Showing papers on "Reflective array antenna published in 2004"

Considerations for source pulses and antennas in UWB radio systems

Abstract: This paper addresses two vital design considerations in ultrawide-band radio systems. One is that radiated power density spectrum shaping must comply with certain emission limit mask for coexistence with other electronic systems. Another is that the design of source pulses and transmitting/receiving antennas should be optimal for the performance of overall systems. The design of source pulses and transmitting/receiving antennas under the two considerations is discussed. First, the characteristics of transmitting/receiving antenna systems are described by a system transfer function. Then, the design of source pulses and transmitting antennas are studied based on the considerations for emission limits. Finally, the design of transmitting and receiving antennas are investigated in terms of pulse fidelity and system transmission efficiency. In the studies, thin wire dipoles with narrow bandwidths and planar dipoles with broad bandwidths are exemplified.

Microstrip antenna phased array with electromagnetic bandgap substrate

Abstract: Uniplanar compact electromagnetic bandgap (UC-EBG) substrate has been proven to be an effective measure to reduce surface wave excitation in printed antenna geometries. This paper investigates the performance of a microstrip antenna phased array embedded in an UC-EBG substrate. The results show a reduction in mutual coupling between elements and provide a possible solution to the "blind spots" problem in phased array applications with printed elements. A novel and efficient UC-EBG array configuration is proposed. A probe fed patch antenna phased array of 7/spl times/5 elements on a high dielectric constant substrate was designed, built and tested. Simulation and measurement results show improvement in the active return loss and active pattern of the array center element. The tradeoffs used to obtain optimum performance are discussed.

Compact wide-band multimode antennas for MIMO and diversity

Abstract: This paper presents broadband multimode antennas for multiple-input multiple-output (MIMO) and diversity applications. The antenna system is not based on spatial diversity, as usual MIMO systems, but on a combination of pattern and polarization diversity. Different modes of self-complementary, thus extremely broadband, spiral and sinuous antennas are used to decorrelate the signals. It is shown that only one antenna is necessary to receive three uncorrelated signals, thus the space required to place the MIMO antenna is very small. Simulation results and measurements of a typical indoor scenario are given.

Ultra wideband antenna

Abstract: Ultra wideband antennas are specifically designed to transmit and/or receive very short time durations of electromagnetic energy. It is well known that UWB antenna design remains the major factor in the progress of UWB technology. This article describes a study of conventional antennas and why they are not suitable for a UWB system.

Detection, location, and imaging of fast moving targets using multifrequency antenna array SAR

Abstract: In this correspondence, we generalize the linear antenna array synthetic aperture radar (SAR) from transmitting single-wavelength signals to transmitting multiple-wavelength signals (called multifrequency antenna array SAR). We show that, using multifrequency antenna array SAR, not only the clutters can be suppressed but also the locations of both slow and fast moving targets can be accurately estimated: A robust Chinese remainder theorem (CRT) is developed and used for the location estimation of fast and slowly moving targets. Simulations of SAR imaging of ground moving targets are presented to show the effectiveness of the multifrequency antenna array SAR imaging algorithm.

Integrated waveguide slot antennas

Abstract: Waveguide slot antennas integrated on microwave laminate are presented, and single and dual slot antennas are described, which operate at 10 GHz.

Investigating the impact of smart antennas on SAR

Abstract: We investigate the impact of smart antennas on specific absorption rates (SAR) at 1.9 GHz. We emulate the operation of the smart antennas by utilizing a mobile telephone prototype configured with two PIFA antennas and applying carriers with different signal phases to them. The SAR of this prototype is simulated using FDTD and is also experimentally determined using a MapSAR system. It is found that the operation of smart antennas on SAR has a significant impact, with SAR changing by over 50% for various signal phases. This leads to the conclusion that if smart antennas are to be utilized in handsets careful investigation of their impact on SAR is needed.

