Capacitively‐loaded CPW shunt stub notch filters

Abstract

different orders at the position of the scatterer in the range-image/ azimuth-frequency domain. This test confirms the reduction of the phase error as the processed order increases. As the order is increased, the response of the CSA tends to the exact response obtained with the RMA. We also check here that a large bandwidth in the azimuth frequency domain can be processed, just as we have commented before.Additional simulations have been carried out under the same conditions, to be able to quantify the dynamic range of the new focusing algorithm. In this case, the scene is formed by nine-point scatterers with reflectivity values of between 0 and Ϫ80 dBm. A Blackmand-Harris window with a peak side-lobe ratio of Ϫ92 dB has been employed. The results demonstrate that the dynamic range of the new algorithm is greater than 70 dB. By comparing the values of reconstructed and actual reflectivities, the maximum error is lower than 1 dB. Table 1 shows the results obtained on applying the near-field wideband CSA up to the seventh order. In practice, the dynamic range will be limited by the presence of noise. CONCLUSIONSFor the first time, an n th -order general expression of the phase impulse response of a synthetic aperture system in the two-dimensional frequency domain has been presented. Thanks to this contribution, additional terms have been formulated and included in the CSA to obtain more accurate images in near-field wideband configurations. The number of extra terms to be considered depends on the particular configuration and the geometry of the measurement, and it can be freely selected in the algorithm because an n th -order expression is now available. The algorithm has been implemented and tested with simulations. An evident improvement has been demonstrated by observing the shape and the magnitude of the reconstructed reflectivity of a point scatterer. Numerical simulations have also shown that the dynamic range is better than 70 -80 dB, even under extreme conditions. Furthermore, this new algorithm can be combined with other extensions of the CSA previously proposed by other authors [6,7].Finally, it is important to note that this extension of the algorithm can be applied to any synthetic aperture system, such as sonars and radars. ACKNOWLEDGMENTSThis study was financially supported by the Generalitat Valenciana, under project no. GV00-036-14, and by the Spanish Commision of Science and Technology (CICYT), under project no. TIC2001-2364-C03-02. INTRODUCTIONIn microwave and millimeter-wave integrated circuits, compact layout is an important issue that is limited by both circuit cross-talk and component size [1]. Filters are particularly important in this regard, as they often are realized using distributed transmission line stubs [2][3][4][5][6] that can occupy significant substrate space. Although several methods have been introduced to effectively reduce stub lengths (e.g. bent lines [7], meander structures [8] and capacitive-loading [9]) it can be difficult to control performance over a broad frequency ban...

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