric, and a band pass filter connected with at least one end portion of the delay line component. 
     Since at least one end portion of the delay line component is equipped with the band pass filter, the frequency transfer characteristics of each amplifier can be adjusted to be matched each other. 
     It is very preferred that the band pass filter is designed so that its frequency transfer characteristics is adjustable. 
     It is also preferred that an input characteristic impedance and an output characteristic impedance are different with each other in the band pass filter. Thus, impedance matching between the delay line component and external circuit connected thereto can be possible. 
     It is preferred that a band pass filter is connected with only one end portion of the delay line component, or that band pass filters are connected with the both end portions of the delay line component, respectively. 
     Furthermore, the present invention provides a method of manufacturing a coaxial cable type delay line component which includes a center conductor, a dielectric which surrounds the center conductor, and an outer conductor which is formed outside the dielectric. The method includes a step of forming the dielectric by linking a plurality of linked independent ceramic dielectric blocks with a predetermined axis length by glass paste and by sintering them to make a long integral member. 
     It is preferred that the dielectric is made of a sintered ceramic dielectric with a large dielectric constant. 
     Also, the present invention provides a method of manufacturing a coaxial cable type delay line component which includes a center conductor, a dielectric which surrounds the center conductor, and an outer conductor which is formed outside the dielectric. The method includes a step of forming the dielectric by mixing ceramic particles in a resin. 
     It is preferred that at least the center conductor is made of a metal conductor with no grain boundary. 
     It is preferred that the center conductor is formed by filling metal material into a center hole of the ceramic dielectric, and by melting and sintering the filled metal material, formed by inserting a pipe-shaped metal conductor into a center hole of the ceramic dielectric, and by expanding the pipe-shaped metal conductor by static inside pressure or explosive gaseous pressure to closely contact to an inside surface of the center hole, or formed by inserting a wire-shaped solid metal conductor into a center hole of the ceramic dielectric. 
     It is also preferred that the outer conductor is formed by covering an outer surface of the ceramic dielectric with a metal paste and by sintering the metal paste, or formed by covering an outer surface of the ceramic dielectric with a pipe-shaped metal conductor. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a block diagram schematically illustrating constitution of a FF type power amplifier. 
     FIG. 2 is a view schematically illustrating a structure of a coaxial cable type delay line component of a preferred embodiment according to the present invention. 
     FIG. 3 is a graph illustrating delay time and insertion loss characteristics in the embodiment of FIG.  2 . 
     FIG. 4 is a view schematically illustrating a structure of a coaxial cable type delay line component of another embodiment according to the present invention. 
     FIG. 5 is a view schematically illustrating a structure of a coaxial cable type delay line component of further embodiment according to the present invention. 
     FIG. 6 is a view schematically illustrating a structure of a coaxial cable type delay line component of still further embodiment according to the present invention. 
     FIG. 7 is a view schematically illustrating a structure of a coaxial cable type delay line component of further embodiment according to the present invention. 
     FIG. 8 is a circuit diagram of an example of each band pass filter used in the embodiment of FIG.  7 . 
     FIG. 9 is a graph for comparing possible range of adjustable frequency transfer characteristics of the delay compensation device in the embodiment of FIG.  7 . 
     FIG. 10 is a view schematically illustrating a structure of a delay compensation device with a coaxial cable type delay line component of still further embodiment according to the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     FIG. 2 is a view schematically illustrating a structure of a coaxial cable type delay line component of a preferred embodiment according to the present invention. 
     In the figure, reference number  20  is a main delay line portion of a delay line component,  21  and  22  are coaxial quarter-wavelength (λ/4) transformer portions which are placed at the both ends of the main delay portion  20 , and  23  and  24  are input and output connectors which are connected to the λ/4 transformer portions  21  and  22 , respectively. 
     The main delay line portion  20  consists of a center conductor  20   a , a ceramic dielectric  20   b  which surrounds the center conductor  20   a , and an outer conductor  20   c  which is formed on the outer surface of the ceramic dielectric  20   b.    
     The λ/4 transformer portions  21  and  22  have center conductors  21   a  and  22   a , ceramic dielectrics  21   b  and  22   b  which surround the center conductors  21   a  and  22   a , and outer conductors  21   c  and  22   c  which are formed on the outer surfaces of the ceramic dielectrics  21   b  and  22   b  respectively. 
     The ceramic dielectric  20   b  of the main delay line portion  20  is formed by linking, along the direction of the coaxial axis, twenty block pieces of cylindrical shaped or polygonal tube shaped and sintered ceramic blocks  20   b   1 - 20   b   20  of post molded and sintered dimensions, the outer diameter of 12 mm, the length along the axis of 15 mm, and the center hole diameter of 1.6 mm. The block pieces are made by sintering of press molded ceramic materials which has a large dielectric constant value ∈r=37 and high quality factor Q≧10000. 
     Each of the ceramic dielectrics of  21   b  and  22   b  of the λ/4 transformer portions  21  and  22  is formed by linking, along the direction of the coaxial axis, two cylindrical shaped or polygonal tube shaped ceramic blocks,  21   b   1  and  21   b   2 ,  22   b   1 , and  22   b    2 , respectively. The ceramic dielectric blocks  21   b   1  and  22   b   1  are made from ceramic material of dielectric constant ∈r=23 and post molded and sintered dimensions, the outer diameter of 12 mm, the length along the axis of 7.5 mm, and the center hole diameter of 1.6 mm. The ceramic dielectric blocks  21   b   2  and  22   b   2  are made from ceramic material with comparatively smaller dielectric constant ∈r=9 and post molded and sintered dimensions, the outer diameter of 12 mm, the length along the axis of 11.5 mm, and the center hole diameter of 1.6 mm. 
     After temporally combining the cylindrical shaped or polygonal tube shaped ceramic dielectric blocks, which compose the ceramic dielectric of the main delay line portion  20   b , and the two ceramic dielectrics  21   b  and  22   b  of λ/4 transformer portions  21  and  22 , by glass paste sintering along the coaxial axis, silver paste is filled in the center holes of the ceramic dielectric blocks and sintered at the temperature of silver melting point 960.5° C. This process can minimize the resistance of the center conductor made from silver paste because of non-grain boundary. 
