Showing papers on "Dipole antenna published in 1983"

Considerations for millimeter wave printed antennas

Abstract: Calculated data are presented on the performance of printed antenna elements on substrates which may be electrically thick, as would be the case for printed antennas at millimeter wave frequencies. Printed dipoles and microstrip patch antennas on polytetrafluoroethylene (PTFE), quartz, and gallium arsenide substrates are considered. Data are given for resonant length, resonant resistance, bandwidth, loss due to surface waves, loss due to dielectric heating, and mutual coupling. Also presented is an optimization procedure for maximizing or minimizing power launched into surface waves from a multielement printed antenna array. The data are calculated by a moment method solution.

Rectangular dielectric resonator antenna

Abstract: An antenna which consists of a resonant rectangular parallelepiped dielectric on top of a ground plane is described. Calculated radiation patterns and measured impedances are presented, and the effects of feed probe length variations are discussed.

The Electromagnetic Field of an Insulated Antenna in a Conducting Or Dielectric Medium

Abstract: Insulated antennas are useful for localized heating as in the hyperthermia treatment of tumors and the extraction of shale oil. The distribution of current in and the admittance of a center-driven dipole embedded in a general medium are reviewed. Formulas for the electric field generated by the currents in the dipole are derived for all points outside the antenna. Near the antenna, the field is elliptically polarized. Formulas for the polarization ellipses are derived and evaluated for antennas with electrical half-lengths Beta/sub L/h = pi/4, pi/2, pi, and 3pi/2, where k/sub L/ =beta/sub L/ + i alpha/sub L/ is the wavenumber of the current, and this is different from the wavenumber of the ambient medium.

Substrate Optimization for Integrated Circuit Antennas

Abstract: The reciprocity theorem and integral equation techniques are employed to determine the properties of integrated-circuit antennas. The effect of surface waves is considered for dipole and slot elements on substrates. The radiation and bandwidth of microstrip dipoles are optimized in terms of substrate thickness and permittivity.

Electric field probes--A review

Abstract: Electric field probes consisting of a dipole antenna, RF detector, nonperturbing transmission line, and readout device have been implemented in a variety of ways. Three orthogonal dipoles are generally used in an E -field probe to provide a response which is nearly isotropic for all polarizations of the incident field. Diode detectors have been used with electrically short or resistivity loaded dipoles to produce very broadband devices (0.2 MHz to 26 GHz). Thermocouple detectors are used to provide true time-averaged data for high peak-power modulated fields. Optical fibers, together with a suitably modulated light source, may be used to form a wide-band nonperturbing data link from the dipole and detector to a remote readout. Application of E -field probes range from the measurement of fields in living animals exposed to nonionizing radiation to the measurement of fields in air for electromagnetic compatability or radiation safety purposes. Probes are available that can measure field strengths from less than 1 V/m to over 1000 V/m (rms).

School of Electrical Engineering.

Abstract: The possibility of making the antenna of an MST radar too large is pointed out. It is not that the signal ceases to become stronger beyond some critical antenna size; the received scattered signal actually becomes weaker as the antenna size is increased whenever the target is in the near field, Fresnel region of the antenna. The Arecibo antenna is a case in point. It is supposed that MST work would benefit to use a feed which illuminated only a portion of the dish.

Broadband isotropic probe system for simultaneous measurement of complex E- and H-fields

Abstract: A broadband isotropic probe system simultaneously measuring the E- and H-field intensities of rf complex, near-field electromagnetic radiation comprises a set of three mutually orthogonal dipole antennas and a set of three mutually orthogonal loop antennas located within the same volume of space. Each antenna has associated circuitry comprising a frequency-response-shaping filter and diode detector to provide a frequency response which is flat over the desired frequency bandwidth. The lengths of the dipoles are kept electrically small so that the EM fields are not perturbed. The diameters of the loops are kept electrically small so that the E-field pickup will be negligible. Coupling between any of the probe's antennas is also minimized by the use of electrically small antennas. Circuit means based on the use of square law detectors is also provided, the circuit including an arrangement of analog or digital data processing portions leading into a display means and a data recorder.

Quadrifilar helix antenna tuning using pin diodes

Abstract: An antenna is tuned in separate discrete frequency bands by changing the ctrical length of the antenna. PIN diodes are placed at predetermined locations on the antenna coaxial cable radiating elements. When it is desired to shorten the antenna for a higher frequency band use, the diodes are biased short circuiting segments of the antenna. When the lower frequency band use is desired, diodes are unbiased so that the diodes act like a very small capacitance shunted by a large resistance which is essentially an open circuit permitting the entire length of the antenna to operate.

