C. Vazquez

Near Field Characterization of an Imaging System Based on a Frequency Scanning Antenna Array

This contribution describes the concept of frequency scanning for imaging applications. The designed frequency scanning antenna array, which works in Ku frequency band, is used for the sectoral illumination of the scene under investigation, enabling the recovery of information restricted to the selected area. While the proposed idea simplifies beam scanning techniques with respect to mechanical or electrically-controlled scanning systems, the price-to-pay is the limitation on the amount of scattered field information. The near field radiation of the frequency scanning antenna array is characterized through an equivalent source model to assess accurately the incident field used in the imaging algorithm. This analysis also enables the evaluation of the frequency steering performance of the antenna in the near field, validating its use for the proposed application.

Microwave Frequency Tripler Based on a Microstrip Gap with Graphene

In this work, a 3x frequency multiplier implemented with a microstrip gap covered with defoiled graphene is presented. The behaviour of the multiplier has been experimentally characterized for the input signal frequency band between 2.5 GHz and 5 GHz. Several graphene-based tripler devices have been implemented with different values for the line width and gap of the microstrip line in order to evaluate the influence of these parameters on the power of the output signal. The output power of the different devices has been measured in the band from 7.5 GHz to 15 GHz for different values of the input power. An almost flat frequency behaviour for the output power is observed along the whole input frequency band.

Submillimeter-Wave Frequency Scanning System for Imaging Applications

A new submillimeter-wave imaging system based on the frequency scanning concept is presented. Using significantly less information than beam-steering techniques, frequency scanning-based imaging systems are able to provide angular information in range-based radar systems which do not allow mechanical or electronic beam steering. Several strategies have been adopted to overcome the low dynamic range due to the propagation losses and non-specular reflection on the object-under-test. Moreover, the system is not only capable of detecting the placement of the objects, but also their profile. In this sense, an imaging application showing the system capabilities for the detection of objects concealed under clothes is presented. Results using 1-D FSAA allowing profile imaging are shown, proving the validity of the proposed system.

Frequency scanning probe for microwave imaging

Microwave imaging techniques have attracted considerable attention as a result of their multiple potential applications in different fields, such as industrial nondestructive testing, detection of buried or concealed objects, noninvasive medical diagnostics, etc. Different theoretical methods and measurement setups have been proposed, based on illuminating the object under investigation with single frequency [1], multi-frequency [1, 2, 3] or Ultra Wide Band (UWB) signals [4]. The scattered radiation is usually measured in different spatial directions (angular diversity), in order to increase the image resolution.

Receiving Phased Antenna Array Based on Injection-Locked Harmonic Self-Oscillating Mixers

A 4 times 1 element receiving phased antenna array is presented with phase-shifter elements based on injection-locked harmonic self-oscillating mixers. Each phase-shifter element provides the double functionality of variable phase-shifter and down-converter. The phase-shifts applied to the input signals coming from the different antenna patch elements can be selected by dc control signals in a continuous range of 450deg. The required dc control voltages are calculated for the different incident angles by means of harmonic balance simulations. The influences of phase-shift and conversion gain errors on the beam-steering frequency performance of the antenna are studied. Also illustrated is how the phase-shifter parameters can be optimized in order to minimize the frequency scanning. A 4 times 1 element receiving phased antenna array, with an input frequency band centered at 11.25 GHz and the output frequency band centered at 1.5 GHz, has been manufactured for the experimental validation of the simulated results. A beam scanning range from -23deg to 23deg has been experimentally obtained.

Frequency Scanning Array Composed of Antipodal Linearly Tapered Slot Antennas

In this work, a frequency scanning array of antipodal linearly tapered slot antennas is presented. The system is capable of performing beam steering from –11 to 10 degrees while sweeping the frequency from 8.25 GHz to 11.5 GHz. The beam scanning is achieved by means of a specially designed feeding network that divides the power and introduces the proper phase shift for each antenna port in the frequency range of interest. Experimental results showing the full array behaviour are also presented.

Frequency scanning slotted waveguide in the sub-millimeter wave band

In this work, a waveguide slotted antenna array working in the sub-millimeter wave band is presented. The antenna performs beam tilting from 68 to 89 degrees in the H-plane while sweeping the frequency from 240 GHz to 310 GHz. Sixteen rectangular slots have been cut in the wide surface of a standard WR-3 brass metal rectangular waveguide to obtain the desired behavior. The antenna has been fabricated combining laser and mechanical prototyping machinery. Experimental results showing the main waveguide slotted antenna array characteristics are also presented.

Novel polarization agile microstrip antenna

A novel agile antenna based on an injection-locked third harmonic self-oscillating mixer is presented in this paper. The phase-shift can be tuned, by varying the varactor control voltage, in range of 450deg. The active circuit allows changing the axial ratio of a dual-polarization antenna. The antenna can switch between radiating RHCP, LHCP and linear polarization with good purity.

Design of a submillimeter microstrip array for beam-scanning applications

A microstrip array antenna with beam-steering capabilities is presented for imaging applications working in the frequency range of 240–279 GHz. A 33 degrees beam-scanning range is achieved. The feeding network allows to change the beam-pointing angle from θ= −8° to θ= 25° while the frequency scanning is performed.

Receiving Polarization Agile Active Antenna Based on Injection Locked Harmonic Self Oscillating Mixers

A polarization agile active antenna with phase shifter elements based on injection locked third harmonic self oscillating mixers is presented. This phase shifting topology provides the double functionality of continuous range phase shifter and downconverter. The phase shift value introduced by each circuit can be easily tuned through a DC voltage within a theoretical continuous range of 450° . The behavior of the isolated phase shifter circuit is studied, both as a function of the control voltage and versus frequency, through harmonic balance and envelope transient simulations. The polarization tuning performance of the complete active antenna is simulated, analyzing the impact of the operating parameters of the phase shifter on the overall behavior. A receiving polarization agile antenna with an input frequency band centered at 11.25 GHz and an output frequency band centered at 1.5 GHz has been manufactured for the experimental validation of the simulated results. A continuous range of polarization tuning has been observed, including two orthogonal linear polarizations along with left hand and right hand circular polarization.