CA2251517C - A microwave switch and method of operation thereof - Google Patents

Abstract

An HTS microwave circuit has two layers formed with metallic film on a substrate. One layer has a first circuit and another layer has a second circuit, the two circuits being coupled to one another. The second circuit has elements that are incompatible with HTS material such as MEMS technology and flip-chip technology. A microwave switch has a first layer that can carry an RF signal and a second layer that has switch elements that are controlled by a DC signal. The RF signal and DC signal are isolated from one another. The switch elements include various technologies including a narrow HTS strip. A single layer HTS microwave switch can also be utilized where the switch element is a narrow HTS line. A method of combing HTS technology with incompatible technologies into one device is provided.

Description

MICROWAVE SWITCH WITH MET'I-IOD OF OPERATION THEREOF
The present invention relates to microwave switches and, more particularly, to the realisation of high temperature superconductive switches and circuits.
5 The majority of communication systems utilise RF switches to achieve dynamic interconnectivity or to improve system reliability by switching to back-up equipment in case of a failure. The two types of switches that are currently being used are electromechanical switches and solid state switches.
Electromechanical switches are usually used in applications where switching to time can be slow while low insertion loss and high isolation are required.
The problem, however, with mechanical switches is that they are bulky.
Solid state switches, on the other hand, are used in applications where switching time must be fast. Although, solid state switches are relatively small in size and mass, their insertion loss performance and power 15 consumption are prohibitively high in many applications.
When working with HTS circuits difficulties have been encountered in attempting to combine incompatible components with H'fS into the FITS
circuit. For example, flip-chip technology and MEMS technology is incompatible with HTS circuits.
2o High Temperature Superconductive (HTS) switches can be used to replace both electromechanical switches and solid state switches in both low and high speed applications. The advantages are low insertion loss, small size, light weight and low power consumption.
It is an object of the present invention to provide a novel 25 configuration for a single layer or multi-layer H'TS switch. It is a further object of the present invention to provide HTS switches by integrating switching elements with an HTS planar circuit.
An HTS microwave circuit has a first layer and a second layer, the first layer having a first HTS microwave circuit extending between an input and an 5 output. The second layer has a second microwave circuit that is coupled to the first circuit. The second circuit has at least one element that is compatible with at least one of MEMS technology and flip-chip technology, but incompatible with HTS material, said at least one element being connected into said second circuit to interact with and control the HTS circuit.
1 o A microwave switch has a first layer and a second layer. The first layer has a first microwave circuit that can carry an RF signal between an input and an output. The second layer has a second microwave circuit that is coupled to the first circuit. The second circuit has at least one switch element that can be controlled between an off position and an on position by 15 a DC signal, the RF signal and the DC signal being isolated from one another.
A microwave switch has an HTS microwave circuit extending between an input and an output. The circuit has a transmission line containing a narrow length of high temperature superconductive material 2o connecting said HTS circuit to ground. The switch has a DC power source connected to said narrow length of high temperature superconductive material. The DC power source is connected to change said narrow length of high temperature superconductive material between superconductive and non-superconductive. There are means to prevent current from said DC

power source from flowing into said circuit beyond said narrow length of high temperature superconductive material.
A method of combining a first HTS circuit with a second circuit having at least one of flip-chip technology, MEMS technology and mechanical technology, said method comprising constructing said first circuit on a first substrate having a ground plane, constructing said second circuit on a second substrate, arranging said substrates to capacitatively or inductively couple said second circuit to said first circuit in controlling said first circuit through said second circuit.

Figure 1 is an exploded perspective view of a two layer HTS switch;
Figure 2 is an enlarged perspective view of the first layer of the switch of Figure 1;
Figure 3 is an enlarged perspective view of a second layer of the t5 switch of Figure 1;
Figure 4 is an enlarged perspective view of a further embodiment of a second layer having switching elements made from HTS materials;
Figure 5 is a side view of a further embodiment of a second layer having switching elements made from a flip-chip technology;
2o Figure 6 is an enlarged side view of a further embodiment of a second layer having switching elements made from micro-electromechanical systems;
Figure 7 is an exploded perspective view of a C-switch;
Figure 8a is a graph of the measured results of a C-switch built in 25 accordance with Figure 7 in the on position;

