Analysis of an air-spaced patch antenna near 1800 MHz

Microstrip antennas are a type of printed antenna which consists of a patch on top of a grounded substrate. A major limitation for the performance of the patch antenna is the dielectric substrate. The idea of using air as dielectric was therefore considered to overcome that limitation because air has the lowest permittivity and no loss. The goal of this work is to build an air-spaced patch antenna, with the minimum resonant frequency at 1800 MHz and with a return loss of at least 10 dB. This work is novel because the air-spaced patch antenna has not been extensively studied. Existing literature on patch antennas with dielectric were used for the design of the antenna (dimensions of the patch, ground plane and height) and to understand the principles of operation of microstrip patch antennas in general. Simulations using the NEC code and experiments in the RF laboratory were used for this air-spaced patch antenna study. The Numerical Electromagnetic Code (NEC) was used as the simulation tool in this work. The air-spaced patch antenna was simulated to find a trend for the variation of the return loss and impedance with the resonant frequency. Simulation also helped determine cases that will not be meaningful to explore in the experiment. The experiment was done in the RF laboratory of Marquette University College of Engineering. Two procedures were used to calculate the patch dimensions using two different sources ([2], [3]). They lead to two patch antennas that were tested. For each antenna, the height of the dielectric substrate and the recess feed distance were varied. Antenna 2 (procedure 2 – [3]) provided the best results with a resonant frequency of 1800 MHz and a return loss of 21 dB. It was found that the error between experimental and simulation resonant frequency is generally 5% or less. This error increases as the dielectric height increases, and as the recess distance increases. Simulation results roughly follow the experimental results trend

High-Order Dual-Port Quasi-Absorptive Microstrip Coupled-Line Bandpass Filters

In this article, we present the first demonstration of distributed and symmetrical all-band quasi-absorptive filters that can be designed to arbitrarily high orders. The proposed quasi-absorptive filter consists of a bandpass section (reflective-type coupled-line filter) and absorptive sections (a matched resistor in series with a shorted quarter-wavelength transmission line). Through a detailed analysis, we show that the absorptive sections not only eliminate out-of-band reflections but also determine the passband bandwidth (BW). As such, the bandpass section mainly determines the out-of-band roll-off and the order of the filter can be arbitrarily increased without affecting the filter BW by cascading more bandpass sections. A set of 2.45-GHz one-, two-, and three-pole quasi-absorptive microstrip bandpass filters are designed and measured. The filters show simultaneous input and output absorption across both the passband and the stopband. Measurement results agree very well with the simulation and validate the proposed design concept

Monitoring thermal ablation via microwave tomography. An ex vivo experimental assessment

Thermal ablation treatments are gaining a lot of attention in the clinics thanks to their reduced invasiveness and their capability of treating non-surgical patients. The effectiveness of these treatments and their impact in the hospital's routine would significantly increase if paired with a monitoring technique able to control the evolution of the treated area in real-time. This is particularly relevant in microwave thermal ablation, wherein the capability of treating larger tumors in a shorter time needs proper monitoring. Current diagnostic imaging techniques do not provide effective solutions to this issue for a number of reasons, including economical sustainability and safety. Hence, the development of alternative modalities is of interest. Microwave tomography, which aims at imaging the electromagnetic properties of a target under test, has been recently proposed for this scope, given the significant temperature-dependent changes of the dielectric properties of human tissues induced by thermal ablation. In this paper, the outcomes of the first ex vivo experimental study, performed to assess the expected potentialities of microwave tomography, are presented. The paper describes the validation study dealing with the imaging of the changes occurring in thermal ablation treatments. The experimental test was carried out on two ex vivo bovine liver samples and the reported results show the capability of microwave tomography of imaging the transition between ablated and untreated tissue. Moreover, the discussion section provides some guidelines to follow in order to improve the achievable performances

