Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2000-09-08
2002-12-31
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S187000, C333S202000, C375S316000
Reexamination Certificate
active
06501346
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to ceramic filters and in particular to a specific design of a ceramic filter for use with a radio-beacon receiver. Radio-Beacon receivers are commonly used in certain Differential Global Positioning Systems (DGPS) for accurate navigational and position-locating needs. The international DGPS radio-beacon networks operate in the rf-band of 283-kHz to 325-kHz. To produce a quality radio-beacon receiver, the front-end filter is required to exhibit high-Q properties to provide high selectivity. Conventional beacon receivers based on prior art design techniques have relied upon multiple-pole discrete component ladder-type front-end filter networks, but these had difficulty in maintaining high attenuation in the stop-band whilst also achieving a narrow pass-band with low ripple and low insertion-loss. Such conventional filter networks also imposed the use of very tight tolerance discrete components and quite often invoked the need for custom manufactured components, particularly for the inductor elements. With these impositions and the constraints of critical layout design to achieve desired characteristics, the conventional solutions proved both costly and somewhat unpredictable.
FIG. 1
is a block diagram of a prior art system for implementing a radio-beacon DGPS receiver. This design entails a combination of analogue processing and digital processing stages. A front-end band pass filter
10
is used to select signals having a frequency in the range of 283 kHz to 325 kHz. The filtered signal is then provided to a multiplier
11
, an Intermediate Frequency (IF) filter
12
and an amplifier
14
to perform dual down-conversion. Exemplary dual down-conversion converts the input signal from 283-kHz to 325-kHz down to 43-kHz to 85-kHz. The down-converted signal is then applied as input to an A-D converter
16
and a digital signal processor
18
. Feedback to the amplifier
14
is provided from the digital signal processor
18
through D-A converter
20
.
BRIEF SUMMARY OF THE INVENTION
An exemplary embodiment of the invention is a novel ceramic filter for use as a front-end filter in an innovative radio-beacon DGPS receiver. The filter includes a plurality of piezo-electric resonant stacks in a multi-stage topology to emulate a discrete component ladder network, representing a band-pass filter derived from a combination of a modified Butterworth filter and Elliptical filter, having a pass-band center frequency at about 304 kHz±1.5 kHz. The ceramic filter uses square and circular shaped ceramic piezo-electric resonant elements to provide enhanced performance and reduced size. The square and circular piezo-electric resonant elements, sandwiched between spring-plates, are arranged in horizontal layers. The filter stages are serially linked, at the necessary stage boundaries, with the spring-plates at the respective layers joined by tabs.
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J.D. Last & D.C. Poppe; “Effect of Skywave Interference on Coverage of Radiobeacon DGPS Stations ”; IEEE Proc.-Radar, Sonar Navig., vol. 144, No. 3, Jun. 1997, pp. 163-168, Jun. 1997.
Cantor & Colburn LLP
Communications Systems International, Inc.
Summons Barbara
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