This communication demonstrates for the first time the capability to independently control the real and imaginary parts of the complex propagation constant in planar, printed circuit board compatible leaky-wave antennas. The structure is based on a half-mode microstrip line which is loaded with an additional row of periodic metallic posts, resulting in a substrate integrated waveguide SIW with one of its lateral electric walls replaced by a partially reflective wall. The radiation mechanism is similar to the conventional microstrip leaky-wave antenna operating in its first higher-order mode, with the novelty that the leaky-mode leakage rate can be controlled by virtue of a sparse row of metallic vias. For this topology it is demonstrated that it is possible to independently control the antenna pointing angle and main lobe beamwidth while achieving high radiation efficiencies, thus providing low-cost, low-profile, simply fed, and easily integrable leaky-wave solutions for high-gain frequency beam-scanning applications. Several prototypes operating at 15 GHz have been designed, simulated, manufactured and tested, to show the operation principle and design flexibility of this one dimensional leaky-wave antenna.

We present the synthesis of one-dimensional (line-source) leaky-wave antennas (LWAs) in substrate integrated waveguide (SIW) technology with modulated geometry, demonstrating the capability to flexibly tailor the radiated fields pattern, both in nearand far-field regimes. The synthesis technique is inspired in holographic concepts, which are related to the existence of modulated leaky waves. A systematic design algorithm to obtain the requested modulation of the SIW width and distance between posts to synthesize the desired radiation pattern is described. Several design examples operating at 15 GHz are reported and experimentally validated, showing the power and versatility of the proposed holographic SIW technology.

The possibility of microwave near-field focusing using a simple width-tapered microstrip leaky-wave antenna is theoretically and experimentally proven in this paper. The design procedure to obtain the modulation of the microstrip width along the antenna length is described, illustrating the conditions and limitations for optimum focusing at a certain focal point and using a given substrate. A 7.5 λ₀ -long microstrip lens is designed to operate at 15 GHz, and its focusing properties are studied. An array of two in-phase microstrip lenses located front-to-front is proposed to obtain a symmetric focusing pattern with higher spatial resolution. Theoretical and experimental results demonstrate the optimum synthesis of a focusing region with focal length of 3 λ₀, presenting focal width of only 0.33 λ₀ , and focal depth of 1.25 λ₀. Finally, it is reported the frequency focus-scanning performance in the range 14-17 GHz. All these features make the proposed microstrip lens a simpler alternative solution to focused planar phased-arrays.

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.

We demonstrate the capability to conform a substrate integrated waveguide leaky-wave antenna (SIW LWA) along an arbitrarily curved line by suitably tapering the leaky mode along the antenna length. In particular, it is shown that by means of locally adjusting the pointing angle of the radiated wave, a coherent plane-wave front in the far-field region can be obtained. Combined with the capability to taper the leakage rate along the antenna, this allows designing antennas with high illumination efficiency, which provides higher directivity when compared with previous conformal LWAs such as the half-mode microstrip LWAs (HMLWAs). These concepts have been validated with both measured and simulated results involving the proposed conformal SIW LWA as well as three different configurations of HMLWA: conformal tapered HMLWA, conformal nontapered HMLWA and conventional rectilinear HMLWA. The antennas have been designed to operate at 15 GHz, and in the case of the SIW LWA an analysis of its frequency scanning response has been performed.

The ability of tapered leaky-wave antennas (LWAs) to synthesize directive radiation diagrams with suppression of the radiation in prescribed angular regions is studied in this work. The synthesis is based on an iterative Fourier technique that has been adapted for the case of LWAs, taking into account that the far field is related to the antenna illumination through an inverse Fourier transform. Results show that the simultaneous tapering of both phase and leakage constants of the leaky mode allow to obtain wide and deep radiation nulls while maintaining the high-gain scanning pattern of LWAs. The limitations of this unconventional tapering technique are also reported, and a practical design is validated with simulations.