Figure 8b is a graph of the measured results of a C-switch built in accordance with Figure 7 in the off position;
Figure 9 is an exploded perspective view of a single layer HTS switch;
Figure l0a is a graph of the measured RF performance of switch constructed in accordance with Figure 9 in the on position; and Figure l Ob is a graph of the measured RF performance of switch constructed in accordance with Figure 9 in the off position;
In Figure 1, there is shown a switch 2 according to the preferred embodiment of the present invention,. The switch 2 consists of two layers 4 to and 6. The layer 4 consists of a first HTS microwave circuit 8 printed on a substrate 10 attached to a ground plane 12. The HTS circuit 8 is assembled in a housing 14 by epoxying the ground plane 12 to the bottom of the housing 14. The input/output 15 and 16 are attached to the HTS circuit 8. Layer 6 consists of a second microwave circuit 17 printed on a substrate 18.
Preferably, there is no ground plane immediately beneath the substrate 18. if desired, a ground plane could be located beneath the substrate 18 with openings where required for coupling purposes. The layer 6 is placed on the top of the layer 4 by using low loss adhesive or any other means. The layer 6 can be spaced apart from the layer 4 by supports (not shown) leaving an air 2o space between the two layers. The circuit is assembled with three on/off switch elements 19a, 19b and 19c. Each switch element has two terminals 20, 21. One terminal 20 is connected to the circuit 17 and the other terminal 21 is connected to a transverse line 24 which is short-circuited to the housing 14.

A plate 25 is a top cover for the switch 2. There is one switch element for each transmission line of the circuit 17.
Figure 2 illustrates a detailed description of the HTS circuit 8. Each of the transmission lines 26a, 26b and 26c represent one port of a T junction.
The three T junctions are connected by HTS transmission lines. The number of sections (T junctions) determines the bandwidth of the switch. The more sections the circuit has, the wider the bandwidth the switch would exhibit.
Thus, a switch can have more than three or fewer than three T junctions. The circuit has two contact pads 28a, 28b made out of gold or any other metals to to allow connections to the input and output connectors.
Figure 3 illustrates a detailed description of the circuit 17 printed on the layer 6- It consists of three transmission lines 22a, 22b and 22c mounted on the substrate such that the centre of the lines 22a, 22b and 22c align with transmission lines 26a, 26b and 26c (not shown in Figure 3) respectively shown in Figure 2. The widths and the lengths of the lines 22a, 22b and 22c do not have to be necessarily the same as the widths and lengths of the lines 26a, 26b and 26c respectively. The lines 26a, 26b and 26c are coupled either capacitatively or inductively to the lines 22a, 22b and 22c respectively. The transmission lines 22a, 22b and 22c are made out of HTS, gold or any other 2o metals. Three switch elements 19a, 19b and 19c are connected to the circuit 17. The switch elements can be PIN, FET or GaAs diodes. One terminal 20 of'each switch element 19a, 19b and 19c is connected to the ends of the transmission lines 22a, 22b and 22c respectively. The other terminal 21 of each switch element 19a, 19b and 19c is connected to the transverse line 24, which is short-circuited to the housing. Mechanical type switches could be used instead of diodes to short circuit the gap between the lines 22a, 22b 22c and the transverse line 24. Alternatively MEMS ( Micro-Electro-Mechanical System) switches could be used for the switch elements 19a, 19b and 19c or mechanical switches could be used. The switch elements are synchronously turned on/off.
The switch shown in Figure 1 is in the ON state when the switch elements are in the ON
state and the switch circuit is in the OFF state when the switch elements are in the OFF state. Thus, the operation of the switch is controlled by the ON/OFF
positions of the switch elements. The switch could be designed to operate in an opposite manner where the switch circuit is ON when the switch elements are OFF and vice versa.
In Figure 4, there is a shown a further embodiment for a circuit 30 of the second layer 6. The same reference numerals are used for those components that are the same as the components of Figure 3. The lines 22a, 22b and 22c are made out of HTS material. The switch elements are narrow transmission lines 32a, 32b and 32c, which are also made out of HTS material. DC current is supplied to the lines 32a, 32b and 32c through inductors 34a, 34b and 34c respectively connected to conductors 35a, 35b and 35c respectively. When the DC current is off, the lines 32a, 32b and 32c are superconductive and a short circuit exists through the transverse line 24 of the layer 6. The switch 2 is then in the ON position and the switch elements are also in the ON position. When the DC current is switched on and is high enough, the narrow transmission lines 32a, 32b and 32c switch from the superconductive state to the non-superconductive state. The switch elements are then in the off position and the switch 2 is in the off position.

