Microwave Hardware Research Articles

200 GHz single chip microsystems for dynamic nuclear polarization enhanced NMR spectroscopy

Dynamic nuclear polarization (DNP) is one of the most powerful and versatile hyperpolarization methods to enhance nuclear magnetic resonance (NMR) signals. A major drawback of DNP is the cost and complexity of the required microwave hardware, especially at high magnetic fields and low temperatures. To overcome this drawback and with the focus on the study of nanoliter and subnanoliter samples, this work demonstrates 200 GHz single chip DNP microsystems where the microwave excitation/detection are performed locally on chip without the need of external microwave generators and transmission lines. The single chip integrated microsystems consist of a single or an array of microwave oscillators operating at about 200 GHz for ESR excitation/detection and an RF receiver operating at about 300 MHz for NMR detection. This work demonstrates the possibility of using the single chip approach for the realization of probes for DNP studies at high frequency, high field, and low temperature.

Towards microwave volumetric additive manufacturing: Generation of a computational multi-physics model for localized curing

Visible light-based volumetric additive manufacturing (VAM) technology has recently enabled rapid 3D printing of optically transparent resins in a single step. There is now strong interest in extending the design space of VAM to include opaque, scattering and composite materials. Microwave energy can penetrate more deeply than visible light into a broader family of materials. For microwaves to be useful for VAM, however it is necessary to have a fundamental understanding of material dielectric properties, microwave field propagation and localization. Here we present a multi-physics microwave beam formed-thermal diffusion model that addresses these needs. The model demonstrates its ability to optimize power delivery and curing time to obtain better thermal control. We validate the model with a proof-of-concept single-antenna experimental system operating at 10 GHz that is able to cure a wide variety of materials, including both optically translucent and opaque epoxy resins loaded with conductive additives with a minimum curing spot of 5 mm. While available microwave hardware operating at 40 Watt power cures the resins in 2.5 min, the model estimates the ability to cure in as less as 6 s at 1 Kilowatt power levels. This computational model and experiments lay the foundation for a future multi-waveguide microwave-based VAM system.

Simple and Easily Connectable Transition from Empty Substrate-Integrated Waveguide to a 3D Printed Rectangular Waveguide

3D printing is one of the most promising manufacturing methods in the most developed technological fields, including microwave hardware fabrication. On the other hand, the well-known manufacturing methods of planar substrate integrated circuits allow high-quality prototypes to be made at low cost and with mass production capabilities. The combination of both manufacturing methods, 2D or 2.5D (substrate integrated circuits) and 3D (3D printed structures), will allow us to take advantage of the main strengths of each technology and minimise disadvantages. In this article, for the first time, a transition structure between the Empty Substrate-Integrated Waveguide (ESIW) technology—a planar waveguide integrated on a printed circuit board—and a standard rectangular waveguide manufactured by 3D printing is proposed. This transition will make it possible to combine planar circuits with 3D structures, thus taking advantage of the benefits of both types of technologies. The fabricated prototype presents low losses (0.6 dB for the transmission coefficient and 15 dB for reflection coefficient), good electrical response (very flat), and simultaneously good mechanical stability and robustness to manufacturing and assembly errors. The proposed design for this transition piece is easily realisable for a wide range of affordable 3D printers. Repeatability is guaranteed and the proposed transition allows us to combine different SIC structures to 3D printed circuits. Hence, this transition will enable advancements in the fabrication of microwave devices, particularly with regard to satellite communications.

Guest Editorial Special Issue on Radar and Microwave Sensor Systems

This Special Issue is devoted to technical papers on radar and sensor systems in microwave and millimeter-wave bands. Massive technological progress has been made in recent years at the microwave device and component level, enabling new research directions on sophisticated microwave and millimeter-wave systems. Among the most significant fields of application for such systems has been sensor technology, with a major emphasis on radar systems. Interest in automotive sensing, wireless human-computer interaction, biometric measurements, industrial monitoring, and target tracking—among many other applications—has driven this interest. Advances in device and component technology are supporting system design concepts that treat the microwave hardware as a co-design element of the system, along with signal processing and antenna design. Such co-design is of particular importance in radar and sensor systems, where a rapidly increasing number of wireless devices and an increasingly crowded spectrum necessitates the design and use of specialized signals (both temporal waveform designs and spatial beamforming) to maintain and improve sensor performance. Systems designed for general broad applicability are becoming more challenging to implement, while specialized systems that co-design the aperture, microwave hardware, and signal processing are becoming increasingly relevant. Technologies such as digital array radar, distributed and networked sensors, computational imagers, high-sensitivity Doppler radars, and integrated millimeter-wave radar, to name only a few, have supported system-level developments.