Time domain sensors for radiated impulsive measurements

Abstract: Discussion of various sensors and radiators commonly used for time domain antenna measurements is presented. The sensors and radiators discussed here are passive and analog devices which convert the electromagnetic quantity of interest to a voltage or current at their terminal ports. Moreover they are primary standards in the sense that their transfer functions can be calculated from their geometries and are flat (constant) across a wide frequency range. One of the major requirements for these sensors and radiators is that the electromagnetic far field, transmitted or received, is a replica or high fidelity derivative of the original pulse. Note that the transmitting transfer function of an antenna is proportional to the time derivative of the receiving transfer function of the same antenna, which follows from the reciprocity theorem. For electric field strength measurements, linear antennas loaded nonuniformly and continuously with resistance, or with both resistance and capacitance are discussed. Also, a conical antenna and an asymptotic conical antenna are discussed from the standpoint of improved characteristics. For an improved directivity, various types of transverse electromagnetic (TEM) horns are considered, e.g., a conducting TEM horn, and a resistively loaded TEM horn.

Integrated receiver antenna device

Abstract: An integrated receiver antenna device comprising a pair of antenna elements providing a spiral antenna for receiving radio frequency signals over a broadband of frequencies with an extended high frequency limit and providing high sensitivity over the broadband of frequencies. The elements each have first and second ends and provide a pair of interwound conductive windings with their first ends positioned proximate to each other at the center of the antenna for providing sensitivity at the high frequency limit of received radio frequency signal, while the second ends of the elements are displaced from the first ends and positioned at the periphery of the antenna. A detector mixer unit is connected between and positioned proximate to the first ends of the antenna elements for deriving radio frequency signals received by the antenna elements and receiving an input signal for providing an oscillating signal at the detector mixer unit for producing an output signal.

Frequency independent shielded loop antenna

Abstract: An antenna is disclosed that is especially useful for radiating and receiving non-sinusoidal electromagnetic waves. The antenna is an efficient and distortion-free radiator of electromagnetic pulses that do not use a sinusoidal carrier. The antenna's size is independent of frequency and the antenna, therefore, can be of small size relative to the wavelength of the radiated electromagnetic waves. When used for reception of electromagnetic wave energy, the antenna performs with low distortion. The basic concept underlying the invention is the modification of the Hertzian electric dipole into an antenna structure that can carry large currents without requiring a large driving voltage. Antennas for the transmission or reception of sinusoidal waves achieve that goal by employing resonant structures. The invention achieves the same result by changing the Hertzian electric dipole into a loop that forms a Hertzian magnetic dipole and preventing the undesirable magnetic dipole radiation by shields of conducting and absorbing materials.

Optimization of radio communication in media with three layers

Abstract: The electromagnetic radiation of an electric dipole in a medium with three layers is examined using dyadic Green's functions. The far zone field for problems of this nature is primarily determined from the lateral wave. It is shown that the excitation of this wave may be reinforced through a dipole inclination and an optimum position may be determined. The radio losses for typical forests were calculated for vertical and horizontal dipoles and for dipoles with an optimum inclination. The theoretical results are in good agreement with the available experimental data.

Time domain modeling of nonlinear loads

Abstract: The behavior of an antenna or scatterer when loaded with a nonlinear element can be changed greatly from that observed under linear conditions. In some cases, the nonlinearity causes effects such as the intermodulation products arising from the nonlinear mixing of two frequencies. In other cases, the nonlinearity may be exploited, for example, to reduce late-time ringing on a pulse-excited antenna. A procedure for treating general nonlinear loads is described and illustrated. This procedure is applied using a computer to several specific types of nonlinearities. The treatment within the framework of the thin-wire approximation to the electric field integral equation is developed. As such, the treatment can be applied to the large class of objects modeled by wires. The nonlinear load types that are considered include those with piecewise-linear voltage-current curves (e.g., one or more diodes), a load with a time varying resistance (which permits modulating the scattered fields), and a general nonlinear load represented by specified voltage-current functions.

Printed circuit balun with a dipole antenna

Abstract: A coplanar printed circuit balun for connecting an unbalanced feedline to a balanced dipole antenna.

