Teresa M. Martín-Guerrero

Simulation of negative permittivity and negative permeability by means of evanescent waveguide Modes-theory and experiment

In this paper, the theoretical foundations of the equivalence between waveguide propagation below cutoff and artificial plasmas are carefully analyzed through the derivation of the propagation constants of normal modes in waveguides filled with anisotropic plasmas. The equivalence between waveguide and dielectric plasma proposed by Marquees et al., which is valid for evanescent TE modes, has a dual counterpart for magnetic plasmas and evanescent TM modes. This new equivalence states that a negative magnetic permeability medium can be simulated by means of TM modes below their cutoff frequencies. The need of an anisotropic filling of the waveguide for the equivalence between plasmas and evanescent modes is also highlighted. To exemplify the applicability of this new equivalence, a structure that implements a double-negative medium has been proposed. Full-wave simulations of the proposed structure and measurements from an experimental setup are presented, both of which corroborate the new equivalences validity.

Experimental performance of a meta-distributed amplifier

Meta-distributed amplifiers (MDAs) constitute a novel class of distributed amplifiers based on the active coupling of two composite-right/left handed transmission lines, and can provide dual-band amplification at two different physical ports. In this contribution, the dual-band gain and noise performance of such active distributed circuits is experimentally demonstrated for the first time using a lumped element-based implementation. Obtained experimental results suggest that the performance of such MDAs can be similar to that of conventional distributed amplifiers as far as gain and noise figure are concerned, but with the added advantage of dual-band amplification.

DERIVATION AND GENERAL PROPERTIES OF ARTIFICIAL LOSSLESS BALANCED COMPOSITE RIGHT/LEFT-HANDED TRANSMISSION LINES OF ARBITRARY ORDER

A circuit theory-based approach for systematically deriving all possible lossless balanced composite right/left-handed transmission lines is described. To illustrate the usefulness of the proposed approach, novel artiflcial transmission line unit-cells with tri- and quad-band behaviour are proposed. It is shown that the number of right-handed or left-handed frequency bands exhibited by such transmission lines is determined by the order of its unit-cell. It is explained why artiflcial lossless balanced transmission lines exhibit a stop-band around each pole of their associated continuous transmission line that can not be closed up. Since this approach allows for the systematic derivation of such transmission line unit-cells of arbitrary order, multi-band components based on metamaterial transmission lines are envisaged.

Planar Broadband Slot Radiating Element Based on Microstrip-Slot Coupling for Series-fed Arrays

A novel planar slot radiating element with applications in series-fed arrays and significant bandwidth enhancement is presented in this communication. The structure is based on the microstrip-slotline coupling and simply consists of a microstrip-fed slot with a symmetrically-arranged strip conductor superimposed onto it. The broad impedance bandwidth (up to 16 GHz) lies in the resulting all-pass section that the strip and the slot make up. A theoretical study of the structure in terms of even and odd modes as well as a straightforward equivalent circuit are provided, which offer the required analytical tools to state the design methodology. Experimental and simulated results corroborate that the strip acts as a mere matching element that does not practically alter the slot radiation characteristics.

Active Distributed Mixers Based on Composite Right/Left-Handed Transmission Lines

Distributed mixers are based on the active coupling of two artificial transmission lines (TLs) and provide ultra-wideband performance. This paper shows that it is possible to design distributed mixers with novel performances if artificial TLs with dispersion diagrams different from those provided by conventional series-inductor/shunt-capacitor TLs are used. In particular, three novel distributed mixers, presenting dual-band/diplexer behavior, with and without image rejection or wideband conversion response with image rejection, are proposed, analyzed, and measured. An ideal continuous model is used to analyze the intrinsic behavior of distributed mixers and to show how to engineer their desired performance by proper design of the phase constants. The limitations derived from the unavoidable discrete implementation of the artificial TLs are also assessed. Finally, three mock-ups are implemented and measured. The experimental results obtained proof these novel distributed mixer concepts and validate the proposed theoretical analysis and design methodology.

