Endfire Beam Research Articles

A Planar End-Fire Circularly Polarized Complementary Antenna With Beam in Parallel With Its Plane

Operation principle and design approach of a novel planar end-fire circularly polarized (CP) complementary antenna is proposed. A vertically polarized printed magnetic dipole and a horizontally polarized printed dipole are combined on the same substrate, and a planar CP antenna with end-fire beam in parallel with its plane is thus designed. Prototype antennas centered at 5.80 GHz are then fabricated and measured to validate the operation principle and the design approach. The experimental prototype reported that the impedance bandwidth ( $20\text{log }\vert\text{S}_{11}\vert ) is about 1.90%, from 5.75 to 5.86 GHz and the 3-dB axial ratio (AR) bandwidth is about 14.48%, from 5.19 to 6.00 GHz. Therefore, the proposed design is applicable as a low-profile handheld reader antenna in radio-frequency identification (RFID) systems.

A Wideband End-Fire Conformal Vivaldi Antenna Array Mounted on a Dielectric Cone

The characteristics of a novel antipodal Vivaldi antenna array mounted on a dielectric cone are presented. By employing antipodal Vivaldi antenna element, the antenna array shows ultrawide bandwidth and end-fire radiation characteristics. Our simulations show that the cone curvature has an obvious influence on the performance of the conformal antenna, in terms of both the bandwidth and the radiation patterns. The thickness and permittivity of the dielectric cone have an effect on the bandwidth of the conformal antenna. Measurement results of both single antenna and conformal antenna array show a good agreement with the simulated results. The measured conformal antenna can achieve a −10 dBS11with bandwidth of 2.2–12 GHz and demonstrate a typical end-fire radiation beam. These findings provide useful guidelines and insights for the design of wideband end-fire antennas mounted on a dielectric cone.

Conception and optimisation of UWB microstrip array antennas for radar applications with ordinary end-fire beam steering characteristic

In this paper, a compact linear array antennas with ultra wideband (UWB) end-fire characteristic for radar applications is proposed. The array antenna consists of four rectangular antenna element with a partial ground plane and a coplanar waveguide (CPW) transmission line of 50 ohm. The proposed array antennas is etched onto a FR4 printed circuit board (PCB) with an overall size of 85 × 32 × 1.58 mm3 and a dielectric constant er = 4.4, it is planar and simple, and it is able to achieve an impedance bandwidth about 72% which is required in various radar applications like weather radars, local air traffic radars and naval radars. Ansoft's high frequency structure simulator (HFSS) and computer simulation tool (CST) softwares are used to calculate and compare the various parameters mentioned after.

Conception and optimisation of UWB microstrip array antennas for radar applications with ordinary end-fire beam steering characteristic

In this paper, a compact linear array antennas with ultra wideband (UWB) end-fire characteristic for radar applications is proposed. The array antenna consists of four rectangular antenna element with a partial ground plane and a coplanar waveguide (CPW) transmission line of 50 ohm. The proposed array antennas is etched onto a FR4 printed circuit board (PCB) with an overall size of 85 × 32 × 1.58 mm3 and a dielectric constant εr = 4.4, it is planar and simple, and it is able to achieve an impedance bandwidth about 72% which is required in various radar applications like weather radars, local air traffic radars and naval radars. Ansoft's high frequency structure simulator (HFSS) and computer simulation tool (CST) softwares are used to calculate and compare the various parameters mentioned after.

Planar Endfire Circularly Polarized Antenna Using Combined Magnetic Dipoles

A novel planar circularly polarized antenna with endfire radiation beam in parallel with the antenna substrate’s plane is proposed. The operation principle of the antenna is analyzed and design guidelines are laid down. Then, an optimized loop-aperture combined antenna is designed and demonstrated to exhibit an endfire beam in parallel with its plane within 5.74-5.88 GHz for $\vert{{\rm S}_{11}}\vert$ lower than $-10~\hbox{dB}$ and axial ratio smaller than 3 dB. The proposed antenna can be used as a low-profile, cost-effective, hand-held reader antenna for radio frequency identification systems .

