Patent Publication Number: US-2007103144-A1

Title: Calibration pattern and calibration jig

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an RF measurement method for a high frequency circuit, a calibration pattern, and a calibration jig and, in particular, relates to an RF measurement method for a high frequency circuit for use in a communication device adapted for a microwave band or a millimeter wave band that is used in mobile communication, optical communication, satellite communication, and the like, and further to a calibration pattern and a calibration jig.  
      2. Description of the related Art  
      In recent years, communication devices used in microwave bands or millimeter wave bands have been more and more miniaturized. Following it, high frequency circuit devices are also required to be further miniaturized, and accordingly, high frequency circuits used in those high frequency circuit devices are required to have proper qualities. In order to accurately evaluate the quality of the high frequency circuit, it is necessary to carry out RF measurement of the high frequency circuit by the use of a highly accurate measurement method, and therefore, there has been an increasing demand for a precise calibration method for setting a standard of the RF measurement.  
      The RF measurement of the high frequency circuit is performed on-wafer. This on-wafer RF measurement normally uses two RF measurement probe heads, each having a signal terminal and a GND terminal, in such a manner as to confront each other. Therefore, an RF measurement probe head calibration pattern is required to have a calibration pattern that corresponds to the RF measurement probe heads to be used.  
      Generally, there are available three kinds of probe heads as RF measurement probe heads. The first one is of a type having three contacts including one signal terminal and GND terminals located on both sides of the signal terminal, respectively. This first one is called, for example, a GSG-type RF measurement probe head.  
      The second one is of a type having two contacts including one signal terminal and one GND terminal wherein, as seeing the contacts from the side of a body of the RF measurement probe head, the signal terminal is arranged on the left side while the GND terminal is arranged on the right side. This second one is called, for example, an SG-type RF measurement probe head.  
      The third one is of a type also having two contacts wherein, however, the signal terminal and the GND terminal in the second SG-type RF measurement probe head are interchanged in position, and therefore, as seeing the contacts from the side of a body of the RF measurement probe head, the GND terminal is arranged on the left side while the signal terminal is arranged on the right side. This third one is called, for example, a GS-type RF measurement probe head.  
      For the RF measurement of the high frequency circuit, two measurement probe heads are used in such a manner as to confront each other. Accordingly, a calibration pattern is required which corresponds to such two measurement probe heads.  
      As a configuration pattern when using the two first GSG-type RF measurement probe heads in the confronting manner, it is possible to calibrate the two GSG-type RF measurement probe heads by the use of a calibration pattern having one signal line with a predetermined characteristic impedance and two GND lines disposed along the signal line on both sides thereof, respectively.  
      On the other hand, when the second SG-type RF measurement probe head and the third GS-type RF measurement probe head are used in the confronting manner, the signal terminals confront each other and the GND terminals confront each other so that, by the use of a calibration pattern having one signal line with a predetermined characteristic impedance and two GND lines disposed along the signal line on one side thereof, the signal terminals can be brought into contact with the same signal line and simultaneously the GND terminals can be brought into contact with the same GND lines, and therefore, it is possible to calibrate the two RF measurement probe heads.  
      However, when the two second SG-type RF measurement probe heads or the two third GS-type RF measurement probe heads are used in the confronting manner, assuming that the signal terminals of the two RF measurement probe heads are brought into contact with a signal line of a calibration pattern, the GND terminals thereof are located on both sides of the signal line, respectively, so that it is necessary to provide GND lines on both sides of the signal line, respectively.  
      On the other hand, if use is simply made of the calibration pattern that is used for calibrating the first GSG-type RF measurement probe heads, i.e. the calibration pattern having the two GND lines disposed along the signal line on both sides thereof, because the GND lines are separated from each other, the calibration cannot be implemented. Then, in view of this, if use is made of, for example, a calibration pattern in which the two GND lines are connected together at each one end thereof to surround the signal line or a calibration pattern in which the two GND lines are connected together at both ends of each of them to fully surround the signal line, the signal terminal of at least one of the RF measurement probe heads is disposed so as to lie across the GND line of the calibration pattern when performing the calibration.  
      As a known technique, there is a disclosure that, in order to suppress parasitic inductance in property examination of a semiconductor integrated circuit device to enable a high-frequency property examination, a pair of an input signal electrode and an output signal electrode and a pair of an input GND electrode and an output GND electrode are disposed on the surface of an IC chip, and these input GND electrode and output GND electrode are electrically connected to a backside electrode, provided on the back side of the IC chip, via conductors provided in through holes formed through the IC chip in a thickness direction thereof, respectively, so as to be electrically connected to each other via the backside electrode, thereby achieving common grounding (e.g. see JP-A-H05-152395, paragraphs [0005] to [0006] and  FIGS. 1 and 2 ).  
      As another known technique, there is a disclosure that, in a square open-stub structure in a high frequency circuit for microwaves or millimeter waves, the voltage amplitude becomes zero at a position of λ/4 from an open-stub open end so that grounding is formed in a high-frequency manner (e.g. see JP-A-2000-101309, paragraph [0006] and  FIG. 5 ).  
      When, as described above, the signal terminal of the RF measurement probe head is disposed so as to lie across the GND line of the calibration pattern, an RF signal affects a measurement value so that the measurement value is largely biased following an increase in signal frequency. For example, observing an input-side reflection property when measurement is performed for a through pattern having a characteristic impedance of 50Ω, the impedance is largely biased from 50Ω following an increase in frequency.  
      Conventionally, use has been made of a high frequency circuit of which the RF measurement can be performed by the use of different kinds of the measurement probe heads, for example, by the use of the SG-type RF measurement probe head and the GS-type RF measurement probe head. However, in order to achieve miniaturization and higher functions, demanded in recent years, of high frequency circuits, it becomes necessary to increase the degree of freedom in circuit arrangement. Consequently, there arises a case where the RF measurement cannot be carried out with the circuit property measurement using the measurement probe heads of the kinds in which the contacts are arranged differently, and it becomes necessary to implement the RF measurement by the use of the second SG-type RF measurement probe heads or the third GS-type RF measurement probe heads.  
      Accordingly, there arises a new problem that when use is made of the second SG-type RF measurement probe heads or the third GS-type RF measurement probe heads as described above, accurate calibration of the RF measurement probe heads cannot be implemented by the use of the conventional calibration pattern.  
     SUMMARY OF THE INVENTION  
      The present invention has been made for solving the foregoing problem and has a first object to provide a property measurement method for a high frequency circuit that can prevent an RF signal from affecting a measurement value in measurement of the RF signal, a second object to provide a calibration pattern that can prevent an RF signal from affecting a measurement value in measurement of the RE signal, and a third object to provide a calibration jig which makes it possible to easily exchange a calibration pattern that can prevent an RF signal from affecting a measurement value in measurement of the RF signal.  
      According to one aspect of the invention, there is provided a high frequency circuit property measurement method comprising: preparing a calibration pattern comprising a substrate, a signal line having one characteristic impedance and extending to have a first and a second end portion on said substrate, a first constant potential line having one end portion disposed close to and with a predetermined interval from said first end portion of the signal line, a second constant potential line having one end portion disposed close to and with a predetermined interval from said second end portion of the signal line, and a conductor for connecting between said first constant potential line and said second constant potential line electrically or in a high-frequency manner; and performing calibration prior to measurement of a to-be-measured circuit by using a first and a second property measurement probe head having the same arrangement of a signal terminal and a constant potential terminal, by bringing the signal terminal and the constant potential terminal of said first property measurement probe head into contact with said first end portion of the signal line and said one end portion of the first constant potential line of said calibration pattern, respectively, and by bringing the signal terminal and the constant potential terminal of said second property measurement probe head into contact with said second end portion of the signal line and said one end portion of the second constant potential line of said calibration pattern, respectively.  
