Abstract:
A multifrequency-band microstrip antenna, for use in microwave to millimeter-wave band, is provided with different thicknesses of dielectric films to optimized the performance in any operating frequencies desired. In a double lamination antena substrate, for example, lamination  1  is made up of a number of dielectric films having a given dielectric constant and thickness, and lamination  2  is made up of a number of dielectric films of another given dielectric constant and thickness. An radiation element is provided between the films in lamination  2 , and a ground plane is provided between the films in lamination  1 . A strip conductor for propagating radio signals is provided in lamination  1  such that the ground plane intervenes between the radiation element and the strip conductor, thereby shielding the radiation element except for a slot formed in the ground plane. The input signal couples to the radiation element through the slot, thereby feeding the radiation element and operating the microstrip antenna.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to antennas, used for transmitting and receiving radio signals in the frequency range of microwave to millimeter-wave bands, having integral power lines and high frequency circuits for signal processing. The present invention relates, in particular, to a microstrip antenna of compact and high-flexbility design, comprising a plurality of radiation elements, provided in a common unit, for use in different frequency bands. 
     Such an antenna would find applications in personal communication systems including entry-control and security cards, terminals for ATM wireless access (AWA), remote-access terminal and others. Because of its compact and low-profile features, the antenna is also suitable for use in interior LAN, needing a multi-band system to overcome the operational problems of fading and shadowing caused by multi-pass interference being experienced in such a network. 
     2. Description of the Prior Art 
     Microstrip antennas are being used for radar, mobile and satellite communication systems, because of their compact, thin and light weight features. 
     Microstrip antennas are particularly suitable for use as active antennas. Active antenna is an antenna having all of the necessary components, such as an antenna element, a feeding circuits, active devices or active circuits, integrally provided on a monolithic substrate, thus producing a compact, low cost and multi-function antenna equipment. 
     FIG. 14A is a perspective view of an example of the configuration of the conventional microstrip antennas, and FIG. 14B is a cross sectional view through a plane at A—A in FIG.  14 A. The device includes an radiation element  102 , a ground plane  101  and a dielectric film member  100 . The radiation element  102 , the ground plane  101  and the dielectric film member  100  constitute a microstrip antenna  104 . A strip conductor  103 , together with the ground plane  101  and the dielectric film member  100  constitute a microstrip line  105 . A signal propagated through the microstrip line  105  couples with the antenna element  102  in accordance with the electromagnetic field generated by the microstrip line  105  and feeds the microstrip antenna  104 . The microstrip  104  is a type of resonators, and the generated radio waves are radiateted into the free space. 
     However, in this type of microstrip antenna, the microstrip line  105  locates in the direction of radiation of the waves with respect to the ground plane  101 , leading to an undesirable problem that the unnecessary radiation from the microstrip line adversely affects the radiation field of the microstrip antenna. 
     To resolve this problem, there has been a suggestion for a different configuration of microstrip antenna such as the one presented in FIGS. 15A,  15 B. 
     FIG. 15A is a perspective view of another example of the conventional microstrip antennas, and FIG. 15B shows a cross sectional view through a plane at A—A in FIG.  15 A. The device includes an radiation element  112 , a ground plane  111  and a first dielectric film member  110 . The radiation element  112 , the ground plane  111  and the first dielectric film member  110  constitute a microstrip antenna  114 . 
     The device also has a strip conductor  113  and a second dielectric film member  115 . The strip conductor  113 , the second dielectric film member  115  and the ground plane  111  constitute a microstrip line  116 . Also, a slot  117  is fabricated on the ground plane  111 . 
     The signal propagated through the microstrip line  116  couples with the radiation element  112  in accordance with the electromagnetic field generated by the microstrip line  116  through the slot  117 , and feeds the microstrip antenna  114 . 
     The unnecessary radiation from the microstrip line  116  in the microstrip antenna shown in FIGS. 15A and 15B generates little adverse effects on the radiation field of the microstrip antenna  114 , because the ground plane  111  intervenes and blocks the parasitic signals from the microstrip line  116  (acting as the power line) affecting the performance of the radiation element  112 . 
     The properties of the microstrip antennas shown in FIGS. 14A,  14 B and FIGS. 15A,  15 B can be obtained from the dielectric constant, the dielectric dissipation factor (tanδ) and the thickness (h) of the first dielectric film substrate  110  (or  100 ), and the conductivity (σ) of the radiation element  102  or  112 . 
     FIG. 16 is a graph showing the relationship between the radiation efficiency and no-load Q of a circular microstrip antenna without considering the effect of the surface wave (refer to K. Hirasawa and M. Haneishi, “Analysis, Design, and Measurement of Small and Low-Profile Antennas”, Artech House, Norwood, Mass. 02062). 
     In this case, if S is the voltage standing wave ratio (VSWR), the bandwidth BW of the microstrip antenna is given by the following equation: 
     
       
         BW=(S−1)/Q 0 S 0.5 . 
       
