Switchable resonator device

A switchable resonator device having a selectable center frequency over a wide radio frequency range comprising a radio frequency signal input and output means, a resonator structure connected between the signal input and output means for respectively receiving and delivering radio frequency input and output signals, the resonator structure using a strip line conductor having a first conductor element with first and second extending portions each providing respective inductance properties, a first switchable means for controllably connecting the first portion of the first conductor element at selected locations along its extension with the second element for varying its inductive properties, a second switchable means for controllably providing a selected capacitance between the second portion of the first conductor element and the second conductor element, and control means providing a control signal to the first and second switchable means for selecting and changing the center frequency of the resonator device at a rapid rate.

BACKGROUND OF INVENTION 
The invention relates to a switchable resonator device, and more 
particularly to a switchable resonator device which has a center frequency 
which is selectable over a wide radio frequency range and may be changed 
rapidly. 
SUMMARY OF THE INVENTION 
Heretofore, electronically tuned resonators have been disclosed which have 
been of the switching variety allowing rapid switching to different center 
frequencies as described in U.S. Pat. No. 4,623,856. It has, however, been 
desirable to provide such devices with very narrowband filter 
characteristics while allowing a high rate of change of the center 
frequency on the order of 7,000 changes per second with a transition time 
of 5 micro seconds and over a wide radio frequency range such as 100 MHz 
to 500 MHz. In addition to achieving such a high rate of frequency change 
or "hopping" rate, it is also desirable to be able to provide high 
stability and repeatability by use of electronic control signals and to 
allow simple coupling between a plurality of switching resonator devices 
to improve its narrow band characteristic and operating properties. 
It is therefore a principal object of the invention to provide a new and 
improved switchable resonator device which has a center frequency which is 
electronically selectable over a wide frequency range. 
Another object of the invention is to provide a new and improved switchable 
resonator device which may have its center frequency switched at a high 
rate over a wide radio frequency range. 
Another object of the invention is to provide a new and improved switchable 
resonator device which may be electronically controlled to provide 
accurate switching of its center frequency with great repeatability and 
with a short transition time between changes. 
Another object of the invention is to provide a new and improved switchable 
resonator device having a high selectivity and filter characteristic for 
the selected center frequency which provides a narrow pass-band. 
Another object of the invention is to provide a new and improved switching 
resonator device utilizing the lumped inductive properties of a strip line 
conductor for providing highly desirable electrical characteristics. 
Another object of the invention is to provide a new and improved switchable 
resonator device, a plurality of which may be connected together for 
providing enhanced performance. 
The foregoing and other objects of the invention will become more apparent 
as the following detailed description of the invention is read in 
conjunction with the drawing.

DETAILED DESCRIPTION 
Referring to the figures, FIG. 1 is a simplified schematic representation 
of the electrical configuration of the switchable resonator device 10 of 
the invention. The device 10 includes an input terminal 12 and an output 
terminal 14 for receiving and delivering radio frequency signals over a 
wide frequency range. The terminals 12 and 14 are connected by conductor 
16. A variable inductor 18 is connected between the line 16 and ground 20, 
while a fixed inductor 22 has one end connected to the line 16 and the 
other end return to ground 20 through a variable capacitor 24. A tuning 
control means 26 provides output signals over lines 28 and 30 for changing 
or switching the inductance of the variable inductor 18 and the 
capacitance of the variable capacitor 24. The tuning control means 26 
provides rapidly changing signals for causing the switching resonator 
device 10 to change the values of its variable components at a high rate. 
Thus, a radio frequency signal which is delivered to the input terminal 12 
is subject to the filtering action of the resonator device for allowing 
the passage of an input signal to the output terminal 14 only within a 
selected narrow band having a center frequency controlled by the tuning 
control means 26. 
