Manuel Sierra-Perez

Electronically Reconfigurable Transmitarray at Ku Band for Microwave Applications

An electronically reconfigurable transmitarray device at 12 GHz is presented in this work. This paper highlights the functioning of this kind of device and thoroughly examines the proposed reconfigurable transmitarray. The architecture is discussed along with the design and selection of all the constituting elements and the prototypes for all of them. In order to add reconfigurability to the transmitarray structure, 360° reflective phase shifters were designed, prototyped and validated for direct application. Eventually, a demonstrative prototype for an active transmitarray with phase shifters was assembled, and radiation pattern measurements were taken in an anechoic chamber to demonstrate the capabilities of this structure.

Low-cost monopulse radial line slot antenna

The authors propose the design of one radial line slot antenna with two simultaneous beams, one broadside beam and one conical beam. The antenna is a radial line slot antenna (RLSA), with the slots placed on the upper plate in concentric rings. The radiating element is a slot pair, designed for getting left hand circular polarization. The antenna has been designed to work in the range of 13.4 GHz and 14 GHz. Both beams are obtained independently through very simple excitation circuits, realized with microstrip technology. These feeding networks include a Butler Matrix Network. Comparing both radiation patterns, amplitude and phase, theta and phi angles of arrival direction can be obtained. This monopulse performance can be used to orientate the pencil beam for satellite communication antennas. Measurements for a first prototype are presented to validate the design.

Low-Profile Dual Circularly Polarized Antenna Array for Satellite Communications in the X Band

A planar antenna is introduced that works as a portable system for X-band satellite communications. This antenna is low-profile and modular with dimensions of 40 × 40 × 2.5 × cm. It is composed of a square array of 144 printed circuit elements that cover a wide bandwidth (14.7%) for transmission and reception along with dual and interchangeable circular polarization. A radiation efficiency above 50% is achieved by a low-loss stripline feeding network. This printed antenna has a 3 dB beamwidth of 5°, a maximum gain of 26 dBi and an axial ratio under 1.9 dB over the entire frequency band. The complete design of the antenna is shown, and the measurements are compared with simulations to reveal very good agreement.

Double-beam parallel-plate slot antenna

This paper presents the design and prototyping of a double-beam linear polarized parallel-plate slot antenna at 12-GHz band. Each beam is separated 27.7/spl deg/ and 27.3/spl deg/, respectively, from broadside direction. Two different radiation patterns are generated, exciting the parallel plate from opposite sides. The radiating elements are composed by three parallel slots, the central slot is close to the resonance, while the side ones are designed to minimize the reflection inside the parallel plate. The length of the slots in the same row is kept constant (periodic walls), and the distance between columns is equal to 0.7 times the wavelength. The designs of the feeding networks and the design of the array of slots generate both beams, pointing toward Hispasat and Astra satellites simultaneously, at the same frequency band. The feeding networks are two microstrip circuits that excite two linear arrays of 24 patches, placed at both sides of the antenna, and generate both quasi-TEM mode plane waves inside the parallel-plate waveguide, propagating from one side to the other.

Printed antenna for satellite communications

An antenna which has been conceived as a portable system for satellite communications based on the recommendations ITU-R S.5802743811-6 [1] and ITU-R S.465-5 [2] for small antennas, i.e., with a diameter lower than 50 wavelengths, is introduced. It is a planar and a compact structure with a size of 40 × 40 × 2 cm. The antenna is formed by an array of 256 printed elements covering a large bandwidth (14.7%) at X-Band with a VSWR of 1.4:1. The specification includes transmission (Tx) and reception (Rx) bands simultaneously. The printed antenna has a radiation pattern with a 3dB beamwidth of 5o, over a 31dBi gain, and a dual and an interchangeable circular polarization.

