Ces travaux de recherche visent à introduire et à généraliser l'utilisation des systèmes différentiels dans les applications RF et Micro-ondes. En particulier, dans la conception de dispositifs pour les fonctions d'amplification à faible bruit. Pour cela, il est indispensable de développer des outils fiables et rigoureux tels que le formalisme des modes mixtes introduit par Bockelman. C'est dans cet esprit que s'inscrit la première phase de l'étude. Le but étant de développer un outil pour l'analyse de la stabilité linéaire des systèmes différentiels à trois et quatre accès. Par ailleurs, les interfaces des circuits numériques ultra-rapides (CNA) sont de topologie différentielle. Ce qui augmente encore l'intérêt de disposer de méthodes rigoureuses pour la conception des systèmes différentiels. Dans la deuxième phase de l'étude la problématique de l'intégration système des CNAs dans les nouvelles générations des chaines de transmission RF des satellites de télécommunications est traitée. La conception d'un balun actif large bande capable d'assurer la conversion de la sortie analogique différentielle du CNA en sortie simple accès (Single-ended) référencée par rapport à la masse est détaillée. Afin de répondre aux contraintes d'intégration, une technologie BiCMOS SiGe 0.25 μm est utilisée pour son implémentation. Les performances obtenues par la mesure de la puce Silicium réalisée respectent les spécifications techniques initiales de l'application. Ce qui permet de valider la méthodologie de conception utilisée. L'objectif final est d'être capable d'intégrer sur un même substrat monolithique le CNA et le balun actif large bande de conversion de modes. / This research work aims to develop analytical tools for the analysis and design of differential systems. While the use of differential circuits in RF reception/transmission chains is increasingly growing, there is no accurate method to study their stability. First the common tools to study RF differential components are introduced. Then, the development of a CAD tool that can be rigorously used to investigate the extrinsic stability of linear differential systems is presented. Finally this tool is applied to study the stability of in a real case. The design addresses a three port component that aims to convert the differential output of digital to analog converter into a single-ended access for a spatial application purpose. This broadband active balun is designed using BiCMOS technology. Measurements are performed and the results are in good agreement with the simulation. All the initial specications are achieved, which validate the approach developed in this study.

This dissertation addresses the design of monolithically integrated phase shifters at S- and L- frequency bands using a commercially available GaAs process from Triquint. The focus of the design is to operate over a wide bandwidth with full 360° phase shift capability, 50 Ω input/output impedance match and low RMS phase and gain errors. The first version of the design is based on passive all-pass phase shifters integrated with wideband amplifiers to compensate for insertion loss. This design uses a 4-bit system to achieve the required phase shift and each bit consists of 3 sections of all-pass filters designed at separate frequencies within the 0.8 – 3 GHz band. Simulation results show a complete 360° phase shift with RMS gain error of less than 0.6 dB and RMS phase error of less than 2.5°. The system is also shown to achieve good input and output impedance matching characteristics. However, the fabricated prototype fails to perform with full functionality due to the excessive number of passive inductors in the design and the resulting mutual coupling. The mutual coupling issue could be solved by spacing out the layout to allow more separation among the inductors. Unfortunately, in the S- and L-bands, this is not an option for this research work as the fabricated design already uses the maximum allowed chip size as determined by the foundry. In addition, larger chip sizes considerably increase the cost in practical applications. To address the challenging needs of small size, wide bandwidth and low frequency applicability, the second design introduced in this dissertation proposes a novel phase shifter implementation that utilizes tunable active differential inductors within all-pass networks. The inductor tuning is used to achieve phase shifts up to 180⁰. A switchable active balanced to unbalanced transition circuit (balun) is included in front of the all-pass network to complement its phase shift capability by another 180°. In addition, the all-pass network is followed by a variable gain amplifier (VGA) to correct for gain variations among the phase shifting states and act as an output buffer. Although active inductors have been previously used in the design of various components, to the best of our knowledge, this is the first time that they have been used in an all-pass phase shifter. The approach is demonstrated with an on-chip design and implementation exhibiting wideband performance for S and L band applications by utilizing the 0.5 µm TriQuint pHEMT GaAs MMIC process. Specifically, the presented phase shifter exhibits 1 × 3.95 mm2 die area and operates within the 1.5 GHz to 3 GHz band (i.e. 2:1 bandwidth) with 10 dB gain, less than 1.5 dB RMS gain error and less than 9° RMS phase error. Comparison with the state-of-the-art MMIC phase shifters operating in S and L bands demonstrates that the presented phase shifter exhibits a remarkable bandwidth performance from a very compact footprint with low power consumption. Consequently, it presents an important alternative for implementation of wideband phase shifters where all-passive implementations will consume expensive die real estate.