     The outer conductors  20   c ,  21   c  and  22   c  are formed by sintering of applied silver paste on the surfaces of the ceramic dielectric blocks  20   b ,  21   b  and  22   b  at the usual temperature of paste melting point about 850° C. 
     Since the ceramic materials for the ceramic dielectric  20   b  in the main delay line portion  20  has a large dielectric constant value ∈r=37 and high quality factor Q≧10000, the characteristic impedance Z 0  of the coaxial main delay line is expressed by the following equation, 
     
       
         Z 0 =377/(2π{square root over ( )}∈r)ln(D/d) 
       
     
     where D is the outer diameter of the coaxial main delay line, and d is the inner diameter of the coaxial main delay line. The use of larger dielectric constant ceramic material gives lower characteristic impedance Z 0  which is usually difficult for direct connection with another device. Typical characteristic impedance of widely used radio frequency equipment is set to 50 Ω. On the other hand, the characteristic impedance of the delay line component according to the present invention is very low and down to about 20 Ω, because dielectric materials of large dielectric constant and center conductors of large diameter are used. Thus, impedance matching is needed in application of this kind of delay line component. For that purpose of impedance matching, the λ/4 transformer portions  21  and  22  are placed at the both ends of the main delay line portion  20 . 
     In this embodiment of the present invention, each one of the λ/4 transformer portions  21  and  22  is structured by two different dielectric blocks,  21   b   1  ( 22   b   1 ) and  21   b   2  ( 22   b   2 ), with different dielectric constants for impedance matching. The dielectric blocks  21   b   1  ( 22   b   1 ) and  21   b   2  ( 22   b   2 ) have different lengths of 7.5 mm and 11.5 mm along the axis so that their lengths are equivalent to λ/4 at the operated frequency. By this structured λ/4 transformer portions  21  and  22 , the impedance matching between the delay line component and external devices is done. 
     In this embodiment of the present invention, also, the ceramic dielectric  20   b  of main delay line portion  20  is made of twenty block pieces of cylindrical shaped or polygonal tube shaped and sintered ceramic blocks along the axis to get 5 to 6 nanoseconds delay time. By increasing the number of cylindrical shaped or polygonal tube shaped ceramic blocks up to a hundred, about 30 nanoseconds delay time can be obtained. 
     FIG. 3 illustrates delay time and insertion loss characteristics of the delay line component in the embodiment of FIG.  2 . 
     As will be apparent from the figure, the insertion loss is kept almost constant in a frequency range up to 2300 MHz, which is sufficient to cover the utilized frequency range in a radio frequency power amplifier used in a radio base station for portable phone communication, and a flat delay time of 5 nanoseconds is achieved. One and a half meters length of the delay line according to the present invention is enough to get 30 nanoseconds delay time, and very small form factor of a delay compensation device is resulted. 
     In the aforementioned embodiment of the present invention, melting sintered silver forms the center conductor. Another metal material like copper is applicable by melting the sintered metal material. And also, pulse-plating method can be applied to form a center conductor on the inside surfaces of the center holes of the ceramic dielectric blocks. In another modification, the center conductor may be formed by rolled thin (thickness of 100 μm) metal (annealed copper, silver, silver plated aluminum) pipe which is inserted into the center holes of the ceramic dielectric blocks and expanded by static inside pressure by press or explosive gaseous pressure by gunpowder and firmly attached or fixed to the inside surfaces of the center holes of the ceramic dielectric blocks. In this case, it is not necessary to temporally combine the ceramic dielectric blocks by glass paste sintering, while the outer conductors on the ceramic dielectric insulator blocks must be soldered each other. By ,insertion of a solid metal wire such as a solid copper, silver or aluminum wire into the center holes of the ceramic dielectric blocks, the center conductor can be formed. 
     In the aforementioned embodiment of the present invention, silver paste sintering is used to form the outer conductors on the surfaces of the ceramic dielectric blocks. However, in modification, the coaxial outer conductor may be formed by covering the ceramic dielectric insulator blocks with a heated and thermally expanded metal pipe of copper, silver or aluminum whose inner diameter is slightly smaller than the outer diameter of the ceramic dielectric blocks at room temperature. Electroless plating method is applicable to form the outer conductor. 
     As for the λ/4 transformer portions, there are many different types of configurations. 
     FIG. 4 schematically illustrates a structure of a coaxial cable type delay line component of another embodiment according to the present invention. 
     In the figure, reference number  40  is a main delay line portion of the delay line component,  41  and  42  are λ/4 transformer portions which are placed at the both ends of the main delay line portion  40 ,  43  and  44  are input and output connectors which are connected to the λ/4 transformer portions  41  and  42 , respectively. 
     The main delay line portion  40  is folded up to get larger delay time by smaller form factor, and consequently it consists of three straight coaxial cable lines  400 ,  401  and  402 , and two curved coaxial cable lines  403  and  404 . 
     Each of the straight coaxial cable lines  400 ,  401  and  402  of the main delay line portion  40  consists of a center conductor  40   a , a ceramic dielectric  40   b  which surrounds the center conductor  40   a , and an outer conductor  40   c  which is formed on the outer surface of the ceramic dielectric  40   b.    
     Each of the curved coaxial cable lines  403  and  404  of the main delay line portion  40  consists of a center conductor  40   a ′, a dielectric  40   b ′ which surrounds the center conductor  40   a ′, and an outer conductor  40   c ′ which is formed on the outer surface of the dielectric  40   b′.    
     The λ/4 transformer portions  41  and  42  have center conductors  41   a  and  42   a , and outer conductors  41   c  and  42   c  which surround the center conductors  41   a  and  42   a  with air gap. 
     The ceramic dielectric  40   b  of the straight coaxial cable lines  400 ,  401  and  402  of the main delay line portion  40  is formed by linking, along the direction of the coaxial axis, twenty block pieces of cylindrical shaped or polygonal tube shaped and sintered ceramic blocks of post molded and sintered dimensions, the outer diameter of 6 mm, the length along the axis of 15 mm, and the center hole diameter of 1.0 mm. Each of the blocks is made by sintering of press molded ceramic materials which has large dielectric constant value ∈r=92 and high quality factor Q≧7000. 