     
     Therefore, the bandwidth of an antenna is inversely proportional to no-load Q, and, to obtain high performance properties in an antenna (high radiation efficiency, wide bandwidths etc.), FIG. 16 shows that it is preferable to have a thick dielectric film. 
     However, when the thickness h exceeds a certain value, the antenna performance becomes degraded because the loss caused by surface waves can no longer be ignored and higher order excitations are generated in the thickness direction. Therefore, in designing a high-performance antenna, the thickness of the dielectric film is the most important parameter. For microstrip antennas in general, the thickness of the dielectric film is chosen in the range of {fraction (1/50)}th to {fraction (1/20)}th of the free-space wavelength of the center frequency. 
     Although microstrip antennas are convenient and advantageous in many respects, they operate in a single frequency band and has a high Q-value, and therefore, if they are to find a wider application possibilities, increased bandwidth of the antenna is mandatory. 
     An attempt has been made to solve these problems by developing a dual-frequency microstrip antenna which is shown in FIGS. 17A,  17 B. 
     FIG. 17A shows a plan view of a dual-frequency microstrip antenna, and FIG. 17B shows a cross sectional view through a plane at A—A in FIG.  17 A. The antenna shown in this drawing is made by laminating two dielectric films  100  having one radiation element  102  between the two films and another radiation element  102  of the same size above the top film  100 . Operating power is supplied to each of the radiation elements  102  through a power pin  200  formed on a ground plane  101  which is disposed opposite and away from the radiation element. 
     In this device, the boundary conditions of the electric and magnetic field components of the top and bottom dielectric films  100  coupled to each of the radiation elements  102  (disposed above and below the dielectric film member  100 ) are different, thereby providing different equivalent dielectric constants to enable the antenna to perform as a dual-frequency microstrip antenna. 
     More specifically, denoting the dielectric constant for the upper dielectric film  100  by εr1 and that for the lower dielectric film  100  by εr2, the equivalent dielectric constant of the upper radiation element can be approximated by (εr1+1)/2 and that for the lower radiation element by (εr1+εr2)/2. 
     For popular film base material such as teflon or polytetrafluoroethylene (PTFE) whose relative dielectric constants εr are about 2.55, there is little change in the equivalent dielectric constant, and the two radiation elements resonate in a close range of frequencies. 
     Therefore, there are cases in which an optimum film substrate thickness for one radiation element is not optimum for the other radiation element, resulting in degradation in the radiation efficiency and bandwidth of the overall antenna. 
     Another type of microstrip antenna designed to overcome the problems discussed above is shown in FIGS. 18A,  18 B. FIG. 18A is a plan view of the antenna and FIG. 18B shows a cross sectional view through a plane A—A in FIG.  18 A. 
     This type of antenna is provided with two different sizes of radiation elements  102   a ,  102   b . Thus, the large radiation element  102   a  provided on the top film acts as a low frequency-band antenna, and the small radiation element  102   b  provided on the lower film acts as a high frequency-band antenna, thereby permitting to choose an optimum film thickness for each of the two dielectric films  100 . 
     However, the dual-frequency microstrip antennas shown so far are designed with a power pin  200 , thus leading to an undesirable effect of unnecessary radiation from the power pin affecting the radiation fields of the radiation elements. 
     A microstrip antenna shown in FIGS. 19A,  19 B is an attempt to solve the problems posed by the antennas presented above. FIG. 19A is a plan view of another example of a dual-frequency antenna, and FIG. 19B is a cross sectional view through a plane at A—A in FIG.  19 A. 
     The dual-frequency antenna is provided with a strip conductor  113  opposite to the top and bottom radiation elements  102   a ,  102   b  with an intervening ground plane  101 . Each of the radiation elements  102   a ,  102   b  is coupled to the strip conductor  113  in its respective electromagnetic field, and are activated th rough a slot  117 . 
     In this type of antenna also, two different sized radiation elements  102   a ,  102   b  are provided as in the case of the antenna shown in FIGS. 18A,  18 B. Therefore, the top radiation element  102   a  acts as a low frequency antenna, and the bottom radiation element acts as a high frequency-band antenna, thereby permitting to choose an optimum film thickness for each of the two dielectric films  100 . 
     However, in the conventional dual-frequency antennas presented so far, it has been difficult to fabricate more than three microstrip radiation elements having distinct operating frequency on a common dielectric film member to realize a multi-band antenna. 
     A microstrip antenna shown in FIGS. 20A,  20 B is an attempt to solve these problems posed by the antennas presented above. FIG. 20A is a plan view of another example of a dual-frequency antenna, and FIG. 20B is a cross sectional view through a plane at A—A in FIG.  20 A. 
