A lumped-LC equivalent circuit to model a novel rectangular bracket shaped defected ground structure (DGS) is presented in this paper. The presented equivalent circuit can accurately predicate the frequency responses, in terms of the magnitude and phase responses of S parameters, of the studied DGS. The lumped LC parameters of the presented model are extracted based on a unit cell of the DGS. Further, the model is found to be applicable in microwave engineering, including microwave filter designs. Some design examples are presented and examined. The studied DGS based microwave filters characterize maximum passband flatness, sharp skirt between the passband and stopband and wide stopband. The studied equivalent circuit model can accurately predicate the frequency responses including the magnitude and phase of S parameters.
Bowtie antenna-based time reversal mirror (TRM), incorporating with randomly distributed and arbitrarily shaped wire metamaterials medium, is proposed to realize super-resolution target detection. The achieved performance for standard and scatterer bowtie antenna TRM is compared and discussed. The dual-band bowtie antennas resonate at 2.45 GHz and 5.2 GHz and a super-resolution of 0.0817 of the free-space wavelength at 2.45 GHz has been achieved. For the first time, studies show that the TRM with microstructure perturbations (namely scatterers) can enhance the resolution in some cases. Proposing a method of super-resolving transmission of electromagnetic waves is very important to realize multi-independent channels in a compact space for the related applications.
The design and implementation of planar multi-way differential power dividers remain a challenge in terms of the compactness and especially, for the achievable characteristic impedance of the quarter-wavelength transformer when considering large number of outputs. In this work, the double-sided parallel stripline is recommended to realize such a power divider with out-of-phase outputs, and explicit design methods are provided. The proposed multi-way power divider was developed without the use of lump elements on a single substrate. For system applications, a prototype operating at 41.6 MHz with 12 pairs of out-of-phase outputs that utilize the microstrip line as the output interfaces was fabricated and examined. At the center frequency of 41.6MHz, the developed prototype measured insertion losses akin to 14.3 dB as compared with the theoretical data of 13.8 dB. The attainable impedance bandwidth ranges from 10 MHz to 80 MHz under a magnitude imbalance of ±0.3 dB. The isolations of the adjacent outputs are about 13.1 dB as compared with the theoretical values of 14.428 dB, and are better than 34 dB for more distant ones. Parameter measurements are in good agreement with the numerical predications, thus demonstrating the realization of the proposed multi-way power divider.
This contribution presents, for the first time, the design of microwave lowpass filter with ultrawide stopband and low insertion loss based on the log-periodic zig-zag defected ground structure (DGS); the design is specifically evolved from the principle of the log-periodic line antenna and the slotline based DGS. Based on the log-periodic property, studies show that ultra-wideband suppression can be realized by increasing the flare angle or the angle subtended by each element of the slotline DGS. The developed filter therefore shows low insertion loss of 0.7 dB within the passband, sharp transition between the passband and the stopband and ultra-wide suppression band from 2.61-26.5 GHz with a 20 dB suppression level. The DGS architecture is simple and easy to realize, and the design is thus useful in many microwave applications. The fabricated prototype filter validates the study, both from simulations and from measurements.