Integrated microwave photonics, an emerging technology combining radio frequency (RF) engineering and integrated photonics, has great potential to be adopted for wideband analog processing applications. However, it has been a challenge to provide photonic integrated circuits with equal levels of function flexibility as compared with their electronic counterparts. Here, we introduce a disruptive approach to tackle this need, which is analogous to an electronic field-programmable gate array. We use a grid of tunable Mach–Zehnder couplers interconnected in a two-dimensional mesh network, each working as a photonic processing unit. Such a device is able to be programmed into many different circuit topologies and thereby provide a diversity of functions. This paper provides, to the best of our knowledge, the first ever demonstration of this concept and shows that a programmable chip with a free spectral range of 14 GHz enables RF filters featuring continuous, over-two-octave frequency coverage, i.e., 1.6–6 GHz, and variable passband shaping ranging from a 55 dB extinction notch filter to a 1.6 GHz bandwidth flat-top filter.

https://ris.utwente.nl/ws/files/6955872/optica-2-10-854.pdf

Programmable photonic signal processor chip for radiofrequency applications

A Debye relaxation model for the permittivity of aqueous glucose solution is given up to 40 GHz. Measurements of aqueous solutions are compared with invasive measurements on over 40 blood samples. Reflection- and transmission-based techniques are explained, concerning the application in biomedical concentration measurements. Wideband measurements on different sensing structures are introduced. Reflection- and transmission-based sensors are applied to a six-port reflectometer, as well as a homodyne vector network analyzer.

Microwave-Based Noninvasive Concentration Measurements for Biomedical Applications

The conventional resonant-type microwave microfluidic sensors made of planar resonators suffer from limited sensitivities. This is due to the existence of several distributed capacitors in their structure, where just one of them acts as a sensing element. This article proposes a very high-sensitivity microwave sensor made of a microstrip transmission line loaded with a shunt-connected series LC resonator. A large sensitivity for dielectric loadings is achieved by incorporating just one capacitor in the resonator structure. Applying sample liquids to the microfluidic channel implemented in the capacitive gap area of the sensor modifies the capacitor value. This is translated to a resonance frequency shift from which the liquid sample is characterized. The sensor performance and working principle are described through a circuit model analysis. Finally, a device prototype is fabricated, and experimental measurements using water/ethanol solutions are presented for verification of the sensing principle.

Ultrahigh-Sensitivity Microwave Sensor for Microfluidic Complex Permittivity Measurement

In this paper, a new type of microwave microfluidic sensor is proposed to detect and determine the dielectric properties of common liquids. The technique is based on perturbation theory, in which the resonant frequency and quality factor of the microwave resonator depend on the dielectric properties of the resonator. A microstrip split-ring resonator with two gaps is adopted for the design of the sensors (i.e., a double split-ring resonator). This resonator is both compact and planar, making it suitable for a lab-on-a-chip approach. Several types of solvents are tested with two types of capillaries to verify sensor performance. At 3 GHz, very good agreement is demonstrated between simulated and measured results.

Novel Microwave Microfluidic Sensor Using a Microstrip Split-Ring Resonator

This paper presents a high-performance substrate-integrated-waveguide RF microelectromechanical systems (MEMS) tunable filter for 1.2-1.6-GHz frequency range. The proposed filter is developed using packaged RF MEMS switches and utilizes a two-layer structure that effectively isolates the cavity filter from the RF MEMS switch circuitry. The two-pole filter implemented on RT/Duroid 6010LM exhibits an insertion loss of 2.2-4.1 dB and a return loss better than 15 dB for all tuning states. The relative bandwidth of the filter is 3.7 ± 0.5% over the tuning range. The measured Qu of the filter is 93-132 over the tuning range, which is the best reported Q in filters using off-the-shelf RF MEMS switches on conventional printed circuit board substrates. In addition, an upper stopband rejection better than 28 dB is obtained up to 4.0 GHz by employing low-pass filters at the bandpass filter terminals at the cost of 0.7-1.0-dB increase in the insertion loss.

