Adjustable saw device

An adjustable surface acoustic wave (SAW) transducer is fabricated on a piezoelectric substrate. The adjustable SAW transducer includes a plurality of SAW interdigital transducer (IDT) fingers disposed on the substrate. Miniature switches are used to provide a plurality of interconnection patterns between the SAW IDT fingers such that a plurality of SAW characteristics can be generated from a single set of SAW IDT fingers.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a Surface-acoustic wave (SAW) device for
 modifying and passing a signal and, more particularly, to a SAW device
 which includes switches for providing connections to selected SAW
 Interdigital Transducer (IDT) fingers of the SAW device producing a
 plurality of SAW characteristics from a common set of SAW IDT fingers.
 2. Description of the Prior Art
 Referring to FIG. 1, a typical SAW device 10 includes an input transducer
 12 and an output transducer 14. Each input 12 and output 14 transducer has
 a plurality of SAW IDT fingers 16 formed on a substrate 18.
 Interconnections between selected SAW IDT fingers 16 are provided by
 connecting each SAW IDT finger 16 to either a first 20, second 22, third
 24 or fourth 26 sum line. A radio-frequency (RF) signal voltage 28 is
 applied between the first 20 second 22 sum lines which provide the
 voltages 28 to the SAW IDT fingers 16 of the input transducer 12 creating
 strains in the piezoelectric substrate 18. If the strains occur with the
 proper periodic pattern across the length of the SAW device 10, an
 acoustic surface wave will be generated. The spacing between SAW IDT
 fingers 16, the interconnection pattern of the SAW IDT fingers 16, and the
 frequency content of the applied voltage difference determines the
 magnitude and phase of the surface acoustic wave. The acoustic wave which
 is launched by this input transducer 12 travels to the output transducer
 14, where it is converted to an output electrical signal. If the SAW IDT
 fingers 16 have the proper spacing and are connected to the sum lines
 20-26 with the proper interconnection pattern, a SAW device 10 having a
 desired signal modification in the time and frequency domains will be
 generated.
 SAW devices 10 formed on a piezoelectric substrate 18 are typically metal
 film formed from photolithography and thin film processes with either
 etching or lift-off techniques. These techniques are typically required
 since the width of each SAW IDT finger 16 and the spacing between adjacent
 SAW fingers 16 are on the micron or submicron level. For typical prior art
 SAW devices 10, the SAW IDT fingers 16 and the sum lines 20-26 are formed
 on the substrate 18 resulting in the SAW fingers 16, the sum lines 20-26
 and the interconnection pattern between SAW IDT fingers 16 being fixed on
 the substrate 18. Since the SAW IDT fingers 16 and sum lines 20-26 are
 fixed on the substrate 18, the typical prior art SAW device 10 provides
 only a single interconnect pattern between SAW fingers 16 and can generate
 a surface acoustic wave only with fixed signal modifications in the time
 and frequency domains. If a different surface acoustic wave is desired, a
 new SAW device having a new interconnect pattern must be fabricated.
 One method used to provide for more than one signal modification is to
 fabricate a plurality of SAW transducers on a single substrate. Then, the
 input or output signal can be switched among several transducers each of
 which provides different properties. The drawback of this method is that
 it gives only a small amount of flexibility and requires more space on the
 substrate. Therefore, what is needed is a SAW device which can provide a
 plurality of signal modification properties from a common set of SAW IDT
 fingers such that the resulting SAW device properties can be changed
 without the need to fabricate a new SAW device.
 SUMMARY OF THE INVENTION
 The aforementioned need in the prior art is satisfied by this invention,
 which provides an adjustable SAW device.
 An adjustable SAW device, in accordance with the invention, comprises a
 plurality of SAW IDT fingers formed on a substrate where the SAW IDT
 fingers together define one set of SAW IDT fingers. Means to provide a
 plurality of interconnection patterns between selected SAW IDT fingers is
 provided whereby the plurality of interconnection patterns can be provided
 from the one set of SAW IDT fingers.
 For a first embodiment of the invention, a plurality of miniature switches
 are positioned on the substrate and are coupled together by a plurality of
 sum lines. The switches are controlled by a plurality of control lines.
 For a second embodiment of the invention, the adjustable SAW device is an
 adjustable filter utilized for a variety of applications.

