Constant Beamwidth Research Articles

Design of Compact Dual-Polarized 1.2–10 GHz Eleven Feed for Decade Bandwidth Radio Telescopes

The Eleven antenna is a log-periodic folded-dipole-pair array with two unique radiation characteristics: a constant beamwidth and a fixed phase center location over a decade bandwidth. This paper presents a new compact design of a 1.2-10 GHz Eleven antenna, as a feed for reflector antennas by re-arranging the geometry of the outermost elements of the antenna. Due to the compact size, it is possible to put the whole feed system inside a compact cryostat and cool it down to cryogenic temperatures, in order to reduce the system noise temperature in radio telescope applications. The new compact Eleven feed has only a 40% volume of the original standard Eleven feed with a very similar performance. This reduces the capacity requirement for the cryogenic cooling system significantly and therefore the power consumption for future radio telescopes, such as the square kilometer array (SKA). The concept behind this compact design is analyzed in the paper. Simulations and measurements presented here have verified the design.

Fabrication and measurements of dynamic response of an SOI based non-planar CMUT array

An SOI based hyperbolic paraboloid geometry capacitive micromachined ultrasonic transducer (CMUT) array has been fabricated to realize a frequency independent constant beamwidth broadband beamforming capability. Detailed fabrication and packaging techniques are presented along with measurement results on individual CMUT cells for transient and steady-state response using a Polytec laser Doppler vibrometer. The measurement results are compared with analytical and 3-D electromechanical finite element analysis using IntelliSuite™. The measured results are in excellent agreement with analytical and FEA results. Measurement results also show that the CMUTs exhibit a flat bandwidth within the specified frequency range. SEM inspection also shows very close agreement between mask features and fabricated geometry that ensures reproducibility of the device with a high degree of fidelity. The CMUT array has been designed for automotive blindspot detection application and works in the 113–167 kHz range.

Digital beamsteering system using acoustic transducer array.

Acoustic signal processing can be applied to sonar, acoustic communications and multimedia applications. Especially transmitting acoustic signal to the desired direction has many applications in military and industry. In this paper, we present digital beamsteering algorithm using parametric array transducers. To generate the desired beampattern, the proposed algorithm utilizes the complex weight instead of time delay. With this complex operation, many algorithms including constant beamwidth algorithm and linear constrained beamforming algorithms can be applied to make versatile transmitting beampatterns. To verify the generated beampattern, we build acoustic beamsteering system by using commercial transducers and LABVIEW software and hardware. The system includes GUI software, which allows user to change many parameters such as number of sensors, complex weight of each sensor, type of transmit data, etc. The GUI can also be easily modified and extended to accommodate the characteristics of transducers. With the laboratory experiments, we verified the performance of the algorithm and system. The proposed algorithm and system can be used to build many application systems such as multimedia, acoustic communications, and sonar system. [Work supported by Grant No. UD100014DD.]

Wideband constant beamwidth coplanar waveguide-fed slot antennas using metallic strip loadings and a widened tuning stub with shaped reflectors

Sectored antennas with wideband operation for wireless communication systems are presented. The proposed configurations are based on a coplanar waveguide fed slot antenna using metallic strip loadings and a widened tuning stub above various reflector shapes. By shaping the reflector, noticeable enhancements in both unidirectional radiation pattern and beamwidth can be achieved while maintaining the simple fabrication and installation. Based on the results obtained, three sector antennas covering 72°, 90°, and 120° beamwidths suitable for five, four, and three sectors, respectively, have been proposed and designed. The simple structural configurations, low cost, and ease of half power beamwidth control of the proposed antennas make the design very attractive for practical implementation. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.

Constant-Beamwidth Loudspeaker Array

A loudspeaker is provided for receiving an incoming electrical signal and transmitting an acoustical signal that is directional and has a substantially constant beamwidth over a wide frequency range. The loudspeaker may include a curved mounting plate that has curvature over a range of angles. The loudspeaker may include an array of speaker drivers coupled to the mounting plate. Each speaker driver may be driven by an electrical signal having a respective amplitude that is a function of the speaker driver's respective location on the mounting plate. The function may be a Legendre function. Alternatively, the loudspeaker may include a flat mounting plate. In this case, the respective electrical signal driving each speaker may have a phase delay that virtually positions the speaker onto a curved surface.

