dBm RF Research Articles

Non-reciprocity in a silicon photonic ring resonator with time-modulated regions.

Non-reciprocity and breaking of the time-reversal symmetry is conventionally achieved using magneto-optic materials. However, the integration of these materials with complementary metal-oxide semiconductor (CMOS)-compatible platforms is challenging. Temporal modulation is a well-suited approach for achieving non-reciprocity in integrated photonics. However, existing experimental implementations based on this method in silicon uses traveling-wave modulation in the whole structure or tandem ring or waveguide modulators, and they lead to high insertion loss and large footprint. In this work we achieve, to the best of our knowledge, the first experimental demonstration of non-reciprocity in a compact single silicon photonic ring resonator with time-modulated regions, fabricated with a CMOS-compatible commercial foundry. We demonstrate symmetry breaking of counter-rotating modes in an active silicon photonic ring resonator by applying phase-shifted RF signals to only two small p-i-n junctions on the ring, without employing traveling-wave modulation in the whole structure. The non-reciprocity is caused by the cross-coupling between the counter-rotating modes of the ring, which breaks their degeneracy. By reversing the polarity of the RF phase difference (e.g. (45°,-45°) asymmetric phases) opposite resonance wavelengths are obtained, with a 16-dB contrast between the transmissions of the asymmetric phases and a low insertion loss of 0.6 dB under 27 dBm RF power. We achieve the highest ratio of the asymmetric transmission to the insertion loss, among the state-of-the-art silicon non-reciprocal integrated optical structures based on time varying modulation. The non-reciprocal ring can be used as a magnetic-free, low-loss, compact, and CMOS-compatible integrated optical isolator.

Opto-RF transduction in Er3+:CaWO4

We use an erbium doped CaWO4 crystal as a resonant transducer between the RF and optical domains at 12 GHz and 1532 nm respectively. We employ a RF resonator to enhance the spin coupling but keep a single-pass (non-resonant) optical setup. The overall efficiency is low but we carefully characterize the transduction process and show that the performance can be described by two different metrics that we define and distinguish: the electro-optics and the quantum efficiencies. We reach an electro-optics efficiency of -84 dB for 15.7 dBm RF power. The corresponding quantum efficiency is -142 dB for 0.4 dBm optical power. We develop the Schrödinger-Maxwell formalism, well-known to describe light-matter interactions in atomic systems, in order to model the conversion process. We explicitly make the connection with the cavity quantum electrodynamics (cavity QED) approach that are generally used to describe quantum transduction.

Effects of Optical Sampling Pulse Power, RF Power, and Electronic Back-End Bandwidth on the Performance of Photonic Analog-to-Digital Converter.

The effects of optical sampling pulse power, RF power, and electronic back-end bandwidth on the performance of time- and wavelength-interleaved photonic analog-to-digital converter (PADC) with eight-channel 41.6 GHz pulses have been experimentally investigated in detail. The effective number of bits (ENOB) and peak-to-peak voltage (Vpp) of converted 10.6 GHz electrical signals were used to characterize the effects. For the 1550.116 nm channel with 5.2 G samples per second, an average pulse power of 0 to -10 dBm input to the photoelectric detector (PD) has been tested. The Vpp increased with increasing pulse power. And the ENOB for pulse power -9~-3 dBm was almost the same and all were greater than four. Meanwhile, the ENOB decreased either when the pulse power was more than -2 dBm due to the saturation of PD or when the pulse power was less than -10 dBm due to the non-ignorable noise relative to the converted weak signal. In addition, RF powers of -10~15 dBm were loaded into the Mach-Zehnder modulator (MZM). The Vpp increased with the increase in RF power, and the ENOB also showed an increasing trend. However, higher RF power can saturate the PD and induce greater nonlinearity in MZM, leading to a decrease in ENOB, while lower RF power will convert weak electrical signals with more noise, also resulting in lower ENOB. In addition, the back-end bandwidths of 0.2~8 GHz were studied in the experiments. The Vpp decreased as the back-end bandwidth decreased from 8 to 3 GHz, and remained nearly constant for the bandwidth between the Nyquist bandwidth and the subsampled RF signal frequency. The ENOB was almost the same and all greater than four for a bandwidth from 3 to 8 GHz, and gradually increased up to 6.5 as the back-end bandwidth decreased from the Nyquist bandwidth to 0.25 GHz. A bandwidth slightly larger than the Nyquist bandwidth was recommended for low costs and without compromising performance. In our experiment, the -3 to -5 dBm average pulse power, about 10 dBm RF power, and 3 GHz back-end bandwidth were recommended to accomplish both a high ENOB more than four and large Vpp. Our research provides a solution for selecting optical sampling pulse power, RF power, and electronic back-end bandwidth to achieve low-cost and high-performance PADC.