DETAILED DESCRIPTION OF THE INVENTION
 Referring now to FIG. 2, the present invention overcomes the limitation of
 the prior art by providing a plurality of SAW IDT fingers 29 disposed on a
 substrate 30. The SAW IDT fingers 29 together comprise a single set of SAW
 fingers. Means are provided to produce a plurality of interconnection
 patterns between preselected SAW IDT fingers 29 whereby a plurality of
 interconnection patterns can be provided from the single set of SAW IDT
 fingers.
 The present invention provides an adjustable SAW device 31 which includes
 an input 32 and output 34 SAW transducer. The input 32 and output 34 SAW
 transducers each include a plurality of SAW IDT fingers 29, miniature
 switches 36, control lines 38 and sum lines 40-46. The miniature switches
 36 are attached to the sum lines 40-46 and provide the means to
 interconnect selected SAW IDT fingers 29. The miniature switches 36 also
 provide the means to vary the interconnect pattern between selected SAW
 IDT fingers 29. The switches 36 can be opened or closed as desired to
 provide a plurality of interconnect patterns between selected SAW IDT
 fingers 29 thereby creating a plurality of time and frequency domain
 signal modifications in a single SAW device 31 thereby creating a
 multiplicity of SAW device characteristics from a single SAW device 31.
 Referring to FIGS. 3 and 4, a side view of a single miniature switch 36 in
 accordance with the preferred embodiment of the invention is shown in FIG.
 3 for the open circuit state and FIG. 4 for the closed circuit state. As
 shown in FIGS. 3 and 4, a single switch 36 includes a control line 38
 formed on the piezoelectric substrate 48. The control line end 50 is
 located at a preselected distance 52 from the end 54 of the SAW IDT finger
 29. The control line 38 is adapted to receive a control voltage 56.
 A dielectric layer 58, formed of insulating material such as silicon
 dioxide, silicon nitride, aluminum oxide, polyamide or the like, is
 attached to the control line 38. A plate 60 is formed of electrically
 conductive material and is attached to the dielectric layer 58. The
 dielectric layer 58 provides an electrical separation between the control
 line 38 and the plate 60. For an input transducer 32 (FIG. 2), the plate
 60 (FIG. 3) is adapted to receive an RF signal 62 from an RF signal line.
 For an output transducer 34 (FIG. 2), the plate 60 (FIG. 3) provides the
 signal 64 to an RF signal line.
 DC return-to-ground means 66 is attached to the plate 60 and provides a DC
 rectum-to-ground while maintaining a high impedance to block out the RF
 signal. The DC return-to-ground means 66 is preferably a resistor 66
 having a high ohmic value. Preferably, the ohmic value of the resistor 66
 is at least an order of magnitude higher than the impedance of the RF
 signal line. Alternatively, the DC return-to-ground means 66 can be an RF
 choke in the form of an inductor. However, a resistor is preferred because
 it will typically be much smaller and lower cost than an inductor.
 A flexible cantilever arm 68 is formed integrally with the plate 60, but it
 could also be a separate component physically connected to the plate 60.
 For the preferred embodiment of the invention, the cantilever arm 68 is
 formed of an electrically conductive material such as aluminum. For an
 alternative embodiment, the arm 68 is formed of a non conductive material,
 such as silicon coated with a conductive material such as aluminum.
 A good electrical connection between the cantilever arm 68 and the SAW IDT
 finger 29 is desirable. As such, the cantilever arm 68 can include a
 metalized switch contact 70. This switch contact 70 consists of a pad of
 electrically conductive material attached to the cantilever arm 68 facing
 the SAW finger 35. The pad 70 is made of a highly conductive metal such as
 gold, platinum or gold palladium, for example, that does not oxidize
 easily and can also be plated with a gold film to provide a highly
 conductive, non-corrosive contact.
 As shown in FIG. 3, in the open position, the cantilever arm 68 extends
 over a portion of the control line 38, over the first gap 52 and over a
 portion of the SAW IDT finger 29 and forms a second gap 71 with the SAW
 IDT finger 29. As shown in FIG. 4, application of a DC voltage 56 to the
 control line 38 creates an electrostatic force 72. The electrostatic force
 72 causes the portion of the cantilever arm 68 that is above the control
 line 38 to flex towards the SAW finger 29. The electrostatic force 72
 causes the cantilever arm 68 to touch the SAW IDT finger 35 closing the
 second gap 71 (FIG. 3) and creating an electrical closed circuit between
 the SAW IDT finger 29 and the cantilever arm 68.
