Daniel Sanchez-Escuderos

Wideband Dual-Polarized Cross-Shaped Vivaldi Antenna

This communication presents a wideband, dual-polarized Vivaldi antenna or tapered slot antenna with over a decade (10.7:1) of bandwidth. The dual-polarized antenna structure is achieved by inserting two orthogonal Vivaldi antennas in a cross-shaped form without a galvanic contact. The measured -10 dB impedance bandwidth (S11) is approximately from 0.7 up to 7.30 GHz, corresponding to a 166% relative frequency bandwidth. The isolation (S21) between the antenna ports is better than 30 dB, and the measured maximum gain is 3.8-11.2 dB at the aforementioned frequency bandwidth. Orthogonal polarizations have the same maximum gain within the 0.7-3.6 GHz band, and a slight variation up from 3.6 GHz. The cross-polarization discrimination (XPD) is better than 19 dB across the measured 0.7-6.0 GHz frequency bandwidth, and better than 25 dB up to 4.5 GHz. The measured results are compared with the numerical ones in terms of S-parameters, maximum gain, and XPD.

Periodic Leaky-Wave Antenna on Planar Goubau Line at Millimeter-Wave Frequencies

A periodic leaky-wave antenna on a planar Goubau line is presented. This transmission line is formed by a planar single-wire waveguide on a thin dielectric substrate. Leakage is produced by adding dipoles along the line on the bottom face of the substrate. A coplanar waveguide is used to feed the antenna, which acts as a smooth transition between the input coaxial cable and the planar Goubau line. The advantage of using this line lies on its losses, lower than those of typical microstrip lines due to the absence of a ground plane. As a result, a higher radiation efficiency than in microstrip-fed antennas can be obtained while keeping similar advantages, e.g., low profile or low production cost. A prototype of the antenna at 40 GHz has been fabricated. Measurements of this prototype are presented in this letter.

Propagation Characteristics of Groove Gap Waveguide Below and Above Cutoff

Recently, gap waveguides have been shown as a potential alternative to convenational waveguides in the millimeter-wave band. Until now, groove gap waveguide (GGW) has been studied through direct correspondence with rectangular waveguide with the same physical dimensions. However, there have been observed differences in the above cutoff propagation characteristics between these two waveguide types. Furthermore, the behavior of GGW below cutoff remains unknown. This work presents a discussion of both below and above cutoff propagation characteristics of GGW, and introduces a simple model that explains the observed GGW behavior and establishes well its propagation characteristics. Two thru-reflect-line calibration kits have been manufactured, and the measurements have good agreement with the proposed analysis model results.

Low-profile planar lens with multilevel FSS for directivity enhancement

An array of apertures or horn antennas are commonly used to obtain high directivity and gain, at the expense of increasing the fabrication complexity. In this paper a new approach is presented based on the use of frequency selective surfaces (FSS). These structures are commonly used to improve the performance of planar antennas within a certain frequency band. This paper shows how a FSS can be also used as a planar lens to increase the directivity of a single open waveguide keeping the low-profile and the ease of manufacturing of this kind of apertures. The proposed FSS is a multilevel metallic hole array (MHA) working at 8 GHz. Results show an increment of the maximum gain of 8 dBi with regard to a single open waveguide, with a small increment of the antennas height.

Low-Loss Circularly Polarized Periodic Leaky-Wave Antenna

This letter presents a periodic leaky-wave array antenna with circular polarization at millimeter-wave frequencies. The antenna is designed on the low-loss planar Goubau transmission line to maximize the radiation efficiency of the antenna. The unit cell of the array is formed by four dipoles located on both faces of the Goubau lines substrate. A prototype has been fabricated and measured. Experimental results show an impedance bandwidth above 15% for |S11| <; -10 dB and a 3-dB axial-ratio bandwidth of 7.6%. The radiation efficiency and maximum gain of the prototype are above 90% and 15.6 dBi, respectively, from 38 to 41 GHz. The maximum gain and the minimum axial ratio present the characteristic steering behavior of leaky-wave antennas.

Reconfigurable Slot-Array Antenna With RF-MEMS

Cylindrical near-field measurement systems are being widely demanded, especially for imaging applications at millimeter-wave frequencies. One of their most important drawbacks is the long time required to perform a full measurement of an antenna. To avoid multiple receivers, the probe is mechanically moved to the points where the field must be measured. The mechanical movement increases the time required to take a full measurement. The process may be sped up in several ways. This letter proposes the use of a pattern reconfigurable slot-array antenna as a probe. The switching among the different patterns is carried out electronically by RF-MEMS, which are placed over the different slots. Simulations and measurements of a model in the X-band are shown in this letter.

Rectangular waveguide with low metallic losses on side walls at THz

A rectangular waveguide for low-loss transmission at THz frequencies is proposed. The waveguide is based on the reflection of the fundamental mode on the side walls. By adding a stratified medium, a low impedance condition is obtained in the inner wall. Attenuation in side walls is eliminated.

New topologies of radial-line slot-dipole array antennas

This paper proposes new topologies of linearly polarized radial-line slot-array antennas (LP-RLSA) which uses slot-dipole pairs as radiating elements. Firstly, the basic design of the antenna with cancelling slots is considered and its benefits and drawbacks are highlighted. The evolution of this configuration leads to more convenient arrangements of the radiating and cancelling elements. Finally, a LP-RLSA composed of doubled rings demonstrates to be the most suitable topology for this kind of antennas.

Double-Fed multilevel frequency selective surface for low-profile planar lens

A multilevel frequency selective surface (FSS) with double feeding is presented in this paper. The FSS is formed by a non-uniform distribution of square holes on several metallic layers. The resulting structure works as a low-profile planar lens that enhances the radiation of the feeding open waveguides. This behavior provides a large rectangular amplitude distribution and a constant phase on the upper plane of the lens. As a result, a high gain and a good side lobe levels are obtained along a wide bandwidth. The gain pattern on main planes at 20.5 GHz and the S-parameters on the input ports for a 3-layer structure are shown in this paper. These results confirm the validity of the proposed structure as a starting point for larger arrays.

Dielectric Bed of Nails in Gap-Waveguide Technology at Millimeter-Wave Frequencies

Gap-waveguide technology is based on the guidance of a quasi-TEM mode between two PEC plates. The confinement is possible due to a PEC/PMC condition on laterals, which prohibits the propagation of waves on those directions. PMC condition is commonly created by means of a metallic bed of nails. This letter examines the possibility of using a dielectric bed of nails to impose the PMC condition. The use of such kind of nails may facilitate the insertion of active components. Measurements for a straight transmission line and a power divider are included to verify the correct behavior of the dielectric bed of nails.