Showing papers on "Feed horn published in 1997"

Feeder link antenna

Abstract: A steerable feeder link antenna is formed of a steerable reflector and a stationary feed horn assembly. A novel feed horn assembly allows dual mode transmit and receive functions for circularly polarized microwaves. The feed horn assembly includes a four arm turnstile junction coupled to a feed horn through the feed horn's side wall to couple transmit frequencies and an axially coupled transmission line for the receive frequencies. Each turnstile junction arm incorporates chokes for the receive frequencies. The transmission line's cut off frequency is above the transmit frequency to prevent transmit signals from interfering with receive signal receivers.

Transmitter that selectively polarizes a radio wave

Abstract: A transmitter provides a radio wave with selectable polarization. The transmitter includes antenna feeds that generate orthogonal radio waves having non-linear polarizations that corresponds to the selectable phase relationships of a first and a second modulating signals. A spacial combination of the non-linear radio waves to produce a linearly polarized radio wave that has an orientation corresponding to a selected phase relationship.

Near field focusing of apertures and reflector antennas

Abstract: Large aperture antennas such as reflectors are commonly used for far-field communications. In these applications the aperture field is uniformly illuminated in phase by a feed antenna, and the radiated beam focuses at infinity. In this study we consider focusing the antenna to a point on its axis near the aperture. Interesting results are obtained for the focused location and its spot size, which may be used in near-field focusing of microwave power, or, near field probing by a radiometer.

Combination nuclear magnetic resonance and electromagnetic induction resistivity well logging instrument and method

Abstract: An apparatus for measuring induction resistivity and nuclear magnetic resonance properties of earth formations penetrated by a wellbore. The apparatus includes a magnet for inducing a static magnetic field in the formations, a transmitter antenna positioned proximal to the magnet and having a principal magnetic axis substantially perpendicular to the principal magnetic field direction of the magnet. The apparatus includes receiver antennas positioned at spaced apart locations from the transmitter antenna, a circuit for generating radio frequency power pulses which is selectively connected to the transmitter antenna, and circuits for measuring the voltages induced in both the transmitter antenna and induced in the receiver antennas. The measuring circuit is adapted to measure voltages in the receiver antennas during the radio frequency power pulses, when the voltages are induced in the receiver antennas by electromagnetic induction. The measuring circuit is also adapted to measure voltages induced in the transmitter antenna between successive power pulses, when the voltages are induced therein by nuclear magnetic resonance.

On-orbit reconfigurability of a shaped reflector with feed/reflector defocusing and reflector gimballing

Abstract: A system and method for changing the radiation pattern of an antenna assembly of a satellite in orbit is provided. The antenna assembly includes a reflector antenna fed by a feed assembly. The reflector antenna transmits and receives signals within a radiation pattern. The reflector antenna and the feed assembly are movably mounted to a sliding mechanism so that they can be displaced with respect to one another. The displacement causes defocusing as the reflector antenna is displaced from the focus point. The defocusing causes the radiation pattern to become more compact or broadened. Thus, the radiation pattern of the satellite provided with a single reflector antenna and a single feed element may be changed while the satellite is in orbit. The system and method include gimballing the reflector antenna to steer the radiation pattern.

Transient Fields of Parabolic Reflector Antennas

Abstract: Requirements to increase the information content of radar and communication systems result in a band width increase and are a reason to investigate and describe the transient fields from ultra wideband (UWB) large antennas1. Furthermore, a need in such an analysis occurs in near field time domain antenna measurements2. In these cases not only the transient far field is of interest. The spatial-temporal near-field distribution is useful too to the optimal antenna arrangement on the complex objects. Mention must be made that many issues of the theory of an impulse radiating antenna. (IRA) are discussed by Carl E. Baum. Everett G. Fart and D. V. Giri3–8. The transient field from the circular focused aperture with uniform held distributions was considered in3. Much attention is given to IRA which consists of a large angle conical TEM feed that attach to a reflector antenna. It was shown that radiated held includes three distinct pacts. The first of these is the direct radiation from the feed structure (prepulse), whirl is of rather low magnitude, but lasts for a fairly long time This is followed by an impulse, which lasts for a brief time and is high in amplitude. Finally, there is a tail expected after the impulse. Closed-form expressions for prepulse were presented in 4. Analysis was extended to include the diffracted fields from the launcher plates and the circular rim of the reflector5. It was shown that there is an exact time-domain match of the spherical and planar TEM waves (inhomogeneous) at the reflector4–7. Thu exact expressions for the acoustic fields on the z axis for a circular aperture were obtained in 8. While the above-mentioned works describe basic properties of transient fields of an IRA, many questions are yet to be investigated.

