Showing papers on "Coaxial antenna published in 1982"

A broad-band annular-ring microstrip antenna

Abstract: A heuristic discussion of the radiation properties of the transverse magnetic (TM 11 ) and (TM 12 ) modes of the annular-ring microstrip antenna is presented, indicating the possibility of the TM 12 mode as a superior microstrip antenna. Rigorous analyses of the resonant frequency characteristics of the antenna are then performed with the matched asymptotic expansions technique and the perturbation approach. The analyses show that the TM 12 mode is decidedly the best mode for microstrip antenna applications while the TM 11 mode, having a high Q -factor, is best reserved for resonator applications. The analyses include the study of the resonant frequencies, bandwidths, and radiation pattern of the antenna. The matched asymptotic expansions technique and the perturbation approach are also shown to agree excellently with each other within their domain of validity.

A method for measuring amplitude and phase of each radiating element of a phased array antenna

Abstract: In the phased array system, excitation amplitudes and phases based on the design are specified for each antenna element in order to synthesize desired beam scannings and radiation patterns. However, due to fluctuations of antenna and feed network characteristics, the amplitude and phase of each antenna element deviate from the desired values. To correct these deviations, the amplitude and phase of each antenna element must be accurately measured under specific operating conditions. In this paper, we employ variable phase shifters connected to the antenna elements and measure only the amplitude variation of the composite electric field of the entire array when the phase of each element is modified. The rotating element electric field vector method in which the measured amplitude variation is numerically processed for obtaining the amplitude and phase of the particular element is theoretically discussed and experimentally tested for its usefulness. The present method can be easily attained by simply adding software to the computer-controlled phased array system.

Standard-Site Method for Determining Antenna Factors

Abstract: 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.

Electronically tunable microstrip antenna

Abstract: A microstrip antenna with a linearly polarized radiating patch is varied in resonant frequency by an electronic tuning technique. A dc bias voltage is combined with the excitation signal to regulate the capacitance of a varactor diode mounted in the antenna structure. In one embodiment the varactor is in shunt with a half wave open circuited radiator and adds electrical length to the antenna, while in another embodiment the varactor is in series with a shorted quarter wave radiator and subtracts electrical length therefrom.

Antenna shape synthesis using characteristic modes

Abstract: An initial effort is described to develop an antenna synthesis procedure by which the shape of a surface of rotation and its current density are deduced from a given far-field radiation pattern which satisfies the conditions of a characteristic mode. Typical results obtained to date are presented to substantiate the method and to illustrate some antenna shapes. A variety of research topics suggested by present efforts are discussed and suggested for future investigation.

Characteristics of annular-ring microstrip antenna

Abstract: The characteristics of an annular-ring microstrip antenna operating in TM11 and TM12 modes are determined experimentally. Our results confirm the main conclusions of a theoretical study published recently by Ali, Chew and Kong and show that: (a) the bandwidth of the TM11 mode is very small while that of the TM12 mode is relatively large, and (b) the lauching efficiency of the TM12 mode is highly sensitive to the feed position while that of the TM11 mode is virtually independent of the feed position.

Three-element antenna formed of orthogonal loops mounted on a monopole

Abstract: A three-element directional/omnidirectional antenna adapted for use in both transmitting and receiving modes. Crossed loop antennas are mounted on top of a monopole whip antenna and are electrically coupled thereto. Each of the loop antennas consists of an outer larger primary loop and an inner secondary loop joined at its base to the primary loop. Both the primary and secondary loops are interrupted at their top ends opposite the point where they join the monopole antenna. A tuning capacitor is coupled between the two halves of each of the primary loops, while a coaxial antenna feeds the two secondary loops. The coaxial cables feeding the secondary loops pass through a dual ferrite choke disposed within the monopole antenna.

Helical antenna structure capable of resonating at two different frequencies

Abstract: An antenna is provided which exhibits a relatively small size and is capable of resonating at two different frequencies. The antenna includes two helically wound elements which resonate at a first resonant frequency. A conductive member extends through and beyond one of the two helical elements to cause the antenna to resonate at a second resonant frequency.

Dipole-disk antenna with beam-forming ring

Abstract: A method of improving the radiation characteristics of a dipole-disk antenna by using a beam-forming ring (BFR) is suggested. The radiation patterns of the dipole-disk antenna are calculated by the moment methods (MM) and the uniform geometrical theory of diffraction (UTD) and are compared with experimental results.

