Jose-Luis Vazquez-Roy

Size Reduction of Mushroom-Type EBG Surfaces by Using Edge-Located Vias

Periodic surfaces made of patches with metallized via holes or grounding pins (ldquomushroomsrdquo) have been shown to have bandgaps in their dispersion diagrams, inside which surface waves cannot propagate. These bandgaps are defined in all directions in the surface structure. The purpose of this work is to show how by changing the position of the metallic via of the mushroom from its center to its edge, the bandgap moves towards lower frequencies. This allows an easy structure size reduction which is critical in many applications. Results prove a size reduction of the unit cell size by approximately 20% by only moving the via position. The conclusions have been validated with measurements.

High Isolation Proximity Coupled Multilayer Patch Antenna for Dual-Frequency Operation

A new method to enhance the isolation between two ports in a dual-frequency proximity coupled patch antenna is presented. The dual-polarized patch antenna has a multilayer substrate configuration to achieve a compact design. In addition, two periodic structures have been included under the two feeding lines to have stopband behavior in the other frequency port. These electromagnetic bandgap (EBG) filters have been realized by introducing mushroom type resonators underneath the antenna feeding lines. Measurements show how the isolation between the feeding ports can be improved by selecting a suitable size for the resonators. The proposed antenna design achieves an isolation higher than 55 dB in the first frequency band (2.1 GHz) and better than 40 dB in the second one (2.45 GHz). Radiation patterns are not affected by the proposed structures showing low cross-polarization levels in both planes at the two frequency bands.

Planar Dual-Mode Horn Array With Corporate-Feed Network in Inverted Microstrip Gap Waveguide

The gap waveguide technology was recently introduced as an alternative to hollow waveguides and substrate integrated waveguides for millimeter-wave applications. This paper presents the design of a 4 ×4 planar dual-mode horn array with low loss corporate feed network realized by using an inverted microstrip gap waveguide. The dual-mode horns are compact and designed to reduce the power losses in grating lobes. It is because the diameters of the horn apertures are larger than two wavelengths to allow more space for the feed network and thereby lower conductive losses. The measurements show very good agreement with simulations, with 10% bandwidth of the return loss, 25 dBi realized gain and about 60% aperture efficiency.

Study and Design of a Differentially-Fed Tapered Slot Antenna Array

The results of a parametric study and design of an ultrawideband dual-polarized array of differentially-fed tapered slot antenna elements are presented. We examine arrays of bunny-ear antennas and discuss the capabilities and limitations of differential antenna technology. As we focus on radio astronomical applications, the absence of a balancing-feed circuit not only reduces the first-stage noise contribution associated to losses in the feed, but also leads to a cost reduction. Common-modes are supported by the antenna structure when a third conductor is present, such as a ground plane. We demonstrate that anomalies may occur in the differential-mode scan impedance. Knowledge of both types of scan impedances, differential and common mode, is required to properly design differential LNAs and to achieve optimal receiver sensitivity. A compromise solution is proposed based on the partial suppression of the undesired common-mode currents through a (low loss) balancing-dissipation technique. A fully steerable design up to 45° in both principal planes is achieved.

Proximity Coupled Microstrip Patch Antenna With Reduced Harmonic Radiation

The purpose of this work is to propose a new method to suppress the harmonic radiation from a microstrip patch antenna with proximity coupled feeding line implemented in a multilayer substrate. The goal of the design is the suppression of the resonances at the 2nd and 3rd harmonic frequencies to reduce spurious radiation due to the corresponding patch modes to avoid the radiation of harmonic signals generated by non-linear devices at the amplifying stage. The study shows the possibility of controlling the second harmonic resonance matching by varying the length of the feeding line. On the other hand, the suppression of the third harmonic is achieved by using a compact resonator. This resonator consists of a printed metallization with a via connected to the ground plane (mushroom type) in a multilayer configuration. Comparing with conventional electromagnetically coupled patch antenna, the radiated power of the proposed antenna at the 2nd and 3rd harmonic frequencies is reduced by 14 dB and 8 dB, respectively.

Compact Reconfigurable Planar EBGs Based on Short-Circuited Hairpin Resonators

This work investigates how to develop compact reconfigurable planar corrugations. The proposed structure has a unit cell of a planar horizontal microstrip corrugation with a modified geometry that resembles a hairpin resonator shape. This configuration is especially compact and it may straightforwardly exhibit a reconfigurable frequency of operation. This initial work evaluates the stop-band filtering properties of a few unit cells below a microstrip line as a proof of concept. Varactor diodes have been employed to change the series capacitance of the unit cells, and consequently, to modify the notched bands produced by the periodic structure. The filtering properties are studied only in one direction as required for corrugations.

On the use of Vivaldi antennas in the detection of partial discharges

Due to their impulsive nature, partial discharges in insulation systems emit in a broad band of frequencies ranging from tens of megahertz to gigahertz. Antennas can be placed at secure distances from the high-voltage source and measure partial discharges pulses on-line. The energy of partial discharges coexists with strong electromagnetic emissions such as frequency modulated radio, television broadcasting and mobile telephones. Then, the antennas should be tuned to detect the emission from partial discharges in bands where the electromagnetic noise is not so important. They should also be capable of receiving in a broad range of frequencies so resonant antennas should be avoided. Vivaldi antennas can be designed to detect emissions from a desired tuned frequency and extended to a band as wide as necessary. This makes them a valuable tool to detect partial discharges avoiding electromagnetic noise present at lower frequencies.

Design of a four-element horn antenna array fed by inverted microstrip gap waveguide

The paper presents the design of a four-element slot coupled dual-mode horn array with microstrip gap waveguide as feed network. We present simulated results for return loss for the feed network both with and without the radiating horn array. We also compare results for two ways to generate the stopband of the parallel-plate modes: the ideal Perfect Magnetic Conductor used during the initial design, and the real bed of nails used in the practical realization. The study is performed at 60 GHz obtaining about 10% bandwidth.

Reconfigurable unit cell for EBG and artificial surfaces based on hairpin resonators

Planar hairpin resonators are considerably compact and can found numerous applications. One of them is its use as unit cell for designing different types of artificial surfaces based on periodic structures, such as EBGs or even “soft” surfaces. In this work we propose to include some varactor diodes in the unit cell with the purpose of providing reconfigurability to the structure in terms of operation frequency. The demonstrator is manufactured in a 1D multilayer version by using a microstrip line and analyzing the transmission parameter S21.

Diplexed dual-polarization proximity coupled patch antenna

A dual-frequency dual-polarization microstrip patch antenna is presented in this paper. These antennas can be realized by feeding two orthogonal modes. Electromagnetic Bandgap Structures (EBG) can be used to reduce the coupling between ports. This concept was originally proposed using a uniplanar compact PBG (UC-PBG) to design a self-diplexing microstrip patch antenna. Another example, is the use of several defected ground structures (DGS) for the feeding lines approaching isolation levels of 60 dB at the nominal frequency. In this work we describe a method to enhance the isolation between two ports in a dual-frequency proximity coupled patch antenna. In our case two filtering lines, based on periodic structure, will be designed to have stopband behavior in the other frequency port. These EBG filters have been realized by introducing mushroom type resonators underneath the antenna feeding lines. Proximity coupled represents one interesting possibility due to spurious radiation reduction. Additionally this multilayer configuration provides choices between two different dielectric substrates in order to achieve a compact design.