Parabolic antenna for measuring the level in containers

Abstract: A parabolic antenna for measuring the level in containers is proposed, a transmitted pulse from a transmitting and receiving device being focused via the parabolic antenna and directed onto the surface of a filled material whose level is to be determined, and. the pulse reflected at the surface of the filled material being received again by the receiving device via the parabolic antenna. For the purpose of introducing the measuring instrument through an opening in the container, the parabolic antenna can be folded and unfolded by being positively moved.

Compact microwave terrestrial radio utilizing monolithic microwave integrated circuits

Abstract: An integrated point-to-point microwave radio frequency unit/antenna (60) has a housing (62), a microwave antenna (68) affixed to the front face of the housing (62), and a microwave radio frequency transceiver electronics package (66) within the housing (62). The transceiver electronics package (66) includes a circuit board having transmitter and receiver intermediate frequency processors (124, 138). The transceiver electronics package (66) further includes a microwave transmitter (102) and a microwave receiver (104), each utilizing monolithic microwave integrated circuit architecture. The signals of the microwave transmitter (102) and microwave receiver (104) are preferably of different frequencies and are diplexed for communication with the antenna (68).

Small radio transmitter receiver system

Abstract: A small radio transmitter receiver system including a transmitter equipped with a concealed transmitting antenna and a receiver equipped with a concealed receiving antenna, the system using a 1.5V-3V battery to provide the necessary working voltage and providing at least two channels for selection, the transmitter being arranged in movable or fixed type as desired, the transmitting frequency of the transmitter being set within 35 MHz to 2.5 GHz for FM stereo or mono audio radio signal transmission as desired.

Antenna feed element for low circular cross-polarization

Abstract: Antenna feed element performance is critical in obtaining low circular cross-polarization in multi-element feed arrays. The antenna feed element described in detail in this paper has been named the septum-polarizer, equalized, choked (SPEC) feed element. It consists of a low axial-ratio circular-waveguide septum polarizer and a conical horn with a single choke/corrugation at the aperture. This produces circularly symmetric, equalized E- and H-plane element patterns with low on-axis and off-axis axial ratios. Breadboard models of the SPEC feed element have been developed and measured results are provided. A flight hardware version of this feed element is being developed for satellite applications. These applications are for large antenna feed arrays that illuminate offset parabolic reflectors. In order to meet the low weight requirements, the flight SPEC feed elements will be constructed of carbon-cyanate-ester with electroless copper plating applied to the internal surfaces.

Microwave antenna feed structure

Abstract: A feed structure for transmitting or receiving microwave energy to or from a reflector includes a waveguide having an input section, intermediate section, and output section. The waveguide has an inner surface of generally rectangular cross section and an outer surface of generally circular cross section. The outer surface includes unique opposing convex surfaces which enables the waveguide to be bent with minimal resulting deformation of the internal rectangular surface. At least one locating surface is provided on the outer surface of the waveguide for determining the orientation of the waveguide. The input section of the waveguide has a threaded cylindrical surface adapted to be connected to a hub having a threaded interior bore which is connected to the reflector. A feed horn integral with the output section of the waveguide and having a circular output aperture is formed by machining the inner surface of the waveguide into a rectangular to circular transition. The intermediate section of the waveguide is curved so that the output aperture of the horn is directed toward the reflecting surface of the reflector, enabling waves transmitted from the aperture toward the reflecting surface to be reflected into space in the form of plane waves.

Feed horn for linearly polarized wave

Abstract: PROBLEM TO BE SOLVED: To obtain an excellent cross polarized wave identification degree and to make the feed horn for a linearly polarized wave small by placing a probe and a reception means in the inside of a waveguide and separating a reception face of a horizontally polarized wave and a reception face of a vertically polarized wave so as not to be on the same face. SOLUTION: A horizontally polarized wave and a vertically polarized wave are led to a circular waveguide 2 via an opening 1. In the case that the direction of an electric field of a vertically polarized wave is in parallel with a probe 9, since the vertically polarized wave is reflected in a ground conductor face 4, the vertically polarized wave is coupled with a tip of the probe 9. A horizontally polarized wave is received by a patch antenna element 8 and coupled with a feeding conductor strip pattern 11 via a slot 6. Then a reception signal is given to a reception signal processing circuit such as an LNB provided on a same side of a printed circuit board 3 via a feeding conductor pattern 11 and a conductor pattern of a signal processing face 5 to which the end of the probe 9 is connected and the reception face of the horizontally polarized wave and that of the vertically polarized wave are separated.

