High aspect ratio transmission lines and filters

There are a significant number of microwave applications, where improvement of such qualities as manufacturing costs, size, weight, power consumption, etc. have attracted much research interest. In order to meet these requirements, new technologies can be actively involved in fabrication of microwave components with improved characteristics. One such fabrication technology is called LIGA (a German acronym with an English translation of lithography, electroforming, and moulding) that allows fabrication of high aspect ratio (tall) structures, and only recently is receiving growing attention in microwave component fabrication. The characteristics of high aspect ratio microstrip and coplanar waveguide (CPW) transmission lines are investigated in this thesis. Very low impedance high aspect ratio CPW transmission lines can be realized. A high aspect ratio microstrip folded half wavelength open loop resonator is introduced. Effective configurations for external and bypass gap coupling with open loop resonators are given. Filters with transmission zeros in the stopband, consisting of high aspect ratio single mode open loop resonators are presented to demonstrate the advantages of high aspect ratio structures in realizing lower external quality factors or tight coupling. The transmission zeros are created by novel coupling routings. Some of the filters are fabricated and the filter responses are measured to validate high aspect ratio coupling structures. High aspect ratio diplexers with increased channel isolation are also designed by appropriately combining filters with transmission zeros. A wideband bandpass filter design method, based on the electromagnetic bandgap (EBG) concept is introduced in this thesis. The wideband filters are miniaturized as a result of using the EBG concept in design. An EBG based wideband filter consisting of unit cells that are realized by using high aspect ratio CPW stepped impedance resonators is also presented. The main advantage of this approach is that the high aspect ratio CPW structures make short unit cells practically realizable, resulting in compact filter structure

A Class of Compact Substrate Integrated Waveguide Filters

This thesis work explores the design of compact and high performance microwave filters using substrate integrated waveguide technology. A substrate integrated waveguide is aplanar version of a conventional waveguide, which is having features like planar circuit integrability, ease of fabrication, low-cost and high power handling. A class of Substrate Integrated Waveguide (SIW) and Half mode Substrate Integrated waveguide (HMSIW) bandpass filters are proposed in this context. Applications like satellite communication uses devices which can withstand high power. Therefore, SIW filters can be used for satellite applications in the microwave bands like Ku, X, C, S, and L etc.The main objective of this thesis is to design SIW bandpass filters using simple planar technology and low-cost substrates. To fulfill this, a class of compact and easily fabricable SIW bandpass filters are proposed for Ku-band (12 − 18GHz) and S-band (2 − 4GHz) applications. These filters are designed using simple electromagnetic band gap (EBG) structures and latest feeding techniques like tapered-via feeding. Filters are designed using low-cost and easily available substrate FR4 with the help of High frequency structural simulator (HFSS) V.14. The dimensions of the filters are optimized and simulation results are analyzed. The proposed Ku-band filter has proven to be compact since its footprint is 160mm2. The S-band filter has been fabricated using low-cost and easily available FR4 substrate. The measurement results are found to be good in agreement with the simulation results. Though the obtained results are similar to the other reported filters, there is a huge demand of compactness in this miniaturization era. Therefore, another well-established concept of Half-mode SIW (HMSIW) technology is used to further reduce the size of the designed filters. So a compact HMSIW bandpass filter is designed for the Ku-band applications which is almost half in size as compared to conventional SIW designs. The return loss is achieved as 45dB and insertion loss is 1.5dB in the passband of the filter, which is promising corresponding to the size. Another similar design is made for X-band (8 − 12GHz) applications using HMSIW technology. The overall footprint of the filter which shows its compactness; is 102mm 2 i.e. almost half the size of its equivalent SIW filter

Microwave Slow-Wave Structure and Phase-Compensation Technique for Microwave Power Divider

In this paper, T-shaped electromagnetic bandgap is loaded on a coupled transmission line itself and its electric performance is studied. Results show that microwave slow-wave effect can be enhanced and therefore, size reduction of a transmission-line-based circuit is possible. However, the transmission-line-based circuits characterize varied phase responses against frequency, which becomes a disadvantage where constant phase response is required. Consequently, a phase-compensation technique is further presented and studied. For demonstration purpose, an 8-way coupled-line power divider with 22.5 degree phase shifts between adjacent output ports, based on the studied slow-wave structure and phase-compensation technique, is developed. Results show both compact circuit architecture and improved phase imbalance are realized, confirming the investigated circuit structures and analyzing methodologies

Enhanced Bandwidth of Band Pass Filter Using a Defected Microstrip Structure for Wideband Applications

