Mariano Barba

Bandwidth Improvement in Large Reflectarrays by Using True-Time Delay

A significant improvement in the bandwidth of large reflectarrays is demonstrated using elements which allow true-time delay. Two identical, large reflectarrays have been designed using different phase distributions to generate a collimated beam. In the former, the phase distribution is truncated to 360deg as is usual in reflectarray antennas, while in the second, the true phase delay is maintained (three cycles of 360deg). The chosen phase-shifter elements are based on previously measured and validated patches aperture-coupled to delay lines. The radiation patterns for both reflectarrays have been computed at several frequencies and the gain is represented as a function of frequency for both cases. Bandwidth curves are presented as a function of the reflectarray size.

A High-Isolation, Wideband and Dual-Linear Polarization Patch Antenna

The design of a dual-polarization stacked patch antenna to be used in GSM-UMTS base station arrays is presented. The patch shows a high matching level in a broadband and isolation between elements that make it a suitable radiating element for base station arrays. Moreover, the most relevant achievement of this element is the isolation between the two polarization ports of the same element in the antenna operating bandwidth. A prototype has been manufactured and measured. The measurements, that match the design objectives, are also presented.

Reflectarray Element Based on Aperture-Coupled Patches With Slots and Lines of Variable Length

A phase-shifter element for printed reflectarrays with more than 4 cycles of phase delay is presented in this work. The proposed reflectarray element allows very linear phase curves and is based on the combination of two previously studied and demonstrated concepts: variable length slots on a ground plane and patches coupled through a slot to variable length lines. In the former, the slots act as inductive loading on the patches depending on their length. With the second concept, the effect of nonconstant path delay is alleviated by the introduction of true-time delay (TTD) lines. The mixed effect allows a much larger range of phase delay to be reached and at the same time to improve the linearity of the phase delay behavior. Two ways of increasing the phase delay range are shown: the increase in length using U-shaped delay lines and the use of high permittivity substrates

Multifed Printed Reflectarray With Three Simultaneous Shaped Beams for LMDS Central Station Antenna

A two-layer reflectarray is proposed as a central station antenna for a local multipoint distribution system (LMDS) in the 24.5-26.5 GHz band. The antenna produces three independent beams in an alternate linear polarization that are shaped both in azimuth (sectored) and in elevation (squared cosecant). The design process is divided into several stages. First, the positions of the three feeds are established as well as the antenna geometry to produce the three beams in the required directions. Second, the phase distribution on the reflectarray surface, which produces the required beam shaping, is synthesized. Third, the sizes of the printed stacked patches are adjusted so that the phase-shift introduced by them matches the synthesized phase distribution. Finally, the radiation patterns are computed for the central and lateral beams, showing a shaping close to the requirements. A breadboard has been manufactured and measured in an anechoic chamber, showing a good behavior, which validates the designing methodology.

X-Band Reflectarray Antenna With Switching-Beam Using PIN Diodes and Gathered Elements

An electronically switching-beam reflectarray antenna to be used in X-band has been designed, manufactured and tested, using PIN diodes as switching device. The antenna has 244 elements arranged in a circular aperture. With the aim of saving electronic devices and reducing both manufacturing complexity and cost, the phase control has been implemented at sub-array level, using aperture-coupled patches gathered by pairs to a common delay line. The antenna was designed to switch the beam between ±5°, in a scanning plane tilted 18.3° with respect to the YZ plane. Each state was obtained by forward biasing one half of the diodes, while the other half remains in reverse biasing. A third state with the beam pointing to 0° was obtained when all the diodes are in reverse biasing. The concept has been demonstrated by manufacturing and testing a breadboard. The measured radiation patterns fulfill the design requirements.