Investigations of SIW Leaky-Wave Antenna for Endfire-Radiation With Narrow Beam and Sidelobe Suppression

A new substrate integrated waveguide (SIW) leaky-wave antenna is investigated for endfire-radiation with a narrow beam and sidelobe suppression. Maximum directivity conditions for endfire-radiation from line sources with different amplitude distributions are theoretically discussed as a design aid. Interestingly, for endfire beams it is seen that designs that have a lower sidelobe level can also have a higher directivity, contrary to what is normally encountered for broadside beams. An SIW leaky-wave antenna with tapered transverse slots on only the top and bottom planes is presented. Compared with a previous leaky-wave antenna having uniform transverse slots on the top plane, the presented leaky-wave antenna has a main beam that can radiate exactly at endfire and also has a lower sidelobe level. The design of the low sidelobe antenna is based on the leaky mode, which loses physical significance as the beam is scanned to the endfire direction. Nevertheless, the antenna retains a good beam shape and a low sidelobe level when it radiates at endfire. A prototype is made, and measured results are consistent with theoretical and simulated results.

Comparing passive source localization and tracking approaches with a towed horizontal receiver array in an ocean waveguide

Approaches for instantaneous passive source localization using a towed horizontal receiver array in a random range-dependent ocean waveguide are examined. They include: (1) Moving array triangulation, (2) array invariant, (3) bearings-only target motion analysis in modified polar coordinates via the extended Kalman filter, and (4) bearings-migration minimum mean-square error. These methods are applied to localize and track a vertical source array deployed in the far-field of a towed horizontal receiver array during the Gulf of Maine 2006 Experiment. The source transmitted intermittent broadband pulses in the 300 to 1200 Hz frequency range. A nonlinear matched-filter kernel designed to replicate the acoustic signal measured by the receiver array is applied to enhance the signal-to-noise ratio. The source localization accuracy is found to be highly dependent on source-receiver geometry and the localization approach. For a relatively stationary source drifting at speeds much slower than the receiver array tow-speed, the mean source position can be estimated by moving array triangulation with less than 3% error near broadside direction. For a moving source, the Kalman filter method gives the best performance with 5.5% error. The array invariant is the best approach for localizing sources within the endfire beam of the receiver array with 7% error.

Linearly aligned superradiant Bose-Einstein condensates diffracted by a single short laser pulse

Multiorder bidirectional superradiant Bose-Einstein condensates (BECs) were generated in a straight line by an irradiation of a single unidirectional short laser pulse along the long axis of a cigar-shaped sodium BEC in a magnetic trap. The probabilities of the diffracted BECs as a function of the laser intensity were well explained by the square of the Bessel functions and it was estimated that the intensity of the end-fire beam was 25$%$ of the laser intensity. The backward diffractions disappeared at pulse duration longer than 5 \ensuremath{\mu}s because of energy conservation. The probability for the $+$first-order diffraction grew exponentially with pulse duration when the backward diffractions disappeared. We observed the linearly aligned diffracted BECs along the propagation direction of the laser beam, regardless of the aspect ratio of the condensates. This fact indicates that the end-fire beam is triggered by the small backreflection from the vacuum window.

Accuracy of passive source localization approaches with a single towed horizontal line-array in an ocean waveguide

Instantaneous passive source localization applying the (1) synthetic aperture tracking, (2) array invariant, (3) bearings-only target motion analysis in modified polar coordinates via the extended Kalman filter, and (4) bearings-migration minimum mean-square error methods to measurements made on a single towed horizontal receiver array in a random range-dependent ocean waveguide are examined. These methods are employed to localize and track a vertical source array deployed in the far-field of a towed horizontal receiver array during the Gulf of Maine 2006 Experiment. The source transmitted intermittent broadband pulses in the 300-1200 Hz frequency range. All four methods are found to be comparable with averaged error of between 9% to 13% in estimating the mean source position in a wide variety of source-receiver geometries. In the case of a relatively stationary source, the synthetic aperture tracking outperforms the other three methods by a factor of two with only 4% error. For a moving source, the Kalman filter method yields the best performance with 8% error. The array invariant is the best approach for localizing sources within the endfire beam of the receiver array with less than 10% error.

Low-frequency sound generation from breaking waves: Experimental measurements and modeling.

