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|United States Patent
October 10, 1972
WAVEGUIDE POWER SWITCH HAVING ALTERNATELY CLOSED SHORTING PLATES
An input waveguide and two output waveguides are arranged in an H-plane
tee. A power switch determines into which one of the output ports the
power will flow. Each of the guides is a rectangular waveguide excited in
the TE.sub.10 mode. The switch includes first and second end plates, each
including a shorting tongue adapted to extend through a transverse slot in
the broadwall of one of the output waveguides to form a shorting plate.
The end plates are mechanically interconnected so that when one plate is
in a closed position, the other plate is withdrawn to an open position
which permits the passage of power. A capacitor screw or stub is located
in one of the output waveguides to compensate for impedance mismatch.
Limit switches are arranged to prevent the transmission of power to the
input waveguide unless the end plates are in an operative position.
Johnson; Ray M. (Danville, CA) |
January 29, 1971|
|Current U.S. Class:
|Current International Class:
||H01P 1/12 (20060101); H01P 1/10 (20060101); H01p 001/10 ()|
|Field of Search:
U.S. Patent Documents
L H. Terpening Co. advertisement, 4-16-51, Copy in 333-985.
Gensler; Paul L.
1. A power switch for selectively coupling microwave power from a rectangular input waveguide excited in the TE10 mode to one of a plurality of output waveguides comprising: connecting
waveguide means interconnecting said input waveguide with said output waveguides and defining a waveguide tee formed in the H plane, said tee including an input port connected to said input waveguide, a first output port having a transverse slot therein
and connected to one of said output waveguides, and a second output port having a transverse slot therein and disposed in the base of the tee and connected to a second one of said output waveguides, said input waveguide and said first output port being
in line with the direction of power flow when said first output port is open, an end plate for each of said output ports, each of said end plates extending within one of said slots and movable in the E plane to open and close one of said output ports,
said end plate associated with said second output port being located in a plane extending perpendicularly of the mouth of the tee so as to form a continuation of a sidewall coupling the in-line ports when said end plate associated with said second port
is in closed position.
2. The switch of claim 1 characterized in that the end plate for said first output port is located at a distance from the mouth of said second output port to minimize reflections back to the source when said first output port is closed and said
second output port is open.
3. The switch of claim 1 further comprising an adjustable stub capacitor located in a broadwall of said second port downstream in the direction of power flow from said second end plate, whereby said stub capacitor is not in circuit when power is
being passed from the input port to the first output port.
4. The switch of claim 1 further comprising means sensing the closed position for each of said end plates for inhibiting the transmission of power to said input waveguide unless one of said end plates is in a fully closed position.
5. The switch of claim 1 further comprising means for interconnecting said end plates for maintaining only one of said end plates in an open position at a time.
6. The switch of claim 5 wherein said means includes a lever mounted to said tee and mechanically interconnected with each of said end plates for moving one of said end plates to a closed position when the other of said plates is moved to an
7. The switch of claim 5 further comprising means responsive to the positioning of either of said end plates in a fully closed position for generating a signal indicative thereof, said signal being capable of enabling the transmission of
microwave energy to said tee.
BACKGROUND OF THE INVENTION
The present invention relates to a power switch for switching microwave power from a rectangular input waveguide to one of two rectangular output waveguides on a mutually exclusive basis.
In some microwave applications it is necessary or desirable to switch the energy flow from one location to another. For example, a single source of microwave energy may be used to energize one of two separate applicators so that when one is
down, the other is excited. Devices are known and have been used to accomplish this function, but commercially available switches are quite expensive.
The present invention provides for a microwave switch which is simple in structure, easy to fabricate, and thus relatively inexpensive. For narrow band applications, the switch of the present invention provides an acceptable impedance match
between input and output, and it is therefore particularly useful for such applications.
