An enhanced equivalent circuit approach for the magnetic/electric interaction of single split-ring resonators (SRRs) with printed lines is presented in this paper. A very simple and efficient lumped-element network is proposed to model the behavior of metamaterial-based printed lines over a wide frequency band. The same circuit topology can be used for the single- and two-mirrored SRRs loaded microstrip line. The corresponding circuit parameters are obtained from the multiconductor transmission line theory as well as from closed-form expressions that make use of just the resonance frequency and minimum of the reflection coefficient (which should be previously extracted from experiments or full-wave simulations). The comparison of our equivalent circuit results with measurements and full-wave simulations has shown a very good agreement in a considerably wider frequency band than other previously proposed simple equivalent circuits.

A configuration of composite resonators consisting of three split-ring resonators is proposed to obtain a triple-band response with two transmission zeros between the passbands. Two new topologies are presented to design triple-band filters with controllable responses. A systematic filter design approach is presented based on a filter coupling model. The model is established to enable triple-band filter design with controlled passbands. Two methods are proposed and compared for the extraction of filter parameters. Coupling between nonadjacent elements is considered in the model and shown to have a significant effect. By changing the orientation of the coupled composite resonators, it is possible to introduce additional transmission zeros. Two sixth-order filter examples illustrate the use of the coupling model with the filter design approach to design filters with specified responses. The limitations of this filter topology are discussed.

This paper presents a novel design of the 1-D frequency scanning antenna array with enhanced scan sector, frequency sensitivity, and sidelobe suppression. The antenna is intended for the direct imaging radar sensors. Modified pentagonal dipoles with impedances ranging from 120 to 1070 Ω are used as radiating elements to provide the required sidelobe suppression. For the antenna design, new types of phase shifters are considered, with respect to their insertion loss, frequency bandwidth, phase shift, and manufacturing simplicity: the double-cell left-handed shifter and its right-handed counterpart. Four linear arrays with eight pentagonal dipoles are combined to obtain the antenna array with higher gain and narrower main beam with respect to constituent linear arrays, but with almost identical H-plane scanning properties. The proposed antenna array was manufactured, and the measured results show an increased scan sector of 55°, high frequency sensitivity of 14.25°/100 MHz, gain of 15.5-17 dBi, and low sidelobe levels of around -20 dB in the whole scanning frequency range. Measured results are in very good agreement with simulations.

Heart rate variability (HRV) describes the time variation in beat-to-beat interval, and reflects the manner in which the cardiovascular regulatory system responds to demands, stress, and illness. A particular advantage of Doppler radar for HRV monitoring is the ability to detect and monitor heart and respiration signals simultaneously, and thus provide independent measures of HRV, and respiration-related fluctuations. High accuracy in obtaining HRV parameters using Doppler radar is achieved using linear demodulation method, including SDNN of about 10 ms, and mean beat to beat interval accuracy of close to 1 ms. In addition, respiration signals were obtained simultaneously with the heart signals, clearly showing a correlation between respiration cycles and heart rate variability.

In this paper, we propose the generalized extraction procedure for retrieval of the effective constitutive parameters for a metamaterial transmission line loaded with asymmetric unit cells. The asymmetric unit cell is replaced with a transmission line immersed in equivalent bianisotropic medium described by effective parameters ε, μ, and Z_c, and bianisotropic parameters u and η. The proposed retrieval procedure is applied to novel dual-band unit cells and compared with the standard Nicolson-Ross-Weir (NRW) method that is originally developed for the symmetric unit cell and then extended to the asymmetric one using the averaged value of reflection coefficients. It has been shown that, in case of pronounced asymmetry, the NRW method gives only the exact value of refraction, but effective permittivity and permeability are considerably different from the exact values since they are calculated by means of the approximate value of characteristic impedance.