A rectangular waveguide filled with anisotropic uniaxial metamaterial with transversal negative effective permeability is investigated both theoretically and experimentally. It is shown that such a waveguide supports propagation of the backward wave below the cutoff frequency, thus, it can be considered as a dual of the ordinary waveguide. The transversal dimension of this waveguide can be arbitrarily smaller than half of a wavelength in the filling material, provided that the transversal permeability is negative. This peculiar behavior may be used for fabrication of miniaturized rectangular waveguides. Several experimental miniaturized waveguides loaded with double ring resonators in 7 GHz frequency band have been designed, fabricated and tested. The measured results revealed backward-wave passband located below the cutoff frequency. Furthermore, it was experimentally shown that the increase of the physical length of the waveguide caused the decrease of the electrical length. This is a direct proof of the backward-wave propagation since the phase of the backward wave increases along the waveguide.

Planar inverted-F antennas (PIFAs) made of woven conductive textiles and of patterns embroidered with conductive threads are investigated. The influence of conductive thread density on antenna properties is considered in both cases. The effect of lockstitch on antenna resonant frequency is quantified. A metallic button is proposed as the transition between textile antennas and classical circuits. A full-textile prototype of a PIFA is designed and shown to operate properly in the ISM 2.4 band.

A partially reflective surface (PRS) antenna design enabling 1-bit dynamic beamwidth control is presented. The antenna operates at X-band and is based on microelectromechanical systems (MEMS) technology. The reconfigurable PRS unit cell monolithically integrates MEMS elements, whose positions are chosen to reduce losses while allowing a considerable beamwidth variation. The combined use of the proposed PRS unit cell topology and MEMS technology allows achieving low loss in the reconfigurable PRS. In addition, the antenna operates in dual-linear polarization with independent beamwidth control of each polarization. An operative MEMS-based PRS unit cell is fabricated and measured upon reconfiguration, showing very good agreement with simulations. The complete antenna system performance is rigorously evaluated based on full-wave simulations and the unit cell measurements, demonstrating an 18° and 23° variation of the half-power beamwidth in the E-plane and the H-plane, respectively. The antenna radiation efficiency is better than 75% in all states of operation.

The dynamic control of the beamwidth of a partially reflective surface (PRS) antenna is reported for the first time. First, a design methodology is proposed by revisiting the PRS antenna theory from the perspective of its reconfigurable beamwidth operation, which is achieved by the control of the reflection magnitude of the PRS. The proposed PRS design only requires one varactor diode per PRS unit cell and a common control voltage for the entire structure. Finally, a fully operational reconfigurable antenna has been fabricated and measured, successfully demonstrating the targeted capability.

Moisture causes detuning and increased losses in textile antennas, and it affects resonant and wideband textile antennas differently. In this work, we studied the effect of moisture on a resonant textile planar inverted-F antenna (PIFA) and a wideband textile monopole antenna. Both antennas were manufactured by embroidering conductive yarn in denim textile. The input reflection coefficient, antenna gain, and gain patterns were measured on both antennas for different moisture contents. The results show that wideband antennas are less affected by moisture in comparison with resonant antennas. For communications applications, large moisture content in the textile antenna should be avoided; therefore a flexible, textile-based waterproofing antenna cover was proposed, manufactured, and tested. On the other hand, the effect of antenna detuning by moisture can be used for moisture-sensing application. This concept was demonstrated on the resonant textile PIFA in transmission and reflection setups, showing that the reflection setup gives better results.