Remarkable progress in terahertz (THz) sources and detectors is followed by the necessity of manipulating of terahertz radiation. Since natural materials can not perform efficient interaction with THz radiation, artificial structures called metamaterials are designed to overcome “THz gap” in this area. A variety of tunable metamaterials using different methods of control are presented and discussed in this review paper.

In this article, we present a physically oriented design of broadband RF negative non-Foster capacitors. The design procedure is based on the matrix decomposition of Linvill’s floating negative impedance converter (NIC). The decomposition allows optimization of the NIC circuit regarding the accuracy of generated capacitance. Furthermore, it provides a clear physical picture of the influence of particular circuit elements on the system properties. The methodology is verified by the design and measurements of a negative capacitor in a 0.5–2 GHz range, suitable for applications in bandpass filters with the NIC-based impedance inverters. Experimental results were found to be in good agreement with the theoretical predictions, verifying the correctness of the presented approach.

An original design of 3D antenna for passive UHF RFID tags is presented. Tags using the proposed near omnidirectional antenna are characterized by almost eliminated read-orientation sensitivity as compared to conventional tags based on planar dipole antennas. As a result the novel tags placed on the cardboard box corner can be read independently on their orientation with respect to reader antennas with two orthogonal (linear or circular) polarizations

A new type of a compact second-order bandpass filter (BPF) with two transmission zeros based on transversal signal-interference technique is proposed in this letter. Unlike other transversal filters published, the proposed structure is composed of artificial right- and left-handed transmission lines, instead of traditional distributed transmission line sections. Such an approach is not only helpful in size reduction, but also promising for frequency-asymmetrical stopband performance achievement. Design equations and guidelines to adjust filter performance are provided in the letter. To validate the proposed design approach, a two-pole BPF was designed, fabricated using multilayer liquid crystal polymer (LCP) technology and measured.

An enhancement technique of quasi-lumped inductance Q-factor is proposed in order to improve loss performance of LTCC filters. Effectiveness of the technique developed is demonstrated by experimental characteristics of a 3-pole bandpass LTCC filter with reduced in-band insertion loss. Figure of merit of a filter is introduced as a universal characteristic that allows comparison of different filters by means of design effectiveness.