Conferences

3D Printed Circuits for RF and Microwave Applications

3-D printing is a promising technique to produce RF and microwave passive circuits. Compared with conventional machining techniques, 3-D printing enables manufacturing complex structures with great geometrical complexity and/or printing the devices into a standalone part without the need of further assembly. Another great advantage of 3-D printing is the significant weight reduction, when the device is printed from polymer and metal coated. 

This paper will present a range of 3-D printed passive circuits investigated at the University of Birmingham. These circuits cover a wide frequency range, from 0.5GHz to 100GHz, and consist of filters, OMT and Butler matrix. Most of the devices are based on lightweight polymers, which are capable of handling high temperature when ceramic filled resin is used.  3-D metal printing is also utilised to produce several designs including a W-band filter. All of the circuits are optimised for 3-D printing, so that enhanced microwave performance and/or considerable weight reduction can be achieved. This cluster of work demonstrates the great potential of using 3-D printing for microwave applications.

Antenna Beam Steering Without Phase Shifters - an 'Old' Technique Revisited

Antenna arrays have a perennial interest and relevance to RF wireless system designers, indeed the rise of 5G is showing their importance is only growing. Most implementations of linear arrays use phase shifters to feed the array and hence form the main-lobe beam. In the 1960s, a technique using RF switches and Fourier analysis was discovered to be a viable alternative to phase shifters - called the Time Modulated Array (TMA). Little modern research has been conducted in this area, despite its likely cost-effective implementation and technical relevance.

This paper presents a brief overview of the TMA, followed by our work into prediction and control of the RF harmonic levels in TMAs. The effect of RF ramping on the switching waveform is analysed first, followed by a novel way of reducing the carrier fundamental (due to the Fourier DC term) produced by TMAs. Finally, a novel RF transistor cascode fast switch is introduced, using 3 gain states, to pragmatically implement the reduction of the carrier fundamental. The transistor cascode in the TMA utilizes binary logic control interfaces, rather than analogue control interfaces, for hardware efficiency. Early simulation results are included.

High Efficiency Microwave Power Amplifiers for Portable Haemostasis Application

Uncontrolled haemorrhage from major trauma is leading mechanisms of death on the battlefield. Studies have shown that this is the case in up to 80% of potentially survivable cases and that approximately 69% of these cases were either torso or junctional based and would be unsuitable for treatment with standard tourniquet methods.

Presented herein is a portable microwave applicator capable of delivering microwave energy at 5.8 GHz to effectively coagulate bleeding sites which cannot easily be controlled under conventional haemostatic modalities. Using similar methods as used in operating theatres for the closure of bleeding vessels during surgery the device can coagulate both blood and specific vessels. This could be used an interim process to facilitate emergency evacuation to a suitable facility or, depending on severity, it can act as a longer-term solution if other facilities are not readily available.

The device consists of a handheld applicator with a radiative tip shaped to allow the user to apply local tamponade to the site whilst delivering energy thus increasing the likelihood of haemostasis. Microwave power of sufficient level to achieve haemostasis is produced within the “power pack” by means of a high efficiency class F power amplifier capable of producing up to 15 W. High efficiency operation of the power amplifier limits the amount of dissipated heat and DC power consumption. Active cooling mechanisms permit effective heat transfer for continuous use of the microwave applicator whilst a removeable battery provides sufficient DC power for each coagulation process and can easily be replaced if further energy delivery is required.

High-resolution Thermoreflectance Imaging of Power Microwave Transistors

The ever-increasing power density of semiconductors used in monolithic microwave integrated circuits (MMICs) and power amplifiers (PAs) mandates good thermal management and accurate temperature measurements are needed to study device reliability, assess temperature gradients, and to validate nonlinear electrothermal model performance.

Thermoreflectance based temperature measurements have been recently applied to high-power microwave semiconductors. The technique determines the temperature by measuring the change in reflectance from a surface due to changing in the index of refraction of the sample.  Since the measurement technique uses visible light, thermoreflectance imaging can achieve a spatial resolution of 290 nm and sub-nanosecond temporal resolution over a wide field of view.   This makes the method well suited to study the thermal dynamics within these transistors.

This presentation will review the capabilities of thermoreflectance measurement, explain the theory behind the thermoreflectance phenomenon, and demonstrate the usefulness of the method and the insights that can be gained by examining several recent measurements.

Millimeter Wave Band Propagation Studies for 5G Networks

Several frequency bands in the range 24-86 GHz have been identified by WRC15 as possible frequencies for future 5G radio networks.  To evaluate the radio channel in these bands, Durham University performed propagation studies in the frequency bands 25-28 GHz, 51-57 GHz and 67-73 GHz using the state of the art multiband Durham channel sounder. Using two transmit and two receive channels in each band, dual polarised measurements of typical indoor and outdoor environments were analysed to estimate a number of channel parameters such as path loss, delay spread and cross polar discrimination.  Results of both directional and omni-directional measurements will be presented outlining contributions to the international telecommunication union recommendations. 

On Wafer and Package Test with an Industrial Solution for MMIC Components

Test approaches have changed over the last years led by the high volume market, the complexity and the diversity of the functions (bare dies and packages) to be tested in a production environment.

Both Software and Hardware developments have been required.

Among these works, three examples are illustrated in this paper:

• Development of pulsed power test bench: combination of new equipment generation and powerful test software. Our approach is based on parallelization of multi parameter measurements, capture simultaneously power sweep and pulsed current (very fast test time). These test benches are used for high power circuits designed on GaAs and GaN technologies
• Development of E-band test benches for on wafer test (LNA, Multiplier, PA, IQ up and down converters)
• Development of software tools for data analysis and decision making (setup validation, monitoring in real time...)

The advance test solution integrates different measurement types: DC, noise, [S] parameters up to 110GHz, power measurements and conversion gain up to 86GHz.

The benefits are a higher flexibility, an easy and fast data access, test time reduction and wide test offers at high frequency.

Schottky Diode Based Frequency Sources to 360 GHz

Signal sources at 100s of GHz rely on technology which is not used in mass production and has traditionally been subject to significant variation in manufacturing accuracy and therefore performance.  Although the relatively recent emergence of MMIC amplifier circuit technologies has demonstrated circuits to a few 100 GHz, the highest power and frequency outputs use Schottky diode based circuits.  In this paper examples of European state-of-the-art frequency multipliers are reported (for example, 100mW Pout at 180GHz) which demonstrate how MMIC-type approaches are employed to improve the performance and ‘useability’ of planar Schottky diode technology beyond 300 GHz.

The Design of a Dual-Band PA for mm-Wave 5G Applications

Considerable time and money are currently being invested in developing millimeter-wave technology for 5G, and there is much debate and lobbying around the most suitable frequency bands for this application. Development work is currently underway in many candidate bands and it is looking increasingly unlikely that a single band will be designated on a worldwide basis for millimeter-wave 5G in the immediate future. This means that the availability of dual-band or multi-band millimeter-wave components will become increasingly attractive.

This paper will describe the design, layout, and performance of a dual-band power amplifier (PA) monolithic microwave integrated circuit (MMIC), capable of electronically switching its operating band between the 26GHz pioneer band identified by the EU's RSPG (24.25 to 27.5 GHz) and the 32GHz band (31.8 to 33.4 GHz). The design was implemented on a commercially available 0.15µm gate length pHEMT process and has an output power capability of 1 W at 1dB gain compression (P-1dB) and a small signal gain of  20dB.