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In this study, we propose a generalized algorithm for far-field radar cross section determination by using 3-D synthetic aperture imaging with arbitrary antenna-scanning surfaces. This method belongs to a class of techniques called image-based near-field-to-far-field transformation. The previous image-based approaches have been formulated based on a specific antenna-scanning trajectory or surface, such as a line, plane, circle, cylinder, and sphere; the majority of these approaches consider 2-D radar images to determine the azimuth radar cross section. We generalize the conventional image-based technique to accommodate an arbitrary antenna-scanning surface and consider a 3-D radar image for radar cross section prediction in both the azimuth and zenith directions. We validate the proposed algorithm by performing numerical simulations and anechoic chamber measurements. [ABSTRACT FROM AUTHOR]

High cross-polarization isolation (CPI) is crucial to the accurate polarization measurement using polarimetric phased array radar (PPAR). In this article, we propose an adaptive direction-dependent polarization state configuration (AD2PSC) method to improve the polarization isolation. Compared with the conventional fixed polarization state of radiated wave whether it is linear, circular, or elliptical polarization state, our AD2PSC approach configures the polarization state on basis of beam steering. To achieve the adaptive configuration of magnitude and phase of the dual-polarization antenna, an improved steepest descent algorithm is put forward. To facilitate the uniform representation for the polarization measurement application of PPAR, the universal expressions of intrinsic and measured backscatter matrices are derived for arbitrary polarization state. The dual-polarization dipole array is used to assess the priority of our proposed method. Compared with the conventional approaches, our approach could obtain higher CPI while being available for a larger scanning range. The configured CPI meets the specific polarization requirement for PPAR. [ABSTRACT FROM AUTHOR]

Polarimetric multiple input and multiple output (MIMO) radar is capable of acquiring target’s high-resolution images and polarization scattering matrix (PSM). In this article, calibration of a polarimetric MIMO array of an instrumentation radar for near-field measurement is achieved at ${X}$ -band by using a rotatable double-antenna polarimetric active radar calibrator (RODAPARC) and a metal cylinder quickly and accurately. The theoretical PSM of the RODAPARC with different antenna rotation angles is derived from Huygens’ radiation electric field which is applicable to different bistatic angles. A polarimetric signal model is adopted to reduce the impact of the RODAPARC on calibration. Experimental studies are conducted on a polarimetric MIMO array which is measured and divided into quasi-monostatic and bistatic transceiver channels for assessment on the calibration performance. Promising calibration results are obtained with a polarization isolation improvement of about 16 dB and great reduction of the polarization channel gain error less than ±0.5 dB in amplitude and ±3° in phase. The calibrated polarization signatures for classic objects are consistent with the theoretical results. [ABSTRACT FROM AUTHOR]

Antenna arrays are frequently used for localization of active communication transmitters or passively reflecting radar targets by evaluating signal phases at spatially distributed antennas. Unfortunately, the localization performance is degraded because of mutual coupling, unknown time delays, and imprecisely known antenna positions, especially if large arrays with spatially distributed antennas are used. Furthermore, these errors are altered until the array is steadily installed at its destination, which occurs because of position misalignment and cable phase instability. Hence, an in-situ array calibration is necessary to perform faultless phase measurements. For this purpose, this article proposes a novel calibration procedure for antenna arrays, correcting both the mutual coupling and positioning errors using an incoherently transmitting beacon. Because the in-situ calibration will be affected by multipath, measurements at random reference positions within the array’s near field are used for calibration. In addition, the algorithm copes with randomly varying path losses because of unknown antenna polarizations and patterns. Calibration measurements are performed, providing physically reasonable results without using an anechoic environment. Furthermore, the calibration results are validated via indoor localization using three antenna arrays that were calibrated with the proposed algorithm. [ABSTRACT FROM AUTHOR]

