Band-elimination filter

Claim 2

A band-elimination filter network comprising in combination, input and output resonators each including a respective pair of electrodes, each pair sandwiching a respective portion of a piezoelectric crystal wafer therebetween, said resonators being linked by acoustic coupling through said wafer, said network being definable by an equivalent ladder network wherein said coupling is represented by an equivalent T circuit having three reactive branches equal to each other in the absolute magnitude of their respective reactances, and reactive means independent of said wafer connected between said resonators, the absolute magnitude of the reactance of said reactive means being equal within a preselected range to the absolute magnitude of the reactance of one of said branches.

Claim 3

Apparatus in accordance with claim 1 wherein said range equals + or - 20 percent.

Claim 4

Apparatus in accordance with claim 1 wherein said reactive means consists solely of a capacitive element connected between one of said electrodes of said input resonator on one side of said wafer and the electrode of said output resonator on the other side of said wafer.

Claim 5

AppaRatus in accordance with claim 3 wherein said range equals + or - 20 percent.

Claim 6

Apparatus in accordance with claim 1 wherein said reactive means consists solely of an inductive element connected between two of said electrodes on the same side of said wafer.

Claim 7

Apparatus in accordance with claim 5 wherein said range equals + or - 20 percent.

Claim 8

A band-elimination filter network comprising, in combination, input and output resonators each including a respective pair of electrodes each sandwiching a respective portion of a piezoelectric crystal wafer therebetween, said resonators being linked by acoustic coupling through said wafer, said network being definable by an equivalent ladder network wherein said coupling is represented by an equivalent T circuit having three reactive branches equal to each other in the absolute magnitude of their respective reactances, and reactive means independent of said wafer connected between said resonators, the characteristic frequency-attenuation plot of said filter exhibiting a single attenuation peak when the absolute magnitude of the reactance of said reactive means equals one of said respective reactances and exhibiting a double attenuation peak with the eliminated band therebetween when the absolute magnitude of the reactance of said reactive means falls within a given range of the absolute magnitude of one of said respective reactances.

Claim 9

A band-elimination filter network comprising, in combination, input and output resonators each including a respective pair of electrodes each sandwiching a respective portion of a piezoelectric crystal wafer therebetween, said resonators being linked by acoustic coupling through said wafer, said network being definable by an equivalent ladder network wherein said coupling is represented by an equivalent T circuit having three reactive branches equal to each other in the absolute magnitude of their respective reactances, and reactive means independent of said wafer connected between said resonators, the characteristic frequency-attenuation plot of said filter exhibiting a single attenuation peak when the absolute magnitude of the reactance of said reactive means equals one of said respective reactances and exhibiting a double attenuation peak with the eliminated band therebetween when the absolute magnitude of the reactance of said reactive means falls within a given range of the absolute magnitude of one of said respective reactances.

Claim 10

Apparatus in accordance with claim 7 wherein said reactive means comprises a capacitive element connected between said resonators from opposite sides of said wafer.

Claim 11

Apparatus in accordance with claim 7 wherein said reactive means comprises an inductive element connected between said resonators on the same side of said wafer.

Claim 12

A band-elimination filter comprising, an acoustically excitable wafer having opposing faces, a first resonator including said wafer and a pair of opposing electrodes mounted on opposing faces of said wafer, a second resonator including said wafer and a second pair of opposing electrodes mounted on opposing faces of said wafer, said first and second resonators being acoustically coupled through said wafer when said wafer is excited for passing energy to a load, reactive means coupling an electrode of one of said resonators to an electrode in the other of said resonators, said resonators and said reactive means exhibiting characteristics of a bandpass filter when said reactive means have an absolute value outside a given range and said resonators and said reactive means exhibiting a band-elimination characteristic when said reactance means has an absolute reactance value lying in said given range, said reactive means having an absolute reactance value in said range, said resonators having respective equivalent motional capacitances C1 and C2 and being coupled to each other by a coefficient of coupling K, said range being equal to Square Root C1C2/K + or - 20%.