Assessment of a Composite Right/Left-Handed Transmission Line-based Distributed Amplifier implemented in microstrip technology

The use of composite right/left-handed transmission lines (CRLH TLs) in the design of active distributed circuits such as distributed amplifiers or distributed mixers has led to potential new applications for these kinds of microwave circuits. In particular, CRLH TL-based distributed amplifiers (DAs), which exhibit multiband amplification performance, have recently been proposed by the authors. In this paper a microstrip implementation of CRLH TL-based DAs is proposed and discussed. The proposed implementation allows for the biasing of the active devices without degrading RF performance. Preliminary simulated results suggest that these new distributed amplifiers can be implemented in microstrip technology without deteriorating their intrinsic multiband amplification performance

Generalized Lattice Network-Based Balanced Composite Right-/Left-Handed Transmission Lines

Artificial transmission lines based on lattice network unit cells can mimic the behavior of actual metamaterial transmission lines without introducing any stopband, as opposite to their conventional counterparts based on T- or II-network unit cells, which can be balanced to suppress the stopbands in the transitions from left- to right-handed bands, but will always present stopbands in the right-handed-to left-handed-band transitions. The aim of this paper is twofold. First, the general properties of lattice network unit cells are discussed using simple circuit theory concepts. As a result, a systematic classification of all possible balanced lattice network-based artificial transmission line unit cells is described. Second, a novel multiband lattice network-based unit cell is presented. The proposed unit cell is made up of a coupled-microstrip section in a host microstrip and requires neither air bridges nor via-holes. Coupled lines have already been used to obtain composite right-/left-handed transmission lines, but a solution, based on wiggly lines, is given in this paper to the problem caused by the different even- and odd-mode phase velocities. As a result, the wideband capabilities of the artificial transmission line are fully exploited, as the theoretical and experimental results corroborate.

A Novel Planar Log-Periodic Array Based on the Wideband Complementary Strip-Slot Element

A novel microstrip log-periodic array based on the broadly-matched complementary strip-slot radiating element is proposed. The array consists of microstrip-fed log-periodically-scaled slots on the ground plane and their complementary stubs on the microstrip layer. Since the radiating element is not resonant, the analysis differs from the previously reported log-periodic arrays. Low scale factor (τ) with high radiation efficiency is possible, since the element radiation efficiency is not resonant and the relative spacing (σ) does not have to be selected for good matching, because the element is intrinsically matched. A design example with τ = 0.909, σ = 0.17 and 15 elements has been analyzed. The achieved bandwidth goes from 2.7 to 8.7 GHz, with a radiation efficiency and a gain of better than 85% and 5 dB, respectively. Moreover, the antenna can be terminated in an open circuit without affecting its performance. Simulated and experimental results show that the radiation pattern is stable over frequency. A method for computing the radiation pattern using equivalent circuits as well as results with a reflector plane for cancelling the beam in one half-space are also included. Due to the good performance, simplicity and low cost, this antenna can be suitable for broadband applications.

Distributed Mixers with Composite Right/Left-Handed Transmission Lines

The use of composite right/left-handed transmission lines (CRLH-TLs) in distributed mixers, instead of the usual right-handed transmission lines (RH-TLs) is explored. The theoretical performance of such mixers is analyzed in two cases: when CRLH-TLs are used in both drain and gate lines, and when a CRLH-TL is introduced only in the gate line. Both cases show that innovative distributed mixer designs can be achieved. In one design the IF is output on a different port for the different RF frequencies, and in another design there is an intrinsic image frequency rejection achieved

Electronically Steerable and Fixed-Beam Frequency-Tunable Planar Traveling-Wave Antenna

The design of an electronically steerable wideband planar traveling-wave antenna is presented. The proposed antenna has a very simple structure based on a microstrip line loaded with several radiating elements and phase shifters between them. The phase shifters are based on tunable capacitances, in order to perform a continuous phase shift between the radiating elements and control the main beam direction. The radiating elements are complementary strip slots that have a very broad impedance bandwidth, thus allowing the antenna to have two different modes of operation: maintaining the main lobe direction over a significant bandwidth, 1.71-2.17 GHz, and performing a main beam scanning over this bandwidth with a maximum angle range of -45° to 45° at 2 GHz.