     An elastic resin type dielectric insulator, which includes ceramic particles of large dielectric constant ∈r=10 is used for the dielectric insulator  40   b ′ of the curved coaxial cable lines  403  and  404  other than rigid sintered ceramic because of the necessity of keeping resistivity against mechanical vibration and impact shock. A metal pipe such as copper, silver or aluminum pipe is used as the outer conductor  40   c ′. The curved coaxial cable lines  403  and  404  are formed so that the characteristic impedance thereof is matched with that of each of the straight coaxial cable lines  400 ,  401  and  402 . 
     In this embodiment of the present invention in FIG. 4, there is no dielectric material in the λ/4 transformer portions  41  and  42  but air between the center and outer conductors. 
     The center conductors  40   a  and  40   a ′ of the main delay line portion  40  are formed by rolled thin (thickness of 100 μm) metal (annealed copper, silver, silver plated aluminum) pipe, which is inserted into the center holes of the ceramic dielectric  40   b  of cylindrical shaped or polygonal tube shaped and sintered ceramic blocks and the attached dielectric  40   b ′. The metal pipe is expanded by static inside pressure by press or explosive gaseous pressure by gunpowder and firmly attached or fixed to the inside surfaces of the center holes of the dielectric blocks. This process can minimize the resistance of the center conductor made from silver paste because of non-grain boundary. 
     The center conductors  41   a  and  42   a  of the λ/4 transformer portions  41  and  42  are made of solid metal cylinders with two staged different diameters  41   a   1  and  41   a   2 ,  42   a   1  and  42   a   2 , respectively. 
     The outer conductor  40   c  of the straight coaxial cable lines  400 ,  401  and  402  of the main delay line portion  40  is formed by covering the ceramic dielectric blocks with a heated and thermally expanded metal pipe such as copper, silver or aluminum pipe whose inner diameter is slightly smaller than the outer diameter of the ceramic dielectric insulator at room temperature. The dimensions of the metal pipe and the heating temperature are to be defined reflecting the operating temperature under actual application conditions. The outer conductors  41   c  and  42   c  of the λ/4 transformer portions  41  and  42  are formed by extending the metal pipe. 
     The use of larger dielectric constant (∈r=92, quality factor Q≧7000) ceramic material as the ceramic dielectric insulator  40   b  of the main delay line portion  40  gives lower characteristic impedance Z 0  which is usually difficult for direct connection with another device as in the previously described embodiment of the present invention shown in FIG.  3 . Typical characteristic impedance of widely used radio frequency equipments is 50 Ω. On the other hand, the characteristic impedance of the delay line component according to the present invention is very low and down to 11.2 Ω, because dielectric materials of large dielectric constant is used and center conductors of large diameter is used in order to decrease the insertion loss. Thus, impedance matching is needed in actual applications of this kind of delay line component. For that purpose of impedance matching, the λ/4 transformer portions  41  and  42  are placed at the both ends of the main delay line portion  40 . 
     In this embodiment of the present invention in FIG. 4, each of the λ/4 transformer portions  41  and  42  has metal cylinders with two staged different diameters and with lengths along the axis which are chosen to be equivalent to their λ/4 at operating frequency. By these configured λ/4 transformer portions, impedance matching between the delay line component and external devices can be done. 
     In this embodiment, the ceramic dielectric  40   b  of each of the straight coaxial cable lines  400 ,  401  and  402  of the main delay line portion  40  is made of twenty block pieces of cylindrical shaped or polygonal tube shaped ceramic blocks which are linked along the axis. By using three of these straight coaxial lines which are serially connected, about 30 nanoseconds of delay time can be obtained. 
     In this embodiment of the present invention shown in FIG. 4, the center conductor is formed by rolled thin (thickness of 100 μm) metal (annealed copper, silver, silver plated aluminum) pipe, which is inserted into the center holes of the ceramic dielectric blocks and is expanded by static inside pressure by press or explosive gaseous pressure by gunpowder and firmly attached or fixed to the inside surfaces of the center holes of the ceramic dielectric blocks. However, as well as done in the embodiment shown in FIG. 2, this center conductor can be formed by melting and then by sintering silver, copper or another metal paste filled inside the center holes of the ceramic dielectric blocks. By insertion of a solid metal wire such as a solid copper, silver or aluminum wire into the center holes of the ceramic dielectric insulator blocks, the center conductor can be formed. And also pulse-plating method can be applied to form a center conductor on the inside surfaces of the center holes of the ceramic dielectric blocks. 
     Also, in this embodiment of the present invention shown in FIG. 4, covering the ceramic dielectric blocks with a heated and thermally expanded metal pipe forms the coaxial outer conductor. However, in modification, sintering of silver paste on the surfaces of the ceramic dielectric blocks and soldering them together may form the outer conductors. If the ceramic dielectric blocks are integral with each other by glass paste sintering, such soldering is not necessary. Electroless plating method is also applicable to form the outer conductor. 
     The λ/4 transformer portions can be structured as shown in FIG. 2, or in FIGS. 5 and 6 which will be described later. 
     FIG. 5 schematically illustrates a structure of a coaxial cable type delay line component of further embodiment according to the present invention. 
     In the figure, reference number  50  is a main delay line portion of the delay line component,  51  and  52  are λ/4 transformer portions which are placed at the ends of the main delay portion  50 ,  53  and  54  are input and output connectors which are connected to λ/4 transformer portions  51  and  52 , respectively. 
     The main delay line portion  50  is folded up to get larger delay time by smaller form factor, and consequently it consists of three straight coaxial cable lines  500 ,  501  and  502 , and two curved coaxial cable lines  503  and  504  for serially connecting the three straight coaxial cable lines  500 ,  501  and  502 . 
     Each of the straight coaxial cable lines  500 ,  501  and  502  of the main delay line portion  50  consists of a center conductor  50   a , a ceramic dielectric  50   b  which surrounds the center conductor  50   a , and an outer conductor  50   c  which is formed on the outer surface of the ceramic dielectric  50   b.    
