Radiation Pattern Of Feed Research Articles

Best Feed Positions and Radiation Patterns of Typical Multibeam Dielectric Lens Antenna

Best Feed Positions and Radiation Patterns of Typical Multibeam Dielectric Lens Antenna

Reflectarray Feeds Augmented With Size-Reducing GRIN Lenses for Improved Power Handling and Aperture Efficiency

The feed for reflectarrays and transmitarrays is crucial for determining the overall antenna aperture efficiency, gain, and power handling. In the past, several methods, such as altering the horn shape to achieve higher modes, have been employed to modify the feed radiation pattern to improve these key parameters. However, another approach is to use gradient index (GRIN) lenses, which offer unprecedented control over the radiation pattern and can be used to shrink the overall antenna. In this paper, we demonstrate highly effective approaches for optimizing GRIN lenses to achieve different design objectives including high gain radiation with a compact feed as well as improved aperture efficiency and power handling. Additive manufacturing is employed to fabricate the lenses, and measured results agree well with simulations.

Bidirectional CPW Fed Quad-Band DRA for WLAN/WiMAX Applications

Due to the size constraint, antennas with compact size are required that can support multibands with single radiating element. Dielectric resonator antenna (DRA) can support multiple modes with good efficiency and gain using single radiating element. In this paper, a quad-band DRA is proposed for WLAN/WiMAX bands using a single CPW feed. Out of four bands, WLAN (2.37-2.55) GHz, (5.15-5.35) GHz, and (5.6-5.83) GHz are achieved by the excitation of fundamental and higher-order modes whereas WiMAX (3.58-3.72) GHz band is achieved by dielectric loading of the DR. Dielectric loading makes it possible to operate the antenna at desired frequency band. Due to the partial ground plane and single coplanar waveguide (CPW) feed radiation pattern of the proposed antenna is bidirectional. The design is efficient in terms of radiation efficiency. Simulated and measured results show that it can be a suitable candidate for WLAN and WiMAX applications.

Low-Profile Scanloss-Reduced Integrated Metal-Lens Antenna

Integrated lens antennas are widely used in high gain and beam steering applications at millimeter-wave frequencies. The ILA has often large height and suffers from significant scan loss. In this article, we demonstrate a low-profile, efficient, and scanloss-reduced integrated metal-lens antenna (IMLA). An IMLA is a combination of a dielectric lens and metal–plate lens. A 16- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> diameter IMLA is designed using the HDPE and 58 stainless steel plates to achieve the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f/d$ </tex-math></inline-formula> of 0.69. The simulated aperture and radiation efficiency of the IMLA are 73% and 92%, respectively. At 76 GHz, the simulated and measured realized gains of the fabricated IMLA are 31.24 and 31 dBi, respectively. The IMLA is designed to steer the main beam to ±30°. The scan loss is reduced by tilting the radiation pattern of the feeds at offset positions along the focal plane. The radiation pattern of the square waveguide feed is tilted using asymmetrical dielectric pins. The asymmetrical dielectric pins reduce the simulated gain scan loss of the IMLA by more than 1.5 dB at 30° steering angle. The simulation results show that the inclination of the feed radiation pattern helps limit the scan loss of the IMLA to 4.1 and 4.3 dB in the H- and E-planes for 30° steering angle, respectively. The measured scan loss of the manufactured IMLA is 3.8 and 6.2 dB in the H- and E-plane, respectively.

A Compact Gap-Waveguide Dual-Polarized Ka-Band Feed for 50dBi Reflector Antennas With Tracking Function

A dual-polarized Ka-band feed based on gap waveguide (GW) technology for an ultra-high-gain reflector antenna is presented. The feed provides SUM-beams for data transfer and DIFF-beams for tracking. The whole reflector antenna is composed of the feed and a dual-reflector Cassegraine antenna. The feed has been prototyped, and the measured reflection coefficients for the horizontally and the vertically polarized SUM-beam ports are below -10 dB and -8 dB over 30.8-38 GHz, respectively. The measured feed radiation patterns agree well with the simulated ones. The dual-reflector Cassegraine antenna has been designed and simulated by using GRASP with the simulated far-field function of the proposed feed, showing that the reflector antenna achieves SUM-beam gains above 50 dBi and the null depth of the DIFF-beams are more than 30 dB below the maximum of SUM-beams.

