Broadband dual-polarized patch antennas fed by capacitively coupledfeed and slot-coupled feed

Designs of broadband dual-polarized patch antennas fed by promising feed structures of a capacitively coupled feed and a slot-coupled feed (antenna A), two capacitively coupled feeds of a 180° phase shift and a slot-coupled feed (antenna B), and two capacitively coupled feeds of a 180° phase shift and two slot-coupled feeds (antenna C) are proposed and experimentally studied. The first two feed designs are for the excitation of a single-element broadband patch antenna, while the last design is for a two-element broadband patch antenna. These proposed patch antennas have a thick air substrate, and the 10 dB return-loss impedance bandwidths obtained for the two polarizations are all greater than 13%. High isolation (<-30 dB for antenna A, <-32 dB for antenna B, <-35 dB for antenna C) between the two feeding ports for the entire impedance bandwidth of the proposed antennas can be obtained. Also, improved cross-polarization levels (>20 dB) in both E and H plane patterns for the two polarizations of antennas B and C are achieved     

A four-input beam-forming downconverter for adaptive antennas

A four-input beam-forming downconverter for adaptive antennas is described. It consists of 2-bit variable gain amplifiers (VGAs), 5-bit local oscillator (LO) signal phase shifters using double RC-bridge circuits, and mixers. The VGAs adjust gain deviation between signal paths. A differential-signal-to-eight-phase-signal converter is employed as a part of the LO phase shifter to reduce the chip size. A maximum phase error of 4.1/spl deg/, which is less than 1/2 LSB, is achieved. This error value indicates that the required phase shifter accuracy and the necessary isolation between the VGAs has been achieved. This beam-forming IC is applicable to receivers with adaptive antennas, and is expected to help to reduce the costs of adaptive antenna systems.     

地基激光辐照近地轨道小尺度空间碎片作用规律研究

通过研究脉冲激光与铝靶碎片的膨胀运动以及冲量耦合的相互作用,仿真分析了铝靶碎片在等离子体作用下的速度和压力时空分布规律以及冲量耦合系数与激光功率密度之间的定量关系;在此基础上,建立了基于地基的脉冲激光辐照近地轨道小尺度空间碎片动力学变轨仿真模型,模拟研究了近地轨道小尺度空间碎片移除过程中轨道偏心率与近地点高度随激光脉冲数目变化的影响规律。结果表明:在最优冲量耦合系数作用下,当脉冲数目达到180次轨道偏心率为0.071时,基于此文的条件可实现近地轨道小尺度空间碎片的有效移除。预期成果可为高能激光移除近地空间碎片技术的应用提供技术指导。     

A new aperture plane method of measuring antenna surface errors

A scheme for measuring surface errors of reflector antennas is proposed in which the phase of the signals from small areas of the wavefront are compared one by one to the phase of the signal from the rest of the wavefront. The comparison is accomplished by periodically changing the phase of the signal from each small area by ±90°. For convenience and economy, the measurement can be made in an aperture plane of an antenna feed system, and can be done in real time with the antenna pointing steadily at the source being observed. Estimates are made of the signal power required for the measurement, and three means of modulating the phase are suggested, one of which allows the surface error of the antenna to be corrected as well as measured     

Cross-slot-coupled microstrip antenna and dielectric resonatorantenna for circular polarization

Circular polarization (CP) design of microstrip antennas and dielectric resonator (DR) antennas through a cross slot of unequal slot lengths in the ground plane of a microstrip line is demonstrated. The proposed CP design is achieved by choosing a suitable size of the coupling cross slot, which results in the excitation of two near-degenerate orthogonal modes of near-equal amplitudes and 90° phase difference. This CP design can be applied to both configurations of microstrip antennas and DR antennas and has the advantages of easy fine-tuning and less sensitivity to the manufacturing tolerances, as compared to their respective conventional single-feed CP designs. For the proposed design applied to a low-profile circular disk DR antenna of very high permittivity studied here, a large CP bandwidth, determined from 3-dB axial ratio, as high as 3.91% is also obtained. Details of the proposed antenna designs are described, and experimental results of the CP performance are presented and discussed     