The present switch may be used in connection with a rectangular waveguide formed into an H-plane tee. The guide is excited in the TE.sub.10 mode, so the H-plane is a plane extending parallel to the broadwalls and along the direction of power
flow. Input power is fed to one of the three ports provided by the tee, and output power is taken from either of the other two ports depending upon the state of the switch. The switch includes first and second end plates, each provided with a shorting
tongue adapted to extend through a transverse slot in the broadwall of its associated output waveguide (or "port") and arranged to slide in the E plane.
The end plates are interconnected mechanically and arranged so that when one end plate is in a position wherein its shorting tongue shorts its associated waveguide, the tongue of the other end plate is withdrawn from its associated output
waveguide to permit power to flow from the input port to the open output port. In the shorting position, the upper and lower portions of the tongue are maintained in electrical continuity with the upper and lower broadwalls respectively of the shorted
output guide. In the open position, the distal end of the shorting tongue is maintained in electrical continuity with the upper broadwall of the open output guide, and a conductive crossbar on the end plate is moved into continuity position with the
corresponding slot on the lower broadwall of the open output guide thereby permitting power to pass through that guide while electrically closing the slots in both broadwalls.
In one embodiment, one of the output ports is in the base leg of the tee, and the end plate for that output waveguide is arranged so that when it is in a closed position, its shorting tongue forms a continuation of the sidewall interconnecting
the input port with the other or in-line output port. Thus, the impedance match between the input waveguide and the in-line output waveguide is excellent. A capacitor screw or stud is located in the output waveguide in the base branch of the tee
downstream of its shorting tongue to compensate for mismatch between the input port and that output port.
Limit switches (or other mechanical or electrical means) may be arranged to prevent the transmission of power through the input waveguide unless the end plates are in operative position, and this is a safety feature to prevent transmission of
power to one of the output guides unless the end plates are in operative positions.
Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing wherein identical reference numerals will
refer to like parts in the various views.
FIGS. 1 and 2 are lower perspective views of a waveguide power switch incorporating the present invention shown in its two operating positions;
FIG. 3 is a diagramatic plan view of a waveguide arranged in an H-plane tee;
FIGS. 4 and 5 are cross sectional and end views of a portion of a switch of FIG. 1 in an open position;
FIGS. 6 and 7 are respectively side and end views of a portion of the switch of FIG. 1 in a closed position;
FIG. 8 is a cross sectional close up view of the finger stock engaging the transverse bar of an end plate; and
FIG. 9 is a perspective view of the finger stock connectors.
Turning first to FIGS. 1 and 2, a rectangular waveguide is arranged in the form of a tee in the H plane, having an input waveguide (or port) generally designated by reference numeral 10, a first output port 11, and a second output port 12. The
output port 11 is sometimes herein referred to as the in-line output port because its center is in line with the center of the input port, and the second output port designated 12 is sometimes referred to as the output port in the perpendicular leg or
base of the tee.
Arrangements other than the one illustrated are possible. For example, the input port could be in the base leg of the tee, and the in-line ports could then both be output ports.
Each of the input and output waveguides is rectangular in cross section. As is well known, each rectangular waveguide has an opposing pair of broadwalls (upper and lower in FIGS. 1 and 2) and an opposing pair of sidewalls. The object of the
invention is, of course to gate microwave power entering at the input port 10 to one or the other, but not both, of the output ports 11, 12. This is accomplished by means of a mechanical toggle assembly generally designated by reference numeral 15. The
microwave power being transmitted is in the TE.sub.10 mode, which means that the electric field vector extends perpendicularly between the broadwalls, and there is no component of the electric field vector perpendicular to the sidewalls Further, there is
no reversal in polarity of the electric field vector across the width of the waveguide.
The waveguide tee is generally designated by reference numeral 16 in FIG. 2, and it is provided with three peripheral flanges for connecting respectively to an input waveguide 17, a first output waveguide 18, and a second output waveguide 19
which, as shown, may be in the form of an elbow leading to a second or alternative load.