Optimal Radiation Pattern of Feed of Luneburg Lens for High-Gain Application

The focus of this communication is to study about the optimal radiation pattern of the feed of Luneburg lens for high-gain application. Based on geometric optics and equivalent aperture theory, the effect of the radiation pattern of the feed on the gain of Luneburg lens is analyzed first. Then the optimal radiation pattern of the feed is predicted by theoretical calculation to guarantee the maximum radiation gain of Luneburg lens, and the half-power beamwidth (HPBW) of the optimal radiation pattern of the feed is near 68° for the Luneburg lens with a radius greater than three wavelengths. To verify the theory, the Luneburg lens antennas fed by the feeds with different radiation patterns working at 10 GHz are analyzed. Finally, a prototype of Luneburg lens with a radius of 100 mm and several different feed antennas are manufactured to verify the theory and the simulation. The final simulated and measured results are consistent with the theory.

Hybrid area exploration–based mobility‐assisted localization with sectored antenna in wireless sensor networks

SummaryIn common practice, sensor nodes are randomly deployed in wireless sensor network (WSN); hence, location information of sensor node is crucial in WSN applications. Localization of sensor nodes performed using a fast area exploration mechanism facilitates precise location‐based sensing and communication. In the proposed localization scheme, the mobile anchor (MA) nodes integrated with localization and directional antenna modules are employed to assist in localizing the static nodes. The use of directional antennas evades trilateration or multilateration techniques for localizing static nodes thereby resulting in lower communication and computational overhead. To facilitate faster area coverage, in this paper, we propose a hybrid of max‐gain and cost‐utility–based frontier (HMF) area exploration method for MA node's mobility. The simulations for the proposed HMF area exploration–based localization scheme are carried out in the Cooja simulator. The paper also proposes additional enhancements to the Cooja simulator to provide directional and sectored antenna support. This additional support allows the user with the flexibility to feed radiation pattern of any antenna obtained either from simulated data of the antenna design simulator, ie, high frequency structure simulator (HFSS) or measured data of the vector network analyzer (VNA). The simulation results show that the proposed localization scheme exhibits minimal delay, energy consumption, and communication overhead compared with other area exploration–based localization schemes. The proof of concept for the proposed localization scheme is implemented using Berkeley motes and customized MA nodes mounted with indigenously designed radio frequency (RF) switch feed network and sectored antenna.

Wideband Cryogenic Receiver for Very Long Baseline Interferometry Applications

One of the critical points concerning radio-astronomy applications regards the power received by the radio telescope, most often extremely faint. Beyond approaches aimed at increasing the collecting area of the radio telescope (at microwave frequencies almost always a reflector antenna), such as for example the use of very long baseline interferometry (VLBI) techniques, a key point is the installation of cryogenic receivers to reduce the system noise temperature. To achieve the lowest noise temperature, it is desirable to cryogenically cool also the feed of the reflector antenna. This is achieved by enclosing the feed in a Dewar to provide the required thermal isolation between the feed and the external environment. However, this enclosure inevitably affects the radiation properties of the feed. This letter presents the development of a cryogenic receiver, composed of a 2–14 GHz quad ridge flared horn and a Dewar, for a notable case where the Dewar is designed to be as compact as possible to minimize not only the thermal and mechanical load, but also the illumination blockage. Indeed, the receiver is intended to be installed on a 12 m reflector antenna for VLBI applications, whose optics require an installation of the feed itself very close to the subreflector. A prototype of the cryogenic receiver has been fabricated and measured, discussing the impact of the Dewar on the feed radiation patterns, input matching, isolation, antenna efficiency, and showing the overall system noise temperature.