An antenna diversity MMIC vector modulator for HIPERLAN with lowpower consumption and calibration capability

The design and performance of a vector-modulator-based phase shifter for high-performance radio local area networks at 5.2 GHz is presented in this paper. Low power consumption is achieved using a 0.6-μm GaAs MESFET process. At a voltage supply of 1.4 V and with a current consumption between 3.5-7 mA, the gain is 0.6 dB and the 1-dB input compression point is -9 dBm. A full 360° phase control range is achieved by combining two of the three vectors, which have phase offsets of 120°, with variable amplitude. Chip size is only 1.3 mm ². The proposed vector modulator applies a new circuit configuration of variable-gain amplifiers to compensate their transmission phase errors. Within a gain control range of 20 dB, the phase error can be reduced to ±3°, which is about a factor of eight better than the results obtained by single FET amplifiers. A simple calibration procedure for the proposed vector modulators is presented to improve the manufacturing yield and to decrease the impact due to temperature changes and aging. A maximum gain error of ±0.8 dB and a maximum phase error of ±7° have been measured after applying this calibration to the designed vector modulator     

Switched angular diversity BSSA array antenna for WLAN

The broadband design of a circular array of bent stacked slot antennas (BSSAs) is presented. The angular diversity provided can mitigate multipath propagation and intersymbol interference occurring in indoor wireless communications. Details of the antenna design and experimental results are presented for a fixed sector configuration at 5.2 GHz. Numerical simulation results are consistent with experiments. The 3 dB beamwidth in azimuth and elevation is ~75 and 50°, respectively, and the directivity is 7.7 dBi. Over the whole HIPERLAN bandwidth, a -18 dB return loss is achieved, with only a 3 dB degradation of secondary radiation lobes     

Printed ring slot antenna for circular polarization

A new design of a microstrip-line-fed circularly polarized printed ring slot antenna is proposed. Circular polarization (CP) radiation of the proposed design is achieved by introducing proper asymmetry in the ring slot structure and feeding the ring slot using a microstrip line at 45° from the introduced asymmetry. The asymmetry introduced in the proposed design is a meandered-slot section and the proposed CP design can be applied to printed square and annular ring slot antennas. Prototypes of the proposed design have been implemented. Experimental results show that good CP radiation performances are obtained and the 3 dB axial-ratio CP bandwidths obtained for the square and annular ring slot antennas are about 4.3% and 3.5%, respectively     

Millimeter-wave amplitude-phase modulator

A millimeter-wave amplitude-phase modulator, using Fox's (polarization) principle of phase changing has been developed. Using this modulator, it is possible to perform the following types of phase modulation: binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), differential QPSK (DQPSK), π/4-DQPSK with peak phase error 5° (rms error: 2°), and peak amplitude error 2% (rms error: 1%) in the frequency range of 36-37.5 GHz. The achievable switching time is less than 35 ns. A low level of insertion loss (1 dB) is achieved. The modulator is able to switch up to 25 dBm of RF power. This modulator can also be used for changing the amplitude of the output wave from 0 to -6 dB with an accompanying phase modulation less than 3°. The modulator is suitable for use in high-speed millimeter-wave communication systems     

Performance of DS/CDMA-based equatorial LEO satellite system usingturbo-codes

Improving the bit error rate (BER) performance at low elevation angles is a crucial determining factor for the capacity of any low earth orbit (LEO) satellite system. In previous work, it has been demonstrated that the BER performance of a DS/CDMA-based equatorial LEO satellite system on a downlink can be improved significantly by using satellite diversity. The authors address the issue of improving BER at low elevation angles by using turbo codes     

Interference-reducing antennas for shortwave broadcast listeners

Principles useful in the design of directional antennas capable of reducing interference in shortwave-broadcast reception are identified. Examples are given of designs which go beyond the time-honored vertical loop. It has been found that significantly improved rejection of both ground- and sky-wave interference can be obtained with minimum modification to the associated receiver, even in typical indoor environments. Measurements suggest that single-source sky-wave signal reductions of 20 dB can be achieved on average. This is sufficient in many instances to give satisfactory separation of two signals on the same frequency of comparable strength and having azimuth differences of 90° or greater. It seems likely that widespread use of these antennas would significantly reduce the severity of co-channel interference in shortwave broadcasting     