FIGS. 2 and 3 disclose a physical embodiment of the switchable resonator 
device 10 having an enclosure 11 with front and back plates 32 and 34 of 
electrically conducting material which may be silver plated to increase 
conductivity, a conductive right side member 36 secured between the front 
and back plates 32 and 34 by bolts 38 within slots 39 to allow adjustment 
of its position (see FIG. 2). An electrically conductive elongated 
rectangular metal plate providing a center block conductor 40 which may be 
silver coated to increase conductivity, is positioned in spaced 
relationship between the front and back plates 32 and 34 and the side 
member 36 (see FIG. 3) by a pair of upper and lower electrically 
insulating blocks 42 and 44. The blocks 42 and 44 are secured by screw 
means 46 with the front and back plates 32, 34, and securely retains 
between them the end 48 of the center block conductor 40 which has its 
other end 50 spaced from the right side member 36 (see FIG. 3). The block 
conductor 40 which is elongated in the direction between its ends 48 and 
50 has side surfaces 51, 51' spaced from the front and back plates 32, 34 
and upper and lower surfaces 52 and 54 which are also spaced from top and 
bottom conductive metal cover plates 56 and 58 which are secured by 
respective screw means 60 and 62 with the front and back plates 32 and 34 
and the right side member 36. The block conductor 40 is one of the 
conductor elements of a shielded strip line conductor having its other 
conductor provided by the shielded enclosure 63 formed by the metal plates 
32 and 34, right side member 36 and top and bottom cover plates 56 and 58 
and considered to be at ground potential. As seen in FIG. 3, the end 48 of 
the block 40 which is reduced in width where it is secured between the 
insulating blocks 42 and 44, is further interengaged by pins 64. 
Compression force is also exerted on the end 48 between the blocks 42 and 
44 by the bolts 66 which engage and extend between the insulating block 44 
an the top cover plate 56 while passing through enlarged openings 67 in 
the block conductor 40 to provide insulation and prevent electrical 
contact therewith. 
A miniature coaxial cable connector 68 is secured with the front plate 32 
spaced intermediate the top and bottom cover plates 56, 58 for receiving 
input radio frequency signals, while a similar miniature coaxial cable 
connector 70 is secured with the back plate 34 at a location in line with 
and directly opposite to the connector 68 for providing output radio 
frequency signals. The outer conductors 69 of the connectors 68 and 70 are 
electrically connected to the conductive front and back plates 32 and 34 
while their center conductors 72 and 74 extend through respective openings 
71 in the plates 32 and 34 to engage opposite sides 51, 51' of the center 
block conductor 40 at directly opposite locations 75, 75' intermediate its 
ends 48 and 50. Connections are also made on opposite sides at locations 
76 (see FIG. 2) of the center block conductor 40 displaced from the 
connections 75, 75' of the center conductors 72 and 74 of the connectors 
68 and 70 as well as connections at the end 50 which will be explained in 
greater detail in connection with FIG. 4. The structure heretofore 
described in connection with FIGS. 2 and 3, thus provides a shielded strip 
line conductor having an insulated center block conductor 40 connected 
between signal input and output terminals, and an outer conductor provided 
by the enclosure 63 encompassing and electrically shielding the center 
block conductor 40. 
FIG. 4 is a diagrammatic representation partially in schematic form showing 
the shielded enclosure 63 provided by the structure shown in FIGS. 2 and 3 
and the center block conductor 40 positioned therein and electrically 
connected at 75, 75' to the center conductors 72 and 74 of the input and 
output signal connectors 68 and 70. The center conductors 72 and 74 are 
connected to the block conductor 40 at directly opposite locations along a 
line 82 partitioning the block conductor 40 into a first larger portion 84 
and a second smaller portion 86. Each of the portions 84 and 86 of the 
block conductor 40 extend transversely on each side of the line 82 and 
provide lumped inductive properties determined by their size, 
configuration, and other well known factors. In the operation of the 
present invention, the variable inductor 18 of FIG. 1 is provided by the 
portion 84 of the block 40 extending from the line 82 towards its end 48. 
The inductive properties are changed and controlled by changing the 
effective length "x" of the portion 84 as shown by the arrow in FIG. 4 
extending from the partitioning line 82. For changing inductance, the 
length "x" is varied by electrically shorting or returning to ground the 
portion 84 at selected opposite points 76 along its extension as will now 
be described in detail. 
