Showing papers in "IEEE Transactions on Microwave Theory and Techniques in 1986"
TL;DR: Very efficient power combining of solid-state millimeter-wave sources may be obtained through the application of quasi-optical resonators and monotfthic source arrays as discussed by the authors, and it is shown that planar source arrays containing 25 individual elements or more result in very efficient power transfer of energy from the source arrays to the fundamental wave-beam mode.
Abstract: Very efficient power combining of solid-state millimeter-wave sources may be obtained through the application of quasi-optical resonators and monotfthic source arrays. Through the theory of reiterative wavebeams (beam modes) with application of the Lorentz reciprocity theorem, it is shown that planar source arrays containing 25 individual elements or more result in very efficient power transfer of energy from the source arrays to the fundamental wave-beam mode. It is further shown that for identical sources within a properly designed quasi-optical power combiner, the output power tends to increase much faster that number of source elements.
324 citations
TL;DR: In this article, a thermal model based on the bioheat equation is also used to predict temperature distributions in volumes where important thermal parameters, particularly blood flow, are varied, and power absorption patterns in Iossy media for this class of applicators are analyzed numerically allowing a quantitative evaluation of both advantages and limitations of this approach.
Abstract: Concentric-ring phased arrays subdivided into sectors (radial slices) can, with appropriate phasing, produce power absorption patterns useful for hyperthermia cancer therapy. The ability of a concentric-ring array to move a focal region along the central axis of the transducer is well known. Less well known is the ability of such an array to produce variable diameter annular (or ring) focal regions. Such focal rings can be effective in heating some tumors if directed around the tumor periphery. These focal rings have been produced in the past by fixed annular focus lenses, or effectively by mechanical scanning of "point" focus ultrasonic transducers. Production of these focal rings by a concentric-ring phased array has the advantage of allowing the focal ring diameter and focal length to be easily changed and scanned by phasing providing much greater heating flexibility. However, under some conditions such arrays produce very large secondary focus effects along the central axis of the amay. Concentric-ring arrays can also provide only patterns of circular symmetry. These problems can be partially solved by dividing the disk of the array into sectors. By appropriate phasing of the sectors, the intensity along the central axis can be greatly reduced. Moreover, appropriate phasing of the rings and sectors can produce patterns that are circularly asymmetric. By controlling these asymmetries, nonspherical tumors can be heated more optimally. Power absorption patterns in Iossy media for this class of applicators are analyzed numerically allowing a quantitative evaluation of both advantages and limitations of this approach. A thermal model based on the bioheat equation is also used to predict temperature distributions in volumes where important thermal parameters, particularly blood flow, are varied.
241 citations
TL;DR: In this article, a broadband automated technique for making frequency-swept measurements of complex permittivity and permeability simultaneously is described, which is computed from S-parameter measurements made on a strip transmission line device loaded with the material under test.
Abstract: A broad-band automated technique for making frequency-swept measurements of complex permittivity and permeability simultaneously is described. Epsilon/sub r/ and µ/sub r/ are computed from S-parameter measurements made on a strip transmission-line device loaded with the material under test. The derivation of epsilon/sub r/ and µ/sub r/ as functions of S/sub 11/ and S/sub 21/ is included, as well as a practical design for a stripline sample holder. Measured epsilon/sub r/ and µ/sub r/ data for several dielectrics and ceramic ferrites is also presented. The technique has been found to have an overall accuracy of better than +-5 percent.
215 citations
TL;DR: In this paper, the authors compared the performance of coplanar waveguide (CPW) transmission line with microstrip in terms of conductor loss, dispersion, and radiation into parasitic modes.
Abstract: Using a full-wave analysis, coplanar waveguide (CPW) transmission line is compared to microstrip in terms of conductor loss, dispersion, and radiation into parasitic modes. It is shown that, on a standard 0.1-mm semiconductor at 60 GHz, the dimensions of CPW can be chosen to give better results in terms of conductor loss and dispersion than microstrip. A calculation of parasitic mode generation is presented for CPW on a semiconductor for an open substrate, for a substrate suspended above a ground plane, and for substrates separated from a ground plane by quartz.
211 citations
TL;DR: In this paper, a class of waveguide structures using a rectangular dielectric strip in conjunction with one or more layered dielectrics is analyzed with a finite-difference method formulated directly in terms of the wave equation for the transverse components of the magnetic field.