High-power, broad-bandwidth HF dipole curtain array with extensivevertical and azimuthal beam control

The design, construction details, and performance of a prototype high-power HRS 12/6/.5 antenna system covering the 6 to 26 MHz international broadcast bands are presented. The antenna has been developed, erected, and tested as part of the Voice of America modernization program to demonstrate the feasibility of controlling the horizontal and vertical apertures and beam directions of high-power, broad-bandwidth (2:1 frequency ratio) antennas. The antenna system provides 11 vertical slews, 15 azimuthal slews, and five azimuthal widths. The peak of the elevation pattern can be steered to angles of 4° to 20° above the horizon and the azimuthal beam can be steered up to ±30° with respect to boresight. Gains range from 16 to 31 dBi. Azimuthal beamwidths between -6 dB points range from 8° to 75°. The antenna is designed to handle the input power of one or more 500-kW double-sideband, amplitude-modulated transmitters. The antenna system has been designed using basic dipole and antenna switching modules from which smaller subarrays (HRS 2/6/.5, HRS 4/6/.5, HRS 8/6/.5, etc.) can be readily developed. The extensive beam control provided by the antenna system enables a shortwave broadcaster to use fewer antennas to reach the same audience. This reduces the land area of the station as well as its acquisition and operating costs     

On the performance of improved quadrature spatial modulation

Quadrature spatial modulation (QSM) utilizes the in‐phase and quadrature spatial dimensions to transmit the real and imaginary parts of a single signal symbol, respectively. The improved QSM (IQSM) transmits two signal symbols per channel use through a combination of two antennas for each of the real and imaginary parts. The main contributions of this study can be summarized as follows. First, we derive an upper bound for the error performance of the IQSM. We then design constellation sets that minimize the error performance of the IQSM for several system configurations. Second, we propose a double QSM (DQSM) that transmits the real and imaginary parts of two signal symbols through any available transmit antennas. Finally, we propose a parallel IQSM (PIQSM) that splits the antenna set into equal subsets and performs IQSM within each subset using the same two signal symbols. Simulation results demonstrate that the proposed constellations significantly outperform conventional constellations. Additionally, DQSM and PIQSM provide a performance similar to that of IQSM while requiring a smaller number of transmit antennas and outperform IQSM with the same number of transmit antennas.     

A new phase-shifterless scanning technique for a two-element activeantenna array

In this paper, a new phase-shifterless beam-scanning technique is proposed and demonstrated for a two-element active antenna array. An internal control line with an embedded amplifier is introduced in the array to provide another injection signal other than the mutual-coupling injection signal between antennas. By mixing the effects of the signals from the control line and mutual coupling, the phase difference between antennas is adjusted by gradually changing the amplifier bias on the control line. A dynamic analysis is presented to explain the scanning mechanism. The measured results showed that, when the control-line amplifier was biased from the off state to fully on state, the radiation pattern of the array was varied smoothly from the out-of-phase mode (with 180° radiation phase difference) to the in-phase mode (with 0° phase difference). During the scanning process, the antenna oscillators were stably locked, with the deviation of the locked frequency lower than 0.35%     

Super-quasiorthogonal space-time trellis codes for four transmit antennas with rectangular signal constellations

In this paper, we present the first super-quasiorthogonal space-time trellis codes (SQOSTTCs) for systems with four transmit antennas using various types of rectangular signal constellations to increase the spectral efficiency up to 5 bits/s/Hz. In our wireless communications system, we define an eight-dimensional (8D) signal constellation as Cartesian product of four two-dimensional (2D) rectangular signal sets. The transmission of an 8D point from the first antenna is achieved by transmitting four concatenated 2D points in four consecutive channel uses. The 2D symbols transmitted from the other three antennas are not independent but so chosen as to form, together with the symbols transmitted from the first antenna, the entries of a 4×4 quasiorthogonal transmission matrix. The union of two sets of quasiorthogonal transmission matrices forms a so-called super-quasiorthogonal signal set. With the 4×4 quasiorthogonal transmission matrices, we then label the state transitions of a trellis diagram describing the operation of the encoder. The simulation results of the frame error rate and the bit error rate demonstrate the excellent performance of our proposed SQOSTTCs.     

