Compensation technique for nonlinear distortion in RF circuits for multi-standard wireless systems

Recent technological advances in the RF and wireless industry has led to the design requirement of more sophisticated devices which can meet stringent specifications of bandwidth, data rate and throughput. These devices are required to be extremely sensitive and hence any external interference from other systems can severely affect the device and the output. This thesis introduces the existing problem in nonlinear components in a multi-standard wireless system due to interfering signals and suggests potential solution to the problem. Advances in RF and wireless systems with emerging new communication standards have made reconfigurablility and tunability a very viable option. RF transceivers are optimised for multi-standard operation, where one band of frequency can act as an interfering signal to the other band. Due to the presence of nonlinear circuits in the transceiver chains such as power amplifiers, reconfigurable and tunable filters and modulators, these interfering signals produce nonlinear distortion products which can deform the output signal considerably. Hence it becomes necessary to block these interfering signals using special components. The main objective of this thesis is to analyse and experimentally verify the nonlinear distortions in various RF circuits such as reconfigurable and tunable filters and devise ways to minimize the overall nonlinear distortion in the presence of other interfering signals. Reconfigurbality and tunablity in filters can be achieved using components such as varactor diodes, PIN diodes and optical switches. Nonlinear distortions in such components are measured using different signals and results noted. The compensation method developed to minimize nonlinear distortions in RF circuits caused due to interfering signals is explored thoroughly in this thesis. Compensation method used involves the design of novel microstrip bandstop filters which can block the interfering signals and hence give a clean output spectrum at the final stage. Recent years have seen the emergence of electronic band gap technology which has “band gap” properties meaning that a bandstop response is seen within particular range of frequency. This concept was utilised in the design of several novel bandstop filters using defected microstrip structure. Novel tunable bandstop filters has been introduced in order to block the unwanted signal. Fixed single-band and dual-band filters using DMS were fabricated with excellent achieved results. These filters were further extended to tunable structures. A dual-band tunable filter with miniaturized size was developed and designed. The designed filters were further used in the compensation technique where different scenarios showing the effect of interfering signals in wireless transceiver were described. Mathematical analysis proved the validation of the use of a bandstop filter as an inter-stage component. Distortion improvements of around 10dB have been experimentally verified using a power amplifier as device under test. Further experimental verification was carried out with a transmitter which included reconfigurable RF filters and power amplifier where an improvement of 15dB was achieved

Compact reconfigurable MIMO antenna for 5G and Wi-Fi applications

Four miniaturized four-element multiple-input multiple-output (MIMO) antenna designs are proposed, designed, and fabricated with dimensions of 26 mm x 26 mm x 0.8 mm each. The first MIMO design operates at 3.5 GHz, while the second operates at 5.2 GHz. The first and second designs are combined into a third design that can be reconfigured to operate at either 3.5 GHz or 5.2 GHz. A new concept of balance is introduced to address the issue of small ground faced by the previous designs. This concept is applied to the third antenna design, resulting in a fourth design of reconfigurable MIMO operating at 5.2 GHz or 3.5 GHz. The antenna demonstrates good impedance matching at both operating frequencies, with isolation levels of approximately 25 dB and 21 dB, envelope correlation coefficients (ECC) less than 0.0001, diversity gain (DG) of around 10 dB at both frequencies, and peak realized gains of 3.5 dBi at 3.5 GHz and 4 dBi at 5.2 GHz. The radiation efficiency of the fourth compact antenna design is approximately 88% at 3.5 GHz and 91% at 5.2 GHz. The measured results show excellent agreement with the simulated results for all four antenna designs

Fixed And Selectable Multiband Isolation Of Double Pole Double Throw Switch Using Transmission Line Stub Resonators For Wimax And Lte