The emergence of CubeSats has opened up the possibilities of advanced space missions with lower costs and faster development times. A major factor that limits the functionality of CubeSats is the absence of high-gain antennas (HGAs) that can sustain a high data-rate link for communications or provide the required spatial resolution for remote sensing. In this work, we discuss the development of one of the largest apertures at Ka-band for CubeSats—a 1 m mesh deployable offset reflector antenna, with a stowed volume of 3U ($10\times 10\times 30 \,\,\text {cm}^{3}$)—to enable precipitation radars that can achieve the required spatial resolution while meeting the stringent mechanical constraints posed by the small CubeSat volume. We detail the critical aspects of this antenna design, including RF characterization, antenna fabrication, and measurement. We also describe a novel deployment mechanism that facilitates the packaging of such a large aperture in a small volume. The antenna demonstrated a measured efficiency of 60%, with a half-power beamwidth of 0.60° at 35.75 GHz. The cost reduction afforded by CubeSats makes launching a constellation of such radar based CubeSats practical, allowing higher temporal sampling rates, which is essential for the observation of weather processes with a short-time evolution. [ABSTRACT FROM AUTHOR]

Scattering properties of millimeter waves (mmW) remain relatively unknown compared to lower frequency bands, although their study is of interest considering the increasing number of civil applications, especially in the $W$ -band. In this communication, we present an efficient measurement setup that provides scattering measurements with spatial and polarization diversities. The targeted application is foreign object debris (FOD) detection and identification for surveillance of airport runways. Most existing systems are monostatic but rapid advances in mmW technology pushes toward the deployment of multistatic radars on either side of airport runways. In the following, we investigate the contribution of multistatic measurements with a special focus on the reconstruction of glass and brake pad debris, courtesy of DGAC (French civil aviation). We also present an efficient approach for making images of FODs. For this, we process scattered field measurements with an additive (with respect to polarization) backpropagation algorithm. First images include all measured points taken from the upper hemisphere. In order to get closer to the final application, we restrict the field of view to receivers facing the transmitter. Both approaches provide very good shape reconstruction of the glass debris and the central zone of the brake pad. To the best of our knowledge, this is the first time that full-3-D measurements have been conducted on FODs in the $W$ -band. It is also the first example of a 3-D qualitative image of FOD obtained from measured data in the $W$ -band. [ABSTRACT FROM AUTHOR]

We propose a complete procedure for synthesizing radiation patterns of leaky waves using binary programmable metasurface. As an example, a binary leaky-wave antenna (BLWA) is designed and fabricated using the fast procedure. By optimizing coding states of all radiation elements of the BLWA, beam forming is realized at a fixed frequency. Full-wave simulations and measurements of the proposed BLWA further prove the effectiveness and practicability of the design procedure. The presented method and BLWA may find many significant applications in novel communication and radar systems. [ABSTRACT FROM AUTHOR]

This paper presents a high-isolation, low cross-polarization dual-polarized patch antenna for multifunction phased array radar applications. Its hybrid feed design has been implemented, and the vertical and horizontal polarizations are excited by a balanced-probe feed and a slot-coupled feed, respectively. Simulations and measurements have demonstrated an input isolation of 45 and 43 dB between the horizontal and vertical ports, respectively. For further improvement in the cross-polarization level, the image feed method is also implemented, and a $2\times 2$ -element array made up of designed elements with image configuration has been fabricated. The simulated and measured S-parameter and radiation patterns of the horizontal and vertical polarizations of the designed $2\times 2$ -element array are presented and the measured cross-polarization level of less than −37 dB is achieved. To examine the performance of the designed element in an array, a $3\times 3$ -element array of designed $2\times 2$ -element subarray is fabricated and tested. In the $6\times 6$ -element measurements, −35.4 and −36 dB cross-polarization levels for horizontal and vertical polarizations are achieved, respectively. Also, using the measured embedded element patterns, the cross-polarization level lower than −36 dB for scan angles up to 45° is achieved. [ABSTRACT FROM PUBLISHER]

