Constant Beamwidth Research Articles

Synthesis of a steerable frequency-invariant radiation pattern for broadband scalable antenna arrays

This paper discusses the synthesis of a steerable frequency-invariant radiation pattern for broadband scalable antenna arrays (SAAs). The proposed method allows to achieve constant beamwidth and beam direction over a 3:1 bandwidth and is based on an appropriate radiating elements’ placement in the SAA and a proper amplitude and phase excitation of the array. Both amplitudes and phases of signals exciting the radiating elements are varied with frequency to ensure the radiation pattern invariance. Additionally, the paper proposes solutions to problems occurring in SAAs i.e., the problem of overlapping radiating elements and the problems of sidelobe and grating lobe reduction. To verify the proposed synthesis method, a set of radiating elements, which operate over a 3−9 GHz frequency range, has been manufactured and measured. The overall radiation pattern of the antenna array has been obtained by a summation of the radiation patterns produced by each of the radiating elements.

Optimal audio beam pattern synthesis for an enhanced parametric array loudspeaker

A parametric array loudspeaker (PAL) generates highly directional audible sound in air with a small aperture size compared to a conventional loudspeaker. But in indoor applications, the long propagation distance of a PAL causes reflections, which disturbs the reproduction of narrow audio beams. Moreover, sound distortion appears along the off-axis direction due to the frequency dependence of the beam width. This study proposed an optimal audio beam pattern synthesis for a PAL-based convex optimization, which can design the audio beam of a PAL with an optimal solution. The proposed method overcame the mentioned limitations by applying it to a length-limited PAL for audio spot control and a multichannel PAL array for a constant beam width audio beam. In a length-limited PAL, the proposed method restricts the audio spot to a smaller region and weakens the sound leakage along the off-axis direction. Whereas in a multichannel PAL array, the proposed method also achieves a constant beam width near the radiator axis. Simulations and experiments verify the effectiveness of the proposed method, which will enhance the performance of a PAL in scenarios where control of the audio beam is required.

Constant-Beamwidth LCMV Beamformer with Rectangular Arrays

This paper presents a novel approach utilizing uniform rectangular arrays to design a constant-beamwidth (CB) linearly constrained minimum variance (LCMV) beamformer, which also improves white noise gain and directivity. By employing a generalization of the convolutional Kronecker product beamforming technique, we decompose a physical array into virtual subarrays, each tailored to achieve a specific desired feature, and we subsequently synthesize the original array’s beamformer. Through simulations, we demonstrate that the proposed approach successfully achieves the desired beamforming characteristics while maintaining favorable levels of white noise gain and directivity. A comparative analysis against existing methods from the literature reveals that the proposed method performs better than the existing methods.

Robust broadband adaptive beamforming with constant beamwidth using frequency difference technique

Constant beamwidth and robustness are two important features for broadband adaptive beamformers. In this paper, a robust broadband adaptive beamformer with a constant beamwidth for uniform linear arrays is proposed. Benefitting from the idea behind the frequency difference (FD) technique, the array observation in frequency bin f is first multiplied by the conjugate form of a reference array output in frequency bin f+f0, which is constructed with a given Gaussian random sequence from the looking direction. In this manner, a frequency-invariant property is obtained by mapping the frequency band of interest to a selected frequency bin f0. To improve the robustness of the proposed method, an iterative method with adaptive uncertainty in the steering vector (SV) is applied to the equivalent array output after the FD operation. The convergence can be accelerated by scaling the uncertainty level of the SV. Due to the FD technique, the proposed method adaptively filters the signal of interest in the FD domain. The effectiveness of the proposed method is verified by numerical simulation.

