Showing papers on "Coaxial antenna published in 1994"

New kind of microstrip antenna: the monopolar wire-patch antenna

Abstract: In reply to the Comment (given by Burbery, R.A., Elect., Lett., vol., p. 745, 1994) we wish to say: (i) Our antenna is a microstrip antenna with a dielectric substrate and a height varying between lambda /20 and lambda /100. At such heights the 'folded dipole' adaptation techniques are not applicable. >

Clustered phased array antenna

Abstract: An array of antenna elements is configured in a lattice-like layer, each element being similarly oriented such that the whole of the antenna elements form a homogeneous two-dimensional antenna aperture surface which can be planar or curved to conform to a desired shape. The antenna elements are connected in a one-to-one correspondence to a matching lattice of mutually similar, multiple-port, wave coupling networks physically extending behind the antenna element array as a backplane of the antenna. Each wave coupling network or "unit cell" couples signals to and/or from its corresponding antenna element and further performs as a phase delay module in a two-dimensional signal distribution network. This invention can be embodied in a conformal, or planar phased array antenna comprising a system of densely-packed resonant cavities feeding a set of resonant slot elements, both configured in an matrix array. Instead of using a corporate feed network to feed each cavity, the array is fed from points on the edges of the array, with each cavity being electromagnetically coupled to each of its adjacent cavities by common wall-coupling means. By adjusting the excitation signal amplitudes and phases at each input feed point on the perimeter, the beam may be steered off the broadside axis in any plane orthogonal to the array aperture.

Antenna array having two dimensional beam steering

Abstract: An array antenna includes a ferrite substrate having a two-dimensional planar array of antenna elements disposed over a first surface thereof and means for applying an external magnetic field having a magnitude and direction which can be varied at least in a plane in which the antenna elements lie. The amplitude and direction of the external magnetic biasing field is varied to control the relative phases between each of the plurality of antenna elements and to steer the direction of a main antenna beam in two dimensions.

Optimization of bow-tie antennas for pulse radiation

Abstract: Resistively loaded bow-tie antennas are considered as radiators for temporally short, broad-bandwidth pulses. Analysis is by the finite-difference time-domain (FDTD) method. The geometrical details of the antenna and the resistive loading along the antenna are chosen to optimize this antenna for pulse radiation. Theoretical results for the reflected voltage in the coaxial feed line and the time-varying radiated electric field are compared throughout with experimental measurements. The optimized, resistive bow-tie antenna is shown to radiate a pulse that more closely resembles that of the excitation than is radiated by a metallic bow tie of comparable size. Issues involving the use of the FDTD method for modeling fully three-dimensional antennas are also discussed. These issues include the use of a simple feed model and the staircasing of the edges of the antenna. >

Human operator coupling effects on radiation characteristics of a portable communication dipole antenna

Abstract: EM coupling effects of a human operator on antenna radiation characteristics, such as the antenna input impedance, radiation patterns, the radiation power (into free space), the power absorbed by the body, the radiation efficiency, etc., of a portable communication dipole antenna were investigated in detail. A realistically shaped 3D man model and an approximate linear dipole antenna were used to model this problem. Coupled integral equations (CIE) and the method of moments (MoM) were employed to numerically solve this antenna-body coupling problem. Numerical examples are presented for the antenna located in front of the head (distance ranging from 5 to 1 cm) or adjacent to the abdomen (0.6 cm distance) at 830 MHz. It is found that, when coupled with the operator body, the antenna input impedance will have significant deviation from those in free space and different positions. Due to the operator body absorption effect, the maximum attenuation of the H-plane antenna gain may reach about 15 dB for the antenna at the head position and 25 dB for the abdomen position, toward the direction of the body side. Also, the antenna radiation efficiency is reduced to the range from 0.72 to 0.29 for the head position and 0.15 for the abdomen position, respectively. Moreover, the cross-polarization field is significant, especially in the E plane of /spl phi/=90/spl deg/. This is important for the antenna RF design and communication link budget consideration of portable radio systems. >