Gain and Polarization Properties of a Large Radio Telescope from Calculation and Measurement: The John A. Galt Telescope

Measurement of the brightness temperature of extended radio emission demands knowledge of the gain (or aperture efficiency) of the telescope and measurement of the polarized component of the emission requires correction for the conversion of unpolarized emission from sky and ground to apparently polarized signal. Radiation properties of the John A. Galt Telescope at the Dominion Radio Astrophysical Observatory were studied through analysis and measurement in order to provide absolute calibration of a survey of polarized emission from the entire northern sky from 1280 to 1750 MHz, and to understand the polarization performance of the telescope. Electromagnetic simulation packages CST and GRASP-10 were used to compute complete radiation patterns of the telescope in all Stokes parameters, and thereby to establish gain and aperture efficiency. Aperture efficiency was also evaluated using geometrical optics and ray tracing analysis and was measured based on the known flux density of Cyg A. Measured aperture efficiency varied smoothly with frequency between values of 0.49 and 0.54; GRASP-10 yielded values 6.5% higher but with closely similar variation with frequency. Overall error across the frequency band is 3%, but values at any two frequencies are relatively correct to ∼1%. Dominant influences on aperture efficiency are the illumination taper of the feed radiation pattern and the shadowing of the reflector from the feed by the feed-support struts. A model of emission from the ground was developed based on measurements and on empirical data obtained from remote sensing of the Earth from satellite-borne telescopes. This model was convolved with the computed antenna response to estimate conversion of ground emission into spurious polarized signal. The computed spurious signal is comparable to measured values, but is not accurate enough to be used to correct observations. A simpler model, in which the ground is considered as an unpolarized emitter with a brightness temperature of ∼240 K, is shown to have useful accuracy when compared to measurements.

A Novel Matched Feed Structure for Achieving Wide Cross-polar Bandwidth for an Offset Parabolic Reflector Antenna System

This letter presents the details of a novel matched feed structure which promises improved cross-polar performance for an offset parabolic reflector antenna. Feed aperture formed by an intersection of circular and rectangular waveguides provides wide cross-polar bandwidth due to the cutoff wave numbers being close for the two modes used in conjugate matching. The mode coefficients and relative phase difference are estimated using particle swarm optimization (PSO) technique for the specified antenna system. Physical optics (PO) is used to evaluate the reflector pattern; feed radiation pattern is obtained using mode field patterns and cutoff wave numbers, which are computed using 2-D finite element method (FEM). The higher order mode which is combined with the main operating mode of the waveguide for conjugate matching is generated using two posts placed behind the aperture. The antenna system performance is evaluated using HFSS and CST Microwave Studio.

Improving the Calibration Efficiency of an Array Fed Reflector Antenna Through Constrained Beamforming

Calibrating for the radiation pattern of a multi-beam Phased array feed (PAF) based radio telescope largely depends on the accuracy of the pattern model, and the availability of suitable reference sources to solve for the unknown parameters in the pattern model. It is shown how the efficiency of this pattern calibration for PAF antennas can be improved by conforming the beamformed far field patterns to a two-parameter physics-based analytic reference model through the use of a linearly constrained minimum variance (LCMV) beamformer. Through this approach, which requires only a few calibration measurements, an accurate and simple pattern model is obtained. The effects of the model parameters on the directivity and sidelobe levels of multiple scanned beams are investigated, and these results are used in an example PAF beamformer design for the proposed MeerKAT antenna. Compared to a typically used maximum directivity (MaxDir) beamformer, the proposed constrained beamforming method is able to produce beam patterns over a wide Field-of-View (FoV) that are modeled with a higher degree of accuracy and result in a significant reduction in pattern calibration complexity.

Prediction of Aperture Efficiency Ripple in Clear Aperture Offset Gregorian Antennas

Electrically small clear aperture dual offset reflector systems often exhibit a directivity ripple over frequency due to the interference of the diffracted field from the sub-reflector with the main beam field. This paper investigates the cause of the ripple, and presents a technique to predict the expected system directivity, including the ripple, using the feed radiation pattern augmented by an efficient simulation strategy in a clear aperture offset Gregorian system. The method allows for accurate prediction of the directivity ripple using a severely under-sampled set of simulation results. Predicted results are compared to several simulations, and agreement to better than 0.5 % is found for the majority of configurations using both analytical and full wave simulated feed patterns.

Offset Dual-Reflector Antenna System Efficiency Predictions Including Subreflector Diffraction

A simple analytical formula for the prediction of diffraction efficiency in offset dual-reflector antenna systems is presented, and its performance evaluated by comparison to commercial software physical optics and method-of-moments simulations. The formula only requires knowledge of the symmetry plane physical configuration of the reflectors and an analytical approximation of the feed radiation pattern, and is therefore very straightforward to implement and use as a design aid. Some example applications of the formula are presented and discussed.