In this paper, we present a new horn antenna that can mechanically reconfigure the beam direction and polarization by combining a traditional linearly polarized horn antenna with an anisotropic Huygens metasurface. Three layers of Jerusalem-cross structures are integrated in a dielectric substrate to form the anisotropic Huygens metasurface; the entire structure has a thickness of about one fifteenth the working wavelength. By placing the metasurface in front of a traditional linearly polarized horn antenna, the main beam of the horn antenna is steered to a predetermined direction. Furthermore, the direction and polarization of the main beam are reconfigurable by rotating the anisotropic Huygens metasurface. The measured results of the antenna confirm the simulated results. Possible applications of the presented antenna include radar detection, base-station communications, and satellite communications. [ABSTRACT FROM AUTHOR]

A frequency reconfigurable phased array element is presented. The operational band of the single port L/S-band antenna can be selected by modifying the element apertures with p-i-n diode switches. The antenna element satisfies strict requirements on its frequency band separation (2.2:1), size, feeding structure, and control lines to be integrated into a phased array system. A multiscale array topology is proposed to achieve wide angle scanning (±60°) in both operational bands of the array. [ABSTRACT FROM AUTHOR]

The direct measurement of the angle rate of moving objects using a radar with a spatially diverse electric field pattern, a measurement analogous to the measurement of the range rate of a moving objects, represents, along with the measurements of range, range rate, and angle, a fourth basic radar measurement. Recently introduced and experimentally demonstrated, the theoretical accuracy of the direct measurement of angle rate is derived in this paper, and it is compared to the measurements of range, range rate, and angle in the context of the optimal signal forms for the best measurement accuracy. Signal forms achieving optimal accuracy for each measurement are discussed; example implementations of high-accuracy measurements are compared to the optimal forms; and the limitations of simultaneous measurements of pairs of measurements are derived. Combining the angle rate measurement with the three other standard radar measurements may provide future radar systems the capability to simultaneously and instantaneously measure the position and 3-D trajectory of moving objects without compromising the accuracy of any individual measurement. [ABSTRACT FROM AUTHOR]

This communication presents a dual-port reconfigurable square patch antenna with polarization diversity for 2.4 GHz. By controlling the states of four p-i-n diodes on the patch, the polarization of the proposed antenna can be switched among linear polarization (LP), left- or right-hand circular polarization (CP) at each port. The air substrate and aperture-coupled feed structure are employed to simplify the bias circuit of p-i-n diodes. With high isolation and low cross-polarization level in LP modes, both ports can work simultaneously as a dual linearly polarized antenna for polarimetric radars. Different CP waves are obtained at each port, which are suitable for addressing challenges ranging from mobility, adverse weather conditions and non-line-of-sight applications. The antenna has advantages of simple biasing network, easy fabrication and adjustment, which can be widely applied in polarization diversity applications. [ABSTRACT FROM PUBLISHER]

CubeSats are positioned to play a key role in Earth Science, wherein multiple copies of the same RADAR instrument are launched in desirable formations, allowing for the measurement of atmospheric processes over a short evolutionary timescale. To achieve this goal, such CubeSats require a high-gain antenna (HGA) that fits in a highly constrained volume. This paper presents a novel mesh deployable Ka-band antenna design that folds in a 1.5 U (10\times 10 \times 15 \,\textcm^3) stowage volume suitable for 6 U (10\times 20 \times 30 \,\textcm^3) class CubeSats. Considering all aspects of the deployable mesh reflector antenna including the feed, detailed simulations and measurements show that 42.6-dBi gain and 52% aperture efficiency is achievable at 35.75 GHz. The mechanical deployment mechanism and associated challenges are also described, as they are critical components of a deployable CubeSat antenna. Both solid and mesh prototype antennas have been developed and measurement results show excellent agreement with simulations. [ABSTRACT FROM PUBLISHER]