Design of Broadband Constant-Beamwidth Conical Corrugated-Horn Antennas [Antenna Designer's Notebook

In this paper, a new design procedure is proposed for the design of wideband constant-beamwidth conical corrugated-horn antennas, with minimum design and construction complexity. The inputs to the procedure are the operating frequency band, the required minimum beamwidth in the entire frequency band, and the frequency in which the maximum gain is desired to occur. Based on these values, the procedure gives a relatively good design with a relative bandwidth of up to 2.5:1. Based on the proposed procedure, a corrugated-horn antenna with a constant beamwidth over the frequencies of 8 to 18 GHz was designed and simulated using commercial software. The designed antenna was also constructed, and its electromagnetic performance was measured. The measured results of the constructed prototype antenna confirmed the simulation results and satisfied the design requirements, validating the proposed design procedure.

SU‐GG‐J‐120: Longitudinal Resolution of the TomoTherapy® MVCT Image and Potential Improvements

Purpose: To quantify the longitudinal resolution of the TomoTherapy® MVCT image and evaluate potential improvements to the resolution. Method and Materials: The image slice sensitivity profile is measured using a thin‐disc method to approximate a delta impulse function in the longitudinal direction. The sensitivity profile is measured for several different helical pitches and beam widths. In addition, the clinical image longitudinal resolution is limited not only by the image slice sensitivity profile, but also by the image spacing. For a constant image slice profile (constant helical pitch and beam width), the image spacing is varied to investigate the impact of image spacing. Results: With the current TomoTherapy® factory settings for the jaw and the default image pitches (Fine, Normal, and Coarse corresponding to 4, 8, and 12 mm of couch translation per gantry rotation), the slice sensitivity profiles are measured to have a full‐width at half‐maximum of 6, 7, and 8 mm for the Fine, Normal, and Coarse pitches, respectively. Reducing the jaw‐width by an amount corresponding to a 3 mm decrease in the field‐width at isocenter, and keeping the same couch speeds of 4, 8, and 12 mm/rot, results in slice sensitivity profiles with a full‐width at half‐maximum of 4, 5, and 7 mm. Finally, using the thin jaw setting and “Normal” pitch (8 mm/rot), images are reconstructed at the default 4 mm interval as well as at a smaller interval of 2 mm. The sagittal and coronal images are observed to have a significantly improved resolution using the smaller image interval. Conclusion: The TomoTherapy® system currently offers users a balance between imaging speed and image quality. However, a thinner jaw setting and reduced image spacing result in significantly improved longitudinal resolution for TomoTherapy® MVCT images, yielding improved image quality at the same scanning speed.

Design of a MEMS discretized hyperbolic paraboloid geometry ultrasonic sensor microarray

Design of a discretized hyperbolic paraboloid geometry beamforming array of capacitive micromachined ultrasonic transducers (CMUT) has been presented. The array can intrinsically provide a broadband constant beamwidth beamforming capability without any microelectronic signal processing. A mathematical model has been developed and verified to characterize the array response. A design methodology has been presented that enables determination of the array's physical dimensions and CMUT modeling in a straightforward manner. Developed methodology has been used to design two discretized hyperbolic paraboloid geometry beamforming CMUT arrays: one in the 2.3 MHz to 5.2 MHz frequency range and another in the 113 kHz to 167 kHz frequency range. CMUTs have been designed using a cross-verification method that involves lumped element modeling, 3-D electromechanical finite element analysis (FEA), and microfabrication simulation. The developed array has the potential to be used in real-time automotive collision-avoidance applications, medical diagnostic imaging and therapeutic applications, and industrial sensing.

Broadband multimode baffled piezoelectric cylindrical shell transducers

Hollow piezoelectric cylindrical shell transducers may be made directional for underwater acoustic applications by the use of suitable acoustical baffles and the operational bandwidth may be extended by using multiple resonant modes. A theoretical and experimental investigation was performed for circumferentially baffled piezoelectric cylindrical shell transducers operating in the zero and one modes of extensional vibration. The frequency responses and directivity patterns were analyzed under various conditions of energizing separate halves of electrodes. It was found that the broadest frequency response with nearly constant beamwidth can be obtained when the two halves of the piezoelectric ring are electromechanically excited 90 deg out-of-phase. The experimental results obtained with a proof-of-concept transducer were in good agreement with the theoretical predictions.

Increasing the direct‐to‐reverberant ratio in rooms with a constant‐beamwidth, wide‐bandwidth loudspeaker array

A constant‐beamwidth, wide‐bandwidth (CBWB) loudspeaker array was used to improve speech intelligibility in two rooms. The CBWB loudspeaker array maintained a constant beamwidth between 500 Hz to 4 kHz. The array had a narrow vertical beam pattern and a wide horizontal beam pattern. During the study, an increase in the direct‐to‐reverberant ratio was observed that correlated with an increase in speech intelligibility (measured with the STI method). The correlation between improved speech intelligibly and an increased direct‐to‐reverberant ratio will be discussed, and the relation between each source’s beam pattern and the direct‐to‐reverberant ratio will be presented. The array was compared to a typical PA source and showed increases in the direct‐to‐reverberant ratio. Room simulations were conducted with CATT‐Acoustic and compared to real‐world measurements. The study showed an increase in the direct‐to‐reverberant ratio in each room, which corresponded to improved speech intelligibility.

