A low-cost microwave filter with improved passband and stopband characteristics using stub loaded multiple mode resonator for 5g mid-band applications

This paper presents the design and implementation of a printed circuit microwave band-pass filter for 5G mid-band applications, using a Stub Loaded Multiple Mode Resonator (SL-MMR) technique. The objective of this article is to introduce a low-cost microstrip filter with improved passband and stopband characteristics, based on a mathematical analysis of stub loaded resonators. The filter cost is reduced by selecting the low-cost FR4 dielectric material as a substrate for the proposed filter. Based on the transmission line model of the filter, mathematical expressions are derived to predict the odd-mode and the even-mode resonant frequencies of the SL-MMR. The mathematical model also highlights the capability of controlling the position of the SL-MMR resonant frequen-cies, so that the 5G sub-band that extends along the range (3.7–4.2 GHz) can perfectly be covered with almost a flat passband. At the resonance frequency, a fractional bandwidth of 12.8% (500 MHz impedance bandwidth) has been obtained with a return loss of more than 18 dB and an insertion loss of less than 2.5 dB over the targeted bandwidth. Furthermore, a pair of parasitic elements is attached to the proposed filter to create an additional transmission zero in the lower stopband of the filter to enhance the suppression of the filter stopband. The measured and simulation results are well agreed, and both reveal the acceptable performance of the stopband and passband characteristics of the filter

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

Tunable Band Pass Filters for Communication Systems

The ever-increasing demand for high communication data rate and high-quality multi-media services; over past few decades, has ignited new avenues in radio architectures. Frequency reconfigurable (or frequency agile) communication systems are among the key architectures for efficient and cost-effective utilization of the allotted frequency spectrum. The emerging concept of on-orbit flexible payload (or programmable payload) in satellite communication is another encouraging development on the horizon. In-addition, tunability in filters used for remote radio unit (RRU) is highly preferred by network operators owing to the high cost of installing RRU both in low density remotely accessed locations and in high density expensive urban locations. Such frequency reconfigurable radio architectures typically demand reconfigurability (tunability) of components within the physical layer as well. Hence, tunable filters play a vital role in realization of frequency reconfigurable communication systems. In general, any fixed frequency filter can be transformed into a tunable filter by introducing tuning elements dedicated to tuning the resonators and the coupling structures. Thus, a tunable filter of order N would require 2N+1 tuning elements to maintain a constant absolute bandwidth (BW) over the tuning range. This use of large number of tuning elements not only increases size and cost, but also adds to the complexity of the tuning control mechanism, particularly when configured in a closed loop system. Over the past decade, a significant research has been carried out to reduce the number of tuning elements by roughly 50% (i.e. with only N tuning elements). The coupling structures are suitably designed to maintain their performance over the tuning range, eliminating N+1, while only N tuning elements are used for tuning the N resonators. The goal here is to further reduce the number of tuning elements to a ‘single tuning element’. The thesis presents several novel configurations for a high-Q tunable band pass filter employing a single tuning element, while maintaining a constant BW, return loss performance and location of the transmission zeros over a wide tuning range. Advanced filter synthesis techniques for both tunable filter and fixed filters are also proposed. A tunable double-septa waveguide (WG) filter is presented employing a single tuning element. The theory of coupling behavior of single septum and double septa to achieve constant absolute BW is explored. The tuning mechanism of the proposed filter is explained with measurement results presented for a Ku-band tunable WG filter designed at 15 GHz with a 2% fractional BW to achieve 15% tuning range. BW variation is observed to be within ±5% while the center frequency is tuned from 14.65 to 17.15 GHz. The filter promises to be useful in emerging 5G millimeter-wave applications, where the filter size is very small to accommodate multiple mechanical tuning elements. Furthermore, the proposed design methodology is scalable, i.e., the tuning mechanism is independent of the filter order. A frequency reconfigurable dual-mode WG filter having an elliptic response is presented. The proposed filter maintains a constant absolute BW and a constant rejection BW (i.e. constant frequency spacing between transmission zeros) over the tuning range. Furthermore, the filter can be tuned using a single tuning mechanism. A 4th order prototype filter at 11.5 GHz with 50 MHz bandwidth and 2 symmetric transmission zeros (± 45 MHz) is fabricated and measured. A novel configuration of a BW reconfigurable WG filter that uses only two tuning elements irrespective of the filter order is proposed. The proposed filter configuration demonstrates that it can achieve a relatively wide BW variations without deviating the center frequency. A 4 pole prototype filter is designed, fabricated and tested at Ku-band. The measured BW tunability of the filter is nearly 35 % from 225 to 320 MHz at 13.375 GHz. To the author’s knowledge, this is the only BW reconfigurable filter that can be tuned with only two tuning elements regardless of the filter order. The thesis also demonstrates the feasibility of realizing a high-Q lambda/2 resonator based tunable coaxial filter, which is tuned by a single rotational tuning element irrespective of the filter order. The proposed filter has low variations in the absolute BW and insertion loss (IL) over a relatively wide tuning range. A prototype four-pole filter is developed at 2.5 GHz with a fractional BW of 4% to verify the concept. The measured tuning range of the filter is 20%, within which the BW variation is better than ±10% and IL variation is better than 0.05 dB. The proposed concept is easily expandable to filters with higher order. Furthermore, the concept is adopted to design a tunable diplexer using only a single tuning mechanism while maintaining the frequency performance of each channel and the frequency spacing between the two channels over the tuning range. The proposed high-Q tunable filter is promising for use in the frequency-agile communication architecture at the cellular base-station and aerospace applications. A novel configuration of a High-Q coaxial tunable filter which employs a single rotational mechanism to tune the filter, while using fixed lambda/4 resonators is also presented. The rotational tuning concept is different from that proposed for the tunable coaxial lambda/2 resonators. A prototype filter is designed for the proof of concept, which has a tuning range of 11.6% from 685 MHz to 770 MHz, over which bandwidth variation is within 10.5±0.7 MHz.. In-addition, the proposed design methodology can be scaled to realize higher order filters. The proposed filter promises to be useful in a wide range of telecommunication applications including flexible payload in aerospace applications