A novel selectable multiband isolation of Double Pole Double Throw (DPDT) switch with switchable transmission line stub resonators has been proposed for applications of WiMAX and LTE in 2.3 and 3.5 GHz bands. In this paper, two DPDT switch designs are proposed; the first design is a fixed DPDT switch, and the second is a selectable DPDT switch. The second design allows selecting only one band and unselecting the other or selecting both of them. However, the first design does not allow so. The transmission line stub resonator used in this design is an open stub resonator with quarter wave of the electrical length. By using a simple mathematical model, the theory of the transmission line stub resonator was discussed where it can be cascaded and resonated at center frequencies of 2.3 and 3.5 GHz. Moreover, the cascaded transmission line stub resonators can be reconfigured between allpass and bandstop responses using discrete PIN diodes. The key advantage of the proposed DPDT with switchable transmission line stub resonators is a multiband high isolation with minimum number of PIN diodes. Therefore, the simulated and measured results showed less than 3 dB of insertion loss, greater than 10 dB of return loss and higher than 30 dB of multiband isolation in 2.3 and 3.5 GHz bands

A miniaturized reconfigurable antenna for modern wireless applications with broadband and multi-band capabilities

A miniaturized frequency reconfigurable antenna, designed with a simple geometric layout on an FR-4 substrate measuring 15 × 21 mm2, offers versatility for various wireless applications is proposed in this paper. By adjusting biasing conditions of integrated PIN diodes, the antenna can operate in three distinct modes: wideband, dual band, and triband configurations. The antenna demonstrates satisfactory gain and presents an omnidirectional radiation pattern. Verification of the antenna’s functionality involved building a prototype and subjecting it to testing. The confirmed compatibility of the antenna with modern wireless requirements, including the need for small antennas capable of operating across multiple bands and modes, is substantiated by the close agreement between simulated and measured results

Antena de placa suspendida con polarización circular y sentido de giro configurable

Introducción: Las antenas con polarización circular (APC) permiten reducir el efecto de rotación de Faraday debido a la presencia de la ionosfera, el cual ocasiona una significante pérdida de potencia frente al caso de utilizar antenas con polarización lineal (ALP) [1]-[2], por lo tanto, estas antenas son ampliamente utilizadas para aplicaciones en telemetría espacial de satélites, sondas espaciales y misiles balísticos entre otras [2]. Por otra parte, las antenas de placa suspendida (APS) brindan la posibilidad de obtener mayores niveles de ganancia máxima y ancho de banda de impedancia frente a las tecnologías convencionales. Así mismo, resulta útil el poder seleccionar el sentido de giro más apropiado, dependiendo de las condiciones de propagación en los enlaces de subida/bajada. Objetivo: Diseñar una (APC) con sentido de giro seleccionable para aplicaciones en satélites pequeños, usando la tecnología (APS), tal que posea niveles de ganancia y ancho de banda superiores a las obtenidas con tecnologías convencionales. Metodología: El diseño de la antena parte de modelos propuestos en la literatura, mediante los cuales se diseña una geometría inicial compuesta por un parche suspendido con alimentación en L y un acoplador híbrido, para luego optimizar dicha geometría mediante análisis paramétricos llevados a cabo con simuladores electromagnéticos apropiados. Resultados: El diseño propuesto presenta un ancho de banda de impedancia del 34.39% y una ganancia máxima de 8.75 dBi a una frecuencia de 2.35GHz. Conclusiones: La técnica de alimentador en forma de L para parches suspendidos mejora el comportamiento de la antena en impedancia, relación axial  y ganancia máxima.  Introduction: Circular polarization antennas (CPA) are able to reduce the “Faraday rotation” effect due to the ionosphere, which causes a significant power losses compared to the case of using linear polarization antennas (LPA) [1]-[2]. Therefore, these antennas are widely used for space telemetry applications of satellites, space probes and ballistic missiles among others [2]. Furthermore, suspended plate antennas (SPA) offer the possibility to obtain largest levels of maximum gain and impedance bandwidth compared to those obtained with conventional technologies. Likewise, it is useful to be able to select the most appropriate sense of rotation, depending on the propagation conditions in the up/down links.  Objective: To design a CPA with configurable sense of rotation for small satellite applications, using SPA technology, such that it has gain and bandwidth levels higher than those obtained with conventional technologies. Method: The antenna design is based on models proposed in the literature, through which an initial geometry consisting of a suspended patch with an L-shaped feeder and a hybrid coupler is designed. Subsequently, geometry optimization by parametric analysis is carried out with appropriate electromagnetic simulators.  Results:  The proposed design has an impedance bandwidth of 34.39% and a maximum gain of 8.75 dBi at a frequency of 2.35GHz. Conclusions: The L-shaped feeder technique for suspended patches improves the behavior of the antenna in axial ratio, impedance and maximal gain