     Each of the curved coaxial cable lines  503  and  504  of the main delay line portion  50  consists of a center conductor  50   a ′, a dielectric  50   b ′ which surrounds the center conductor  50   a ′, and an outer conductor  50   c ′ which is formed on the outer surface of the dielectric  50   b′.    
     The λ/4 transformer portions  51  and  52  have center conductors  51   a  and  52   a , ceramic dielectrics  51   b  and  52   b  which surround the center conductors  51   a  and  52   a , and outer conductors  51   c  and  52   c  which are formed outside the ceramic dielectrics  51   b  and  52   b , respectively. 
     The ceramic dielectric  50   b  of the straight coaxial cable lines  500 ,  501  and  502  of the main delay line portion  50  is formed by linking, along the direction of the coaxial axis, twenty block pieces of cylindrical shaped or polygonal tube shaped and sintered ceramic blocks of post molded and sintered dimensions, the outer diameter of 6 mm, the length along the axis of 15 mm, and the center hole diameter of 1.0 mm. Each of the blocks is made by sintering of press molded ceramic materials which has large dielectric constant value ∈r=92 and high quality factor Q≧7000. 
     In modification, a resin including ceramic particles of large dielectric constant may be used as the dielectric material of the coaxial cable lines. In this case, to get a large value of relative dielectric constant like ∈r=92 is difficult, consequently physical design of such delay line must be done assuming lower relative dielectric constant value. 
     The ceramic dielectric  50   b ′ of the curved coaxial cable lines  503  and  504  of the main delay line portion  50  is formed by linking, along the direction of the coaxial axis, eighteen block pieces of cylindrical shaped or polygonal tube shaped and sintered ceramic blocks of post molded and sintered dimensions, the outer diameter of 6 mm and the center hole diameter of 1.0 mm. Each block is made by sintering of press molded ceramic materials which has large dielectric constant value ∈r=92 and high quality factor Q≧7000. Each of the ceramic blocks is in fact reshaped after press molding to make a curved center hole along the curved axis of the coaxial cable line. In modification, the block may be formed by press molding in half pieces divided by a plane which passes the axis and by putting together the press-molded half pieces. 
     In this embodiment, the ceramic dielectrics of  51   b  and  52   b  of the λ/4 transformer portions  51  and  52  are made of stacked two cylindrical shaped or polygonal tube shaped ceramic dielectric blocks along the axis,  51   b   1  and  51   b   2 ,  52   b   1  and  52   b   2  respectively. The ceramic dielectric blocks  51   b   1 and  52   b   1  are made from ceramic material with large dielectric constant and post sintered dimensions, an outer diameter of smaller than 6.0 mm, and the center hole diameter of 1.0 mm. The ceramic dielectric blocks  51   b   2  and  52   b   2  are also made similarly with post sintered dimensions, an outer diameter of smaller than that of the blocks  51   b   1  and  52   b   1 , and the center hole diameter of 1.0 mm. Therefore, the effective dielectric constants of the transformers are comparatively smaller than that of the main delay line portion  50  due to composite structures of air and ceramic dielectric, and consequently the characteristic impedance becomes higher. 
     The center conductors  50   a  and  50   a ′ of the main delay line portion  50  and the center conductors  51   a  and  52   a  of the λ/4 transformer portions  51  and  52  are formed by rolled thin (thickness of 100 μm) metal (annealed copper, silver, silver plated aluminum) pipe, which is inserted into the center holes of the ceramic dielectric  50   b  and  50   b ′ of cylindrical shaped or polygonal tube shaped ceramic blocks. The metal pipe is expanded by static inside pressure by press or explosive gaseous pressure by gunpowder and firmly attached or fixed to the inside surfaces of the center holes of the dielectric insulators. This process can minimize the resistance of the center conductor made from silver paste minimized because of non-grain boundary. 
     The outer conductors  50   c  and  50   c ′ of the main delay line portion  50  is formed by covering the ceramic dielectric blocks with a heated and thermally expanded metal pipe of copper, silver or aluminum whose inner diameter is slightly smaller than the outer diameter of the ceramic dielectric insulator at room temperature. The dimensions of the metal pipe and the heating temperature are to be defined reflecting the operating temperature under actual application conditions. The outer conductors  51   c  and  52   c  of the λ/4 transformer portions  51  and  52  are formed by extending the metal pipe. 
     The use of larger dielectric constant (∈r=92, quality factor Q≧7000) ceramic material as the ceramic dielectric insulators  50   b  and  50   b ′ of the main delay line portion  50  gives lower characteristic impedance Z 0  which is usually difficult for direct connection with another device as in the previously described embodiment of the present invention shown in FIG.  4 . Typical characteristic impedance of widely used radio frequency equipments is 50 Ω. On the other hand, the characteristic impedance of the delay line component according to the present invention is very low and down to 11.2 Ω, because dielectric materials of large dielectric constant and center conductors of large diameter are used. Impedance matching is needed in actual applications of this kind of delay line component. For that purpose of impedance matching, the λ/4 transformer portions  51  and  52  are placed at the both ends of the main delay line portion  50 . 
     In this embodiment of the present invention in FIG. 5, each of the λ/4 transformer portions  51  and  52  has two ceramic dielectric cylinders whose outer diameters are different each other and lengths along the axis are chosen to be equivalent to their λ/4 at operating frequency. By these configured λ/4 transformer portions, impedance matching between the delay line component and external device can be done. 
     In this embodiment, the ceramic dielectric  50   b  of the straight coaxial cable lines  500 ,  501  and  502  of the main delay line portion  50  is formed by linking, along the direction of the coaxial axis, twenty block pieces of cylindrical shaped or polygonal tube shaped and sintered ceramic blocks. By using three of these straight coaxial lines which are serially connected, about 30 nanoseconds of delay time can be obtained. 
     In the embodiment of the present invention shown in FIG. 5, the center conductor is formed by rolled thin (thickness of 100 μm) metal (annealed copper, silver, silver plated aluminum) pipe, which is inserted into the center holes of the ceramic dielectric blocks and is expanded by static inside pressure by press or explosive gaseous pressure by gunpowder and firmly attached or fixed to the inside surfaces of the center holes of the ceramic dielectric blocks. In modification, however, this center conductor can be formed by melting sintered silver, copper or another metal paste filled inside the center holes of the ceramic dielectric blocks if the ceramic dielectric blocks are not made of ceramic particle mixed resin dielectric. By insertion of a solid metal wire into the center holes of the ceramic dielectric insulator blocks, the center conductor can be formed. Also, pulse-plating method can be applied to form a center conductor on the inside surfaces of the center holes of the ceramic dielectric blocks. 