     The antenna shown in FIG. 20A is provided with half-wavelength dipoles  201   a ˜ 201   f  having different resonant lengths printed on a dielectric film member  100 , and opposite to the dipoles  201   a ˜ 201   f , there is provided a strip conductor  113  with an intervening ground plane  101 . Each of the dipoles  201   a ˜ 201   f  couples with the strip conductor  113  in its respective electromagnetic field through a slot  117 , and is activated to generate signal waves of different frequencies, thereby performing as a multifrequency-band antenna. 
     However, because such a dual-frequency microstrip antenna is designed so that the half wavelength dipoles  201   a ˜ 201   f  are all printed on a common dielectric film member  100 , and consequently, the frequency range for optimum performance is limited. 
     Further limitation of the antenna configuration based on the printed dipoles  201   a ˜ 201   f  is that, because the dipoles are meant to couple through the slot  117 , there is a physical limitation to the number of dipoles which can be arranged within the coupling distance of the slot  117 . 
     Therefore, it is difficult to fabricate simultaneously two microstrip radiation elements, having a widely separated operating frequencies, on a common dielectric film substrate using the approach shown in FIGS. 20A,  20 B. In other words, the conventional dual-frequency microstrip antenna could not provide a multi-band capability in one device unit which performs well in any desired operating frequencies over a wide range of frequencies. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a compact and multi-function microstrip antenna of multi-band capability having a plurality of dielectric films of thicknesses, which are optimized for a plurality of different operating frequencies, fabricated on a monolithic substrate, so as to provide optimal performance in the operating frequency range of microwave to millimeter-wave, in such a manner as to facilitate the incorporation of integrated circuits within -the antenna. 
     The object is achieved in an antenna comprising: a multi-lamination microstrip antenna comprising: a plurality of dielectric laminations, each lamination comprising: a plurality of dielectric film members, each dielectric film member having a selected dielectric constant and a selected film thickness; an radiation element in contact with a film surface of one dielectric film member disposed in one lamination; and a ground film member, in functional association with the radiation element, in contact with another film surface of another dielectric film member disposed in another lamination different than the one lamination. 
     A further aspect of the invention is that the antenna may be provided with: a high frequency signal line, disposed opposite to the radiation element with the ground plane intervening between the high frequency signal line and the radiation element, in contact with a film surface of a dielectric film member in a lamination; and a slot formed on the ground film member for receiving input signals into the radiation element so as to enable the input signals to couple with the radiation element in accordance with the electromagnetic field generated by the high frequency signal line to drive the radiation element. 
     A further aspect of the invention is that the antenna may be provided with: a high frequency signal line, disposed opposite to the radiation element with the ground plane intervening between the high frequency signal line and the radiation element, in contact with a film surface of a dielectric film member in a lamination; a slot formed on the ground film member; and a conductor member for operatively connecting an end of the high frequency signal line with the radiation element, so as to produce a direct electrical connection to drive the radiation element. 
     An aspect of the antenna presented above is that the conductor member is an open ended cavity termed a via-hole. 
     Still another aspect of the antenna presented above is that the high frequency signal line is a microstrip line. 
     Still another aspect of the antenna presented above is that wherein the high frequency signal line is a tri-plate line. 
     Still another aspect of the antenna presented above is that the antenna is provided with a plurality of the radiation elements. 
     Still another aspect of the antenna presented above is that the antenna is provided with electronic circuit means for processing signals received by and transmitting from the radiation element, disposed in contact with a dielectric film member in a lamination. 
     Still another aspect of the antenna presented above is that the antenna is provided with electronic circuit means for processing antenna signals in operative contact with the ground film member. 
     Still another aspect of the antenna presented above is that a cavity space is formed by removing at least one dielectric film member. 
     Still another aspect of the antenna presented above is that circuit element means are provided at an interface between the dielectric film members. 
     Still another aspect of the antenna presented above is that the circuit element means are capacitors. 
     Still another aspect of the antenna presented above is that the circuit element means are resistors. 
     Still another aspect of the antenna presented above is that the dielectric film member is an alumina ceramic material. 
     The final aspect of the antenna presented above is that the dielectric film member is a polyamide film. 
     The outstanding features of the invention are summarized below. 
     The multi-lamination configuration of the present microstrip antenna allows radiation elements and ground planes to be placed between any dielectric film members, allows the film thickness to be selected freely and successively to meet a wide range of operating frequency bands, and allows equi-potential connection to the ground planes to be made through the corresponding open ended cavities or via-holes. 
