Cross-polar Radiation Patterns Research Articles

An optimal design of a cylindrical polarimetric phased array radar for weather sensing

[1] An optimal design of a cylindrical polarimetric phased array radar (CPPAR) for weather sensing is presented. A recently introduced invasive weed optimization (IWO) technique is employed to obtain the desired radiation pattern of the CPPAR. Instead of optimizing each element excitation in a large array (with expensive calculation costs), the modified Bernstein polynomial distribution, defined by seven parameters, is used to optimize the current distribution for the CPPAR. The simulation results show that the desired sidelobe levels (SLLs) and beam width are achieved in a computationally effective manner. Furthermore, the imaged feed arrangement is used to suppress the cross-polarization level. Both co-polar and cross-polar radiation patterns for broadside and off-broadside directions are presented to show the performance of the optimized CPPAR.

Bias in Copolar Correlation Coefficient Caused by Antenna Radiation Patterns

We present a theoretical study of the bias in the copolar correlation coefficient caused by cross-polar radiation patterns and by unmatched horizontal and vertical copolar radiation patterns. The analysis of the bias induced by cross-polarization radiation is carried out for both modes of operation of polarimetric radars, designated as the simultaneous transmission and reception of horizontally and vertically polarized waves and the alternate transmission of horizontally and vertically polarized waves, respectively. The bias caused by unmatched horizontal and vertical copolar radiation patterns as a function of slight differences in pointing angles and beamwidths is also analyzed. In well-designed weather radars, for the purpose of hydrometeor classification, the overall acceptable bias in the copolar correlation coefficient should be less than about 0.01. The levels of cross-to-copolar gain ratios for acceptable performance are indicated. Ultimately, pointing angle and beamwidth tolerances are indicated for horizontal and vertical copolar antenna patterns.

Bias in Differential Reflectivity due to Cross Coupling through the Radiation Patterns of Polarimetric Weather Radars

Abstract Examined is bias in differential reflectivity and its effect on estimates of rain rate due to coupling of the vertically and horizontally polarized fields through the radiation patterns. To that end, a brief review of the effects of the bias on quantitative rainfall measurements is given. Suggestions for tolerable values of this bias are made. Of utmost interest is the bias produced by radars simultaneously transmitting horizontally and vertically polarized fields, as this configuration has been chosen for pending upgrades to the U.S. national network of radars (Weather Surveillance Radar-1988 Doppler; WSR-88D). The bias strongly depends on the cross-polar radiation pattern. Two patterns, documented in the literature, are considered.

L-strip proximity fed shorted rectangular microstrip antenna for mobile communication

A dual-band L-strip proximity fed shorted rectangular microstrip antenna is proposed and investigated theoretically simulated by HFSS and experimentally. Proposed radiating patch is located about (17.5 mm) above the ground plane. Return Loss and co- and cross polar radiation pattern are presented. Computed and measured results of return loss are in good agreement. The effect of the geometric parameters of the proposed antenna, such as length of the vertical and horizontal portion of the L-strip is also investigated. The impedance bandwidth (−10 dB return loss) 32.5% (calculated) and 33.00% (measured) for the proposed antenna are achieved for optimized antenna design. Significant size reduction (i.e., ∼85%) is obtained as compared with conventional rectangular patch of same resonant frequency. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1567–1571, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25235

A Wideband Slot-Coupled Stacked-Patch Array for Wireless Communications

In this letter, a novel slot-coupling feeding technique is used to realize a dual-polarized 2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex> </formula> 1 microstrip stacked patch array for mobile wireless communication systems. The array is intended as a basic module for base-station linear arrays, whose final size depending on beamwidth and gain requirements. Each array element is fed through two microstrip lines arranged on the basis of a sequential rotation technique. Each stacked square patch is excited through a square ring slot realized in the feeding network ground plane. Design procedure, simulation results and measurement data are presented for a 2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\,\times\,$</tex></formula> 1 array working in the GSM 1800–1900 band (1710–1910 MHz), UMTS band (1920–2170 MHz), ISM band (2400–2484 MHz), and UMTS 3G expansion band (2500–2690 MHz) or, alternatively, WiMAX band (2300–2700 MHz), with a resulting 45% percentage bandwidth (reflection coefficient <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${&lt;-}$</tex></formula> 10 dB). Due to both the symmetry properties of the novel slot-coupling feeding configuration and the implementation of a sequential rotation technique, good results have been obtained in terms of port isolation and cross-polar radiation patterns.

Optimised design of multi-band cellular base station antenna array for GSM and UMTS deployment

A tri-band dual polarised printed patch array is designed for GSM and UMTS cellular deployment using an efficient moment method code driven by a marginal distribution optimisation algorithm. Novel techniques are introduced to expedite analysis while maintaining adequate accuracy, and two methods are used to aggregate elements into an array for pattern synthesis: unequal spacing and phasing. Optimisation criteria such as cross-polar isolation, return loss and radiation pattern characteristics are successfully achieved in simulation, and a measured prototype element supports the antenna concept.