By the two layer arrangement disclosed, the RF and DC signals are isolated from one another.
In Figure 5, there is shown a further embodiment of a circuit 36 on the layer 6. T'he same reference numerals are used in Figure 5 as those used 5 in Figure 3 for those components that are identical. The circuit 36 and the transverse line 24 are laid out in a manner similar to that shown in Figure 3 for the circuit 17 and the transverse line 24 on the substrate 18 except that the two circuits 36, 24 are interconnected using flip-chip technology. The transmission lines (22a, 22b and 22c - of which only 22a is shown in Figure to 5) which make up the circuit 36 as well as the transverse line 24 are made from metal that is compatible with flip-chip technology. Substrate 18 is also made of a material that is compatible with flip-chip technology. A chip 37, supported by chip bumps 38 is connected between the transmission line 22a and the transverse line 24. A chip and chip bumps will also connect the 15 transmission lines 22b (not shown) to the transverse line 24 and a further chip and chip bumps will connect the transmission line 22c (not shown) to the transverse line 24 even though only one chip 37 is shown in Figure 5.
The chip 37 can be a PIN or FET diode, which is connected to a DC power supply (not shown). The DC power supply switches the chip on and off, 2o thereby causing the switch 2 to turn on and off respectively. The flux which is typically generated during the soldering process of the chip bumps can damage HTS material. The two layer circuit where the bottom layer 4 uses HTS material as shown in Figure 2 while the top layer 6 employs the flip-chip technology allows the combination of flip-chip technology with HTS

technology as the layer 6 can be manufactured separately from the layer 4.
The diode shown in Figure 5 is in chip form. Alternatively, the diode could be in encapsulated form (not shown) where the diode is attached between the line 22a and the transverse line 24 using wire bonding or other suitable 5 means. The configuration of the layer 6 shown in Figure 5 still permits the isolation between IRF and DC signals.
In Figure 6, there is shown yet another embodiment of a circuit 39 on the layer 6. The same reference numerals are used in Figure 6 for those components that are identical to the components of Figure 3. As with Figure l0 5, only one transmission line 22a is shown, but the transmission lines 22b and 22c are laid out in a manner similar to that shown in Figure 3. As can be seen, a microelectromechanical (MEMS) system 40 connects the transmission line 22a of the circuit 39 with the transverse line 24. Second and third MEMS switches (not shown) would connect transmission lines 22b 15 and 22c (also not shown) to the transverse line 24. The MEMS switches are placed on the substrate 18 to interconnect the circuits 39 with transverse line 24 using conventional MEMS technology. MEMS technology is not directly compatible with HTS technology but the layer 6 can be manufactured using conventional MEMS technology separate and apart from the layer 4, which 2o can use HTS technology. After manufacture, the two layers can be brought together.
The three embodiments of the layers 6 shown in Figures 4, 5 and 6 respectively can be substituted for the embodiment shown in Figure 3 of the layer 6 and placed into the switch 2 of Figure 1. While the embodiment shown in Figure 6 is the preferred embodiment, there may be circumstances requiring particular performance characteristics where one of the other embodiments will be preferred.
Figure 7 shows a preferred embodiment for a C-switch 42. An HTS
5 switch 42 consists of two layers 4 and 6. Layer 4 consists of an HTS circuit 44 having four ports 46a, 46b, 46c and 46d printed on a substrate 10 attached to a ground plane 12. The layer 6 has a circuit 48 consisting of several transmission lines SOa, SOb, SOc, SOd, SOe, SOf, SOg, SOh mounted on a substrate 18 to align with the lines 47a, 47b, 47c, 47d, 47e, 47f, 47g, 47h 10 respectively of the layer 4. The circuit 44 is assembled in a housing by attaching the ground plane 12 to a bottom of the housing 52 using epoxy soldering or any other means. A bottom side of the layer 6 is attached to the top side of the layer 4 using adhesive or any other suitable means. The switch elements (not shown) could be of the semiconductor type or 15 mechanical type. Each switching element has two terminals. One terminal is attached to the lines SOa-SOh while the other terminal is attached to circuits 60a, 60b, 60c and 60d, which are short circuited to the housing 52. The plate 25 is used as a cover for the circuits shown.
Figures 8a and 8b show the measured results for an HTS C-switch 42 20 as described in Figure 7. The graph shown in Figure 8a is a graph of the isolation and return loss when the switch is on and the graph shown in Figure 8b is a graph of the isolation and return loss when the switch is off. The switching elements used in the switch 42 for the measured results shown are the narrow HTS line switching elements shown in Figure 4.