Wide-band nulling performance versus number of pattern constraints for an array antenna

Abstract: The problem of wide-band pattern hulling for an array antenna is addressed, in particular the relation between the number of constraints imposed and the sidelobe suppression achieved. The two constraint methods considered are multiple nulling over a narrow angular sector and hulling of the pattern and its derivatives at a single point. To first order the sidelobe cancellation is shown to be independent of the actual pattern type and is determined by only two parameters: the number of null constraints M and the number of sidelobes v to be cancelled. The latter parameter directly translates into a desired hulling bandwidth \Delta f . A numerical solution to the problem is offered in the form of curves, from which the number of nulls required to suppress a jammer over a given bandwidth can be conveniently estimated. This number is indicative of how many degrees of freedom a conventional adaptive antenna system must allocate to attain a specific hulling performance.

Coaxial dipole antenna with extended effective aperture

Abstract: A coaxial dipole antenna includes a first radiator which is approximately one quarter wavelength long. A second radiator exhibits length less than one quarter wave length and is coupled to the feed port by a reactive element which has an electrical reactance which is insufficient to increase the electrical length of the second radiator to one quarter of the wavelength. The length of a dipole antenna is substantially shortened while an effective aperture of one half wavelength is maintained by causing a portion of the transceiver housing to radiate in phase with the antenna.

The optimum feed voltage for a dipole antenna for pulse radiation

Abstract: A solution is presented for the time-domain voltage waveform which must be applied to the input terminals of a dipole antenna in order to maximize the amplitude of the radiated electric field at a specified time and far-field position. A constraint on the energy of the applied signal is used, and the applied signal is assumed to be bandlimited. The solution provides an upper bound on the maximum physically realizable electric field strength available from a dipole antenna, for fixed energy and bandwidth. Numerical examples are presented, and the effects of signal bandwidth, feed position, elevation angle, and dipole length are shown. The optimum solution is also compared with the response of a Gaussian input voltage pulse, and improvements of 6 dB or more are noted.

A new MIC slot-line aerial

Abstract: The design and performance of a new microwave integrated circuit (MIC) slot-line antenna is presented. The new antenna has a narrower beam for the same order of gain as that of the conventional MIC dipole and resonator antennas. The antenna operates in X -band with a gain of 6 dB and a sidelobe level of 10 dB. It can be easily integrated with other MIC components.

A modular approach for the design of microstrip array antennas

Abstract: A method for the design of medium gain (15-25 dB) microstrip array antennas is described. A modular approach is utilized in which a given antenna is used as a building block for higher gain antennas. A series of X -band antennas were built in this way, and the results seem to validate the usefulness of the method.

Omnidirectional, circularly polarized, cylindrical microstrip antenna

Abstract: A microstrip cylindrical antenna comprised of two concentric subelements on a ground cylinder, a vertically polarized (E-field parallel to the axis of the antenna cylinder) subelement on the inside and a horizontally polarized (E-field perpendicular to the axis) subelement on the outside. The vertical subelement is a "wraparound" microstrip radiator. A Y-shaped microstrip patch configuration is used for the horizontally polarized radiator that is wrapped 1.5 times to provide radiating edges on opposite sides of the cylindrical antenna for improved azimuthal pattern uniformity. When these subelements are so fed that their far fields are equal in amplitude and phased 90° from each other, a circularly polarized EM wave results. By stacking a plurality of like antenna elements on the ground cylinder, a linear phased array antenna is provided that can be beam steered to the desired elevation angle.

Directivity optimization for Yagi-Uda arrays of shaped dipoles

Abstract: A method is presented for the maximization of the directivity of Yagi-Uda arrays whose elements are not straight conductors. The optimum shapes as well as the positions of the array elements are determined, both of which depend on the radius of the conductors. The moment method is used in the optimization process. An example shows that an optimized Yagi-Uda array of three 1.5 \lambda elements can achieve a maximum directivity of 11.8 dB.

An Implantable Electric-Field Probe of Submillirneter Dimensions

Abstract: Many areas of biological research await the development of practical electric (E)-field probes with submillimeter dimensions for in situ measurements of RF electromagnetic fields. This paper reports on the design, fabrication, and testing of such a probe. The probe consists of a 0.6-mm dipole antenna zero-bias Schottky barrier diode and a unique highly resistive output lead structure. Experimental results indicate the probe does not perturb the field under investigation and is linear over a range of field strengths from less than 60 to over 1200 V/m. The probe has been designed so as to he independent of the media in which measurements are being made.

Dielectric and width effect on H -plane and E -plane coupling between rectangular microstrip antennas

Abstract: Theory and numerically computed results are presented for mutual coupling between two rectangular microstrip antenna patches. E -plane alignment and H -plane alignment are the two patch orientations considered. The s -parameter matrix element s_{11} is used to study the mutual coupling. Extensive results are provided for s_{11} covering several relative substrate dielectric constants, antenna patch widths, and antenna patch separations. Results are also given for resonant frequency, resonant impedance behavior, and radiation pattern at resonance.