Effect of the shorting posts on short circuit microstrip antennas

Abstract: In many antenna applications, the size of the antenna is considered as an important factor in the design process. Therefore, short circuit microstrip antennas are widely used because the short circuit antenna can realize the same resonant frequency, at about half the size of the standard microstrip antenna. The shorted microstrip antenna is constructed by short-circuiting the zero potential plane of an ordinary microstrip antenna excited with a dominant mode. Physically, this short circuit may be complete, by wrapping a copper strip around the edge of the antenna, or it may be simulated by shorting posts. From the manufacturing point of view, construction of shorting posts is much easier than wrapping a copper strip around the edge of the antenna. In the present paper, the effect of such shorting posts on the performance of the microstrip antenna is studied experimentally. However, the effect of the shorting posts depends on different parameters like the number of the posts, the radius of each post and the thickness of the microstrip antenna which determines the length of the posts. The effect of each of these parameters is investigated and presented. >

Planar antenna with helical antenna array and waveguide

Abstract: There is provided an improved planar antenna, for use in satellite communication, capable of providing higher aperture efficiency, improved circular polarization and increased production tolerability. The antenna comprises a waveguide and an array of M x N helical antenna elements, wherein M and N are integers. The waveguide includes a primary feeder waveguide and a set of M secondary feeding waveguides, wherein each of the M secondary feeding waveguides is provided with N helical antenna elements, each of the secondary feeding waveguides is coupled to the primary feeder waveguide through an aperture so that received signals from N helical antenna elements in each of the second feeding waveguides are combined at the primary feeder waveguide.

Construction of a slot-coupled planar antenna for dual polarisation

Abstract: A new type of feeding technique for a dual polarisation antenna is presented. The proposed feeding system was experimentally investigated for both a single element antenna and basic planar array antenna. This antenna system demonstrated high performance in both isolation characteristics and radiation patterns.

Gamma matched, helical dipole microwave antenna with tubular-shaped capacitor

Abstract: A catheter shaft carries a coaxial cable (220), the terminal end of which contains a dipole antenna (214) with opposing first and second helical elements (214A, 214B). This first and second helical elements (214A, 214B) originate from a common connection (222) to an outer conductor (224) of the coaxial cable (220). A tubular-shaped capacitor (200) is connected between an inner conductor (218) of the coaxial cable (220) and a point (232) on the second helical element (214B) where the resistive component of the antenna's impedance matches the characteristic impedance of the coaxial cable (220). This match minimizes reflective losses of the antenna (214), thereby maximizing power transfer to the antenna (214). The antenna (214) has an effective electrical length which is equal to one half the wavelength of the radiation emitted, independent of the physical length of the antenna (214).

A diversity antenna for very small 800-MHz band portable telephones

Abstract: A diversity antenna comprising a short whip antenna top loaded with a small cylinder and a new built-in antenna has been developed for very small portable telephones in the 800-MHz band. Wire-grid analyses and whip antenna experiments yielded good radiation characteristic results when the equivalent electrical length of the whip antenna equalled a half wavelength. The built-in antenna features extreme compactness, its size being one-third that of a conventional planar inverted-F antenna. The characteristics were investigated experimentally, and an antenna of 3.5 cc volume with a gain of -1 dBd and a bandwidth of 30 MHz was designed at 879 MHz. Finally, the diversity characteristics were subjected to field measurements and a diversity correlation of 0.26 was obtained. >

Effect of an air gap around the coaxial probe exciting a cylindrical dielectric resonator antenna

Abstract: Results of an experimental study pertaining to the effect of an air gap surrounding the feed probe of a cylindrical dielectric resonator (CDR) antenna on its input impedance and resonance frequency are presented. The antennas under consideration consist of a CDR positioned on a conducting ground plane and fed by a coaxial probe to excite either the TM/sub 01/ or HEM/sub 11/ antenna modes.

