George Hotopan

MICROSTRIP ANTENNA DESIGN BASED ON STACKED PATCHES FOR RECONFIGURABLE TWO DIMENSIONAL PLANAR ARRAY TOPOLOGIES

In this work, a probe fed microstrip antenna design for the implementation of two dimensional arrays with individually fed radiating elements is presented. The performance of the antenna element, both isolated and in a 4 £ 4 flxed array topology, is analysed using ADS and HFSS simulation software. Prototypes of the antenna element and of the array are manufactured and measured for the experimental validation of the design.

MILLIMETER WAVE MICROSTRIP MIXER BASED ON GRAPHENE

In this work, a millimeter wave microstrip frequency-mixer design based on graphene is presented. The desired frequency mixing behavior is obtained using a nonlinear component consisting in a microstrip line gap covered by a graphene layer. The circuit includes microstrip fllters that have been designed to obtain a high isolation between the input and output ports. The nonlinear behavior of the frequency mixer has been experimentally evaluated in the 38.6{40GHz input signal frequency range, for difierent values of the input power and local oscillator power.

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.

Defected Ground Structure for Coupling Reduction between Probe Fed Microstrip Antenna Elements

The mutual coupling between elements of a microstrip antenna design based on stacked patches has been studied in an array conflguration. In order to mitigate the mutual coupling, a defected ground structure based on narrow, closely spaced rectangular slots has been proposed. Two arrangements with three and flve slots have been studied and optimised in an array conflguration with 0:7‚0 element separation. For the experimental validation of the simulated results, prototypes of two element antenna arrays with both DGS designs, as well as without DGS, have been manufactured and measured.

Optimization of the Synchronization Bandwidth of Rationally Synchronized Oscillators Based on Bifurcation Control

In this work, a nonlinear technique for the optimization of the synchronization bandwidth of Rationally Synchronized Oscillators (RSO) is presented. The circuit is forced to operate near a Hopf bifurcation point which is created around the frequency of the input reference signal. Under this operating regime, the reference signal is strongly amplified and the synchronization bandwidth of the circuit is considerably improved. A 5–3GHz rationally synchronized oscillator has been optimized using the proposed method. The manufactured RSO provides a 5 MHz synchronization bandwidth with a reference signal power of −22 dBm, in good agreement with simulation results.

A novel phaseless frequency scanning based on indirect holography

A phase retrieval technique for multifrequency scattered field acquisition is presented in this paper. The proposed setup is based on indirect holography schemes so that it combines the desired signal with a known reference signal. The setup is used together with a two-dimensional frequency scanning (FS) antenna and, therefore, the positions of scatterers can be retrieved without the need of moving either the antenna or the objects.

Design and Analysis of a Multi-Carrier Tx-Rx System Based on Rationally Synchronized Oscillators for Localization Applications

In this work, a novel multi-carrier Tx-Rx system based on rationally synchronized oscillators to be used in RF-source localization applications is presented. The Tx subsystem is composed by two rationally synchronized oscillators, with different operation frequency, which share the reference signal. This signal is transmitted together with the one generated by the oscillators. In the Rx subsystem, the reference signal is provided by an oscillator which is synchronized with the received reference signal. According to the simulation results, with the proposed approach, the determination of the relative phase variation suffered by the transmitted signals, due to the propagation channel, can be achieved with an error less than 0.6◦. It is also shown that the dynamic response of the system can be optimized by properly selecting the operation point of all oscillators.

Millimeter Wave Subharmonic Mixer Implementation Using Graphene Film Coating

In this work, a subharmonic frequency mixer for millimeter wave applications has been designed. The mixing and multiplication phenomena are simultaneously achieved via a nonlinear component consisting in a microstrip line gap covered by a graphene fllm coating. The circuit structure is made up of various fllters, which have been optimized to ensure high port-to-port isolation. The nonlinear behavior of the subharmonic frequency mixer has been experimentally evaluated within the 39{40.5GHz RF frequency band. The frequency downconversion is achieved by mixing the RF signal with the second harmonic component of a 17.9GHz LO signal. Conversion losses are minimized by generating a return path for IF, through the use of a quarter wavelength open-ended stub.

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.