Improving speech intelligibility in reverberant rooms

Speech intelligibility in rooms with long reverberation times has long been a problem for acousticians. This problem is exacerbated when the option for acoustic treatments is not an option for a variety of reasons. In this study, a constant-beamwidth, wide-bandwidth (CBWB) loudspeaker array was used to improve speech intelligibility in two multipurpose rooms where treatment was not an option. A CBWB loudspeaker array was designed with independent beam pattern control on both the horizontal and vertical axes. A wide horizontal beam pattern and narrow vertical pattern were designed to achieve constant coverage from 500 Hz to 4 kHz. The array incorporates four separate arrays, two with nested elements, and linear-phase FIR filters to maintain constant beamwidth over the three octaves of interest. Room simulations were conducted with CATT-Acoustic and the array was implemented and compared to a source with a more conventional coverage pattern. The STI method was used to measure speech intelligibility at several positions throughout the rooms. The study showed an improvement in speech intelligibility and a reduction in measured reverberation times.

A constant beamwidth transducer for ultrasonic applications

A new class of transducers that produce uniform wide beams (∼20 deg) at ultrasonic frequencies (∼1–2 MHz) is being developed by the US Navy for ultrasonic applications. These transducers will provide a wide insonified field of view for two‐dimensional ultrasonic imaging arrays. The design features a larger volume of active material, relative to conventional planar designs, which allows the application of higher drive fields. The prototype described in this article was driven to 200 VRMS and produced a sound pressure of 203 (dB re Pa at 1 m) at a frequency of 2.0 MHz. The details of the ultrasonic constant beamwidth transducer (CBT) design, its fabrication, and measured performance are presented. The ultrasonic CBT described in this paper will soon be incorporated into the Navy’s Underwater Sound Reference Division (USRD)’s Transducer Standards Loan Program.

The Eleven Antenna: A Compact Low-Profile Decade Bandwidth Dual Polarized Feed for Reflector Antennas

A novel dual polarized ultrawide-band (UWB) feed with a decade bandwidth is presented for use in both single and dual reflector antennas. The feed has nearly constant beam width and 11 dBi directivity over at least a decade bandwidth. The feed gives an aperture efficiency of the reflector of 66% or better over a decade bandwidth when the subtended angle toward the sub or main reflector is about 53/spl deg/, and an overall efficiency better than 47% including mismatch. The return loss is better than 5 dB over a decade bandwidth. The calculated results have been verified with measurements on a linearly polarized lab model. The feed has no balun as it is intended to be integrated with an active 180/spl deg/ balun and receiver. The feed is referred to as the Eleven antenna because its basic configuration is two parallel dipoles 0.5 wavelengths apart and because it can be used over more than a decade bandwidth with 11 dBi directivity. We also believe that 11 dB return loss is achievable in the near future.

Acoustic beamforming of a parametric speaker comprising ultrasonic transducers

A directional audible sound can be generated in air by means of the nonlinear interaction between intense amplitude modulated (AM) ultrasonic waves, which attracts much attention in the audio industry. In the case of sound reproduction by a parametric speaker comprising an array of ultrasonic transducers, a novel algorithm with Chebyshev window has been proposed to control the sidelobe level of the beam pattern by utilizing the acoustic nonlinearity and array signal processing technique. Furthermore, the beamforming approach is extended to the design of a broadband beamformer. In this paper, a single sideband modulation (SSB) system is developed for transmitting audio signal due to its efficient use of both power and bandwidth. By adding different weightings to the carrier and sideband frequencies, a constant beamwidth beamforming is achieved and confirmed in the simulation experiments.

Novel multiple phase centre reflector antenna for GMTI radar

Adaptive cancellation of stationary clutter for a ground moving target indicator (GMTI) radar requires antenna sensing using multiple apertures. In essence, simultaneous independent observations of the target plus clutter are required. Conventionally, multiple antenna apertures can be achieved through the use of physically separated antennas, or antennas which can be controlled so that subsections are used to receive. Herein, the use of reflector antennas to effect multiple phase centres is described. Multiple feedhorns pointed laterally from the focal point of the reflector are first reviewed, with capabilities and limitations discussed. A new technique for achieving multiple phase centres with a reflector antenna is then introduced. This technique is based on the excitation and combination of TE and/or TM modes from a single antenna feedhorn. It is shown that, by proper combination of multiple TE modes from a single feedhorn, radiation patterns with separate phase centres can be produced from the same reflector. TE and TM modes can also be combined to effect the same, but this is omitted for brevity. The characteristics of the resulting radiation patterns are analysed with a view towards maximising the separation of the antenna phase centres while maintaining symmetry between the patterns and minimising the reduction in gain and constant phase beamwidth with respect to the reflector's conventional radiation pattern.