     Therefore, it is possible to select a thickness of any dielectric film so as to optimize the performance of an radiation element for a specific operating frequency within a wideband frequency range, thereby producing a microstrip antenna capable of handling a large separation in the receiving and transmitting frequencies or in the operating frequency bands. 
     Lamination thickness and the film thickness can be freely selected to suit any requirement, therefore, it possible to produce a multifrequency-band antenna on a monolithic substrate, capable of operating in a plurality of different operating frequency bands within frequency range of microwave to millimeter-wave. Furthermore, the design of the antenna allows two or more radiation elements having slightly different resonant frequencies to be provided on different local regions of one thin dielectric film member, thereby permitting to increase the bandwidth of the antenna without degrading the performance of either radiation element. 
     Further, because the dielectric constant of each of the film members can be freely selected, selection of a film material having a high dielectric constant allows a reduction in the size of the radiation element, and the selection of a film material having a low dielectric constant material allows an increase in the gain and efficiency of the antenna. 
     By selecting such materials as alumina, aluminum nitride and silicon as the film material for their good thermal compatibility with the semiconductor substrate often used in such applications, it is not only possible to incorporate a microstrip antenna into a monolithic microwave integrated circuit (MMIC) formed on a semiconductor substrate, but also to produce a multi-function antenna by enabling such functions as active antenna to be incorporated into the antenna. 
     Further, such an active radiation element can be produced economically because capacitor and resistor elements can be placed at the interface between appropriate film members, thereby allowing to integrate active devices or active circuits with the antenna, without the need for installing chip condensers. This approach to circuit integration permits the use of Wilkinson divider to configure power combining circuits, thereby lowering the mutual coupling between antenna elements through the feeding circuits. 
     Further, the lamination structure allows a higher degree of freedom in designing power and biasing lines, compared with the conventional designs, because these elements can be placed in any suitable lamination and it allows more choices of circuits and means for power supply. More specifically, the lamination structure permits power to be supplied directly using the via-holes and signal coupling to be achieved through the slots. It offers a further advantage that power combining circuits can be either a microstrip or a tri-plate line configuration, so that shorting interconnections which are effective in suppressing undesired modes which plague the tri-plate line configuration can be achieved by using via-holes rather than soldering used in the conventional approach. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a perspective view of the antenna of embodiment 1 of the present invention. 
     FIG. 1B is a cross sectional view through a plane at A—A in FIG.  1 A. 
     FIG. 2 is a cross sectional view of the antenna of embodiment 2 of the present invention. 
     FIG. 3A is a graph showing the results of measurement of return loss for a microstrip antenna having a 10 GHz band. 
     FIG. 3B is a graph showing the results of measurement of return loss for a microstrip antenna having an 18 GHz band. 
     FIG. 4 is a cross sectional view of the antenna of embodiment 3 of the present invention. 
     FIG. 5 is a cross sectional view of the antenna of embodiment 4 of the present invention. 
     FIG. 6 is a cross sectional view of the antenna of embodiment 5 of the present invention. 
     FIGS. 7A,  7 B are cross sectional views of the antenna of embodiment 6 of the present invention. 
     FIG. 8A is a plan view of the antenna of embodiment 7 of the present invention. 
     FIG. 8B is a cross sectional view through a plane at A—A in FIG.  8 A. 
     FIG. 9A is a plan view of the antenna of embodiment 8 of the present invention. 
     FIG. 9B is a cross sectional view through a plane at A—A in FIG.  9 A. 
     FIG. 10A is a plan view of the antenna of embodiment 9 of the present invention. 
     FIG. 10B is a cross sectional view through a plane at A—A in FIG.  10 A. 
     FIG. 11A is a plan view of the antenna of embodiment 10 of the present invention. 
     FIG. 11B is a cross sectional view through a plane at A—A in FIG.  11 A. 
     FIG. 12A is a plan view of the antenna of embodiment 11 of the present invention. 
     FIG. 12B is a cross sectional view through a plane at A—A in FIG.  12 A. 
     FIG. 13A is a plan view of the antenna of embodiment 12 of the present invention. 
     FIG. 13B is a cross sectional view through a plane at A—A in FIG.  9 A. 
     FIG. 14A is a perspective view of a conventional microstrip antenna. 
     FIG. 14B is a cross sectional view through a plane at A—A in FIG.  14 A. 
     FIG. 15A is a perspective view of another conventional microstrip antenna. 
     FIG. 15B is a cross sectional view through a plane at A—A in FIG.  15 A. 
     FIG. 16 is a graph of radiation efficiency and no-load Q for a conventional circular microstrip antenna. 
     FIG. 17A is a plan view of a conventional dual-frequency microstrip antenna. 