      Accordingly, in a high frequency circuit property measurement method according to the present invention, neither of the signal terminals of the first and second property measurement probe heads is disposed so as to lie across the constant potential line of the calibration pattern.  
      Therefore, since an RF signal does not affect either of the signal terminals of the first and second property measurement probe heads, accurate calibration can be achieved so that the property measurement of the high frequency circuit is precisely carried out. Consequently, selection of high frequency circuits can be accurately performed to thereby improve the yield of high frequency circuit devices.  
      According to another aspect of the invention, there is provided a calibration pattern comprising: a substrate; a signal line having one characteristic impedance and extending to have a first and a second end portion on said substrate; a first constant potential line having one end portion disposed close to and with a predetermined interval from said first end portion of the signal line; a second constant potential line having one end portion disposed close to and with a predetermined interval from said second end portion of the signal line; and a conductor for connecting between said first constant potential line and said second constant potential line electrically or in a high-frequency manner.  
      Accordingly, a calibration pattern according to the present invention is advantageous in a high frequency circuit property measurement as either of the signal terminals of the RF measurement probe heads does not lie across the GND line even when the SG-type RF measurement probe heads or the GS-type RF measurement probe heads are used so as to confront each other with their signal terminals being brought into contact with the signal line of the calibration pattern.  
      Therefore, the RF signal does not affect the measurement value so that there is no occurrence of the measurement value being largely biased following an increase in signal frequency. Consequently, it is possible to implement the calibration of the RF measurement probe heads with high accuracy.  
      According to still another aspect of the invention, there is provided a calibration jig comprising: a calibration pattern comprising, a substrate, a signal line having one characteristic impedance and extending to have a first and a second end portion on said substrate, a first constant potential line having one end portion disposed close to and with a predetermined interval from said first end portion of the signal line, a second constant potential line having one end portion disposed close to and with a predetermined interval from said second end portion of the signal line, and a conductor for connecting between said first constant potential line and said second constant potential line electrically or in a high-frequency manner; and a dielectric substrate having a recessed portion formed on the surface thereof for exchangeably mounting therein the calibration pattern.  
      Accordingly, a calibration jig according to the present invention is advantageous in a high frequency circuit property measurement as the calibration Jig makes it possible to carry out calibration at predetermined required frequencies by the use of one jig.  
      Consequently, selection of high frequency circuits can be accurately and easily performed to thereby improve the yield of high frequency circuit devices with the simple process.  
      Other objects and advantages of the invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific embodiments are given by way of illustration only since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
       FIG. 2  is a sectional view of the RF measurement calibration pattern taken along a line II-II in  FIG. 1 .  
       FIG. 3  is an exemplary diagram showing the state where RF measurement probe heads are in contact with the RF measurement calibration pattern according to Embodiment 1 of the present invention.  
       FIG. 4  is a block diagram for explaining a measurement system for a high frequency circuit according to the present invention.  
       FIGS. 5 and 6  are block diagrams for explaining a method of performing zero correction of the measurement system for the high frequency circuit according to the present invention.  
       FIG. 7  is an exemplary diagram showing a measurement system when performing S-parameter measurement of a high frequency circuit, according to the present invention.  
       FIGS. 8, 9 ,  10 , and  11  are exemplary diagrams showing the calibration method when carrying out the S-parameter measurement of the high frequency circuit, according to the present invention.  
       FIG. 12  is a sectional view of an RF measurement calibration pattern according to one embodiment of the present invention.  
       FIG. 13  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
       FIG. 14  is a sectional view of the RF measurement calibration pattern taken along a line XIV-XIV in  FIG. 13 .  
       FIG. 15  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
       FIG. 16  is a sectional view of the RF measurement calibration pattern taken along a line XVI-XVI in  FIG. 15 .  
       FIG. 17  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
       FIG. 18  is a sectional view of the RF measurement calibration pattern taken along a line XVIII-XVIII in  FIG. 17 .  
       FIG. 19  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
       FIG. 20  is a sectional view of the RF measurement calibration pattern taken along a line XX-XX in  FIG. 19 .  
       FIG. 21  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
       FIG. 22  is an exemplary diagram showing the state where RF measurement probe heads are in contact with the RF measurement calibration pattern according to Modification 6 of the present invention.  
       FIG. 23 ,  FIG. 24 , and  FIG. 25  are plan views of an RF measurement calibration pattern according to one embodiment of the present invention.  
       FIG. 26  is a sectional view of the RF measurement calibration pattern taken along a line XXVI-XXVI in  FIG. 25 .  
       FIG. 27 ,  FIG. 28  ,  FIG. 29 ,  FIG. 30 ,  FIG. 31 ,  FIG. 32 ,  FIG. 33 ,  FIG. 34 ,  FIG. 35 ,  FIG. 36 , and  FIG. 37  are plan views of an RF measurement calibration pattern according to one embodiment of the present invention.  
       FIG. 38  is a plan view of an RF measurement calibration jig according to one embodiment of the present invention.  
       FIG. 39  is a sectional view of the RF measurement calibration jig taken along a line XXXIX-XXXIX in  FIG. 38 . 
    
    
      In all figures, the substantially same elements are given the same reference numbers.  
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Embodiment 1  
       FIG. 1  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  FIG. 2  is a sectional view of the RF measurement calibration pattern taken along a line II-II in  FIG. 1 . In the drawings to be referred, the same symbols represent the same or corresponding components, respectively.  
      In  FIGS. 1 and 2 , there is shown an RF measurement calibration pattern  10  being one example of Embodiment 1.  
      The RF measurement calibration pattern  10  comprises a dielectric substrate  12  serving as a substrate. A signal line  14  having a specific characteristic impedance of, for example, 50Ω is disposed on the surface of the dielectric substrate  12 . The signal line  14  has a linear shape with both opposite ends and comprises a metal layer  141  and a gold-plating layer  142  disposed on the surface of the metal layer  141 . Those both opposite ends of the signal line  14  will be referred to as, for example, a first end portion  14   a  and a second end portion  14   b , respectively.  
      A first GND pad  16  serving as a first constant potential line is disposed with a predetermined interval defined between itself and the first end portion  14   a  of the signal line  14 . The first GND pad  16  has a front end portion located on a prolongation of the signal line  14  in its longitudinal direction and is electrically separated from the signal line  14 . The other end portion of the first GND pad  16  is connected to a through-hole electrode  18 .  
      The first GND pad  16  is connected to a backside metal layer  22 , disposed on the back side of the dielectric substrate  12 , via the through-hole electrode  18  and a via hole  20  formed by burying a conductor in a through hole formed through the dielectric substrate  12  in its thickness direction. The first GND pad  16  comprises a metal layer  161  and a gold-plating layer  162  disposed on the surface of the metal layer  161 . In this embodiment, the through-hole electrode  18  connected to the first GND pad  16  is formed by the metal layer  161  part of which also forms the first GND pad  16 .  
      Further, a second GND pad  24  serving as a second constant potential line is disposed with the predetermined interval defined between itself and the second end portion  14   b  of the signal line  14 . The second GND pad  24  has a front end portion located on a prolongation of the signal line  14  in its longitudinal direction and is electrically separated from the signal line  14 . The other end portion of the second GND pad  24  is connected to a through-hole electrode  18 .  
      The second GND pad  24  is connected to the backside metal layer  22 , disposed on the back side of the dielectric substrate  12 , via the through-hole electrode  18  and a via hole  20  formed by burying a conductor in a through hole formed through the dielectric substrate  12  in its thickness direction. The second GND pad  24  comprises a metal layer  241  and a gold-plating layer  242  disposed on the surface of the metal layer  241 . In this embodiment, the through-hole electrode  18  connected to the second GND pad  24  is formed by the metal layer  241  part of which also forms the second GND pad  24 .  