Differential constant-beamwidth beamforming with cube arrays

In this paper, we present an azimuth and elevation constant-beamwidth (CB) differential beamforming approach for cube arrays. We decompose a global cube beamformer into a Kronecker-product (KP) of three sub-beamformers: two constant-beamwidth beamformers along the y and z axes, and a tunable super-directive (SD) beamformer along the x-axis. We propose two design methods to derive cube beamformers whose either white noise gain (WNG) or directivity factor (DF) may be set by design. We show that the CB threshold frequency with respect to the azimuth and elevation angles, and the WNG and DF performance, can be controlled by the number of microphones along each axis. In addition, we focus on the particular case of merely a single microphone along the x-axis, which yields a rectangular azimuth and elevation CB beamformer. We demonstrate that its CB threshold frequencies are controlled by the number of microphones along the y and z axes, and show that the WNG and DF performance measures are maximized when the two axes are equal in size. Finally, we analyze the performance of the proposed beamformers through simulations of speech signals in various reverberant scenarios, including deviations in the desired speech signal’s direction of arrival (DOA). We show that the proposed beamformers outperform previously-presented beamformers and the traditional SD and delay-and-sum (DS) beamformers, particularly in terms of the intelligibility of their corresponding time-domain enhanced signals.

COMPACT CORRUGATЕD HORN ANTENNA INITIAL DESIGN FOR MICROWAVE DIAGNOSTICS IN URAGAN-2M STELLARATOR

In this paper, a well-known design procedure is proposed for the design of wideband constant-beam width conical corrugated horn antennas, with minimum design and construction complexity. The inputs to the procedure are the operating frequency band, the required minimum beam width 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 2.1:1. Based on the proposed procedure, a corrugated horn antenna with a constant beam width over the frequencies of 10 to 14 GHz was designed and simulated using commercial software. This paper presents initial design for the development of quasi-optical corrugated conical horn for reflectometry diagnostics for the Uragan-2M stellarator plasma experiments.

Design and Realization of Ultra-wideband Constant Beamwidth Beamforming in a Waveguide Environment

Array signal processing technology has been widely used in signal detection and underwater target radiation noise measurement. A design and realization method of an ultra-wideband and high-robustness constant beamwidth beamformer based on a vertical nested array is proposed. Using the nested array multiplexing, the ultra-wideband constant beamwidth beamforming was realized by using fewer array elements; the main lobe of each sub-band beam in the designed band was made to approach the desired constraint value based on the convex optimization method; the beamforming robustness and array gain were improved through the constraint of the weight vector two-norm. In the paper, the influence on beamforming due to inconsistent array element amplitude-phases in a measured waveguide environment is analyzed. The computer simulation was used to realize the measurement of constant beamwidth beamforming within a 100-octave band range in the measured waveguide environment and verify the effectiveness of the proposed method.

An Ultrawideband Nested Coaxial Waveguide Feed Antenna for Radio Astronomy

We describe a new type of ultrawideband feed antenna based on nested coaxial waveguides. The feed is for radio astronomy applications and covers two closely spaced bands: 400&#x2013;800 and 900&#x2013;1800 MHz. New design techniques are described for a three-cavity choke, a wideband iris matching network, and printed circuit board (PCB) excitation structures. The design methods were developed to improve broadband impedance matching, to control radiation patterns, to separate bands, and to suppress unwanted waveguide modes. The feed has nearly constant beamwidth over the entire 4.5:1 frequency range and a stable phase center. On an <inline-formula> <tex-math notation="LaTeX">$f/D=0.43$ </tex-math></inline-formula> reflector antenna, the aperture efficiency exceeds 70&#x0025; and the phase efficiency exceeds 95&#x0025;. Other features include low ohmic loss and a compact, lightweight, and low-cost structure. Experimental results are shown for a scaled prototype to verify the design methodology. The methods described are general and can be applied to continuous frequency coverage on reflectors of different geometries.