     FIG. 17B is a cross sectional view through a plane at A—A in FIG.  17 A. 
     FIG. 18A is a plan view of another conventional dual-frequency microstrip antenna. 
     FIG. 18B is a cross sectional view through a plane at A—A in FIG.  18 A. 
     FIG. 19A is a plan view of another conventional dual-frequency microstrip antenna. 
     FIG. 19B is a cross sectional view through a plane at A—A in FIG.  19 A. 
     FIG. 20A is a plan view of a conventional microstrip antenna having a multi-band radiation element. 
     FIG. 20B is a cross sectional view through a plane at A—A in FIG.  20 A. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, various embodiments will be explained with reference to the drawings. 
     FIG. 1A is a perspective view of the antenna of embodiment 1, and FIG. 1B is a cross sectional view through a plane at A—A in FIG.  1 A. 
     The following reference numerals are used to describe the antenna: first dielectric film members  1  constituting lamination  1 ; second dielectric film members  2  constituting lamination  2 ; a ground plane  11 ; a radiation element  12 ; strip conductor  13 ; a microstrip antenna  14 ; a microstrip line  15 ; and a slot  16 . 
     Film surfaces of each of the dielectric film members  1  and  2  are designated in FIG. 1A as, starting at the bottom,  1   a ,  1   b ,  1   c ,  1   d  and  2   a ,  2   b ,  2   c ,  2   d  and  2   e . The ground plane is fabricated on the film surface  1   c , and the radiation element  12  is fabricated on the film surface  2   e.    
     The radiation element  12  functions as a microstrip antenna  14  in conjunction with the first and second dielectric film members  1  and  2 , formed above the film surface  1   c , serving as the dielectric substrate for the radiation element  12 . 
     The microstrip line  15  is constituted by the strip conductor  13  fabricated on the film surface  1   b  in conjunction with the first dielectric film member  1  and the ground plane  11 . 
     The microstrip antenna  14  operates as follows. A signal propagating through the microstrip line  15  couples with the radiation element  12  in accordance with the electromagnetic field generated by the microstrip line  15  through the slot  16  provided on the ground plane  11  so as to feed the microstrip antenna  14 . 
     When the microstrip antenna  14  (acting as a resonator) is excited, radio waves are radiateted upwards into the free space in FIG.  1 B. 
     According to the configuration of embodiment 1 shown in FIG. 1, the ground plane  11  and the radiation element  12  may be located between first or second dielectric film members  1  or  2 , in either lamination  1  or  2 . 
     Further, the film thickness of the second dielectric film member  2  is selected to be less than that of the first dielectric film member  1 . Therefore, as shown in embodiment 2 shown in FIG. 2, by changing the locations of the ground plane and the radiation element as indicated by  11   a  and  12   a , the film thickness for the dielectric film member can be freely altered as need, to optimize the performance of the microstrip antenna by selecting an optimum substrate thickness for each operating frequency. Accordingly, even in cases of widely separated transmission and reception frequencies or widely different operating frequency bands, it becomes possible to make a microstrip antenna, exhibiting a high performance in any frequency band, on one common substrate. 
     Also, the antenna shown in FIG. 2 is able to suppress unnecessary radiation from the microstrip lines  15 ,  15   a , because the microstrip lines  15 ,  15   a  are shielded from the radiation elements  12 ,  12   a , respectively, by the ground planes  11 ,  11   a.    
     Also, the radiation element  12  can be miniaturized by using such materials as alumina, aluminum nitride and silicon for the first dielectric film member  1 . The values of the thermal expansion coefficient for these materials are quite compatible with the expansion values of semiconductor materials commonly used in making devices for the frequency range of microwave to millimeter-wave, therefore, it facilitates fabrication of integrated electronic circuits on the semiconductor substrate, thereby realizing active antenna systems. 
     By arranging the dielectric constant for the second dielectric film member  2  to be less than that for the first dielectric film member  1 , the equivalent dielectric constant at high frequencies for the microstrip antenna can be made small to produce a antenna with wide bandwidth characteristics. 
     FIGS. 3A,  3 B are graphs showing the return loss of a microstrip antenna of the configuration shown in FIG.  2 . The device is provided with both a 10 GHz band and an 18 GHz band. FIG. 3A shows the antenna performance in the 1 GHz band and FIG. 3B shows the same in the 18 GHz band. 
     The structural parameters for the first and second dielectric film members  1 ,  2 , and those for the 10 GHz band and the 18 GHz band are shown in Tables 1 and 2. 
     In the microstrip antenna used for these measurements, the feeding line is provided on the same side as the radiation element  12  but shielded by the ground plane  11  to enable on-wafer measurement, and the power is supplied directly to the line through a through-hole provided on the top surface of the wafer. 
     The locations of the radiation element, the ground plane and the core conductor of the microstrip line referred to in Tables 1, 2 are indicated on the film surfaces  1   a ,  1   c ,  2   a  and  2   c  in FIG.  1 B. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Properties 
                 First Dielectric Film 
                 Second Dielectric Film 
               