Referring now to the schematic showing of FIG. 3, there are formed adjacent the in-line output port 11 of the tee 16 first and second slots, the one shown in the upper broadwall being designated 20. The lower slot is designated 21 and can be
seen in FIGS. 4-7. Similarly, first and second slots are formed respectively in the upper and lower broadwalls at the mouth of the second output port 12, the upper slot being illustrated in FIG. 3 and designated 22. These latter slots are formed in
vertical alignment with each other, and they are located such that a plate passing through them will form a continuation of the sidewall 23 of the input port so as to be continuous with the sidewall 24 of the first output port 11.
Returning now to FIGS. 1 and 2, first and second end plates 25 and 26 are associated respectively with the slots 22 and 20. Each of the end plates 25, 26 is similar in structure and operation, so that only the end plate 26 need be described in
greater detail for a complete understanding of the invention.
Referring now to FIGS. 1, 2, 5 and 7, the end plate 26 is formed in two sections 27, 28 joined together along the line 29. Each section 27, 28 is formed from a flat sheet of conductive metal, such as aluminum. First and second vertical side
slots 30 and 31 are formed in section 27. The slots 30, 31 are in line with and adapted to receive respectively the sidewalls 24 and 24a of the first output port 12 when the end plate 26 is forced downward into its closed position, as seen in FIGS. 2
and 7. The section 28 is in the form of a U so that when it is joined to the section 27, there is a rectangular opening 32 communicating with the slots 30, 31. The opening 32 has a width slightly larger than the width of the waveguide and a height
slightly less than the height of the waveguide. A central tongue 33 is formed in the upper section 27 of the plate 26 which is adapted to extend through the upper and lower slots 20, 21 in the upper and lower broadwalls of the guide when the end plate
26 is lowered to a closed position, as seen in FIGS. 2 and 7. The U-shaped section 28 includes a transverse or cross bar 35 which defines the lower edge of the central opening 32, and vertical leg members 36, 37 which define the sides of that opening.
As best seen in FIGS. 4 and 6, located on either side of the upper transverse broadwall slot 20 are finger connectors designated 40 and 41 respectively. Similar finger connectors 42 and 43 are located on either side of the lower broadwall slot
21. The finger connectors 40-43 may best be appreciated from FIG. 9 wherein the finger connector 42 is seen in perspective as including an angle iron 44 and a continuous strip 45 of individual fingers 46 each having a crescent-shaped distal end to form
a resilient contactor for the end plate 26. Preferably, the strip 45 and fingers 46 are made from beryllium copper to provide good electrical conductivity and desired resiliency during contact.
When the plate 26 is in an open position wherein microwave power flows from the input port 10 to the first output port 11, the lower end of the tongue 33 is engaged by the finger contactors 40, 41 to provide electrical continuity in the upper
broadwall of the waveguide, and the transverse bar 35 is contacted by the finger contactors 42, 43 (see FIG. 4). FIG. 8 is a close up illustration of the lower contactors 42, 43 in engagement with the transverse bar 35 of the end plate 26. When the end
plate 26 is in an open position, the end plate 25 is in a closed position, as will be described presently.
When the end plate 26 is in a closed position, the base of the tongue 33 is engaged by the upper finger contactors 40, 41 and the lower distal edge of the tongue 33 is engaged by the lower finger contactors 42 and 43. Thus, in a closed position,
the tongue 33 forms an electrical short between the upper and lower broadwalls.
Turning now to the toggle assembly 15, in the upper central portion of the end plate 26 there is formed an opening 50 which receives one prong of a bifurcated end of an elongated lever arm 51 which is disposed in a generally longitudinal
direction of the in-line ports of the tee 16. The other end of the lever 51 is similarly bifurcated, but in a perpendicular direction to the direction of elongation of the arm 51. This second bifurcated end has one prong received within an aperture 52
formed in the upper central portion of the end plate 25. The center of the lever arm 51 is pivotally connected as at 53 to an upstanding support 54 which is welded to the upper broadwall of the waveguide. Through this mechanism, when the end plate 26
is pushed upwardly, the end plate 25 is lowered to a closed position; and conversely, when the end plate 25 is raised to an open position, the end plate 26 is closed. As has already been mentioned, the end plate 25 is similar in structure and operation
to the end plate 26, so that when the end plate 25 is in an open position, microwave energy passes from input port 10 to the output port 12 in the perpendicular leg of the tee 16. When the end plate 25 is lowered to a closed position, the tongue thereof
(designated by reference numeral 56 in FIG. 2 ) extends into the slot 22 and forms a continuation of the sidewalls 23, 24 of the in-line portions of the waveguide tee.