Design and Synthesis of Parallel-Connected Dielectric Filter Using Chain-Function Polynomial

Design and synthesis of parallel connected die-lectric filters using chained function polynomials are pre-sented in this paper. This filter will offer reduced sensitivity to fabrication tolerance while preserving its return loss response within the desired bandwidth in comparison to traditional Chebyshev filters. A novel transfer function FN according to chained is derived for fourth and sixth-order filters and the synthesis technique is presented. To demon-strate the feasibility of this approach, the circuit simulation based on parallel connected topology is carried out in ADS while the design and simulation of the fourth-order filter in dielectric technology in HFSS. Considerable sensitivity analysis is conducted to prove a better fabrication toler-ance of the filter. In terms of implementation, this design technique will serve as a very useful mathematical tool for any filter design engineer

Design and Synthesis of Parallel-Connected Dielectric Filter Using Chain-Function Polynomial

Design and synthesis of parallel connected die-lectric filters using chained function polynomials are pre-sented in this paper. This filter will offer reduced sensitivity to fabrication tolerance while preserving its return loss response within the desired bandwidth in comparison to traditional Chebyshev filters. A novel transfer function FN according to chained is derived for fourth and sixth-order filters and the synthesis technique is presented. To demon-strate the feasibility of this approach, the circuit simulation based on parallel connected topology is carried out in ADS while the design and simulation of the fourth-order filter in dielectric technology in HFSS. Considerable sensitivity analysis is conducted to prove a better fabrication toler-ance of the filter. In terms of implementation, this design technique will serve as a very useful mathematical tool for any filter design engineer

Miniaturized Microwave Devices and Antennas for Wearable, Implantable and Wireless Applications

This thesis presents a number of microwave devices and antennas that maintain high operational efficiency and are compact in size at the same time. One goal of this thesis is to address several miniaturization challenges of antennas and microwave components by using the theoretical principles of metamaterials, Metasurface coupling resonators and stacked radiators, in combination with the elementary antenna and transmission line theory. While innovating novel solutions, standards and specifications of next generation wireless and bio-medical applications were considered to ensure advancement in the respective scientific fields. Compact reconfigurable phase-shifter and a microwave cross-over based on negative-refractive-index transmission-line (NRI-TL) materialist unit cells is presented. A Metasurface based wearable sensor architecture is proposed, containing an electromagnetic band-gap (EBG) structure backed monopole antenna for off-body communication and a fork shaped antenna for efficient radiation towards the human body. A fully parametrized solution for an implantable antenna is proposed using metallic coated stacked substrate layers. Challenges and possible solutions for off-body, on-body, through-body and across-body communication have been investigated with an aid of computationally extensive simulations and experimental verification. Next, miniaturization and implementation of a UWB antenna along with an analytical model to predict the resonance is presented. Lastly, several miniaturized rectifiers designed specifically for efficient wireless power transfer are proposed, experimentally verified, and discussed. The study answered several research questions of applied electromagnetic in the field of bio-medicine and wireless communication.Comment: A thesis submitted for the degree of Ph