Northern Telecom Limited

Nortel Networks Corporation

Ji-Dong Dai

Yufeng Xu

John Choo Saw

Zhuo-Hui Chen

Mark S Suthers

Thomas P Cameron

Conrad F Gratton

David R Seniuk

A surface wave device is made by forming conductors on a surface of a piezoelectric material in a conductor pattern defined by exposing photoresist via a reticle. The conductor pattern is provided on the reticle in two parts each defining a set of substantially alternate fingers of the pattern, and the photoresist is exposed by two overlaid exposures each via a respective one of the two parts of the conductor pattern. Exposed photoresist can optionally be developed between the two exposures, and conductors can optionally be formed on the surface between the two exposures. The method reduces diffraction limits, permitting manufacture of surface wave devices with sub-micron linewidths for filtering at increased frequencies.

Method of making surface wave devices

A surface wave device comprises first and second SPUDT (single phase unidirectional transducer) resonator filters each comprising first and second transducers, which are preferably RSPUDTs (resonant SPUDTs), the resonator filters being the same except that one transducer of the second resonator filter is a mirror image of the corresponding transducer of the first resonator filter to provide a phase difference of 180.degree.. The surface wave device serves as a balun by having an unbalanced signal connection to the first transducers, and a balanced signal connection comprising signal connections to the second transducer of each of the first and second resonator filters. The resonator filters can be arranged side by side on a common piezoelectric substrate.

Surface wave device balun resonator filters

A longitudinally coupled double mode surface wave resonator comprises two reflectors, two lateral IDTs (inter-digital transducers), and a centre IDT arranged on a surface of a piezoelectric substrate, for coupling surface waves longitudinally between the IDTs. The two lateral IDTs operate with opposite signal phases by virtue of opposite connections, opposite polarities, or oppositely phased spacings from the centre IDT. Alternatively, or in addition, the centre IDT is divided into two oppositely phased halves. A filter comprising one or more resonators can replace both a filter and a balun in a radio frequency circuit.

Longitudinally coupled double mode surface wave resonators

A surface wave device filter comprises two 2-pole waveguide coupled double mode resonators (WCRs) electrically connected together in cascade. To permit narrowing of the filter passband for improved out-of-band rejection, e.g. for use of the filter as an intermediate frequency channel filter in a wireless communications system, while maintaining good matching for low ripple in the passband, a shunt capacitance is connected in parallel with the static capacitances of the two WCRs. The shunt capacitance is constituted by interdigital fingers provided on the same piezoelectric substrate as one or both of the WCRs, perpendicularly to the WCR fingers to avoid surface wave interference, conveniently in space otherwise used by rails of the WCRs, optionally with oppositely phased fingers to cancel surface waves generated by these fingers. A capacitance can be similarly provided on the same substrate as any other type of surface wave device.

Surface wave device with capacitance

A cascaded surface wave device filter comprises two 2-pole surface wave device filters connected in cascade. The 2-pole filters each provide a balun function between balanced and unbalanced signal connections, and have either their unbalanced or their balanced signal connections interconnected in the cascade to reduce electromagnetic feedthrough and improve spurious mode suppression. The 2-pole filters are conveniently longitudinally coupled double mode surface wave resonators which are described, or transversely coupled double mode surface wave resonators. Higher order filters can be provided by connecting further 2-pole filters in the cascade. The cascaded filter is particularly useful for filtering at radio and intermediate frequencies in cellular radio equipment.

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Kanata, Canada

Ji-Dong Dai