Investigation of the Double-Y Balun for Feeding Pulsed Antennas Jaikrishna Venkatesan 232 Pages Directed by Dr. Waymond Scott, Jr. In this research, a double-y balun implemented with coplanar waveguide (CPW) and coplanar strip (CPS) was investigated for use with pulsed antennas. The balun was modeled using two commercial electromagnetic simulators: Momentum and HFSS. Using these numerical solvers, design information such as the design of CPW bridges, aspect ratio of the double-y balun, and stub lengths of the CPW and CPS open and short stubs were studied. A dipole, along with the outer conductor of a coaxial line was modeled in NEC. The model was used to study the currents along the arms and feedline of balanced and unbalanced dipoles. Normalized amplitude patterns were generated along the azimuth and elevation planes for balanced and unbalanced dipoles. These patterns were used later for comparison with measured patterns. Experimental work was conducted to measure the performance of a double-y balun designed to feed a resistively loaded V-dipole. The performance of the balun was investigated via VSWR, insertion loss, and antenna pattern measurements. Antenna pattern measurements along the azimuth plane were conducted for a 5 cm dipole fed without a balun, a 5 cm dipole fed with the double-y balun, a 5 cm dipole fed with the sleeve balun, a 12 cm dipole fed without a balun, and a 12 cm dipole fed with the double-y balun. The dipoles fed without a balun were fed directly with a 50 W coaxial line. An optical link, consisting of a laser modulator (LM) unit and a laser receiver (LR) unit, was constructed to measure the patterns along the elevation plane of the above dipoles. Resulting patterns agreed closely with patterns generated with NEC models. In addition, the patterns of a resistively loaded V-dipole were measured along the E-plane using the optical link. The measured patterns for the V-dipole were compared with numerical results obtained from literature. The experimental work conducted in this research illustrates the improvement obtained in the patterns of a dipole and a resistively loaded V-dipole with the use of the double-y balun.

In recent years, passive radio frequency (RF) tags that communicate using modulated backscatter radiation have shown great potential for use in inventory management, parcel and postal tracking, for use as remote sensors, and in a host of other Radio Frequency Identification (RFID) applications. However, for the widespread use of these tags to become reality, much basic research is needed to reduce the cost, increase the range, and increase the reliability of the RF tag. This research seeks to enhance the performance of passive RF tags by developing a series of tests, or radio assay, to measure the following: the performance of RF tag antennas as a function of antenna material and manufacturing technique and the antenna performance when attached to various materials. The radio assay experiments are designed for RF tag antennas that operate in the far field of the tag reader and communicate using modulated backscatter radiation at 915 MHz. Three flexible, folded dipoles, printed on plastic substrates, were measured in the radio assay experiments. The results of the experiments include the following: the antenna gain penalty (relative to a baseline antenna) for each antenna material and manufacturing technique, the antenna gain penalty (relative to the free space antenna gain) due to material losses when the tag antenna is attached to an object, and the benefits (in terms of antenna gain) of tuning each tag antenna to the material to which it is attached. The results are presented in a form to aid RF engineers in the design of RF tag system link budgets.

Advances in technology have placed a great emphasis on the design of broadband antennas as well as antenna miniaturization to cope with the demands of making electronic and handheld communication devices smaller and more efficient. In this thesis, the design and fabrication of a frequency independent antenna and a narrow-band planar microstrip Balun are presented. An analysis of frequency selective surfaces is also introduced in order to demonstrate their capability to miniaturize antenna thickness. Lastly, s-parameters measurements and efficiency characterization are performed to determine the radiation properties of surface mount chip inductors in order to determine the feasibility of using them as electrically small antennas.Two types of frequency independent antennas are considered due to their planar geometries, the Equiangular and Archimedean spiral antennas. Frequency independent antennas are radiating devices that have frequency independent impedance and pattern properties because their shape is specified only in terms of angles.The Balun is designed to meet the need of a feeding element for the Archimedean spiral antenna. A Balun is a three port device that connects an unbalanced transmission line such as a coaxial line to a balanced feed line such as the one required by two-arm spiral antennas. The Balun discussed in this work is designed to operate at 2.4 GHz with a 200 MHz bandwidth and to transform the antenna input impedance to a 50-ohm reference impedance. The main characteristics from this device that distinguish it from commercially available structures are its low cost, planarity, and compact footprint. The balancing capability of this Balun is shown by the close agreement between the measured and simulated results. Antennas can be potentially miniaturized in the z-direction by replacing the PEC ground plane separated from the antenna by a lambda /4 thick substrate with a frequency selective surface (FSS) structure that allows the ground plane conductor to be in close proximity to the antenna without affecting its radiation performance. The FSS layer operating at 2.4 GHz presented in this thesis is static (not tuned) and thus the overall bandwidth reduces approximately to the bandwidth obtained with the narrow-band Balun.