     In this embodiment of the present invention shown in FIG. 5, covering the ceramic dielectric blocks with a heated and thermally expanded metal pipe forms the coaxial outer conductor. However, in modification, sintering of silver paste on the surfaces of the ceramic dielectric blocks if the ceramic dielectric blocks are not made of ceramic particle mixed resin dielectric may form the outer conductors. Electroless plating method is also applicable to form the outer conductor. 
     The λ/4 transformer portions can be structured as shown in FIGS. 2 and 4, or in FIG. 6 which will be described later. 
     FIG. 6 illustrates a structure of a coaxial cable type delay line component of still further embodiment according to the present invention. 
     In the figure, reference number  60  is a main delay line portion of the delay line component,  62  is a λ/4 transformer portion which is placed at an end of the main delay line portion  60 ,  63  and  64  are input and output connectors which are connected to λ/4 transformer portions respectively, and  65  and  66  are metal blocks. Although it is not shown in FIG. 6, there is another λ/4 transformer portion at the other of the main delay line portion. 
     The main delay line portion  60  is folded up to get larger delay time by smaller form factor, and consequently it consists of three straight coaxial cable lines  600 ,  601  and  602 , and two curved coaxial cable lines (only one curved coaxial cable line  603  is shown in FIG. 6) for serially connecting the three straight coaxial cable lines  600 ,  601  and  602 . 
     Each of the straight coaxial cable lines  600 ,  601  and  602  of the main delay line portion  60  consists of a center conductor  60   a , a ceramic dielectric  60   b  which surrounds the center conductor  60   a , and an outer conductor  60   c  which is formed on the outer surface of the ceramic dielectric  60   b . The curved coaxial cable line  603  of the main delay line portion  60  consists of a center conductor  60   a ′, a dielectric  60   b ′ which surrounds the center conductor  60   a ′, and the metal block  66  as the outer conductor which surrounds the dielectric  60   b ′. The other curved coaxial cable line is also similarly built. 
     The λ/4 transformer portion  62  consists of a center conductor  62   a , a ceramic dielectrics  62   b  which surrounds the center conductors  62   a , and the metal block  66  as the outer conductor which surrounds the dielectric  62   b ′. The other λ/4 transformer portion is also similarly built. 
     The ceramic dielectric  60   b  of the straight coaxial cable lines  600 ,  601  and  602  of the main delay line portion  60  is formed by linking, along the direction of the coaxial axis, twenty block pieces of cylindrical shaped or polygonal tube shaped and sintered ceramic blocks of post molded and sintered dimensions, the outer diameter of 6 mm, the length along the axis of 15 mm, and the center hole diameter of 1.0 mm. Each of the blocks is made by sintering of press molded ceramic materials which has large dielectric constant value ∈r=92 and high quality factor Q≧7000. 
     In modification, a resin including ceramic particles of large dielectric constant may be used as the dielectric material of the coaxial cable lines. 
     The ceramic dielectric  60   b ′ of the curved coaxial cable lines  603  of the main delay line portion  60  is formed by a cylindrical shaped or polygonal tube shaped ceramic block with the center hole diameter of 1.0 mm. The ceramic materials also has large dielectric constant value ∈r=92 and high quality factor Q≧7000. Actually, the ceramic dielectric  60   b ′ is formed by filling ceramic dielectric in trenches of semi-circular or semi-polygonal cross section which are semi-circularly dug on two divided half metal blocks and by combining the half metal blocks. In a modification, an elastic resin type dielectric insulator including ceramic particles of large dielectric constant whose effective dielectric constant ∈r=10, may be used for the dielectric insulator  60   b ′ of the coaxial cable line  603  other than rigid sintered ceramic because of the necessity of keeping resistivity against mechanical vibration and impact shock. 
     In this embodiment, the ceramic dielectric of  62   b  of the λ/4 transformer portion  62  is made of stacked two cylindrical shaped or polygonal tube shaped ceramic dielectric blocks along the axis,  62   b   1  and  62   b   2 , respectively. The ceramic dielectric block  62   b   1  is made from ceramic material with large dielectric constant and post sintered dimensions, an outer diameter of larger than 6.0 mm, and the center hole diameter of 1.0 mm. The ceramic dielectric blocks  62   b   2  is also made similarly with post sintered dimensions, an outer diameter of smaller than that of the block  62   b   1 , and the center hole diameter of 1.0 mm. 
     The center conductors  60   a  and  60   a ′ of the main delay line portion  60  and the center conductors of the λ/4 transformer portions are formed by insertion of a solid metal wire into the center hole of the ceramic dielectric of cylindrical shaped or polygonal tube shaped ceramic blocks which are linked along the coaxial axis. By this process, the resistance of the center conductor made of a solid continued metal wire of non-grain boundary can be minimized and this process obtains very small insertion loss. 
     The outer conductor  60   c  of each of the straight coaxial cable lines  600 ,  601  and  602  of the main delay line portion  60  is formed by covering the ceramic dielectric blocks with a heated and thermally expanded metal pipe of copper, silver or aluminum whose inner diameter is slightly smaller than the outer diameter of the ceramic dielectric insulator at room temperature. The dimensions of the metal pipe and the heating temperature are to be defined reflecting the operating temperature under actual application conditions. The outer conductors of the curved coaxial cable line  603  and the λ/4 transformer portion  62  are formed by the metal block  66  as previously described. 
     The manufacturing method in this embodiment of the present invention is as follows. First, a silver plated copper solid wire as a center conductor, coaxial ceramic dielectric blocks for straight coaxial cable lines of the main delay line portion, and a copper pipe as outer conductors are assembled. Then, two parts of the copper solid wire are bent for the center conductor of curved coaxial cable lines using a jig. Thereafter, the curved coaxial cable line is assembled by combining two divided metal blocks, on which trenches of semi-circular or semipolygonal cross section are semi-circularly dug and ceramic dielectric is filled, and sandwiching the bent copper wire portions as the center conductor. At the both ends of the transmission line of the main delay line portion  60 , λ/4 transformer portions are placed. These transformer portions are also built in the metal blocks  65  and  66 . 