Diversity performance of multiport dielectric resonator antennas

Single-structure dual and triple linearly polarised cylindrical dielectric resonator antennas (CDRAs) with respective excitation sets of two orthogonal modes and three degenerate modes at 120° to each other are investigated for operation as compact multiport antennas. The diversity performance of these multiport CDRAs is evaluated using theoretical expressions of envelope correlation coefficient, mean effective gain (MEG) and MEG ratio in conjunction with simulation and experimental S-parameter results. The multiport CDRAs portray low mutual coupling (<−6.5 dB), different feed radiation pattern and polarisation directions, low envelope correlation coefficients (<0.27) between feed points and near-equal branch MEG ratios (within±1.8 dB). Thus, they satisfy the diversity performance benchmarks for application as compact multi-polarised diversity or multiple-input multiple-output antennas.

Multiple Phase Center Performance of Reflector Antennas Using a Dual Mode Horn

A new application for reflector antennas is proposed and developed. Using the aperture theory, a phase center on the reflector aperture is determined and shown that, its location is dependent on the field distribution. The proposed concept is, initially, verified by using a symmetric reflector. It is shown that the phase center is located at the aperture geometric center, when the reflector is illuminated symmetrically about its principal planes. Then, a dual mode feed, employing TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> modes, is used for generating different reflector illuminations, and causing displacement of its phase center. The concept is then extended to offset reflectors, and the influence of the reflector geometry on the phase center displacement and other reflector electrical parameters is investigated. Based on the established feed radiation pattern requirements, a feed horn is designed using circular waveguide that can propagate both modes. By modifying the amplitude and phase of the modes in the horn, a controlled asymmetric reflector aperture field is achieved. A prototype feed horn is fabricated and tested for its dual mode radiation patterns. The results are in good agreement with simulations. The reflector phase center properties are then investigated, by using the designed feed. A reflector-feed assembly, with its dual phase center capability, was developed for improving the performance of the ground moving target indicator radars. The concept allows the conversion of a single reflector to two or more reflectors, simply by modifying the mode excitation amplitudes and phases, in the feed alone

Taking into account the radiation pattern of a practical feed for a Luneberg lens

A method of taking into account the real feed radiation pattern for a Luneberg lens is proposed. According to this, the field of a feed with the given radiation pattern is expanded into series in spherical harmonics. Using this approach, it is possible to introduce the radiation patterns of real feeds into strict electrodynamic solution for a Luneberg lens, thus significantly refining a mathematical model of the antenna.

Aperture-field uniformity and cross-polarization level of dual parabolic cylindrical reflectors

For dual parabolic cylindrical reflectors, the field distribution over the aperture is calculated. This aperture-field distribution is a function of the feed orientation, and feed radiation pattern, the feed polarization, and the geometry of the configuration, in particular, the focal lengths of the two reflectors and the angle between them. The effects of these parameters on the uniformity of the co-polar component and the level of the cross-polar component of the aperture field are studied, and some representative results are presented. It is shown that by a proper selection of the geometrical parameters of the system, a high degree of co-polar field uniformity on the aperture can be maintained. Therefore, the system can be used as a compact antenna range to test large antennas.

Pattern analysis of paraboloids fed by rectangular waveguides employing multipole expansion techniques

A multipole expansion technqiue is developed for calculating the co-polar and cross-polar radiation patterns of a prime-focus paraboloid fed by a dominant-mode rectangular waveguide feed. Initially, the feed radiation pattern is expressed in terms of electric and magnetic multipoles of different orders which are subsequently used to obtain the secondary radiation patterns (co-polar and cross-polar) in explicit closed form in the form of a rapid by a converging algebraic series. The validity of the analysis is effectively demonstrated by calculating the co-polar and cross-polar patterns of a typical paraboloid and comparing and results with calculations based on the direct numerical integration of the physical optics currents induced on the reflector surface.

Feed radiation patterns modified by a dichroic plate

The 20 GHz copolar radiation patterns of a feed 4.25 cm from a flat dichroic plate 15 cm in diameter have been computed using a mode-matching technique. The results are in good agreement with the measured patterns.

Calculation of dielectric-aerial-radiation patterns

Brown and Spector's theory of the dielectric-rod aerial is extended and refined by considering the effect of the rod on the feed-radiation pattern. A correction function is deduced which includes an additional phase-correction term.