Abstract: A class of dielectric waveguide structures using a rectangular dielectric strip in conjunction with one or more layered dielectrics is analyzed with a finite-difference method formulated directly in terms of the wave equation for the transverse components of the magnetic field. This leads to an eigenvalue problem where the nonphysical, spurious modes do not appear. Moreover, the analysis inclndes hybrid-mode conversion effects, such as complex waves, at frequencies where the modes are not yet completely bound to the core of the highest dielectric constant, as well as at frequencies below cutoff. Dispersion characteristic examples are calculated for structures suitable for millimeter-wave and optical integrated circuits, such as dielectric image lines, shielded dielectric waveguides, insulated image guides, ridge guides, and inverted strip, channel, strip-slab, and indiffused inverted ridge guides. The numerical examples are verified by results available from other methods.
202 citations
TL;DR: In this article, the millimeter-wave absorption efficiency for the human body with and without clothing was analyzed and it was shown that up to 95% of the incident energy may be absorbed in the skin with dry clothing, with or without an intervening air gap, acting as an impedance transformer.
Abstract: With recent advances in millimeter-wave technology, including the availability of high-power sources in this band, it has become necessary to understand the biological implications of this energy for human beings. This paper gives the millimeter-wave absorption efficiency for the human body with and without clothing. Ninety to ninety-five percent of the incident energy may be absorbed in the skin with dry clothing, with or without an intervening air gap, acting as an impedance transformer. On account of the submillimeter depths of penetration in the skin, superficial SAR'S as high as 65-357 W/Kg have been calculated for power density of incident radiation corresponding to the ANSI guideline of 5 mW/cm/sup 2/. Because most of the millimeter-wave absorption is in the region of the cutaneous thermal receptors (0.1 - 1.0 mm), the sensations of absorbed energy are likely to be similar to those of IR. For the latter, threshold of heat perception is near 0.67 mW/cm/sup 2/, with power densities on the order of 8.7 mW/cm/sup 2/ likely to cause sensations of "very warm to hot" with a latency of 1.0+-0.6s. Calculations are made for thresholds of hearing of pulsed millimeter waves. Pulsed energy densities of 143-579 µJ/cm/sup 2/ are obtained for the frequency band 30-300 GHz. These are 8-28 times larger than the threshold for microwaves below 3 GHz. The paper also points to the need for evaluation of ocular effects of millimeter-wave irradiation because of high SAR's in the cornea.
201 citations
TL;DR: In this article, a novel method for transient analysis of Iossy transmission lines with arbitrary nonlinear terminal networks is presented, where the uniqueness of this approach is that they develop time-domain Green's functions for the multiport transmission-line systems by terminating the ports in quasi-matched loads.
Abstract: A novel method for transient analysis of Iossy transmission lines with arbitrary nonlinear terminal networks is presented. The uniqueness of this approach is that we develop time-domain Green's functions for the multiport transmission-line systems by terminating the ports in quasi-matched loads. This ensures Green's functions of a short duration. Hence, the amount of frequency-domain data necessary to obtain time-domain Green's functions is modest. These Green's functions are then convolved with the line port voltages. With this technique one can analyze responses of multiconductor transmission lines with arbitrary nonlinear loads (even with memory) as we have at any instant of time Thevenin's equivalent of the linear portion of the system. An example is presented to illustrate the application of this technique to multiconductor nonlinearly loaded transmission lines.
187 citations
TL;DR: In this paper, the authors describe the application of the finite-difference method in the time domain to the solution of 3D eigenvalue problems, where the equations are discretized in space and time, and steady state solutions are then obtained via Fourier transform.
Abstract: This paper describes the application of the finite-difference method in the time domain to the solution of three-dimensional (3-D) eigenvalue problems. Maxwell's equations are discretized in space and time, and steady-state solutions are then obtained via Fourier transform. While achieving the same accuracy and versatility as the TLM method, the finite-difference-time-domain (FD-TD) method requires less than half the CPU time and memory under identical simulation conditions. Other advantages over the TLM method include the absence of dielectric boundary errors in the treatment of 3-D inhomogeneous planar structures, such as microstrip. Some numerical results, including dispersion curves of a microstrip on anisotropic substrate, are presented.
180 citations
TL;DR: In this article, an approach to synchronizing the phases of several oscillators for coherent power combining either in a conventional power-combining circuit or in free space as each oscillator drives an antenna element in a phased array is presented.
