The use of side-mounted loop antennas on platforms to obtain nearly omnidirectional radiation

Antennas mounted to vehicles at VHF frequencies are limited to whip and loop antennas. Often, mechanical constraints force antenna placement to be less than optimal. In this work, we investigate the use of side-mounted loops on rectangular conducting platforms. It will be shown that tall thin platforms radiate similar to a dipole. In addition, as the thickness increases, the loop antennas can radiate in a nearly omnidirectional fashion if the antenna-mounted sides of the platform are not too wide. In effect, a narrow platform width implies return currents for a loop antenna that remain mostly vertical.     

Package-level integrated antennas based on LTCC technology

We propose a novel package topology integrating multilayer miniaturized antennas. Such a functional package is suitable for the design of a system-on-chip device, or of system-on-package applications. A stacked patch antenna is designed and integrated in a package using a low temperature co-fired ceramic process. The overall size of the package is 10.3/spl times/10.3/spl times/1.3 mm/sup 3/, and this package contains an 8.3/spl times/8.3/spl times/0.7 mm/sup 3/ internal space for the integration of chip-scale packaged components. The package is mounted on a 20/spl times/20 mm/sup 2/ ground plane to miniaturize the volume of the system. The antenna is designed to have two neighboring resonant frequencies at 5.264 and 5.355 GHz, resulting in a 140 MHz impedance bandwidth. However, the measured resonant frequencies occur at slightly higher frequencies due to manufacturing tolerances. Radiation patterns are similar to a conventional patch antenna. In addition, various parasitic effects rooted in the package size, ground size, antenna height, SMA connector, via misalignment, and the number of via holes and their locations are fully investigated.     

An analysis of the performance of a handset diversity antennainfluenced by head, hand, and shoulder effects at 900 MHz .I. Effectivegain characteristics

A diversity antenna for portable telephones, which Is composed of a whip antenna and a planar inverted F-antenna (PIFA) operating at 900 MHz, has been analyzed. The analysis includes the electromagnetic effects of a human operator. Wire-grid analysis yielded the radiation efficiency, mean effective gain, correlation coefficient, and diversity gain characteristics under various incident wave propagation environments with whip length, head-to radio separation, and inclination of the radio from the vertical as parameters. The analysis has been carried out using a homogeneous human phantom model, which includes a head, a hand, and a left shoulder. The effective gain characteristics in multipath propagation environments is described. The analytical results indicate the structural and environmental requirements for designing the diversity antenna with a high diversity effect under practical use conditions     

A novel electromagnetically coupled microstrip antenna with arotatable patch for personal handy-phone system units

In this paper, we propose a novel electromagnetically coupled microstrip antenna with a rotatable patch to overcome the problems associated with the conventional whip antenna for the personal handy-phone system (PHS). The structure of the newly developed antenna installed in actual PHS units is described. Its fundamental characteristics such as radiation pattern, bandwidth, and gain are shown. The performance of the antenna in actual propagation environments is also clarified. It is shown that this novel antenna is superior to the conventional whip antenna and achieves efficient performance in commercial PHS service     

HFSWR单极子交叉环天线阵的自适应抗干扰

为了提高高频表面波雷达的抗干扰能力,结合现代天线理论和自适应数字信号处理技术,以宽频带单极子交叉环天线为基本单元,设计了高频表面波雷达自适应抗干扰的宽频带接收天线阵系统,同时给出了高频表面波雷达天线自适应抗干扰的软硬件实现方案.     

Internal Ultrawideband Monopole Antenna for Wireless USB Dongle Applications

A novel, ultrawideband (UWB) monopole antenna suitable to be mounted on the printed circuit board (PCB) of a wireless, universal, serial-bus (USB) dongle as an internal antenna is presented. The proposed antenna in the study is a U-shaped, metal-plate monopole antenna, easily fabricated from bending a simple metal plate onto a foam base of a compact size of 6times11times20 mm³. The antenna mainly comprises a pair of wide-ended radiating arms and a bevel-feed transition. When the antenna is mounted at the top portion of the PCB, one end of the radiating arm is also short-circuited to the system ground plane. With the proposed antenna structure, which can provide a very wide operating bandwidth of larger than 7.6 GHz, the antenna impedance bandwidth can easily cover the 3.1-10.6 GHz UWB band. Details of the antenna design are described, and experimental results of the constructed prototypes are presented and discussed     

Measured relative responses toward the zenith of short-whip antennas on vehicles at high frequency