      Accordingly, the first GND pad  16  and the second GND pad  24  are electrically connected together via the conductors, i.e. the through-hole electrodes  18 , the via holes  20 , and the backside metal layer  22 . In this embodiment, the first GND pad  16  and the second GND pad  24  are grounded, but may not necessarily be grounded if electrically conducted via the through-hole electrodes  18 , the via holes  20 , and the backside metal layer  22 .  
       FIG. 3  is an exemplary diagram showing the state where RF measurement probe heads are in contact with the RF measurement calibration pattern according to Embodiment 1 of the present invention.  
      In  FIG. 3 , an RF measurement probe head  30  and an RF measurement probe head  32  are disposed so as to confront each other like in an ordinary measurement state. In the description of this embodiment, the two RF measurement probe heads  30  and  32  are both, for example, SG-type RF measurement probe heads.  
      In calibration, a signal terminal  301  (indicated as S in  FIG. 3 ) of the RF measurement probe head  30  is in contact with the signal line  14  while a GND terminal  302  (indicated as G in  FIG. 3 ) thereof is in contact with the first GND pad  16 . Further, a signal terminal  321  (indicated as S in  FIG. 3 ) of the RF measurement probe head  32  is in contact with the signal line  14  while a GND terminal  322  (indicated as G in  FIG. 3 ) thereof is in contact with the second GND pad  24 .  
      When the calibration is carried out using the RF measurement calibration pattern  10 , either of the signal terminal  301  and the signal terminal  321  does not lie across the GND line. Therefore, an RF signal does not affect a measurement value so that there is no occurrence of the measurement value being largely biased following an increase in signal frequency. Consequently, it is possible to implement the calibration of the RF measurement probe head  30  and the RF measurement probe head  32  with high accuracy.  
      Now, description will be given about a calibration method for the RF measurement probe heads.  
       FIG. 4  is a block diagram for explaining a measurement system for a high frequency circuit according to the present invention.  FIGS. 5 and 6  are block diagrams for explaining a method of performing zero correction of the measurement system for the high frequency circuit according to the present invention. This zero correction method is carried out when, for example, performing noise measurement or input/output measurement of the high frequency circuit.  
      As shown in  FIG. 4 , the measurement system for the high frequency circuit is as follows.  
      A signal from a signal source  36  is input into a to-be-measured circuit  40  via an input circuit  38 . The signal input is measured by a first power meter  37  disposed between the signal source  36  and the input circuit  38 . The signal input into the to-be-measured circuit  40  is performed via an SG-type RF measurement probe head  32  like that shown in  FIG. 3 .  
      An output from the to-be-measured-circuit  40  is delivered to an output circuit  46  via, for example, an SG-type RF measurement probe head  30  like that shown in  FIG. 3  and the signal output is measured by a second power meter  48 .  
      Description will be given about the zero correction method for the high frequency circuit measurement system shown in  FIG. 4 . 
      (1) First, in  FIG. 5 , the signal source  36  and the input circuit  38  are connected together via the first power meter  37  and further the second power meter  48  is connected to an RF input-side end surface of the to-be-measured circuit  40 . In this state, a correction value is input into the first power meter  37  so that the power at the RF input-side end surface of the to-be-measured circuit  40  coincides with the output power at an end surface of the signal source  36 .    

      This correction value corresponds to a passing loss of the input-side circuit of the measurement system and, by carrying out this correction, a power value, obtained at the first power meter  37 , of an output portion of the signal source  36  and the power at the RF input-side end surface of the to-be-measured circuit  40  become equal to each other. 
      (2) Then, as shown in  FIG. 6 , the RF measurement calibration pattern  10  is introduced in place of the to-be-measured circuit  40  in the high frequency circuit measurement system shown in  FIG. 4  and correction is carried out for a passing loss of the output-side circuit of the measurement system.    

      Specifically, in the measurement system shown in  FIG. 6 , the signal terminal  321  and the GND terminal  322  of the SG-type RF measurement probe head  32  serving as the RF input-side end surface of the to-be-measured circuit  40  are brought into contact with the signal line  14  and the second GND pad  24  of the RF measurement calibration pattern  10 , respectively, while the signal terminal  301  and the GND terminal  302  of the output-side RF measurement probe head  30  are brought into contact with the signal line  14  and the first GND pad  16  of the RF measurement calibration pattern  10 , respectively. This contact state is the same as that shown in  FIG. 3 .  
      In this state, a correction value is input into the second power meter  48  so that a value obtained at the second power meter  48  coincides with a value obtained at the first power meter  37 . This correction value corresponds to a passing loss of the output-side circuit of the measurement system.  
      After implementing the correction for the passing loss of the input-side circuit and the passing loss of the output-side circuit as described above, noise measurement and input/output measurement of the to-be-measured circuit are carried out.  
      Since the calibration is carried out using the RF measurement calibration pattern  10 , either of the signal terminal  301  and the signal terminal  321  does not lie across the GND line during the calibration. Therefore, an RF signal does not affect the measurement value so that there is no occurrence of the measurement value being largely biased following an increase in signal frequency. Consequently, it is possible to implement the calibration of the RF measurement probe head  30  and the RF measurement probe head  32  with high accuracy.  
      Now, description will be given about a calibration method when performing S-parameter measurement, as one example of calibration.  
       FIG. 7  is an exemplary diagram showing a measurement system when performing S-parameter measurement of a high frequency circuit, according to the present invention.  FIGS. 8, 9 ,  10 , and  11  are exemplary diagrams showing the calibration method when carrying out the S-parameter measurement of the high frequency circuit, according to the present invention. Herein, as one example, description will be given about a case where a SOLT method is used.  
      In  FIG. 7 , an RF measurement probe head  30  and an RE measurement probe head  32  are connected to a network analyzer (NWA)  50  via, for example, coaxial cables  52 , respectively. By bringing the RF measurement probe head  30  and the RF measurement probe head  32  into contact with a high frequency circuit, i.e. a to-be-measured circuit  40 , the S-parameter measurement is carried out. In this event, it is necessary to derive a correction value for the coaxial cable  52  and the RF measurement probe head  30  and a correction value for the coaxial cable  52  and the RF measurement probe head  32 .  
      Next, description will be given about the calibration method when implementing the S-parameter measurement. 
      (1) Referring to  FIG. 8 , the RF measurement probe head  30  and the RF measurement probe head  32  are each connected to a resistance pattern  54  having a circuit characteristic impedance of, for example, 50Ω to thereby carry out measurement for calibration of the network analyzer  50 .     (2) Referring to  FIG. 9 , the RF measurement probe head  30  and the RF measurement probe head  32  are each put in an open state to thereby carry out measurement for the calibration of the network analyzer  50 .     (3) Referring to  FIG. 10 , the RF measurement probe head  30  and the RF measurement probe head  32  are each connected to a short pattern  56  to thereby carry out measurement for the calibration of the network analyzer  50 .     (4) Referring to  FIG. 11 , the RF measurement probe head  30  and the RF measurement probe head  32  are connected to the RF measurement calibration pattern  10  to thereby carry out measurement for the calibration of the network analyzer  50 .    

      Specifically, the signal terminal  321  and the GND terminal  322  of the RF measurement probe head  32  are brought into contact with the signal line  14  and the second GND pad  24  of the RF measurement calibration pattern  10 , respectively, while the signal terminal  301  and the GND terminal  302  of the RF measurement probe head  30  are brought into contact with the signal line  14  and the first GND pad  16  of the RF measurement calibration pattern  10 , respectively. This contact state is the same as that shown in  FIG. 3 . In this state, the measurement is carried out for the calibration of the network analyzer  50 .  