Abstract: This paper presents a novel approach to synchronizing the phases of several oscillators for coherent power combining either in a conventional power-combining circuit or in free space as each oscillator drives an antenna element in a phased array. A set of nonlinear differential equations is derived to predict the system's behavior. These equations are used in the computer-aided design and construction of a demonstration three-oscillator inter-injection-locked system at VHF. Good qualitative agreement between initial experimental results and theoretical predictions is observed, and applications of the inter-injection-locking concept to systems are discussed.
178 citations
TL;DR: In this paper, the authors computed the characteristic impedance of wide slots etched on an electrically thin substrate of low dielectric constant epsilon/sub r/ and provided design data for these slotlines.
Abstract: Computed results on the characteristic impedance of wide slots etched on an electrically thin substrate of low dielectric constant epsilon/sub r/ are presented. These results combined with those in [1] provide design data for these slotlines. Curves are presented for epsilon/sub r/= 2.22, 3.0, 3.8, and 9.8. Comparison is shown for the characteristic impedance between the present calculations and those available in the literature for high-epsilon/sub r/ substrates. Empirical formulas, based on least-square curve fitting, are presented for the normalized slot wavelength lambda'/lambda/sub 0/ and the characteristic impedance Z/sub 0/ over the range 0.0015<=W/lambda/sub 0/<=1.0, 0.006<=d/lambda/sub 0/<=0.06, 2.22<=epsilon/sub r/<=9.8.
172 citations
TL;DR: In this paper, the dispersion of coplanar-type transmission lines was extended to the terahertz regime to examine the distortion of picosecond electrical pulses, and an approximate dispersion formula was also reported for CAD applications.
Abstract: The dispersion of coplanar-type transmission lines has been extended to the terahertz regime to examine the distortion of picosecond electrical pulses. Dispersion of coplanar waveguides is compared to equivalent microstrip lines. Agreement with available experimental data is demonstrated for coplanar strips, An approximate dispersion formula for coplanar waveguides is also reported for CAD applications.
TL;DR: In this paper, a finite-element approach to the quasi-TEM analysis of several different types of isolated and coupled microwave transmission lines is described, where the first and higher order ordinary elements, as well as singular and infinite elements, are used to solve for the potential and field distributions in the cross section of the line.
Abstract: This paper describes a finite-element approach to the quasi-TEM analysis of several different types of isolated and coupled microwave transmission lines. Both the first- and higher order ordinary elements, as well as singular and infinite elements, are used to solve for the potential and field distributions in the cross section of the line. Next, the cross-sectional field distribution is inserted in a variational expression to compute the capacitance per unit length of the line, and the effective permittivity and characteristic impedance of the line are obtained from the capacitance value. A perturbational approach is developed for estimating the losses due to conductor and dielectric dissipation and computing the attenuation constant. Both the upper and lower bounds for the capacitance and the characteristic impedance are found by solving the original and the corresponding dual problem. Lines treatable by this method may contain an arbitrary number of arbitrarily shaped conductors, including a system of conductors placed either above a single ground plane or between two parallel ground planes, and inhomogeneous dielectric regions that can be approximated Iocally by a number of homogeneous subregions. The results obtained using the finite-element procedure have been compared for various types of microwave transmission lines and have been found to agree well with available theoretical and measured data.
TL;DR: In this paper, an improved finite-element method for the analysis of dielectric waveguiding problems is formulated and compared with exact and earlier finite element solutions, where the divergence relation /spl nabla/ · H = 0 is satisfied and the spurious, nonphysical solutions which have been necessarily included in the solutions of earlier vectorial finite element methods are completely eliminated in the whole region of propagation diagram.
Abstract: An improved finite-element method for the analysis of dielectric waveguiding problems is formulated rising the transverse magnetic-field component. In this approach, the divergence relation /spl nabla/ · H = 0 is satisfied and the spurious, nonphysical solutions which have been necessarily included in the solutions of earlier vectorial finite-element methods are completely eliminated in the whole region of a propagation diagram. To verify the accuracy of the present method, numerical results for a rectangular metallic waveguide half filled with dielectric are presented and compared with exact and earlier finite-element solutions. Dielectric rectangular waveguides are also analyzed for both isotropic and anisotropic cases.
TL;DR: In this article, a cylindrical dielectric-loaded resonators are analyzed and the fields within the dielectricsloaded region are postulated as the superposition of hybrid, TE, or TM modes of the infinite dielectoric-loaded waveguide, while the fields in the end regions of the resonators were described by the normal modes of a homogeneously filled waveguide.