In this thesis, a low-profile, high-gain, ultra-wideband (UWB) planar dipole antenna is presented for radar imaging applications. The antenna is loaded with open complementary double concentric split-hexagonal-ring resonators (LC tank) and chip resistors, and backed with a novel double-layer FSS reflector for gain enhancement. A broadband microstrip to parallel-plate transformer is designed as the feeding structure of the antenna to provide impedance matching and balanced-to-unbalanced transition. The measurement results show the proposed antenna operates over the frequency bandwidth of 0.65-3.8 GHz with S11< -10 dB (VSWR) and smooth gains in the range of 6.2-9 dBi.

The work is focused on antennas integrated into the helmet. They preferred planar antennas with different polarization and different feed. They consider possible positions on the helmet, or into helmet.

In this dissertation, some multi-function and flexible RF/microwave devices have been studied to solve the issues in the modern microwave system designs. First, a power divider with two functions is proposed. The first function is a zero-phase delay power divider using zero-phase impedance transformer. The second function is a power divider with impedance transforming property. To achieve the first function, the two arms are treated as zero-phase impedance transformers. When the phase requirement is relaxed, the second function is obtained. Shunt transmission line stubs are employed to connect the isolation resistor, which provides great flexibility in the design. Then, a balun with transparent termination impedance and flexible open arms is designed. The design parameters of the balun are independent to the port impedance. This property allows the balun to work with different system impedances. Furthermore, the two output ports of the balun do not need to be connected together, which enables the device to have a very flexible structure. Finally, the continuous research of a tunable/reconfigurable coupler with equal output impedance is presented. In addition to the tunable/reconfigurable responses, unequal output impedance property is added to the microstrip line coupler. To shrink the size at the low frequency and make it easy for fabrication at higher frequency, the coupler is redesigned using lumped components. To validate the design theories, simulations are carried out. Moreover, prototypes of the power divider and the balun are fabricated and characterized. The simulation and measurement results match well with the theoretical calculation.

No description available.

As wireless devices and radar systems become more ubiquitous, there is a growing need for wideband multi-standard RF-SOCs. To enable the advantages of multi-standard systems, reconfigurable RF front ends are needed. Because of the large number of RF signals in wideband systems, tunability and linearity become important parameters. Prior work has shown tunable LC filters to be advantageous in the microwave regime. A balanced-to-unbalanced (balun) transformation circuit is required to support the differential nature of a tunable LC filter. An active balun that also performs as a transconductor to drive the LC tank would relax the design requirement for the LNA and remove a passive balun that would have to precede the LNA. This thesis discusses the linearization of active baluns and presents a comparison between two 4 to 7 GHz tunable BPF designs with active baluns implemented in 0.18 μm SiGe BiCMOS technology. Fourth order filtering is achieved by subtracting two 2nd order LC-tanks. This approach allows 3-dB bandwidth to be tunable from 10% to 20%. In each design, a linearized input active balun is employed to drive the LC-tanks from a single-ended input while preserving noise figure and IIP3 performance. Two different linearization techniques are applied for the balun designs. Simulated NF ranges from 7.5 to 13 dB and IIP3 averages about 5 dBm with the peak value of 21 dBm. / Master of Science / As wireless devices and radar systems become more ubiquitous, there is a growing need for Radio Frequency (RF) integrated circuits that can support multiple frequency bands and standards. Because of the large number of RF signals, robust tunability and power handling of the electronics become important parameters. Power handling is important because the amplifier and the filter can generate distortions if the power going through them becomes too high. Prior work has shown integrated tunable inductor-capacitor (LC) resonance based filters to be advantageous in the microwave frequency regime compared to integrated switched capacitor based filters. A balancedto-unbalanced (balun) conversion of the RF signals is needed to support the differential nature of the LC resonators. This thesis discusses transistor-based balun designs that can be integrated into front-end LC filter chips. The goal is to reduce distortion in the filter under the present of large number of RF signals and to keep noise of the circuit in reasonable range. The designs are implemented in 0.18 μm SiGe BiCMOS integrated circuit technology and simulated in commercial computer aided design software; predicted performance is competitive with the state of the art. The fabricated chips will be characterized in future work.