      In this event, the characteristic impedance of the RF measurement calibration pattern  10  should be equal to that of the resistance pattern  54 .  
      Using results of the measurements (1) to (4), calculation is carried out for correcting respective S parameters.  
      Thereafter, the S-parameter measurement of the to-be-measured circuit  40  is implemented using the coaxial cable  52  and the RF measurement probe head  30  in the calibrated state and the coaxial cable  52  and the RF measurement probe head  32  in the calibrated state.  
      Also in this calibration, since the calibration is carried out using the RF measurement calibration pattern  10 , either of the signal terminal  301  and the signal terminal  321  does not lie across the GND line. Therefore, an RF signal does not affect the measurement value so that there is no occurrence of the measurement value being largely biased following an increase in signal frequency. Consequently, it is possible to implement the calibration of the RF measurement probe head  30 , the RF measurement probe head  32 , and the coaxial cables  52  with high accuracy.  
      Modification 1  
       FIG. 12  is a sectional view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      A plan view of the RF measurement calibration pattern  58  shown in  FIG. 12  is the same as  FIG. 1  being the plan view of the RF measurement calibration pattern  10  of Embodiment 1. Further, the RF measurement calibration pattern  58  shown in  FIG. 12  is sectioned along a line corresponding to the line II-II in  FIG. 1 .  
      The RF measurement calibration pattern  58  is formed by further disposing a dielectric layer  60  so as to cover the backside metal layer  22  of the RF measurement calibration pattern  10 .  
      When performing measurement using the RF measurement probe head  30  and the RF measurement probe head  32  that are disposed in such a manner as to confront each other, if calibration is carried out using the RF measurement calibration pattern  58 , either of the signal terminal  301  and the signal terminal  321  does not lie across the GND line like in case of the RF measurement calibration pattern  10 . Therefore, an RF signal does not affect the measurement value so that there is no occurrence of the measurement value being largely biased following an increase in signal frequency. Consequently, it is possible to implement the calibration of the RF measurement probe head  30  and the RF measurement probe head  32  with high accuracy. Further, even when the backside metal layer  22  is set to a constant potential, for example, a ground potential, since the backside metal layer  22  is covered with the dielectric layer  60 , it is possible to stably carry out the calibration of the RF measurement probe head  30  and the RF measurement probe head  32  regardless of the state of a place where the RF measurement calibration pattern  58  is disposed.  
      Modification 2  
       FIG. 13  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  FIG. 14  is a sectional view of the RF measurement calibration pattern taken along a line XIV-XIV in  FIG. 13 .  
      In the RF measurement calibration pattern  62  shown in  FIGS. 13 and 14 , a backside metal layer  64  extends to the surface of a dielectric substrate  12  via side surfaces thereof so as to be electrically connected to end portions, each on the side remote from or not adjacent to a signal line  14 , of a first GND pad  16  and a second GND pad  24 , respectively. Therefore, the through-hole electrodes  18  and the via holes  20 , which are provided in Embodiment 1, are not provided.  
      That is, the end portions, each on the side not adjacent to the signal line  14 , of the first GND pad  16  and the second GND pad  24  are directly connected to each other so as to be electrically conducted.  
      In the RF measurement calibration pattern  62  thus structured, in addition to the effect of the RF measurement calibration pattern  10 , it is possible to increase areas of portions of the backside metal layer  64  disposed on the side surfaces of the dielectric substrate  12 , and therefore, it is possible to reduce parasitic inductance components that are generated when the first GND pad  16  and the second GND pad  24  are commonly grounded.  
      Modification 3  
       FIG. 15  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  FIG. 16  is a sectional view of the RF measurement calibration pattern taken along a line XVI-XVI in  FIG. 15 .  
      In the REF measurement calibration pattern  66  shown in  FIGS. 15 and 16 , open stubs  68  serving as conductors are connected to end portions, each on the side not adjacent to a signal line  14 , of a first GND pad  16  and a second GND pad  24 , respectively.  
      By setting a size of the open stub  68  to a quarter of a wavelength of frequency of a signal to be measured, the first GND pad  16  and the second GND pad  24  are connected together via the open stubs  68  in a high-frequency manner. Therefore, in the RF measurement calibration pattern  66 , in addition to the effect of the RF measurement calibration pattern  10  of Embodiment 1, the via holes  20  and the backside metal layer  22  in the RF measurement calibration pattern  10  or the backside metal layer  64  extending to the surface of the dielectric substrate  12  via the side surfaces thereof in the RF measurement calibration pattern  62  of Modification 2 becomes unnecessary so that the production of the RF measurement calibration pattern is facilitated.  
      Modification 4  
       FIG. 17  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  FIG. 18  is a sectional view of the RF measurement calibration pattern taken along a line XVIII-XVIII in  FIG. 17 .  
      In the RF measurement calibration pattern  70  shown in  FIGS. 17 and 18 , end portions, each on the side not adjacent to a first end portion  14   a  or a second end portion  14   b  of a signal line  14 , of a first GND pad  16  and a second GND pad  24  are connected together via an extended portion  72  of the GND pads to form an S-shape on the surface of a dielectric substrate  12 , while the signal line  14  crossing this extended portion  72  has an air bridge  14   c  formed at a portion thereof and straddles the extended portion  72  at this air bridge  14   c.    
      In the RF measurement calibration pattern  70 , in addition to the effect of the RF measurement calibration pattern  10  of Embodiment 1, the via holes  20  and the backside metal layer  22  in the RF measurement calibration pattern  10  or the backside metal layer  64  extending to the surface of the dielectric substrate  12  via the side surfaces thereof in the RF measurement calibration pattern  62  of Modification 2 becomes unnecessary so that the production of the RF measurement calibration pattern is facilitated. There may be a case where the characteristic impedance of the air bridge  14   c  of the signal line  14  differs from that of a portion other than the air bridge  14   c  of the signal line  14  and, in this case, it may be necessary to determine a width of the air bridge  14   c  so that the impedance of the air bridge  14   c  matches that of the portion other than the air bridge  14   c.    
      Modification 5  
       FIG. 19  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  FIG. 20  is a sectional view of the RF measurement calibration pattern taken along a line XX-XX in  FIG. 19 .  
      In the RF measurement calibration pattern  74  shown in  FIGS. 19 and 20 , end portions, each on the side not adjacent to a signal line  14 , of a first GND pad  16  and a second GND pad  24  are connected together via an extended portion  72  to form an S-shape on the surface of a dielectric substrate  12 , while this extended portion  72  has an air bridge  72   a  formed at a portion thereof and straddles the signal line  14  at this air bridge  72   a.    
      The RF measurement calibration pattern  74  thus structured exhibits an effect like that of the RF measurement calibration pattern  70  of Modification 4.  
      There may be a case where the characteristic impedance of the air bridge  72   a , under which the signal line  14  is located, of the extended portion  72  does not match that of the other portion and, in this case, it may be necessary to change a width of the line in consideration thereof.  
      Modification 6  
       FIG. 21  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      In the RF measurement calibration pattern  76  shown in  FIG. 21 , a first GND pad  16  is disposed with a predetermined interval defined between itself and a first end portion  14   a  of a signal line  14 . What differs from the RF measurement calibration pattern  10  resides in that the first GND pad  16  in this modification has a front end portion disposed along the signal line  14  so as to confront the signal line  14 . The first GND pad  16  is electrically separated from the signal line  14 . The other end portion of the first GND pad  16  extends in a direction away from the signal line  14  and is connected to a through-hole electrode  18 .  
      Further, a second GND pad  24  is disposed with the predetermined interval defined between itself and a second end portion  14   b  of the signal line  14 . The second GND pad  24  also has a front end portion disposed along the signal line  14  so as to confront the signal line  14  and is electrically separated from the signal line  14 . The other end portion of the second GND pad  24  extends in a direction away from the signal line  14  and is connected to a through-hole electrode  18 .  