The first at-sea measurements capable of spatially resolving the individual breaking wave contributions at frequencies below 400 Hz, where collective bubble oscillations are believed to be the dominant sound generation mechanism, were conducted in shallow water (200 m) near San Clemente Island in March/April 1995 using a vertical array deployed from the RP/FLIP. The time-frequency structure of the noise generated from individual breaking waves was obtained using the endfire beam of a vertical array along with optical measurements of the locations, sizes, and lifetimes of those breaking waves. Strong acoustic bursts in time coincidence with the larger breaking wave events were observed. Approximately one-third of breaking wave source spectra contained large peaks at 40–60 Hz. Additionally, a theoretical model based on the excitation of an entrained bubble cloud by individual point sources is presented to explain the low-frequency peaks evident in the measured source spectra. Statistical characterizations of the association of breaking-wave size and the broadband acoustic energy will be presented. [Work supported by ONR base funding at NRL.]

Using ambient noise and vector sensor arrays to form a subbottom profiler

Surface‐generated ambient noise is distributed in time, but its correlation produces a strong impulse that is excellent for imaging the ocean floor. This technique has been experimentally demonstrated using vertical line arrays of pressure phones. The up‐looking endfire beam (for ambient noise traveling down) is cross‐correlated with the down‐looking endfire beam (for the ambient noise reflected from the bottom, traveling up). Each layer in the bottom produces a distinct reflection. Previous work has required somewhat large vertical arrays. A towed horizontal array would be much better and allow us to make measurements with a mobile platform. The problem is that a horizontal line array cannot distinguish up from down—a broadside beam is symmetric with respect to the axis of the array. Vector sensors, sensing both pressure and particle velocity, have additional degrees of freedom for overcoming such ambiguities. We will show how vector sensors make it possible to implement such an ambient noise subbottom profiler, either in a greatly reduced vertical array or in a horizontal (towed) array configuration. We will also show results of processing data collected on a four‐element vector sensor array and a much larger pressures‐only array during the Makai experiment.

Tower-based breaking wave noise measurements

A tower-based sea surface noise experiment began collecting data January 2006 in the shallow waters (25 m) approximately 75 km off the coast of Savannah, Georgia. A 32-phone, three nested-aperture, vertical hydrophone array was deployed nominally 100 m from a Navy tower that stands 50 m above the water surface. A high-resolution video camera was mounted near the top of the tower along with a dual-polarized marine-band radar to record the location, size, and lifetime of the surface expressions of the breaking waves above of the array. The array is cabled back to the tower for power and signal collection. The tower is microwave-linked to shore for internet-based control and data retrieval. To date, measurements have been made in wind speeds ranging from 5–21 m/s and wave heights of 1–3.4 m over a 6-month period. Empirical relationships between the time-frequency structures of the generated noise, obtained on the endfire beam of the array, and the size of the surface expressions of the breaking waves will be given for a range of environmental conditions. [Work supported by ONR base funding at NRL.]

A compact and broadband microstrip antenna design using a geometrical-methodology-based artificial neural network

A new artificial neural-network-based methodology for a microstrip antenna design was studied and presented. The methodology is applicable to DCS, GSM, WLL, WLAN, large band planar antennas, and fractals. In this paper, we present five applications of this methodology, three of which are applicable in the WLL, 802.11a, and 802.11b antenna standards. The two others are broadband designs with 500 MHz and 1 GHZ bandwidth, respectively. All the antennas radiate an end-fire beam, and have compact sizes of 29 mm /spl times/ 25 mm, 10 mm /spl times/ 13.5 mm, 10.3 mm /spl times/ 17.2 mm, 35 mm /spl times/ 25 mm, and 35 mm /spl times/ 25 mm, respectively.

Breaking wave noise measurements at frequencies below 400 Hz

A sea surface noise experiment was conducted in shallow water (200 m) near San Clemente Island in March/April 1995 using a vertical array deployed from the RP/FLIP. Measurements of the time-frequency structure of the noise generated from individual breaking waves were obtained using the endfire beam of a vertical array along with optical measurements of the locations, sizes, and lifetimes of those breaking waves. Strong acoustic bursts in time coincidence with the larger breaking wave events were observed. There is no apparent correlation between the smaller breaking wave occurrences and low-level acoustic noise at the sea surface in this frequency band. These acoustic measurements were the first at-sea measurements capable of spatially resolving the individual breaking wave contributions at frequencies below 400 Hz where collective bubble oscillations are believed to be the dominate sound generation mechanism.

