Abstract:
A circuit including: at least one radio frequency microstrip conductor; and, a least one vanadium oxide region electrically coupled to the at least one radio frequency microstrip conductor; wherein, the at least one vanadium oxide region is substantially conductive in a first temperature range, and substantially non-conductive in a second temperature range.

Description:
FIELD OF INVENTION 
     The present invention relates to a switch apparatus for high frequency signals, and particularly to an apparatus for switching between transmit and receive modes in phased array radar devices. 
     BACKGROUND OF THE INVENTION 
     Phased array radar antennas are generally known and implemented. Phased array antennas include apertures formed from a multitude of radiating elements. Each element is individually controlled in phase and amplitude. In this manner, desired radiating patterns and directions may be achieved. By rapidly switching the elements to switch beams, multiple radar functions may be realized. 
     Referring now to  FIG. 1 , there is shown a conventional transmit/receive switching circuit arrangement  100  for a phased array radar antenna. Circuit  100  includes a microstrip coupled to an input terminal P 1  and to a transmit terminal P 3  and capacitors  120 ,  130 . “Microstrip”, as used herein, generally refers to a transmission line used for transmitting high frequency signals, such as radio frequency or microwave frequency signals. A microstrip may typically take the form of a thin, strip-like transmission line mounted on a flat dielectric substrate, that is in-turn mounted on a ground plane. Capacitors  120 ,  130  are coupled to a receive terminal P 2 , a bias terminal BIAS, and ground through radio frequency (RF) diodes  140 ,  150 . Transmit terminal P 3  is coupled to a waste load  110 . 
     When a sufficiently positive bias BIAS is provided, diodes  140 ,  150  essentially provide short-circuit conditions, such that signals are steered from input terminal P 1  to transmit terminal P 3  and hence waste load  110 . When a sufficiently negative bias BIAS is provided, diodes  140 ,  150  essentially provide open circuit conditions, such that signals are steered to receive terminal P 2 . Circuitry  100  and its operation are generally known in the phased-array radar arts. 
     However, such a configuration and operation undesirably introduces signal losses, due to the incorporation of wires, jumpers and materials that affect RF performance and compromise circuit performance. Accordingly, it is desirable to eliminate these wires, jumpers and materials, such as those associated with the depicted diodes, while maintaining selective transmit and receive functionalities. 
     SUMMARY OF THE INVENTION 
     A circuit including: at least one high frequency microstrip conductor; and, a least one vanadium oxide region electrically coupled to the at least one radio frequency microstrip conductor; wherein, the at least one vanadium oxide region is substantially conductive in a first temperature range, and substantially non-conductive in a second temperature range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Understanding of the present invention will be facilitated by consideration of the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings, wherein like numerals refer to like parts and: 
         FIG. 1  illustrates a diagram of conventional phased-array radar transmit/receive switching circuitry; 
         FIG. 2  illustrates a diagram of phased-array radar transmit/receive switching circuit arrangement according to an aspect of the present invention; 
         FIG. 3  illustrates a VO 2  interdependence of resistance and temperature that may be used according to an aspect of the present invention; 
         FIG. 4  illustrates a circuit arrangement according to an aspect of the present invention; 
         FIGS. 5   a  and  5   b  illustrate predicted operational characteristics of the arrangement of  FIG. 4  in first and second modes; 
         FIG. 6  illustrates a circuit arrangement according to an aspect of the present invention; 
         FIGS. 7   a  and  7   b  illustrate predicted operational characteristics of the arrangement of  FIG. 6  in first and second modes according to an aspect of the present invention; 
         FIG. 8  illustrates a circuit arrangement according to an aspect of the present invention; 
         FIG. 9  illustrates a circuit configuration according to an aspect of the present invention; 
         FIG. 10  illustrates a circuit configuration according to an aspect of the present invention; 
         FIG. 11  illustrates a circuit configuration according to an aspect of the present invention; 
         FIG. 12  illustrates a circuit configuration according to an aspect of the present invention; 
         FIG. 13  illustrates a circuit configuration according to an aspect of the present invention; and, 
         FIG. 14  illustrates a circuit configuration according to an aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for the purpose of clarity, many other elements found in typical radar antenna arrays and signal processing systems. Those of ordinary skill in the art may recognize that other elements and/or steps are desirable and/or required in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein. 