     The use of larger dielectric constant (∈r=92, quality factor Q≧7000) ceramic material as the ceramic dielectric insulators  60   b  and  60   b ′ of the main delay line portion  60  gives lower characteristic impedance Z 0  which is usually difficult for direct connection with another device as in the previously described embodiment of the present invention shown in FIG.  5 . 
     Typical characteristic impedance of widely used radio frequency equipments is 50 Ω. On the other hand, the characteristic impedance of the delay line component according to the present invention is very low and down to 11.2 Ω, because dielectric materials of large dielectric constant and center conductors of large diameter are used. Impedance matching is needed in actual applications of this kind of delay line component. For that purpose of impedance matching, λ/4 transformer portions are placed at the both ends of the main delay line portion  60 . 
     In this embodiment of the present invention in FIG. 6, each of the λ/4 transformer portions has two different diameter ceramic dielectric cylinders with air gaps whose lengths along the axis are chosen to be equivalent to their λ/4 at operating frequency. By these configured λ/4 transformer portion, impedance matching between the delay line component and external device can be done. 
     In this embodiment, the ceramic dielectric  60   b  of the straight coaxial cable lines  600 ,  601  and  602  of the main delay line portion  60  is formed by linking, along the direction of the coaxial axis, twenty block pieces of cylindrical shaped or polygonal tube shaped and sintered ceramic blocks. By using three of these straight coaxial lines which are serially connected, about 30 nanoseconds of delay time can be obtained. 
     In the embodiment of the present invention shown in FIG. 6, the center conductor is formed by insertion of a solid metal wire into the center hole of the ceramic dielectric of cylindrical shaped or polygonal tube shaped ceramic blocks which are linked along the coaxial axis. In modification, however, this center conductor can be formed by melting sintered silver, copper or another metal paste filled inside the center holes of the ceramic dielectric blocks if the ceramic dielectric blocks are not made of ceramic particle mixed resin dielectric. The center conductor may be formed by rolled thin (thickness of 100 μm) metal (annealed copper, silver, silver plated aluminum) pipe, which is inserted into the center holes of the ceramic dielectric blocks and is expanded by static inside pressure by press or explosive gaseous pressure by gunpowder and firmly attached or fixed to the inside surfaces of the center holes of the ceramic dielectric blocks. Also, pulse-plating method can be applied to form a center conductor on the inside surfaces of the center holes of the ceramic dielectric blocks. 
     In this embodiment of the present invention shown in FIG. 6, covering the ceramic dielectric blocks with a heated and thermally expanded metal pipe forms the coaxial outer conductor. However, in modification, sintering of silver paste on the surfaces of the ceramic dielectric blocks if the ceramic dielectric blocks are not made of ceramic particle mixed resin dielectric may form the outer conductors. Electroless plating method is also applicable to form the outer conductor. 
     The λ/4 transformer portions can be structured as shown in FIGS. 2,  4  and  5 . 
     FIG. 7 schematically illustrates a structure of a coaxial cable type delay line component of further embodiment according to the present invention. 
     In the figure, reference number  70  is a delay line component,  71  and  72  are band pass filters which are placed at the both ends of the delay line component  70 . 
     The delay line component  70  is almost similar with the main delay line portion  20  shown in FIG.  2 . The delay line component  70  consists of a center conductor  70   a , a ceramic dielectric  70   b  which surrounds the center conductor  70   a , and an outer conductor  70   c  which is formed on the outer surface of the ceramic dielectric  70   b.    
     The band pass filters are designed with feature of a function of adjusting frequency characteristics. 
     The ceramic dielectric  70   b  of the main delay line portion  70  is formed by linking, along the direction of the coaxial axis, twenty block pieces of cylindrical shaped or polygonal tube shaped and sintered ceramic blocks of post molded and sintered dimensions, the outer diameter of 12 mm, the length along the axis of 15 mm, and the center hole diameter of 1.6 mm. Each of the blocks is made by sintering of press molded ceramic materials which has large dielectric constant value ∈r=37 and high quality factor Q≧10000. 
     Using of the ceramic dielectric blocks of high temperature resistivity as for the dielectric material can realize sintering of silver paste for formation of center and outer conductors. However, ceramic particles mixed resin materials are applicable for the dielectric material, if low temperature assemble processing is applied. 
     After temporally fixing the cylindrical shaped or polygonal tube shaped ceramic dielectric blocks, which compose the ceramic dielectric  70   b  of the main delay line portion  70 , by glass paste sintering along the coaxial axis, silver paste is filled in the center holes of the ceramic dielectric blocks and then sintered at the temperature of silver melting point 960.5° C. This process can minimize the resistance of the center conductor made from silver paste minimized because of non-grain boundary. 
     The outer conductors  70   c  is formed by sintering of applied silver paste on the surfaces of the ceramic dielectric blocks of dielectric  70   b  at the usual temperature of silver paste melting point about 850° C. 
     FIG. 8 illustrates a schematic example of the band pass filters  71  and  72  which are used in the delay compensation device shown in FIG.  7 . 
     As will be apparent from the figure, each of the band pass filters  71  and  72  is a filter which consists of capacity coupled two staged resonators of ceramic dielectrics. By adjusting screws  71   a - 71   e  and  72   a - 72   e  shown in FIG. 7, capacitance values of the filter can be changed, and consequently the frequency transfer characteristics can be controlled. 
     A typical radio frequency power amplifier has a frequency transfer characteristic of single-humped or double-humped resonance curve. The band pass filters  71  and  72  are adjusted to get maximally flat type or Chebyshev type curve, and thus the overall frequency transfer characteristic of the radio frequency power amplifier with the delay compensation device which includes these band pass filters can be compensated. 
