Luca Di Palma

Circularly Polarized Transmitarray With Sequential Rotation in Ka-Band

We present here the design and demonstration of a circularly polarized (CP) transmitarray antenna operating in Ka-band and illuminated by a linearly polarized (LP) source. The proposed design is based on a CP unit-cell with simulated insertion loss of 0.2 dB at 30 GHz. In order to improve the axial ratio (AR) bandwidth, the sequential rotation technique is applied to the full array configuration. A model based on a hybrid in-house simulation tool is also proposed to predict accurately the array performance. The realized prototype, formed by 400 unit-cells, has 1 bit of phase resolution. The measured broadside gain is 22.8 dBi at 30 GHz with a 3-dB bandwidth of 20% in right-handed CP (RHCP). The obtained 3-dB AR bandwidth of 24.4% is comparable with higher resolution designs.

Analytical Model of Connected Bi-Omega: Robust Particle for the Selective Power Transmission Through Sub-Wavelength Apertures

In this paper, we present a new analytical model of the connected bi-omega structure consisting of two bi-omega particles connected together through their arms. A single bi-omega particle consists of a pair of regular equal omegas with mirror symmetry. Assuming the individual bi-omega particle electrically small, the equivalent circuit is derived, in order to predict its resonant frequency. Then, two bi-omega particles are connected together, obtaining a symmetric structure that supports two fundamental modes, with even and odd symmetries, respectively. The proposed analytical model, then, is used to develop a procedure allowing the design of the particle for a desired resonant frequency. The effectiveness of the proposed analytical model and design guidelines is confirmed by proper comparisons to full-wave numerical and experimental results. We also demonstrate through a proper set of experiments that the resonant frequencies of the connected bi-omega particle depend only on the geometrical and electrical parameters of the omegas and are rather insensitive to the practical scenario where the particle itself is actually used, e.g. in free-space, rectangular waveguide or across an aperture in a metallic screen.

Design of a Waveguide Diplexer Based on Connected Bi-Omega Particles

In this letter, we propose a new waveguide diplexer based on the employment of connected bi-omega particles. The component consists in a junction between three waveguides with the same cross-section. At either of the junction sections between the feeding waveguide and the two output ones, we place a set of connected bi-omega particles. The two sets of particles have different dimensions, in order to resonate at two different frequencies, enabling, thus, the frequency selective transmission required for the diplexer operation. The design is supported by proper full-wave numerical simulations and measurements.

1-Bit Reconfigurable Unit Cell for Ka-Band Transmitarrays

This letter presents an electronically reconfigurable, linearly polarized unit cell for transmitarray applications in Ka-band. A 1-bit phase resolution (namely with two phase states 0 ° and 180 °) is obtained using two p-i-n diodes mounted on a slot-loaded patch antenna. The design, realization, and experimental characterization in a standard waveguide simulator are reported. The measured insertion losses only reach 1.09 and 1.29 dB for the two-phase states, respectively, with a 3-dB transmission bandwidth of about 11.2%.

Design of Wideband Dual Linearly Polarized Transmitarray Antennas

Dual linearly polarized transmitarray antennas with wideband performance are investigated in X-band. Their designs are based on unit-cells with bandpass response. Their structures consist of three conducting layers printed on two identical dielectric substrates glued with a bonding film. Detailed experimental results demonstrate excellent polarization independence, with expected performance and properly preserved radiation characteristics for each polarization. The measured data are in excellent agreement with full-wave simulation results.

Extracting power from sub-wavelength apertures by using electrically small resonators: Phenomenology, modeling, and applications

In this contribution, we review our recent work on the extraction of the electromagnetic power from electrically small apertures by using metamaterial-inspired resonators. First, we present an antenna interpretation of the power transmission through sub-wavelength apertures and discuss the questioned concept of “enhanced transmission”. Then, we present the so-called “connected bi-omega particle” and the related analytical model. After that, exploiting proper numerical and experimental examples, we also show that the electromagnetic response of such a particle is not influenced by the surrounding environment. This unique property makes the particle a suitable candidate for the implementation of microwave components based on the selective power extraction from electrically small apertures. Finally, the application of the proposed concepts to the design of innovative microwave components, such as waveguide filters, diplexers, power-splitters, modal filters, horn antennas, etc. will be considered and demonstrated through proper numerical and experimental results.

New metamaterial-inspired antenna concepts based on enhanced microwave transmission through sub-wavelength apertures

In this contribution, we investigate the tunneling and radiating phenomena associated to coupled biomega particles placed across a sub-wavelength aperture. We show that, when properly excited, the strong resonances arising in this inclusion may lead to dramatically enhanced transmission through the sub-wavelength aperture. The description of the physical phenomena behind the operation of the proposed setup and the discussion on its possible applications in a new family of radiating components will be the subject of the present paper. The results of this investigation are supported by a newly proposed analytical representation of the bi-omega inclusion, whose results are in good agreement with full-wave numerical simulations.

LHCP/RHCP reconfigurable transmitarray in Ka-band

In this contribution, we propose the design of a circularly-polarized reconfigurable transmitarray based on a 1-bit unit-cell (i.e. with two phase states, 0° and 180°) operating in linear polarization. Applying the sequential rotation technique, the possibility to switch between the two circular (LHCP/RHCP) polarizations will be presented. The numerical results obtained for a 400-element transmitarray radiating at broadside show a maximum gain of 20.3 dBi at 29 GHz with a cross polarization discrimination better than 30 dB. The -3dB bandwidth in gain reaches 14%.

Circularly-polarized reconfigurable unit-cell for transmitarray applications in Ka-band

In this contribution, we propose a new reconfigurable unit-cell design operating in circular polarization in Ka-band. Two p-i-n diodes are integrated in order to achieve a phase resolution of 1 bit (0°/180° are the possible phase states). An insertion loss of about 1 dB at 29 GHz with a 3-dB relative bandwidth of 14.5% has been numerically demonstrated.

Design and experimental characterization of a reconfigurable transmitarray with reduced focal distance

In this contribution, we study the design and experimental characterization of a reconfigurable transmitarray in X-band with reduced focal distance. To this end, we consider an illumination with four feed horn antennas in two different configurations. The focal distance and the horn configuration in the focal plane have been optimized with an in-house simulation tool. The effects of source placement errors and excitation unbalances are also studied. The numerical results show a reduction of the focal distance by a factor 1.8 if compared with the single-source case, for a reconfigurable 400-element transmitarray designed in X-band. Moreover, generation of multiple beams is considered and demonstrated numerically for spatial power combining applications. The experimental results obtained in radiation are in good agreement with the numerical predictions. This multiple-source transmitarray exhibits similar radiation performances as the single-source one in terms of gain, bandwidth and beam tilting capabilities, but with about half its volume. This technique seems very attractive for a better integration on various platforms such as vehicles, drones, aircrafts, buildings, etc