In this paper, the bandwidth enhancement of bandpass filter (BPF) is proposed by utilizing defected microstrip structure (DMS). The initial micro strip BPF which is designed to have the bandwidth 1GHz with the center frequency of 3.5GHz is deployed on FR4 Epoxy dielectric substrate with overall size and thickness of 14mm x 24mm and 1.6mm, respectively. The proposed filter consists of two parallel coupled lines centred by ring-shaped, to enhance the bandwidth response, an attempt is carried out by applying DMS on the ligne center with a ring-shaped of initial filter. Here, the proposed DMS is constructed of the arrowhead dumbbell. Some parametrical studies to the DMS such as changing to obtain the optimum geometry of DMS with the desired bandwidth response. From the characterization result, it shows that the utilization of DMS on to the microstrip ligne of filter has widened 3dB bandwidth response up to 1.8GHz ranges from 2.55GHz to 4.35GHz yielding an enhanced wideband response for various wideband wireless applications

Design and Development of a Compact and Vialess Microstrip Ultra-Wideband Bandpass Filter

In radio frequency and microwave systems, filters are the most essential component to select the required signals. They are built together with other components such as mixers, amplifiers, oscillators and switches. Filters work by blocking the unwanted signals and allowing the desired signals through them before feeding it into other components or devices. In the latest interest and future radio frequency and microwave high speed communication technology like Ultra-Wideband (UWB), a bandpass filter with large bandwidth (> 500 MHz) is required to fulfill the specifications. This is due to the UWB format signal which uses very short time pulse wave within 1.0 ns to 0.1 ns. This thesis presents theories, methods, parameters, simulations and measurements of designed and development of bandpass filters to support UWB communication systems. There are four types of bandpass filters which are designed and developed to operate within 3.1 GHz to 10.6 GHz to support the UWB frequency range specification.Initially, the designed model is derived from J-inverter which it is a transformation of low pass to bandpass Chebyshev filter. Type of response is chebyshev since it is able to perform an equal-ripple return loss response in the whole passband. The equal-ripple return loss response can keep the insertion loss almost flat in the whole pass band and sharp-out-of-band rejection response. In the thesis, bandpass filters are designed and developed based on five poles quarterwavelength short-circuited stubs model. The model is theoretically capable to expand the frequency bandwidth by tuning its h (interior admittance level of the stubs) factor. The related mathematical equations are applied into mathematical software to speed up the optimization of h factor and obtain the required admittance level for stubs and transmission lines. The first bandpass filter has successfully shown the expansion in frequency bandwidth to support Ultra-wideband specifications. The filter uses five vias to short-circuit stubs to the ground. Stubs, transmission lines admittance and h are tuned slightly to expand the fractional bandwidth (FBW) more than 100 %. The measured scattering parameters are |S21| = 1.27 dB and S11 = -7.8 dB respectively. The second bandpass filter is improved by reducing the short-circuited via elements. First and second stubs are shared on the first via while fourth and fifth stubs share on the third via. Only third stub has its own via thus creating new transformation filter shape nicknamed as “Butterfly”. This new shaped has 109 % of measured fractional bandwidth, lower scattering parameters |S21| which is below than 0.85 dB and S11 is better than -11.6 dB. Besides, it also reduces the number of via insertion in microstrip fabrication process.The third bandpass filter has totally eliminates vias and thus simplifies the microstrip fabrication process. Vias are replaced by microstrip patched capacitors. At microwave frequencies, these capacitors are parasitic elements and their parameters contribute to the successful performance in S-parameters measurement. The measured scattering parameters |S21| and S11 are better than 1 dB and -16.9 dB respectively. The fourth filter is improved in terms of scale dimension and group delay compares to the third filter. The structure is via-less and the filter uses less microstrip patch capacitors to perform compact size with “Butterfly” shape. By reducing microstrip patched capacitors, the filter shows better S-parameters measurements in the UWB passband with the lowest scattering parameters |S21| 0.53 dB and S11 of -14.8 dB. The group delay varies minimum within 0.47 ns in the whole UWB pass band

An Overview of Recent Development of the Gap-Waveguide Technology for mmWave and Sub-THz Applications

The millimeter-wave (mmWave) and sub-terahertz (sub-THz) bands have received much attention in recent years for wireless communication and high-resolution imaging radar applications. The objective of this paper is to provide an overview of recent developments in the design and technical implementation of GW-based antenna systems and components. This paper begins by comparing the GW-transmission line to other widely used transmission lines for the mmWave and sub-THz bands. Furthermore, the basic operating principle and possible implementation technique of the GW-technology are briefly discussed. In addition, various antennas and passive components have been developed based on the GW-technology. Despite its advantages in controlling electromagnetic wave propagation, it is also widely used for the packaging of electronic components such as transceivers and power amplifiers. This article also provided an overview of the current manufacturing technologies that are commonly used for the fabrication of GW-components. Finally, the practical applications and industry interest in GW technology developments for mmWave and sub-THz applications have been scrutinized.Funding Agencies|European Union - Marie Sklodowska-Curie [766231WAVECOMBEH2020-MSCA-ITN-2017]</p