Abstract: Analysis of cylindrical dielectric-loaded resonators is reviewed. The fields within the dielectric-loaded region are postulated as the superposition of hybrid, TE, or TM modes of the infinite dielectric-loaded waveguide, while the fields in the end regions of the resonators are described by the superposition of the normal modes of a homogeneously filled waveguide. Numerical results are presented which reveal that accurate representation of the fields in the resonant structure generally require several modes. Hence, the resonant modes cannot be correlated directly with single waveguide modes. A new method for mode identification is proposed. For a wide range of parameters, the resonant frequencies, mode charts, field expansion coefficients, field intensity, and distributions are presented. Excellent agreement of the mode charts with resonant frequency measurement results are obtained.
TL;DR: In this paper, a numerical method for the solution of scattering of the H-and E-plane waveguide junctions is described, which is a combination of the boundary-element method and the analytical method.
Abstract: A numerical method for the solution of scattering of the H-and E-plane waveguide junctions is described. The approach is a combination of the boundary-element method and the analytical method. A general computer programs has been developed using the quadratic elements (higher order boundary elements). To show the validity and usefulness of this formulation, computed results are given for a right-angle corner bend, a T-junction, an inductive strip-planar circuit mounted in a waveguide, a waveguide-type dielectric filter, and an inhomogeneous waveguide junction, and a linear taper. Comparison of the present results with the results of the finite-element method shows good agreement.
TL;DR: In this article, a coaxial line terminated by a gap is considered, the gap being filled with an unknown material, and the relationship linking the measured admittance to the dielectric properties is obtained from a theoretical analysis of the electromagnetic field in the tine.
Abstract: A coaxial line terminated by a gap is considered, the gap being filled with an unknown material. This cell enables measurements of complex permittivity of dielectric materials to be made. The relationship linking the measured admittance to the dielectric properties is obtained from a theoretical analysis of the electromagnetic field in the tine. The equivalent-circuit parameters of a coaxial line terminated by a gap are obtained all higher order waves excited at the discontinuity are taken into account. The measurements show good agreement between measured and calculated data from dc to 12.4 GHz.
TL;DR: In this paper, a planar microstrip antenna array and a 95 GHz IMPATT oscillator circuit were fabricated on highly insulating silicon substrates, and a combined monolithic-hybrid integration technique was used to attach the discrete IMPATT diode to the resonator circuit.
Abstract: The application of molecular beam epitaxy (MBE) and X-ray lithography for the fabrication of monolithic integrated millimeter-wave devices on high-resistivity silicon has been investigated. Process compatibility and the retention of high-resistivity characteristics were measured using the spreading resistance method and Hall measurements after various process steps. Microstrip resonators of ring and linear geometry were fabricated ou 10 000 Omega · cm silicon substrates. For linear microstrip resonators, the attenuation was found to be less than 0.6 dB/cm at 90 GHz. A 95-GHz IMPATT oscillator circuit and a planar microstrip antenna array have been fabricated on highly insulating silicon substrates. For the oscillator, a combined monolithic-hybrid integration technique was used to attach the discrete IMPATT diode to the resonator circuit. The oscillator does not require tuning elements. Preliminary experimental results are 8 mW of output power with 0.2 percent efficiency at 95 GHz.
TL;DR: In this article, the authors derived the expressions for the fields for a horizontal electric dipole over a Iossy dielectric medium backed by an imperfect ground plane, and showed that fields at the air-dielectric interface are independent of the ground plane conductivity.
Abstract: In most microstrip transmission lines, analysis is made assuming that a quasi-TEM mode exists and propagates down the line. The primary objective of this paper is to obtain the region of validity of this assumption. The second objective of this paper is to derive the expressions for the fields for a horizontal electric dipole over a Iossy dielectric medium backed by an imperfect ground plane. It is shown that, to a first approximation, fields at the air-dielectric interface are independent of the ground plane conductivity. Since we are interested in coupfing between lines, our interest is in the computation of the fields primarily at the air-dielectric interface. Finally, numerical results are presented to show where the quasi-static approximations deviate from the exact solution for a given microstrip geometry as the frequency of operation or the observation point is changed.
