Butterworth filter

About: Butterworth filter is a research topic. Over the lifetime, 6187 publications have been published within this topic receiving 69070 citations.

An ultra-narrowband HTS bandpass filter

Abstract: This paper presents the measured results of an HTS ultra-narrowband bandpass filter with a 100 kHz bandwidth. This filter, with a fractional bandwidth of 0.014% and a center frequency of 700 MHz, represents a previously unrealized portion of filter parameter space. This filter was realized using a five-pole Chebyshev filter design and was fabricated using an HTS microstrip configuration. This filter required very high Q, very weak coupling, and a strong reduction in parasitics. Unloaded Qs of 135,000 were achieved with a resulting insertion loss of 1.37 dB. Even resonator Qs of 20,000 would lead to a filter loss of 9 dB. A noise figure of 1 dB was achieved for a complete system with this filter and a cryogenic low-noise amplifier.

Efficient tunable IIR and allpass filter structures

Abstract: A new recursive filter structure is proposed which can be controlled on-line using a single parameter. The structure can be used for interpolation in timing synchronisation of digital communications receivers. The technique is illustrated with an example of the implementation of a tunable fractional delay allpass filter using the Thiran design technique.

Robust Signal Quality Monitoring and Detection of Evil Waveforms

Abstract: The ability to monitor and detect problematic distortions in the received GPS-SPS signal is a task of critical importance. Detection of these satellite signal anomalies or “evil waveforms” can be accomplished using detailed monitoring of the correlation peak. Using the “Second- Order Step” threat model for evil waveforms, previous analysis has attempted to show that monitoring sufficient to satisfy GBAS and SBAS requirements for Category I precision approaches may be obtained from a receiver design that requires minimal modifications to existing GPS hardware. A “robust” signal quality monitor (SQM) design methodology has been developed for this purpose. This report evaluates the best current evil waveform (EWF) signal quality monitoring configuration, SQM2b, using this methodology. First, it compares the maximum regional pseudorange errors (PRE’s), computed at varying elevation angles, to the maximum allowable pseudorange (MERR) errors. Second, it examines the sensitivity of these results to differential group delay variations of up to 150ns. In addition, it examines the effects of user filter magnitude response. Using SQM2b, neither group delay variations nor changing MERR’s were found to pose a threat to standard E-L correlators in any of the four protected regions. However, they did induce some small, unacceptable ∆∆ receiver errors. To account for this, a “notch” was removed from the critical protected region to exclude those unprotectable ∆∆ receiver configurations. It was also shown that user PRE’s were sensitive to transition bandwidth variations. To mitigate this sensitivity it was recommended that the minimum airborne filter transition bandwidth be upper-bounded by that of the 6th-order Butterworth filter.

High-selectivity dual-band stepped-impedance bandpass filter

Abstract: A highly selective dual-band stepped impedance bandpass filter is presented. The filter has two tunable passbands. Two finite out-of-band transmission zeros are realised, which have high selectivity.