Second- and Third-Harmonic Backscatter Through a Bandstop Filter Using Defected Ground Structure

In this brief, a novel harmonic-backscatter-rectifier (HBR) is introduced for simultaneous rectification and harmonic-based uplink. The proposed (HBR) employs a rectifier to generate both DC power and the harmonic carriers for backscattering communication, and a dual-band reconfigurable band-stop filter using defected ground structure (DGS) to modulate the second and third harmonics with low-power consumption and same input impedance at f0 all the time. As a proof of concept, an HBR prototype operating at 1.85 GHz was designed and experimented. An uplink data rate of 8 Mbps (4 Mbps × 2) was achieved when the HBR was fed with -10 dBm RF power, and the data modulation consumed less than 27.7 pJ/bit. In addition, a passive harmonic tag was implemented with the proposed HBR and a low-power binary sequence generator, which demonstrated a continuous uplink of 12 kbps at -6 dBm RF power.

3-D-Printed Dual-Band Rectenna System for Green IoT Application

This paper describes the novel fully 3D-printed dual-band RF energy harvester suitable for wireless sensor network green IoT applications. The proposed energy harvesting system is composed of a dual-band circular omnidirectional monopole antenna array with a T-junction power divider, RF rectifier, and an impedance matching network. The circular monopole antenna array is conformed to a cylindrical substrate to achieve the compact system. The Villard multiplier-based rectifier has been used for the conversion of RF signal to DC voltage. The presented rectenna is fabricated using a 3D printable, biodegradable, conformal and an economical substrate. The test is performed in an RF ambient environment. The manufactured configuration obtained conversion efficiencies of 67.29% with output voltage of 1.39 V and 42.16% with output voltage of 1.1 V at 0 dBm RF input power in 2.4 GHz and 5.2 GHz frequency bands respectively. The proposed configuration’s simulated and measured results are in concordance with each other. The study emphasizes the potential of 3D-printed rectenna in terms of cost-effective prototyping.

Design of RF energy harvester for 700 MHz

Abstract Radio frequency energy harvester is the conversion of ambient radio frequency electromagnetic waves into usable electrical energy, powering low-power devices without traditional power sources. In this paper, a novel RF energy harvester is proposed for 700 MHz frequency band. For the purpose of rectification, a Greinacher voltage rectifier cum multiplier is used in the circuit and Schottky Diode HSMS-2852 is used for implementing a rectifier. The LC impedance matching is implemented to improve the circuit performance of the harvester including conversion efficiency and output voltage. Simulation of the rectifier is done using the PathWave Advanced Design System (ADS) software. The rectifier shows the optimized performance at 5 kΩ load impedance. Simulation results show the highest efficiency of 33.1 % and an output voltage of 3.2 V with 8 dBm RF power at 700 MHz input frequency.

A Startup Control Method for Plasma Lamps by Using Fractional-N Phase-Locked Loop Microwave Driver

The microwave-driven plasma light source has the feature of the full spectrum, similar to sunlight, and has broad application prospects. Startups of plasma lamps are very difficult since the plasma density and the resonator impedance are changing constantly with the warm-up process and the RF driver can hardly couple the power to the plasma efficiently. This paper presents a startup control method for plasma lamps by using an integrated fractional-N phase-locked loop (PLL) as the RF signal source. An RF control module including a 21 dBm RF source with a band of 430–460 MHz and detection circuits for the RF driver is developed, and the startup process of the plasma lamp is further studied by analyzing the return loss of the resonator under the plasma load. According to the test result, the maximum frequency deviation of the RF control module is 3.3 kHz over the working temperature range of −40–80 °C. The designed RF control module is used to drive a high-power amplifier to start the plasma lamp automatically. It takes 79 s to achieve the stable arc operation from the gas breakdown. The return loss of the resonator is −26 dB, with an incident power of 171 W and reflected power of 418 mW, indicating that the RF driver and the plasma achieve good coupling. Compared with continuous wave, the luminous flux of the lamp powered by RF pulse improves by 18% under the same electric power. This startup control method has stable performance, small temperature drift, and an effective control function for plasma lamps.