 As shown in FIG. 3, removing the DC voltage 56 from the control line 38
 removes the electrostatic force 72 (FIG. 4) which causes the cantilever
 arm 68 to restore its original shape and cease electrical contact with the
 SAW IDT finger 29 providing an electrical open circuit between the SAW IDT
 finger 29 and the cantilever arm 68.
 In the preferred embodiment, shown in FIG. 2, a plurality of switches 36
 are utilized for a single SAW device 31. For this embodiment, each SAW IDT
 finger 29 has two switches 36, one located at each end of each SAW IDT
 finger 29. A separate control line 38 formed on the piezoelectric
 substrate 48 is provided for each switch 36. Each control line 38 is
 adapted to receive a separate DC voltage. Four dielectric layers 58 are
 provided which are each formed of insulating material. Each dielectric
 layer 58 is attached to a plurality of control lines 38. Four sum bars
 40-46 are formed of electrically conductive material with each sum bar
 40-46 being attached to a separate dielectric layer 58. The first 40 and
 second 42 sum bars are adapted to receive an RF signal. DC
 return-to-ground means 66 are attached to each sum bar 40-46. Cantilever
 arms 68 are electrically connected to each sum bar 40-46. Applying a DC
 voltage to selected control lines 38 closes only select switches 36
 providing a first interconnect pattern between the SAW fingers 29 of the
 SAW device 31. Selectively varying the application of DC voltages to
 selected control lines 38 varies the interconnect pattern between the SAW
 IDT fingers 29 of the SAW device 31 providing a unique signal modification
 in the time and frequency domains with each combination of closed and open
 switches 36.
 If desired, the interconnection pattern of the adjustable SAW device 31 can
 be configured remotely by placing the adjustable SAW device 31 in a remote
 controlled system such that when a control signal is transmitted to and
 received by the remote control system, the remote control system provides
 a DC signal to the proper control lines 38 closing the desired switches
 36. This is particularly useful in satellite applications where the
 control signals are generated on the ground and transmitted to the
 satellite.
 The present invention has the capability to interconnect all or only some
 of the SAW IDT fingers 29 which in essence provides the capability to skip
 some of the SAW IDT fingers 29. An interconnect pattern which skips some
 of the SAW IDT fingers 29 is representative of a conventional SAW
 interconnect pattern which is useful for a lower frequency than that
 created by providing interconnections between all SAW IDT fingers 29.
 Referring to FIG. 5, a first embodiment of the invention combines switches
 36 and direct attachments 74 of the SAW IDT fingers 29 with the sum lines
 40-46 in a single SAW device 75. This embodiment provides a partly
 adjustable SAW device 75 which uses fewer switches 36 and control lines 38
 than the embodiment previously described but still provides for a great
 degree of flexibility.
 Referring to FIG. 6, a portion 76 of a SAW device is shown for a second
 embodiment of the invention in which the control lines 77 are dispersed on
 a substrate 78 such that the spacing between adjacent control lines 77 is
 progressively increased. This embodiment can simplify the fabrication of
 the adjustable SAW device since the control lines 77 and spacing between
 control lines 77 can be widened as the control lines 77 disperse in the
 substrate 78 simplifying adaptation of the control lines 77 for receiving
 a DC voltage.
 Referring to FIG. 7, a portion 79 of a SAW device is shown for a third
 embodiment of the invention in which a plurality of metal traces 80 are
 electrically coupled to the SAW IDT fingers 81. The metal traces 80 are
 coupled to the SAW IDT fingers 81 at a first end 82 and disperse in the
 substrate 83. The spacing between adjacent metal traces 80 increases with
 dispersion of the metal trace 80 in the substrate 83 so that the width of
 each metal trace 80 can be increased from the first end 82 to the second
 end 84 of each metal trace 80. For this embodiment, a switch 84 is located
 at each end 84 of each metal trace 81. Coupling metal traces 80 to the SAW
 IDT fingers 81 and dispersing the metal traces 80 in the substrate 82
 simplifies fabrication of the adjustable SAW device 79 by allowing a
 larger separation between successive switches 84 allowing the switches 84
 to be physically larger. The metal traces 80 have a minimal effect on the
 generation of the surface acoustic wave since the metal traces 80 disperse
 and are therefore not parallel and do not have the proper spacing to
 effectively create the surface acoustic wave.