Spiral-mode microstrip (SMM) antennas and associated methods for exciting, extracting and multiplexing the various spiral modes

Abstract: A first spiral-mode microstrip (SMM) antenna has an antenna element situated over and spaced from a parallel ground plane. The antenna element is a frequency-independent planar structure having a plurality of spiraling arms extending outwardly in a plane from a central portion, the arms having respective feed points to excite the spiral modes. Of particular significance, a shorting mechanism connects one or more arms to the ground plane element for influencing the shape of the electromagnetic radiation pattern. A second embodiment of the SMM antenna is constructed as the first, but has a center feed and an off-center feed, and further comprises shorting mechanisms situated well within the periphery of the antenna element. A third embodiment of the SMM antenna is constructed similar to the first, but has a concentric gap situated within the arms so that there is, in effect, a first antenna element having a first plurality of arms and a second concentric antenna element having a second plurality of arms. Capacitors, inductors, and electrical/mechanical switches can be included in the shorting mechanism to facilitate multi-mode, multi-function, and/or broadband operations. By recognizing that the SMM antenna is equivalent to a slot antenna or a magnetic current antenna, a super-thin fourth SMM antenna can be constructed and is a fourth embodiment of the present invention. In this super-thin antenna, the distance between the antenna element and the ground plane is less than or equal to 0.03 of the geometric mean wavelength of the operating band.

Coplanar waveguide fed coplanar strip dipole antenna

Abstract: A novel coplanar waveguide fed coplanar strip dipole antenna is presented. Return loss data as well as antenna patterns are shown. The antenna is matched with the use of a novel, wideband balun.

Compact conical antennas for wide-band coverage

Abstract: A broadband antenna with a vertically polarized, omnidirectional electric field is studied. The design of the antenna and its feeding system in the wide frequency range from 20 to 1000 MHz is described and the driving-point impedance determined. Also calculated are the voltage standing-wave ratio (VSWR) and the input impedance of a transmission line connected to the antenna. More efficient operation at low frequencies is obtained by adding a length of transmission line to form a resonant section with the antenna. The effect of the different properties of the earth's surface on the field pattern is treated in a companion paper. >

Antenna coupler for portable cellular telephones

Abstract: An extended retractable wire-type antenna of a portable cellular telephone is coupled to a coaxial cable extending from a remote external antenna by a coupler including an elongated body formed by two mating longitudinal sections molded of a rigid plastics material. The body sections have longitudinally spaced opposing hook-shaped tabs which clip onto the extended antenna in response to slight flexing of the antenna. The sections define an internal cavity for receiving the coaxial cable at one end and for positioning an approximately quarter wave length cable conductor element adjacent the extended antenna in parallel relation to produce an effective inductive connection. A plastic screw prevents sliding of the coupler on the retractable antenna.

Directional antenna for vehicle entry system

Abstract: The invention uses a modified Yagi-Uda antenna as a directional antenna for remote entry applications for transportation vehicles. To reduce the area that the antenna requires for packaging in a vehicle headliner, the antenna employs a shared reflector for plural reception zones on opposite sides of the vehicle. Since the antenna is packaged close to body sheet metal, a folded dipole is used as the antenna feed element to increase input impedance and simplify impedance matching with the receiver.

FD-TD analysis of Vivaldi flared horn antennas and arrays

Abstract: This paper summarizes a detailed computational study of Vivaldi flared horn antenna designs including single element, double element crossed-pair subarray elements, and linear arrays using the finite-difference time-domain (FD-TD) method. FD-TD, which numerically solves Maxwell's time dependent curl equations, accounts for the complex geometrical and electrical characteristics associated with this antenna design and array implementation. Validations have been made relative to a moment method (MM) model of an electrically large linearly tapered slot antenna. Also, good correlation is shown to exist in the primary features of the antenna patterns between computed and measured data for all cases. This work has achieved a number firsts for the FD-TD methodology. It represents the first "exact" computational model of a single quad Vivaldi slot antenna; the first "exact" computational model of a phased array of Vivaldi quad elements; and the first FD-TD model to demonstrate grating lobes for a phased array antenna of any sort. Lastly, this research represents an extensive study of the largest grid-based antenna models conducted to date. >