Antennas for Nonsinusoidal Waves: II-Sensors

Abstract: The use of the basic large-current radiator?discussed in a previous paper?and the Hertzian electric dipole as sensor is investigated If the sensor works into a large resistive load, typically implemented by an emitter follower, its output voltage varies like the electric field strength, while a capacitive load produces an output voltage proportionate to the integral of the field strength The maximum energy is transferred to a load impedance that is equal to the radiation resistance of the antenna This is the same result as in the case of sinusoidal waves, but the radiation resistance for nonsinusoidal waves differs from that for sinusoidal waves An effective aperture can be defined, which is again analogous, but not equal, to the same concept used for sinusoidal waves

Matching properties of arbitrarily large dielectric covered phased arrays

Abstract: A method is presented for approximating the impedance or admittance properties of arbitrarily large but finite dielectric covered phased arrays which use a plane wave expansion of the fields radiated by the elements The method is general in its application to dipole, slot, or waveguide geometries even though results from dipoles near resonance are used in this paper Results calculated using the method are compared to a well-established procedure for an array in free space Further results for a dipole array in a dielectric slab are presented, and a problem which occurs due to a surface wave phenomenon is dealt with in an approximate manner using the insights possible from the physical interpretations of the method The method is also shown to be valuable in its predictions of edge effects and behavior of impedances across the extent of large finite arrays which methods that work with infinite arrays or small finite arrays cannot accomplish

Spiral antenna with selectable impedance

Abstract: A monopulse spiral antenna system of the type having a minimum of three, interwound spiral arms for multimode, direction of arrival sensing, is disclosed in which the antenna arms are shaped and arranged in an overlapping configuration that allows the interarm impedance of the antenna to be adjusted, substantially independently of other electrical properties of the antenna, for matching of the antenna impedance of a mode forming network while preserving the broadband, directional capabilities of the antenna. Several different embodiments of the impedance adaptive antenna are disclosed including a preferred, eight-arm exponential spiral in which the arms are conductive strips transversely inclined relative to a plane formed by the spiral so that opposed and parallel surfaces of adjacent arm strips create a dominant interarm capacitance that in turn determines the overall input impedance of the antenna. Furthermore, the opposed, proximate surfaces of the strip-shaped arms are dimensioned, spaced and inclined at an angle that adapts the input impedance of the antenna to a value matching that of the mode forming network.

Numerical analysis of 4-arm Archimedean spiral antenna

Abstract: The radiation fields of a 4-arm Archimedean spiral antenna excited with three types of balanced mode, M1(1, j, ?1, ?j), M2(1, ?1, 1, ?1) and M3(1, ?j, ?1, j), are evaluated on the basis of the current distributions which are determined numerically. An axial beam and conical beams are presented with experimental results. It is demonstrated that an axial ratio of less than 3 dB can be obtained over a wide angle range of about ± 60°, when the spiral is excited with modes 1 and 2. It is also found that the axial ratio for mode 3 is liable to be deteriorated by the reflected current, particularly around the spiral axis.

Phase scanned microstrip array antenna

Abstract: A microstrip array antenna, including spaced radiator elements supplied w microwave power and separated from an underlying ground reference plane by a layer of dielectric material, in which the antenna beam is phase scanned by periodically closing switching devices connected between the reference plane and at least one null point of each radiator element. In one embodiment, the radiator elements are identical rectangular patches disposed along a path, each patch having a length parallel to the path of one-half wavelength and a width transverse to the path not exceeding one wavelength in the underlying dielectric material at the antenna operating frequency. The patches are connected in series to receive microwave power by conductive strip elements whose widths are selected to effect a desired distribution of radiated microwave power from the patches.

Radiation Characteristics of Traveling-Wave Antennas Excited by Nonsinusoidal Currents

Abstract: In this paper, the idea about traveling-wave antennas excited by nonsinusoidal currents for high-resolution exploration is advanced. First the analytic expressions of the radiation waveforms in the far zone produced by a single transient of current traveling along a straight wire are derived in time domain. Then the radiation characteristics of traveling-wave antennas excited by nonsinusoidal current, such as the mean-power pattern functions and the directivity, are given, and the space waveform control and radiation efficiency are discussed. Based on previous results, the radiation waveforms of dipole antennas excited by pulse current are obtained from time- domain analysis. In a practical example, comparing these waveforms with corresponding waveforms obtained from frequency-domain analysis and measured data in [4] and [13], good agreements are obtained in various radiation directions. Some errors in [14] are also pointed out and corrected.