               
                   
               
             
             
               
                 Specific Dielectric 
                 9.6 
                 3.3 
               
               
                 Constant 
               
               
                 Number of Films 
                 4 
                 4 
               
               
                 Lamination Thickness 
                 250 μm 
                 25 μm 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Properties 
                 10 GHz Band 
                 18 GHz Band 
               
               
                   
                   
               
             
             
               
                   
                 Location of Radiation 
                 2e 
                 2e 
               
               
                   
                 Element 
               
               
                   
                 RE Resonant Length 
                 5 mm 
                 3.2 mm 
               
               
                   
                 RE width 
                 3 mm 
                 1.8 mm 
               
               
                   
                 Location of Ground 
                 1a 
                 1c 
               
               
                   
                 Member 
               
               
                   
                 Location Strip Conductor 
                 1c 
                 2a 
               
               
                   
                 Center Frequency 
                 10.43 GHz 
                 17.87 GHz 
               
               
                   
                 Film Thickness 
                 0.O38λ0 
                 0.036λ0 
               
               
                   
                 Bandwidth (VSWR&lt;2) 
                 2.8% 
                 2.9% 
               
               
                   
                   
               
               
                   
                 Notes: RE - radiation element;  
               
               
                   
                 VSWR - voltage standing wave ratio  
               
             
          
         
       
