Emerging Trends in Techniques and Technology as Applied to Filter Design

In the last decade, the filter community has innovated both design techniques and the technology used for practical implementation. In design, the philosophy has become "if you can't avoid it, use it", a very practical engineering approach. Modes previously deemed spurious are intentionally used to create in-line networks incorporating real or imaginary transmission zeros and also reduce the number of components and thus further miniaturize; spurious responses are re-routed to increase the passband width or stopband width, frequency variation in couplings is used to create complex transfer functions, with all of these developments using what was previously avoided. Clever implementations of baluns into passive and active networks is resulting in a new generation of noise-immune filters for 5G and beyond. Finally, the use of a diakoptic approach to synthesis has appeared an evolving approach in which small blocks ("singlets", "doublets", etc.) are cascaded to implement larger networks, (reducing the need for very complex synthesis), with this new approach promising a large impact on the implementation of practical structures. Filter technology has migrated towards "observe it and then adapt it", pragmatically repurposing tools not specifically originally intended for the applications. Combinations of surface wave and bulk wave resonators with L-C networks are improving the loss characteristics of filters in the region below 2 GHz. Lightweight alloys and other materials designed for spacecraft are being used in filters intended for space, to provide temperature stability without the use of heavy alloys such as Invar. Fully-enclosed waveguide is being replaced in some cases by planar and quasiplanar structures propagating quasi-waveguide modes. This is generically referred to as SIW (Substrate Integrated Waveguide). Active filters trade noise figure for insertion loss but perhaps will offer advantage in terms of size and chip-level implementation. Finally, the era of reconfiguration might be approaching, as the basic networks are evolving, perhaps lacking only the appearance of lower-loss, higher-IP solid-state tuning elements

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

Miniaturized High-Q Tunable RF Filters

This dissertation focuses on the investigation and development of novel efficient tuning techniques and the design of miniaturized high-Q tunable RF filters for high-performance reconfigurable systems and applications. First, a detailed survey of the available tuning concepts and state-of-art tunable filters is provided. Then, a novel so-called inset resonator configuration is presented for the applications of fixed and tunable coaxial filters. The design procedure of frequency tunable filters with constant absolute bandwidth (CABW) is described, and various tunable inset filters are implemented, offering many desirable merits, including the wide tuning range and stable high-Q with minimum variation. For wide octave frequency tuning ranges with CABW, a second novel concept is presented using so-called re-entrant caps tuners. Beside simplicity and compactness, this technique also features enhanced spurious performance and wider tuning capabilities than the conventional means. Also, in this dissertation, various miniaturized reconfigurable dual-band/dual-mode bandpass filters and diplexers are presented using compact dual-mode high-Q TM-mode dielectric resonators. Furthermore, a novel microfluidic-based ultra-wide frequency tuning technique for TM010-mode dielectric resonators and filters is introduced in this dissertation. In addition to the very wide tuning window, this mechanism has key advantages of low-cost, simplicity, and intrinsic switch-off. Lastly, the dissertation includes a novel bandwidth reconfiguration concept with multi-octave tuning using a single element for coaxial bandpass filters. This mechanism brings many features including the fast tuning, constant high-Q, intrinsic switch-off, and wide BW-reconfiguration

Continuously Tuned Ku-Band Cavity Filter Based on Dielectric Perturbers Made by Ceramic Additive Manufacturing for Space Applications

International audienceThis paper presents a concept of a tunable cavity resonator composed of a resonating cavity and a dielectric perturber. This tunable resonator is designed and measured to prove the tuning mechanism obtained by varying the angle of rotation of the perturber. A rotation from 0 to 90 produces a tuning ratio of 1:1.25, i.e., a tuning range of 22.2% around 11.5 GHz while maintaining an unloaded Q factor between 1500 and 2300. After this first experimental validation, a third-order bandpass filter is then designed and measured using the same base principle. Using a single mechanical movement, all three resonators’ perturbers are synchronously rotated to create a third-order Chebyshev bandpass filter maintaining a 516±38-MHz bandwidth (for a return loss better than 10 dB) from 9.915 to 12.189 GHz. A 20.6% tuning range is then obtained at approximately 11 GHz with an estimated Q factor from 1400 to 2150. These performances have been obtained by using specifically shaped dielectric perturbers, which have been made by a ceramic additive manufacturing (AM) process (stereolithography). This technology has enabled the perturbers’ specific geometries and embedded supporting elements to be feasible. A sixth-order Chebyshev bandpass filter has also been theoretically proposed using full wave simulations

SPICA:revealing the hearts of galaxies and forming planetary systems : approach and US contributions

How did the diversity of galaxies we see in the modern Universe come to be? When and where did stars within them forge the heavy elements that give rise to the complex chemistry of life? How do planetary systems, the Universe's home for life, emerge from interstellar material? Answering these questions requires techniques that penetrate dust to reveal the detailed contents and processes in obscured regions. The ESA-JAXA Space Infrared Telescope for Cosmology and Astrophysics (SPICA) mission is designed for this, with a focus on sensitive spectroscopy in the 12 to 230 micron range. SPICA offers massive sensitivity improvements with its 2.5-meter primary mirror actively cooled to below 8 K. SPICA one of 3 candidates for the ESA's Cosmic Visions M5 mission, and JAXA has is committed to their portion of the collaboration. ESA will provide the silicon-carbide telescope, science instrument assembly, satellite integration and testing, and the spacecraft bus. JAXA will provide the passive and active cooling system (supporting the

The Apertif Surveys:The First Six Months

Apertif is a new phased-array feed for the Westerbork Synthesis Radio Telescope (WSRT), greatly increasing its field of view and turning it into a natural survey instrument. In July 2019, the Apertif legacy surveys commenced; these are a time-domain survey and a two-tiered imaging survey, with a shallow and medium-deep component. The time-domain survey searches for new (millisecond) pulsars and fast radio bursts (FRBs). The imaging surveys provide neutral hydrogen (HI), radio continuum and polarization data products. With a bandwidth of 300 MHz, Apertif can detect HI out to a redshift of 0.26. The key science goals to be accomplished by Apertif include localization of FRBs (including real-time public alerts), the role of environment and interaction on galaxy properties and gas removal, finding the smallest galaxies, connecting cold gas to AGN, understanding the faint radio population, and studying magnetic fields in galaxies. After a proprietary period, survey data products will be publicly available through the Apertif Long Term Archive (ALTA, https://alta.astron.nl). I will review the progress of the surveys and present the first results from the Apertif surveys, including highlighting the currently available public data