Vicente Losada

In this paper the authors describe the design of a broadband aperture-stacked patch (ASP) microstrip antenna based on a filtering equivalent circuit. The antenna consists of two stacked microstrip patches that are fed by a microstrip line through a resonant aperture. An equivalent circuit is proposed for the antenna consisting of three LC parallel resonators, out of which two resonators are inductively coupled and two resonators are capacitively coupled. The equivalent circuit is de-embedded from the antenna response by means of the least squares method, and the dimensions of the antenna are adjusted in such a way their equivalent circuit matches the response of a broadband third order filter. The reference filter is used as a mean to ensure broadband matching of the antenna. Following this design strategy, a broadband ASP antenna has been designed, fabricated and measured at a center frequency of 5.5 GHz with a bandwidth of roughly 45%.

This paper proposes the design of broadband microstrip antennas fed by differential microstrip lines. The designed broadband antennas are composed of two capacitively coupled rectangular stacked patches excited through a dog-bone shaped aperture by short-circuited differential microstrip lines. The short-circuited lines are symmetrically located with respect to the apertures so that their differential-mode (DM) naturally excites the aperture, while their common-mode (CM) is intrinsically rejected. The DM design of the antennas is based on an equivalent second-order filter circuit consisting of two capacitively coupled parallel LC resonators, which helps to ensure the DM broadband impedance matching of the antenna. Two different 2 × 2 arrays using the proposed antennas have been designed, fabricated and measured, one involving four 180° hybrids and three power dividers in the feeding network, the other involving one 180° hybrid and six power dividers. Bandwidths larger than 25%, gains around 12 dBi and cross-polarization below -25 dB have been achieved by the two arrays at a center frequency of 5.5 GHz.

In this article, the authors propose a lumped circuit methodology for the design of broadband stacked microstrip patch antennas fed through an aperture. First, an equivalent circuit (EC) is introduced for the antenna. The EC consists of an $LC$ series resonator modeling the feed plus two capacitively coupled $LC$ parallel resonators accounting for the radiating patches. Then, a deembedding procedure based on total least squares method is introduced to determine all the parameters of the antenna EC. Second, the circuit stage modeling the patches is designed as a second-order Chebyshev filter based on coupled resonators. Since the standard Chebyshev approach leads to circuit parameters that cannot be physically obtained in practice, a modified second-order quasi-Chebyshev design is presented, which can be physically implemented by stacking one conventional rectangular patch above one rectangular patch with both inner and meandering slots. The proposed methodology is used to design an antenna with over 30% bandwidth at a center frequency of 5.57 GHz. A prototype has been fabricated and measured, and good agreement has been found between simulations and experiments.

In this work circularly polarized flat reflectarray antennas are designed to work at downlink frequencies in Ku- and Ka-band. The design approach for circular polarization radiation combines both the variable rotation technique (VRT) and the element size variation technique (ESVT). The reflectarray element employed consists of a rotable split ring operating at 12 GHz (Ku-band) that surrounds two orthogonal sets of parallel dipoles of variable size operating at 20 GHz (Ka-band). Rotations of split rings and different sizes of dipoles are exploited as degrees of freedom by VRT and ESVT for designing focused beams dual band dual circular polarized reflectarrays. The split ring can be used to achieve single focused beams for circular polarization by VRT at 12 GHz, and the set of orthogonal dipoles can be used to achieve two focused beams for dual circular polarization by ESVT at 20 GHz. In this way, the reflectarray element has been used to design two flat dual band circularly polarized reflectarrays that generate three pencil beams either in the same direction or in different directions: one pencil beam with right-hand circular polarization (RHCP) at 12 GHz and two pencil beams with both RHCP and left-hand circular polarization (LHCP) at 20 GHz. The designed reflectarrays are carried out under local periodicity assumption by means of in-house electromagnetic software that applies the Method of Moments in the Spectral Domain. Validations of the in-house electromagnetic software show significant CPU time savings with respect to CPU time consumption provided by commercial software of general purpose as CST electromagnetics software. Numerical results of radiation patterns produced by the designed reflectarrays show efficiencies around 65% and a bandwidth of 6% for a main beam cross-polarization discrimination of 25 dB. The numerical results are satisfactorily validated by CST software and a tolerance errors study has been numerically carried out with acceptable results.

A reflectarray antenna capable of operating independently in the transmit frequencies (from a satellite) in Ku-band (11-13 GHz) and Ka-band (19-20 GHz) has been proposed and demonstrated. To prove that independent beams can be optimized in each frequency band using separate feeds, a 25-cm demonstrator that generates a focused beam in dual polarization (linear or circular) has been designed, manufactured, and tested. The reflectarray cells comprise two stacked sets of coupled parallel dipoles for each polarization, which permits an independent optimization of the phase for each frequency and polarization. The simulated and measured radiation patterns for both copolar and cross-polar components are in good agreement in Ku- and Ka-bands.

A unifying principle explaining the numerical bounds of quantum correlations remains elusive, despite the efforts devoted to identifying it. Here, we show that these bounds are indeed not exclusive to quantum theory: for any abstract correlation scenario with compatible measurements, models based on classical waves produce probability distributions indistinguishable from those of quantum theory and, therefore, share the same bounds. We demonstrate this finding by implementing classical microwaves that propagate along meter-size transmission-line circuits and reproduce the probabilities of three emblematic quantum experiments. Our results show that the “quantum” bounds would also occur in a classical universe without quanta. The implications of this observation are discussed.

A reflectarray antenna with improved performance is proposed to operate in dual-polarization and transmit-receive frequencies in Ku-band for broadcast satellite applications. The reflectarray element contains two orthogonal sets of four coplanar parallel dipoles printed on two surfaces, each set combining lateral and broadside coupling. A 40-cm prototype has been designed, manufactured, and tested. The lengths of the coupled dipoles in the reflectarray cells have been optimized to produce a collimated beam in dual polarization in the transmit and receive bands. The measured radiation patterns confirm the high performance of the antenna in terms of bandwidth (27%), low losses, and low levels of cross polarization. Some preliminary simulations at 11.95 GHz for a 1.2-m antenna with South American coverage are presented to show the potential of the proposed antenna for spaceborne antennas in Ku-band.

A novel non-uniform sinusoidally modulated half-mode microstrip structure with application to near-field focused leaky-wave radiation in the backward Fresnel zone is proposed. First, it is presented a dispersion analysis of the constituent backward leaky wave in the sinusoidally modulated unit cell in half-width microstrip technology. This information is then used to design a finite non-uniform line that focuses the radiated fields at the desired point. Finally, eight similar line sources are arranged in a radial array to generate a three-dimensional focused spot located at the desired focal length over the simple central coaxial feeding. Simulated and experimental results are presented to validate the proposed simple approach.

An angular bandpass filter is designed. The structure is made of an array of chains of interconnected Split Ring Resonators. It may be applied for increasing directivity of antennas or reducing grating sidelobes. The main advantage over previous angular filters is the smaller thickness of the structure which is a small fraction of the wavelength while previous designs had always a thickness near one wavelength.