     Referring now to  FIG. 2 , there is shown phased-array antenna transmit/receive switching circuit  200  according to an aspect of the present invention. Circuit  200  includes a microstrip coupled to an input terminal P 1  and a transmit terminal P 3  and receive terminal P 2 , and ground through switching devices  240 ,  250 . Transmit terminal P 3  is coupled to waste load  110 . 
     Switching devices  240 ,  250  may be operated in a first mode, that essentially provides a low resistance condition, such that signals are steered from input terminal P 1  to transmit terminal P 3 , and hence waste load  110 . Switching devices  240 ,  250  may be operated in a second mode, that essentially provides a high resistance condition, such that signals are steered to receive terminal P 2 . In the illustrated case, switching devices  240 ,  250  are temperature dependent. Consistently, subjecting devices  240 ,  250  to a first temperature range effects their operation in the first mode to have a first conductance, while subjecting them to a second temperature range effects their operation in the second mode to have a second conductance. 
     As will be understood by those possessing an ordinary skill in the pertinent arts, such a control mechanism is separate from the RF signal path. Accordingly, such an approach advantageously may omit the above-discussed wires, jumpers and materials that affect RF performance and compromise circuit performance. 
     According to an aspect of the present invention, switching devices  240 ,  250  may take the form of vanadium oxide interconnections, such as vanadium (IV) oxide (VO 2 ) material containing interconnections. Other vanadium oxide materials, such as vanadium (II) oxide (VO), vanadium (III) oxide (V 2 O 3 ) and vanadium (V) oxide (V 2 O 5 ) may also be suitable for use. The present invention will be further discussed as it relates to vanadium (IV) oxide, for non-limiting purposes of explanation. 
     Referring now also to  FIG. 3 , there is shown the resistivity (rho in Ω-cm) of VO 2  as a function of temperature (T in ° C.) between a theoretical maximum resistivity in an “ON” state and a theoretical minimum resistivity in an “OFF” state. As may be ascertained therefrom, VO 2  has a resistivity corresponding to a high conductance, or almost a short-circuit or on-state condition, e.g., the first mode (e.g., &lt;0.01 Ω-cm), in a temperature range above about 72° C. Further, VO 2  has a resistivity corresponding to a low conductance, or almost an open-circuit or off-state condition, e.g., the second mode (e.g., &gt;1 Ω-cm), in a temperature range less than about 62° C. Accordingly, a VO 2  based electrical interconnection may be selectively operated in the first and second modes (e.g., on and off states) by selectively controlling the temperature thereof to be within these temperature ranges (e.g., the above-identified first and second temperature ranges). For example, a VO 2  based electrical interconnection may be selectively operated in the first mode by making the temperature thereof around 80° C. And, the same VO 2  based electrical interconnection may be selectively operated in the second mode by making the temperature thereof around 60° C. 
     According to an aspect of the present invention, the temperature of VO 2  based electrical interconnections may be selectively altered using any suitable heating and/or cooling means, such as resistive based heaters, thermal electric coolers, thermo ionic micro-coolers and/or radiant heaters. Resistive heaters and thermal electric coolers are generally known. For example, the entire circuit  200  may be brought to around 60° C., using a conventional heating/cooling approach, while VO 2  regions are selectively heated to around 80° C. using resistive heaters positioned near (e.g., above, below and/or alongside) them. Another suitable approach, using thermo ionic coolers is presented in co-pending, commonly assigned, U.S. patent application Ser. No. 11/370,766, entitled SWITCH APPARATUS, filed Mar. 8, 2006, the entire disclosure of which is hereby incorporated by reference herein. 
     As will be recognized by those possessing an ordinary skill in the pertinent arts, such an approach to switching high frequency (e.g., RF or microwave) signals is applicable to a wide variety of implementations. Non-limiting examples are presented herein for purposes of further explanation. 
     Referring now to  FIG. 4 , there is shown a half-wave resonator circuit structure  400  according to an aspect of the present invention. Half-wave resonators are known to be useful in RF signal applications, including phased-array radar antenna transmit/receive applications. Structure  400  includes a gold microstrip transmission line  410  disposed upon an alumina substrate and extending between terminals P 1  and P 2 . Structure  400  also includes a conductive line  420 . Line  420  may also be formed of gold, for example. Electrically coupled to one or more ends of line  420 , are interconnects  430 . In the illustrated embodiment, interconnects  430  take the form of VO 2  regions. As is known, the resonant frequency of a half-wave resonator is dependent upon the length of the resonator itself. By altering the length of the resonator (e.g., line  420 ), the resonance frequency also changes. 
