Showing papers by "Dimitra Psychogiou published in 2020"

Avoiding RF Isolators: Reflectionless Microwave Bandpass Filtering Components for Advanced RF Front Ends

Abstract: RF/microwave bandpass filters (BPFs) are fundamental components in high-frequency RF transceivers. On the transmitter side, they limit the transmitted RF signal bandwidth by suppressing out-of-band spurious signals and intermodulation products, which are primarily generated by the nonlinear active stages and can affect other RF systems. On the other hand, in the receiver, they reject out-of-band interfering/jamming signals and noise. Whereas a large variety of microwave BPFs have been proposed in the technical literature for multiple technologies (e.g., [1] and [2]), most of these BPF devices achieve their filtering functionality by means of the frequency-selective power reflection processing of the RF input signal. This means that those RF signals allocated within the operational bandwidth of the BPF are transmitted to the output terminal (with some tolerable added in-band loss and reflective-type filter, hence decreasing the mixer conversion gain.

Fully-Reconfigurable Non-Reciprocal Bandpass Filters

Abstract: This paper reports on the RF design of quasi-elliptic non-reciprocal bandpass filters (BPFs) with fully-reconfigurable transfer function. It is demonstrated that by modulating the resonant frequency of its constituent resonators, the RF signal propagation is only enabled in one direction-e.g., from port 1-to-2-whereas it is sufficiently suppressed in the reverse one. Furthermore, by varying the resonant frequency of the BPF's resonators, the transfer function in the forward direction can be tuned in terms of frequency and bandwidth (BW) and can be intrinsically switched-off. For practical demonstration purposes, a lumped-element prototype centered at 300 MHz was designed manufactured and measured. It demonstrated a 1.15:1 center frequency tuning and a 2.77:1 BW tuning range while maintaining a non-reciprocal behavior. For all tuning states, the minimum inband insertion loss in the forward direction was measured between 1.7 and 4.3 dB, whereas the isolation in the reverse direction was measured up to 30.9 dB.

Frequency-Selective Limiters Using Triple-Mode Filters

Abstract: This paper presents the first frequency-selective limiter (FSL) with both power-activation and user-prompted override that also features a reconfigurable threshold power and frequency tuning with closed-loop feedback The FSL is based on a tunable absorptive bandstop-to-all-pass filter with integrated electronics Three distinct modes are available: user-defined bandstop, power-activated bandstop, and all-pass mode In the user-defined bandstop mode, the FSL presents a measured notch of 45-55 dB at an user-defined center frequency within 15-2 GHz tuning range The out-of-band insertion loss is less 08 dB In the power-activated mode, the FSL switches intrinsically between its bandstop and all-pass responses based on the incident power level at any user-defined power threshold and frequency within the 15-2 GHz range In the all-pass mode, the measured loss is less than 31 dB at the user-defined center frequency and less 08 dB elsewhere The measurements are conducted including the two SMA connectors and the associated connector-to-microstrip transitions The threshold power level is tunable in the -45 to +8 dBm range The filter is designed and fabricated with high-quality substrate-integrated cavities with an extracted resonator unloaded quality factor (Qu) of 300 The unique features and the measured RF performance of the presented FSL are state-of-the-art results

High-Order Coaxial Bandpass Filters With Multiple Levels of Transfer Function Tunability

Abstract: This letter reports on high-order coaxial-resonator-based bandpass filters (BPFs) with multiple levels of transfer function tunability, namely center frequency ( $f_{\mathrm {cen}}$ ), bandwidth (BW), and intrinsic switching off. They are based on cascaded multi-resonant cells, each exhibiting one pole and two transmission zeros (TZs), and in-line resonators. The proposed concept allows for high-order quasi-elliptic responses without cross couplings that can be reconfigured by only tuning the resonators’ $f_{\mathrm {cen}}$ . Low-cost integration using 3-D printed cavities and varactor-based PCB tuners is also shown. For proof-of-concept validation purposes, a five-pole/four-TZ BPF with $f_{\mathrm {cen}}$ tuning 1.3–1.77 GHz (1.4:1), BW tuning: 62–217 MHz (3.5:1), and an intrinsic switching-off state with >35 dB of isolation was manufactured and measured.

