Filter having direct and cross-coupled resonators

Claim 2

A microwave band pass filter having a flat delay characteristic over the pass band and a maximally flat amplitude characteristic, the filter comprising a first series of resonant elements, means for coupling an input signal to a resonant element of the first series, the resonant elements in the first series being directly coupled in consecutive order, a second series of resonant elements arranged with each resonant element opposite and in substantial alignment with a different resonant element in the first series, means coupled to a resonant element in the second series for obtaining an output signal, the resonant elements in the second series being directly coupled in consecutive order, and means between the first and second series cross coupling opposed resonant elements in the two series and providing multiple paths of different lengths for wave energy in the band pass proceeding from the input to the output of the filter.

Claim 3

The microwave band pass filter according to claim 1, wherein the first series of consecutively directly coupled resonant elements is formed by an interdigital line, the second series of consecutively directly coupled resonant elements is formed by another interdigital line, and the means between the first and second series is a ground plane plate having apertures providing cross coupling between opposed digits.

Claim 4

The microwave band pass filter according to claim 1, wherein the mathematical relation between the direct coupling along the arrays and the cross coupling between opposed elements depends upon an odd polynomial 0n (t) and a Hurwitz polynomial Dn(t), thus where 3 n S12(t) is the scattering transfer function kappa 0 for n odd kappa 1 for n even t tanh p, where p is the normalized complex frequency variable.

Claim 5

The microwave band pass filter according to claim 1, wherein the first series of consecutively directly coupled resonant elements is formed by a sequence of resonant cavities, the second series of consecutively directly coupled resonant elements is formed by a another sequence of resonant cavities having common walls separating them from the opposed resonant cavities in the first series, and the cross-coupling means between opposed cavities in the first and second series are apertures in the common walls.

Claim 6

A band pass filter having a flat delay characteristic and a flat amplitude characteristic over the pass band, the filter comprising a first serial array of consecutively directly coupled resonant elements; means for coupling an input signal to a terminal resonant element of the first serial array; a second serial array of consecutively directly coupled resonant elements arranged with each of its resonant elements opposite and in substantial alignment with a different resonant element in the first array; means coupled to a terminal resonant element in the second serial array for obtaining an output signal; means between the first and second arrays cross coupling opposed resonant elements in the two arrays; the cross-coupling means and the resonant elements providing multiple paths of different lengths for wave energy proceeding from the input to the output of the filter; and the filter being further characterized in that the mathematical relation between the direct coupling along the arrays and the cross coupling between opposed elements depends upon an odd polynomial On (t) and a Hurwitz polynomial Dn(t), thus where 3 n S12(t) is the scattering transfer function kappa 0 for n odd kappa 1 for n even t tanh p, where p is the normalized complex frequency variable.

Claim 7

A band pass filter having a flat delay characteristic and a flat amplitude characteristic over the pass band, the filter comprising a first serial array of consecutively directly coupled resonant elements; means for coupling an input signal to a terminal resonant element of the first serial array; a second serial array of consecutively directly coupled resonant elements arranged with each of its resonant elements opposite and in substantial alignment with a different resonant element in the first array; means coupled to a terminal resonant element in the second serial array for obtaining an output signal; means between the first and second arrays cross coupling opposed resonant elements in the two arrays; the cross-coupling means and the resonant elements providing multiple paths of different lengths for wave energy proceeding from the input to the output of the filter; and the filter being further characterized in that the mathematical relation between the direct coupling along the arrays and the cross coupling between opposed elements depends upon an odd polynomial On (t) and a Hurwitz polynomial Dn(t), thus where 3 n S12(t) is the scattering transfer function kappa 0 for n odd kappa 1 for n even t tanh p, where p is the normalized complex frequency variable.