Integrated antennas on silicon substrates for communication over free space

Abstract: This letter reports the feasibility of using 2-mm-long on-chip antennas for communication over free space. Integration of antennas into radio frequency integrated circuits (RFICs) eliminates external transmission line connections and sophisticated packaging, which should lower the cost of wireless systems operating above 10 GHz. Mobile microwave probe stands have been developed for measurements at varying antenna pair separations. Antenna-pair gains for 2-mm-long integrated zigzag dipole antennas fabricated on 20-/spl Omega/-cm silicon substrates have been characterized near 24 GHz for separations up to 15 m. The antenna-pair gains show R/sup -2/ dependence up to /spl sim/4-5 m. The antennas were found to be sufficient for use up to 5 m and possibly larger separations.

A wide-band small size microstrip antenna proximately coupled to a hook shape probe

Abstract: A rectangular shorted patch is designed to achieve a wideband performance and size reduction. The patch size is reduced to 25% of the full size patch with over 30% matching bandwidth. A hook shape probe excites the patch approximately. The effect of hook parameters is investigated. A comparison between the L-shape and the hook-shape probe is given. Some of the numerical results are verified experimentally. A 16 elements array is analyzed with different feeding arrangements indicating an improvement of the array performance.

Configurable arrays for steerable antennas and wireless network incorporating the steerable antennas

Abstract: An reconfigurable array of variable conductive elements is provided for reflecting, filtering and steering electromagnetic radiation across a wide range of frequencies. The reconfigurable array is combined with a transmitting antenna to make a steerable antenna. The reconfigurable array surrounds the transmitting antenna and reflects all transmissions except on selected radials where apertures in the reconfigurable array are formed for permitting transmission lobes. The reconfigurable arrays can be arranged in stacked layers to make transceiving multiband antennas. Communications networks using the steerable antennas and arrays are also disclosed.

Applied physics Nanotube antennas

Abstract: An antenna array that is metres high and wide can detect and transmit radio waves. This effect has now been demonstrated at much smaller electromagnetic wavelengths in a nanoscale array of carbon nanotubes.

Space-tapered circular (ring) array

Abstract: This paper describes how the space-tampered linear array, designed to achieve a given linear distribution, can be extended to circular arrays. In linear array, Taylor distribution and uniform-amplitude array elements is used to approximate it. Spacing of the element is done so that the width associated with each element matches the scaled integral of the distribution along the same length. Each array element samples half spacing on each side.

Phased array antenna system with variable electrical tilt

Abstract: A phased array antenna system with variable electrical tilt comprises an array of antenna elements etc. incorporating a divider dividing a radio frequency (RF) carrier signal into two signals between which a phase shifter introduces a variable phase shift. A phase to power converter converts the phase shifted signals into signals with powers dependent on the phase shift. Power splitters divide the converted signals into two sets of divided signals with total number equal to the number of antenna elements in the array. Power to phase converters etc. combine pairs of divided signals from different power splitters this provides vector sum and difference components with appropriate phase for supply to respective pairs of antenna elements etc. located equidistant from an array centre. Adjustment of the phase shift provided by phase shifter changes the angle of electrical tilt of the antenna array.

Compact antennas for UWB applications

Abstract: A report on an investigation of spherical, disc, and half-disc antennas in the frequency and time domains with the objective of developing small planar versions of the antennas. These antennas have an omni-directional impulse response in azimuth and pulse duration of 0.5-0.65 nanoseconds. In addition, the measured data show a reasonable peak received signal in a pulse communication link using two identical antennas.

Performance of a wideband (3-14 GHz) dual-pol array

Abstract: A test array of 25/spl times/25 dual-pol flared dipoles ("bunny-ears") was built and tested. It was designed for 3-14 GHz applications with a low profile (1.2 cm thick). The egg-crate radiating aperture can be integrated with a thin radome and the multi-layer feed to form a load-bearing structure of an airborne platform. The array has an instantaneous bandwidth of 10 GHz, manifested by an impulse response with 100 ps rise time. Smooth well-behaved "active" element patterns in the E-, H-, and diagonal plane were observed. Cross-pol components were typically 30 dB below the co-pol at broadside and 20 dB on average at 60 degree off axis. Element gain over the band was measured and the data tracked fairly well with the theoretical curve defined by the element's unit area gain (4/spl pi/A//spl lambda//sup 2/).

