Antenna gain calibration on a ground reflection range

The absolute gain of wide-beam antennas may be accurately measured using the method described. Both the theoretical and practiced aspects of gain calibration on a ground reflection antenna range are presented. The measurement procedures developed were used to calibrate a log-periodic antenna at selected frequencies from 250 to 400 MHz. Measured data at 300 MHz is tabulated and error contributions are analyzed, yielding a measurement accuracy ofpm0.27dB with a 95 percent confidence interval.     

Accurate measurement of antenna gain and polarization at reduced distances by an extrapolation technique

A new technique is described for determining power gain and polarization of antennas at reduced range distances. It is based on a generalized three-antenna approach which, for the first time, permits absolute gain and polarization measurements to be performed without quantitative a priori knowledge of the antennas. The required data are obtained by an extrapolation technique which includes provisions for rigorously evaluating and correcting for errors due to proximity and multipath interference effects. The theoretical basis provides a convenient and powerful approach for describing and solving antenna measurement problems, and the experimental method employed illustrates the utility of this approach. Examples of measurements are included which exhibit errors in gain as small aspm0.11dB (3sigma).     

Near-field gain of a horn and an open-ended waveguide: Comparison between theory and experiment

Generating a standard electromagnetic field requires knowledge of the gain of the transmitting antenna. The theory and supporting experimental measurements of the near-field gain of a pyramidal horn and an open-ended waveguide (OEG) at 450 MHz are given. The empirical near-field gain for the OEG is derived from experimental results obtained by a two-antenna method at about 2 GHz. The theoretical nearfield gain for the rectangular pyramidal horn is derived from Schelkunoff's formula. Two independent near-field gain measurements of these antennas are made using a three-antenna method and a transfer-standard-probe method. The discrepancy between theoretical and experimental results is typically less thanpm 1dB.     

Using Free-Space Transmission Loss for Evaluating Anechoic Chamber Performance

Performance of a rectangular RF anechoic chamber is evaluated by measuring the relative insertion loss versus separation distance between the sources of chamber illumination and small dipole or open waveguide antennas on a particular measurement axis. Measured data are compared to free-space transmission loss calculated using finite-range source antenna gains. A lack of fit between measured insertion loss and calculated transmission loss is a measure of reflections from chamber surfaces assuming the finiterange gain calculations are exact for the separation distances considered. Experimental results show excellent agreement between a smooth-curve fit to the measured data and the calculated free-space data. Standard fields in this chamber are used for calibrating hazard meters and dipole antennas used for field-strength measurements.     

A New Method of Calculating 3-Meter Site Attenuation

A new method of calculating 3-m site attenuation is described. To obtain an accurate site-attenuation curve, the problem of coupling between antennas is formulated in the form of coupled integral equations for the antenna currents, and solved by the method of moments (MOM). The site-attenuation curve thus obtained shows about 1.3-dB larger attenuation than that given in an IEC document. The deviations in the site-attenuation curve due to the impedance mismatch between the coaxial cable and the measuring equipment, and the influence of the antenna conductor radius on the attenuation curve are also considered. Finally, the calculated site attenuation is compared with the measured attenuation data available in the literature.     

RF Front-End Passive Circuit Implementation Including Antenna for ZigBee Applications

This paper presents a front-end passive circuit module for ZigBee applications using low-temperature co-fired ceramic technology. The front-end part consists of an antenna, a bandpass filter, a switch, and two baluns. In antenna design, the solenoid shape is employed for reducing the size of the antenna, resulting in an overall size of 9times16.4times1.82 mm³ and a gain of -1.4 dBi. As for the filter, two types of filters are suggested. First, the lumped-type filter employing a high-Q spiral inductor has more than 20-dB attenuation at both stopbands, very near to the passband. Secondly, the semilumped-type filter adopting an edge coupled line and a loading capacitor provides a group delay of below 5 ns and is adequate for the full module structure due to the structure flexibility. A balun is evaluated using lumped components instead of a transmission line and, thus, it provides an insertion loss of only 0.3 dB and a phase difference of 180deg between balanced signals. Based on these components, an RF front-end module including attaching pads for an RF integrated circuit (IC) and baseband IC is implemented. In case of using the lumped-type filter, the insertion loss of the front-end module is 6.5 dB, and the group delay is below 7 ns. In case of adopting the semilumped-type filter, the insertion loss is 6.2 dB, and the group delay is below 4 ns. The overall size of the former and latter is 25.14times28.5times0.68 mm³ and 25.66times25.58times1.17 mm³, respectively     