This communication presents the experimental results of a ultrawideband 2–18-GHz dual-polarized Vivaldi antenna array for airborne radar measurements of snow. The antenna design is based on the previously reported all-metal flared-notch array by Kindt and Pickles for operation over the frequency range 0.7–9 GHz. An antenna array prototype consisting of $8 \times 8$ active dual-polarized elements was fabricated with precise aluminum machining and tested in the anechoic chamber. Beamsteering upto 30° was experimental demonstrated from 2 to 18 GHz. The measurement results are in a good agreement with the full-wave simulation results in both polarization configurations. Preliminary sample results from data collected using the Vivaldi array are also presented. The antenna array enables full polarimetric measurements of snow-over-sea-ice for estimating the snow-water-equivalent (SWE), as well as fine-resolution mapping of snow-air and snow-ice interfaces for estimating thickness. [ABSTRACT FROM PUBLISHER]

This study investigates the impact that the acquisition surface has on the internal coverage of an object in the context of radar-based near-field microwave (MW) breast imaging. We define an acquisition surface as the surface over, which data are collected. Three different three-dimensional (3-D) data acquisition surfaces are investigated: 1) cylindrical, 2) hemispherical, and 3) patient specific. Three 3-D numerical breast models are used for the study. A realistic ultra-wideband (UWB) antenna generates incident fields and records the total fields. The responses from targets are analyzed, and object coverage is evaluated in terms of range distances, cross-range distances, and cumulative radiated power directed into the object by the antenna array embedded in the acquisition surface. Images are formed to verify these observations. We demonstrate that a patient-specific acquisition surface provides greater responses from targets, superior object coverage and improved images compared to the other acquisition surfaces studied. [ABSTRACT FROM PUBLISHER]

A 77-GHz transmit-array on dual-layer printed circuit board (PCB) is proposed for automotive radar applications. Coplanar patch unit-cells are etched on opposite sides of the PCB and connected by through-via. The unit-cells are arranged in concentric rings to form the transmit-array for 1-bit in-phase transmission. When combined with four-substrate-integrated waveguide (SIW) slot antennas as the primary feeds, the transmit-array is able to generate four beams with a specific coverage of \pm 15^\circ. The simulated and measured results of the antenna prototype at 76.5 GHz agree well, with gain greater than 18.5 dBi. The coplanar structure significantly simplifies the transmit-array design and eases the fabrication, in particular, at millimeter-wave frequencies. [ABSTRACT FROM PUBLISHER]

A fundamental analytical description is given for antenna insertion phase variation with polarization and is demonstrated through interferometer measurements of several Ka-band antenna elements. Detailed knowledge of the antenna phase variation is critical for high fidelity angle measurement in interferometer and phase comparison monopulse systems where two antennas may not have identical phase response to varying polarization. Detailed derivation of the phase variation is obtained by preserving the argument of the normalized complex voltage. Antennas with different polarization properties are shown to have different phase responses to incident wave polarization orientation which can produce significant spatial angle errors. The analytical development presented here can be used to specify antenna polarization properties during design to ensure tolerable error performance. Alternatively, compensation for the phase variation can be implemented in real-time using the analytical expressions and knowledge of the incident wave polarization properties. [ABSTRACT FROM PUBLISHER]

An improved method of more than halving the turn on frequency of a 4-arm log-periodic (LP) antenna for dual-circularly polarized (CP) bidirectional use is demonstrated. The ground plane currents of a slot-LP are manipulated by varying “ground plane” shape to form a ring-turnstile-slot LP aperture and thus extend the overall antenna bandwidth. The proposed concept is used to design and fabricate an antenna that is 2.3 times smaller than the conventional 4-arm LP and works from 500 MHz to 3 GHz. Microstrip impedance transformer/balun is used to feed the LP thus allowing for bidirectional use and much simpler beamforming network for dual-polarized operation. VSWR and far-field behavior of the antenna are characterized and its high-power thermal stability is demonstrated through a high-power test. The advantages over the previously designed ring-turnstile-LP configuration are highlighted and the design principles undertaken to make the antenna high-power capable are illustrated. The prototyped antenna is meant not only to illustrate the proposed concept but also as a viable high-power bidirectional antenna. [ABSTRACT FROM PUBLISHER]