 Referring to FIG. 8, for a fourth embodiment of the invention, the
 adjustable SAW device 86 is configured as an adjustable filter 87 to
 provide a plurality of different preselected filter characteristics. By
 altering the open and closed states of the switches 36 (FIGS. 2-4), the
 adjustable SAW device 86 (FIG. 8) can be configured as a bandpass filter,
 a notched filter, an adaptive filter, an equalizer or any other filter
 known to one skilled in the art.
 For example, referring to FIG. 9, for a fifth embodiment of the invention,
 the adjustable SAW device 88 is configured as an adjustable filter 89
 which is programmed in phase as well as amplitude so that any selected
 passband shape, examples of which are shown in FIGS. 10a-10c, can be
 provided by the adjustable filter 89.
 Referring to FIGS. 11 & 12, for a sixth embodiment of the invention, the
 adjustable SAW device 90 is configured as an adjustable notched filter 91
 which is configured to pass all frequencies in a selected frequency band
 except for selected frequencies 92, known in the art as a notch 92 within
 the band. One or more notches 92 can be provided from a single adjustable
 notched filter 91 at the same time by interconnecting the SAW fingers 36
 (FIG. 2) of the adjustable SAW device 90 to provide a preselected
 interconnection pattern which provides the desired notches 92. These
 notches 92 can be altered as needed through electrical command of the
 switches 36 (FIG. 2) on the SAW IDT fingers 29.
 Referring to FIG. 13, for a seventh embodiment of the invention, the
 adjustable SAW device 96 can be configured as an adaptive filter 97 which
 dynamically responds to, and tracks, an input signal 98. The adaptive
 filter 97 is configured to provide a preselected filter response 99. An
 input spectrum 100 containing the input signal 98 is passed through the
 adjustable SAW device 96 generating an output 101 which is provided to the
 signal analysis means 102. A feedback condition is achieved by coupling
 the output 101 to the filter control electronics 103.
 The filter 97 is initially configured to provide for wideband operations
 corresponding to a low signal-to-noise ratio (SNR). The output 101 is
 analyzed by the signal analysis means 102 for the presence of the input
 signal 98. Following signal identification and characterization, the
 center frequency 104 of the filter response 99 is adjusted to match the
 center frequency 105 of the input signal 98. The bandwidth of the
 adjustable filter 97 is reduced to maximize the received SNR. Or, the
 bandwidth of the adjustable filter 97 is shaped to provide a matched
 filter response which is approximately matched to the electrical
 characteristics of the input signal 98. By providing feedback, the filter
 97 can dynamically track and process the input signal 98 in a high SNR or
 matched detection mode.
 Alternatively, the adjustable SAW device 96 can be configured to provide a
 narrow bandwidth, corresponding to a high SNR, or a matched filter mode.
 The adjustable filter 97 can be configured to provide a filter response 99
 having a selected center frequency 104 to scan the input spectrum 100 for
 the desired signal 98. To do so, the adjustable SAW device 96 is
 configured as a filter element which is configured to provide selected
 filter response characteristics such as center frequency, bandwidth and
 impulse response. The adaptive filter 97 is configured to be optimized as
 a narrow bandpass filter around an incoming signal 98 in order to reject
 out-of-band noise 106 thereby maximizing the detection SNR.
 Referring to FIGS. 14-16, for an eighth embodiment of the invention, the
 adjustable SAW device 108 can be configured as an electrically operated
 equalizer 109. Complex microwave units 110 contain multiple electrical
 components, each of which can vary slightly from desired nominal
 electrical characteristics. When the electrical characteristics of each
 electrical component are combined together, the resultant signal 112 often
 exhibits an undesirable effect such as rolloff over a passband as shown in
 FIG. 15.
 In prior art systems, the undesirable effects are sometimes compensated for
 by passing the resultant signal 112 through equalizers (not shown), which
 are configured to compensate for the undesirable effects and correct the
 shape of the passband. These prior art equalizers are usually custom
 designed and/or manually adjusted to provide the proper compensation for
 the signal 112. By replacing the prior art equalizers with a single
 adjustable SAW device 108 and configuring the adjustable SAW device 108 as
 an electrically operated equalizer 109, selected attenuation can be
 provided over the band to compensate for the undesirable effects. The
 advantage over a prior art equalizer is that the adjustable SAW equalizer
 109 requires no physical adjustment and can be manufactured and installed
 together with the other components in the unit 110. The unit 110 and
 adjustable SAW device 108 can then be adjusted to provide preselected
 outputs and a preselected corrected frequency response 114 as shown in
 FIG. 16 during testing of the unit 110. This enables low-cost
 manufacturing along with relatively loose specifications for individual
 components within the unit 110, while retaining precise unit performance.