UHF Band Short Range Propagation Model

The purpose of this study is to characterize the indoor and indoor–outdoor propagation in different scenarios, using monopole antennas working at 410 and 890 MHz. Propagation of narrow band and wide bands have been studied. In scenarios with a continuous variation of the distance between the transmitter and receiver antenna (1 D scenarios), we use a log-distance path loss model to determine the equations that describe the mean value of the path loss. In scenarios where the position of the receiver is not a uniform function of the distance between the transmitter and the receiver, we represent the basic propagation gain as a function of the measurement point index. Results show that the indoor propagation gain can be described using two slopes propagation model. For the multiwall attenuation loss it is shown that each wall has an attenuation of almost 2.5 dB at 410 MHz increasing to almost 4 dB at 890 MHz. The obstruction gain (loss) due to human beings shows that this can be within a 40 dB interval.     

Calculation of Site Attenuation from Antenna Factors

A site-attenuation model expressed in terms of the antenna factors of the transmit and receive antennas is presented. Both horizontal and vertical polarizations are included, as are the effects of mutual coupling between closely spaced horizontal antennas. Expressing site attenuation in terms of antenna factors allows the use of broad-band antennas with their attendant advantages over tunable dipoles. Measured and calculated results for a variety of sites, antennas, and geometries are compared in the frequency range of 30 MHz to 1 GHz.     

Solution of Maxwell's equations for log-periodic dipole antennas

A theory of the log-periodic dipole antenna, which is a solution of the antenna boundary-value problem, is presented here. The theory is derived from Maxwell's equations by solving the wave equation in cylindrical coordinates and satisfying all boundary conditions. The theory is not limited to the log-periodic dipole antenna, but can be easily modified and applied to other antenna configurations using parallel linear elements. The radiation coupling between all antenna elements is taken into account; the calculated results show good agreement with the measurements. Current distributions, radiation patterns, and antenna input impedances are considered, and the application of this theory to the problem of optimal log-periodic dipole antennas is presented as well. Such an antenna obtained by numerical computation is discussed in detail.     

Factors Affecting Earth-Satellite Millimeter Wavelength Communications

The use of millimeter wavelengths for earth-satellite transmissions is suggested by the large bandwidths and high gain with small antennas possible at these wavelengths. The factors discussed are 1) propagation path loss, 2) refraction, and 3) antenna temperature. The attenuation through the entire atmosphere over the millimeter spectrum is given as a function of elevation angle of the antenna beam. The attenuation and scattering loss due to water and ice particles varies over a wide range of values depending on the number of particles and their sizes. Refraction by the atmosphere is less than one milliradian for elevation angles for which the absorption is low enough to make the transmission practical. Fluctuations due to refraction may, however, be quite severe. Contribution to antenna temperatures from the atmosphere, the earth, the sun and moon are given for earth-based antennas and antennas in space.     

Standard-Site Method for Determining Antenna Factors

A method for calibrating antennas from site attenuation measurements made on an open-field site is described. The method, termed the standard-site method because the accuracy of the results depends on the quality of the measuring site, requires neitller the use of a standard antenna nor the generation of a standard field. The antenna factors of a number of broad-band antennas calibrated by the standard-site method over the frequency range 30?1000 MHz show good agreement with the antenna factors found by the standard-antenna method.     

A cavity-backed dipole antenna with wide-bandwidth characteristics

This communication describes a cavity-backed dipole antenna that has a broad-band VSWR response, unidirectional radiation patterns, and almost constant gain (10.5 pm 1dB) over an operating bandwidth of 1.8: 1. Measured pertinent electrical characteristics are presented.     

