High-order input-reflectionless quasi-elliptic-type wideband bandpass filter using dual-mode slotline resonator

2022 Asia-Pacific Microwave Conference (APMC), 29 November to 02 December 2022, Yokohama, Japan.A high-order input-reflectionless quasi-elliptic-type wideband bandpass filter (BPF) that exploits a complementary-diplexer-based topology is reported. Firstly, a fourth-order wideband microstrip-to-microstrip vertical transition employing a dual-mode slotline resonator as the reflective-type BPF channel is designed. It features a sharp-rejection BPF response with two close-to-passband transmission zeros (TZs). To attain broadband input-reflectionless behavior, a shunt resistively-terminated microstrip π-shape network is used as the absorptive bandstop-filter (BSF) channel. The RF theoretical operational principle of the conceived broadband BPF is detailed. Compared to prior-art high-order input-/two-port-reflectionless wideband BPFs, the proposed BPF features not only improved passband flatness at the passband edges, but also relatively-high stopband power-attenuation levels and power-absorption ratios. For experimental-validation purposes, a two-layer fourth-order BPF microstrip prototype centered at 1 GHz is developed and tested.European CommissionAgencia Estatal de Investigació

Spurious suppression techniques for 3-D printed coaxial resonator bandpass filters

Design methods to enhance the passband-to-stopband bandwidth of coaxial bandpass filters (BPFs) are reported. Stopband enhancement is achieved by: 1) introducing a transmission zero (TZ) through mixed electromagnetic (EM) coupling and 2) by reducing the RF signal coupling to one of the spurious modes by varying the relative orientation of the RF posts. A low-cost additive manufacturing (AM) concept is proposed as the key-enabling integration scheme for these types of filters due to 1) easing the manufacturing of otherwise complex geometries and 2) allowing for monolithic integration. For proof-of-concept demonstration purposes a two-pole prototype and a four-pole prototype were designed at 3.5 and 3.6 GHz. They were manufactured using a low-cost stereolithography apparatus (SLA)-based 3-D printer. The BPFs exhibited low insertion loss (IL < 0.5 dB) and a 4.5 stopband-to-passband ratio with 35 dB rejection, which is the highest among the existing spurious-free coaxial cavity-based BPFs

Multiband magnetless isolators and circulators with reconfigurable bandpass filtering capabilities

This article reports on the RF design and practical validation of new classes of magnetless multiband isolators and circulators with reconfigurable bandpass filtering capabilities. They are based on transversal frequency-selective signal paths shaped by frequency-tunable and spatiotemporally modulated resonators. Each path creates a passband that can be independently controlled in terms of frequency and direction of propagation. Thus, the overall network may exhibit 1-to- $K$ frequency-reconfigurable non-reciprocal passbands. The operating principles and schematic of the magnetless and reconfigurable filtering isolator concept are first demonstrated through circuit-based simulations of two-and three-path transversal filtering networks (i.e., two-and three-band networks). The independent modulation parameters of the bands are determined through detailed parametric analyses. Next, the concept is extended to the design of magnetless, multiband filtering circulators. The operating and design principles of the circulator are expounded through a circuit schematic and an ideally simulated dual-band example. For practical demonstration purposes, three lumped-element (LE) prototypes, two isolators, and one circulator, shaped by two or three RF signal paths (i.e., two and three passbands), were implemented at very high frequency (VHF) band. They exhibited a maximum in-band isolation (IS) up to 50 dB. Moreover, a frequency tuning of up to 1.22:1 and change of directionality are achieved

GaAs MMIC nonreciprocal single-band, multi-band, and tunable bandpass filters

This article reports on the RF design and practical development of active MMIC single-band, multi-band, and tunable bandpass filters (BPFs) with lossless and nonreciprocal transfer functions. They are based on series-cascaded lumped-element frequency-selective cells that are coupled with MMIC-based FETs. The FETs introduce gain and counteract the loss of the lossy elements. Furthermore, due to their unilateral behavior, nonreciprocal transfer functions can be obtained. This allows for an RF codesigned filtering isolator functionality to be created within a single RF component. By cascading multiple frequency-selective cells, both single-band and multi-band transfer functions with and without transmission zeros (TZs) can be realized. The basic operating principles of the MMIC concept are first described through parametric studies on different types of frequency-selective cells. These are followed by tunable and higher selectivity design methodologies. For practical demonstration purposes, four MMIC prototypes were designed, built, and measured using a commercially available GaAs process. They include a three-cell frequency-tunable BPF, two dual-band BPFs, and a quasi-elliptic BPF

X-band quasi-elliptic non-reciprocal bandpass filters (NBPFs)

This article reports on the design and practical development of RF co-designed MMIC components that exhibit the function of a bandpass filter and an RF isolator. They are based on cascaded non-reciprocal frequency-selective stages (NFSs), one-pole/two-transmission zero (TZ) multi-resonant stages, and impedance inverters. The combination of these components results in a two-port network that exhibits a nonreciprocal quasi-elliptic bandpass filter (NBPF) response in the forward direction and full RF signal cancellation in the reverse one. The operating principles of the NBPF are presented through various circuit-based design examples of low- and high-order configurations. For proof-of-concept demonstration purposes, NBPF prototypes were designed on an MMIC GaAs process and were experimentally validated at X-band. They include a two-pole/two-TZ NBPF and a three-pole/four-TZ NBPF