Development Of Microwave Bandpass Filter Using Defected Ground Structure In Comparison With Multilayer And Dielectric Resonator Filters

Bandpass filters perform an important filtering task in a radio transceiver. The narrow stopbands and low gradient in transition bands of conventional parallel-coupled or electromagnetic band gap (EBG) are two (2) of the challenges in designing a bandpass filter. This thesis will introduce three (3) structures of bandpass filter. The first is a new combination of parallel-coupled and defected ground structure (DGS) that operates at a center frequency of 7.8 GHz for mobile satellite application. In essence, this combination structure has resulted to high Q-factor and slow wave which contributes to a high slope and spurious suppression. Cylindrical dielectric resonators were also applied to the circuit in order to increase the return loss in the passband or to enhance the bandwidth of the design. The Zirconate Tin Titanate, ZrSnTiO3 ( r = 37.4, tangent loss = 0.002) dielectric resonator and RO3003 substrate with dielectric constant and tangent loss of 3.0 and 0.0013 respectively were applied in this project. The overall dimension of the circuit was 47.2 mm × 19.16 mm, while the size of the rectangular DGS was 1 mm × 7.36 mm. The second structure is a combination of end-coupled and split ring resonators in a multilayer configuration that operate at 3.47 - 3.79 GHz for Worldwide Interoperability for Microwave Access (WiMAX) application. A modified split ring was introduced to obtain the additional sub-resonators from the magnetic coupled between vertical layers in order to increase the coupling effect from the multilayer structure. The Flame Retardant 4 (FR-4) substrate with dielectric constant, r of 4.6 was used as a core material

Enhancement of Millimeter-Band Transceivers with Gap Waveguide Technology

Mención Internacional en el título de doctorIt is known to all that year after year in modern society there is an urgent demand to consume wirelessly, and even stream ever larger multimedia content. High-frequency technologies have made it possible to go from transmitting analog voice and SMS text messages, to now transmitting live video in 4K quality from a mid-range smartphone. The way to measure these advances is by the bandwidth (Mb/s) reserved for each network user and the cost required to achieve it. To achieve even higher bandwidths, it is essential to improve signal coding techniques or increase the frequency of the signal, for example: to the mmWave bands (25GHz - 100 GHz), where these high-frequency techniques come into play. However, there is a frequency limit where current planar technology materials - such as the printed circuit boards used to build RF devices - are so lossy that they are not suitable at these mmWave frequencies. Current commercial solutions consist of guiding the electromagnetic energy with hollow metallic waveguides, but they suffer from the problem that as the frequency increases the diameter of these waveguides gets smaller and smaller, so manufacturing tolerances increase exorbitantly. Not to mention that they are usually manufactured in two parts, one upper and one lower, whose joints are not always perfect and produce energy losses. With these issues in mind, in 2009 the theory and basic science of a new electromagnetic energy guidance technology called Gap Waveguide was proposed, which is based on the use of metasurfaces constructed with periodic elements similar to a bed of nails. There are several implementations of this technology, but the three main ones are: Ridge, Groove and Inverted Microstrip Gap Waveguide. The latter is the most compatible with conventional planar manufacturing technologies and therefore the most cost-effective, although it also has drawbacks mainly in terms of losses when compared to the other versions. This thesis aims to deepen the study of the Inverted Microstrip guidance technology, its limitations and to develop with it some of the needed components in RF systems such as filters, diplexers, amplifiers, antennas, etc. Regarding the methodology for this thesis, a commercial simulation software for the analysis of antennas and components, CST Microwave Studio [1], has been used. AWR Microwave Office [2], a circuit simulator, has also been used to complement the simulations. On the other hand, there is a laboratory for the manufacture of prototypes in printed technology (with some limitations in terms of resolution) and the corresponding measurement laboratory, which includes network analyzers up to 40 GHz, spectrum analyzers and an anechoic chamber.This thesis arose under the Spanish Ministry of Science and Innovation (MINECO) and European Regional Development Fund (ERDF) project, called "Antenna for Mobile Satellite Communications (SATCOM) in Ka-Band by means of metasurfaces (2016-2019)", with reference TEC2016-79700-C2-2-R. Under this contract, the author signed an FPI research contract.Programa de Doctorado en Multimedia y Comunicaciones por la Universidad Carlos III de Madrid y la Universidad Rey Juan CarlosPresidente: Íñigo Cuiñas Gómez.- Secretario: Ángela María Coves Soler.- Vocal: Astrid Algaba Brazále

