KEYWORDS: Photomicroscopy, Oscillators, Receivers, Linear filtering, Bandpass filters, Logic, VHF band, Signal detection, Sensors, Digital signal processing
High speed frequency dividers are critical parts of frequency synthesisers in wireless systems. These dividers
allow the output frequency from a voltage controlled oscillator to be compared with a much lower external
reference frequency that is commonly used in these synthesisers. Common trade-offs in high frequency dividers
are speed of division, power consumption, real estate area, and output signal dynamic range. In this paper
we demonstrate the design of a high frequency, low power divider in 0.18 µm SiGe BiCMOS technology. Three
dividers are presented, which are a regenerative divider, a master-slave divider, and a combination of regenerative
and master-slave dividers to perform a divide-by-8 chain. The dividers are used as part of a 60 GHz frequency
synthesizer. The simulation results are in agreement with measured performance of the regenerative divider.
At 48 GHz the divider consumes 18 mW from a 1.8 V supply voltage. The master-slave divider operates up to
36 GHz from a very low supply voltage, 1.8 V. The divide-by-8 operates successfully from 40 GHz to 50 GHz.
This paper demonstrates the use of modern electromagnetic simulation software to design and develop a selection of three novel transmission line transitions, for operation at mm-wavelengths, and an improvement in the performance of existing transitions. Specifically, our three case studies analyse (i) a microstrip-to-stripline transition, (ii) an inverted microstrip transition, and (iii) a mtripline-to-finline transition. The important concepts are described and the tools available are explained. A number of novel and effective designs are presented as examples.
Microstrip patch antenna arrangements offer many advantages. They provide low profiles, are light-weight and are easily integrated with the monolithic circuitry that has been embraced for miniaturised RF sensing systems. This paper presents the designs of 8-16 GHz bandwidth log-periodic and aperture-stacked based antenna arrangements. These antennas are examined in the light of the existence of alternatives (e.g., a Vivaldi tapered slot sensor) for operation as broadband sensing elements.
Microstrip patch antenna arrangements offer several well known advantages over other sensors including their low profile (and hence conformal nature), light weight, low-cost in production and compatibility with packaged miniaturised monolithic integrated and optoelectronic integrated circuitry. The major drawback of microstrip patch sensing solutions remains its inherently narrow bandwidth of ~ 2%. Although there has been intensive research to enhance bandwidth based on different strategies e.g., implementing stacked planar parasitic patches and thick substrate configurations and adopting low inductive techniques for feeding microstrip antennas, best approaches for broadening bandwidth for high frequency miniaturised sensor operation (>10 GHz) remain unclear. This paper discusses the development of broadband microstrip sensors for high frequency radiometric sensing operations. It considers the design and fabrication of frequency scanning sensors for Ku (~17 GHz) band operation comprising a microstrip transmission line network of series linked junctions feeding pairs of rectangular patches.
Although electronically scanned antenna arrays can provide effective mm-wave search radar sensors, their high cost and complexity are leading to the consideration of alternative beam-forming arrangements. Rotman lenses offer a compact, rugged, reliable, alternative solution. This paper considers the design of a microstrip based Rotman lens for high-resolution, frequency-controlled scanning applications. Its implementation in microstrip is attractive because this technology is low-cost, conformal, and lightweight. A sensor designed for operation at 77 GHz is presented and an ~80° azimuthal scan over a 30 GHz bandwidth is demonstrated.
The application of biotelemetry in the case of a RF controllable microvalve is discussed. Biotelemetry implies the contactless measurement of different electrical and nonelectrical parameters measured on human or animal subjects. A biotelemetry system consists of a transmitter and a receiver with a transmission link in-between. Transmitted information can be a biopotential or a nonelectric value like arterial pressure, respiration, body temperature or pH value. Transducers convert nonelectrical values into electrical signals. Radio frequency (RF) telemetry allows a patient greater mobility. Above all, the application of wireless communication becomes more and more popular in microinvasive surgery. Battery powered implants are most commonly used, but batteries must be changed after a period of time. To avoid this, wireless transcutaneous radio frequency (RF) communication is proposed for the powering and control of medical implants.
KEYWORDS: Antennas, Lens design, Sensors, Radar, Signal attenuation, Signal to noise ratio, Control systems, Microwave radiation, Adaptive control, Interference (communication)
The 77 GHz band has been reserved for intelligent cruise control in luxury cars and some public transport services in America and the United Kingdom. The Rotman lens offers a cheap and compact means to extend the single beam systems generally used, to fully functional beam staring arrangements.
Rotman lenses have been built for microwave frequencies with limited success. The flexibility of microstrip transmission lines and the advent of fast accurate simulation packages allow practical Rotman lenses to be designed at mm-wavelengths. This paper discusses the limitations of the conventional design approach and predicts the performance of a new Rotman lens designed at 77 GHz.
Rotman lenses have the potential to solve many problems associated with high frequency antenna arrays. Offering compact, rugged and reliable means of forming muli-beam, staring array sensing arrangements, these lenses may prove very useful if robust solutions to some important problems are to be found. This paper presents the performance of a Rotman lens design and discusses the challenges associated with the design of these lenses.
KEYWORDS: Antennas, Sensors, Collision avoidance, Lens design, Signal to noise ratio, Radiometry, Telecommunications, Matrices, Staring arrays, Ka band
Rotman lenses offer a compact, rugged and reliable means of forming multi-beam staring array sensing arrangements. The successful implementation of Rotman devices, that operate at mm-wave frequencies, is important to a wide range of applications ranging from covert military operations and collision avoidance in cars and boats in poor weather, to landing aids for aircraft. This paper discusses the development of a Ka-band microstrip-based Rotman lens that is to be used in collision avoidance and other military related roles.
Multi-beam approaches using beam-forming antenna array architectures
have been identified as one solution for overcoming the limited
fields-of-view provided by highly directional mm-wave sensors.
Rotman lenses offer a compact, rugged and reliable alternative to
electronically scanned antenna technologies but architectures that
operate at frequencies > 20 GHz perform poorly at higher frequencies
on account of greater losses and dispersion. This paper outlines the
design process for providing Rotman-based lenses, examining various
levels of simulation that are needed for designs that function at K
and W-band frequencies. The impact of using mictrostrip structures
is demonstrated.
Heart sounds can be utilized more efficiently by medical doctors when they are displayed visually, rather than through a conventional stethoscope. A system whereby a digital stethoscope interfaces directly to a PC will be directly along with signal processing algorithms, adopted. The sensor is based on a noise cancellation microphone, with a 450 Hz bandwidth and is sampled at 2250 samples/sec with 12-bit resolution. Further to this, we discuss for comparison a piezo-based sensor with a 1 kHz bandwidth. A major problem is that the recording of the heart sound into these devices is subject to unwanted background noise which can override the heart sound and results in a poor visual representation. This noise originates from various sources such as skin contact with the stethoscope diaphragm, lung sounds, and other surrounding sounds such as speech. Furthermore we demonstrate a solution using 'wavelet denoising'. The wavelet transform is used because of the similarity between the shape of wavelets and the time-domain shape of a heartbeat sound. Thus coding of the waveform into the wavelet domain is achieved with relatively few wavelet coefficients, in contrast to the many Fourier components that would result from conventional decomposition. We show that the background noise can be dramatically reduced by a thresholding operation in the wavelet domain. The principle is that the background noise codes into many small broadband wavelet coefficients that can be removed without significant degradation of the signal of interest.
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