 Referring to FIGS. 17 and 18, for a ninth embodiment of the invention, the
 adjustable SAW device 116 is configured as an adjustable filter 117 to
 replace a plurality of filters 118 which are known to one skilled in the
 art as a bank of filters 118. Prior art communication systems 119 employ
 banks of either SAW bandpass filters 118 or SAW delay lines (not shown).
 The prior art system 119 switches to only one filter 118 or delay line at
 a time depending on the needs of the user. In the case of the bandpass
 filters 118, each filter 118 has a different bandwidth. In the case of the
 delay lines, the different delay lines have different time delays and
 durations of the impulse response.
 For the present invention a single adjustable SAW device 116 is configured
 as an adjustable filter 117 such that a single adjustable filter 117
 replaces the entire bank of filters 118. The SAW IDT fingers 36 (FIG. 2)
 of the adjustable SAW device 116 (FIG. 17) can be interconnected in a
 preselected manner to provide a desired filter characteristic at any time
 thereby providing size, cost and weight advantages over the prior art bank
 of filters 118 since multiple filters 118, of which only one is being used
 at a time, are replaced by a single adjustable filter 117.
 In addition, while the bank of filters 118 must switch between a finite
 number of filters 118 each having a fixed design and fixed electrical
 characteristic, the adjustable filter 117 can not only be configured to
 provide the same electrical characteristics as that provided by the bank
 of filters 118, but can also be configured to provide additional
 preselected electrical characteristics which are not available from the
 bank of filters 118. For example, if the prior art filter bank 118 covers
 bandwidths of 1, 2 and 4 MHz, the adjustable filter 117 could be
 configured to provide the same bandwidths of 1,2 and 4 MHz plus additional
 selected bandwidths such as 0.85 MHz, 1.57 MHz, etc., thereby providing a
 filter 117 with increased versatility.
 The adjustable filter 117 can be disposed in a satellite (not shown) and
 configured to be remotely programmed such that the adjustable filter 117
 could be reconfigured upon receipt of a signal from the earth to provide a
 new filter characteristic remotely. This would provide for a plurality of
 new bandwidths to be transmitted to the satellite at any time during the
 life of the satellite.
 Referring to FIG. 19, for a tenth embodiment of the invention, a plurality
 of adjustable SAW devices 120,121 are configured to provide an adjustable
 variable rate signal processing matched filter element 122. Digital
 communications systems, most notably emerging wireless systems, employ
 spectrally efficient modulation techniques such as QPSK, OQPSK, M-PSK AND
 GPSK. These modulation rates all manipulate the carrier phase to convey
 information. To maintain the narrow bandwidths dictated by current
 communications, regulations necessitate a smooth carrier phase transition.
 This transition is usually accomplished by shaping the data pulses with
 either a raised cosine or gaussian filter. The receiving system contains a
 filter which is matched to the transmitter's filter to achieve optimum
 detection. As the matched filter's impulse response is a function of the
 data rate, different data rates dictate using different filters. A more
 detailed description of matched filters can be found on page 298 of the
 book Surface Acoustic Wave Devices and Their Signal Processing
 Applications, written by Colin Campbell and published by Academic Press,
 Inc., in 1989.
 By configuring adjustable SAW devices 120,121 to provide an adjustable
 matched filter 122, a single adjustable matched filter 122 can be used to
 provide matched filter characteristics for a wide range of data rates by
 selectively configuring the response of each adjustable SAW device 120,121
 for the desired data rate. With the addition of appropriate control
 electronics 124, a data link 126 could be constructed with a continuously
 variable data rate that optimizes system BER.
 Referring to FIGS. 20 and 21, for an eleventh embodiment of the invention,
 a pair of adjustable SAW devices, 128,130 are disposed in a RADAR system
 132 and are configured to provide a jam resistant RADAR matched filter.
 Each adjustable SAW device 128,130 is configured to create a signal 134
 having a plurality of RADAR pulses 136,138 with each RADAR pulse 136,138
 having a different amplitude and bandwidth characteristic. Varying the
 interconnect pattern of the adjustable SAW devices 128,130 varies the
 amplitude and bandwidth of each RADAR pulse 136,138 such that a hostile
 emitter(not shown) cannot gain complete knowledge of the characteristics
 of the transmitted signal 140 from the received pulse history and
 therefore cannot easily generate false returns to deceive the RADAR system
 132.