Experiment and simulation of microwave detection using IQ demodulation method for breast tumor screening

Breast cancer has become the most diagnosed cancer in the world. Microwave detection the breast tumor is attractive due to its high dielectric property contrast between different tissues of tumor. In this paper, we proposed an In-phase-Quadrature (IQ) demodulation-based method to detect the breast tumor with microwave at a frequency of 1.3 GHz. The microwave detection system consists of two signal generators, 12 transmitting/receiving antennas, two talent switches, a phantom and an IQ-Mixer. The amplitude information at the receiving antennas can be obtained by analyzing the difference frequency signals generated with two microwave signal generators. We also use the finite-difference time-domain (FDTD) method for simulation verification, which can simulate the propagation of the electromagnetic wave. Through experiments and simulations of microwave hardware system and FDTD method, it can be proved that the results are consistent. The experimental and simulation results show that when the tumor phantom diameter decreases or its depth from the receiving antenna increases, whether there is a tumor phantom can be clearly distinguished. Moreover, we also explore the effects of different tumor phantom locations on the receiving antennas. The results show that it is feasible to detect the breast tumor with the IQ demodulation method based on microwave.

Substrate integrated circuits for high frequency of opto electronics

Another age of high-recurrence coordinated circuits is displayed, which is called substrate incorporated circuits (SICS). Current cutting edge of circuit plan and implementation stages dependent on this new idea are assessed and dis-cussed in delail. Various potential outcomes and various favorable circumstances of the SICS are appeared for microwave, millimeter-wave and opto hardware applications. Down to earth models are delineated with hypothetical and trial results for substrate coordinated waveguide (SIW), substrate incorporated chunk waveguide (SISW) and substrate incorporated non-transmitting dielectric (SI") direct circuits. Future innovative work patterns are likewise dis-cussed regarding ease imaginative plan of millimeter-wave and optoelectronic coordinated circuits.

Plastic and metal additive manufacturing technologies for microwave passive components up toKaband

AbstractThis paper illustrates the different possibilities given by additive manufacturing technologies for the creation of passive microwave hardware. The paper more specifically highlights a prototyping scheme where the 3D-printed plastic parts can be used as initial proofs of concept before considering more advanced 3D-printed parts (metal parts, for instance). First, a characterization campaign has been made on common plastics used by a 3D printer using the fused deposition modeling and material jetting (Polyjet©) technologies. The impact of the manufacturing strategy (high-speed or high-accuracy) on the part roughness, as well as on the dielectric material permittivity and loss tangent, has been specifically studied at 10 and 16 GHz. Based on a specifically optimized and deeply explained characterization method, the conductivity of a coating based on silver paint has also been characterized on such plastic parts at 10 and 40 GHz. These plastic materials and coating have been used for the creation of quasi-elliptic and tuning-free bandpass filters centered at 6 and 12 GHz and compared with a similar filter made of stainless steel by selective laser melting. Finally, a compact rectangularTE10to circularTE01mode converter also undergoes one prototyping step out of plastic before moving to an advanced part made out of stainless steel. This mode converter, which is made in a single part, is designed to operate from 28 to 36 GHz as a tuning-free final demonstrator.

A semi-dynamic heart model for UWB microwave transmission simulations and hardware evaluation

In this paper, we present a simplified semi-dynamic heart model for investigation of microwave transmission heart monitoring systems between 1.5 and 4 GHz in both simulation and measurement. We aim to validate that our proposed heart model is able to represent the heart structure at microwave frequencies by comparing our model to an accurate numerical heart model (anHM) from the ITIS foundation virtual population. Our simple numerical heart model (snHM) (simulation) and physical heart model (pHM) (measurement) are evaluated in a simplified human chest model using an UWB biomedical sensor. In simulation, the transmission parameter shows agreement with the time domain peak of −94.5 dB for the snHM and −96.4 dB in the anHM. The anHM and pHM transmission signal characteristics were then compared showing good agreement. Our heart model is able to represent the heart between 1.5 and 4.0 GHz and represents a step toward a real time dynamic heart model for hardware evaluation.