Antenna beamwidth is a critical parameter that dictates the performance of a radar system. For a microstrip leaky wave antenna (MLWA) to achieve a narrow beam, it requires not only a long aperture, but also a small attenuation constant. In this paper, a two-section MLWA is proposed to achieve a small attenuation constant. The complex propagation constant of the proposed structure is first derived using the transverse resonance method (TRM). An antenna cross section is then designed using TRM and a short prototype is built and measured. It is shown that the resulting complex propagation constant agrees well with that calculated using TRM. Next, the antenna design is extended to a long aperture to demonstrate its narrow-beam performance based on full-wave simulation. Finally, the implications of employing a narrow-beam MLWA for radar applications are discussed. [ABSTRACT FROM PUBLISHER]

Retrieving far-field radar cross-section information from near-field data is a well-established methodology. However, existing algorithms impose many restrictions on the underlying measurement procedure. In this paper, algorithms are presented which are based on plane-wave decompositions and hierarchical groupings. Consequently, arbitrarily located monostatic near-field samples with arbitrary polarization information can be processed with full consideration of the radar antenna characteristics, where the computational complexity is identical to other fast approaches. The method uses scattering coefficients based on a Cartesian plane-wave scattering matrix as unknowns for the solution of the transformation problem. With this matrix description, the complete polarimetric information is obtained with a single transformation. Numerical examples are given to prove the usefulness of the algorithm. [ABSTRACT FROM PUBLISHER]

A planar passive retrodirective antenna (RDA) array with polarization rotation property is proposed in this paper using the substrate integrated waveguide (SIW) technology, which can be used in monostatic radar applications. The proposed RDA array adopts planar bandwidth-enhanced SIW cavity-backed wide slot antennas as the radiation elements. The polarization rotation property can be achieved by using radiation elements in two different configurations. A W-band prototype RDA array with 16 radiation elements is designed and fabricated using the single-layer printed circuit board (PCB) process at 79 GHz for automotive short-range radar applications. The measurement setup for monostatic and bistatic radar cross section (RCS) responses as well as the calibration process are presented. The retrodirective property and the polarization rotation property are realized by the proposed RDA array. The simulated and measured results of monostatic and bistatic RCS responses are in good agreement, which can cover an incident angle of \pm 17^\circ from bore-sight with its normalized monostatic RCS response dropped by about 3 dB. [ABSTRACT FROM PUBLISHER]

Highly crevassed ice surfaces at ice-sheet margins and fast-flowing glaciers significantly scatter radar signals. The scattered signals, often known as surface clutter, mask weak echoes from the ice-bed interface. Large wing-mounted antenna arrays are essential to synthesizing low-sidelobe patterns to reduce surface clutter. However, wing-mounted arrays are susceptible to structural flexure, which causes amplitude and phase errors that result in shifting and filling of desired array pattern nulls. In this communication, we characterize the effects of wing flexure on array beamformation using a scaled array model, and we present a compensation method to mitigate phase center errors caused by wing flexure. The compensation greatly improves clutter suppression through improved null formation. Experimental results show that we obtain an average of 7.5 dB improvement in the signal-to-interference noise ratio. [ABSTRACT FROM PUBLISHER]

The first measurements of moving humans using a dual-mode millimeter-wave radar sensor are presented. The radar sensor is comprised of a Doppler detection mode for measuring the radial velocity of a moving object, as well as a recently developed interferometric mode for directly measuring the angular velocity. Combining the two detection modes, it is shown that the motion of a walking human can be detected and measured regardless of the direction of trajectory relative to the radar sensor. Such a capability has the potential to significantly improve the effectiveness of security radars, and may apply to a broad range of other motion detection radar applications. The frequency shifts imparted on the signal in both Doppler and interferometric detection modes are measured in the time-frequency domain, and show that as the trajectory moves from a completely radial motion to a completely angular motion, the Doppler frequency shift decreases while the interferometric frequency shift increases. The two detection modes therefore represent complementary measurements, improving the ability to measure the motion of randomly moving objects. [ABSTRACT FROM PUBLISHER]

