Transformation of Generalized Chebyshev Lowpass Filter Prototype to Suspended Stripline Structure Highpass Filter for Wideband Communication Systems

This paper presents the transformation of generalized Chebyshev lowpass filter prototype to highpass filter using Suspended Stripline Structure (SSS) technology. The study involves circuit analysis to determine generalized Chebyshev responses with a transmission zero at finite frequency. The transformation of the highpass filter from the lowpass filter prototype provides a cutoff frequency of 3.1 GHz with a return loss better than -20 dB. The design is simulated on a Roger Duroid RO4350 with a dielectric constant, εr of 3.48 and a thickness of 0.168 mm. The simulation performance results show promising results that could be further examined during the experimental works. This class of generalized Chebyshev highpass filter with finite transmission zero would be useful in any RF/ microwave communication systems particularly in wideband applications where the reduction of overall physical volume and weight as well as cost very important, while maintaining its excellent performance

Microwave integrated circuit broadband filters and contiguous multiplexers

A novel design and construction technique for Microwave Integrated Circuit broadband filters and a contiguous multiplexer is presented together-with experimental results on a number of devices. The multiplexer is formed from a cascade of diplexers each containing a highpass and lowpass filter. Basedon the generalised Chebyshev prototype, selective low loss microwave filters for these diplexers are designed having new suspended substrate configurations. Octave bandwidths are achieved for the high pass channels. The contiguous multiplexer built has three outputs 4 - 8 GHz, 8 - 12 GHz and 12 - 18 GHz and is constructed on a single substrate approximately 2" x 1 ¼”. Experimental results show each channel has low pass band loss and highly selective responses at the bandedges and the multiplexer will meet the normal environmental conditions. Also, due to the printed circuit realisation, a high degree of population tracking can be readily achieved. Detailed computer analysis of the devices is presented and results are in very close agreement with the experimental results. Suitable constructional techniques are developed so the final multiplexer could be manufactured on a commercial basis

Filter Design for the Spectral Optimization of UWB Signals

Projecte realitzat en col.laboració amb el centre Universität Karlsruhe (TH

Electronically reconfigurable wideband microwave filters

Many systems require multi function capability in the filter aspects of systems; the method currently used is filter banks which take up a lot of board space. It is thought that reconfigurable filters hold the key to replacing filter banks in order to save board space and thus potentially increasing functionality of the systems. The aim of this research is to develop electronically reconfigurable microwave filters for future communication systems. The project investigates some key design issues of reconfigurable filters. Circuits were modelled and full-wave electromagnetic simulations were performed for the investigation. Experimental work was carried out to demonstrate advanced reconfigurable microwave devices. The components used in each concept investigated were pin diodes due to their superior performance in wideband and high frequency applications. Firstly a single coupled line concept was looked at for bandwidth reconfigurability. This concept was then further developed for industrial applications by simply cascading these sections to obtain a high selective filter. A design method was developed for any number of cascades both with and without an impedance transformer; the use of LCP was used to increase flexibility due to its desirable characteristics. The most desirable outcome would be filter to simultaneously control bandwidth and frequency. In order to tackle this issue the coupled line concept was adapted to incorporate frequency tunability, along with a design method being presented. Furthermore, a cascaded highpass/ lowpass filter was also explored for this concept for added flexibility in the design of a filter capable of control of both bandwidth and center frequency

Investigations on some planar microwave filters

Filters are substantial microwave components. RF/Microwave filters can be implemented using transmission lines. In this thesis microstrip bandpass filters had been designed for RF/microwave applications. Some novel techniques like implementing the open split koch loop resonators, open split square loop resonators, and star shaped multi-mode resonators are implemented in designing the microstrip bandpass filters. Microstrip filters are used in this report to design bandpass filters because of their compact sizes. The goal of this thesis is to investigate on some planar microwave bandpass filters. In this thesis four novel compact bandpass filters has been designed and simulated, specifically three pole koch resonator, seven pole koch resonator, three pole square loop resonator and compact UWB bandpass filter using MMR. The design and simulation of each and every filter is given in detail with including all the required specifications. From the previous research studies it is evident that, to design a good bandpass filter there should be a smooth passband and good stopband with higher insertion loss in the stopband. The four designs which are explained in this thesis has these important factors, which makes these filters useful for the microwave applications