      The first GND pad  16  and the second GND pad  24  are not located exactly face to face, but are disposed so as to confront each other via the signal line  14  interposed therebetween.  
      The first GND pad  16  and the second GND pad  24  are electrically connected together via the through-hole electrodes  18 , via holes  20 , and a backside metal layer  22 .  
      A sectional view, taken along a line XXI-XXI in  FIG. 21 , of the RF measurement calibration pattern  76  corresponds to  FIG. 2 .  
      Further, like the RF measurement calibration pattern  58  of Modification 1, the RF measurement calibration pattern  76  may further have a dielectric layer  60  disposed to cover the backside metal layer  22 ,  
       FIG. 22  is an exemplary diagram showing the state where RF measurement probe heads are in contact with the RF measurement calibration pattern according to Modification 6 of the present invention.  
      In  FIG. 22 , like in case of the RF measurement calibration pattern  10 , an RF measurement probe head  30  and an RF measurement probe head  32  are disposed so as to confront each other. These two RF measurement probe heads  30  and  32  are both, for example, SG-type RF measurement probe heads.  
      When the calibration is carried out using the RF measurement calibration pattern  76 , either of a signal terminal  301  of the RF measurement probe head  30  and a signal terminal  321  of the RF measurement probe head  32  does not lie across the GND line. Therefore, an RF signal does not affect a measurement value so that there is no occurrence of the measurement value being largely biased following an increase in signal frequency. Consequently, it is possible to implement the calibration of the RF measurement probe head  30  and the RF measurement probe head  32  with high accuracy.  
      Further, since the signal terminal  301  of the RF measurement probe head  30  and the signal terminal  321  of the RF measurement probe head  32  confront each other with a distance defined therebetween in a longitudinal direction of the signal line  14  and are located close to each other in a lateral direction, the crosstalk is reduced so that the calibration can be carried out with high accuracy.  
      Modification 7  
       FIG. 23  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      The RF measurement calibration pattern  78  shown in  FIG. 23  has basically the same structure as the RF measurement calibration pattern  62  of Modification 2 shown in  FIGS. 13 and 14 . What differs from the RF measurement calibration pattern  62  resides in that while the first GND pad  16  and the second GND pad  24  of the REF measurement calibration pattern  62  each have a front end portion located on a prolongation of the signal line  14  in its longitudinal direction, a first GND pad  16  and a second GND pad  24  of the RF measurement calibration pattern  78  each have a front end portion disposed along a signal line  14  and a backside metal layer  64  is in contact with side surfaces of the first GND pad  16  and the second GND pad  24 , respectively.  
      The other structure of the RF measurement calibration pattern  78  is the same as that of the RF measurement calibration pattern  62 . A sectional view, taken along a line XXIII-XXIII in  FIG. 23 , of the RF measurement calibration pattern  78  corresponds to  FIG. 14 .  
      Therefore, in the RF measurement calibration pattern  78 , in addition to the effect of the RF measurement calibration pattern  62 , since the signal terminal  301  of the RF measurement probe head  30  and the signal terminal  321  of the RF measurement probe head  32  confront each other with a distance defined therebetween in a longitudinal direction of the signal line  14  and are located close to each other in a lateral direction, the crosstalk is reduced so that the calibration can be carried out with high accuracy.  
      Modification 8  
       FIG. 24  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      The RF measurement calibration pattern  80  shown in  FIG. 24  has basically the same structure as the RF measurement calibration pattern  66  of Modification 3 shown in  FIGS. 15 and 16 . What differs from the RF measurement calibration pattern  66  resides in that while the first GND pad  16  and the second GND pad  24  of the RF measurement calibration pattern  66  each have a front end portion located on a prolongation of the signal line  14  in its longitudinal direction, a first GND pad  16  and a second GND pad  24  of the RF measurement calibration pattern  80  each have a front end portion disposed along a signal line  14 .  
      The other structure of the RF measurement calibration pattern  80  is the same as that of the RF measurement calibration pattern  66 . A sectional view, taken along a line XXIV-XXIV in  FIG. 24 , of the RF measurement calibration pattern  80  corresponds to  FIG. 16 .  
      Therefore, in the RF measurement calibration pattern  80 , in addition to the effect of the RF measurement calibration pattern  66 , since the signal terminal  301  of the RF measurement probe head  30  and the signal terminal  321  of the RF measurement probe head  32  confront each other with a distance defined therebetween in a longitudinal direction of the signal line  14  and are located close to each other in a lateral direction, the crosstalk is reduced so that the calibration can be carried out with high accuracy.  
      Modification 9  
       FIG. 25  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  FIG. 26  is a sectional view of the RF measurement calibration pattern taken along a line XXVI-XXVI in  FIG. 25 .  
      The RF measurement calibration pattern  82  shown in  FIG. 25  has basically the same structure as the RF measurement calibration pattern  70  of Modification 4 shown in  FIG. 17 . What differs from the RF measurement calibration pattern  70  resides in that while the first GND pad  16  and the second GND pad  24  of the RF measurement calibration pattern  70  each have a front end portion located on a prolongation of the signal line  14  in its longitudinal direction, a first GND pad  16  and a second GND pad  24  of the RF measurement calibration pattern  82  are disposed along a signal line  14  and each have a front end portion disposed side by side with a first end portion  14   a  or a second end portion  14   b  of the signal line  14 .  
      The other structure of the RF measurement calibration pattern  82  is the same as that of the RF measurement calibration pattern  70 .  
      Therefore, in the RF measurement calibration pattern  82 , in addition to the effect of the RE measurement calibration pattern  70 , since the signal terminal  301  of the RF measurement probe head  30  and the signal terminal  321  of the RF measurement probe head  32  confront each other with a distance defined therebetween in a longitudinal direction of the signal line  14  and are located close to each other in a lateral direction, the crosstalk is reduced so that the calibration can be carried out with high accuracy.  
      Modification 10  
       FIG. 27  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      The RF measurement calibration pattern  84  shown in  FIG. 27  has basically the same structure as the RF measurement calibration pattern  74  of Modification 5 shown in  FIGS. 19 and 20 . What differs from the RF measurement calibration pattern  74  resides in that while the first GND pad  16  and the second GND pad  24  of the RF measurement calibration pattern  74  each have a front end portion located on a prolongation of the signal line  14  in its longitudinal direction, a first GND pad  16  and a second GND pad  24  of the RF measurement calibration pattern  84  are disposed along a signal line  14  and each have a front end portion disposed side by side with a first end portion  14   a  or a second end portion  14   b  of the signal line  14 .  
      The other structure of the RF measurement calibration pattern  84  is the same as that of the RF measurement calibration pattern  74 .  
      A sectional view, taken along a line XXVII-XXVII in  FIG. 27 , of the RF measurement calibration pattern  84  corresponds to  FIG. 20 .  
      Therefore, in the RF measurement calibration pattern  84 , in addition to the effect of the RF measurement calibration pattern  74 , since the signal terminal  301  of the RF measurement probe head  30  and the signal terminal  321  of the RF measurement probe head  32  confront each other with a distance defined therebetween in a longitudinal direction of the signal line  14  and are located close to each other in a lateral direction, the crosstalk is reduced so that the calibration can be carried out with high accuracy.  