     
     From FIGS. 3A,  3 B, it can be seen that it is possible to provide two antenna functions (10 GHz band antenna and 18 GHz band antenna) of widely separated frequency bands of about the same bandwidth in one microstrip antenna. 
     Further, because the dielectric constant and the film thickness for the second dielectric film members  2  for lamination  2  is less than those for the first dielectric film members  1  for lamination  1 , it would be possible to manufacture a microstrip antenna having a frequency band in excess of 200 GHz by using the multi-lamination configuration shown above. It should be noted that, in this case, the film thickness would be {fraction (1/50)} to {fraction (1/20)} of the wavelength of the center frequency. It has thus been demonstrated that it is possible to manufacture a microstrip antenna having any desired number of operating frequency bands. 
     FIG. 4 is a cross sectional view of an antenna of embodiment 3. The same reference numerals as those shown in FIGS. 1A,  1 B have been retained. 
     As in FIGS. 1A,  1 B, the antenna comprises: lamination  1  having first dielectric film members  1 ; lamination  2  having second dielectric film members  2 ; and the film surfaces are, starting from the bottom,  1   a ,  1   b ,  1   c ,  1   d ,  2   a ,  2   b ,  2   c ,  2   d  and  2   e . A ground plane  11  is provided on the film surface  1   c , a ground plane  17  is provided on the film member  1   a  and an radiation element  12  is provided on the film member  2   e.    
     Antenna structure  12  functions as a microstrip antenna  14  in conjunction with the dielectric film members  1  and the dielectric film members  2 , provided above the film surface  1   c , serving as the laminated dielectric bases therefor. 
     The strip conductor  13  is provided on the film surface  1   b . The strip conductor  13 , the dielectric film members  1 , the ground plane  11  and the ground plane  17  constitute a tri-plate line  18 . 
     The operation of the antenna will be explained below. 
     A signal propagated through the tri-plate line  18  couples with the radiation element  12 , in accordance with the electromagnetic field, through the slot  16 , and feeds the microstrip antenna  14 . The microstrip antenna  14  acting as a resonator radiates signal waves upwards into the free space shown in FIG.  4 . 
     In the conventional design of a tri-plate line, there has been a problem of noise generation due to the parallel mode (transverse excitation mode, TEM, waves) causing power leakage and undesired coupling and similar interference problems. These problems can be resolved by providing shorting pins for the ground planes in the vicinity of the supply point (slot), however, according to the antenna configuration of embodiment 3, shorting pin connection can be replaced with a through-hole (open ended cavity), so as not to resort to solder connections as in the conventional antenna. 
     FIG. 5 is a cross sectional view of the antenna of embodiment 4. The same reference numerals for the components have been maintained. 
     The antenna comprises: lamination  1  having first dielectric film members  1 ; lamination  2  having second dielectric film members  2 ; and the film surfaces are, respectively from the bottom,  1   a ,  1   b ,  1   c ,  1   d ,  2   a ,  2   b ,  2   c ,  2   d  and  2   e . A ground plane  11  is provided on the film surface  1   c , and an radiation element  12  is provided on the film member  2   e.    
     The radiation element  12  functions as a microstrip antenna  14  in conjunction with the first dielectric film members  1  and the second dielectric film members  2 , provided above the film surface  1   c , serving as the dielectric laminated substrate therefore. 
     The strip conductor  13  is provided on the film surface  1   b . The strip conductor  13 , the first dielectric film member  1 , the ground plane  11  constitute a microstrip line  18 . 
     The operation of the microstrip antenna will be explained below. 
     A signal propagated through the microstrip line  15  feeds the microstrip antenna  14  directly through the via-hole (open ended cavity)  19 . The microstrip antenna  14  acting as a resonator radiates signal waves upwards into the free space shown in FIG.  4 . 
     FIG. 6 is a cross sectional view of an antenna of embodiment 5. The same reference numerals for the components as those used above are retained. 
     In this embodiment, two different power combining circuits configuration, a microstrip line  15  and a tri-plate line  18 , are integrated in one substrate. The antenna of the present invention is compatible with different feeding methods as demonstrated in this embodiment. 
     FIGS. 7A,  7 B are cross sectional views of an antenna of embodiment 6. The components are mostly the same as before but an electronic circuit has been added. 
     In this embodiment device, the electronic circuits  20 , which is fabricated on the semiconductor substrate, are integrated with the microstrip antenna. 
     There are two electronic circuits  20  provided for each of the antennas shown in FIGS. 7A,  7 B, but the circuits are located in different regions of lamination  1 . 
     In more detail, in the antenna shown in FIG. 7A, a local region of lamination  1  has be en removed to expose a portion of the ground plane  11 , and one of the electronic circuits  20  is buried in the bared area. The other circuit  20  is located on the external film surface of the outermost dielectric film member  1 . 
     In contrast, in the antenna shown in FIG. 7B, a local region of the lamination  2  has been removed to produce a cavity, wherein one electronic circuit  20  is mounted on the exposed surface of the first dielectric film member  1  while the other electronic circuit  20  is mounted on the external surface of the outermost film member  2  in lamination  2 . 
     As demonstrated in this embodiment, the microstrip antenna of the present invention not only minimizes transmission loss between the high frequency circuit and the radiation element by integrating the radiation element with the electronic circuits fabricated on the semi-conductor substrate but also enables to produce a compact and low-profile active antennas of various configurations including phased-array antenna. 
     Additionally, the technique of removing a local region of the lamination substrate and mounting the electronic circuit on the bared region of the dielectric film member enables to shorten the length of the wire connecting the electronic circuit and the high frequency line, thereby further decreasing the transmission loss as well as the antenna thickness. The design of the antenna further allows the heat generated in the electronic circuits to be radiated effectively by sharing the ground plane  11  for the circuits as well as for the microstrip antenna  14 , or by forming the circuits on a substrate material having compatible thermal expansion characteristics. 