TL;DR: In this paper, an integral representation for a plane wave incident on a lossy half-space containing a cylindrical object of arbitrary cross-section and electrical properties is proposed, where the induced current distribution in the object is obtained from the backscattered field measurement in amplitude and phase.
Abstract: Many diagnostic techniques in geophysics and civil engineering are based on the interaction of electromagnetic waves with objects buried in homogeneous or stratified media. Most of the investigations are concerned with the detection of buried objects, but a few papers have dealt with the problem of identifying the objects. The proposed method is based on the integral representation for a plane wave incident on a lossy half-space containing a cylindrical object of arbitrary cross section and electrical properties. The induced current distribution in the object is obtained from the backscattered field measurement in amplitude and phase. In order to improve the spatial resolution of the image, the scattered field is measured for different plane wave incidence and frequencies. Results of numerical simulations concerning the shape and size of the object for different values of soil electromagnetic parameters are presented in this paper.
TL;DR: In this article, the generalized scattering matrix (GSM) is used for characterizations of cascaded microstrip step discontinuities, symmetric stubs, and offset step.
Abstract: Detailed algorithms are presented for characterizations of cascaded microstrip step discontinuities, symmetric stubs, and offset step. The analysis is based on the generalized scattering matrix techniques after the equivalent waveguide model is introduced for the microstrip line.
TL;DR: In this article, a systematic variety of frequency-dependent numerical results for the shielded microstrip impedance step are presented for two very common groups of dielectric substrates as a function of stepwidth ratio in the range of normalized frequencies.
Abstract: A systematic variety of frequency-dependent numerical results hitherto unavailable are presented for the shielded microstrip impedance step. The computational method used is a rigorous full-wave spectral-domain approach developed by Jansen. The given data describe the steps for two very common groups of dielectric substrates as a function of stepwidth ratio in the range of normalized frequencies where it behaves like a two-port. They represent new MIC design information and are compared with quasi-static results and the widely used magnetic-wall waveguide approximation. Beyond this, they are validated against the sparse step-discontinuity data available from previous rigorous approaches.
TL;DR: In this article, the authors review the status of magnetostatic wave (MSW) resonators and describe, in detail, the theory of operation of the recently developed straight-edge resonators.
Abstract: The purpose of this paper is to review the status of magnetostatic wave (MSW) resonators and to describe, in detail. the theory of operation of the recently developed straight-edge resonators. These resonators are based on magnetostatic waves propagating in high Q cavities fabricated in thin ferrimagnetic films. The resonance frequency of these resonators can be tuned via a bias magnetic field. The theory of propagation of magnetostatic wave devices in periodic arrays will be briefly described followed by a detailed overview of the different configurations for MSW resonators. Three distinct classes of resonators will be discussed 1) resonators based on array reflectors (deposited metals and etched grooves) will be described in detail; 2) guided-wave ring resonators will be discussed; and 3) the theory of operation and design criteria for the straight-edge resonators will be described. Each class will be evaluated, pointing out the advantages and drawbacks, and whenever applicable, the power handling properties and the phase noise performance will be given.
TL;DR: A new method of pulse compression, the binary power multiplier (BPM), a device which multiplies RF power in binary steps which doubles the input power and halves the input pulse length is described.
Abstract: This paper describes a new method of pulse compression, the binary power multiplier (BPM), a device which multiplies RF power in binary steps. It comprises one or more stages, each of which doubles the input power and halves the input pulse length. Practical designs are described and expressions for their compression efficiency are derived. The usefulness of pulse compression for accelerator design is illustrated and compared with the pulse compression system currently in use at the Stanford Linear Accelerator Center.
TL;DR: In this paper, a narrow-wall multiple-slot coupler suitable for inexpensive and very accurate metal-etching manufacturing techniques is proposed and optimized for the R140-waveguide band (12.4-18 GHz).
Abstract: A compact narrow-wall multiple-slot coupler suitable for inexpensive and very accurate metal-etching manufacturing techniques is proposed and optimized. A computer-aided design theory based on the method of field expansion of eigenmodes considers the effects of finite insert thickness and higher order mode interaction, step discontinuities, and changes in width. Computer-optimized design data for --20-, --8.34-, and --3-dB couplers in the R140-waveguide band (12.4--18 GHz) are given. These data are transferable into other common waveguide bands, e.g., R620 band (50-75 GHz), by suitable frequency scaling calculations. A metal-etched 12-slot coupler prototype for a midband frequency of about 15 GHz achieves a +-1-dB bandwidth of the --3-dB coupling of about 3.2 GHz together with a measured isolation of typically 35-40 dB (minimum 25 dB at the band limits). The measurements show good agreement with theory.