Absorption efficiency analysis and optical resonator simulation of Ho:YLF laser pumped with Tm:fiber laser

In this paper, a Tm:fiber laser pumped Ho:YLF laser is simulated. The absorption efficiency, optimum crystal length, and optical resonator are analytically studied and simulated using LASCAD software, and the atomic-level degeneracies are considered in evaluating the absorption efficiency. In this way, the absorption efficiencies of 65% and 87% are obtained for single-pass 30 mm Ho:YLF crystal with doping concentration 0.5% and 1% respectively. These calculated efficiencies are verified by our experimental measurements and they coincide with acceptable errors. To estimate a proper length for the Ho:YLF crystal with specified doping concentration, the up-conversion, and the reabsorption effects are considered. As a result, we find the 30 mm length crystal is suited for reducing the absorption threshold and prohibiting reabsorption while saturation is controlled. The threshold power and slope efficiency for 65 W pumped powers are calculated by LASCAD software, and the thermal lens focal length of −665 mm is obtained. For a nearly constant beam width inside the cavity and suitable beam overlap efficiency, a concave-concave configuration is chosen for the optical resonator. In the continuous-wave operation, the output power is funded to be 38.4 W and the slope efficiency would be 66%.

Constant-Beamwidth Beamforming with Concentric Ring Arrays.

Designing beampatterns with constant beamwidth over a wide range of frequencies is useful in many applications in speech, radar, sonar and communication. In this paper, we design constant-beamwidth beamformers for concentric ring arrays. The proposed beamformers utilize the circular geometry to provide improved beamwidth consistency compared to beamformers which are designed for linear sensor arrays of the same order. In the proposed configuration, all sensors on each ring share the same weight value. This constraint significantly simplifies the beamformers and reduces the hardware and computational resources required in a physical setup. Furthermore, a theoretical justification of the beamforming method is provided. We demonstrate the advantages of the proposed beamformers compared to the one-dimensional configuration in terms of directivity index, white noise gain and sidelobe attenuation.

E- and H-Plane Constant Beamwidth Horn Antenna Over 4:1 Frequency Band

A wideband corrugation slot, called stepped-shape slot, is proposed in the design of E-plane corrugated double-ridged horn antenna (DRHA) with H-plane pin sidewalls to extend the constant beamwidth bandwidth (BW) of horn antennas. Closed-form expressions for the input admittance of the new slot are derived, and the BW is compared with the BWs of other conventional corrugations. The proposed slot presents wideband characteristics with a BW ratio of more than 4:1. The use of stepped-shape slot in a corrugated wall keeps the surface reactance capacitive over a relatively large frequency band. The H-plane sidewalls of the designed antenna are formed by curved pinwalls. The flare includes ridges to extend the frequency range, and the E-plane walls are corrugated with a wideband slot to improve the beamwidth constancy in elevation. Thus, constant beamwidth horn antenna (CBWHA) is obtained at both azimuth and elevation planes over the desired frequency band from 4.5 to 18 GHz. The measured performance of the proposed CBWHA reveals wideband characteristics with 31.0° ± 2.5° H-plane and 37.4° ± 5.2° E-plane half power beamwidths over 4:1 frequency range.

Measurement of underwater target radiated noise based on nested biconical array

In order to measure the radiated noise of underwater low-noise targets, it is often necessary to measure the radiated noise in the near-field condition, and the array must have a certain spatial directivity to suppress the noise. In this paper, a novel volume array nested biconical array is proposed and designed, which is supported by a near-field focusing constant beamwidth beamforming algorithm. The array has the ability to receive the underwater target radiated noise with constant beamwidth, accuracy and high gain. The performance of the array is tested and evaluated in shallow sea and deep sea respectively, and compared with the traditional vertical array.