Radiation pattern and properties of double-flared diagonal horn antenna

This article is concerned with analytical model for radiation pattern of a new double-flared diagonal horn antenna using “plane wave spectra technique for 3D fields”. The double-flared diagonal horn antenna is accomplished by adding one more set of flares in E- and H-planes with equal flare angles into conventional diagonal horn. The copolarized and cross-polarized radiation patterns in E-, H-, and D-planes have been computed utilizing the analytical model and reported in the article. The parametric studies on peak cross-polarization level have carried out. The radiation performance of double-flared and conventional diagonal horns for same length and aperture size are also compared. It is investigated that double-flared diagonal horn antenna posses better peak cross-polarization level (≈−16.5 dB) in D-plane (±45° plane) in comparison of conventional diagonal horn (≈−15.5 dB) at design frequency and retains almost circularly symmetric radiating beam at lower values of elevation angles. Also, double-flared diagonal horn has better matches with free-space and has slightly lower gain (≤0.5 dB) in comparison of conventional diagonal horn. The work presented here can provide useful design guidelines for development of prototypes of double-flared diagonal horn, which may find potential application in satellite communication and imaging applications etc. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

Dual-Band Electronically Switchable Shorted Patch Antenna

An improved design of a shorted patch antenna with electronic switching of the operating bands is proposed. PIN diodes are used as switches for connecting four shorting posts to the ground plane. With reverse biased diodes the antenna operates at 2 GHz, while with forward biased diodes the operating frequency is 4 GHz. Two electronically switched impedance matching networks are designed, one for each band. The impedance matching networks are electronically switched with the same bias voltage used for switching the patch resonant frequency. The E- and H-plane co-polarization and cross-polarization radiation patterns are measured in both bands. The results show good radiation characteristics and lower cross-polarization levels in comparison to previous designs.

Design and Study of Wide-Band Patch Antenna Fed by Meandering Probe

A wide-band probe fed patch antenna with low cross polarization and symmetrical broadside radiation pattern is proposed and studied. By employing a novel meandering probe feed and locating a patch about 0.1/spl lambda//sub 0/ above a ground plane, a patch antenna with 30% impedance bandwidth (SWR<2) and 9 dBi gain is designed. The far field radiation pattern of the antenna is stable across the operating bandwidth. Parametric studies and design guidelines of the proposed feeding structure are provided.

Curvilinear Fresnel-Zone Plate Lens Antenna: Vector Radiation Theory

A generalized vector diffraction theory of the half-open curvilinear Fresnel zone plate (FZP) tens antenna that is valid for any lens profile shape is presented. It is an extension to the vector Kirchhoff diffraction theory for the plane half-open FZP lens antenna and is based on the conical-segment lens profile approximation. An equation for the electric far-field vector is derived from which follow the expressions for the co- and cross-polarization radiation patterns and directive gain. The proposed theory is utilized for a numerical analysis and comparison of 140-GHz curvilinear half-open FZP lens antennas grouped in two distinct sets: (a) Set I: antennas with different in shape FZP lenses (plane, conical, parabolic and spherical) having the same number of zones. All eurvilinear FZP antenna lenses are designed for similar gain, co- and cross-polarization performance and bandwidth, regardless of the lens-profile. (b) Set II: antennas with different in shape FZP lenses and different number of zones. Since this affects gain, polarization and bandwidth performance, to make the characteristics of these FZP lens antennas practically equal to those of Set I, antenna feeds with different gain patterns have been used.

Analysis and design of L-probe proximity fed-patch antennas

In this paper, the finite-difference time-domain (FDTD) method is employed to analyze L-probe proximity-fed rectangular patch antennas. Numerical results for the input impedance, co- and cross-polarization radiation patterns are presented and compared with the measurements. Good agreement between the computed and measured results is obtained. The effects of geometric parameters on the characteristics of the L-probe patch antenna are extensively studied. For design purposes, the variation of input impedance at resonance with different geometric parameters is plotted on a Smith chart. Mutual coupling between two L-probe patch antennas is also investigated.

On the available diversity gain from different dual-polarized antennas

Dual-polarized antennas are traditionally characterized in terms of port-to-port isolation and co- and cross-polar radiation patterns. For base station antennas in a mobile communications system, the critical parameter is instead the far-field coupling between the two channels. In a mobile communication system, base station antennas with a nominal /spl plusmn/45/spl deg/ to vertical linear polarization are commonly used. Such antennas are difficult to design with constant polarization characteristics in azimuth. We calculate the antenna output power correlation and diversity gain under Rayleigh fading conditions and different values of the environment cross-polar discrimination. Two different antennas are compared: a dual-polarized aperture coupled patch and a slanted dipole configuration, both over an infinite groundplane. We show that the aperture coupled patch provides lower output correlation and higher diversity gain than the slanted dipoles in all investigated cases.