Blade antenna with shaped dielectric

Abstract: A Tee slot blade antenna for aircraft and other high speed vehicles has a pair of dielectric sections, one section extending longitudinally along the blade and the other extending transversely from an intermediate location along the longitudinal section. The resonant frequency of the antenna is determined by the length of each section and the position of the transverse section along the longitudinal one, while the characteristic impedance is a function of the width of each section. The Tee slot antenna is capable of operating over a wide bandwidth on a smaller blade than prior single slot antennas. A Tee slot antenna designed for one frequency range can be combined with either a single slot antenna or another Tee slot antenna designed for another frequency range on the same antenna blade, without impairing the bandwidth of either antenna.

Slotted antenna array excited by a coplanar waveguide

Abstract: The letter gives a new concept of exciting slotted antenna arrays. There both the slots and the feeder are etched on the same side of the printed circuit board. A channel is cut perpendicular to the slots and a coplanar waveguide for exciting the slots is inserted into the channel. The concept has been experimentally verified on a model.

Broadband circular disc microstrip antenna

Abstract: A technique for broadening the bandwidth of the circular disc microstrip radiating element is described. Theory based on a simple circuit model is introduced and comparison with experimental work is shown. From this model, a matching circuit is devised, the resulting element giving a bandwidth of 35% (to a VSWR of 1.5) near 8 GHz. This makes the circular disc element suitable for a wide range of radar and communications antenna systems.

Antenna apparatus capable of resonating at two different frequencies

Abstract: An antenna is provided which exhibits an overall shortened length with respect to the length of the conventional sleeve dipole type antenna. The antenna includes an upper radiating element coupled to a tank circuit to induce resonance at a first resonant frequency and further includes a helical element electrically coupled to a sleeve member which cooperate to resonate at a second resonant frequency.

Empirical helix antenna design

Abstract: Empirical design relations are presented for a uniform diameter helical antenna operating in the axial mode. The antenna peak gain, HPBW, and bandwidth are expressed as a function of the helix design parameters (diameter, pitch angle, and number of turns). Computed values are compared with experimental data for various helix configurations.

Bi-loop antenna system

Abstract: A bi-loop antenna system comprises an array of four bi-loop antennas equally spaced from the array axis and fed in phase and with equal power. Each antenna comprises an electrical conductor configured as two substantially identical open-ended coplanar loops, preferably square in shape, having colinear axes parallel to the array axis and electrically connected together, the open ends defining two closely spaced feed points at the middle of the array. The array is fed by a four-way coaxial power divider with output ports connected to the antennas, respectively, remote from the feed points thereof by coaxial lines of equal length. A balun comprising a portion of one of the loops of each antenna and a closely spaced coextensive conductive strip connects the inner and outer conductors of the coaxial cable to the two feed points, respectively, of the antenna. In a preferred embodiment, the conductors of each antenna are formed on a dielectric sheet or board by printed circuit techniques. This antenna system produces a horizontally polarized omnidirectional radiation pattern over an octave bandwidth and has a VSWR response of the input impedance with a value less than 2:1 over the octave bandwidth.

Novel leaky-wave antenna for millimetre waves based on groove guide

Abstract: A new type of leaky-wave antenna, with a simple longitudinally continuous configuration, is described. The antenna is based on the groove guide, a low-loss waveguide for millimetre waves.

Microwave oven with dual feed excitation system

Abstract: A microwave oven with a dual feed excitation system comprising in one form of the invention a rotating antenna supported from the top cavity wall and a slotted radiating chamber supported from the bottom cavity wall. The antenna and radiating chamber are coupled to the magnetron output probe by a waveguide having a central section for receiving energy from the magnetron probe; a first section for coupling energy from the central section to the antenna and a second section for coupling energy from the central section to the radiating chamber. The fractional apportionment of the total energy from the magnetron between antenna and radiating chamber is a function of the impedance presented by each. The impedance of the antenna varies as the antenna rotates. The impedance of the chamber is particularly sensitive to food load parameters such as dielectric constant, which changes as the food cooks. Thus, the fractional distribution of energy between antenna and chamber varies during the cooking process, resulting in improved cooking performance.

Broadband antennae employing coaxial transmission line sections

Abstract: The deviation in operating frequency which antenna system elements can handle without serious transmission line mismatch is increased by constructing the antenna such that the inner portions (40, 42) of its legs (40,48 and 42,50) are formed of coaxial transmission line connected so that the outer conductor serves as part of the radiator, and so that the inner and outer conductor of the line cooperate to form compensation stubs whose impedance varies with frequency in a manner to cancel or oppose the reactance which the antenna legs exhibit with frequency change. The stubs are connected in series or in parallel with the antenna feed point and parasitic elements. Surge impedance is selected so that the antenna driven elements (nearly resistive) and signal source, and parasitic elements that incorporate the invention, are mismatched at band end frequencies and center band frequency in apparoximately like amount. The impedance is selected such that the antenna (somewhat reactive) and signal source are more nearly matched at frequencies midway between center band frequency and band edge frequencies.