Microwave antennas for infrastructure health monitoring

Infrastructure health monitoring (IHM) is a technology that has been developed for the detection and evaluation of changes that affect the performance of built infrastructure systems such as bridges and buildings. One of the employed methods for IHM is wireless sensors method which is based on sensors embedded in concrete or mounted on surface of structure during or after the construction to collect and report valuable monitoring data such as temperature, displacement, pressure, strain and moisture content, and information about defects such as cracks, voids, honeycombs, impact damages and delamination. The data and information can then be used to access the health of a structure during and/or after construction. Wireless embedded sensor technique is also a promising solution for decreasing the high installation and maintenance cost of the conventional wire based monitoring systems. However, several issues should be resolved at research and development stage in order to apply them widely in practice. One of these issues is that wireless sensors cannot operate for a long time due to limited lifetime of batteries. Once the sensors are embedded within a structure, they may not be easily accessible physically without damaging the structure. The main aim of this research is to develop effective antennas for IHM applications such as detection of defects such as gaps representing cracks and delaminations, and wireless powering of embeddable sensors or recharging their batteries. For this purpose, modelling of antennas based on conventional antipodal Vivaldi antennas (CAVA) and parametric studies are performed using a computational tool CST Studio (Studio 2015) including CST Microwave Studio and CST Design Studio, and experimental measurements are conducted using a performance network analyser. Firstly, modified antipodal Vivaldi antenna (MAVA) at frequency range of 0.65 GHz – 6 GHz is designed and applied for numerical and experimental investigations of the reflection and transmission properties of concrete-based samples possessing air gap or rebars. The results of gap detection demonstrate ability of the developed MAVA for detection of air gaps and delivery of power to embeddable antennas and sensors placed at any depth inside 350-mm thick concrete samples. The investigation into the influence of rebars show that the rebar cell can act as a shield for microwaves if mesh period parameter is less than the electrical half wavelength. At higher frequencies of the frequency range, microwaves can penetrate through the reinforced concrete samples. These results are used for the investigating the transmission of microwaves at the single frequency of 2.45 GHz between the MAVA and a microstrip patch antenna embedded inside reinforced concrete samples at the location of the rebar cell. It is shown that -15 dB coupling between the antennas can be achieved for the samples with rebar cell parameters used in practice. Secondly, a relatively small and high-gain resonant antipodal Vivaldi antenna (RAVA) as a transmitting antenna and modified microstrip patch antenna as an embeddable receiving antenna are designed to operate at 2.45 GHz for powering the sensors or recharging their batteries embedded in reinforced concrete members. These members included reinforced dry and saturated concrete slabs and columns with different values of mesh period of rebars and steel ratio, respectively. Parametric study on the most critical parameters, which affect electromagnetic (EM) wave propagation in these members, is performed. It is shown that there is a critical value of mesh period of rebars with respect to reflection and transmission properties of the slabs, which is related to a half wavelength in concrete. The maximum coupling between antennas can be achieved at this value. The investigation into reinforced concrete columns demonstrates that polarisation configuration of the two-antenna setup with respect to rebars and steel ratios as well as losses in concrete are important parameters. It is observed that the coupling between the antennas reduces faster by increasing the value of steel ratio in parallel than in vertical configuration due to the increase of the interaction between electromagnetic waves and the rebars. This effect is more pronounced in the saturated than in dry reinforced concrete columns. Finally, a relatively high gain 4-element RAVA array with a Wilkinson power divider, feeding network and an embeddable rectenna consisting of the microstrip patch antenna and a rectified circuit are developed. Two wireless power transmission systems, one with a single RAVA and another with the RAVA array, are designed for recharging batteries of sensors embedded inside reinforced concrete slabs and columns with different configurations and moisture content. Comparison between these systems shows that the DC output voltage for recharging commonly used batteries can be provided by the systems with the single RAVA and the system with the RAVA array at the distance between the transmitting antenna and the surface of reinforced concrete members of 0.12 m and 0.6 m, respectively, i.e. the distance achieved when the array is 5 times longer that the distance achieved with a single antenna

Millimeter Wave Radar Object Detection Through Frequency Selective Surfaces

Millimeter wave (mmWave) radar systems are a leading technology in autonomous vehicle object sensing. The radar’s ability to detect surrounding objects is critical to its performance. One method of increasing object detection performance is to enhance object visibility. Frequency selective reflectors can increase object visibility. This work examines the performance of a mmWave 77 GHz radar system developed by Texas Instruments in conjunction with frequency selective surfaces. Two bandpass frequency selective surfaces are designed and fabricated using a loaded cross aperture configuration to analyze their application to object detection. The chosen design frequencies are 8 GHz and 79 GHz. The frequency selective surfaces are designed and simulated in 3-D electromagnetic simulation software, High Frequency Structure Simulator (HFSS). The frequency selective surfaces are fabricated on 127μm thick FR4 dielectric. The 8 GHz frequency selective surface demonstrates bandpass center frequency at 8.12 GHz. The 8 GHz and 79 GHz frequency selective surface reflection characteristics are compared to a copper sheets with the same physical cross section as each respective design. Although different testing methodology is used for each design, both frequency selective surfaces demonstrate bandpass characteristics at their respective design frequencies