Microfluidic Particle Separation and Detection System Based on Standing Surface Acoustic Wave and Lensless Imaging.

Separation and detection of micro-particles or cells from bio-samples by point-of-care (POC) systems are critical for biomedical and healthcare diagnostic applications. Among various microfluidic separation techniques, acoustophoresis-based technique has the advantages of label-free and good biocompatibility. However, most of the existing separation techniques are bulky and require additional equipment for analysis. We proposed a platform, which integrates an acoustophoresis-based separation device and a lensless imaging sensor into a compact standalone system to tackle this challenge. Standing Surface Acoustic Wave (SSAW) is utilized for label-free particle separation, while lensless imaging is employed for seamless particle detection and counting using self-developed dual-threshold motion detection algorithms. In particular, we specially optimized the design of microfluidic channel and interdigital transducers (IDTs) for higher performance bioparticle separation, designed a heat dissipation system for the suppression of fluid temperature, and proposed a novel frequency-temperature-curve based method to determine the appropriate signal driving frequency for IDTs. At 2 μL/min flow rate, separation efficiency of 93.52% and purity of 94.29% for 15 μm microbead were achieved in mixed 5μm and 15μm microbead solution at a 25 dBm RF driving power, and similar results for mixed 10 μm and 15 μm microbead solution. The results showed that the integrated platform has an excellent capability to seamlessly separate, distinguish, and count microbeads of different sizes. Such a platform and the design methodologies offer a promising POC solution for label-free cell separation and detection in biomedical diagnostics.

Broadband RCN-based RF-rectifier with a large range of power for harvesting ambient wireless energy

In this paper, a broadband RF-rectifier with a wide scale of RF input power levels, using FR-4 substrate, is proposed. A wideband resistance compression network (RCN) is applied to achieve the unique RF-rectifier design approach. The method improves the matching performance of the circuit over a broader range of the available input RF signals and frequency. The RF-rectifier circuit is configured in two sections. The two sections are configured using a modified L-section matching network (MN) through a series impedance transformer (ITx). A wideband RCN integrates the two RF-rectifier segments to a 50 Ω transmission line (TL). The design provides a wider span of accessible RF power from −15 to 15 dBm via a 2 kΩ load terminal. The proposed RF-rectifier achieved a simulated and measured fractional percentage bandwidth (FBW) of 38.5% and 38% from 1.780 to 2.620 GHz and 1.780 to 2.610 GHz, respectively. The maximum measured RF-to-DC PCE and output DC voltage (Vdc) realized by the proposed RF harvester are 75.5% and 3.2 V, respectively. The design also reached a high PCE of 88.25% and 15.10%, respectively, from the quad-tone signals at 10 and −20 dBm RF input power. The proposed RF-rectifier’s ambient evaluation produces a Vdc of 0.322 V and also activated a low-power bq25504-674 evaluation module (EVM) at 0.682 V.

Low Phase Noise Direct-Modulation Optoelectronic Oscillator

A direct-modulation OEO (DM-OEO) generating stable 10 GHz and 20 GHz signals is presented. A single loop and a dual loop approach are implemented and compared. We show an output signal of 15 dBm RF power, and a phase noise as low as −135 dBc/Hz at 10 kHz offset from the 10 GHz carrier. The 20 GHz second harmonic exhibits a noise level of −127 dBc/Hz at 10 kHz. A high spur level reduction is also obtained in the dual loop architecture.

Fabrication and modeling of antenna integrated uni-traveling-carrier photodiodes

The fabrication and modeling of bow-tie antenna integrated uni-traveling carrier photodiodes (UTC-PD) are presented. The experimental results show that a −10.68 dBm RF power can be obtained from the 4 × 50 μm2 area UTC-PD at 100 GHz. The device is modeled by high frequency simulation software. The trend of variation of the measured terahertz (THz) power with frequency matches well with the simulation results. Based on the model, the effects of the shape and the contact pads of the antenna on the THz power emission properties of the device are studied numerically, which helps to further optimize the device design.