Panel sessions

The lunchtime panel sessions at the International Microwave Symposium (IMS) provide a platform for a spirited discussion on topics of interest to the Microwave Theory and Techniques community. During each 80-min session, short presentations by a number of leading experts will set the stage for a debate with an emphasis on audience participation. At IMS2014, we will have three panel sessions. A session will address the opportunities that exist for new devices, applications, and high-frequency (HF) use of graphene materials. Another session will discuss the new approaches for massive online open courses (MOOCs) that offer a modern yet controversial approach to university teaching. There will also be a joint IMS/Radio-Frequency Integrated Circuit (RFIC) Symposium lunchtime panel session on the impact of spectrum explosion on the microwave (MW) hardware that needs to respond to demands at multiple frequency ranges. Short summaries for the three panel sessions are given.

RF and Microwave Hardware Challenges for Future Radio Spectrum Access

Radio technology for future broadband wireless applications presents a remarkable research opportunity for the RF transceiver and circuit design community. A survey is presented of the low-noise amplifier, frequency conversion, filtering, and transmitter techniques that are being explored for future wireless devices that require wide tuning range, flexible modulation formats, low dc power, and low cost. In all cases, the traditional disadvantages of broadband design approaches can be mitigated by taking advantage of higher levels of integration afforded by CMOS and BiCMOS technologies and improved circuit design approaches.

Remediation of oil-contaminated drill cuttings using continuous microwave heating

This paper outlines a novel, continuous pilot-scale microwave treatment process for the remediation of oil-contaminated drill cuttings from North Sea drilling activities. The underlying scientific methodology is highlighted, and the development of the continuous processing concept is discussed. Continuous tests were carried out at throughputs up to 250 kg/h using microwave hardware capable of delivering up to 15 kW of microwave power at 2.45 GHz. It is shown that the cuttings can be remediated to below the offshore discharge threshold of 1% oil on cuttings, and that clean-up can occur to below 0.1% oil, which is the classification for non-hazardous waste. The trade-off between applied power, throughput and residual oil content is shown for tests carried out continuously over several hours. The energy consumption of the process is also shown in relation to the remediation levels achieved. The results obtained with the continuous pilot-scale system are compared with previous batch laboratory studies.

Microwave Sampling Beamformer—Prototype Verification and Switch Design

In this study, a four-element prototype of the microwave sampling beamformer structure is constructed and tested. The prototype is composed of the microwave hardware and control hardware. A new compact switch is designed and utilized in the structure. The control circuitry is a four-branch time delay and pulsewidth control circuits along with p-i-n diode drivers. The beamforming structure is designed to have 8-bit phase shifter resolution and 12-bit attenuation resolution. For each antenna element the phase shift and attenuation are controlled through the time delay and pulsewidth of the corresponding pulse train. Different beamforming examples such as beam steering, sidelobe level (SLL) control and null forming are examined with the prototype. It is observed that the structure scans the beams to the proper steering angles. SLL close to -30 dB and nulls deeper than -30 dB are measured.

Microwave Imaging of the Breast

Microwave imaging for medical applications has been of interest for many years. Recently, microwave imaging for breast cancer detection has gained attention due to advances in imaging algorithms, microwave hardware and computational power. The breast is relatively translucent to microwaves, accessible for imaging, and there appears to be a significant electromagnetic property contrast between tumors and healthy tissues. Therefore, breast imaging may be the first clinically viable application of microwave imaging. This paper reviews recent developments in passive, hybrid, and active approaches to microwave breast cancer detection.

Temperature compensation of total power radiometers

This paper describes a new technique to compensate output variations of total power radiometers due to physical temperature changes of the instrument. This technique performs the correction without the addition of expensive microwave hardware required in Dicke switching or many other widely used methods. A characterization period, over which the input antenna temperature is known, indicates the appropriate output adjustment needed for a change in physical temperature of the radiometer. The method effectively corrects the output in an example radiometer system built with inexpensive commercially available parts. For a 30-K variation in physical temperature, the measured data shows an improvement from 60-K peak-to-peak error to 6.9 K with an average absolute error of 1.1 K.