      As described above, the RF measurement calibration pattern according to Embodiment 1 comprises the dielectric substrate, the signal line having one characteristic impedance of, for example, 50Ω and extending to have the first and second end portions on the dielectric substrate, the first GND pad having one end portion disposed close to and with a predetermined interval from the first end portion of the signal line, the second GND pad having one end portion disposed close to and with a predetermined interval from the second end portion of the signal line, and the through-hole electrodes, the via holes, and the backside metal layer for electrically connecting between the first GND pad and the second GND pad, or the backside metal layer extending to the surface of the dielectric substrate via the side surfaces thereof for electrically connecting between the first GND pad and the second GND pad, or the open stubs for connecting between the first GND pad and the second GND pad in a high-frequency manner. With this structure, even when the SG-type RF measurement probe heads or the GS-type RF measurement probe heads are used so as to confront each other with their signal terminals being brought into contact with the signal line of the calibration pattern, either of the signal terminals of the RF measurement probe heads does not lie across the GND line. Therefore, the RF signal does not affect the measurement value so that there is no occurrence of the measurement value being largely biased following an increase in signal frequency. Consequently, it is possible to implement the calibration of the RF measurement probe heads with high accuracy.  
      Further, in the high frequency circuit property measurement method for carrying out the calibration by the use of the RF measurement calibration pattern according to Embodiment 1, since the RF signal has no effect on either of the signal terminals of the first and second property measurement probe heads, the accurate calibration can be achieved so that the property measurement of the high frequency circuit is precisely carried out. Consequently, selection of high frequency circuits can be accurately performed to thereby improve the yield of high frequency circuit devices.  
      The foregoing description has been given about the case where the SG-type RF measurement probe heads are used. However, if the first GND pad and the second GND pad are arranged so as to be in a reflected image relation with respect to the center axis of the signal line, the present invention is also applicable to a case where the GS-type RF measurement probe heads are used.  
     Embodiment 2  
       FIG. 28  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      The RF measurement calibration pattern  86  shown in  FIG. 28  has basically the same structure as the RF measurement calibration pattern  76  of Modification 6 of Embodiment 1 shown in  FIG. 21 . What differs from the RF measurement calibration pattern  76  resides in that there is further disposed a third GND pad  88  serving as a third constant potential line that confronts face to face the first GND pad  16  of the RF measurement calibration pattern  76  via the signal line  14  at the first end portion  14   a  thereof and is electrically separated from the signal line  14 .  
      The third GND pad  88  has a front end portion disposed along the signal line  14  and confronting face to face a front end portion of the first GND pad  16  via the signal line  14 . The other end portion of the third GND pad  88  extends in a direction away from the signal line  14  and is connected to a through-hole electrode  18 .  
      The third GND pad  88  is electrically connected to the backside metal layer  22  via the through-hole electrode  18  and a via hole  20 . Therefore, the third GND pad  88  is electrically connected to the first GND pad  16  and the second GND pad  24 .  
      The structure of the third GND pad  88  is the same as that of the first GND pad  16 , wherein a gold-plating layer is disposed on the surface of a metal layer. In this embodiment, the through-hole electrode  18  connected to the third GND pad  88  is formed by the metal layer part of which also forms the third GND pad  88 .  
      A sectional view taken along a line XXVIII-XXVIII in  FIG. 28  corresponds to  FIG. 2 .  
      In the RF measurement calibration pattern  86  according to Embodiment 2, an SG-type RE measurement probe head is put in contact at the second end portion  14   b  of the signal line  14  while an SG-type, GS-type or GSG-type RF measurement probe head is contactable at the first end portion  14   a  of the signal line  14 .  
      When performing calibration for property measurement of a high frequency circuit by the use of the SG-type RF measurement probe heads, by the use of the GS-type RF measurement probe heads wherein the second GND pad  24  is arranged so as to be in a reflected image relation with respect to the center axis of the signal line from the current state, or by the use of the SG-type RF measurement probe head and the GS-type or GSG-type RF measurement probe head confronting thereto, if the calibration is carried out using the RF measurement calibration pattern  86 , either of the signal terminals does not lie across the GND line as described in Embodiment 1. Therefore, an RF signal does not affect the measurement value so that there is no occurrence of the measurement value being largely biased following an increase in signal frequency. Consequently, it is possible to implement the calibration of the RF measurement probe heads with high accuracy.  
      Modification 11  
       FIG. 29  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      The RF measurement calibration pattern  90  shown in  FIG. 29  is a modification of Embodiment 2, but has basically the same structure as the RF measurement calibration pattern  78  of Modification 7 of Embodiment 1 shown in  FIG. 23 . What differs from the RF measurement calibration pattern  78  resides in that there is further disposed a third GND pad  88  that confronts the first GND pad  16  of the RF measurement calibration pattern  78  via the signal line  14  and is electrically separated from the signal line  14 . The third GND pad  88  has a front end portion disposed along the signal line  14  and has a side surface contacting the backside metal layer  64  like the first GND pad  16 . Therefore, the first GND pad  16 , the second GND pad  24 , and the third GND pad  88  are electrically connected together.  
      A sectional view taken along a line XXIX-XXIX in  FIG. 29  corresponds to  FIG. 14 .  
      Therefore, the RF measurement calibration pattern  90  is applicable when performing calibration for property measurement of a high frequency circuit by the use of the SG-type RF measurement probe heads, by the use of the GS-type RF measurement probe heads wherein the second GND pad  24  is arranged so as to be in a reflected image relation with respect to the center axis of the signal line from the current state, or by the use of the SG-type RF measurement probe head and the GS-type or GSG-type RF measurement probe head confronting thereto, and exhibits an effect like that of Modification 7 of Embodiment 1.  
      Modification 12  
       FIG. 30  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      The RF measurement calibration pattern  92  shown in  FIG. 30  is a modification of Embodiment 2, but has basically the same structure as the RF measurement calibration pattern  80  of Modification 8 of Embodiment 1 shown in  FIG. 24 . What differs from the RF measurement calibration pattern  80  resides in that there is further disposed a third GND pad  88  that confronts the first GND pad  16  of the RF measurement calibration pattern  80  via the signal line  14  and is electrically separated from the signal line  14 . The third GND pad  88  has a front end portion disposed along the signal line  14  and an open stub  68  is connected to an end portion, on the side not adjacent to the signal line  14 , of the third GND pad  88 .  
      By setting a size of the open stub  68  to a quarter of a wavelength of frequency of a signal to be measured, the first GND pad  16 , the second GND pad  24 , and the third GND pad  88  are connected together via the open stubs  68  in a high-frequency manner.  
      A sectional view taken along a line XXX-XXX in  FIG. 30  corresponds to  FIG. 16 .  
      Therefore, the RF measurement calibration pattern  92  is applicable when performing calibration for property measurement of a high frequency circuit by the use of the SG-type RF measurement probe heads, by the use of the GS-type RF measurement probe heads wherein the second GND pad  24  is arranged so as to be in a reflected image relation with respect to the center axis of the signal line from the current state, or by the use of the SG-type RF measurement probe head and the GS-type or GSG-type RF measurement probe head confronting thereto, and exhibits an effect like that of Modification 8 of Embodiment 1.  
      Modification 13  
       FIG. 31  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      The RF measurement calibration pattern  94  shown in  FIG. 31  is a modification of Embodiment 2, but has basically the same structure as the RF measurement calibration pattern  82  of Modification 9 of Embodiment 1 shown in  FIGS. 25 and 26 . What differs from the RF measurement calibration pattern  82  resides in that there is further disposed a third GND pad  88  that confronts the first GND pad  16  of the RF measurement calibration pattern  82  via the signal line  14  and is electrically separated from the signal line  14 . The third GND pad  88  is disposed along the signal line  14  and has a front end portion disposed side by side with the first end portion  14   a  of the signal line  14 . The third GND pad  88  is connected to the first GND pad  16  and the second GND pad  24  via the extended portion  72  on the surface of the dielectric substrate.  
      A sectional view taken along a line XXXI-XXXI in  FIG. 31  corresponds to  FIG. 26 .  