Microwave Antennas for Energy Harvesting Applications

In the last few years, the demand for power has increased; therefore, the need for alternate energy sources has become essential. Sources of fossil fuels are finite, are costly, and causes environmental hazard. Sustainable, environmentally benign energy can be derived from nuclear fission or captured from ambient sources. Large-scale ambient energy is widely available and large-scale technologies are being developed to efficiently capture it. At the other end of the scale, there are small amounts of wasted energy that could be useful if captured. There are various types of external energy sources such as solar, thermal, wind, and RF energy. Energy has been harvested for different purposes in the last few recent years. Energy harvesting from inexhaustible sources with no adverse environmental effect can provide unlimited energy for harvesting in a way of powering an embedded system from the environment. It could be RF energy harvesting by using antennas that can be held on the car glass or building, or in any places. The abundant RF energy is harvested from surrounding sources. This chapter focuses on RF energy harvesting in which the abundant RF energy from surrounding sources, such as nearby mobile phones, wireless LANs (WLANs), Wi-Fi, FM/AM radio signals, and broadcast television signals or DTV, is captured by a receiving antenna and rectified into a usable DC voltage. A practical approach for RF energy harvesting design and management of the harvested and available energy for wireless sensor networks is to improve the energy efficiency and large accepted antenna gain. The emerging self-powered systems challenge and dictate the direction of research in energy harvesting (EH). There are a lot of applications of energy harvesting such as wireless weather stations, car tire pressure monitors, implantable medical devices, traffic alert signs, and mars rover. A lot of researches are done to create several designs of rectenna (antenna and rectifier) that meet various objectives for use in RF energy harvesting, whatever opaque or transparent. However, most of the designed antennas are opaque and prevent the sunlight to pass through, so it is hard to put it on the car glass or window. Thus, there should be a design for transparent antenna that allows the sunlight to pass through. Among various antennas, microstrip patch antennas are widely used because they are low profile, are lightweight, and have planar structure. Microstrip patch-structured rectennas are evaluated and compared with an emphasis on the various methods adopted to obtain a rectenna with harmonic rejection functionality, frequency, and polarization selectivity. Multiple frequency bands are tapped for energy harvesting, and this aspect of the implementation is one of the main focus points. The bands targeted for harvesting in this chapter will be those that are the most readily available to the general population. These include Wi-Fi hotspots, as well as cellular (900/850 MHz band), personal communications services (1800/1900 MHz band), and sources of 2.4 GHz and WiMAX (2.3/3.5 GHz) network transmitters. On the other hand, at high frequency, advances in nanotechnology have led to the development of semiconductor-based solar cells, nanoscale antennas for power harvesting applications, and integration of antennas into solar cells to design low-cost light-weight systems. The role of nanoantenna system is transforming thermal energy provided by the sun to electricity. Nanoantennas target the mid-infrared wavelengths where conventional photo voltaic cells are inefficient. However, the concept of using optical rectenna for harvesting solar energy was first introduced four decades ago. Recently, it has invited a surge of interest, with different laboratories around the world working on various aspects of the technology. The result is a technology that can be efficient and inexpensive, requiring only low-cost materials. Unlike conventional solar cells that harvest energy in visible light frequency range. Since the UV frequency range is much greater than visible light, we consider the quantum mechanical behavior of a driven particle in nanoscale antennas for power harvesting applications

Frequency-reconfigurable antenna using ellipse-shaped patch with defected ground structure