FDTD optimizations of the bandwidth of the hat feed for MM-wave reflector antennas

Abstract: The hat antenna is a low sidelobe reflector antenna for radio link applications in the MM-wave band. In the present paper we describe how the hat feed has been analyzed by using the computer code V2D Solver based on the FDTD method. The FDTD method has resulted in a big break through in the possibility of numerically controlling the radiation performance of the hat feed. In particular, the bandwidth has been tuned to a return loss better than 20 dB over a 10% bandwidth.

The hexagonal horn as an efficient Gaussian beam launcher

Abstract: A new type of feed horn-the hexagonal horn-is proposed and investigated by means of Gaussian-Hermite beam-mode analysis. The electric-field distribution at the horn aperture plane is approximated. The polarization efficiency is 88.66%. The fractional power in the fundamental beam mode is about 85%. The near- and far-field radiation patterns are calculated. The high fractional power in the fundamental beam mode of the horn indicates that it can be used as an efficient Gaussian beam launcher in quasi-optical systems.

Coaxial feed array for a short focal-length reflector

Abstract: The design of array feeds for deep dishes is complicated by the need to closely pack the elements to minimize scan gain loss and coma sidelobes. An example is the design of a 4-element multibeam feed for the Lovell radio telescope at Jodrell Bank, UK, which is prime-focus fed reflector with a diameter (D) of 76.2 m and f/D=0.3, where f is the focal length. The multibeam feed was developed to reduce the time required for large-area surveys of the sky near the 21 cm wavelength (1.33-1.43 GHz). A suitable multibeam feed for the Lovell radio telescope has been designed by CSIRO. However, the design approach could be used in other applications requiring an array feed for a short focal-length reflector. To design the multibeam feed, new software that analyses circular/coaxial horn arrays by a mode-matching method was used. The effects of mutual coupling between the feeds, discontinuities and steps in the elements and a finite-sized ground plane are included in the analysis. This paper describes the design of the feed array and gives the predicted and measured results for a C-band model. Results are described also for when the array is used as a feed for the Lovell radio telescope.

Dual frequency feed horn for an antenna

Abstract: A steerable feeder link antenna is formed of a steerable reflector and a stationary feed horn assembly. The feed horn assembly allows dual mode transmit and receive functions for circularly polarized microwaves and includes a four arm turnstile junction (4) coupled to the feed horn (3) through the feed horn's side wall to couple transmit frequencies, and an axially coupled transmission line for the receive frequencies. Each turnstile junction arm incorporates chokes to block the receive frequencies. The axially coupled transmission line's cut off frequency is above the transmit frequency to prevent transmit signals from interfering with receive signal receivers.

Pattern correction in large deployable reflector antennas with phased array feed

Abstract: Recently, engineers have focused on developing mobile satellite communications systems using GEO, MEO and LEO satellites. We are now studying an on-board antenna for future S-band mobile satellite communications using hand-held terminals. This antenna is carried on a GEO satellite, and consists of a large deployable mesh reflector and a primary feed using an active phased array. It has the advantage of beam forming flexibility. For example, when its radiation pattern changes due to an amplifier problem, we can obtain the desired pattern by adjusting the only excitation phase of the array feed. We first present the satellite antenna's configuration, then describe pattern correction by adjusting the excitation phase of the array feed.

Optimization of a submillimeter wave hologram CATR

Abstract: The optimization of a submillimeter wave hologram type of compact antenna test range (CATR) is studied with a combined analysis of an exact near-field aperture integration (physical optics) and a finite difference time domain (FDTD) method at 500 GHz. The effect of altering the feed horn radiation pattern is discussed.