Compact Substrate-Integrated Bandstop Filters Using Double-Resonant Coaxial Resonators

Abstract: This letter reports on the RF design and practical development of miniaturized substrate-integrated-(SI)-coaxial-resonator-based bandstop filters (BSFs). Size compactness is achieved through the use of double-resonant coaxial resonators that are shaped by two coupled capacitively loaded posts within the volume of a circular cavity. The operating principles of the double-resonant SI-coaxial-resonator-based BSF concept are demonstrated by means of coupled-resonator diagrams and synthesized examples of both single-stage and multi-stage higher order BSF configurations. For proof-of-concept validation, various single- and two-stage coaxial-resonator-based BSF prototypes were designed, manufactured, and measured at $S$ -band.

Reconfigurable All-Pass-to-Bandstop Acoustic-Wave-Lumped-Element Resonator Filters

Abstract: Acoustic-wave lumped-element resonator (AWLR)-based filters with reconfigurable all-pass-to-bandstop transfer function are reported. They are based on in-series cascaded resonant stages that comprise two parallel RF signal paths, namely: 1) a thru-line and 2) an AWLR-based resonant section. Reconfigurability is achieved by altering the phase of the thru-line through varactors. In this manner, the filter response can be reconfigured from an all-pass to an enhanced fractional bandwidth (FBW)—i.e., wider than the electromechanical coupling coefficient $k_{t}^{2}$ —bandstop one. For practical validation, two prototypes were designed and tested. They include 1) a single-stage prototype with insertion loss (IL) $2.4~k_{t}^{2}$ ), and a stopband isolation of 21.2 dB and 2) a two-stage prototype that exhibits an all-pass mode with IL $3.8~k_{t}^{2}$ ) and a tunable isolation between 20 and 43 dB.

Quasi-Absorptive Substrate-Integrated Bandpass Filters Using Capacitively-Loaded Coaxial Resonators

Abstract: This paper reports on the RF design of highly-selective substrate-integrated (SI) bandpass filters (BPFs) with two-port symmetrical quasi-absorptive characteristics. The proposed filter concept is based on a two-pole/one-transmission-zero (TZ) bandpass (BP) filtering section that is loaded at its input/output ports with resistively-terminated second-order bandstop (BS) sections. It features size compactness and low inband insertion loss (IL) that are obtained through: i) high-quality-factor SI capacitively-loaded coaxial resonators and ii) a BP section that is shaped by two resonators and a frequency-dependent coupling. Various synthesized examples and practical implementation aspects are discussed through coupled-resonator-based synthesis and linear simulations. For proof-of-concept demonstration purposes, an experimental prototype shaped by six SI resonators was designed, built, and measured. It exhibits a highly-selective symmetrical quasi-absorptive filtering transfer function with one TZ at the upper passband side and the following characteristics: center frequency: 3.68 GHz, 3-dB bandwidth: 590 MHz (16%), minimum in-band IL: 1 dB (including SMA connectors), in-band group delay: 1.79±0.5 ns, and return loss<10 dB for frequencies between 2.9 GHz and 4.9 GHz (i.e., 1.69:1 spectral ratio).