Demonstration of a Shaped Beam Reflectarray Using Aperture-Coupled Delay Lines for LMDS Central Station Antenna

A shaped-beam reflectarray based on patches, aperture-coupled to delay lines is demonstrated for local multipoint distribution system (LMDS) central station antennas, in the 10.10-10.70 GHz band. The antenna must cover a 60deg-sector in azimuth with a squared cosecant pattern in elevation. The design process consists of two steps. First, a phase-only pattern synthesis technique is applied to obtain the required phase-shift distribution on the reflectarray surface which generates the shaped pattern. The second stage consists of determining the length of the delay lines, aperture-coupled to the square patches, in order to achieve the phase distribution synthesized in the previous step. Two reflectarray antennas have been designed, one for vertical (V) and the other for horizontal (H) polarization. A breadboard for V-polarization has been manufactured and tested in an anechoic chamber, showing a good agreement between theoretical and measured radiation patterns.

Electronic controllable reflectarray elements in X band

This paper shows the design and measurements of two types of reflectarray (RA) elements with electronic control for pattern reconfigurability in X band (10.5 GHz). The radiating element consists of a patch which is coupled to a microstrip line through a slot. This structure can produce a wide range of phase shift in the re-radiated signal with a very linear response. By adding a proper electronic controllable phase-shifter to the line section it is possible to control the reflected signal allowing the pattern reconfigurability through a proper design. Two different phase-shifters have been studied: one is based on PIN diodes and allows a phase change by discrete steps. The second uses a varactor diode which allows a continuous phase-shift in the range of 120o, which would be valid for some cases of reconfigurable antennas. These elements have been validated using a Waveguide Simulator. Index Terms – Reflectarray antennas, reconfigurable antennas.

Design, Manufacturing and Test of a Dual-Reflectarray Antenna With Improved Bandwidth and Reduced Cross-Polarization

A dual-offset reflectarray demonstrator has been designed, manufactured and tested for the first time. In the antenna configuration presented in this paper, the feed, the sub-reflectarray and the main-reflectarray are in the near field one to each other, so that the conventional approximations of far field are not suitable for the analysis of this antenna. The antenna is designed by considering the near-field radiated by the horn and the contributions from all the elements in the sub-reflectarray to compute the required phase-shift on each element of the main reflectarray. Both reflectarrays have been designed using broad-band elements based on variable-size patches in a single layer for the main reflectarray and two layers for the sub-reflectarray, incident field. The measured radiation patterns are in good agreement with the simulated results. It is also demonstrated that a reduction of the cross-polarization in the antenna is achieved by adjusting the patch dimensions. The antenna measurements exhibit a 20% bandwidth (12.2 GHz-15 GHz) (with a reduction of gain less than 2.5 dB) and a cross-polar discrimination better than 30 dB in the working frequency band.

Characterization of a Reflectarray Gathered Element With Electronic Control Using Ohmic RF MEMS and Patches Aperture-Coupled to a Delay Line

A reflectarray element with electronic phase control implemented by ohmic MEMS switches is characterized and validated in the X-band. The proposed element is based on two patches aperture-coupled to a microstrip network with a common delay line, forming a sub-array, in order to reduce both cost and manufacturing complexity in large reflectarrays. The electrical length of the line can be modified through the inclusion of a series switch between different segments of the microstrip line. The ohmic electrostatic switch has been designed for RF applications and manufactured on a coplanar line. The transition between the coplanar line of the MEMS and the microstrip delay line has been implemented using gold wires which have been bonded to the printed pads. This connection leads to a high impedance line. The MEMS switches have been characterized using reflection and transmission measurements on microstrip lines for deducing an equivalent circuit, which has been used in the validation of the gathered element with electronic phase control measured using waveguide simulator. The same approach has been applied to evaluate a 2-bit reflectarray element.

A Switchable Multiple Beam Antenna for GSM-UMTS Base Stations in Planar Technology

A broadband antenna for GSM1800-UMTS base stations with multiple switchable beams in azimuth is presented in this paper. The multiple beams are obtained by means of a broadband Butler matrix. The radiating element is broadband and consists of two stacked patches. The elevation pattern is shaped with null filling and upper lobe reduction that has been achieved by means of a broadband corporate feed network implemented in microstrip technology. Photographs and measurements of the manufactured prototypes are presented confirming that the design of all of the elements is correct