Monopulse waveguide patch array antenna in 37 GHz band

We present a circularly polarized patch array in 37 GHz frequency, within a narrowband application (less than 1%) for signal detection. The designed array needs to have some specific requirements related to its radiation pattern (monopulse configuration to identify the input direction of a signal), circular polarization (RHCP) with an axial ratio under 3 dB, low sidelobe level in the sum pattern, and high gain. Taking into account this last requirement and the working frequency a lossless scheme is needed, and the waveguide feed provides it. The coupling mechanism from the waveguides to the radiating elements is made by inside microstrip lines. The radiating element is a modified circular patch easily manufactured on printed circuit.

An Embedded Lightweight Folded Printed Quadrifilar Helix Antenna: UAV telemetry and remote control systems.

An embedded folded, printed, quadrifilar helix antenna (FPQHA) with a wide-angle coverage for unmanned aerial vehicles (UAVs) telemetry and remote control systems is presented in this article. The novelty of this design is that the FPQHA needs to be designed carefully due to UAV tail dimensions and weight constraints while maintaining a high performance to be integrated in the inner part of the UAV tail fuselage to reduce aerodynamic drag. The radiating terminal, formed by a folded, printed, four-helix, radiating section and a compact feeding network, is designed to provide left-handed, circular polarization (LHCP). The complete design offers a very homogeneous pattern in azimuth with a very good axial-ratio (AR) level over a wide range of elevation angles. The use of low-loss and lightweight materials is also an advantage of this design. The wide radiation pattern favors its use for multielement communication systems. Finally, the antenna performance results are obtained mounted inside a UAV tail platform.

Generalized eigenspace beamformer based on CG-Lanczos algorithm

The generalized eigenspace beamformer (GEIB) has been presented as an efficient way to build a beamformer robust to calibration and pointing errors. Its main drawback is the great computational cost needed to develop the whole structure (mainly associated to obtaining the projection matrix). In this paper, the relation between conjugate gradient and Lanczos algorithm is used to modify the conjugate gradient algorithm [robust conjugate gradient method (RCGM)] so the eigenstructure of the correlation matrix can be obtained directly. The numerical problems associated to the loss of orthogonality in successive gradient vectors have also been overcome via selective orthogonalization (SO). In this way, the proposed RCGM is also robust to numerical problems. The overall computational cost in the construction of the GEIB has been reduced from O(N/sup 3/+N/sup 2/) to O(3N/sup 2/) by using the RCGM instead of a conventional projection algorithm. Computer simulations are also presented to demonstrate the merits of the algorithm.

A Canonical UTD Solution for Electromagnetic Scattering by an Electrically Large Impedance Circular Cylinder Illuminated by an Obliquely Incident Plane Wave

A uniform geometrical theory of diffraction (UTD) solution is developed for the canonical problem of the electromagnetic (EM) scattering by an electrically large circular cylinder with a uniform impedance boundary condition (IBC), when it is illuminated by an obliquely incident high frequency plane wave. A solution to this canonical problem is first constructed in terms of an exact formulation involving a radially propagating eigenfunction expansion. The latter is converted into a circumferentially propagating eigenfunction expansion suited for large cylinders, via the Watson transform, which is expressed as an integral that is subsequently evaluated asymptotically, for high frequencies, in a uniform manner. The resulting solution is then expressed in the desired UTD ray form. This solution is uniform in the sense that it has the important property that it remains continuous across the transition region on either side of the surface shadow boundary. Outside the shadow boundary transition region it recovers the purely ray optical incident and reflected ray fields on the deep lit side of the shadow boundary and to the modal surface diffracted ray fields on the deep shadow side. The scattered field is seen to have a cross-polarized component due to the coupling between the TEz and TMz waves (where z is the cylinder axis) resulting from the IBC. Such cross-polarization vanishes for normal incidence on the cylinder, and also in the deep lit region for oblique incidence where it properly reduces to the geometrical optics (GO) or ray optical solution. This UTD solution is shown to be very accurate by a numerical comparison with an exact reference solution.

Geoda: Conformal adaptive antenna of multiple planar arrays for satellite communications

This is a brief of the development of a new multiple-array antenna, working on the 1.7 GHz band. The main purpose of the project is to establish communications between a satellite constellation and the terrestrial station. Signals from the constellation is followed by the antenna by means of an adaptive beam system.