Pattern analysis of uniform circular array

Abstract: The radiation characteristics of a uniform circular array with linear centrally-fed dipole elements, used for smart antenna systems, are analyzed in this paper. The radiation patterns of the array and the gain of the array over a single element are derived based on the thin-wire model. Numerical simulations using the thin-wire model and the method of moments (MoM) have been conducted and compared for a half-wavelength dipole array. Simulations using the MoM demonstrate that the wire diameter of the elements has no significant effect on normalized azimuthal and elevation patterns for a given pattern design. Normalized azimuthal patterns by the thin-wire model and the MoM are in good agreement with each other, while normalized elevation patterns by the thin-wire model are inaccurate since mutual coupling is not considered in the model. Wire diameter affects the radiation resistance and thus determines the amplitude of the radiation field.

Radar device capable of scanning received reflection waves

Abstract: The present invention relates to a radar device for forming multi-beams in multiple channels from reflected waves of a transmitted wave by using a minimum number of antennas. The device has: antennas used for both transmission and reception A 1 –A 4 ; transmission/reception switching means 5 of each antenna; a transmitter 2 ; and a receiver 4 for receiving the reflected waves of the transmitted wave. The ratio of the distance between adjacent antennas A 1 and A 2 to the distance between adjacent antennas A 2 and A 3 or A 3 and A 4 is 1:2. The transmitted signal is transmitted from each of the antennas selected sequentially and the received signal is processed by DBF in a signal processing controller 1 , wherein eleven channels can be implemented by using four antennas and a space for six antennas.

Switched parasitic antennas and controlled reactance parasitic antennas: a systems comparison

Abstract: Two antenna arrays (variable reactance and switched parasitic antennas) form part of a larger number of antenna types targeted for use as smart antennas (or adaptive antennas). A comparison is presented between the characteristics of small switched parasitic antenna arrays and varactor controlled parasitic antenna arrays. The beam widths of the two antennas are similar, but the control system and support electronics are much simpler for the switched parasitic antennas. The systems requirements of some of the applications of smart antennas are discussed in the light of the performance characteristics of these two antenna types. In most applications of these smart antennas, precise angular control of the main beam is not a critical issue for most applications. If null positioning or if precise direction finding of multiple sources is a major requirement, only the varactor controlled parasitic antenna type offers this functionality.

Enhancing WLAN security with smart antennas: a physical layer response for information assurance

Abstract: We examine methods to extend IEEE 802.11 to incorporate adaptive antennas, thereby enhancing security. The focus is on the adaptation that is required to the overall system to take advantage of adaptive antennas. We consider a system architecture that makes use of beamforming antennas and power control to take advantage of the multiple propagation channels typically available in WLAN applications.

Method for deciding array spacing of array antenna by using genetic algorithm and array antenna having sofa structure with irregular array spacing

Abstract: A method for determining an array space of an array antenna by using a genetic algorithm and an array antenna having a soft structure with irregular array spacing are disclosed. The array antenna having a sofa structure with irregular array spacing, includes: a plurality of radiation elements having an inclined angle based on a horizontal plane and arranged with irregular array spacing for radiating and receiving an radio wave; a plurality of phase shifters for amplifying radiation signals radiated from the plurality of radiation elements and receiving signals received from the plurality of radiation elements, and controlling phases of the radiation signals and the receiving signals; and a radio wave signal coupler for dividing a transmitting signal to the radiation signals, transferring the divided radiation signals to the plurality of phase shifters and coupling the receiving signals from the plurality of phase shifters.

A generalized method of modeling the sensitivity of array antennas at system level

Abstract: A general method is presented for modeling the overall sensitivity of array antennas having a beamforming network using S-parameters for every RF system block. This method is applicable for both aperture arrays and focal plane arrays.

Side lobe level optimization in phased array antennas using genetic algorithm

Abstract: The sidelobe level (SLL) of linear and planar phased arrays is optimized using a genetic algorithm (GA). The amplitude and phase of the current of the antennas are all taken as variables to be controlled. As a final example, the design specifications for a 100 element linear array and a 100 element planar array are given. The linear and planar arrays are also optimized over scan angle. Simulation results are presented as several plots. Successful applications show that the GA can be used as a general tool for pattern synthesis of arbitrary arrays.