Time-varying fading reduction method for digital mobile radio

Abstract: The method involves switching bursts of a transmitter output signal or a receiver input signal alternating between several antennas. Preferably, the radio receiver and the radio transmitter have each at least two separate antennas (AS1,AS2) which receive and transmit the same information (I), respectively, in the form of bursts. The information is processed in a signal conditioning circuit (AS) in the transmitter to form bursts. The receiver and the transmitter each include a switch (U1) which switches the two antennas between two bursts.

Optical transmitter/receiver interface for sealed environments and method of using same

Abstract: An optical interface includes at least two transmitters and receivers capable of transmitting and receiving, respectively, high bandwidth optical signals. A first transmitter/receiver assembly which includes at least one such transmitter and one such receiver is mounted inside a computer having a shell which maintains a hermetic seal. The transmitter and receiver of the first transmitter/receiver assembly face a transparent portion of the computer shell. A second transmitter/receiver assembly also includes at least one transmitter and receiver which are mounted outside the computer shell facing the transparent portion of the shell, with each transmitter and receiver of the second transmitter/receiver assembly opposite a corresponding receiver or transmitter of the first transmitter/receiver assembly. High bandwidth optical signals of up to 1 Gb/s are transmitted to and from the computer across the transparent portion of the shell while the hermetic seal is maintained.

Spherical wave blockage in reflector antennas

Abstract: The effects of the spherical wave blockage in reflector antennas is investigated. This problem is likely to occur in axially symmetrical feed antennas of single- and dual-reflector type in both single- and dual-reflector configurations, owing to the presence of primary feeds and their supports including struts that are normally placed between the primary source and the main reflector. The main reflector blockage due to large obstacles is estimated by the well-known null-field technique that employs flat polygonal plate models of the masking structures to define the obscured area. Although this same approach may be used to predict the spherical wave blockage due to the struts, a more rigorous but yet efficient technique is also employed, which consists of superimposing to the primary field the high-frequency scattered field from the struts. This field is calculated by using scattering coefficients that are derived by locally approximating the actual structure, by an infinite circular cylinder. This latter formulation is compared with the null-field technique and validated by an experimental campaign. The measurement setup is particularly useful for isolating spherical wave-blockage effects. It consists of a single-reflector offset antenna where a single strut is mounted with its axis parallel to that of the focusing parabola, thus, practically enforcing the plane wave blockage to vanish. Comparisons with the measurements have shown that the null-field approach is adequate for predicting the secondary pattern for large polygonal obstacle, but it is unsatisfactory to treat the strut blockage. It is found that this latter can be successfully described with the more rigorous high-frequency approach.

Cutoff and bandwidth characteristics of a circular coaxial waveguide with four symmetrically placed double ridges

Abstract: A dielectric-cone-loaded, hybrid-mode feed horn was developed for broadband applications (Clark and James 1995). Using the mode-matching method, that analysis showed that the bandwidth of this feed horn is extremely broad, and it can be excited by using a coaxial waveguide for dual-band applications. However, the limited bandwidth of the exciting coaxial waveguide inhibits the full potential of the horn to be realised. In order to couple the incoming/outgoing waves from the wideband horn without sacrificing its broad dual-band capability, we propose a coaxial waveguide with four symmetrically placed double ridges. The cutoff and bandwidth characteristics of the proposed structure are analysed using the modified Ritz-Galerkin method, and the results are compared with those obtained using the finite-element method.

Multiple-antenna transmission with partial side information

Abstract: We consider a single user, narrowband channel with multiple transmit antennas and a single receive antenna. The channel is characterized by a vector /spl alpha//spl I.oarr/ of gains and phases, perfectly known at the receiver and partially known at the transmitter. By varying the amount and kind of side information at the transmitter, we evaluate the gap between perfect channel knowledge and no channel knowledge in terms of expected SNR.

Numerical analysis of planar bicone and TEM horn array antennas

Abstract: Focused radiation of high power radio frequency (RF) transients has previously been achieved using reflector antennas fed by single spark-gap switches. An attractive alternative would use an array of many medium-power sources, which are capable of lower pulse-to-pulse jitter than the spark gaps, and would offer the added advantage of time-delay scanning. This paper presents the results of theoretical and numerical modeling of candidate radiating elements for ultrawideband (UWB) arrays. The elements examined are TEM horns that connect to one another at the mouths, and their limiting case, the planar bicone.

