Dimitra Psychogiou

Single/multi-band Wilkinson-type power dividers with embedded transversal filtering sections and application to channelized filters

This paper addresses the exploitation of signal-interference concepts for the realization of single/multi-frequency Wilkinson-type filtering power dividers in planar/lumped-element technologies. By embedding transversal signal-interference filtering sections into the arms of conventional Wilkinson-type power-divider topologies, RF/microwave power-distribution actions with intrinsic mono/multi-band bandpass filtering capabilities can be obtained. Analytical equations and rules for the theoretical synthesis of this dual-function device are derived. The generalization of the approach to multi-stage schemes for enhanced-performance designs or for the shaping of frequency-asymmetrical responses is also discussed. Furthermore, for practical demonstration, three prototypes are developed and characterized. They are a microstrip quad-band circuit for the 1-5 GHz range, a dual-band lumped-element device for the band of 0.2-0.6 GHz, and a new type of two-branch channelized active bandpass filter at 3 GHz that makes use of single-band versions of this dual-behavior component as signal-division/combination blocks.

Tunable VHF Miniaturized Helical Filters

In this paper, a miniaturization technique and a tuning concept that enable the realization of highly miniaturized and frequency reconfigurable helical filters are reported for the first time. The proposed filter design is based on tunable helical resonators with an internal volume of only 8.6 cm 3 and variable capacitive loading. A second-order bandpass filter was built and measured as a proof-of-concept demonstrator. The helical filter is manufactured with a CNC process and tuning is achieved through piezoelectrically actuated tuners, which are bonded over the helix apex. A measured center frequency tuning between 257-365 MHz was realized with an insertion loss between 0.3-3.2 dB including connector losses. The measured filter bandwidth varied between 6%-7.7%. Tunable resonators were also manufactured so as to extract the unloaded quality factor. It was measured between 392-639 for a center frequency tuning of 2.5:1 (156.5-395 MHz).

Large Stroke Staggered Vertical Comb-Drive Actuator for the Application of a Millimeter-Wave Tunable Phase Shifter

This paper presents the design, fabrication, and characterization of a MEMS actuator with large static deflection as a waveguide-mounted variable millimeter-wave phase shifter. The actuator is composed of a pair of interdigitated microplates actuated by vertical comb-drives and suspended by SU-8 torsional springs. The SU-8 spring possesses a thin metallization top layer and a reverse-T-shaped cross-section enabling low torsional stiffness and high in-plane stability. A maximum mechanical deflection of 10.3° is obtained under a dc actuation voltage of 35 V. The dynamic characterization of the device shows that the resonance frequency of the torsional mode is well separated from the other three bending modes, confirming the designed low torsional stiffness and high in-plane stability. The torsional viscoelastic creeping is measured as a function of time at different loads and shows a maximum of 0.5° for an applied voltage of 27.5 V. A high operation cycle test is conducted and the metalized SU-8 spring withstands 800 million cycles without showing fatigue. RF measurements show that a variable mechanical deflection angle between 0° and 8.2° results in a variable transmission phase shift up to 58.0°. The measured insertion loss is always below 5.1 dB at 98 GHz, corresponding to a figure of merit of 11.5°/dB.

A microdevice with large deflection for variable-ratio RF MEMS power divider applications

In this paper, we present the design and fabrication of a large deflection MEMS actuator directly integrated as a variable-ratio radio frequency (RF) power divider in a waveguide. The device is based on a tilting microplate suspended by SU-8 springs and driven by a vertical comb drive actuator. The fabricated device is characterized by laser Doppler vibrometer and white light interferometer measurements. The dynamic measurement confirms the resonance frequency of the torsional mode being around 370 Hz, from which the spring stiffness has been extracted and used for static modeling of the device. The fabricated microplate devices achieved deflection angles of 5.9° with a dc actuation voltage of 30 V. First RF transmission measurements show good agreement with results from electromagnetic field simulations. A variable power split ranging from equal division up to a ratio of more than 1:2 is measured at 82.5 GHz whilst keeping the amount of dissipated power below 25%. This is the first reported actuated RF MEMS device integrated in a metal waveguide operating at such high frequency.

Fully-Reconfigurable Bandpass/Bandstop Filters and Their Coupling-Matrix Representation

A new type of a tunable microwave filtering device with reconfigurable bandpass-filter (BPF) and bandstop-filter (BSF) operational modes is reported. It consists of series-cascaded BPF/BSF stages which are formed by two resonating nodes, one non-resonating node (NRN), and two impedance inverters. Each BPF/BSF stage results in two transmission zeros (TZs) that are generated at the natural frequencies of the constituent resonators, whose spectral locations can be reconfigured by tuning the resonating elements. Thus, multi-TZ BPF/BSF responses can be synthesized in the overall circuit which features fully-controllable performances by means of TZ reallocation. The coupling-matrix representation of the proposed frequency-agile BPF/BSF scheme is demonstrated. Moreover, an S-band two-stage prototype based on frequency-reconfigurable evanescent-mode cavity resonators is fabricated to experimentally validate the predicted behavior.