Comparative study of wireless sensors for measuring the energy consumption of human running

With the rapid development of technologies such as communications, embedded computing, and sensors, wireless sensor network technology has become more mature and its applications have become more and more extensive. The development of technology has brought great convenience to people's lives and work. At the same time, people's activity and exercise are greatly reduced, causing health problems such as physical weakness. In this regard, designing a research based on wireless sensors to measure human walking and running is of great significance to promote the development of people's physical health. This paper presents a design scheme for human exercise energy consumption detection, researches and designs the coordinator, router node and host computer monitoring system of wireless sensor network. In the human motion energy consumption detection system implemented in this paper, the communication effect between the coordinator and the router node is good, and there are fewer problems such as node loss and data loss. The host computer monitoring interface is simple and easy to operate, easy to use, and can run stably. This solution does not need wiring, reduces the point of failure, reduces the cost, and has good scalability, laying a foundation for the further development of the human motion detection system, and has a wide range of application prospects and practical values. This paper is based on two constant beam width algorithms to carry out the experimental research on the energy consumption of human walking and running, and analyze the results of the energy consumption experiment. Experimental results show that the two constant beamwidth beamforming algorithms have relatively good constant beamwidth effect, which basically verifies the correctness of the theoretical analysis results and can be applied to target noise measurement.

Efficient Beamforming Technique Based on Sparse MIMO Array and Spatial Filter Bank

Spatial diversity gained through different beamforming techniques in antenna array is one of the main advantages over the single antenna. Antenna complexity and beamwidth broadening at the scanning angles other than broadside are downsides of antenna arrays that prevent its practical implementation from some applications. In this letter, we propose an efficient beamforming method based on the sparse multiple-input–multiple-output (MIMO) array and spatial filter bank (SFB). The sparse MIMO array produces narrow beams while significantly reduces the number of array elements without compromising system performance. Multiple main beams are chosen from grating lobes by SFB. By combining sparse array geometry and SFB, we can achieve a narrower beamwidth with less antenna elements, multiple beams, and constant beamwidth. The burden of system will be transferred from the frontend hardware to the signal processing back end.

Frequency Invariant Beamforming for a Small-Sized Bi-Cone Acoustic Vector-Sensor Array.

In this work, we design a small-sized bi-cone acoustic vector-sensor array (BCAVSA) and propose a frequency invariant beamforming method for the BCAVSA, inspired by the Ormia ochracea’s coupling ears and harmonic nesting. First, we design a BCAVSA using several sets of cylindrical acoustic vector-sensor arrays (AVSAs), which are used as a guide to construct the constant beamwidth beamformer. Due to the mechanical coupling system of the Ormia ochracea’s two ears, the phase and amplitude differences of acoustic signals at the bilateral tympanal membranes are magnified. To obtain a virtual BCAVSA with larger interelement distances, we then extend the coupling magnified system into the BCAVSA by deriving the expression of the coupling magnified matrix for the BCAVSA and providing the selecting method of coupled parameters for fitting the underwater signal frequency. Finally, the frequency invariant beamforming method is developed to acquire the constant beamwidth pattern in the three-dimensional plane by deriving several sets of the frequency weighted coefficients for the different cylindrical AVSAs. Simulation results show that this method achieves a narrower mainlobe width compared to the original BCAVSA. This method has lower sidelobes and a narrower mainlobe width compared to the coupling magnified bi-cone pressure sensor array.

DRGH Antenna With Improved Gain and Beamwidth Performance

Double-ridge guide horn (DRGH) antennas are widely used in antenna and EMC testing facilities as feed antennas and gain transfer standards. Increasing the low-frequency gain to obtain a more constant 3 and 10 dB beamwidth, over the operating frequency band of 1–18 GHz, will result in a more uniform illumination of the devices under test. In this communication, the ridge profiles of a conventional DRGH antenna with dimensions complying with the requirements of MIL-STD-461F are modified to produce a more constant beamwidth, especially from 3 GHz upward. The width of the ridges is tapered along the axial length of the DRGH to increase effective radiating aperture and reduce the beamwidth, at lower frequencies. An accurate numerical model was developed of the conventional 1–18 GHz DRGH antenna and modified ridges were implemented. The radiation properties of a prototype antenna were measured in a compact antenna range. Simulated and measured results are presented for the modified DRGH antenna.