The new feed system for the SETI Institute Woodbury site 30-m-diameter Cassegrain antenna

Abstract: The 30-m-diameter C-band Cassegrain antenna on the Woodbury site (near Georgia, Atlanta) is used by the SETI Institute as a verification station for SETI observations. We have supplied a feed system to enable this antenna to now operate from 1-3 GHz with a single feed configuration, consisting of a feed-horn and an orthomode transducer (OMT). While it was the norm to provide several feeds to cover such a bandwidth, and switch-in the individual feeds as required, there are obvious advantages in having only one feed system. In addition to the 1-3 GHz SETI requirement, the antenna will also, in the future, be required to operate up to 7 GHz. The feed horn was designed to cover the 1-7 GHz range; the limit to 3 GHz is in the performance of the OMT connected to the feed horn. Nevertheless, at frequencies above 3 GHz, in particular 4.2 and 5-6 GHz, reduced performance on a single polarization (where a return loss as low as 3 dB was tolerable) was of interest. To this end, measurements were taken to 7 GHz.

Broadband omnidirectional microwave antenna with decreased sky radiation and with a simple means of elevation-plane pattern control

Abstract: An omnidirectional microwave antenna comprises a paraboloidal reflector disposed above the ground and facing downwardly with a substantially horizontal aperture and a substantially vertical axis. A vertically oriented feed horn is located below the paraboloidal reflector on the axis of the paraboloidal reflector and has a phase center located near the focal point of the paraboloidal reflector. A conical reflector extends downwardly away from the periphery of the feed horn for reflecting radiation received vertically from the paraboloidal reflector in a horizontal direction away from the conical reflector, and for reflecting horizontally received radiation vertically to the paraboloidal reflector. A radome extends downwardly from the outer periphery of the paraboloidal reflector and includes an absorber material for absorbing radiation propagated laterally from the feed horn and the conical reflector above the aperture of the feed horn.

Effect of feed cross-polarization on the cross-polar characteristics of a shaped dual reflector antenna

Abstract: The two common forms of shaped reflector antennas for linear polarization applications are the dual gridded reflector antenna (with two orthogonally polarized surfaces) and a dual reflector antenna with a single surface main reflector and a single surface subreflector. The superior cross-polar performance in a dual gridded reflector is obtained by a combination of the polarizing grid and the separation between the feeds for the two polarizations. In this configuration the feed cross-polarization has a second order effect on the overall cross-polar performance. In a dual reflector antenna, the geometry inherently results in a low cross-polar performance if it satisfies the optimum cross-polar condition. Since the reflector induced cross-polarization is very low, the feed cross-polarization has a significant effect on the overall antenna cross-polar performance. This paper describes the effect of feed cross-polar performance on the antenna cross-polar performance of a shaped dual reflector antenna.

Design of a high isolation dual-polarized offset parabolic reflector

Abstract: In some Ka-band interactive wireless applications, there is need for high isolation between transmit and receive signals at the customer site. If the isolation from the two polarizations at the antenna level is to exceed 50 dB, ordinary cost-effective ortho-mode transducers (OMT) used in conjunction with reflector geometries do not normally provide isolations of this magnitude in the whole range of the required bandwidth. This paper discusses the design of a dual-polarized reflector antenna with a gain of about 35 dBi, with side-lobe levels better than 20 dB, and with isolations between the vertical and horizontal polarizations greater than 50 dB. The transmit frequency was considered to be 29.1 GHz and the receive frequency was considered to be 28.5 GHz. Of the three design choices, namely, the front-fed configuration, the Cassegrain configuration, and the offset configuration, the last configuration in conjunction with a polarizer was chosen. The advantages of the offset configuration are reduced blockage, high efficiency and good return loss. The necessity of using a polarizer, which inevitably introduces some blockage makes the offset geometry the only viable option.

Rear feed source for reflector antenna

Abstract: A rear feed source for a reflector antenna and an antenna using such a source. The source includes at least one horn connected to a waveguide. The horn has at least two inclined walls forming an aperture, each wall being extended by a wall with a different inclination. This invention can be applied to radars, notably surveillance radars.

A new design of TEM horn antennas for pulse radiation

Abstract: For the convenience of practical applications, the pulse radiation antennas used in ground penetrating radar should not only be directive, efficient and distortionless on radiation, but also be as small as possible in size. In this paper, we present a new design of a TEM horn antenna that can meet the above requirements.