Copolar and cross-polar radiation of Vivaldi antenna on dielectric substrate

The copolar and cross-polar radiation patterns of the Vivaldi antenna on a dielectric substrate are calculated and validated by measurements. The method involves a two-step procedure. The electric field distribution across the antenna slot aperture is calculated first. The radiated fields are then calculated, using Green's functions. The continuous exponential tapered shape is approximated by annular linearly tapered sections. The conical transmission-line theory and a variational method yield the electric field in each section. The radiation calculation is based on closed-form expressions for the dyadic Green's function of an elementary electric field source in a conducting half sheet. Both copolar and cross-polar radiation patterns of the Vivaldi antenna are calculated by integrating the Green's functions weighted by the electric field distribution over the antenna aperture. The effect of lateral truncation is taken into account by defining weighting patterns. The method is validated by original measurements and limitations of the model are discussed. Antenna directivity and sensitivity are calculated.

Bandwidth enhancement of U-slot microstrip antenna using a rectangular stacked patch

Experimental and simulation results of a coaxially fed U-slot microstrip antenna stacked with a rectangular patch are presented. Results include impedance bandwidth, copolar and cross-polar radiation patterns, and gain. The antenna impedance bandwidth is about 44.7%, with a slightly smaller 3 dB gain bandwidth. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 21: 393–395, 1999.

Experimental and theoretical study of groove guide horn antennas at W-band

Novel horn antennas constructed from groove guide have been analysed and measured at W-band. The desired radiation pattern could be achieved by optimising the guide dimensions. In the present study, the co-polarisation and cross-polarisation radiation patterns of horns with rectangular-, trapezoidal- and V-groove have been evaluated by using the Method of Lines. For verification purposes, horns with V-groove were fabricated and their performance were measured. The predicted data were close to the measured data.

Broadband active microstrip antenna design with the simplified real frequency technique

This paper deals with the design of broadband active microstrip antennas where the amplifier is integrated with the radiator. Theoretically sound definitions for gain and noise figure of the active antenna are introduced, and their relationships with the definitions for the composing circuit and radiator parts are explained. A sequential design procedure is presented that allows the straightforward and optimal design of transmitting and receiving antennas with multiple active stages, taking into account input and output matching, the gain-versus-frequency curve as well as the noise performance. The theoretical concepts are illustrated with two examples: one of a transmitting active antenna and one of a receiving antenna. The former one is a two-stage design that achieves nearly 25% of bandwidth with regard to gain and matching and 24 dB gain improvement as compared to the matched passive antenna. The second one is a receiving antenna (one stage) with a measured noise figure of 1.2 dB in a bandwidth of over 17% and a gain improvement of 11.9 dB over the corresponding passive antenna. Finally co- and cross-polar radiation patterns in E- and H-plane prove that the antennas also have favorable radiation characteristics in a wide bandwidth (at least 18%). >

G-band dielectric core horn

The design, fabrication and performance of a 175.5–191.5 GHz dielectric core horn is presented for the first time. Good agreement is shown between predicted and measured copolar and crosspolar radiation patterns.

Frequency-scanning grating-reflector antenna for multibeam satellite communications

The analysis and design of a circularly polarized frequency-scanning grating-reflector antenna is presented. The antenna is intended for a multibeam satellite communication system, covering 3.1 degrees north-south and 7.2 degrees east-west with 25 spot beams. Frequency scanning is used for the north-south coverage, while the east-west coverage is obtained by the use of a cluster feed. The grating reflector consists of a planar frequency-scanned reflection grating with a quasi-periodic lattice geometry. The frequency-scanned grating reflects the incident field into a diffracted field composed of the first-order diffracted grating lobe. A focus-feed position for the diffracted field is obtained by a proper design of the quasi-periodic lattice geometry. Design principles for the planar grating-reflector antenna are presented together with an analysis method for predicting copolar and cross-polar radiation patterns. The analysis method is verified by experimental results. >

Axial crosspolarization in reflector antennas due to asymmetric cross-polar feed patterns

The on-axis cross-polarisation of a reflector antenna illuminated by a feeding system with an asymmetric cross-polar radiation pattern is examined. A graph is presented from which the cross-polarisation discrimination (XPD) of the reflector antenna can be simply obtained.

Propagation and radiation behaviour of a longitudinally slotted horn with dielectric-filled slots

It is proposed that the slots of a longitudinally slotted horn be filled with a dielectric material. This is shown to considerably reduce the required slot depths for achieving low crosspolarisation; thus more feasible and economic design of such a horn is possible. Design curves for the modal propagation constants of the first two modes against the frequency, the dielectric constant of the slot filling material and the geometrical constants of the horn are presented. The co- and cross-polar radiation patterns are calculated, and it is found that peak crosspolar level &lt; − 50 dB can be achieved at certain frequencies and a level &lt; − 30 dB can be achieved over about 13% bandwidth.