The response toward the zenith of an untuned 16.5- foot vertical whip antenna mounted on the rear comer of a jeep, relative to the response of a half-wave horizontal dipole at 15 feet above ground, was measured at high frequency with an ionospheric sounder. At 4 MHz, the relative response of the whip was -52.5 dB, and it increased with frequency at a rate greater than 12 decibels per octave (i.e., greater than frequency to the fourth power). The absolute power gain of the whip at 4 MHz was estimated at about -37.5 dB, ±6 dB relative to an isotropic radiator, and the variation with frequency was approximately a fifth-power law [i.e., Gp≈ -70 + 55 log10(fMHz) dB] in the frequency range of 4 to 8 MHz. The short-path sky-wave signal received by the untuned whip can be enhanced by about ±10 dB, ±4 dB relative to that received with a vertical whip, by bending the whip away from the vehicle at an angle of 30° or more. When the same whip is bent forward and tied down over the hood of the vehicle, the received sky-wave signal is enhanced by only +3 dB, ±4 dB. These results should apply regardless of whether the vehicle is traveling in open or wooded terrain.     

Radiation patterns of a mode transducing antenna

Radiation patterns for the general case ofTE_{0n}excitation of Wengenroth's mode transducing antenna are derived. The antenna seems well suited for application as a launcher for electron cyclotron resonance heating (ECRH) plasma heating. Gain and launching efficiency are calculated. Very good agreement is found between predictions and experimental results forTE_{01}mode excitation.     

VHF helicopter antennas that incorporate the airframe and reducerotor modulation

Antennas at VHF frequencies mounted to small (with respect to wavelength) helicopter platforms are usually limited to whip and loop antennas. Antenna placement and rotor position can drastically change antenna performance due to induced currents on the platform. This work illustrates deliberate antenna-platform interactions that cause induced currents to reinforce and improve the radiating system performance. Additionally, rotor modulation effects can be simultaneously limited. This is accomplished by using oppositely placed loop antennas at a location on the airframe that is nominally one wavelength in circumference. The resulting broadcast pattern admits low cross-polarization radiation and low copolarized rotor modulation, but is not uniform. The dipole moment of the loops dictates this nonuniformity. Double-loop antennas are used to create a more uniform broadcast pattern without sacrificing the desired low cross-polarized radiation and low copolarized rotor modulation     

An omnidirectional microwave antenna for use on spacecraft

The qualitative theory, design, and development of a parallel-plate waveguide-fed antenna, suitable for flush-mounted broad-band spacecraft applications, are presented. The antenna makes use of wedge-like metal posts placed uniformly about the periphery of the feed plates to provide both structural strength and practical interconnection routes for cables without disrupting the antenna impedance and patterns. Measurements taken on the antenna, which is mounted on spheroids up to 50 wavelengths in circumference, are presented; equatorial patterns are omnidirectional withinpm 0.25dB, and polar patterns have beam widths similar to a half-wave dipole.     

The small bare loop antenna immersed in a dissipative medium

The input admittance of a small thin-wire circular loop antenna, driven by a slice generator, immersed in a dissipative medium, is considered. It is found that the solution given by Storer for the loop antenna in a lossless medium can be carded over readily by replacingzeta_{0}byzeta, andk_{0}byk. The numerical values of the normalized input conductance and input susceptance of a small loop antenna, namelybeta b leq 0.3,Omega = 10, are calculated. It is to be noted that the input susceptance is practically independent ofkwhile the input conductance changes as much as seventeen times in this special case.     

The circular loop antenna immersed in a dissipative medium

Investigations were made of the radiating and circuit properties of circular loop antennas when immersed in conducting media with various loss tangents. The following quantities were experimentally examined and compared with the available theoretical results. 1) Driving point admittanceY_{in}of circular loops as a function of the circumference per wavelength,2pib/lambda = betab. 2) Current amplitude and phase distributions. 3) Field patterns. In each case the loss tangentsigma/omegaepsilon_{r}epsilon_{0}of the medium (conductivitysigma, permittivityepsilon_{r}epsilon_{0}) is taken as a parameter. The experimental results are in good agreement with the theory. A comparison between the behavior of the loop in a conducting medium and those of a linear dipole was made wherever possible. It was discovered that there is a cut off size beyond which the driving point admittance of a linear dipole is the same whether or not its ends are connected to form a loop. This particular loss tangent is 1.06, and the cut off size islambda/2. A circular loop antenna withbetab= 1.0is excited predominantly in a dipole mode and its field pattern resembles that of a two element dipole array. A study was made to determine how this pattern becomes more like that of a monopole as the loss tangent of the solution is increased.     