A monolithic vertical integration concept for compact coaxial-resonator-based bandpass filters using additive manufacturing

This paper reports on a compact, low-cost and low-loss monolithic integration concept for additively-manufactured coaxial-resonator-based bandpass filters (BPFs). Size compactness and low weight are achieved by vertically-stacking capacitively-loaded coaxial resonators and by monolithic integration that eliminates the need for assembly screws or fixtures. Furthermore, the proposed vertical integration concept allows for: i) flexible cross couplings to be realized enabling highly-selective transfer functions through transmission zero (TZ) generation and ii) for fairly complex geometries to be manufactured using low-cost stereolithography apparatus (SLA). For proof-of-concept demonstration purposes, a two-pole BPF with fractional bandwidth (FBW) of 8.5% and a three-pole/one-TZ BPF with FBW 6.2% at 3.8 GHz were designed, SLA-manufactured and measured. They exhibited low-levels of insertion loss ( 1,833 and wide spurious-free operation

Continuously variable W-band phase shifters based on MEMS-actuated conductive fingers

This paper presents four continuously variable W-band phase shifters in terms of design, fabrication, and radiofrequency (RF) characterization. They are based on low-loss ridge waveguide resonators tuned by electrostatically actuated highly conductive rigid fingers with measured variable deflection between 0.3° and 8.25° (at a control voltage of 0-27.5 V). A transmission-type phase shifter based on a tunable highly coupled resonator has been manufactured and measured. It shows a maximum figure of merit (FOM) of 19.5°/dB and a transmission phase variation of 70° at 98.4GHz. The FOM and the transmission phase shift are increased to 55°/dB and 134°, respectively, by the effective coupling of two tunable resonances at the same device with a single tuning element. The FOM can be further improved for a tunable reflective-type phase shifter, consisting of a transmission-type phase shifter in series with a passive resonator and a waveguide short. Such a reflective-type phase shifter has been built and tested. It shows a maximum FOM of 101°/dB at 107.4GHz. Here, the maximum phase shift varied between 0° and 377° for fingers deflections between 0.3° and 8.25

A frequency transformation for co-designed multi-passband/multi-embedded-notch RF filters

IEEE A class of multi-resonant RF filtering stage that exhibits a multi-band bandpass filtering transfer function with embedded in-band notches is presented. It is derived from the application of a composed lowpass-to-multi-passband/multi-stopband frequency transformation that converts the normalized lowpass prototype into the proposed multi-passband/multi-embedded-notch filtering cell. Thus, when employed in higher-order filtering networks, high-selectivity multi-band bandpass-filter (BPF) counterparts with embedded in-band stopbands are synthesized. Furthermore, two different approaches for out-of-band transmission-zero (TZ) generation in these type of filters to achieve sharp-rejection characteristics into them are detailed. The operational foundations of the engineered multi-passband/multi-embedded-notch filtering stage are described, along with several illustrative first-to-multi-order theoretical design examples with/without stopband TZs. Moreover, for experimental-demonstration purposes, a proof-of-concept microstrip prototype of a third-order dual-band BPF with two and one embedded notches in its lower and upper transmission bands, respectively, is manufactured and characterized

Tunable quasi-reflectionless bandpass filters using substrate integrated coaxial resonators

This brief reports on the electromagnetic (EM) design and the practical development of frequency-reconfigurable quasi-reflectionless bandpass filters (BPFs) using substrate integrated coaxial (SIC) resonators. The filter concept is based on in-series-cascaded quasi-reflectionless stages that are shaped by a first-order bandpass section and two resistively-terminated first-order bandstop sections. For the first time, we explore the realization of these filters using tunable SIC resonators that exhibit high quality factor (Q) and can be widely tuned with commercially-available linear piezoelectric actuators. Synthesized examples alongside various EM design and practical integration aspects are discussed in detail. The concept is experimentally validated at S-band through the manufacturing and testing of two reconfigurable (one-stage and two-stage) prototypes

Non-reciprocal balanced bandpass filters with quasi-elliptic response

This paper reports on the RF design and practical development of a non-reciprocal balanced bandpass filter (BPF) that exhibits a highly-selective quasi-elliptic response in the forward direction of propagation that is shaped by four transmission poles and two transmission zeros (TZs). By modulating some of the filterâ s resonators with phase-progressed AC signals, a non-reciprocal response is obtained in the differential mode. Its common-mode is also highly suppressed due to the incorporation of a balanced network that results in two additional TZs and resistive loss that are unique to the common-mode. The filter order can be increased by cascading additional resonators. For validation purposes, a microstrip prototype centered at 725 MHz was designed, manufactured, and measured. It showed a high isolation in the differential-mode reverse transmission of up to 62.1 dB. Moreover, the common-mode was suppressed by over 45 dB in a bandwidth greater than one octave