Micro-structured ferroelectric superlattice for efficient acousto-optic devices

In this thesis we have investigated and proposed acoustic superLattices (ASLs) made of periodically poled ZX-cut lithium niobate (PPLN) associated ith coplanar electrodes as an effective alternative for surface acoustic wave (SAW) generation. In order to examine the acoustic transduction in the SL transducer we have developed and employed two modeling techniques. i.e . scalar approximation and finite element method (FEM) analysis (2-D nd 3-D modeling) implemented in COMSOL MULTIPHYSICS. Both techniques give similar results with respect to the characteristics of generated SAW modes. The calculated results obtained with the 3-D FEM simulation confirmed the Rayleigh nature of the generated SAW, showing that the excited SAW in the ASL is similar to that of the standard interdigitated transducer (IDT). From the propagation analysis in 2-D FEM simulation. we obtained that in addition to the SAW, the ASL transducer excites longitudinal bulk acoustic wave (L-BAW). Moreover. the 2-D model showed that the SAW excited by the ASL transducer does not propagate but it is rather confined within the transducer. Several ASL transducers, with different lattice periods, have been realized and characterized, also to validate the modeling and design tools . One and two-portelectrical measurements have been performed to evaluate the electro-acoustic response. In addition laser interferome try has been carried out o determine the out-of-plane component of the SAW displacement. With respect to the standard IDT configuration using the same crystal orientation, he efficiency of the SAW generation in the proposed designs is similar, while, for the same grating period, the resonance frequency that can be achieved is two times larger. In addition to the SAW, unlike its lOT counterparts, the ASL transducer can excite the L-BAW, as it had been predicted by the modeling. The two-port measurements have shown that the SAW signal collected at the receiver is small, indicating that the SAW energy remains essentially confined within the transmitter. This experimental result too is in agreement with the aforementioned theoretical predictions. After the experimental validation of the modeling, we designed and fabricated acousto-optic (AO) filters incorporating the ASL transducer. ASL struc tures with 20 tm period and coplanar electrodes have been realized along with 6 m wide Ti-LiNb03 optical channel waveguide. In that way monolithic and integrated (waveguide) SAW based AO filters and L-BAW based bulk AO filters have been demonstrated. As for integrated SAW based 0 filter, a 3-dB optical bandwidth of 2.5 nm, center wavelength of 1456 nm, and -20 dB distance of 14.49 nm are obtained at the SAW resonance frequency of 189.94 MHz. Such filter requires 1 W RF power to achieve nearly complete polarization conversion. As for the bulk AO filter. a center Wavelength of 1472.5 nm is measured at the L-BAW resonance frequency of 328 MHz. In the bulk AO filter. full conversion cannot be reached even at RF power up to 2 W. Comparing to the integrated (waveguide) filter. the efficiency of the bulk filter is significantly lower. The AO filter's central wavelength can be tuned by changing the RF power. We investigated several designs to improve the AO filter efficiency. By optimizing the ASL transducer (coplanar electrodes with electrode width of 70 urn and gap of 20 t m), nearly complete optical switching at very low electrical powers (50mW) has been obtained, this corresponding to an improvement factor of 20 compared to previous results. An appropriate mass-loading, placed on the surface and in between the electrodes of a coplanar LiNb03 ASL, has allowed achieving strong lateral confinement of the acoustic field, thus leading to a significant improvement of the AO filter performance

Design and Testing of Simple, Electrically Small, Low-Profile, Huygens Source Antennas with Broadside Radiation Performance

© 2016 IEEE. The efficacy of a simple, electrically small, low-profile, Huygens source antenna that radiates in its broadside direction is demonstrated numerically and experimentally. First, two types of electrically small, near-field resonant parasitic (NFRP) antennas are introduced and their individual radiation performance characteristics are discussed. The electric one is based on a modified Egyptian axe dipole NFRP element; the magnetic one is based on a capacitively loaded loop NFRP element. In both cases, the driven element is a simple coax-fed dipole antenna, and there is no ground plane. By organically combining these two elements, Huygens source antennas are obtained. A forward propagating demonstrator version was fabricated and tested. The experimental results are in good agreement with their analytical and simulated values. This low profile, ∼0.05λ0, and electrically small, ka = 0.645, prototype yielded a peak realized gain of 2.03 dBi in the broadside direction with a front-to-back ratio of 16.92 dB. A backward radiating version is also obtained; its simulated current distribution behavior is compared with that of the forward version to illustrate the design principles

Fibre-meshed Textile Electromagnetic Structures

This thesis investigated novel textile electromagnetic structures fabricated by a commercial computerized knitting machine. Different electronics such as elliptical waveguides, slotted waveguide antennas (SWA) and frequency selective surfaces (FSS) working at microwave band had been realized with fully textile materials. Knitted polyester was used as a dielectric and silver embedded yarn was knitted to create conducting patterns. Most of the textile electromagnetic structures in this thesis were the first time proposed to the public. Their performances were studied in both simulation and measurement