Strategies for Time Domain Characterization of UWB Components and Systems

In this work new methods and criteria for the analysis of Ultra Wideband (UWB) components and systems are introduced. This permit to have a deeper insight into the component characteristics like signal distortion, ringing and dispersion, introduced by the non-ideal behavior of the UWB components over the wide frequency band. The developed analyses are the basis for correction and optimization strategies for the features of the UWB components and systems, compensating for their non-idealities

A study of tunable filters technology in RF/microwave engineering

Due to increasing demand for wireless communication systems, and because of the stringent requirements of the congested RF-frequency spectrum, reconfigurable/tunable filters have advanced significantly in recent years. Tunable filters can be tuned to different frequency bands constituted a qualitative shift in the field of civil and military communications because of their great potential to minimise the size, complexity, power consumption and cost of traditional filter banks. At the same time, high performance is becoming increasingly important to meet the modern communication systems’ specifications. Against this background, this dissertation provides a study of tunable filters technology in RF/microwave Engineering. In order to accomplish this study, several tunable filters using different tuning approaches have been presented in this dissertation. A mechanically tuned lowpass filter is presented achieving a good tuning range over the filter’s passband. The suspended substrate stripline (SSS) topology has been utilized to obtain a high-quality response while the generalized Chebyshev responses has been applied to obtain flexible transmission zeros in terms of controlling their locations. Tuning was achieved by using a fabricated mechanical structure to tune a set of five SSS resonators synchronously. A systematic numerical design of this type of filters has been offered with full equations’ derivations and consequentially manufactured samples are validated experimentally and presented in this work. A novel design of a narrow tunable bandwidth bandpass filter with two transmission zeros has been developed. In this project, two different structures were combined containing the microstrip structure to simplify the integration with other system parts and the SSS structure to obtain high quality response. Moreover, it introduces two transmission zeros at both sides of the filter’s passband without the need of using the conventional cross coupling method. Furthermore, two different tuning approaches have been used, one for tuning the bandwidth and the two transmission zeros while the second one was for fine tuning. An extensive design methodology and a numerical design example for both, the fixed and tunable filters have been presented and consequentially the proposed design has been proven experimentally. A new cascaded bandpass filter is presented offering an outstanding response with relatively small number of cascaded elements. This filter utilizes the characteristics of the Step Impedance resonators (SIR) in terms of their flexibility of controlling the spurious response and the insertion loss by changing the ratio of the filter’s high to low impedance. In addition, it offers high quality responses by using SSS structures. The filter’s design methodology is presented, extensively illustrated with a numerical example and proven experimentally. A tuning feasibility of the cascaded SSS filter has been introduced where the electrical tuning has been used to tune the lower side of the passband while the upper side is mechanically tuned. The proposed tuning approach has been simulated by using an EM full-wave simulation software and presented whereas the manufacturing was unfortunately postponed due to the end of the research time

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

Novel miniature microwave quasi-elliptical function bandpass filters with wideband harmonic suppression