In Figure 9, there is shown a single layer switch 61 having a circuit 62 on a layer 64 of a substrate 65. The switch elements are narrow HTS lines 66a, 66b and 66c driven by DC current in the same manner as those shown in Figure 4, but not shown in detail in Figure 9. Capacitors 68a, 68b and 68c 5 are located at the end of each of the three transmission lines 69a, 69b and 69c. Conductors 34a, 34b and 34c extend from conductors 35. The circuit 62 is mounted in a housing 70 having an input 72 and output 74 with a cover 76. Isolation between RF and DC is achieved by the capacitors 68a, 68b and 68c. The layer 64 is bonded into the housing 70 by epoxy (not shown).
to Figures l0a and l Ob shown the measured results of the switch 61 of Figure 9.
It can be seen that Figure l0a is a graph of the isolation and return loss when the switch is on and Figure lOb is a graph of the isolation and return loss when the switch is off.
The present invention can be used to construct different types of 15 switches including single pole double throw switches and with various switch matrices. While >=iTS switches are the preferred embodiment, the lower layer in a two layer switch can be made with a gold film on the substrate in place of the HTS film. Similarly, the transmission lines extending between an input and output can be made from I-STS film, gold 2o film or other suitable metallic film. The number of transmission lines and switch elements will vary with the bandwidth desired. While the present invention has been described as a switch and that is the preferred embodiment, the two layer embodiment can be used to interact with and control microwave circuits. Further, the present invention can be used to construct H'TS microwave circuits using two layers to combine technologies that are incompatible with HTS into the HTS circuit. This is accomplished by dividing the circuit into two layers and constructing part of the circuit on the first layer and part of the circuit on the second layer.
Although the present invention has been fully described by way of example in connection with a preferred embodiment thereof, it should be noted that various changes and modifications will be apparent to those skilled in the art. Therefore unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as 1 o being included therein.

Claims (28)

1. An HTS microwave circuit comprising a first layer and a second layer, said first layer having a first HTS microwave circuit extending between an input and output, said second layer having a second microwave circuit that is coupled to said first circuit, said second circuit having at least one element that is compatible with at least one of MEMS technology and flip-chip technology, but incompatible with HTS material, said at least one element being connected into said second circuit to interact with and control said HTS circuit.

2. A microwave circuit as claimed in Claim 1 wherein said first layer is a substrate having a ground plane with said first circuit formed thereon and said second layer is a substrate with said second circuit formed thereon.

3. A microwave circuit as claimed in Claim 2 wherein said first circuit and said second circuit are formed on said substrates as a film.

4. A microwave circuit as claimed in Claim 2 wherein said first circuit has three transmission lines and there are three elements of said at least one element, said three elements being selected from the group of MEMS technology, flip-chip technology and mechanical technology.

5. A microwave circuit as claimed in Claim 4 wherein each element has two terminals, one terminal being connected to a part of said second microwave circuit that is coupled to said first circuit and another terminal being connected to a part of said second circuit that is short circuited.

6. A microwave circuit as claimed in Claim 5 wherein said circuit is located in a housing and part of said second circuit that is short circuited is short circuited to said housing.