Claim 13

A band-elimination filter comprising, an acoustically excitable wafer having opposing faces, a first resonator including said wafer and a pair of opposing electrodes mounted on opposing faces of said wafer, a second resonator including said wafer and a second pair of opposing electrodes mounted on opposing faces of said wafer, said first and second resonators being acoustically coupled through said wafer when said wafer is excited for passing energy to a load, reactive means coupling an electrode of one of said resonators to an electrode in the other of said resonators, said resonators and said reactive means exhibiting characteristics of a bandpass filter when said reactive means have an absolute value outside a given range and said resonators and said reactive means exhibiting a band-elimination characteristic when said reactance means has an absolute reactance value lying in said given range, said reactive means having an absolute reactance value in said range, said resonators having respective equivalent motional capacitances C1 and C2 and being coupled to each other by a coefficient of coupling K, said range being equal to Square Root C1C2/K + or - 20%.

Claim 14

A band-elimination filter comprising in combination, an acoustically excitable piezoelectric wafer having opposing faces, a first resonator including said wafer and a pair of opposing electrodes mounted on opposing faces of said wafer, a second resonator including said wafer and a second pair of opposing electrodes mounted on opposing faces of said wafer, said first and second resonators being acoustically coupled through said wafer with a coefficient of coupling K when said wafer is excited by passing energy to a load, and reactive means coupling an electrode of one of said resonators to an electrode in the other of said resonators, said resonators having respective equivalent motional capacitances C1 and C2, said reactive means having a reactance magnitude in the range of Square Root C1C2/K + or - 20%.

Claim 15

A band-elimination filter comprising in combination, an acoustically excitable piezoelectric wafer having opposing faces, a first resonator including said wafer and a pair of opposing electrodes mounted on opposing faces of said wafer, a second resonator including said wafer and a second pair of opposing electrodes mounted on opposing faces of said wafer, said first and second resonators being acoustically coupled through said wafer with a coefficient of coupling K when said wafer is excited by passing energy to a load, and reactive means coupling an electrode of one of said resonators to an electrode in the other of said resonators, said resonators having respective equivalent motional capacitances C1 and C2, said reactive means having a reactance magnitude in the range of Square Root C1C2/K + or - 20%.

Claim 16

Apparatus in accordance with claim 11 wherein said reactive means consists Of only a single capacitive element connected between an electrode of said first resonator and an electrode of said second resonator on opposite sides of said wafer.

Claim 17

Apparatus in accordance with claim 11 wherein said reactive means consists of only a single inductive element connected between an electrode of each of said resonators on the same side of said wafer.

Claim 18

A band-elimination filter network comprising in combination, input and output resonators each including a respective pair of electrodes each sandwiching a respective portion of a piezoelectric crystal wafer therebetween, said resonators being linked by acoustic coupling through said wafer, means for connecting a signal source across said input resonator, means including an impedance inverter network having a primary and a secondary circuit for connecting a load to said output resonator, said primary being connected across said output resonator and said secondary, oppositely poled, being connected across said load, and a capacitive element connected by way of said impedance inverter network between one of said electrodes of said input resonator and one of said electrodes of said output resonator on the same side of said wafer.

Claim 19

A band-elimination filter network comprising in combination, input and output resonators each including a respective pair of electrodes each sandwiching a respective portion of a piezoelectric crystal wafer therebetween, said resonators being linked by acoustic coupling through said wafer, means for connecting a signal source across said input resonator, means including an impedance inverter network having a primary and a secondary circuit for connecting a load to said output resonator, said primary being connected across said output resonator and said secondary, oppositely poled, being connected across said load, and a capacitive element connected by way of said impedance inverter network between one of said electrodes of said input resonator and one of said electrodes of said output resonator on the same side of said wafer.

Claim 20

Apparatus in accordance with claim 14 wherein the equivalent motional capacitances of said resonators are C1 and C2, respectively, the coefficient of said coupling being K and the magnitude of reactance of said capacitive element being within the range of Square Root C1C2/K + or - 20%.