Radio Over FSO Communication Using High Optical Alignment Robustness 2D-PDA and its Optical Path Switching Performance

We propose a 30 GHz radio over free-space optical (FSO) communication system for indoor wireless communication applications using a newly developed high-speed photodetector array (PDA) device. The new device performs the role of a photodetector with high optical alignment robustness and also acts as a 30 GHz optical-to-radio converter. Small high-speed photodetectors of 30 mm size are arranged in a 6 × 6 square-shaped alignment to achieve -4.4 dBm RF output at 30 GHz with an external amplifier. A 3-5 dB in-plane RF power distribution in the 4 × 4 PDA region was evaluated. To confirm the proposed concept, a 1 m long radio transmission over a 1.5 m long FSO transmission setup was demonstrated by switching the optical paths. We successfully confirmed a high data rate of up to 21.1 Gbps using several modulation formats under a static optical path switching condition. Additionally, stable and reproducible error vector magnitudes with a range of approximately 9% were recognized during the 10 switching cycles under a dynamic optical path switching condition.

Waveform Optimization Using RF Pulse Signal on Voltage-Doubler Broadband Rectenna

In this article, the DC-output improvement of a broadband rectenna has been demonstrated using pulse signal. The pulse waveform is optimized by varying its duty cycle as well as its modulation frequency. The rectenna operating from 1.6 to 2.8 GHz is characterized experimentally with low/medium RF power and different loads. The optimized waveform has a duty cycle that varies between 1 and 20 % for a modulation frequency between 1 and 6 MHz. The results show that the DC voltage and the efficiency are improved over the frequency band of interest, particularly for frequencies below 1.8 GHz and those above 2.6 GHz. The DC-output improvement, compared to the 1-tone signal, is characterized by the calculation of voltage/efficiency gain. High gain values are experimentally obtained: close to 14 dB at 1.675 GHz and -20 dBm RF power. The voltage gain is greater than 0 dB for low (3 kΩ) and high (100 kΩ) loads. At 2.4 GHz and for a low load of 3 kΩ, 4-dB gain is measured at -30 dBm. For a load of 100 kΩ, the efficiency goes from 8.3 % for the 1-tone to about 74.7 % for the optimized waveform, at -15 dBm RF power level.

A laser patterned zero bias Au/Al2O3/Mo metal-insulator-metal diode rectifier for RF detection

Metal-insulator-metal (MIM) diode is considered as a promising candidate for various high frequency applications owing to its tunneling dominant ultra-fast switching time. The zero bias operation of these diode rectifiers is very desirable for detection of low power RF signals. In the present work, an Au/Al2O3/Mo MIM diode integrated with coplanar waveguide (CPW) is fabricated and its rectification response is evaluated at zero bias i.e. without applying any external dc biasing across the diode. The complete device structure was patterned using the facile direct laser beam lithography technique forming the junction area of diode as small as 1 µm2. The as fabricated diode exhibited maximum sensitivity of 9.4 A/W at zero volt leading to significant zero bias rectification performance. The direct rectification at 5 MHz and 10 MHz were obtained with rectification ratios of 2.33 and 1.57, respectively while at 7 GHz frequency with 0 dBm RF power, the maximum rectified dc current was measured as 7 µA. The zero bias RF to dc conversion efficiency of the device was estimated as 0.55%.

An RF-Energy Harvester and IR-UWB Transmitter for Ultra-Low-Power Battery-Less Biosensors

A fully integrated 802.15.4a-LRP-UWB-PHY- and ETSI-compliant impulse-radio ultra-wide-band (IR-UWB) transmitter (TX) front-end, powered by an RF-energy-harvester in 180 nm CMOS technology, is presented. The TX is working in the 7 GHz band transmitting with -42 dBm at 5.12 kbps data rate, consuming 1.89 μW. Two circuit implementations of RF-energy-harvesters are presented and, based on measurements, a combined and optimized structure is proposed which is capable of generating 5 μW dc-power at -13.3 dBm RF input power at a frequency of 868 MHz. According to the overall SoC power budget, this amount of harvested energy is sufficient to power the IR-UWB-TX front-end, an ADC with pre-amplifier and the digital core logic for a wireless bio-sensing chip. Furthermore, improvements of the presented IR-UWB TX circuitry are discussed.