The end plates 25, 26 are formed in upper and lower sections as illustrated in order to facilitate assembly to their associated waveguide sections. Rectangular plates or pads 60 and 60a join the arms 36, 37 of the U-shaped section 28 to the
upper section 27 of the end plate 26 after the section 26 is installed with its tongue 33 located in the slot 20. One of the screws which secures the plate 60a acts as a raised contact point for engaging an arm 61 of a limit switch 62, the arm 61 being
resiliently biased toward the end plate 26. When the end plate 26 is lowered to a closed position, the contact screw engages a roller at the end of the arm 61 of the limit switch 62 to close that switch, thereby generating a signal permitting power to
be transmitted from the source to the input waveguide 10. The limit switch 62 is conventionally mounted to the sidewall of the tee 16 in the position shown. A similar arrangement of joining plates and limit switch (not shown) are provided in operative
relation with the end plate 25 so that plate may be easily assembled to its guide and a second signal is generated when that end plate is in a fully lowered position. Preferably one or the other of the signals from each of the two limit switches must be
present before the power sources are connected to the input waveguide 17; and this serves as a safety feature inhibiting the coupling of power unless the switch 15 is completely in one of its two operational positions.
When a rectangular waveguide is excited in the TE.sub.10 mode, as already mentioned, the electric field vector extends perpendicularly between the broadwalls and the current vector extends in the vertical (or Y direction in the convention used in
this field). Thus, contact of the shorting tongue is not necessary at the sides of the guide in order to achieve continuity. The finger contacts which are advantageously used because they permit sliding of the end plates are therefore used only at the
top and bottom of the guide, and the end plates are provided with slots adjacent the shorting tongue (such as the slots 30, 31 in FIG. 5) to allow the passage of the shorting plate relative to the sidewalls of the waveguide with the sidewalls being
received to those slots.
In order to determine the location of the end plates 25, 26 in the illustrated embodiment, I prefer to first install the end plate 25 as described, and then with the end plate 25 opened and its output properly terminated in an absorbing load, to
vary the location of a shorting plate in the first output port 11 until reflective power at the input port 10 is minimized. This will determine the location of the end plate 26 relative to the second output port; and the stub capacitor 65 will then be
adjusted to match impedances. The stub capacitor 65 is downstream (in the direction of power flow) of the end plate 25 so that its effects are not observed when that end plate is in a closed position.
Thus, when power is transmitted from port 10 to port 11, there is little or no mismatch because the end plate 25 forms a continuum of sidewall between the input and output ports. However, when the power is being transmitted from port 10 to port
12, there is a mismatch in impedance which is compensated by the capacitive screw 65 in FIG. 3. Although such compensation is not effective over a wide bandwidth, nevertheless, it has been found to be sufficient for the ISM bandwidths.
A switch of the type has been illustrated and described herein has been fabricated in a WR 975 waveguide and operated with 25 kw of average continuous wave power. The leakage out of a closed port was less than the maximum acceptable power
density radiation limit of 10 mw/cm.sup.2.
Having thus described in detail a preferred embodiment of the inventive waveguide power switch, persons skilled in the art will be able to modify some of the structure that has been disclosed and to substitute equivalent elements for those which
have been described while continuing to practice the invention; and it is, therefore, intended that all such modifications and substitutions be covered as they are embraced within the spirit and scope of the appended claims.
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