Yeo Tat Soon

Wideband Bandpass Filters With SAW-Filter-Like Selectivity Using Chip SAW Resonators

Bandpass filters with surface acoustic wave (SAW)-filter-like selectivity and much wider bandwidth compared to conventional SAW filters are presented. The proposed topology consists of SAW resonator networks and parallel coupled lines. Each ladder type resonator network has a series resonator and two shunt resonators to define the upper and lower cutoff frequencies and realize the sharp passband selectivity. Analysis of the proposed SAW resonator network and a comparison with a traditional ladder type SAW filter is provided. Two filters are designed, fabricated, and measured using chip SAW resonators and microstrip coupled lines on Rogers RO4003C. As the available SAW resonators are discrete, they are connected together using 1-mil bond wires to form the SAW resonator network. The resonators are also wire bonded to the coupled lines and ground patch. The bandwidth of the two filters is 10.5% and 17%, respectively, which is much wider than conventional SAW filters with a bandwidth of a few percent. An analysis is provided for the bulk wave effects, ripples due to finite transducer, gratings of resonators, and second-order effects from series and parallel resonators, which cause deterioration of the passband performance. The impact of bond wire inductance and parasitic coupling, which cause spurious responses at the stopbands, are also discussed.

Wideband bandpass filters with high passband selectivity using SAW-like resonators

A wideband bandpass filter (BPF) using two cascaded sections, each consisting of a SAW-like resonator and one or two transmission lines, is proposed. The lower and higher transitions of the passband are separately defined by the SAW-like resonators. The roll-off at the band edges can be controlled by properly designing the SAW-like resonators to achieve a highly selective passband. As an example, a prototype BPF centered at 0.42 GHz is implemented on PCB, in which the SAW-like resonators are realized by lumped elements. The measured filter has a 3-dB bandwidth of 47% and high passband selectivity is observed. To obtain a wideband rejection, one transmission line in the filter is loaded with an open stub and a low pass filter is added. Experimental results show good high out-of-band rejection up to more than 20 GHz.

The impact of range chirp on chirp scaling algorithm

The chirp scaling algorithm (CSA) is considered as an efficient SAR imaging algorithm. The existence of the range-uncompressed chirp is the necessary condition for CSA to be used. However, if the range chirp is large in the high squint angle case, there will be a strong coupling between the range chirp and azimuth frequency. This coupling will render the relationship between range curvature and Doppler frequency non-linear and hence make the CSA lose its precision in such a case. An analysis about this coupling effect and a compensating method are given in this paper. Computer simulation has confirmed the coupling effect. A possible solution to this problem is also mentioned.

Non-iterative spotlight SAR autofocusing using a modified phase-gradient approach

The phase-gradient autofocus (PGA) technique is robust over a wide range of imagery and phase error functions but the convergence usually requires 4-6 iterations. The authors propose to speed up the estimation convergence by selectively increasing the pool of quality synchronisation sources and not to be limited by the range pixels of the SAR map. This is highly probable since each range bin contains more than 1 prominent scatterers across the integration aperture. It is also highly probable that the least brightest selected scatterer in a range gate may turn out to be of higher energy as compared to the maximum brightest scatterer of another gate. With appropriate target filtering to finally select the quality scatterers out of the large pool and higher-order phase error measurement tool, the new algorithm achieves near convergence quality without iteration. The authors named this solution the Quality PGA algorithm (QPGA).

Real time synthetic aperture radar (SAR) preprocessor design via three-dimensional modular filtering architecture

Synthetic aperture radar (SAR) systems are increasingly demanding for real real-time performance. As part of an effort to develop a real-time range-Doppler digital SAR processor to produce image maps of the scanned area immediately as raw data are collected, this paper describes the conceptual architecture design for a high-speed front-end video pre-filtering. The evolved architecture consists of richly interconnected planes of novelly-adapted Modified Transverse FIR parallel tapped delay elements. Both the range and azimuth prefilterings are performed simultaneously in a continuous input-output flow without the need to worry about corner turning caused by azimuth preprocessing on data samples that are collected in the range direction.

An Over-Complete Dictionary Design Based on GSR for SAR Image Despeckling

In this letter, we explore the concept of group sparse representation (GSR) to exploit the intrinsic structure of synthetic aperture radar (SAR) image. Noting that dictionary design is a crucial factor in GSR performance, we propose an over-complete dictionary to better fit the SAR image despeckling problem. This over-complete dictionary consists of the prespecified dictionaries and learned dictionary. Different kinds of dictionaries emulate the image from different angles. In this way, we can simultaneously obtain better performance on speckle noise suppression and image detail preservation. The experimental results on real SAR images demonstrate that the proposed over-complete dictionary based on GSR can achieve more effective speckle reduction as well as image detail preservation.

A K a -band lumped element dual-behavior resonator (DBR) filter in standard 0.13-μm CMOS technology

A Ka-band lumped element Dual-Behavior Resonator (DBR) filter in 0.13-μm CMOS is presented. The DBR filter consists of Dual-Behavior Resonators (DBRs) and inverters connecting the DBRs. The inverters and the DBRs, which define the stopband transmission zeros, are realized by CMOS spriral inductors and metal-insulator-metal (MIM) capacitors. A second order DBR filter with two transmission zeros is designed and fabricated in standard 0.13-μm CMOS technology. The measured filter has a 3-dB bandwidth of 15% at the center frequency of 27.8 GHz. High rejections larger than 48 dB are realized at the two transmission zero frequencies of 20.2 GHz and 37 GHz.

Modified eigen-image approach to radar target identification

This paper proposes a modification to the eigen-image classifier approach to Automatic Target Recognition (ATR), which improves classification performance in the case where intra-class variation is large.

Processing spotlight SAR data without azimuth oversampling in range migration algorithm

In applying the Range Migration Algorithm (RMA) to process spotlight SAR data, the data has to be oversampled in azimuth. A novel post-processing algorithm is introduced here to eliminate the oversampling. It involves removing the bulk of the azimuth compression and re-focusing the targets using a SPECAN type approach. Some localized artifacts exist but they can be removed by an additional processing step in generating a complimentary image. Point target experiments were successfully performed to verify the algorithm.