A concept of plasma-enabled tuning of radio frequency systems is introduced and experimentally verified in this paper. Specifically, a commercial gas discharge tube (GDT) is employed as a plasma cell integrated in an inductor-capacitor (LC) resonator. The principal factor affecting the characteristics of the LC circuit with the embedded GDT, studied for the first time in this paper, is the decrease in the cathode sheath thickness and thus increase in the capacitance of the plasma cell with increasing current in the abnormal glow discharge regime. The reduction of plasma cell resistance is an additional factor. The sample LC resonator demonstrates frequency tunability by 55% in the range of 240-372 MHz, while the discharge current increases up to 90 mA, at the expense of reduction in quality factor from 62 to 5 as a result of ohmic losses. Theoretical estimates based on the fundamental principles of glow discharges supplemented by circuit simulations show good agreement with measurements. The local minimum in frequency behavior of the resonator's quality factor is shown to be related to frequency-dependent plasma parameters. The results of this paper indicate that plasma tuning techniques could be a viable alternative for emerging applications.

Plasma-Enabled Tuning of a Resonant RF Circuit

Modern wireless devices operate on multiple frequency bands and, thus, can benefit from frequency-reconfigurable radio frequency (RF) components, especially filters that are typically larger in size and are required for every frequency band. In addition, many applications, such as wearable electronics, desire stable performance from the devices when they are bent or flexed. However, most of the reconfigurable filters are built on rigid substrates and utilize expensive discrete RF switches, which needs to be soldered to the filters. In this work, we present a fully printed filter that achieves reconfigurability through printed vanadium dioxide (VO2)-based switches that are extremely low cost and do not require any soldering for their attachment. The filter design is based on a dual-mode resonator, which enables a second-order filter despite a single resonator, thus helping in making the filter compact. It also helps in maintaining a decent insertion loss (2.6 dB), despite relatively low conductivity of the metallic ink. The switches, when activated thermally through a printed heater at the backside, reconfigure the frequency from 4 to 3.75 GHz. The filter has been realized on a flexible Kapton substrate, making the filter conformable to any surface. Measurements under various bending conditions reveal stable performance, making this filter design suitable for a number of wearable and the Internet-of-Things applications.

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Additively Manufactured Dual-Mode Reconfigurable Filter Employing VO₂-Based Switches

/pdf/microwave-front-end-subsystems-design-for-its-gps-3grj1b5twk.pdf

Microwave front-end subsystems design for ITS/GPS applications

This brief focuses on the radio frequency (RF) de- sign of novel high-quality-factor (Q) reflective-type bandstop filters (BSFs) with narrow bandwidth (BW), small physical size, and large stopband attenuation levels. They are realized by merging acoustic-wave-lumped-element resonators (AWLRs) and lumped-element impedance inverters in a single filter architec- ture. In this manner, deep stopband notches that correspond to resonators with effective quality factors (Qseff ) on the order of 1000 are created. Furthermore, the obtained rejection bands exhibit fractional BWs that are no longer restricted by the electro- mechanical coupling coefficient k 2 of the constituent acoustic wave (AW) resonators as opposed to the traditional all-AW filters. Experimental prototypes of first- and third-order frequency-static BSFs were built and tested at 418 MHz to validate the proposed concept. Measured stopbands with 3-dB BWs from 0.2 to 0.5 MHz, maximum stopband attenuation in the range of 15-43 dB, and passband insertion loss between 0.37 and 1.6 dB are reported. Moreover, an electronically switchable BSF with dynamic notch allocation is presented as a practical demonstrator device for switchable RF-interference suppression. A design methodology that relates to coupled-resonator filter formalism is also addressed to facilitate the systematic theoretical synthesis of the engineered AWLR-based reflective-type BSFs.

High-Q Bandstop Filters Exploiting Acoustic-Wave-Lumped-Element

A lumped-element varactor-tuned bandpass filter (BPF) with variable center frequency and constant absolute bandwidth (BW) is presented in this paper. Mixed electric/magnetic inter-resonator coupling schemes—implemented with parallel LC resonators—facilitate the actualization of an almost constant BW passband over a wide frequency tuning range (1.6∶1). The linearity performance of the varactor-tuned BPF is studied and an investigation to reduce the RF swing on the filters' tuning elements is presented. A third-order lumped-element BPF was designed, built and measured. It exhibited a tunable center frequency between 230–370 MHz with constant 3-dB bandwidth of 56.3 ± 0.2 MHz across the entire frequency band. Within this band, the insertion loss was measured between 0.9–1.4 dB and the third-order intermodulation intercept point (IIP3) was measured between 28.1–41.4 dBm.

Jin Li

Papers

A Compact L-Band Bandpass Filter with RF MEMS-Enabled Reconfigurable Notches