 Referring to FIG. 22, for a twelfth embodiment of the invention, the
 adjustable SAW device 142 is designed and configured so that both the
 input 144 and output 146 transducers are chirped transducers 144,146. A
 more detailed discussion of chirped transducers can be found in Chapter 9,
 titled The SAW Linear FM Chirp Filter of the Surface Wave Acoustic Wave
 Devices reference mentioned above. The transducers 144,146 are configured
 to have closely spaced narrow fingers 148 at the left ends 150,152 of both
 transducers 144,146 respectively, and then increasing finger width and
 spacing between fingers 148 toward a maximum at the right ends 154,156 of
 both transducers 144,146 respectively.
 In chirped transducers, only a small group of properly spaced fingers 148
 are effective at any particular frequency. The highest frequency waves
 will propagate from the left end 150 of the input transducer 144 to the
 left end 152 of the output transducer 146, and the lowest frequency waves
 will propagate from the right end 154 of the input transducer 144 to the
 right end 156 of the output transducer 146. Similarly, waves of
 intermediate frequency propagate between intermediate points in the
 transducers 144,146. If the transducers 144,146 are identical, the delay
 is constant for all frequencies even though different regions of the
 transducers 144,146 are effective at different frequencies.
 The switches 158 are used to connect only the fingers 148 associated with
 the frequencies which are desired to pass through the transducer 144,146.
 For example, if each finger 148 in each transducer 144,146 is connected to
 alternating sum bars, the chirped transducer 142 will have a wide filter
 passband characteristic. On the other hand, if a small group of fingers
 148 are connected to alternating sum bars at the left end 150 of the input
 transducer 144; and, if a small group of fingers 148 are connected to
 alternating sum bars at the left end 152 of the output transducer 146, the
 chirped transducer 142 will have a narrowband high frequency filter
 characteristic. The chirped transducer 142 can be adjusted by means of the
 switches 158 and control lines 160 to take on characteristics which
 provide passbands having preselected center frequencies and bandwidths,
 stopbands having a preselected width and frequency, as well as preselected
 multiple passbands.
 Referring to FIGS. 23 & 24, for a thirteenth embodiment of the invention,
 the adjustable SAW device 162 is configured to provide an adjustable
 programmable tapped delay line 162. The typical prior art SAW tapped delay
 line 164 is a SAW device which adds together signals over a sequence of
 equally spaced 166 delays 168. The individual sub-transducers 170 at each
 delay 168 are known in the art as taps 170. If the taps 170 are
 interconnected to the sum lines 172,174 with the proper interconnect
 pattern, the tapped delay line 164 can be used as a correlator for a
 phase-coded signal. If the tapped delay line 164 is implemented in a
 traditional prior art SAW device where all the fingers and interconnection
 are formed on the substrate as shown in FIG. 24, the electrical
 characteristics of the tapped delay line 164 are permanently fixed. To
 solve this problem, field effect transistors (FETs, not shown) can be used
 to switch the phase of the taps 170 and control the amplitude of the taps
 170 allowing the phase of the taps 170 to be switched and the amplitude of
 the taps 170 to be changed as desired. However, the field effect
 transistor must be made of a semiconductor material (not shown) and
 mounted with or near the taps 170 to facilitate connection to each tap
 170. By configuring an adjustable SAW device 162 as a programmable
 adjustable tapped delay line 162, switching of the phase of the taps 176
 can be provided without the need for FETs. The switches 178 can be
 fabricated directly on the SAW substrate 180 simplifying assembly and RF
 connection problems.
 Referring back to FIG. 2, the adjustable SAW device 31 utilizes switches 36
 to provide an interconnect pattern between selected SAW fingers 29 and
 vary that interconnect pattern as desired allowing a plurality of time and
 frequency domain characteristics out of a single SAW device 31 thereby
 overcoming the fixed characteristics limitations of a typical SAW device
 10 (FIG. 1). One or more adjustable SAW devices 31 (FIG. 2) can be
 disposed in a variety of systems, such as communication systems, and can
 be configured as adjustable or adaptive filters to replace a bank of
 filters thereby saving weight, cost and space.
 It will be appreciated by persons skilled in the art that the present
 invention is not limited to what has been shown and described hereinabove.
 The scope of the invention is limited solely by the claims which follow.