Coaxial waveguide commutation feed network for use with a scanning circular phased array antenna

Abstract: A dominant TEM mode and a pair of spatially orthogonal TE 11 modes suitably excited at the input ports of a coaxial waveguide commutator portion of a coaxial waveguide commutation feed network are employed to generate a commutatable low-sidelobe amplitude distribution at symmetrically disposed peripheral output ports of the coaxial waveguide commutator The resulting low-sidelobe amplitude distribution can be used to feed radiating elements of an associated circular phased array antenna The coaxial waveguide commutator is configured, inter alia, with a linearly tapered inner conductor surrounded by a uniform tube outer conductor to achieve a smoother TEM-dominant mode characteristic impedance transition from the input port plane to the output port plane thereof Employment of this feed geometry, in conjunction with balanced four-port feeding of the coaxial waveguide commutator which inhibits the higher order TE modes, increases the bandwidth capability while maintaining low insertion loss

Shaped wire antennas with maximum directivity

Abstract: The optimum shape of a wire antenna for maximum directivity is obtained by applying the method of moments and the simplex method for function minimisation. Antenna shape is approximated by piecewise parabolas, and the effects of wire radius on current distribution are considered.

Self contained antenna test device

Abstract: Twin lead transmission lines are positioned in close coupling relationshipo linearly polarized and planar arrays of antenna radiating elements to provide a self contained instantaneous antenna test and measurement system Near field energy from the transmission lines is coupled to the transversely arranged antenna dipole elements to permit testing without degrading antenna performance Signals induced on the radiating elements are of uniform amplitude and linearly changing phase equivalent to those of a far field plane wave Various tests such as antenna failure and performance characteristic measurements, including gain, pattern and phase difference, can be made automatically A balanced power divider distributes RF power equally to the twin lead transmission lines and a system processor controls phase shifter scanning elements and analyzes the various output parameters to provide the desired test and measurement information concerning the selected array of dipoles and components

Antenna with tunable helical resonator

Abstract: An antenna suitable for use in the high frequency (HF) ranges includes a resonator tunable over a predetermined frequency band. The resonator consists of an insulated wire wound over a dielectric rod. Tuning is effected by sliding a metallic sleeve disposed in frictional contact over the wire. A multiplicity of these resonator units may be mounted on a single collar at different angles. Each of the resonator units will respond to a particular frequency. The remaining devices operate as a load on the antenna assembly. The antenna assembly may also be mounted on a conventional mobile antenna by means of an adaptor unit.

Slot antenna with face mounted baffle

Abstract: An improved planar slot array antenna comprising a conducting fence or baffle interposed between the two halves of the antenna in a plane perpendicular to the flat plate or E-field.

Antenna element having non-feed conductive loop surrounding radiating element

Abstract: The directivity as well as the gain of an antenna element associated with a finite length reflector, which includes a feed antenna such as a dipole antenna and a reflector having a finite length of several wavelengths or less, are improved by disposing a non-feed loop element having a peripheral length of about 2 wavelengths along a common imaginary plane with the feed antenna so as to surround the feed antenna. Preferably, the non-feed loop element is disposed in parallel to the reflector, and more preferably it is disposed nearly symmetrically with respect to the center of the feed antenna.

Spiral array antenna

Abstract: PURPOSE:To obtain a thin spiral array antenna whose manufacturing processing is simple by printing spirals, feeders, and feeding circuits on one dielectric substrate. CONSTITUTION:Two-wire circular spirals 1a-1c, feeding points 11a-13b, microstrip lines 14a and 14b, branch points A, and D-G, and out-of-phase phase shifting parts B and C are printed on the dielectric substrate 10 fixed on a reflecting plate 17 through supporting columns 16a-16d. A current fed from a coaxial plug 15 is divided through the phase shifting parts B and C into two 180 deg. out-of-phase currents, which flow to the two-wire spirals constituting antenna elements together with the reflecting plate. The spiral array antenna driven as mentioned above radiates a circular polarized wave at right angles to the substrate 10.

Blockage-free space fed antenna

Abstract: A space fed antenna with a folded path to reduce the distance between a phased array and the focal point of such array is shown to be made up of: (a) a first plurality of vertically polarized antenna elements incorporated in the phased array; (b) a second plurality of cross-polarized antenna elements disposed to form a polarization-twisting screen at a distance from the first plurality of vertically polarized antenna elements equal to one-third the focal length of such elements; and (c) a third plurality of latching circulators connected between selected pairs of cross-polarized antenna elements in the polarization-twisting screen so that such pairs also may function as a feed array for the space fed antenna.