     Referring now also to  FIGS. 5A and 5B , there are shown non-limiting exemplary illustrations of a predicted resonance with the VO 2  interconnects in the first mode or “on” state ( FIG. 5A ), and in the second mode or “off” state ( FIG. 5B ). Predicted resonance in “on” state is represented by point m 1  having frequency of about 7.980 GHz and amplitude of about −16.784 dB in  FIG. 5A  whereas the predicted resonance in “off” state is represented by point m 1  having a frequency of about 10.000 GHz and amplitude of about −5.067 dB in  FIG. 5B . It is predicted that the resonance frequency of resonator  400  may be changed from 10 GHz (in an “off” state) to 7.980 GHz (in an “on” state) by thermally transitioning regions  430  from the second mode to the first mode (e.g., changing the temperature thereof from 60° C. to 80° C.), for example. 
     Referring now also to  FIG. 6 , there is shown a half-frequency trap circuit structure  600  according to an aspect of the present invention. Half-frequency traps are also known to be useful in RF signal applications. Structure  600  includes a gold microstrip transmission line  610  upon an alumina substrate that extends between terminals P 1  and P 2 . Structure  600  also includes a conductive trap line  620 , that may be formed of gold, for example. Electrically coupled between trap line  620  and line  610  is interconnect  630 . In the illustrated embodiment, interconnect  630  takes the form of a VO 2  region. 
     Referring now also to  FIGS. 7A and 7B , it is predicted the trap may be engaged by thermally transitioning region  630  from the second mode to the first mode (e.g., changing the temperature thereof from 60° C. to 80° C.), thereby changing the operational characteristics of structure  600  ( FIG. 7A  is with the VO 2  conductor on,  FIG. 7B  is with the VO 2  conductor off). Point m 1  of  FIG. 7A  represents a frequency of 5.000 GHz at an amplitude of −29.188 dB, when the VO 2  conductor is on whereas point m 1  represents a frequency of 5.000 GHz at an amplitude of −0.080 dB in  FIG. 7B  when the VO 2  conductor is off. 
       FIG. 6  illustrates a structure useful for switching entire circuit regions or elements into the circuit including line  610 . While  FIG. 6  illustrates a trap that is selectively switchable into and out of the circuit including line  610 , other circuit elements could be switched in and out as well. Such an approach may be used to realize circuit  200  of  FIG. 2 . 
     Referring now also to  FIG. 8 , there is shown a VO 2  interconnect employing embodiment  800  of circuit  200  ( FIG. 2 ). Structure  800  includes a gold microstrip transmission line  810  disposed upon an alumina substrate and extending between terminals P 1 , P 2  and P 3 . As may be seen therein, VO 2  interconnect region  840  may be used to implement switch  240  ( FIG. 2 ), while VO 2  interconnect region  850  may be used to implement switch  250  ( FIG. 2 ). As will be understood by those possessing an ordinary skill in the pertinent arts gold lines  842 ,  852  may be coupled to ground. 
     Referring now also to  FIG. 9 , there is shown a ¼ wave coupler circuit structure  900  incorporating VO 2  interconnections. Structure  900  includes input and through nodes P 1 , P 2 . Structure  900  also includes a ¼ wave coupled node P 3  and an isolated node P 4 . Nodes P 1 , P 2  are coupled to one another using a gold microstrip  910  upon an alumina substrate. Microstrip  910  includes a conventional ¼ wave coupling region  950 . Sufficiently proximate to coupling region to effect coupling when in a conductive mode, is a VO 2  interconnect  940 . Interconnect  940  may take the shape of a conventional ¼ wave coupling region  960 . A gold microstrip  920  couples node P 3  to VO 2  interconnect  940 . A gold microstrip  930  couples node P 4  to VO 2  interconnect  940 . When interconnect  940  is thermally activated to be conductive, conventional ¼ wave coupling from node P 1  to node P 3  is effected. When interconnect  940  is not conductive, e.g., in the above-identified second mode, node P 1  is essentially isolated from node P 3 . Thus, as described above, a great number of high frequency circuit interconnections may be effected using thermal dependent switching according to an aspect of the present invention, while eliminating conventional circuit interconnects that may otherwise lead to undesirable signal losses. 