Research on Bearing Fault Monitoring Technology Based on the Acoustic Array in Working Environment

At present the most widely used method in mechanical fault diagnosis is feature extraction based on vibration signal analysis, but the test results are not accurate. Fault diagnosis method based on acoustic measurement can overcome this shortcoming, although traditional acoustic measurement based on single channel is susceptible to interference and it is difficult to obtain effective signals under strong background noise or complex testing environment. Directional noise measurement technology based on acoustic array and beamforming method can effectively suppress background noise. In this paper, the 3D constant beam width beam forming array is used to extract the broadband radiated noise from the monitored equipment and the sensitive frequency bands corresponding to different fault stages of bearings are preprocessed to obtain the corresponding eigenvectors. BP Neural Network is used to identify the fault of the tested bearings. The results show that the 3D microphone array based on constant beam width beam forming can effectively suppress the interference of environmental noise to ensure the validity of monitoring data and improve the reliability of fault diagnosis.

Robust Wideband Adaptive Beamforming With Null Broadening and Constant Beamwidth

In the cases of rapidly moving interference and look-direction error, robustness and output signal to interference and noise ratio (SINR) of conventional wideband adaptive beamforming methods are degraded severely. In order to solve these problems, a robust wideband adaptive beamforming with null broadening and constant beamwidth is proposed. We first propose a taper matrix constructed by adding virtual interferences for null broadening, where the reference frequency and number of virtual interferences of taper matrix are determined based on numerical methods. This is followed by reconstructing the array covariance matrix based on taper matrix. Spatial response variation (SRV) constraint is then applied for a constant beamwidth over the entire frequency band. Finally, the adaptive weight vector for null broadening and constant beamwidth is obtained by using Lagrange multiplier method. The effectiveness of proposed method is verified by numerical simulations.

Near‐constant beamwidth quadruple bandwidth double‐ridged horn antenna design

It is well known that the beamwidths of horn antennas are inversely proportional to frequency. Previous studies point to minimum ±12% beamwidth stability within a maximum of 2.5:1 bandwidth (BW) ratio. To extend this BW, a design methodology for broadband double-ridged horn antenna (DRHA) is proposed and applied to 4.5-18 GHz frequency band. Firstly, a conventional DRHA is designed and studied to compare the beamwidth variation of wideband horn antennas. By explicitly addressing the shortcomings of conventional DRHA, DRHA is redesigned and near-constant beamwidth DRHA is proposed using the modifications implemented on the sidewalls. The antenna utilises ridges to extend the frequency band, unlike other wideband constant beamwidth horns. The authors show that ridged horns, whose dimensions are appropriately designed and modified, can have stable beamwidths. Then, properly positioned curved pinwalls are designed to provide considerable improvement in H -plane beamwidth constancy. Broadband double-ridged waveguide-to-coaxial adapter is also designed for 50 Ω reference. The prototype is manufactured, and the measured antenna exhibits wideband characteristics with 30.9° ± 2.7° half power beamwidth in H -plane over 4:1 BW ratio. This variation corresponds to ±8.7% beamwidth stability along with the target frequency band.

Window-Based Constant Beamwidth Beamformer.

Beamformers have been widely used to enhance signals from a desired direction and suppress noise and interfering signals from other directions. Constant beamwidth beamformers enable a fixed beamwidth over a wide range of frequencies. Most of the existing approaches to design constant beamwidth beamformers are based on optimization algorithms with high computational complexity and are often sensitive to microphone mismatches. Other existing methods are based on adjusting the number of sensors according to the frequency, which simplify the design, but cannot control the sidelobe level. Here, we propose a window-based technique to attain the beamwidth constancy, in which different shapes of standard window functions are applied for different frequency bins as the real weighting coefficients of microphones. Thereby, not only do we keep the beamwidth constant, but we also control the sidelobe level. Simulation results show the advantages of our method compared with existing methods, including lower sidelobe level, higher directivity factor, and higher white noise gain.