     In each of the embodiments shown above, one radiation element has been provided for one antenna, but it is obvious that, the arrangement concept can be applied equally well to an array antenna having a plurality of antenna strictures. 
     Also, in each of the foregoing embodiments, circular microstrip antenna have been shown, but it is permissible to utilize any other shapes such as rectangular, triangular and so on. 
     FIG. 8A is a plan view of embodiment 7. FIG. 8B is a cross sectional view through a plane at A—A in FIG.  8 A. The same reference numerals are retained, and their explanations are omitted. 
     The microstrip antenna of embodiment 7 is provided with a large radiation element  12  for low frequency range on the external surface of lamination  2 , and a smaller radiation element  12   a  is provided between the dielectric film members in lamination  2 . 
     FIG. 9A is a plan view of embodiment 8. FIG. 9B is a cross sectional view through a plane at A—A in FIG.  9 A. The same reference numerals are retained, and their explanations are omitted. 
     The microstrip antenna of embodiment 8 is provided with half wavelength printed dipoles  21   a ˜ 21   c  of different resonant lengths in lamination  2 , either on the outer surface of the lamination or between the film members. 
     The microstrip antennas shown in FIGS. 8A,  8 B and  9 A,  9 B enable to not only increase the bandwidths of the radiation elements by providing two or more radiation elements having slightly different resonant frequencies on different local regions of a thin dielectric film member, thereby permitting to increase the bandwidths without degrading the performance of either radiation element, as well as to optimize the thickness of the dielectric film for each radiation element. In other words, the antenna of embodiments 7, 8 enable to increase bandwidths without degrading the performances of the radiation elements. 
     It should also be noted that, in embodiment 6, a local region of lamination  1  or  2  was removed for the insertion of an electronic circuit, but it is also conceivable to insert an radiation element or to leave it bare. 
     FIG. 10A is a plan view of the antenna of embodiment 9. FIG. 10B is a cross sectional view through a plane at A—A in FIG.  10 A. The same reference numerals are retained, and their explanations are omitted. 
     In the microstrip antenna of embodiment 9, a local region of a second dielectric film member  2  in lamination  2  has been removed, and an radiation element  12  has been fabricated on the exposed film surface of the bared region, thereby minimizing the dielectric loss in the microstrip antenna  14  and increasing the gain and the radiation efficiency of the radiateted signal waves. 
     FIG. 11A is a plan view of the antenna of embodiment 10. FIG. 11B is a cross sectional view through a plane at A—A in FIG.  11 A. The same reference numerals are retained, and their explanations are omitted. 
     In the antenna of embodiment 10, a space is produced below the radiation element  12 , by removing a part of the dielectric films  1  and  2  in laminations  1  and  2 , thereby lowering the equivalent dielectric coefficient of the microstrip antenna  14  and improving the gain and the bandwidth. 
     Further, in any of the foregoing embodiments, it is possible to provide various circuit components (capacitors and resistances etc.) in the bonding interfaces between the first and second dielectric film members. 
     FIG. 12A is a plan view of an antenna of embodiment 11. FIG. 12B is a cross sectional view through a plane at A—A shown in FIG.  12 A. The same reference numerals are retained, and their explanations are omitted. 
     In the microstrip antenna of this embodiment, a capacitor member  23  is disposed at the bonding interface between laminations  2  and  1 , i.e., the bottom film surface of the second dielectric film members  2  and the top film surface of the dielectric film member  1 . The capacitor member  23  is electrically connected to an electronic circuit  20  through a via-hole  19  and a bonding wire  24 . By adopting such a design, it becomes possible to eliminate a DC-biased chip condenser which is essential in installing certain electronic circuit  20  (functional device and monolithic microwave integrated circuit (MMIC) chip etc.), thereby lowering the cost of producing the active antenna by eliminating the cost of installing such DC biased chip condenser. 
     If a resistor is installed, it may be utilized for a Wlkison divider to provide a superior inter-terminal isolation, thereby decreasing the adverse effects of interactions between the radiation elements due to the power combining circuit incompatibility. 
     Further, in each of the foregoing embodiments, two laminations of dielectric film members (first and second dielectric film members) are used, but it should be noted that there is no particular limitation in the number of laminations which can be produced. 
     FIG. 13A is a plan view of an antenna of embodiment 12, and FIG. 13B is a cross sectional view through a plane at A—A in FIG.  13 A. The same reference numerals are retained, and their explanations are omitted. 
     The microstrip antenna of this embodiment is provided with lamination  1  comprising a plurality of first dielectric film members  1 , lamination  2  comprising a plurality of second dielectric film members  2 , and lamination  3  comprising a plurality of third dielectric film members  25 . The microstrip antenna of this embodiment thus comprises a three kinds of dielectric laminations with lamination  1  common to laminations  2 ,  25 . An radiation element  12  is provided in lamination  2 , an radiation element  12   a  in lamination  3 , a ground plane  11  and a strip conductor  13  are provided in lamination  1 . This configuration produces a bi-directional multifrequency-band microstrip antenna which radiates signals upwards and downwards into the free spaces above and below the antenna shown in FIG. 13B, with a common ground plane  11  disposed in lamination  1 . 
     In all of the foregoing embodiments, dielectric laminations comprise four film members, but the number of films is not particularly limited to such a number, and any number of desired films may be incorporated in a lamination. It is also permissible to use two radiation elements to produce a phase difference of 90 degrees between the signal terminals. It is also possible to provide a notched element to produce circularly polarized waves.