An airborne surveillance radar demonstrator

Advances in signal processing technology offer the radar designer an increasing opportunity to develop sophisticated detection and imaging algorithms. However, the design of many existing surveillance radar systems is such that the development, proving and implementation of even the smallest algorithmic changes can require costly and time-consuming equipment modifications. In the design of future radar systems there is therefore a strong case for the use of a programmable processor which is separated from the microwave hardware by a clearly defined interface. This paper presents some results from a research programme which has developed such a rapid prototyping environment by interfacing an existing in-service airborne maritime surveillance radar to a commercially available computer workstation and a high-bandwidth tape recorder.

Polarimetric radiometer configurations: potential accuracy and sensitivity

Ocean wind speed and direction can be assessed with a polarimetric radiometer system measuring the full set of Stokes parameters. There are two fundamentally different ways of implementing the polarimetric radiometer system: polarization combining and correlation radiometer systems. Also, within each fundamental category there are significant tradeoffs. This paper discusses the different implementation possibilities. Paramount issues are potential instrument stability and sensitivity as well as the tradeoff between increased microwave hardware complexity and fast digital correlator circuitry. It is concluded that each implementation has its role to play, but for a given application the choice of system configuration is important. Following these considerations, a second-generation airborne, imaging, polarimetric radiometer system, used by the authors for ocean wind vector sensing, is described and discussed.

Historical perspectives on commercial and nonmilitary government space applications of microwave systems in the Baltimore/Washington area

The Baltimore/Washington area has made significant contributions to commercial and nonmilitary government space applications of microwaves. These cover a wide swath extending from R&D laboratory items, basically experimental/proof-of-concept, to space-qualified microwave hardware, subsystems, and systems that were launched and operated in space, to operational Earth terminal subsystems. Microwave efforts also included elements in the design of communications satellite systems, satellite payloads and hardware, and satellites for remote sensing, their payload and some hardware, and radiowave propagation on the slant (Earth-satellite) path. Unique contributions include the Applied Technology Satellite-6 (ATS-6), the discovery and characterization of gigahertz ionospheric scintillation, possibly the first electronically steerable phased array and the invention and implementation of the waveguide multimode filter, the first space-qualifiable monolithic-microwave integrated-circuit chips and subsystems, state-of-the-art altimeters, possibly the first Cesium clock for space and the first high Tc microwave filter.

An X-band solid-state FM-CW weather radar

FM-CW radar has grown to a mature state owing to new breakthroughs in microwave and computer hardware. Applications of FM-CW radar so far have been mainly in the field of tropospheric research, meteorology and ship navigation. The paper describes a radar to be used for rain-rate determination and rain-cell contouring. The central themes are system fundamentals, system design and construction, and real-time processing of the radar. The new radar is purely solid state, with a CW power of 1 watt. Owing to the use of X-band frequencies, the radar waves need to be corrected for spatial expansion and for rain-induced attenuation along the radar path, using real-time processing. Results demonstrate the potential capability for suppressing coherent ground clutter as well as for detecting rain cells.

A simple microwave technique for plasma density measurement using frequency modulation

Describes a simple method of determining the phase variation unambiguously during microwave interferometric measurement. The frequency of the Klystron source is modulated with the help of staircase voltage pulse. The height of each stair is adjusted such that the corresponding phase shift in the test branch with an additional path length is 90 degrees . Signals, proportional to cosine and sine of the phase shift due to plasma, can be generated in the same channel and plasma density information can be inferred. The microwave hardware remains the same as in conventional interferometry and the cost of such a scheme is low.

An Analysis of short pulse and dual frequency radar techniques for measuring ocean wave spectra from satellites

A four‐frequency moment characterization of backscatter from the near‐vertical is applied to an analysis of the short pulse (SP) and dual frequency (DF) microwave techniques. It is found that (1) the range reflectivity modulation spectrum closely approximates the directional wave slope spectrum. Harmonic distortion is small and is a minimum near 10° incidence. (2) The SP measurement SNR (signal‐to‐noise ratio) is typically 20–30 dB greater than the narrowband DF SNR. The difference in SNR is the ratio of the range beam extent to pulse length, minus the ratio of beam‐limited to pulse‐limited Doppler spreads. It is concluded that narrowband DF measurements are basically impractical. To be practical, the DF technique must be ‘widebanded.’ SP measurements on the other hand are found to be practical, using existing space‐qualified microwave hardware.