This paper presents the design of a directional folded dipole antenna integrated in an embedded wafer level ball grid array (eWLB) package, the comparison of different antenna designs and the influence of the silicon die and neighboring antennas within the package to the radiation behavior. The co-integration of the antenna and the silicon-based monolithic microwave integrated circuit (MMIC) in a system in package (SiP) approach is a convenient solution to suppress lossy radio frequency (RF) transitions and to simplify the design and the manufacturing of radio frontends significantly. The proposed SiP is focused on 77-GHz automotive radar applications. The MMIC contains the 77-GHz signal source and a transceiver with amplifier and mixer. The gain of different antennas in different constellations within the package is shown. [ABSTRACT FROM PUBLISHER]

We propose a novel design to reduce the radar cross section (RCS) and enhance the gain of a patch antenna by using partially reflecting surface (PRS). The PRS consists of two layers of metallic patterns on both sides of a dielectric slab. The metallic pattern on the bottom side is utilized to construct Fabry-Perot resonance cavity with ground plane of a patch antenna, while it is designed to absorb most of the incident wave on the top side. The PRS can enable the patch antenna to simultaneously achieve high gain and low RCS. Measurement results show that the antenna gain is enhanced by about 6.5 dB at 11.5 GHz, and its RCS is dramatically reduced in a broad frequency range from 6 to 14 GHz, compared with the traditional patch antenna without the PRS. [ABSTRACT FROM PUBLISHER]

In this communication, the application of sub-millimeter-wave imaging radars for collision avoidance and navigation of autonomous platforms in indoor environments is investigated. The polarimetric backscattering phenomenology of walls and doorways are studied to aid the design and system specifications of such radar systems. Polarimetric backscatter measurements of different wall covers, such as dry-wall, concrete blocks, wood, etc., as a function of incidence angle are carried out using a network analyzer operating at J-band. Also an instrumentation radar operating at 215 GHz is setup to collect backscatter data from corridors in an indoor setting. At each radar position, radar range profiles for both vertical and horizontal polarizations as a function of angle are used to form polar images for obstacle detection. It is shown that horizontally polarized incident wave can generate higher backscatter level and less reflection from smooth walls at steep angles of incidence and thus is the preferred polarization for this application. The polar images at each location are then co-registered in a global coordinate matrix to form a complete map of the interior layout. Feature extraction and image processing methods are then applied to remove multipath and enhance the radar map of building interiors. [ABSTRACT FROM AUTHOR]

Resistive loaded antennas are widely used in ground penetrating radar scenarios due to their good pulse radiation behavior and small size. Despite these facts their implementation into an antenna housing with absorber material and shielding leads to a quite cumbersome ground penetrating radar component not suitable for integration into a bottom hole assembly (BHA). Furthermore, the metallic bottom hole assembly influences the pulse radiation behavior in a negative way. This article describes an antenna design optimized for integration into a bottom hole assembly, incorporating simulation and measurement. As a result, ground penetrating radar usage may now be extended to the field of logging/measuring while drilling, maximizing the information about the surrounding media during the drilling process. [ABSTRACT FROM PUBLISHER]

This paper shows the antenna design of an integrated 122-GHz radar sensor. The sensor consists of a SiGe IC with a complete radar circuit and two antennas for transmitting and receiving the 122-GHz signal. The IC and the antennas are integrated into a low-cost plastic package that is assembled using wire bond technology. The antenna design was specifically optimized regarding the integration into the package and the compensation of the parasitic effects of the wire bond interconnect. First, the antenna design and its novel feeding technique based on a GCPW transmission line are explained. Then, measurement results including the wire bond interconnect are presented. Finally, details of the complete radar sensor are given. [ABSTRACT FROM PUBLISHER]

The characterization of the subsurface can be performed by full-waveform inversion of electromagnetic data. The modeling process relies on the ability to retrieve the scattered field Green's function from the measured data using sets of antenna characteristic global reflection and transmission coefficients. Crucial for a successful implementation of this technique is the understanding of uncertainties involved in the acquisition of the antenna calibration and survey measurements, and how these propagate in the parameter estimation results. We find that averaging a number of possible Green's functions obtained from one measurement with several antenna characteristic coefficients sets works remarkably well in reducing the uncertainties. The accuracy of the inversions improves using characteristic coefficients acquired as close as possible to the measurement conditions. A clear relation between dynamic range and system resolution is highlighted, based on the number of effective bits contained in the data. [ABSTRACT FROM PUBLISHER]