     FIG. 9 compares possible range of adjustable frequency transfer characteristics of the delay compensation device in the embodiment of FIG.  7 . As will be understood, by adjusting the frequency transfer characteristic curve between the solid line A and the dot-dash-line B or by selecting a filter for a proper transfer characteristic, the overall frequency transfer characteristic of the radio frequency power amplifier can be easily adjusted to a flat curve. 
     The use of larger dielectric constant (∈r=37, quality factor Q≧10000) ceramic material as the ceramic dielectric insulator  70   b  of the main delay line portion  70  gives lower characteristic impedance Z 0  which is usually difficult for direct connection with another device as in the previously described embodiment of the present invention shown in FIG.  6 . Typical characteristic impedance of widely used radio frequency equipments is 50 Ω. On the other hand, the characteristic impedance of the delay line component according to the present invention is very low and down to 20 Ω, because dielectric materials of large dielectric constant and center conductors of large diameter for small insertion loss are used. Impedance matching is needed in actual applications of this kind of delay line component. The band pass filters  71  and  72  are designed to have different input and output impedance so that a way for impedance matching is provided, and they are placed at the both ends of the main delay line portion  70 . 
     In this embodiment of the present invention shown in FIG. 7, the ceramic dielectric insulator  70   b  of main delay line portion  70  is formed by linking, along the direction of the coaxial axis, twenty block pieces of cylindrical shaped or polygonal tube shaped and sintered ceramic blocks to get 5 to 6 nanoseconds delay time. By increasing the number of cylindrical shaped or polygonal tube shaped ceramic dielectric blocks up to one hundred, about 30 nanoseconds delay time is obtained. 
     In this embodiment of the present invention, melting sintered silver forms the center conductor. In modification, another metal material like copper is applicable. In further modification, the center conductor may be formed by rolled thin (thickness of 100 μm) metal (annealed copper, silver, silver plated aluminum) pipe which is inserted into the center holes of the ceramic dielectric blocks and expanded by static inside pressure by press or explosive gaseous pressure by gunpowder and firmly attached or fixed to the inside surfaces of the center holes of the ceramic dielectric blocks. In still further modification, the center conductor may be formed by insertion of a solid metal wire into the center holes of the ceramic dielectric blocks. And also pulse-plating method may be applied to form a center conductor on the inside surfaces of the center holes of the ceramic dielectric blocks. 
     In the embodiment of the present invention, silver paste sintering is used to form the outer conductors on the surfaces of the ceramic dielectric blocks. In modification, the coaxial outer conductor may be formed by covering the ceramic dielectric insulator blocks with a heated and thermally expanded metal pipe of copper, silver or aluminum whose inner diameter is slightly smaller than the outer diameter of the ceramic dielectric blocks at room temperature. Electroless plating method is also applicable to form the outer conductor. 
     In the above description of the embodiment of the present invention, a band pass filter is place at each end of the main delay line portion  70 . However, in modification, a band pass filter for the purposes of adjusting the overall frequency transfer characteristic and impedance matching may be placed at one end of the main delay line portion, and a λ/4 transformer portion for the purpose of impedance matching may be placed at the other end. If a target frequency transfer characteristic curve is obtained by such configuration of a band pass filter and a λ/4 transformer portion, it is much better from smaller insertion loss point of view. The used band pass filters may be different type such as cavity or helical type band pass filter other than dielectric resonator type, and the number of stages is not limited to two. 
     FIG. 10 schematically illustrates a structure of a delay compensation device with a coaxial cable type delay line component of still further embodiment according to the present invention. 
     In the figure, reference number  100  is a main delay line portion of the delay compensation device,  101  is a band pass filter placed at one end of the main delay line portion  100 , and  102  is a λ/4 transformer portion placed at the other end of the main delay line portion. 
     The main delay line portion  100  is almost similar with the main delay line portion  60  of the embodiment of the present invention shown in FIG.  6 . The main delay line portion  100  is folded up to get larger delay time by smaller form factor, and consequently it consists of three straight coaxial cable lines  1000 ,  1001  and  1002 , and two curved coaxial cable lines  1003  and  1004  for serially connecting the straight coaxial cable lines  1000 ,  1001  and  1002 . 
     Each of the straight coaxial cable lines  1000 , 1001  and  1002  of the main delay line portion  100  consists of a center conductor  10   a , a ceramic dielectric  100   b  which surrounds the center conductor  10   a , and an outer conductor  100   c  which is formed on the outer surface of the ceramic dielectric  100   b.    
     Each of the curved coaxial cable lines  1003  and  1004  of the main delay line portion  100  consists of a center conductor  100   a ′, a dielectric  100   b ′ which surrounds the center conductor  100   a ′, and an outer conductor  100   c ′ which is formed on the outer surface of the dielectric  100   b′.    
     The λ/4 transformer portion  102  has a center conductor  102   a  and an outer conductor  102   c  which surrounds the center conductor with air gap. 
     The ceramic dielectric  100   b  of the straight coaxial cable lines  1000 ,  1001  and  1002  of the main delay line portion  100  is formed by linking, along the direction of the coaxial axis, twenty block pieces of cylindrical shaped or polygonal tube shaped and sintered ceramic blocks of post molded and sintered dimensions, the outer diameter of 6 mm, the length along the axis of 15 mm, and the center hole diameter of 1.0 mm. Each of the blocks is made by sintering of press molded ceramic materials which has large dielectric constant value ∈r=92 and high quality factor Q≧7000. 
     In a modification, a resin including ceramic particles of large dielectric constant may be used as the dielectric material of the coaxial cable line, although there are some application limitations of its dielectric constant and manufacturing process. 
     An elastic resin type dielectric insulator, which includes ceramic particles of large dielectric constant ∈r=10 is used for the dielectric insulator  100   b ′ of the curved coaxial cable lines  1003  and  1004  other than rigid sintered ceramic because of the necessity of keeping resistivity against mechanical vibration and impact shock. A metal pipe such as copper, silver or aluminum pipe is used as the outer conductor  100   c ′. The curved coaxial cable lines  1003  and  1004  are formed so that the characteristic impedance thereof becomes 11.2 Ω. 
     In this embodiment of the present invention in FIG. 10, there is no dielectric material in the λ/4 transformer portion  102  but there is air between the center and outer conductors. 