      Therefore, the RF measurement calibration pattern  94  is applicable when performing calibration for property measurement of a high frequency circuit by the use of the SG-type RF measurement probe heads, by the use of the GS-type RF measurement probe heads wherein the second GND pad  24  is arranged so as to be in a reflected image relation with respect to the center axis of the signal line from the current state, or by the use of the SG-type RF measurement probe head and the GS-type or GSG-type RF measurement probe head confronting thereto, and exhibits an effect like that of Modification 9 of Embodiment 1.  
      Modification 14  
       FIG. 32  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      The RF measurement calibration pattern  96  shown in  FIG. 32  is a modification of Embodiment 2, but has basically the same structure as the RF measurement calibration pattern  84  of Modification 10 of Embodiment 1 shown in  FIG. 27 . What differs from the RF measurement calibration pattern  84  resides in that there is further disposed a third GND pad  88  that confronts the first GND pad  16  of the RF measurement calibration pattern  84  via the signal line  14  and is electrically separated from the signal line  14 . The third GND pad  88  is disposed along the signal line  14  and has a front end portion disposed side by side with the first end portion  14   a  of the signal line  14 . The third GND pad  88  is connected to the first GND pad  16  and the second GND pad  24  via the extended portion  72  on the surface of the dielectric substrate.  
      A sectional view taken along a line XXXII-XXXII in  FIG. 32  corresponds to  FIG. 20 .  
      Therefore, the RF measurement calibration pattern  96  is applicable when performing calibration for property measurement of a high frequency circuit by the use of the SG-type RF measurement probe heads, by the use of the GS-type RF measurement probe heads wherein the second GND pad  24  is arranged so as to be in a reflected image relation with respect to the center axis of the signal line from the current state, or by the use of the SG-type RF measurement probe head and the GS-type or GSG-type RF measurement probe head confronting thereto, and exhibits an effect like that of Modification 10 of Embodiment 1.  
      As described above, the RF measurement calibration pattern according to Embodiment 2 comprises the dielectric substrate, the signal line having one characteristic impedance of, for example, 50Ω and extending to have the first and second end portions on the dielectric substrate, the first GND pad having one end portion disposed close to and with a predetermined interval from the first end portion of the signal line, the second GND pad having one end portion disposed close to and with a predetermined interval from the second end portion of the signal line, the third GND pad confronting face to face the first GND pad via the signal line, and the through-hole electrodes, the via holes, and the backside metal layer for electrically connecting together the first GND pad, the second GND pad, and the third GND pad, or the backside metal layer extending to the surface of the dielectric substrate via the side surfaces thereof for electrically connecting together the first GND pad, the second GND pad, and the third GND pad, or the open stubs for connecting together the first GND pad, the second GND pad, and the third GND pad in a high-frequency manner. With this structure, even when the SG-type RF measurement probe heads, the GS-type RF measurement probe heads, or the SG-type RF measurement probe head and the GS-type or GSG-type RF measurement probe head are used so as to confront each other with their signal terminals being brought into contact with the signal line of the calibration pattern, either of the signal terminals of the RF measurement probe heads does not lie across the GND line. Therefore, the RF signal does not affect the measurement value so that there is no occurrence of the measurement value being largely biased following an increase in signal frequency. Consequently, it is possible to implement the calibration of the RF measurement probe heads with high accuracy.  
      Further, in the high frequency circuit property measurement method for carrying out the calibration by the use of the RF measurement calibration pattern according to Embodiment 2, since the RF signal has no effect on either of the signal terminals of the first and second property measurement probe heads, the accurate calibration can be achieved so that the property measurement of the high frequency circuit is precisely carried out. Consequently, selection of high frequency circuits can be accurately performed to thereby improve the yield of high frequency circuit devices.  
     Embodiment 3  
       FIG. 33  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      The RF measurement calibration pattern  98  shown in  FIG. 33  is formed by further disposing, on the RF measurement calibration pattern  86  of Embodiment 2, a fourth GND pad  100  serving as a fourth constant potential line that confronts the second GND pad  24  via the signal line  14  and is electrically separated from the signal line  14 .  
      The fourth GND pad  100  has a front end portion disposed along the signal line  14  at the second end portion  14   b  thereof and confronting face to face a front end portion of the second GND pad  24  via the signal line  14 . The other end portion of the fourth GND pad  100  extends in a direction away from the signal line  14  and is connected to a through-hole electrode  18 .  
      The fourth GND pad  100  is electrically connected to the backside metal layer  22  via the through-hole electrode  18  and a via hole  20 . Therefore, the fourth GND pad  100  is electrically connected to the first GND pad  16 , the second GND pad  24 , and the third GND pad  88 .  
      The structure of the fourth GND pad  100  is the same as that of the first GND pad  16 , wherein a gold-plating layer is disposed on the surface of a metal layer. In this embodiment, the through-hole electrode  18  connected to the fourth GND pad  100  is formed by the metal layer part of which also forms the fourth GND pad  100 .  
      A sectional view taken along a line XXXIII-XXXIII in  FIG. 33  corresponds to  FIG. 2 .  
      In the RF measurement calibration pattern  98  according to Embodiment 3, the RF measurement probe head of any type, i.e. any of the SG-type RF measurement probe head, the GS-type RF measurement probe head, and the GSG-type RF measurement probe head, is usable or contactable at each of the first end portion  14   a  and the second end portion  14   b  of the signal line  14 .  
      When performing calibration for property measurement of a high frequency circuit by the use of any type or types of the RF measurement probe heads, the calibration can be carried out using the RF measurement calibration pattern  100 . When the calibration is implemented using the RF measurement calibration pattern  100 , either of the signal terminals of the RF measurement probe heads of any type or types does not lie across the GND line of the RF measurement calibration pattern  100  as described in Embodiment 1. Therefore, an RF signal does not affect a measurement value so that there is no occurrence of the measurement value being largely biased following an increase in signal frequency. Consequently, it is possible to implement the calibration of the RF measurement probe heads with high accuracy.  
      Modification 15  
       FIG. 34  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      The RF measurement calibration pattern  102  shown in  FIG. 34  is a modification of Embodiment 3, but is formed by further disposing, on the RF measurement calibration pattern  90  of Modification 11 of Embodiment 2 shown in  FIG. 29 , a fourth GND pad  100  that confronts the second GND pad  24  via the signal line  14  and is electrically separated from the signal line  14 . The fourth GND pad  100  has a front end portion disposed along the signal line  14  and has a side surface contacting the backside metal layer  64  like the first GND pad  16 . Therefore, the first GND pad  16 , the second GND pad  24 , the third GND pad  88 , and the fourth GND pad  100  are electrically connected together.  
      A sectional view taken along a line XXXIV-XXXIV in  FIG. 34  corresponds to  FIG. 14 .  
      In the RF measurement calibration pattern  102  according to Modification 15, the RF measurement probe head of any type, i.e. any of the SG-type RF measurement probe head, the GS-type RF measurement probe head, and the GSG-type RF measurement probe head, is usable or contactable at each of the first end portion  14   a  and the second end portion  14   b  of the signal line  14 .  
      When performing calibration for property measurement of a high frequency circuit by the use of any type or types of the RF measurement probe heads, the RF measurement calibration pattern  102  enables the calibration of the RF measurement probe heads and exhibits an effect like that of Modification 11 of Embodiment 2.  
