Double-throw miniature electromagnetic microwave switches...

Details Double-throw miniature electromagnetic microwave switches... Double-throw miniature electromagnetic microwave switches...

2001-07-30

2003-07-15

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Long line elements and components

Switch

C333S105000

Reexamination Certificate

active

06593834

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to miniature electromagnetic switches for microwave systems. More specifically, the invention relates to a miniature double-throw electromagnetic switch for operation in microwave or millimeter wave frequencies.
2. Description of the Prior Art
Switches are basic building blocks of communication electronics and are widely used for telecommunications applications such as signal routing, redundancy switching, impedance matching networks and adjustable gain amplifiers. Mechanical relay, PIN diode and FET are the common microwave switches. Mechanical relays offer the benefits of low insertion loss, large off-state isolation, high linearity and high power handling capabilities. However, they consume a significant amount of power and are bulky, heavy and slow. Semiconductor switches such as PIN diode and FET provide much faster switching speed and smaller size and weight but are inferior in insertion loss, isolation, linearity and power handling capabilities than mechanical relays.
Microwave switches providing the advantageous properties of both the mechanical relay and semiconductor switch are then highly desirable, especially for space, airborne and mobile telecommunications applications. Micromachining technologies promise to enable the fabrication of such switches, i.e., switches with the high microwave performance of mechanical switches but also with the small size, weight and power consumption of semiconductor switches. Furthermore, conventional microelectronics fabrication processes are usually used for micromachining, making the integration of such miniature switches with other active electronics possible.
In U.S. Pat. No. 6,016,092 entitled “Miniature Electromagnetic Microwave Switches and Switch Arrays” filed on Aug. 8, 1998 by C. X. Qiu, L. S. Yip and Y. C. Shih, single-pole single-throw micro electromagnetic switches in a coplanar waveguide, a microstrip or stripline form were described. A double-throw switch in a stripline form was also described. More recently, in U.S. patent application Ser. No. 09/400,256 entitled “Double-throw Miniature Electromagnetic Microwave Switches” filed on Sep. 21, 1999 by the same inventors of the above U.S. patent, double-throw micro electromagnetic switches in a microstrip form and a coplanar waveguide form and with controlled magnetization are disclosed. These single-pole double-throw switches are useful to the fabrication of microwave modules, which require a plurality of switches for operation at microwave or millimeter wave frequencies.
Two schematic views of a prior art of a miniature double-throw electromagnetic switch (
20
) disclosed in U.S. patent application Ser. No. 09/400,256 entitled “Double-throw Miniature Electromagnetic Microwave Switches”, filed on Sep. 21, 1999 by L. S. Yip, C. X. Qiu and Y. C. Shih, hereinafter called Double-throw Switch A, are shown in FIGS.
1
(
a
) and
1
(
b
). FIG.
1
(
a
) shows a schematic top view of the Double-throw Switch A (
20
) and FIG.
1
(
b
) shows the schematic cross-sectional view of the switch (
20
) taken along line A-A′ in FIG.
1
(
a
). The double-throw switch A (
20
) is fabricated on a dielectric substrate (
21
) with a ground plane (
22
in FIG.
1
(
b
)) deposited on backside of the dielectric substrate (
21
). An input microstrip line (
23
a
) and a first output microstrip line (
25
) are deposited on a front side of the dielectric substrate (
21
). It is seen that the input microstrip line (
23
a
) and the first output microstrip line (
25
) are aligned in such a way that a continuous microstrip line can be formed when the two are connected electrically. The input microstrip line (
23
a
) and the first output microstrip line (
25
) are separated by a gap (
24
) having a length, (L
g
). A first cantilever (
23
b
) with a length (
26
) is deposited over the gap (
24
) (see FIG.
1
(
b
)). A layer of permanent magnetic material (
27
) is deposited on part of the first cantilever (
23
b
). A second output microstrip line (
28
) having a second cantilever (
29
) is deposited so that the second cantilever (
29
) is suspended over the first cantilever (
23
b
). The second output microstrip line (
28
) may be deposited on the same dielectric substrate (
21
) with the input microstrip line (
23
a
) and the first output microstrip line (
25
), or on a different dielectric substrate. The second cantilever (
29
) overlaps part of the first cantilever (
23
b
) in region without the magnetic film (
27
) so that when the first cantilever (
23
b
) is pushed upwards, a leading portion of the first cantilever (
23
b
) can make electrical contact with the second cantilever (
29
). The overlap between the first cantilever (
23
b
) and the first output microstrip line (
25
) is (
36
) whereas the overlap between the first cantilever (
23
b
) and the second cantilever (
29
) is (
37
). A layer of dielectric material (
22
′) such as SiO
2
or polyimide is applied on the ground plane (
22
). A miniature electromagnetic coil (
30
) is deposited or attached to the dielectric material (
22
′). Width (
31
) of the input microstrip line (
23
a
) and the first output microstrip line (
25
) is selected to be substantially equal to the width (
32
) of the second output microstrip line (
28
). Values of (
31
) and (
32
) are determined by the thickness (
33
, in FIG.
1
(
b
)) of the dielectric substrate (
21
), the dielectric constant, and the central frequency of the microwave signals to transmit for low loss operation. The second output microstrip line (
28
) may be arranged so that it makes an angle of roughly 90 degrees with respect to the input microstrip line (
23
a
) and the first output microstrip line (
25
).
The operation of the Double-throw Switch A (
20
) is as follows. When no current is applied to the miniature electromagnetic coil (
30
) (I=0), no magnetic force is applied to the first cantilever (
23
b
) and the first cantilever (
23
b
) is in a normal position in between the first output microstrip line (
25
) and the second cantilever (
29
) of the second output microstrip line (
28
). When a positive current (I>0) is applied to the miniature electromagnetic coil (
30
), so that the direction of the magnetic field (B
e
) induced is substantially parallel and opposite to the magnetic moment (B
m
, in FIG.
1
(
b
)) of the permanent magnetic film (
27
), an attraction force will be caused on the first cantilever (
23
b
). When the current (I) exceeds a pull-down threshold or when the force is sufficiently large, the first cantilever (
23
b
) will be deformed so that the first cantilever (
23
b
), attaching to the input microstrip line (
23
a
), will get in contact with the first output microstrip line (
25
). Microwave signals applying to the input microstrip line (
23
a
) will be allowed to reach the first output microstrip line (
25
). Since there is no electrical contact between the first cantilever (
23
b
) and the second cantilever (
29
), which is connected to the second output microstrip line (
28
), the incoming microwave signals will not reach the second output microstrip line (
28
). When the current (I) through the miniature electromagnetic coil (
30
) is reversed, so that the direction of the magnetic field (B
e
) induced is substantially parallel and along the magnetic moment (B
m
) of the permanent magnetic film (
27
), a repulsion force will be caused on the first cantilever (
23
b
). When the reverse current (I) exceeds a push-up threshold or the repulsion force is sufficiently large, the first cantilever (
23
b
) will be pushed away from the first output microstrip line (
25
) and eventually get in contact with the second cantilever (
29
) connected to the second output microstrip line (
28
). Microwave signals supplying to the input microstrip line (
23
a
) will not be allowed to reach the first output microstrip line (
25
). Since there is electrical contact between the first cantilever (
23
b
) and the second cantilever (
29
), the incoming microwave signals w

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