Recently, there has been an increased demand for single systems that can handle different wireless communication applications simultaneously. Often, it is impractical to allocate multiple antennas to the same system, so multifunctional antennas are a critical necessity. Also, most existing frequency-reconfigurable antennas (FRA) are made from non-transparent materials, but a transparent antenna may be useful in scenarios where the antenna should not impair visibility. Furthermore, wideband-to-narrowband reconfigurability has potential for use in future cognitive radio systems. This thesis focuses on FRAs with wideband-tonarrowband reconfigurability that use transparent and non-transparent materials. The ultra-wideband antenna design uses an ellipse-shaped patch, thereby yielding a 7.77 GHz impedance bandwidth from 2.83 GHz to 10.66 GHz. The first FRA is obtained by introducing a pair of annular ring slots defected ground structure (DGS) resonator with metal switches. Its initial wideband operation mode from 3 GHz to 6 GHz can be reconfigured into six additional bandwidth modes with a dual-band operation centred at 3.7 GHz and 5.8 GHz and five single-band modes resonating at 4.2 GHz, 4.58 GHz, 4.86 GHz, 5.7 GHz and 6 GHz. Meanwhile, a FRA for the Wireless Local-Area Network applications is reconfigured from a pair of rectangular DGS resonators integrated with PIN diodes. The antenna is able to switch between a narrowband operation centred at 5.8 GHz and a wideband operation in the range of 3.5 - 5.97 GHz. Finally, a semi-transparent antenna with a wideband-to-narrowband frequency mode is achieved by integrating an E-shaped DGS resonator and PIN diodes to disrupt the current flow. The antenna exhibits an impedance bandwidth from 3 GHz to 6 GHz in the wideband mode and a resonance at 4.75 GHz when operated in the narrowband mode. All prototypes are fabricated and measured to verify the simulated results. The gain of antenna fabricated using the AgHT-4 transparent material is about 59% lower compared to FR-4 due to the electrical loss of the transparent film

Frequency Reconfigurable Antennas for Airborne Applications.

With the widespread improvement of wireless communication systems and appearing the new generation of mobile telecommunications such as 4G as well as 5G, a transmission of information with high data rate is feasible. Antenna is an important part of telecommunication systems where the information is transmitted and received. Most importantly, to improve the communication link and cover more users, in particular in base station antenna, it is necessary to steer the beam radiation of the antenna. This can be carried out mechanically as well as electronically which each one has its drawback and advantage. In mechanical approach, the installation infrastructure brings more difficulty. Also, in electronic methods due to using the phase shifter, it incurs a large loss and complexity to the design. In this thesis, first and foremost, a reconfigurable radiation pattern antenna based on frequency selective surfaces is introduced. To implement that idea, a modified electric-field coupled (ELC) resonators is presented, which works at 2.4 GHz. To transmit and reflect the illuminated power a pin diode is integrated in the middle of ELC resonator, where by turning “on” or “off”, the resonant frequency of transmission coefficient is shifted to a desired frequency band. Then, the stair-case monopole antenna operating at 2.4 GHz is proposed in the next part which is surrounded by octagon FSS walls, where each one consists of a 2x3 ELC inclusions. By switching “on” three FSS walls and keeping remaining walls in off-state, the radiation pattern in azimuth plane is switching from omnidirectional to directional pattern. To validate, a prototype of antenna along with eight FSS walls incorporated by pin-diode is fabricate and attached to the control unit part. The measured reflection coefficient of the antenna is less than -10 dB over 2.35-2.55 GHz. The measured radiation pattern in H-plane clearly shows a directional beam in different states with a measured realized gain of more than 5 dBi. To receive a maximum power in a random angle, a transmitted antenna propagates power and the aforementioned antenna with FSS panel is switched in 8 cases by control unit part. Finally, a design of control unit interface with proposed reconfigurable pattern antenna is presented and discussed in more details

Printed monopole antenna with tunable band-notched characteristic for use in mobile and ultra-wide band applications

YesA tunable band-notch printed monopole antenna is presented, exhibiting a wide impedance bandwidth from 1.5 to 5.5 GHz with good impedance matching (VSWR ≤ 2) and a tunable rejected frequency band from 2.38 to 3.87 GHz. The band-notching is achieved by adding an inner chorded crescent element within a driven element of a similar shape. By varying the value of the varactor which is placed between the inner and outer arcs, the desired variable rejected can be obtained. Simulated and measured results show wide impedance bandwidth with a tunable band notch, stable radiation patterns, and consistent nearly constant gain. The antenna is suitable for mobile and portable applications