TL;DR: In this article, a ferrite-loaded coupled-slot finline with the ferrite magnetized parallel with the direction of propagation is presented for isolators and a four-port circulator in novel finline structures.
Abstract: Promising preliminary results are presented for isolators and a four-port circulator in novel finline structures in the frequency range 26.5-40.0 GHz. The basic configuration is a ferrite-loaded coupled-slot finline with the ferrite magnetized parallel with the direction of propagation. The nonreciprocal effects of the odd mode propagating alone and of the odd and even modes propagating are described. All structures exhibit a 20-dB isolation bandwidth greater than 3.6 GHz. It is suggested that such structures would also be suitable for higher frequencies.
TL;DR: In this article, the effect of ignoring complex modes on finline discontinuity problems is investigated, and it is shown that the modal energy distribution at both sides of the discontinuity may be greatly affected by overlooking complex modes, even if they are not strongly excited.
Abstract: The effect of ignoring complex modes on the solution of finline discontinuity problems is investigated. It is shown that the modal energy distribution at both sides of the discontinuity may be greatly affected by overlooking complex modes, even if they are not strongly excited. lt is also shown that disregarding only one mode of a pair of complex modes, while taking the other into account, results in a contradiction to the principle of complex power continuity across the discontinuity plane. Comparison to measured data is also given to justify the validity of the numerical results.
TL;DR: In this paper, the authors designed a corrugated square waveguide polarizer with the method of field expansion into eigenmodes, which includes higher order mode interaction between the step discontinuities.
Abstract: Profiled depth corrugated square waveguide polarizers are designed with the method of field expansion into eigenmodes, which includes higher order mode interaction between the step discontinuities. Computer-optimized design data are giyen for a compact Ku-band prototype with an exponentially varying depth function that achieves 90° +- 1° differential phase shift shift within the separate 11.9-12.3-GHz and 17.5-17.9-GHz frequency bands. The maximum VSWR is only about 1.02. Further design examples include a linearly profiled depth function, which provides a short design, and a polarizer with iris thicknesses suitable for metal-etching manufacturing technique. The theory is verified by comparison with available measured results.
TL;DR: In this article, the distortion of an electrical pulse caused by dispersion as it propagates along a microstrip line is investigated, and a model for dispersion of the phase constant is selected to meet the frequency, accnracy, and microstrip parametric requirements.
Abstract: The distortion of an electrical pulse caused by dispersion as it propagates along a microstrip line is investigated. A model for dispersion of the phase constant is selected to meet the frequency, accnracy, and microstrip parametric requirements. Numerical integration and Taylor series expansion approximation techniques are used to compute the shape of dc dispersed pulses having square and Gaussian envelope shapes. Taylor series expansion methods are more convenient for the analysis of RF pulses.
TL;DR: In this article, exact transverse electric and magnetic mode solutions of four triangular cross-section waveguides have been found via a new general method using Snell's law and superposition of plane waves.
Abstract: Exact transverse electric and magnetic mode solutions of four triangular cross-section waveguides have been found via a new general method using Snell's law and superposition of plane waves. This paper presents results for 1) equilateral, 2) 30°, 30°, 120°, 3) isosceles right, and 4) 30°, 60° right triangular waveguides. The electric and magnetic field solutions form finite sums of separable rectangular harmonics and are the only waveguides of triangular cross section for which such solutions have been found.
TL;DR: In this article, thermal imaging, nonperturbing temperature probes, and E-field sensitive diodes were used to quantify the SAR patterns in human models exposed to UHF mobile-antenna fields.
Abstract: Thermography, nonperturbing temperature probes, and E-field sensitive diodes were used to quantify the SAR patterns in human models exposed to UHF mobile-antenna fields. The exposure conditions include man, woman, and child models in the standing position close to roof- and trunk-mounted antenna; man sitting in the back seat near a trunk-mounted antenna; child kneeling in the back seat and looking through the rear window. Incident power densities near the antennas were also measured. Based on the current ANSI radio-frequency protection guide, the exemption of 7-W input power will violate the ANSI primary exposure criterion, but satisfies the 8-W/kg exclusion clauses. A maximum power of 3.5 W would satisfy all of the ANSI guides.