An analysis of the performance of a handset diversity antennainfluenced by head, hand, and shoulder effects at 900 MHz .II.Correlation characteristics

For pt.I see ibid., vol.50, no.3, p.830-44 (2001). In Part I of this two-part paper, we described the effective gain characteristics of the handset diversity antenna comprising a retractable whip antenna and a built-in planar inverted F antenna (PIFA). In order to achieve a high diversity effect, the correlation between the diversity branches must be small while at the same time maintaining a high effective gain, and this is contained in this paper. Further analysis includes an evaluation of the diversity gain with which the diversity effect shown by the analyses of the effective gain in Part I and the correlation in Part II is described. In addition, the mechanism for obtaining a small correlation coefficient is clarified by investigating the amplitude and phase radiation patterns when the whip length and the body inclination angle are changed. From these we obtain various numerical results that provide sufficient insight for design purposes. The validity of the analytical results is verified by an experiment in an indoor radio wave propagation environment     

CPW-fed folded-slot antenna for 5.8 GHz RFID tags

A coplanar waveguide (CPW)-fed capacitive folded-slot antenna is proposed for the radio frequency identification (RFID) application at 5.8 GHz. The antenna is fabricated on a 30/spl times/30 mm substrate. The measured bandwidth and antenna gain are 7.5% and 4.2 dBi, respectively. Radiation patterns are almost omnidirectional in the H-plane. These properties and the compact and uniplanar structure make the antennas suitable for use as RFID tags.     

Criteria for nearly omnidirectional radiation patterns for printed antennas

Radiation from printed antennas is investigated with emphasis placed on producingbar{E}- andbar{H}-plane radiation patterns that are as nearly omnidirectional as possible. This is achieved using criteria which are derived for a nonzero radiation field extending down to the layer surface (radiation into the horizon). It is determined that this phenomenon arises when a surface wave pole coincides with a branch point in the complex plane. A simple ray optics interpretation is given for the phenomenon, and graphs are presented to easily enable design of printed antenna geometry to achieve nearly omnidirectionalbar{E}- orbar{H}-plane patterns.     

Micromachined Loop Antennas on Low Resistivity Silicon Substrates

The integration of K-band (20-40 GHz) full wavelength square wire- and slot-loop antennas on low resistivity (11-70 Omegacm) silicon substrates is addressed. By the use of polymer or silicon oxide/nitride membranes to support the slot or wire loop over micromachined trenches the efficiency of the antennas is enhanced while the majority of the bulk silicon within the aperture of the antenna is preserved to enable the integration of active devices. A 3.6times3.6 mm² large slot loop antenna chip with 200 mum micromachined trench width yields 1.5 dBi gain at 29.5 GHz, while 1.0 dBi gain is obtained at 24 GHz for a wire loop antenna on a 4.5times4.5 mm² large chip with 360 mum wide trenches     

Tunnel Diode Oscillator in an Open Structure

This paper describes a theoretical and experimental evaluation of the oscillation conditions of a microwave tunnel diode integrally mounted at the feed point of a semicircular loop antenna. The oscillation conditions are based on a quasi-linear equivalent circuit where the diode load impedance is the complex radiation impedance of the semicircular loop antenna. The results of a radiation impedance calculation based on a Fourier transform method are presented. Diode fabrication techniques are described and experimental results are reported to be consistent with the theory.     

Folded loop antenna for mobile hand-held units

The vertical folded loop antenna, modeled as wire and printed radiating element mounted on a conducting box, simulating a cellular telephone with and without dielectric coating, is analyzed. The finite-difference time-domain (FDTD) method is used to calculate radiation patterns and input impedance. The results are compared with measurements and with NEC data. Very good agreement is obtained in all cases. Parasitic loading is used to enhance the bandwidth of the printed element. The antenna meets the design requirements for existing and future mobile communication systems     

Monolithic millimeter-wave IMPATT oscillator and active antenna

A single-chip millimeter-wave transmitter module in which GaAs IMPATT diodes are monolithically integrated with a microstrip resonator and a loop antenna is discussed. Devices operating at 43.3 GHz produce 27-mW CW output power with 7.2% conversion efficiency. Radiation patterns of linear arrays of such radiating elements were determined as a function of interelement spacing and number of elements. The oscillator chip was also directly coupled to and power combined in waveguides, producing an inexpensive millimeter-wave source     

A design of AM/FM mobile telephone triband antenna

In vehicles, antennas for AM/FM broadcasting (BC) and cellular mobile telephone (MT) are usually mounted on the car's body. However, a triband antenna which can be used for both AM/FM BC and MT is more desirable to decrease the number of antennas. An outline of the general design for the AM/FM MT triband antenna with coils is described. Next, the design of a new triband antenna with double sleeves instead of coils is presented. The double sleeves consist of two coaxial lines connected in series. It is shown that the triband antenna with double sleeves has good characteristics, including radiation patterns and voltage standing-wave ratio (VSWR)