Filters are integral components in all wireless communication systems, and their function is to permit predefined band of frequencies into the system and reject all other signals. The ever-growing demand in the use of the radio frequency (RF) spectrum for new applications has resulted in the need for high performance microwave filters with strict requirements on both inband and out-of-band characteristics. High selectivity, high rejection, low loss and extremely wide spurious-free performance are required for both transmitter and receiver channels. In addition, these devices need to be highly compact, easy to integrate within transceivers and should be amenable to low cost manufacturing. High selectivity is essential to enable the guard band between adjacent channels to be reduced thus improving the efficiency of the RF spectrum and hence increasing the capacity of the system. A low insertion-loss, high return-loss and small group-delay in the passband are necessary to minimize signal degradation. A wide stopband is necessary to suppress spurious passbands outside the filter’s bandwidth that may allow spurious emissions from modulation process (harmonic, parasitic, intermodulation and frequency conversion products) and interfere with other systems. The EMC Directive 89/336/EEC mandates that all electronic equipment must comply with the applicable EN specification for EMI. This thesis presents the research work that has resulted in the development of innovative and compact microstrip bandpass filters that fulfil the above stringent requirements for wireless communication systems. In fact, the proposed highly compact planar microstrip filters provide an alternative solution for existing and next generation of wireless communications systems. In particular, the proposed filters exhibit a low-loss and quasi-elliptic function response that is normally only possible with filter designs using waveguides and high temperature superconductors. The selectivity of the filters has been improved by inserting a pair of transmission zeros between the passband edges, and implementing notched rejection bands in the filter’s frequency response to widen its stopband performance. The filter structures have been analysed theoretically and modelled by using Keysight Technologies’ Advanced Design System (ADS™) and Momentum® software. The dissertation is essentially composed of four main sections. In the first section, several compact and quasi-elliptic function bandpass filter structures are proposed and theoretically analysed. Selectivity and stopband performance of these filters is enhanced by loading the input and output feed-lines with inductive stubs that introduce transmission zeros at specified frequencies in the filter’s frequency response. This technique is shown to provide a sharp 3-dB roll-off and steep selectivity skirt with high out-of-band rejection over a wide frequency span. In addition, the 3-dB fractional bandwidth of the filters is shown to be controllable by manipulating the filter’s geometric parameters. Traditional microwave bandpass filters are designed using quarter-wavelength distributed transmission-line resonators that are either end-coupled or side-coupled. The sharpness of the filter response is determined by the number of resonators employed which degrades the filter’s passband loss performance. This results in a filter with a significantly larger footprint which precludes miniaturization. To circumvent these drawbacks the second section describes the development of a novel and compact wideband bandpass filter with the desired characteristics. The quasi-elliptic function filter comprises open-loop resonators that are coupled to each other using a stub loaded resonator. The proposed filter is shown to achieve a wideband 3-dB fractional bandwidth of 23% with much better loss performance, sharp skirt selectivity and very wide rejection bandwidth. The third section describes the investigation of novel ultra-wideband (UWB) microstrip bandpass filter designs. Parametric study enabled the optimization of the filter’s performance which was verified through practical measurements. The proposed filters meet the stringent characteristics required by modern communications systems, i.e. the filters are highly compact and miniature even when fabricated on a low dielectric constant substrate, possess a sharp quasi-elliptic function bandpass response with low passband insertion-loss, and ultra-wide stopband performance. With the rapid development of multi-band operation in modern and next generation wireless communication systems, there is a great demand for single frequency discriminating devices that can operate over multiple frequency bands to facilitate miniaturization. These multi-band bandpass filters need to be physically small, have low insertion-loss, high return-loss, and excellent selectivity. In the fourth section two miniature microstrip dual-band and triple-band bandpass filter designs are explored. A detailed parametric study was conducted to fully understand how the geometric parameters of the filters affected their performance. The optimized filters were fabricated and measured to validate their performance

New configurations for RF/microwave bandstop and lowpass filters

This thesis presents new, compact configurations for RF/microwave bandstop and lowpass filters for embedded passive applications. A simple design methodology is presented for designing the folded-transmission line filters on a microstrip platform. Unlike the conventional stub-loaded filter designs, the proposed folded-line filters will have practical dimensions for a wide range of electrical specifications, making physical implementation realizable. Further compactness is achieved by folding the transmission lines in a multi-layered environment. A back-to-back microstrip with through-holes in the ground plane is considered for this purpose. Closed-form design equations for the frequency independent R, L, C components have been developed for implementation in the circuit model of the through-ground via. The proposed configurations offer significant footprint reduction compared to the conventional geometries. Several lowpass and bandstop filters are designed in single and multi-layered environments, and the theoretical response is validated by full-wave EM simulation as well as with measurement.Keywords: Bandstop/lowpass, RF/microwave, New configurations, Planar filter