Reconfigurable Single/Multi-Band Filtering Power Divider Based on Quasi-Bandpass Sections

A new class of adaptive Wilkinson-type filtering power divider that simultaneously exhibits single/multi-band operation, frequency tuning, and controllable number of passbands is reported. It exploits the incorporation of single/multi-band quasi-bandpass sections into the input/output terminals of the power divider, whose quarter-wavelength-long transmission-line segments are reused as impedance inverters between the quasi-bandpass stages. In this manner, bandpass-type transfer functions are realized at the output nodes along with the power-distribution functionality. For experimental validation, a reconfigurable dual-band prototype that features tunable passbands in the range 0.8-1.2 GHz is designed, manufactured, and tested.

Series-cascaded absorptive notch-filters for 4G-LTE radios

This paper focuses on novel filtering architectures for LTE-band transmit and receive RF-filters. For the first time, it is demonstrated that advanced filtering components with low insertion loss (2.8-4.9 dB) and large attenuation stopbands (25-50 dB) can be created by series-cascaded absorptive bandstop filters with quality factors even as low as 12-45. Transmit and receive filter modules for LTE-band 1 duplex circuits are shown. Lumped-element absorptive bandstop filters with the highest reported Q of 43 at 2 GHz are presented. Tunability of the presented filter arc hitectures is also discussed.

Hybrid Acoustic-Wave-Lumped-Element Resonators (AWLRs) for High-

A new class of bandpass filters with quasi-elliptic frequency response, small physical size, and effective quality factors (Qseff) of the order of 1000 are presented. They are based on novel hybrid acoustic-wave-lumped-element resonator (AWLR) modules that enable the realization of bandpass filters with fractional bandwidths (FBWs) that are much larger (0.91-5.1 kt2) than the electromechanical coupling coefficient (kt2) of conventional acoustic wave (AW) resonator filters that exhibit FBWs between 0.4-0.8 kt2. In addition, they exhibit Qseff that are 25-50 times larger than in traditional lumped-element filter architectures. Quasi-elliptic single-pole bandpass filters (one pole and two zeros) made up of commercially available one-port surface AW resonators and surface-mount-device components are manufactured and measured at 418 MHz. Various passbands with FBW between 0.07% and 0.4% and insertion loss below 1.25 dB (i.e., Qseff in the range of 1525-5150) are demonstrated. Second-order bandpass filters (two poles and four zeros) with 0.24% FBW and less than 1.15 dB of insertion loss (i.e., Qseff of 4000) are also shown to improve the passband selectivity and out-of-band rejection. These filters feature dynamic stopband characteristics by tuning the position of their transmission zeros. The operating principle, theoretical analysis, and design guidelines of the AWLR module, as well as a comparison with traditional all-AW ladder-type filters, are also reported. An original and rather simple RLC-circuit equivalent of AW resonators that facilitates the incorporation of spurious modes into a simple Butterworth-Van-Dyke model for a more accurate synthesis of AWLR-based filters is extracted from measured two-port S-parameters.

Q

In light of todays crowded radio spectrum and the high level of receiver sensitivity required to receive very weak signals, mitigating interference (cosite, intentional jamming, or from other sources) has become a very important topic of research. The recent controversy regarding the use of spectrum close to the global positioning system (GPS) bands is the motivation for the IEEE Microwave Theory and Techniques Society 2014 International Microwave Symposium (IMS2014) Tunable Radio-Frequency (RF) Microelectromechanical Systems (MEMS) Filter Student Design Competition, held in Tampa, Florida. Although there are frequency bands reserved for GPS, there is sometimes interference from undesired signals from a variety of sources, such as radio emissions in adjacent bands, intentional/unintentional jamming, and naturally occurring space weather. Ensuring the continuity of GPS service requires the protection of its spectrum from interference. This competition was intended to interest students in the design of innovative RF front-end solutions to address this issue. This article describes the work of the winners of the first-place award.

Bandpass Filters With Quasi-Elliptic Frequency Response

Ultra-narrowband absorptive bandstop filters (ABSFs) are presented in this letter. They are based on a hybrid RF-design approach in which high-unloaded quality-factor (Q) acoustic wave (AW) resonators and low-Q lumped-element components are effectively combined to create narrow fractional-bandwidth (FBW) stopbands that exhibit theoretically infinite attenuation and effective quality factor (Qeff) of the order of a thousand. The proposed ABSF design approach is experimentally validated with two manufactured prototypes at 418 MHz that consist of commercially-available surface acoustic wave (SAW) resonators and surface mounted devices (SMDs). Measured FBWs as narrow as 0.02% that correspond to a Qeff of 10,000 and maximum stopband isolation of 68 dB validate the conceived ABSF design concept.