A Planar Antenna on Flexible Substrate for Future 5G Energy Harvesting in Malaysia

This article presents a planar monopole antenna on flexible substrate for middle band 5G (3.5 GHz) application in Malaysia. The antenna has been designed and optimized for its gain and efficiency with an improved performance in contrast of flexible substrate-based other antennas. The antenna resonates at 3.53 GHz and it has a -10dB bandwidth of 545 MHz. The bending effects of this antenna on the S-parameter and gain have also been investigated. The antenna is able to suppress all the other frequency bands until 20 GHz. The designed antenna has been utilized with a newly designed rectifier to act as an rectenna at 3.5 GHz for RF energy harvesting applications. A reasonable amount of DC output voltage of 930 mV, and a Power Conversion Efficiency of 43.5% have been obtained while 0 dBm RF input power is delivered to the rectifier input terminal. Apart from the utilization as an energy harvester being connected with the proposed rectifier, the designed antenna on flexible substrate can also be employed to biomedical and sensor applications.

High-Speed and High-Power MUTC Photodiode Working at 1064 nm

We demonstrate low-dark-current, high-speed and high-power back-illuminated flip-chip-bonded modified uni-traveling carrier photodiodes operating at 1064 nm. The photodiodes with $15~\mu \text{m}$ and $18~\mu \text{m}$ diameters achieve 18.6 dBm RF output power at 55 GHz and 19.4 dBm RF output power at 41 GHz, respectively. The bandwidth is analyzed with parameters obtained from S-parameter fitting. There is good agreement between measured and calculated bandwidths.

UWB antenna with dynamically reconfigurable notch band using rectenna and active booster

In this study, an ultra-wideband (UWB) monopole antenna with a dynamically reconfigurable notch band, along with the associated RF-triggered power management unit (PMU) that enables the dynamic reconfigurability, are presented. The UWB monopole antenna has a rectangular slot which hosts a J-shaped stub, electrically connected with the radiator using one PIN diode switch. When the diode is OFF, the monopole antenna has a UWB characteristic, while when it is turned ON a frequency notch is created at 5.6 GHz. The diode is fed from a PMU that consists of a rectenna and a DC-to-DC active booster. When the rectenna that consists of a patch antenna and a rectifier receives a -11 dBm or higher 5.6 GHz signal, it rectifies the RF signal into a sufficiently high DC voltage. The rectified DC voltage is applied to the cascaded DC-to-DC booster as enabling signal, and the booster provides at its output terminal sufficient DC power to actuate the PIN diode and thus dynamically reconfigure the UWB antenna. The dynamically reconfigurable notch band is created immediately in response to the reception of an external, -11 dBm RF signal at 5.6 GHz, and it disappears in real time immediately after the external RF signal is removed.

Design and development of 3 kW pulsed solid-state RF power amplifier using two LDMOS in parallel configuration at 1 MHz

A 3 kW and 1 MHz pulsed solid state RF amplifier has been designed and developed to drive TH581 tetrode tube based RF amplifier to realise 100 kW pulsed RF source. The driver amplifier is operated with 1 ms pulse width at 50 Hz repetition rate. The 3 kW RF power is obtained by operating two Gemini pair LDMOS transistors (VDD=50 V) in parallel configuration at device itself and having single ended topology with common lumped element based input and output matching network. The amplifier delivers 3 kW RF power when fed by 25 dBm RF input drive from the signal generator. This scheme eliminates the need of RF combiner and divider which results in low loss, high efficiency, lesser number of components, simple and compact design.

A low phase noise oscillator based on substrate integrated coaxial line technology

In this article, a miniaturized resonator based on substrate integrated coaxial line technology (SICL) is presented. The SICL resonator consists of a hairpin half-wavelength open-ended coaxial line element and two symmetrical parallel coaxial feed lines. The gap between the feed lines and the hairpin element can be adjusted properly to obtain a steep phase change, which can result in a higher group delay peak and achieve a superior phase noise performance. Based on the proposed SICL resonator, an X-band oscillator has been designed and demonstrated by using low-cost printed circuit boards (PCBs). Great consistency between the measured and simulated results is verified. According to the measured results, the oscillation frequency of the SICL oscillator is 10.0625 GHz with −1.81 dBm RF output power, and the phase noise is −138.6 dBc/Hz@1 MHz. The statistic figure of merit (FOM) is −206.1 dBc/Hz@1 MHz.