A 1.2–1.6-GHz Substrate-Integrated-Waveguide RF MEMS Tunable Filter

In this paper, dielectric constants of lossy organic liquids are measured using oscillation frequency shifts of a negative-resistance voltage-controlled oscillator (VCO). The design and working principle of the oscillator and the effect of material loss are presented in detail. The proposed method provides relatively large frequency shifts of 10-110 MHz for lossy test sample volumes of 50-200 μL whose dielectric constants are between 2-13 at 4.5 GHz, thereby allowing good resolution in dielectric-constant measurement. To make the system self-sustained, the VCO is used as part of a frequency synthesizer system for frequency-to-voltage conversion and digital extraction of the frequency shift using a unique detection algorithm. The dielectric constant of several organic liquids have been extracted to an accuracy better than 2% using sample volumes of 50-200 μL , and has excellent agreement with reported values. The applicability of this system for sensing dielectric mixtures has also been shown, and volume fraction estimation has been demonstrated to an accuracy of around 1%.

A Self-Sustained Microwave System for Dielectric-Constant Measurement of Lossy Organic Liquids

This paper introduces a novel tunable SIW filter implemented using PIN diode switching elements The two-pole filter provides six states ranging from 155 GHz to 20 GHz (25% tuning) Fractional bandwidth ranges from 23% – 30% with insertion loss less than 54 dB and return loss greater than 14 dB over the entire tuning range Each SIW cavity is tuned by perturbing via posts connecting or disconnecting to/from the cavity's top metal layer In order to separate the biasing network from the SIW filter, a three-layer PCB is fabricated using Rogers RT/duroid substrates

http://ieeexplore.ieee.org/iel5/5606055/5614756/05616684.pdf

Tunable SIW bandpass filters with PIN diodes

Developing radio-frequency (RF), microwave, and millimeter-wave systems requires low-cost, mass-producible, high-performance, and high-yield technologies for passive and active sections. Dealing with radio coexistence and strong coupling between different subsystems while maintaining or even reducing the size and weight of the final system is a very challenging task. This is more important when designing passive circuits such as resonators, antennas, highly selective filters, couplers, power dividers, and circulators [1], [2]. Classical waveguide technology was, and in some cases still is, the mainstream for designing high-performance passive circuits and systems [3], [4]. However, these bulky and heavy concomitants are not suitable for integration and low-cost mass production. Via posts were first used under the name laminated waveguides [5] in 1998 and as a subset of substrate integrated circuits [6] in 2001 to form a planar waveguide structure. Then, by the introduction of the substrate integrated waveguide (SIW) technology as we know it today by Deslandes and Wu [7], a remedy for the full integration of active and passive circuits in a planar fashion was found [7]-[11]. Using this method, a nonplanar rectangular waveguide can be made in a planar form that is compatible with the existing printed circuit board (PCB) and lowtemperature cofired ceramic techniques [12]. Conductive walls in classical waveguides are replaced with planar-compatible PCBs via posts in SIW structures. Similar to classical metallic waveguides, by shortening the two openings of the SIW structure at both ends, SIW cavities can also be formed.

Tunable SIW Structures: Antennas, VCOs, and Filters

In this letter, a miniaturized, ultra-wideband (UWB) filter with notch using a slow-wave co-planar waveguide (CPW) multiple-mode resonator (MMR) is presented. By employing a slow-wave CPW MMR, the resonator length is reduced by 40% at mid-band frequency compared to the conventional CPW MMR. The proposed UWB filter employs stub-loaded microstrip-CPW transitions that improve the rejection skirt and defected ground structures (DGS) to provide better stopband rejection. A novel bridge structure is proposed to create a notch in the filter passband to reject WLAN interference. A passband from 3.1 to 10.6 GHz (110% bandwidth around 6.85 GHz) with a rejection notch at 5.65 GHz is achieved with insertion loss of 0.9 dB and return loss better than 10 dB. Using DGS, a rejection greater than 22 dB is achieved from 11 to 16 GHz while still having a 25% reduction in filter size compared to the conventional case. Design, simulation and measurement of filter prototypes are presented.

Vikram Sekar

Papers

A 1.2–1.6-GHz Substrate-Integrated-Waveguide RF MEMS Tunable Filter

A Self-Sustained Microwave System for Dielectric-Constant Measurement of Lossy Organic Liquids

Tunable SIW bandpass filters with PIN diodes

Tunable SIW Structures: Antennas, VCOs, and Filters

Miniaturized UWB Bandpass Filters With Notch Using Slow-Wave CPW Multiple-Mode Resonators