Omni-dualband antenna and system

Abstract: An omnidirectional dual band antenna system includes a radome and an antenna in the radome. The antenna has a linear array of lower frequency band driven elements, a linear array of higher frequency band driven elements and a linear array of parasitic elements, spaced in parallel planes with the array of higher frequency band driven elements in the middle. The parasitic elements couple to the higher frequency band driven elements and reshape the radiation pattern of the higher frequency band driven elements to correct for distortion caused by the lower frequency band driven elements.

Space-time coding for distributed antenna arrays

Abstract: Recently, there has been significant interest in employing space-time codes in a distributed fashion, where a codeword is spread across antennas at large geographical separations. In such situations, the differences in path delays between disparate transmit antennas and the receiver often requires the consideration of space-time codes that are robust to such offsets. In this paper, this problem is motivated from the application of public safety radio. The optimal receiver is derived, and a number of codes are obtained. Finally, a matched filter bound analysis and numerical results are presented to demonstrate the performance gains of the derived codes relative to other approaches.

Systems and methods for dynamically compensating signal propagation for flexible radar antennas

Abstract: A system for dynamically compensating signal propagation for flexible radar antennas receives measurement signals indicating the position of selected locations of an antenna array. The future shape of the antenna array at a future time is predicted, and compensation signals are applied to signals generated or received by the antenna elements. The compensation signals are based on the future shape of the antenna array.

Characteristics of planar dipoles printed on finite-size PCBs in UWB radio systems

Abstract: Effects of PCB with system ground planes on the planar dipoles for UWB applications are studied using an FDTD algorithm. The impedance and transfer characteristics of the antennas are investigated. Furthermore, the waveforms of received pulsed signals in both UWB single-band and multi-band schemes are examined.

Base station device achieving effective use of frequencies by changing structures of antennas

Abstract: A base station device provided with a plurality of antennas has a mode, in which all the antennas are used, and a mode, in which the plurality of antennas are divided into a plurality of groups each including two or more antennas to be used independently. An array antenna pattern is formed selectively in these modes. When the array antenna pattern is to be formed in the mode of using all the antennas, a signal of one synthesizer is applied to transmission/reception circuits of all the antennas. In the mode of using antennas divided into the plurality of groups, signals of different synthesizers are supplied to the transmission/reception circuits of the antennas.

Radar device with switch matrix for adaptive beamforming in receive path and switching of transmit path

Abstract: The present invention relates to a radar device for forming multi-beams in multiple channels from reflected waves of a transmitted wave by using a minimum number of antennas. The device has: antennas used for both transmission and reception (A1-A4); transmission/reception switching means (5) of each antenna; a transmitter (2); and a receiver (4) for receiving the reflected waves of the transmitted wave. The ratio of the distance between adjacent antennas A1 and A2 to the distance between adjacent antennas A2 and A3 or A3 and A4 is 1:2. The transmitted signal is transmitted from each of the antennas selected sequentially and the received signal is processed by Digital Beam Forming (DBF) in a signal processing controller (1), wherein eleven channels can be implemented by using four antennas and a space for six antennas.

Optimization of linear sparse array antennas consisting of electromagnetically coupled apertures

Abstract: A design technique for sparse array configurations consisting of dielectric-filled, open-ended waveguide antennas is discussed. The position of the elements in the thinned array are determined by applying a genetic algorithm that searches for configurations with the lowest side-lobe level. By employing as design parameter the relative inter-element spacing, the formulated optimization problem allows for an arbitrary deployment of the elements on the aperture. The design strategy accounts for the mutual coupling between elements, as well. To this end, an efficient technique for estimating the Generalized Scattering Matrix of a-periodic arrays is proposed.

Novel UWB antennas - theory and simulation

Abstract: Novel UWB antennas have been invented by Artimi Limited (patent filed). The bandwidth of this structure is significantly larger than previously documented antennas, such as the bow-tie design. The design allows physically small UWB antennas to be constructed simply as a printed circuit etch. This paper presents the theory and simulation results.