      Modification 16  
       FIG. 35  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      The RF measurement calibration pattern  104  shown in  FIG. 35  is a modification of Embodiment 3, but is formed by further disposing, on the RF measurement calibration pattern  92  of Modification 12 of Embodiment 2 shown in  FIG. 30 , a fourth GND pad  100  that confronts the second GND pad  24  via the signal line  14  and is electrically separated from the signal line  14 . The fourth GND pad  100  has a front end portion disposed along the signal line  14  and an open stub  68  is connected to an end portion, on the side not adjacent to the signal line  14 , of the fourth GND pad  100 . Therefore, the first GND pad  16 , the second GND pad  24 , the third &amp;ND pad  88 , and the fourth GND pad  100  are connected together in a high-frequency manner.  
      A sectional view taken along a line XXXV-XXXV in  FIG. 35  corresponds to  FIG. 16 .  
      In the RF measurement calibration pattern  104  according to Modification 16, the RF measurement probe head of any type, i.e. any of the SG-type RF measurement probe head, the GS-type RF measurement probe head, and the GSG-type RF measurement probe head, is usable or contactable at each of the first end portion  14   a  and the second end portion  14   b  of the signal line  14 .  
      When performing calibration for property measurement of a high frequency circuit by the use of any type or types of the RF measurement probe heads, the RF measurement calibration pattern  104  enables the calibration of the RF measurement probe heads and exhibits an effect like that of Modification 12 of Embodiment 2.  
      Modification 17  
       FIG. 36  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      The RF measurement calibration pattern  106  shown in  FIG. 36  is a modification of Embodiment 3, but is formed by further disposing, on the RF measurement calibration pattern  94  of Modification 13 of Embodiment 2 shown in  FIG. 31 , a fourth GND pad  100  that confronts the second GND pad  24  via the signal line  14  and is electrically separated from the signal line  14 . The fourth GND pad  100  is disposed along the signal line  14  and has a front end portion disposed side by side with the second end portion  14   b  of the signal line  14 . The fourth GND pad  100  is connected to the first GND pad  16 , the second GND pad  24 , and the third GND pad  88  via the extended portion  72  of the GND pads on the surface of the dielectric substrate.  
      A sectional view taken along a line XXXVI-XXXVI in  FIG. 36  corresponds to  FIG. 26 .  
      In the RF measurement calibration pattern  106  according to Modification 17, the RF measurement probe head of any type, i.e. any of the SG-type RF measurement probe head, the GS-type RF measurement probe head, and the GSG-type RF measurement probe head, is usable or contactable at each of the first end portion  14   a  and the second end portion  14   b  of the signal line  14 .  
      When performing calibration for property measurement of a high frequency circuit by the use of any type or types of the RF measurement probe heads, the RF measurement calibration pattern  106  enables the calibration of the RE measurement probe heads and exhibits an effect like that of Modification 13 of Embodiment 2.  
      Modification 18  
       FIG. 37  is a plan view of an RF measurement calibration pattern according to one embodiment of the present invention.  
      The RF measurement calibration pattern  108  shown in  FIG. 37  is a modification of Embodiment 3, but is formed by further disposing, on the RF measurement calibration pattern  96  of Modification 14 of Embodiment 2 shown in  FIG. 32 , a fourth GND pad  100  that confronts the second GND pad  24  via the signal line  14  and is electrically separated from the signal line  14 . The fourth GND pad  100  is disposed along the signal line  14  and has a front end portion disposed side by side with the second end portion  14   b  of the signal line  14 . The fourth GND pad  100  is connected to the first GND pad  16 , the second GND pad  24 , and the third GND pad  88  via the extended portion  72  of the GND pads on the surface of the dielectric substrate.  
      A sectional view taken along a line XXXVII-XXXVII in  FIG. 37  corresponds to  FIG. 20 .  
      In the RF measurement calibration pattern  108  according to Modification 18, the RF measurement probe head of any type, i.e. any of the SG-type RF measurement probe head, the GS-type RF measurement probe head, and the GSG-type RF measurement probe head, is usable or contactable at each of the first end portion  14   a  and the second end portion  14   b  of the signal line  14 .  
      When performing calibration for property measurement of a high frequency circuit by the use of any type or types of the RF measurement probe heads, the RF measurement calibration pattern  108  enables the calibration of the RF measurement probe heads and exhibits an effect like that of Modification 14 of Embodiment 2.  
      As described above, the RF measurement calibration pattern according to Embodiment 3 comprises the dielectric substrate, the signal line having one characteristic impedance of, for example, 50Ω and extending to have the first and second end portions on the dielectric substrate, the first GND pad having one end portion disposed close to and with a predetermined interval from the first end portion of the signal line, the second GND pad having one end portion disposed close to and with a predetermined interval from the second end portion of the signal line, the third GND pad confronting face to face the first GND pad via the signal line, the fourth GND pad confronting face to face the second GND pad via the signal line, and the through-hole electrodes, the via holes, and the backside metal layer for electrically connecting together the first GND pad, the second GND pad, the third &amp;ND pad, and the fourth GND pad, or the backside metal layer extending to the surface of the dielectric substrate via the side surfaces thereof for electrically connecting together the first GND pad, the second GND pad, the third GND pad, and the fourth GND pad, or the open stubs for connecting together the first GND pad, the second GND pad, the third GND pad, and the fourth GND pad in a high-frequency manner. With this structure, even when the RF measurement probe heads of any combination among the SG-type RF measurement probe head/heads, the GS-type RF measurement probe head/heads, and the GSG-type RF measurement probe head/heads are used so as to confront each other with their signal terminals being brought into contact with the signal line of the calibration pattern, either of the signal terminals of the RF measurement probe heads does not lie across the GND line. Therefore, the RF signal does not affect the measurement value so that there is no occurrence of the measurement value being largely biased following an increase in signal frequency. Consequently, it is possible to implement the calibration of the RF measurement probe heads with high accuracy.  
      Further, in the high frequency circuit property measurement method for carrying out the calibration by the use of the RF measurement calibration pattern according to Embodiment 3, since the RF signal has no effect on either of the signal terminals of the first and second property measurement probe heads of any combination, the accurate calibration can be achieved so that the property measurement of the high frequency circuit is precisely carried out. Consequently, selection of high frequency circuits can be accurately performed to thereby improve the yield of high frequency circuit devices.  
     Embodiment 4  
       FIG. 38  is a plan view of an RF measurement calibration jig according to one embodiment of the present invention.  FIG. 39  is a sectional view of the RF measurement calibration jig taken along a line XXXIX-XXXIX in  FIG. 38 .  
      In  FIGS. 38 and 39 , the RF measurement calibration jig  110  includes, as one example, the RF measurement calibration pattern  62  of Modification 2 of Embodiment 1 shown in  FIGS. 13 and 14 . Note that use can be made of any of the foregoing RF measurement calibration patterns of Embodiment 1, Embodiment 2, and Embodiment 3.  
      A dielectric substrate  112  of the RF measurement calibration jig  110  is formed with a recessed portion  112   a  for mounting therein the RF measurement calibration pattern  62 . The recessed portion  112   a  is formed so as to exchangeably receive therein RF measurement calibration patterns, one at a time, having different lengths. Therefore, it is possible to carry out calibration at predetermined required frequencies with one jig.  
      As described above, the RF measurement calibration jig according to this embodiment makes it possible to carry out calibration at predetermined required frequencies by the use of one jig. Consequently, selection of high frequency circuits can be accurately and easily performed to thereby improve the yield of high frequency circuit devices with the simple process.  
      The foregoing description has been given about the RF measurement calibration pattern using the dielectric substrate. However, the effect can be similarly achieved even when a signal line and respective GND pads are formed on a wafer instead of the dielectric substrate.  
      As described above, the high frequency circuit property measurement method according to the present invention is suitable for an RF measurement method for a high frequency circuit for use in a communication device adapted for a microwave band or a millimeter wave band that is used in mobile communication, optical communication, satellite communication, and the like.  
      While the presently preferred embodiments of the present invention have been shown and described. It is to be understood these disclosures are for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.