     According to an aspect of the present invention, VO 2  interconnections and gold conductive lines may be formed on an alumina substrate using the following methodology. For example, VO 2  interconnects and gold conductive lines may be formed on a substrate using conventional photolithography and etch processes. An about 500 nm thick film of metallic vanadium may then be deposited on the patterned substrate using a suitable thin film deposition process, such as resistive (thermal) evaporation, e-beam evaporation or sputtering. The film may then be annealed in about 110 mTorr of Oxygen at about 560 C for about 24 hours, to create vanadium oxide. The film may then be patterned using conventional photolithography and etching, or direct write lithography, to the desired geometry. 
     As will be understood by those possessing an ordinary skill in the pertinent arts, vanadium oxide interconnections have many other uses as well. For example, and referring now also to  FIG. 10 , an array  1000 , such as a two-dimensional or three-dimensional array of conductors  1010  may include integrated VO 2  regions  1020  that provide for dynamically reconfigurable signal paths. This may prove particularly advantageous for switching between modules in dual-band radar applications, such as for L-band and x-band signal paths. 
     By way of further, non-limiting example, and referring now also to  FIG. 11 , RF phase shifting may be accomplished using structure  1100 . Structure  1100  includes gold conductor  1110  and variable length conductive lines  1120 . Each variable length line  1120  includes selectively conductive VO 2  regions  1130 ,  1140 . Other conductive line portions may optionally be included. The variable length of one or more of the lines  1120  may be used to tune a phase shift, as will be understood by those possessing an ordinary skill in the pertinent arts. By selectively turning on and off selectively conductive VO2 regions  1130 ,  1140  in two illustrated exemplary lines  1120 , a phase shift of 90 degrees may be achieved. 
     Coupler tuning may also be accomplished using VO 2  regions.  FIG. 12  illustrates a structure  1200  including conductive lines  1210 ,  1220 . Lines  1210 ,  1220  may be formed of gold, for example. Structure  1200  also includes VO 2  material structures  1230 ,  1240 . Structures  1230  include variable length lines  1235 , akin to lines  1120  of  FIG. 11 , and variable depth slots  1237 , also akin to shortened lines  1120  of  FIG. 11 . Structure  1240  includes lines  1245  and slots  1247 . As will be understood by those possessing an ordinary skill in the pertinent arts, active fine tuning of combiner directivity for increased high power combiner efficiency over frequency can be realized using structure  1200 . The variable conductive length of conductive lines  1235 ,  1245  may be used to vary the even mode impedance, while the variable conductive depth of slots  1237 ,  1247  may be used to vary the odd mode impedance. 
     A yet further example is provided in  FIG. 13 , which illustrates VO 2  interconnects being used to provide for amplifier tuning.  FIG. 13  illustrates a structure  1300  including a conductor  1310  and amplifier  1320 . Structure  1300  also includes VO 2  material regions  1330 ,  1350  and  1360 , and interconnects  1340 . Regions  1330  may be individually thermally controlled to selectively add capacitance to circuit  1300 . Interconnects  1340  may be individually thermally controlled to selectively couple additional capacitance (represented by elements  1370 ,  1380 ) into structure  1300 . Regions  1350  may be individually thermally controlled to selectively add inductance into structure  1300 . Regions  1360  may be individually thermally controlled to selectively change the harmonic tuning of structure  1300 . 
     Referring now to  FIG. 14 , and by way of yet further non-limiting exemplary implementation, VO 2  regions may be individually thermally actuated to provide for phased array radar antenna element tuning.  FIG. 14  illustrates a structure  1400 . Structure  1400  generally includes a conventional dipole and ground plane. VO 2  regions  1410 ,  1420  may be individually thermally controlled to selectively modify the dipole dimension and ground plane spacing to improve matching at select frequencies. 
     While the foregoing invention has been described with reference to the above-described embodiment, various modifications and changes can be made without departing from the spirit of the invention. Accordingly, all such modifications and changes are considered to be within the scope of the appended claims.