     The center conductors  100   a  of the main delay line portion  100  are formed by rolled thin (thickness of 100 μm) metal (annealed copper, silver, silver plated aluminum) pipe, which is inserted into the center hole of the ceramic dielectric  100   b  of cylindrical shaped or polygonal tube shaped ceramic blocks. The metal pipe is expanded by static inside pressure by press or explosive gaseous pressure by gunpowder and firmly attached or fixed to the inside surfaces of the center holes of the dielectric blocks. This process can minimize the resistance of the center conductor made from silver paste because of non-grain boundary. 
     The center conductor  102   a  of the λ/4 transformer portion  102  is made of two different diameter solid metal cylinders,  102   a , and  102   a   2 . 
     The outer conductor  100   c  of the straight coaxial cable lines  1000 ,  1001  and  1002  of the main delay line portion  100  is formed by covering the ceramic dielectric blocks with a heated and thermally expanded metal pipe of copper, silver or aluminum whose inner diameter is slightly smaller than the outer diameter of the ceramic dielectric insulator at room temperature. The dimensions of the metal pipe and the heating temperature are to be defined reflecting the operating temperature under actual application conditions. The outer conductor  102   c  of the λ/4 transformer portion  102  is formed by extension of the metal pipe. 
     Similarly with the band pass filter in FIG. 7, the band pass filter  101  consists of capacity coupled two staged resonators of ceramic dielectrics. By adjusting screws  101   a - 101   e , capacitance values of the filter can be changed, and consequently the frequency transfer characteristics can be controlled. 
     A typical radio frequency power amplifier has a frequency transfer characteristic of single-humped or double-humped resonance curve. The band pass filter  101  is adjusted to get maximally flat type or Chebyshev type curve, and thus the overall frequency transfer characteristic of the radio frequency power amplifier with the delay compensation device which includes these band pass filter can be compensated. By adjusting the frequency transfer characteristic curve of the band pass filter  101  or by selecting a filter for a proper transfer characteristic, the overall frequency transfer characteristic of the radio frequency power amplifier can be easily adjusted to a desired curve. 
     The use of larger dielectric constant (∈r=37, quality factor Q≧10000) ceramic material as the ceramic dielectric insulator  100   b  of the main delay line portion  100  gives lower characteristic impedance Z 0  which is usually difficult for direct connection with another device as in the previously described embodiment of the present invention. Typical characteristic impedance of widely used radio frequency equipments is 50 Ω. On the other hand, the characteristic impedance of the delay line component according to the present invention is very low and down to 11.2 Ω, because dielectric materials of large dielectric constant and center conductors of large diameter for small insertion loss are used. Impedance matching is needed in actual applications of this kind of delay line component. For that purpose of impedance matching, the band pass filter  101  in addition to adjusting the overall frequency transfer characteristic is place at one end of the main delay line portion  100 , and the λ/4 transformer portion  102  is placed at the other end. 
     In this embodiment of the present invention in FIG. 10, the λ/4 transformer portion  102  has two different diameter solid metal cylinders whose electrical lengths along the axis are chosen to be equivalent to λ/4 at operating frequency. 
     In this embodiment, the ceramic dielectric insulator  100   b  of the straight coaxial cable lines  1000 ,  1001  and  1002  of main delay line portion  100  is formed by linking, along the direction of the coaxial axis, twenty block pieces of cylindrical shaped or polygonal tube shaped and sintered ceramic blocks. Using of these three the straight coaxial lines which are serially connected provides about 30 nanoseconds of delay time. 
     In this embodiment of the present invention shown in FIG. 10, the center conductor is formed by rolled thin (thickness of 100 μm) metal (annealed copper, silver, silver plated aluminum) pipe, which is inserted into the center holes of the ceramic dielectric blocks and is expanded by static inside pressure by press or explosive gaseous pressure by gunpowder and firmly attached or fixed to the inside surfaces of the center holes of the ceramic dielectric blocks. In modification, this center conductor may be formed by melting sintered silver, copper or another metal paste filled inside the center holes of the ceramic dielectric blocks as the embodiment of the present invention shown in FIG.  2 . In further modification, the center conductor may be formed by insertion of a solid metal wire such as copper, silver or aluminum wire into the center holes of the ceramic dielectric blocks. And also pulse-plating method may be applied to form a center conductor on the inside surfaces of the center holes of the ceramic dielectric blocks. 
     In this embodiment of the present invention shown in FIG. 10, covering the ceramic dielectric blocks with a heated and thermally expanded metal pipe forms the coaxial outer conductor. In modification, the outer conductors may be formed by sintering of silver paste on the surfaces of the ceramic dielectric blocks. Electroless plating method is also applicable to form the outer conductor. 
     In the above description of the embodiment of the present invention, only one band pass filter is placed at one end of the main delay line portion  100 , and a target frequency transfer characteristic curve is obtained by such configuration of a band pass filter and a λ/4 transformer portion. This is much better from smaller insertion loss point of view. Of course, two band pass filters can be place at the both ends. The used band pass filters may be different types such as cavity type or helical type other than dielectric resonator type, and the number of stages is not limited to two. 
     A few embodiment of the present invention have been described in detail, but it is particularly understood that invention is not limited thereof and thereby. There may be many different physical placements of components referred in the present invention reflecting actual physical requirements. Connecting directional couplers at ends of a transmission line is very effective from FF featured power amplifier design point of view. Impedance matching can be done at different impedance values other than 50 Ω. 
     Many widely different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims. 
     As described above, the delay line component is consists of ceramic dielectric of large dielectric constant, and consequently the length of such line can be short, the physical size becomes small, and small insertion loss can be obtained due to short length of the line. Thanks for applying dielectric materials of large quality factor Q, the insertion loss can be greatly reduced. Also, since the delay line component by the present invention is built as coaxial structure, the frequency transfer characteristic is very flat and stable. 
     Furthermore, because adjustments of impedance matching and frequency transfer characteristics are done by inserted adjustable band pass filters, the overall frequency transfer characteristics are easily adjusted to the target after assembling a radio frequency power amplifier system by the delay compensation device and also volume production of such FF featured power amplifier systems of very small IMD components is possible.