Effects of antenna height, antenna gain, and pattern downtiltingfor cellular mobile radio

Results of wideband path loss and delay spread measurements using high gain, high and low antenna heights with pattern tilting are presented. The measurements were done in the frequency range 905-915 MHz, at two existing cellular mobile radio (CMR) sites. Also presented are potential approaches for analyzing data from high gain antennas. It is shown that, to a large extent, existing models can be used to predict path loss for high gain antennas with downtilting. The results further support the notion that high sites together with high gain antennas and suitably selected pattern tilting can result in a significant reduction in path loss and delay spread, as well as reduction in power transmitted from the cell site and reduction in system interference     

Comparison of mutual coupling of blade antennas with predictionsbased on minimum-scattering antenna theory

The utility of the minimum-scattering antenna model in describing the mutual coupling between two L-band aircraft blade antennas is examined. The communication and sensor requirements of many aircraft, particularly those used by the military, frequently necessitate antennas being placed in close proximity to one another. For such cases, the relatively simple minimum-scattering antenna model provides a very good approximation of the measured mutual coupling of blade antennas and eliminates the need for solving coupled integral equations     

Designing classical offset inverse-Cassegrain dual-reflector antennas from combinations of prescribed geometric parameters

This paper proposes a simple procedure for the design of classical offset inverse-Cassegrain dual-reflector antennas from combinations of prescribed geometric parameters. We will provide a list of 21 parameters from which the antenna system is fully characterized. However, only five of these parameters need to be provided by the antenna designer as the remaining 16 parameters can be calculated in closed form using the equations provided here.     

A comparison of electric field-strength standards for the frequencyrange of 30-1000 MHz

Published results about site attenuation and transmission loss measurements as well as antenna factor calculations and calibrations are summarized. The antenna types discussed are precision dipoles, a microstrip patch antenna, open-ended waveguides, and horn antennas as well as TEM-cells. The best values for agreement between theory and experiments that were reported for the transmission losses were in the range of 0.25-0.4 dB. An experimental comparison between precision reference dipoles and a TEM-cell that was performed in the Seibersdorf calibration laboratory is described with deviations of no more than 0.15 dB in the antenna factor or field-strength     

Compact Ka-Band Lens Antennas for LEO Satellites

Two new compact lens antenna configurations are presented and compared for data link communications with LEO satellites at 26 GHz. These lenses match a secant type radiation pattern template in the elevation plane while having a mechanically scanned sector beam in azimuth to enhance gain as much as possible. No rotary joints or multiple feeds are required and emphasis is put also on the compactness of the proposed solutions (< 6lambda₀). Two alternative lens configurations are evaluated numerically and experimentally: one is based on modified axial-symmetric dome lens geometry, and the other one consists of a full 3-D double-shell lens antenna. In contrast to current nearly omnidirectional antennas, the directivity of our lens prototypes is above 15.4 dBi. Up to 4.2 dB loss obtained in the prototypes can be significantly reduced by using lower loss dielectrics and matching layers, without affecting the conclusions. The numerical and experimental results are in good agreement with the radiation specifications given the compact size of the antennas.     

Design of the compact UHF RFID meander-line antenna loaded with CPW elements

In this paper, Coplanar Waveguide (CPW) elements are used to load UHF RFID meander-line antennas. Although, the insertion of these elements allow to design small antennas their gain decrease depending on the CPW structures are connected. In this sense, a new location to print CPW elements in the meander-line antenna is proposed aiming not to deteriorate the gain. A multi-objective optimization algorithm is applied in the meander-line antennas loaded with CPW elements in different positions and a comparison between their performances is done. To validate the computational model of the proposed antenna its input impedance is measured.     

Formulation of normalized site attenuation in terms of antennaimpedances [EMI measurement applications]

General formulas for normalized site attenuation (NSA) are derived in terms of antenna impedances by using the two-port circuit theory to show the effects of mutual coupling. The investigations focus on the antenna factors and antenna calibration procedures that are appropriate for NSA, and the validity of the NSA concept is discussed on the basis of these theoretical investigations. The NSA measurements are found to be appropriate for site validation when using broadband antennas having constant antenna factors. It is theoretically concluded, however, that the original concept of the NSA may not be applicable to the use of tuned dipole antennas, even after adopting the correction factors specified in the existing ANSI standard. NSA is shown to require different correction factors if the antennas have changeable antenna factors     

Analysis, Design and Realization of a Novel Directive Ultrawideband Antenna

In this paper, we present a simple log-periodic-dipole-array (LPDA) solution that allows us to achieve good ultrawideband (UWB) performances. The antenna has been manufactured and the measurements agree well with the theoretical predictions. The antenna presents an average gain of 8 dB and a return loss better than $-10~{rm dB}$ over the band from 4.2 to 10.6 GHz. Both the measured antenna transfer function and the computed effect on pulse transmission show good performances in comparison with already known UWB antennas.