Antenna device for portable equipment

Abstract: An improved antenna device for small size portable communication equipment comprising circuits (23) for transmitting and/or receiving radio signals as well as a chassis (25) and a feeding point (22) providing the electrical coupling of the antenna device to the communication equipment. The antenna device comprises a hollow helical antenna (6) fixed externally on the chassis and an antenna rod slidable through the helical antenna and being part of a straight radiator (1). The helical antenna (6) is of quarter-wave type and is coupled constantly via the feeding point (22) to the circuits (23). The straight radiator (1) is a quarter-wave radiator and the antenna device is provided with a switching device (2, 12, 13), which couples via the feeding point (22) the quarter-wave radiator (1) to the circuits (23) in parallel with the helical antenna (6) when the antenna rod is extended, while the switching device (2, 12, 13) substantially decouples the quarter-wave radiator from the circuits (23) and the feeding point (22) when the antenna rod is retracted.

Improved internal antenna for hand-held terminals

Abstract: An analysis is made of the performance of a radiation-coupled dual-L antenna (RCDLA). In the simulation the antenna is mounted on the back side of the hand-held terminal, making use of the metallic housing as a shielding structure. The simulations show that this structure has a similar performance to that of the recently proposed full short circuit planar inverted-F antenna (FS-PIFA) in terms of shielding and radiation characteristics. In terms of bandwidth, size, and matching capabilities the RCDLA outperforms the FS-PIFA. Placement of the antenna on the back side of the housing instead of the top of the terminal results in a radiation pattern that points away from the user's head regardless of the antenna type.

Comment: New kind of microstrip antenna: the monopolar wire patch antenna

Abstract: The monopole wire patch antenna is described as a new invention. It is, in fact, a member of a well known family of monopole variants, well known and much used in the aircraft antenna industry. Some of the early development work was done by Seeley in the late 1950s. The antenna had also been developed by Willoughby and was the subject of UK patents.

Combination GPS and VHF antenna

Abstract: A combination antenna for aircraft application is disclosed. The antenna has a shell similar to that of a conventional VHF communication antenna, but it houses a monopole VHF and a volute GPS antennas. Provisions are made to enable the GPS antenna to be situated beneath the VHF antenna, but yet have full view of the upper hemisphere and avoid interference even though no structural shielding is provided. The combination antenna is mountable on the pre-existing base used for the conventional single VHF communication antenna and is operable with the pre-existing cable used to transmit the signal of the replaced single VHF communication antenna.

Resonant frequency of a tunable rectangular microstrip patch antenna

Abstract: The resonant frequency of a coaxial-probe-fed rectangular microstrip antenna tuned by a number of passive metallic posts suitably placed within the antenna's boundary is obtained by using the resonant frequency expression in the absence of the post. The resonant frequency in the absence of the post is calculated from the fringing field extension and effective relative permittivity expressions. The theoretical resonant frequency results of tunable rectangular patch antenna obtained by using this method are in good agreement with experimental results available in the literature. © 1994 John Wiley & Sons, Inc.

Directional antenna, in particular dipole antenna

Abstract: In order to produce a directional antenna which is superior to those of the prior art, and especially a dipole antenna which is easier to manufacture and of simpler design, and also has enhanced electrical properties, the dipole with its circuit balancing element (7) according to the invention is made of the material of the reflector (5). The dipole and the circuit balancing element (7) project from the reflector wall (5) through corresponding areas which are cut out and/or punched out, up to a region (11) where they join with the remaining material of the reflector wall (5), and are preferably bent outwardly in relation to the plane of the reflector wall in the region of the point (11) where they immediately join with the remaining material of the reflector wall (5).