Miniaturised and reconfigurable planar filters for ultra-wideband applications

An increasing demand for electromagnetic spectrum has resulted from the emergence of feature-rich and faster throughputs wireless applications. This necessitates the developments of dynamic reconfigurable or multifunctional systems to better exploit the existing spectrum. Future wireless devices will be expected to communicate over several bands with various other devices in order to fine tune the services they provide to the user. Each band may require a separate RF transceiver and such modern wireless multi-band multi-mode communication systems call for high performance, highly integrated compact modules. Since the Federal Communications Commission (FCC) released the unlicensed frequency band 3.1-10.6 GHz for ultra-wideband (UWB) commercial communications, the development race for commercialising UWB technology has seen a dramatic increase around the world. The aim of this research is to develop reconfigurable planar microwave filters for ultrawideband applications. The project investigates some key design issues of reconfigurable filters, which are being observed constantly in the latest development and realisation of microwave filters. Both analytical and numerical methods are performed to construct a realistic and functional design. Two different types of frequency reconfigurability are investigated in this thesis: discrete (e.g. PIN diode, Optical switch) and continuous (e.g. varactor diode). Using the equivalent circuits and considering the direct coupled filter structure in most cases, several topologies with attractive features are developed for future communication systems. The proposed works may be broadly categorised into three sections as follows. The first section explores a square ring shape close loop resonator along with an opencircuited stub in the symmetry plane. To realise a reconfigurable frequency states within the same spectrum, an innovative approach is developed for this case. An optical or photoconductive switch, comprised of a silicon die activated using near infrared light is investigated as a substitute of PIN diode and performances are evaluated to compare the feasibilities. In addition, a in-band interference rejection technique via externally coupled Tshape resonator is shown. However, it is observed that both structures achieve significant size reductions by utilising the inner part of the resonators. To improve the filter selectivity, a convenient design approach generating a pair of transmission zeros between both passband edges and a single zero in the stop band for harmonic suppression is discussed in the second section. Moreover, the development of notched rejection bands are studied and several novel methods to create a single and multiple notched bands employing the square ring shape structure are proposed. On inspection, it is found that the notch structure can be implemented without deteriorating the filter performances. The discussions are supplemented with detailed design examples which are accompanied by theoretical, simulated and experimental results in order to illustrate the filter development process and showcase practical filter performance. The third section reveals a novel highly compact planar dual-mode resonator with sharp rejections characteristics for UWB applications. A bandwidth reconfiguring technique is demonstrated by splitting its even-mode resonance. Filter structure with the dual-mode resonator is shown to have a relatively wide tuning range, significantly low insertion loss and a constant selectivity along with frequency variations in comparison to similar published works. Finally, the earlier dual-mode structure are modified to realise a dual wideband behaviour. A detail analysis with comprehensive design procedures is outlined and a solution for controlling the frequency bandwidths independently according to the application interest is provided. In line with the previous section, experimental verification is presented to support and supplement the discussions

Microwave Filters Based on New Design Concepts in Several Technologies with Emphasis on the Printed Ridge Gap Waveguide Technology

Microwave filters have been an interesting research topic for more than half a century. Since any communication system is required to use some microwave filters, considerable effort is being made to optimize the performance and size of these filters. As operating frequency is on the rise, filter design becomes more challenging with the demand for low insertion losses and low cost. As low cost might require the use of printed circuit technology, high performance demands waveguide technology that drives the cost to unacceptable levels. There is a need for a new technology that achieves both requirements of low cost and high performance. The new technology of ridge gap waveguide that was proposed in 2011 shows promising characteristics as a new guiding structure, especially for high-frequency bands. Therefore, it is necessary to design and propose classic or even new filtering devices on this technology. Here, we propose the use of this technology to design practical and efficient microwave filters. The work of this thesis can be divided into three major parts: (1) Developing efficient codes and methods to optimize the computationally expensive structure of ridge gap waveguide or any other large-scale microwave filter device. (2) Characterizing cavity structures on ridge gap waveguide and using them in the design of simple microwave filters. (3) The third part will discuss more advanced and practical filters, especially using printed ridge gap waveguide technology. The ultimate goal of this thesis is to design and propose state of the art designs in the field of microwave filters that can satisfy the requirements of today’s advanced communication systems and to be cost efficient and compete with other rival technologies. We achieved these objectives using efficient optimization, efficient design techniques, and fabrication of the models using advanced technology