7. A microwave circuit as claimed in Claim 2 wherein said first circuit has two transmission lines and there are two elements of said at least one element of said second circuit.

8. A microwave circuit as claimed in any one of Claims 1, 2 or 3 wherein the second circuit includes a DC signal that is isolated from a RF
signal of said second microwave circuit.

9. A microwave circuit as claimed in any one of Claims 5, 6 or 7 wherein said second circuit has a DC signal that is connected to pass microwave energy through each element or not to pass microwave energy through each element.

10. A microwave circuit as claimed in any one of Claims 5, 6 or 7 wherein said elements are diodes selected from the group of PIN, FET and GaAs.

11. A microwave circuit as claimed in any one of Claims 1, 2 or 3 wherein said second circuit is coupled to said first circuit by one of capacitatively or inductively.

12. A microwave switch comprising a first layer and a second layer, said first layer having a first microwave circuit that can carry an RF
signal between an input and output, said second layer having a second microwave circuit that is coupled to said first circuit, said second circuit having at least one switch element that can be controlled between an off position and an on position by a DC signal, said RF signal and said DC signal being isolated from one another.

13 13. A microwave switch as claimed in Claim 12 wherein said first layer is a substrate having a ground plane and said second layer is a substrate, said first circuit and said second circuit being formed on said substrates.

14. A microwave switch as claimed in Claim 13 wherein said first and second circuit are formed on said substrates as films.

15. A microwave switch as claimed in Claim 14 wherein said at least one element is selected from the group of a MEMS switch, flip-chip technology, mechanical switch technology and an HTS narrow strip that becomes non-superconductive when a high enough DC current flows through said narrow strip.

16. A microwave switch as claimed in Claim 12 wherein said at least one element is a diode selected from the group of PIN, FET and GaAs.

17. A microwave switch as claimed in any one of Claims 12, 13 or 15 wherein said first circuit has two transmission lines and there is one switch element in said second circuit for each transmission line of said first circuit.

18. A microwave switch as claimed in any one of Claims 12, 13 or 15 wherein said first circuit has three transmission lines and there is one switch element of said second circuit for each transmission line of said first circuit.

19. A microwave switch as claimed in Claim 12 wherein each switch element has two terminals, one terminal being connected to a part of said second circuit that is coupled to said first circuit and another terminal being connected to a part of said second circuit that is short circuited.

20. A microwave switch as claimed in Claim 14 wherein said switch has a plurality of inputs and outputs.

21. A microwave switch as claimed in any one of Claims, 12, 13 or 15 wherein said first microwave circuit is an HTS circuit.

22. A microwave switch as claimed in Claim 12 wherein said film is selected from the group of microstrip and stripline and said second circuit is coupled to said first circuit by one of capacitatively and inductively.

23. A microwave switch comprising an HTS microwave circuit extending between an input and an output, said circuit having a transmission line containing a narrow length of high temperature superconductive material connecting said HTS circuit to ground, said switch having a DC power source connected to said narrow length of high temperature superconductive material, said DC power source being connected to change said length of high temperature superconductive material between superconductive and non-superconductive, with means to prevent current from said DC power source from flowing into said circuit beyond said narrow length of high temperature superconductive material.

24. A switch as claimed in Claim 23 wherein said means for preventing current from said DC power source from flowing into said circuit beyond said narrow length of high temperature superconductive material is a capacitor located between said length of high temperature superconductive material and said HTS circuit beyond said length of high temperature superconductive material.

25. A switch as claimed in Claim 23 wherein there are two transmission lines, each transmission line having a narrow length of narrow high temperature superconductive material connecting that transmission line to ground.

26. A switch as claimed in Claim 23 wherein there are three transmission lines, each transmission line having a length of narrow high temperature superconductive material connecting one transmission line to ground.

27. A switch as claimed in Claim 26 wherein said switch has a plurality of inputs and a plurality of outputs.

28. A method of combining a first HTS circuit with a second circuit having at least one of flip-chip technology, MEMS technology and mechanical technology, said method comprising constructing said first circuit on a first substrate having a ground plane, constructing said second circuit on a second substrate, arranging said substrates to capacitatively or inductively couple said second circuit to said first circuit and controlling said first circuit through said second circuit.