The land mobile satellite communication channel-recording,statistics, and channel model

The communication channel between the MARECS satellite at 26°W and a cruising van was measured and recorded in European areas exhibiting satellite elevations from 13 to 43°. Different environments and mobile antennas were tested. The results of an extensive statistical evaluation include spectra of the fading amplitude; probability density, and distribution of the received signal power; and the percentage of time for fade and nonfade periods. Based on the physical phenomena of multipath fading and signal shadowing, an analog model of the land mobile satellite channel which can readily be used for software and hardware fading simulation is developed. The most important parameter of this model is the time-share of shadowing. The Rice factor which characterizes the channel during unshadowed periods, can vary from 3.9 to 18.1 dB. Block error probability density, error gap distribution, and block error probability are discussed     

低轨卫星自跟踪技术分析

针对低轨(LEO)卫星无信标信号时,传统自跟踪方式无法对其进行有效跟踪的问题,提出了全数字跟踪体制。对采用频分时分复合多址(FDMA/TDMA)体制的低轨卫星,采用宽带检测结合窄带跟踪的方法,快速准确地提取方位俯仰误差,实现了对目标卫星的高精度跟踪。对采用码分多址(CDMA)体制的低轨卫星,采用频域跟踪的方法,实现了低信噪比条件下对目标卫星的高精度跟踪。     

Design of active phase shifters based on multichannelheterojunction field effect transistors (MCHFET's)

Design criteria of active phase shifters based on GaAs/AlGaAs multichannel (MC) HFET in the frequency range 4-60 GHz are presented. The phase characteristics of MCHFET devices were studied using the computer aided design program TOUCHSTONE. The dependence of transmission phase on various intrinsic elements in the equivalent circuit model as a function of control gate bias was also studied. There are limited gate bias ranges which correspond to the active regions of the two conducting wells for which a quasi-linear continuous phase shift for analog applications was achieved. Continuously varying the gate bias from V_gs=-1.9 V to V_gs=-0.6 V results in a quasilinear phase shift of 10°, 15°, 21°, and 29° at f=12, 20, 30, and 60 GHz, respectively. Similarly, varying the gate bias from V_gs =-0.4 V to V_gs=0.7 V a quasi-linear phase shift of 21°, 26°, 27°, and 23° at f=12, 20, 30, and 60 GHz, respectively, was achieved. The gain variation was less than 3 dB in these bias regions. With digital applications in mind, a maximum differential phase shift of around 50° was obtained by switching the gate bias discretely. The transmission phase of single gate MCHFET mostly depends on variation of gate source capacitance with gate bias rather than on other intrinsic elements. The dependence of phase shift on various geometrical and structural parameters is also presented. To test the practicality of the device, other scattering parameters (e.g., S₁₁, S₂₂, S₁₂) and the noise figure (NF) were finally studied     

An X-band experimental model of a millimeter-waveinterinjection-locked phased array system

An interinjection-locked 10 GHz model of a millimeter-wave phased-array system has been built and tested. It has been successfully demonstrated that this novel technique can be used to control limited-scan phased-array antennas. A beam shift of ±5° has been achieved with only one phase shifter in a four-oscillator system. Adaptability to monolithic fabrication and a reduction in the number of phase shifters required make this method attractive for use at millimeter-wave frequencies     

A compact single layer injection-locked linear scanning array

A compact, single layer, CPW-fed, patch scanning array architecture using injection locking at 9.83 GHz is presented. The patch antennas are printed on the front side of the substrate while the electronics are situated at the back side leading to a simple and compact design. The unit element for the array is a self oscillating active patch antenna with a GaAs FET centered behind the patch for tight packing. The feedback for the oscillator is provided through electromagnetic coupling using a twin-slot arrangement behind the patch. A low power control signal is injected through parasitic coupling at the CPW side of the circuit. Phase shifting of the elements is achieved by electronically adjusting the gate voltage of the GaAs FETs. A scan range of -12°- +9.5° is obtained for a four element prototype array