Substrate-Integrated Coaxial Bandpass Filters With Symmetrical Quasi-Absorptive Response

Abstract: This paper discusses a new class of substrate-integrated coaxial (SIC) resonator-based bandpass filters (BPFs) with symmetrical/two-port quasi-reflectionless behavior and quasi-elliptic-type power transmission response. The proposed quasi-absorptive SIC BPF concept is based on in-series-cascaded two-pole/one-transmission-zero (TZ) BPF modules that are resistively terminated with first-order bandstop filtering sections. High levels of filtering selectivity and low in-band insertion loss are obtained by using high-quality-factor coaxial-cavity resonators and a mixed electromagnetic (EM) inter-resonator coupling. The enabling capabilities of the engineered quasi-absorptive SIC-based BPF concept are discussed through various theoretical examples and the manufacturing and testing of an S-band prototype with the following performance metrics: center frequency of 3.75 GHz, minimum in-band insertion loss equal to 0.75 dB, 3-dB passband bandwidth (BW) of 540 MHz, and 10-dB-referred quasi-reflectionless BW equal to 1.93 GHz.

Co-Designed High-Efficiency GaN Filter Power Amplifier

Abstract: In this paper, we demonstrate a high-efficiency 4.7 GHz 4-W power amplifier with input and output matching networks designed as complex-impedance port filters, within a sub-6 GHz 5G band. The port impedances are determined by the load- and source-pull of a GaN HEMT for an efficiency-power tradeoff. The measured performance shows PAE=55% over a 9% fractional bandwidth, with 10 dB rejection at 4.5 and 5 GHz. Comparison with a cascaded PA-filter circuit shows 25% lower loss with a simultaneous 20% reduction in footprint.

Quasi-elliptic dual-band bandpass filters based on series-cascaded multi-resonant cells

Abstract: This paper reports on quasi-elliptic dual-band bandpass filters (BPFs) that were designed for the Filter Student Design Competition of the 2019 European Microwave Week The proposed lumped-element (LE) BPF concept is based on two dual-band transversal cells and one multi-resonant cell that allow the realization of symmetric and asymmetric dual-band transfer functions shaped by six poles and five transmission zeros A compact implementation scheme based on LE series resonators is proposed for size compactness and wide spurious free out-of-band response For proof-of-concept demonstration purposes, a dual-band LE prototype with two passbands centered 1 and 15 GHz was designed, manufactured, and measured It exhibited the following radio frequency measured performance characteristics Passbands centered at 102 and 145 GHz, minimum insertion loss levels of 20 and 27 dB, and bandwidth of 146 and 105 MHz, respectively, for the first and the second passband, and out-of-band rejection >30 dB between 0 and 894 MHz, 117–134 GHz, and 172–69 GHz

Tunable High-Order Multi-Band Bandpass Filters Using Transversal Multi-Resonant Cells

Abstract: This paper reports on the design of tunable high-order multi-band bandpass filters (BPFs). The proposed concept lays its foundations on series-cascaded multi-band stages, each of them shaped by two identical transversal multi-resonant cells. The transfer function characteristics of each band are tuned by a pair of resonators in each cell that control the center frequency, bandwidth (BW), and mode of operation—bandpass or all-reject—. The overall BPF exhibits a multi-band transfer function with 1-to-N bands that can be independently tuned in terms of frequency, BW, and number. The operating principles of this multi-passband filter concept are demonstrated through simulated examples of a quad-band BPF and the measurement of a tri-band microstrip prototype.

Quasi-Elliptic Coupled-Line-Based Balanced Bandpass Filters with Ultra-Wide Stopband Characteristics

Abstract: This paper presents the RF design of new types of balanced quasi-elliptic bandpass filters (BPFs). They are based on modified capacitive-loaded coupled line configurations and exhibit: i) highly-selective quasi-elliptic power transmission response in the differential (DD) mode of operation with ultra-wide stopband suppression and ii) ultra-wide common (CC) mode suppression. The proposed filter concept is presented by means of linear circuit analysis. For proof-of-concept demonstration purposes, a microstrip prototype operating at a center frequency of 3.45 GHz was designed, manufactured and measured. The proposed filter exhibits the following RF performance characteristics: 3-dB fractional bandwidth= 4.3%, > 20 dB out-of-band rejection from DC-3.24 GHz and 3.64-16 GHz, and >11 dB of CC mode suppression from DC to >16 GHz. Good agreement is observed between simulated and measured S-parameters.