A packaging solution for the integration of an MMIC and a thin film antenna into a single surface-mountable package is presented. It is based on an air cavity in the package base into which the MMIC is placed. All package-to-MMIC interconnects are routed through the antenna substrate and all connections are realized using flip chip technology. Thus wire bonds are eliminated within the whole package. A broadband flip chip interconnect is used to connect MMIC and antenna. As the antenna is situated above an air cavity, a large bandwidth is also achieved for the antenna. An antenna-in-package prototype is presented to demonstrate the feasibility of the assembly process and to test the antenna performance including the flip chip interconnect. The influence of an additional package cover is analyzed by measuring the antenna covered with two different lids. [ABSTRACT FROM AUTHOR]

Antenna arrays with low sidelobes in the cross-track direction are needed for sounding and imaging ice-sheets margins including outlet glaciers. Weak radar signals from the ice-bed interface are often masked by off-vertical surface clutter from extremely rough crevassed surfaces in ice-sheet margins. Synthetic aperture radar (SAR) processing can be used to synthesize a large array for reducing clutter in the along-track direction. Low-sidelobe transmit- and receive-antenna patterns must be generated from a limited size array in the cross-track direction. Airborne antenna pattern measurements are critical to verifying pattern characteristics in the presence of a non-ideal ground plane and neighboring aircraft structures, as well as in-flight operational dynamics. In this paper, we describe a set of airborne measurements performed to determine and optimize antenna patterns for the very high frequency (VHF) array used to sound and image polar ice sheets. We measured antenna patterns by flying over a relatively smooth ice surface at an altitude of about 2700 m. The pattern data were obtained by processing the surface echoes with aircraft rolled from left to right over more than five cycles. We also simulated antenna patterns using a three-dimensional computer model of the entire airborne platform and compared with experimental results. The discrepancies between the measured and simulated results are less than 2.7 dB for 85% of the data samples. The measured pattern data will be used to optimize our array processing algorithms. [ABSTRACT FROM PUBLISHER]

We propose an approach to the design of array-based, 2D echo generators. The radiating elements are located on non-uniform grids and the quiet zone (QZ) design specifications are enforced at non-uniformly spaced sampling locations. The approach, based on a singular values optimization process, allows dimensioning the size of the echo generator to meet the QZ specifications, defining the number and locations of the QZ sampling points and of the radiators to control the ill-conditioning when searching for the excitation coefficients, dramatically reducing the number of radiating elements, and finding the excitations by a Singular Value Decomposition approach. The performance of the method in terms of QZ field behavior and robustness against realization errors is numerically assessed. An experimental validation of the technique is also presented. [ABSTRACT FROM AUTHOR]

A high-efficiency self-shielded microstrip-fed Yagi-Uda antenna has been developed for 60 GHz communications. The antenna is built on a Teflon substrate (\varepsilonr = 2.2) with a thickness of 10 mils (0.254 mm). A 7-element design results in a measured S 11 of < -10~dB at 56.0 – 66.4 GHz with a gain> 9.5 ~dBi at 58 – 63 GHz. The antenna shows excellent performance in free space and in the presence of metal-planes used for shielding purposes. A parametric study is done with metal plane heights from 2 mm to 11 mm, and the Yagi-Uda antenna results in a gain> 12 ~dBi at 58 – 63 GHz for h = 5 -8~mm. A 60 GHz four-element switched-beam Yagi-Uda array is also presented with top and bottom shielding planes, and allows for 180^\circ angular coverage with < 3~dB amplitude variations. This antenna is ideal for inclusion in complex platforms, such as laptops, for point-to-point communication systems, either as a single element or a switched-beam system. [ABSTRACT FROM AUTHOR]