Low-frequency volume scattering measurements from the central Mediterranean

Broadband (200–1500 Hz) measurements of direct path volume scattering were made in May of 1991 in the central Mediterranean’s Ionian Sea and adjacent Medina Bank. Acoustic sources used in these measurements were explosive charges detonated several hundred meters below a vertical line array (VLA) receiver. Reverberation was processed from the upward looking end-fire beam of the VLA yielding highly resolved scattering strengths in depth and frequency for the upper 400 m of the water column. Analysis of the spectral characteristics of the volume scatter data reveals that the dominant scattering emanates from diffuse, broadband strata which are confined to the thermocline region of the water column. The applicability of classic swimbladder scattering models to describe these layers is presented in addition to the spatial variability observed in volume scatter from deep (Ionian Sea) to shallow (Median Bank) ocean areas.

Low-frequency volume reverberation measurements

An experimental technique has been developed to measure broadband low-frequency volume reverberation. Experiments were performed in the North Atlantic with broadband explosive sources in conjunction with the end-fire beam of a vertical line array to provide scattering strength contours from measurements sampled in both frequency (∼12 Hz) and depth (∼4 m). The average effective resolution in frequency (∼100 Hz) and depth (∼30 m) resulted from signal processing procedures and geometrical effects associated with the measurements. During the measurements a SIMRAD scientific echo sounder system was utilized. This system incorporates split-beam processing technology to provide the most accurate in-situ assessment, analysis, and display of biological target strength and fish length distributions. The experimental and analysis techniques are described along with representative examples that compare high and low scattering levels observed during the experiment.

Bispectrum of ship-radiated noise

The bispectrum of ship-radiated noise is estimated. The noise was received on a towed array being towed by the same ship that served as the noise source. The array was beamformed such that the forward end-fire beam pointed toward the towing platform and the broadside beam sampled the environment without the radiated noise of the ship. The results show that there exist frequency-dependent bispectral components in the ship's radiated noise, whereas the ambient noise does not contain any significant bispectral components. Since the existence of a nonzero frequency-dependent bispectrum indicates the existence of nonlinear components in the noise-generating mechanism, it is concluded that the radiated noise of the towing platform contains such nonlinear mechanisms. Also, the bispectrum has the capability of indicating the presence of transients in the data. This property will be briefly discussed, and it will be shown that the data under analysis contain transients. Based on these results, it is concluded that the bispectrum could be used to indicate the existence of transient and nonlinear sources that would normally be hidden in the background noise when the usual spectral estimation procedures are applied.

Bispectrum of ship-radiated noise

The bispectrum of ship-radiated noise is estimated. The noise was received on a towed array being towed by the same ship that served as the noise source. The array was beamformed such that the forward endfire beam pointed toward the towing platform and the broadside beam sampled the environment without the radiated noise of the ship. The results show that there exist frequency-dependent bispectral components in the ship’s radiated noise, whereas the ambient noise does not contain any significant bispectral components. Since the existence of a nonzero frequency-dependent bispectrum indicates the existence of nonlinear components in the noise-generating mechanism, it is concluded that the radiated noise of the towing platform contains such nonlinear mechanisms. Therefore, the bispectrum could be used to indicate the existence of such noise sources as would normally be hidden in the background noise when the usual spectral estimation procedures are applied.

Jacobi arrays and circle relationships

The previously derived Jacobi array is a vanishingly short equispaced linear array which maximizes the directivity for one endfire beam. For n sensors the directivity is n2, and for small n there is little fall-off for practical designs. It is related to the Gegenbauer array which maximizes directivity with two symmetrical endfire beams; and to the Legendre array which minimizes radiated power under certain constraints. It is explained why the pattern of zeros, for these and for some other polynomial arrays, has to obey a circle relationship, and a more accurate circle relationship is presented.

End-fire hybrid array antennas

A heuristic approach useful in the design of end-fire array antennas is described. When an array is scanned "beyond end fire," the last elements of the array, in the direction of the end-fire beam, generally receive net power transmitted by other elements of the array. This received power might conceivably be recirculated and reradiated at the price of substantial complexity in the feed network. It is relatively simple to absorb this power in appropriate resistive loads at the price of reduced gain. The resulting end-fire antenna is a hybrid-array consisting of two classes of elements: elements excited directly and elements excited parasitically. A compromise termination of these parasitic elements in reactive loads especially determined to preserve desired pattern characteristics is examined.