Paraxial theory of slow self-focusing.

We present a theory of slow self-focusing that is paraxial in nature, gives the field including the phase and eikonal explicitly, while it also agrees with the results of variational and moments theories. After presenting the features of the theory, particularly its similarity to the central force problem, we go on to reformulate the theory for an absorbing medium. We find that the laser beam focuses to a constant beamwidth with a small phase-front curvature depending on the extent of absorption. The theory is applicable to a whole range of saturating nonlinearities although it specializes to two plasma cases, the ponderomotive force based and the relativistic electron quiver based nonlinearities, for definitive results.

Design of a MEMS acoustical beamforming sensor microarray

This paper describes the design methodology for a microelectromechanical systems (MEMS)-based acoustical beamforming sensor microarray. The proposed acoustical array offers the potential of controlled directional sensitivity with constant beamwidth when used in conjunction with the appropriate digital signal processor. The array has been designed for use in a hearing instrument with a digital beamsteering engine to provide controlled directional sensitivity and constant beamwidth over the audio frequency range to improve speech intelligibility in noisy and reverberant environments. A MEMS-based packaging solution that allows the sensor array to be mounted in the ear canal is also described. The MEMS sensor-package interface features microspring contacts that enable low impedance connectivity between the sensor array and the related microelectronics. This allows the array to be easily removed for cleaning or replacement purposes.

A synthesized tri-modal directional transducer

A new cylindrical transducer, which achieves directional beams through the synthesis of the omni, dipole, and quadrupole extensional modes of vibration is presented. The three cylindrical radial modes are related in resonant frequency by the formula fn=f0(1+n)1/2, where n=0, 1, and 2, respectively, and may be excited individually or together by the selection of the circumferential voltage distribution. It will be shown that, in the frequency band between the dipole and quadrupole modes, a simple four-step real voltage distribution can be used to synthesize a smooth transmitting response with constant beamwidth patterns. From this comparatively simple, small diameter transducer, steered beam widths of 90 deg and 10 dB front to back ratios can be obtained. Theoretical and measured transmitting response and beam pattern results on a 4.5-in.-diam. cylindrical transducer design will be presented and compared in the operating frequency range from 15 to 20 kHz. [SBIR work supported by ONR and SPAWAR.]

An ultrawide-bandwidth tapered resistive TEM horn antenna

A novel stable beamwidth, ultrawide-bandwidth low-scattering antenna is presented. This antenna is a modified version of the conducting slotline bowtie hybrid (SBH) antenna with resistive sheets (Rcards) introduced into the guiding structure design. Since the resistive sheets can attenuate creeping wave fields, much smaller rolled edges are needed in the Rcard SBH antenna. Moreover, due to the Rcard's partially transparent nature with respect to electromagnetic fields, the radar cross section (RCS) associated with this new antenna is smaller than the original conducting rolled edge one. By employing an optimization process based on the concept of the genetic algorithm, one can easily design the Rcard SBH antenna to obtain a very stable antenna beamwidth and phase center in both the E- and H-planes across the entire operating frequency bandwidth. Because of its constant beamwidth, low RCS, and broad-band features, the Rcard SBH antenna is an ideal antenna for many applications such as a compact range feed. Calculated and measured results are presented to demonstrate the performance of this new antenna.

Anisotropy in microdevices produced by micromachining of cold-rolled NiTi sheets

Abstract The process of fabrication and characterisation of three types of NiTi microdevice are described: a double-beam cantilever of constant beam width and two designs of cantilever of stress-optimised width profile, with thicknesses ranging from 17 to 95 μm produced by cold rolling. The technology of electrolytic photoetching was used as a versatile tool for micromachining. The transformation behavior of the specimens was investigated by differential scanning calorimetry and electrical resistance measurements. Anisotropies caused by rolling-induced textures have been investigated by beam-bending experiments. Strong anisotropies were found in results on thickness-dependent Young’s modulus in the parent phase as well as in the beam-bending characteristics in the rhombohedral and martensitic phase. For beam directions transverse to the rolling direction, beam-bending experiments revealed a thickness dependence of hysteresis associated with the martensitic transformation, which was not observed in the rolling direction. Cantilevers with stress-optimised width profile display favorable beam-bending characteristics compared with cantilevers of constant beam width due to an optimum use of the shape memory effect.