At various opposite locations 76 such as at locations 88 and 88', 90 and 
91', and 92 and 92', pairs of switching means 94 and 94' are connected for 
selectively electrically shorting or returning to ground 20 selected 
points by connection to the shielded enclosure 63. Each switching means 
94, 94' includes a series connected combination of a bypass capacitor 96 
and a semiconductor switching diode 98 connected between each of the 
plurality of locations 76 and the shielding enclosure 63. Control signals 
delivered are over respective lines 100 to the junction of capacitors 96, 
96' and diodes 98, 98' of each switching means 94, 94' and controls the 
conductivity of the diodes 98, 98'. The control signals provide a bias 
signal to each of the diodes 98 which alternatively renders it either non 
conductive or conductive for effectively connecting its bypass capacitors 
96, 96' to the ground potential in effect grounding the selected contact 
points 76 of the extending portion 84 of the block conductor 40 for 
controlling its inductance value. Since the radio frequency input signal 
is of high frequency, it is readily bypassed to ground by capacitors 96, 
96' while the capacitors 96, 96' serve to block the dc biasing signals 
provided by the line 100. A radio frequency choke 102 is also provided in 
series with each control signal line 100 to attenuate radio frequency 
signals, while a blocking capacitor 104 which connects the signal lines 
100 to ground also serves to bypass radio frequency signals. 
A second plurality of switching means 106 are also provided for selectively 
connecting one or more of a plurality of tuning capacitors 108, such as 
capacitors C.sub.1, C.sub.2, . . . C.sub.n, between the end surface 109 of 
the extending portion 86 of the center block conductor 40 to ground 
potential provided by the shielding enclosure 63. For this purpose, each 
of the switching means 106 includes a tuning capacitor 108 in series with 
a semiconductor switching diode 110, bridging the end surface 109 and the 
enclosure 63. A plurality of signal control lines 112 are provided for 
delivering a biasing signal respectively to the junctions of each tuning 
capacitor 108 and diode 110 for rendering its diode 108 conductive or non 
conductive. The control signals for biasing the respective diodes 108 may 
be provided through a choke 102' and utilizing a blocking capacitor 104' 
as described in connection with the signal lines 100 for the same purpose. 
In this manner, by delivering selected biasing signals to the capacitors 
108 and diodes 110, various values of selected capacitances can be 
provided in series with the lumped inductance of the extending portion 86 
of the center block conductor 40 for providing the series inductance 22 
and variable capacitance 24 as represented in FIG. 1, under control of 
control signals from the tuning control means 26. 
In addition to the tuning capacitors 108, which are electronically 
controlled, an adjustable trimmer capacitor C.sub.x may be connected 
directly between the end surface 108 of the extending portion 86 of the 
center block conductor 40 and the shielding enclosure 63 for adjusting or 
calibrating purposes. The trimmer capacitor which is selected to have a 
low series resistance value for radio frequency signals by its connection 
in parallel with the switching means 106 assures a low resistance value 
for enhancing high performance characteristics for the circuit. 
FIG. 5 is a schematic diagram corresponding to FIG. 1 and showing in 
greater detail the switching resonator device 10 as described in 
connection with FIG. 4. For this purpose, the elongated portion 84 of the 
center block conductor 40 connected with the center conductors 72, 74 of 
connectors 68, 70 providing the variable inductor 18 is shown separately 
from the elongated portion 86 providing the fixed inductor 22 which is 
returned to ground through variable capacitor 24 (FIG. 1). One end of the 
elongated portion 84 connected by the conductors 72, 74 is shown connected 
to the input and output terminals 12, 14, and the pairs of opposite 
locations 76 along its length towards its end 48 are respectively 
connected by the plurality of switching means 94, 94'. The effective 
length "x" of the portion 84 is controlled by the switching means 94, 94'. 
