J.L. Gomez-Tornero

1D-Leaky Wave Antenna Employing Parallel-Plate Waveguide Loaded With PRS and HIS

A new type of one-dimensional leaky-wave antenna (LWA) with independent control of the beam-pointing angle and beamwidth is presented. The antenna is based on a simple structure composed of a bulk parallel-plate waveguide (PPW) loaded with two printed circuit boards (PCBs), each one consisting of an array of printed dipoles. One PCB acts as a partially reflective surface (PRS), and the other grounded PCB behaves as a high impedance surface (HIS). It is shown that an independent control of the leaky-mode phase and leakage rate can be achieved by changing the lengths of the PRS and HIS dipoles, thus resulting in a flexible adjustment of the LWA pointing direction and directivity. The leaky-mode dispersion curves are obtained with a simple Transverse Equivalent Network (TEN), and they are validated with three-dimensional full-wave simulations. Experimental results on fabricated prototypes operating at 15 GHz are reported, demonstrating the versatile and independent control of the LWA performance by changing the PRS and HIS parameters.

A Fabry–Pérot Antenna With Two-Dimensional Electronic Beam Scanning

A novel fixed-frequency electronically steerable Fabry-Pérot Antenna (FPA) with electronic two-dimensional (2-D) (azimuth and elevation) steering capability is presented. The configuration is based on a centrally fed Fabry-Pérot cavity (FPC) loaded with a tunable high impedance surface (HIS). Varactor diodes are used to electronically tune the HIS reflection coefficient, forming four azimuthal sectors that are independently controlled by four control signals, respectively. It is demonstrated that this simple configuration generates a pencil beam that can be pointed to eight discrete azimuthal directions, whereas continuous elevation scanning is also attained simultaneously for each azimuthal direction by controlling the leaky-wave propagation constant. The theory, simulation analysis, and experimental results obtained from a prototype operating at 5.5 GHz are presented to validate the antenna design.

Higher order modes of the Ridged Coaxial Waveguide

The higher order TE and TM modes of the ridge coaxial waveguide are rigorously studied and presented for the first time. The generalised transverse resonance technique has been used for the efficient full wave calculation of the cutoff frequencies and field distributions. The agreement with commercially available software packages is very good. Parametric studies are presented, where the dependence of the cutoff frequencies on the geometrical characteristics is quantified

E-plane Filters with Selectively Located Transmission Zeros

The possibility to produce transmission zeros at selectively located finite frequencies is reported for bandpass filters compatible with the conventional E-plane topology. The structure is based on etching resonant apertures on a thin all-metal E-plane insert, which are coupled in parallel. We demonstrate that different combinations of the horizontal (overlap) length and vertical distance between the resonators can produce the same coupling coefficient while introducing transmission zeros at different frequencies. This allows for selective location of the transmission zero for each pair of resonators, which is demonstrated by means of 2nd order filter examples. Two prototypes have been designed and fabricated producing sharp roll-off at either the lower or higher cutoff frequency. Good agreement between numerical and experimental results validate our argument. Moreover compared to conventional E-plane filters, the parallel coupling topology is shown to reduce the overall dimensions by about 50% and shift the spurious resonance by about 1 GHz at x-band while maintaining the low-cost and mass-producible characteristics.

Correction of dielectric losses in practical leaky-wave antenna designs

In this paper, the leaky-mode theory is applied to take into account for the dielectric losses in millimetre waveband inhomogeneous leaky-wave antennas. A practical dielectric-filled cosine-tapered periodic leaky-wave antenna working in the 45 GHz band is studied, showing how the desired sidelobes level and directivity are spoilt due to the effect of the losses. An iterative procedure is used to correct the negative effects of the losses in the radiation patterns of the leaky-wave structure. It is also shown the practical limits of the proposed correction approach. The leaky-mode theory is applied for the first time to compensate the losses in a practical leaky-wave antenna in hybrid waveguide printed circuit technology. This leaky-mode theory is validated with full-wave three-dimensional finite element method simulations of the designed antenna.

An E-plane EBG waveguide for dispersion compensated transmission of short pulses

The resolution of radar applications can significantly suffer from pulse broadening along the propagation in homogeneous hollow waveguides. The latter occurs due to the strongly dispersive nature of the fast waves in the waveguides. A low-cost solution to this problem is here proposed, employing an EBG type of waveguide, compatible with traditional E-plane fabrication techniques. By means of an example, here we demonstrate the reduction of the pulse spreading as it propagates along this type of waveguide.

Mm-wave low-profile reflection polarizer

This paper proposes a mm-wave low-profile reflection polarizer based on single layer anisotropic impedance surfaces. It is demonstrated that by virtue of anisotropy it is possible to independently control the reflection characteristics of the two orthogonal components of a linearly-polarized incident plane waves and therefore achieve polarization conversion. A W-band prototype has been designed and its performance characteristics are evaluated. The 1.5 dB axial ratio relative bandwidth exceeds 51 %, while low loss and better than previously reported angular stability are also demonstrated. The structure is compatible with traditional PCB etching techniques and does not require stacking of multiple layers.

Waveguide loaded with metamaterial surface for dispersion linearization: Numerical and experimental results

The pole and zero matching method has been applied for the dispersion analysis of waveguides loaded with metamaterial surfaces. Very good agreement with commercial software packages has been observed. This allows to produce a synthesis procedure, where the admittance characteristics of the metasurface are designed to meet the dispersion requirements. A matched finite structure has been designed and fabricated. Preliminary experimental results suggest successful matching of the structure.

Analysis of sub-wavelength cavity leaky-wave antennas with high-impedance surfaces

We present simple and accurate analysis techniques to simulate and design high-gain Fabry-Perot resonant leaky-wave antennas (LWA). To control the radiation properties of these antennas, two metallodielectric periodic structures are used, one acting as a partially reflective surface (PRS) and a second acting as a high impedance surface (HIS). Full-wave method of moments (MoM) is employed for the estimation of the near fields within the LWA. Invoking reciprocity, this allows for a fast estimation of the radiation patterns. Moreover, a simple transverse equivalent network (TEN) is employed from which the leaky-mode complex propagation constant is obtained. Numerical results are presented to demonstrate the capabilities of these techniques.