Antenna configuration of an electromagnetic detection system and an electromagnetic detection system comprising such antenna configuration

Abstract: Antenna configuration of an electromagnetic detection system for detecting and/or identifying detection labels, comprising a first and a second antenna array which in operation are connected with a transmitter and/or receiver of the detection system. The first antenna array comprises a plurality of current loops substantially located in one plane, which together enclose a surface which at least partly overlaps a surface enclosed by a current loop of the second antenna array. The second antenna array also comprises a plurality of current loops substantially located the plane referred to.

Slot antenna with reduced ground plane

Abstract: A slot antenna has a substantially reduced ground plane by defining the slot within a loop of a narrow conductive strip, for example a deposited metal, around a slot opening less than one half the wavelength of the intended signal frequency to be received by the antenna. A conductor such as a central conductor of a coaxial cable coupled to the conductive strip on one side of the slot, while another conductor such as the ground shield of the coaxial cable is terminaled at a position across the slot from the central conductor terminal. In addition, the gain and bandwidth of the antenna may be improved by adding a similarly constructed loop or loops of slot antenna in parallel to the first slot to form an overlapping series of loops. Such a modification forms a ground plane with an overlapping series of loop conductors. As a result, the present invention permits a convenient, window mounted antenna assembly, as well as a particularly advantageous combination of window panel of a motor vehicle, as is particularly well adapted for use with remote keyless entry systems as well as cellular telephone systems.

Conformal multifunction shared-aperture antenna

Abstract: A shared aperture, multifunction conformable antenna has a spiral-mode microstrip (SMM) antenna portion having a spacer for maintaining the SMM antenna in spaced relationship to a ground plane, with dielectric material therebetween. The SMM antenna portion is substantially surrounded by a loop antenna which is spaced therefrom and which is electrically connected to the spiral-mode portion by a high frequency choke to block FM broadcast band signals from the SMM antenna. An AM-broadcast-band-blocking capacitor functions to route AM signals to the SMM antenna portion. The spiral-mode antenna receives signals at frequencies above 300 MHz, the loop antenna receives signals in the FM band, and both the loop antenna and the spiral-mode antenna receive signals in the AM band.

Modulated backscatter microstrip patch antenna

Abstract: The invention provides a microstrip patch antenna for emitting backscatter-modulated signals in response to a received signal. The antenna has two segments that are connected together by a switch. When the switch is ON, the antenna is a full wave length antenna with its two segments out-of-phase with each other, thus producing minimal backscatter. When the switch is OFF, the two segments of the antenna act in concert with each other to produce a backscatter-modulated signal. Multiple pairs of such antennas can be connected together to make a single antenna with increased signal power.

Antenna apparatus and antenna system

Abstract: An antenna apparatus comprises a dielectric substrate, an earth conductor mounted on one surface of the substrate and forming a microstrip transmission line, an upper conductor mounted on the other surface of the substrate and forming a microstrip transmission line, an antenna element formed integrally with the microstrip transmission lines, and a delayed wave opening situated in the earth conductor in confronting relationship with the upper conductor.

Antenna for portable radio devices

Abstract: The present invention concerns an antenna for portable radio devices including a helical antenna coupled at the base to a transmitter/receiver. The pitch of a conductive material helix constituting the helical antenna varies according to the height of the helix. It decreases from the base of the helical antenna towards its top.

Wideband circularly-polarized loop antenna

Abstract: A simple loop antenna without loading is introduced to radiate a circularly-polarized wave with a broad bandwidth. This antenna consists of a rhombic loop with one point opened and located above a ground plane. A proposed technique to control the current distribution is (1) to open one point at an appropriate position on the loop and (2) to change the loop configuration. The antenna characteristics including axial ratio, current distribution, radiation pattern and input impedance are calculated by the method of moments. The calculated results are in good agreement with the measured data. >