Only one set of opposite switching means 94, 94' at a time is rendered 
conductive by signals from the tuning control means 26. Thus, if the 
control means 26 delivers a conductive biasing signal to line 100A, such 
signal is delivered to oppositely positioned switching means 94, 94' 
connecting at locations 88, 88', electrically shorting the portion 84 at 
these locations to provide its longest extension or length "x." This 
provides the greatest value of lumped inductance for the variable inductor 
18. When a conductive biasing signal is provided by the tuning control 
means 26 to the line 100B, switching means 94, 94' are rendered conductive 
for shorting the portion 84 at locations 90, 90' closer to its end 
contacted by the input and output conductors 72, 74, shortening its 
effective length "x." This provides a smaller value of a lumped inductance 
for the inductor 18. In the illustration provided, the delivery of a 
conductive biasing signal by the tuning control means 26 to the line 100C, 
renders conductive the pair of switching means 94, 94' engaging the 
portion 84 at locations 92, 92' closest to where the conductors 72, 74 
engage the portion 84, providing the shortest length "x," and the lowest 
value of lumped inductance for the conductor 18. Of course, although only 
three pairs of switching means 94, 94', are illustrated in FIG. 5, a large 
number of pairs of switching means 94, 94' may be provided at various 
locations along the portion 84 determined by design circumstances for 
selecting various predetermined inductance values for the variable 
inductor 18. The semiconductor switching diodes utilized may be PIN diodes 
and energized by PIN diode drivers for providing efficient and high speed 
switching operations, and although delivery of bias signals to the various 
electrical lines 100 by the tuning control means 26 is shown in FIG. 5 by 
mechanical switch means 101, this is for illustrative purposes only, it 
being understood that such signals are delivered at a high rate to 
selected control lines 100 by electronic signal generating means which are 
well known. 
The elongated body 86 providing the inductance of the fixed inductor 22 
having one end connected to the center conductors 72, 74 of the connectors 
68, 70 is also illustrated in FIG. 5 with its other end 50 connected to 
the plurality of switching means 106. The extending portion 86 of the 
block conductor 40 provides the lumped inductance of inductor 22 which is 
fixed, while the signals delivered by the tuning control means 26 over the 
control lines 112 select one or more of the tuning capacitors 108 for 
providing the variable capacitor 24 connected in series with the inductor 
22 to ground 20. Although only several switching means 106 are shown, any 
number may be utilized as required by design circumstances for providing 
the combination of capacitors 108 for tuning the switchable resonator 
means 10 in desirable increments over wide band as selected by the control 
signals. The tuning control means 26, thus provides one or more signals 
over the lines 112 for selecting the desired combination of tuning 
capacitors 108 for changing its frequency from one value to another over 
the radio frequency range. Although the tuning control means 26 in FIG. 5 
shows mechanical switches 101' for selecting the control lines 112 for 
appropriate biasing energization, it is understood this is also merely 
illustrative and that well known means are utilized for providing biasing 
signals at a high rate for achieving the desired operation. The diodes 
utilized by switching means 106 may also be of the PIN diode type and PIN 
diode drivers may be utilized for their energenization. 
In operation, the tuning control means 26 provides signals to the control 
lines 100 for energizing a pair of switch means 94, 94' to render their 
diodes conductive, while at the same time energizing and rendering 
conductive a combination of switch means 106 for achieving the desired 
tuning operation for the switchable tuning device 10. Such control signals 
are concurrently provided to the switching means 94, 94', and 106 and 
sequentially altered as required for "hopping" from one frequency to 
another at a high rate, as may be required to achieve the desired 
operation. The particular structure of the device 10 disclosed allows 
accurate tuning of the center frequency of the device 10 over a wide 
frequency range, such as 100 to 500 MHz with a transitional time of not 
greater than 5 micro seconds. Such results are achieved by the particular 
configuration of the components providing the lumped inductors and by the 
switching means utilized in association therewith. This configuration of 
the switching resonator device 10 also allows a pair of switching means 
94, 94' to be energized for varying the inductance of the inductor 18 for 
achieving coarse tuning of the device 10, while the capacitance of the 
variable capacitor 24 may be provided by a multiplicity of capacitors 108 
as required, to permit the desired degree of fine tuning of the device 10 
by providing a plurality of small increments. The structure also provides 
highly desirable band-pass filter characteristics for the device 10 which 
will now be described in greater detail in connection with the graphs of 
FIGS. 6, 7 and 9. 
FIG. 6 is a graph illustrating the insertion loss characteristics achieved 
by the tuning of the switchable resonator device 10 to several center 
frequencies. Thus, the curve 120 shows the device 10 tuned to a center 
frequency of 222 MHz with a small insertion loss of 0.8 db, and the second 
curve 122 shows a peak at the center frequency of 306 MHz with small 
insertion loss of 0.6 db. As shown, the insertion loss increases with 
frequency deviation from the center frequency, serving to selectively pass 
the signals over a narrow frequency pass-band about the center frequency, 
while attenuating other frequencies. The change in center frequency of the 
device 10 between the curves 120 and 122, was achieved by maintaining the 
variable inductor 18 at its maximum value, and varying the variable 
capacitor 24 between several of its values upon the delivery of 
appropriate control signals by the tuning control means 26. 
FIG. 7 is a graphic representation similar to FIG. 6 of the band-pass 
characteristics of the switchable resonator device 10 providing band-pass 
curves 124, 126, 127, and 128 for insertion loss, with peaks at respective 
center frequencies of 223 MHz, 264 MHz, 285 MHz, and 310 MHz. The curves 
124 and 126 provide a small insertion loss of 0.8 db, at their center 
frequencies, while the curves 127 and 128 at their center frequencies 
provide a small insertion loss of 0.6 db. These curves also illustrate the 
increase of insertion loss with deviation about their center frequencies, 
providing the desired pass-band characteristics for allowing passage 
through the device 10 of the desired radio frequency signals and 
effectively attenuating the non selected frequencies. The various center 
frequency characteristics illustrated in FIG. 7, were achieved by 
utilizing various combinations of control signals for enabling selected 
switching means 94, 94' and 106. 
FIG. 8 illustrated in block form the connection of several single 
switchable resonator devices 10 and 10' in a cascade arrangement in which 
an input radio frequency signal is delivered to the input terminal 12' of 
the resonator device 10. The output signal of device 10 is delivered over 
a 50 ohm line to the input of the second single switchable resonator 
device 10'. The second device 10' delivers its output signal to the output 
terminal 14'. When the switchable resonator devices 10 and 10' are 
switched in synchronism to the same band-pass center frequencies, enhanced 
characteristics are achieved. This is illustrated in the graphic 
representation of FIG. 9 for several center frequencies. 
FIG. 9 by its band-pass characteristic curves 130, 132 and 134 illustrates 
the enhanced characteristics of the cascaded devices 10 and 10' of the 
invention for center frequencies of 322 MHz, 363 MHz and 403 MHz. The 
curve 130 has an insertion loss of 1.2 db at its center frequency, while 
the curves 132 and 134 each provide the same insertion loss of 0.8 db at 
their respective center frequencies. It is noted that the curves of FIG. 9 
show a rapid increase in insertion loss as the frequency deviates from its 
center frequency. This characteristic provides a higher degree of 
selectivity and narrower pass-band characteristic which is achieved by the 
cascading arrangement. 
The switchable resonator device described is useful as a highly selective 
high power fast electronically tunable bandpass filter, also known as 
tracking filters and frequency hopping (agile) filter which may be 
required to suppress spurious radio emissions generated by high power 
frequency agile transmitters. Such filters are of special importance in 
the field of military communications where a plurality of collocated 
frequency "hopping" transmitters and receivers must operate simultaneously 
and in the same frequency band. The presence of such a filter between each 
radio and the antenna not only suppresses the unwanted out-of-band radio 
emissions but more importantly eliminates "adjacent channel interference" 
which is caused by adjacent radio transmitters operating simultaneously in 
the vicinity of the transmit/receive frequency. Using such a filter, 
therefore, provides a high degree of channel selectivity to both 
transmitters and receivers of tactical frequency hopping radio systems. 
The present invention which has narrow bandpass characteristic can be used 
with or without additional coupling to produce its filtering capability. 
The present switchable resonator device can also be used as a building 
block to form multi-resonator tunable bandpass filters by cascading or 
coupling a plurality of such resonators to achieve high degree of 
selectivity and increased out-of-band rejection. 
It will, thus, of course, be understood that although a particular 
embodiment of the invention has been described in the specification and 
drawing contained herein for purposes of illustration, various 
modifications and changes may be made in the structures described without 
departing from the spirit of the invention.