Compact range measurement systems for electrically small test zones

Traditional range requirements are evaluated for spherical and compact range measurement systems. It is shown that a compact range system is more appropriate for targets three wavelengths (λ) and larger because of the chamber size needed to meet these requirements. Commercially available compact range systems are, however, normally restricted to 10 λ or larger targets because of the excessive diffraction associated with currently available compact range reflectors. It is shown that this limitation could be overcome by using a blended rolled edge compact range reflector. For example, a 9 λ×9 λ blended rolled edge reflector can be used to measure 3 λ targets at the lowest frequency of operation. As the frequency of operation increases, the test zone of the reflector approaches one half the reflector's linear dimension, which is consistent with presently available compact range systems     

Offset dual-shaped reflectors for dual chamber compact ranges

The application of the theory of the synthesis of offset dual-shaped reflectors to the design of compact ranges is examined. The object of the compact range is to provide a uniform plane wave with minimum amplitude and phase ripple over as large a volume as possible for a given size reflector. Ripple can be lowered by reducing the edge diffraction from the reflector producing the plane wave. This has been done either by serrating or rolling the edge. An alternative approach is to use dual offset-shaped reflector synthesis techniques to produce a reflector aperture distribution that is uniform over most of the aperture, but with a Gaussian taper near the edge. This approach can be used together with rolling and/or serration if desirable. The amount of phase and amplitude ripple obtained with two different dual-shaped reflector designs is studied as a function of position in the plane wave zone and reflector size in wavelengths. The amount of both transverse and longitudinal (z-component) cross polarization is studied     

Method for testing reflector antennas at THz frequencies

The possibilities of applying far-field, near-field, and compact-range techniques to reflector antennas in the THz frequency range are discussed. Other methods, such as defocusing and combining of the mechanical-reflector-surface measurements and the feed-horn-radiation patterns, are also discussed. A recently introduced hologram type of compact range is described. It may be concluded from the analysis of the different methods that the far-field method can be discarded due to atmospheric effects. The near-field method remains a possibility. However, an expensive, high-quality, moving stage is needed, and phase errors caused by flexible cables have to be dealt with. In some cases, a defocusing method, to bring the far field closer, may prove to be practical. Technically, the most-feasible and least-expensive method appears to be the hologram type of compact range. In this method, a planar-amplitude hologram is used to form the required plane wave. The hologram is inexpensive to manufacture, and it is also less sensitive to surface-accuracy errors than a reflector     

一种新型VHF/UHF双频宽带车载全向天线

提出了一种工作在VHF/UHF频段的双频段宽带垂直极化车载鞭状天线。天线在VHF中馈车载鞭状天线的下辐射体顶端加一个UHF频段8λ40 MHz/4同轴扼流套,将上辐射体分为三段并在段间串接两个λ840 MHz/2倒相线圈,在天线底部加同轴扼流圈,完成了一种VHF中馈鞭状天线与一副UHF三元串联馈电直线阵天线复合的新型VHF/UHF双频段超宽频带垂直极化车载全向天线。该天线在VHF频段(30 MHz~225 MHz),UHF频段(800 MHz~880 MHz)内均具有良好的辐射特性。增益在VHF频段为1.5~4.5 dB i,在UHF频段大于6 dB i。     

Compact antenna test range reflector edge treatment

The physical optics technique is used to compare the performance of single offset compact antenna test ranges with different reflector edge treatments and rim shapes. A comparison between reflector edge taper and rim serrations in controlling edge diffraction is demonstrated     

An array feed approach to compact range reflector design

A novel methodology is presented for the design of array feeds for compact range reflectors. The principal design strategy is to illuminate the rim of a standard, circular-aperture reflector with an array pattern null. This results in a reduction in the level of edge-diffracted fields present in the quiet zone. Since low-frequency performance is improved without dedicating reflector surface area to edge treatment, the potential quiet zone size is maximized. Implementation of the technique requires only a few real-valued array excitation coefficients. It is demonstrated that various quiet zone field performance trade-offs can be made by varying either the excitation coefficients or the array size. The quality of the quiet zone field is compared with that of a uniformly illuminated serrated reflector. The operational bandwidth and the effects of both random and systematic array excitation coefficient errors are evaluated     

舰船超短波通信侦察系统侦察效能评估

文中通过对三种传播预测模型的产生背景及适用条件的对比分析,结合Matlab仿真结果与实测数据的比较,选择Longley—Rice模型为海上超短波通信传输损耗模型,根据传输损耗模型计算接收点场强,并计算出接收点所需最小接收场强,依据时间概率模型判定舰船超短波通信侦察系统的有效侦察距离,根据有效侦察距离对舰船超短波通信侦察系统侦察效能进行评估。     

Pattern measurements of reflector antennas in the compact range andvalidation with computer code simulation

The measurements were performed at the University's compact range facility. They demonstrated: (1) the excellent dynamic range that can be achieved with antenna pattern measurements in a compact range facility; and (2) the excellent validation achieved for the calculated patterns of two 8-ft diameter reflector antennas. The compact range has a rolled edge modification to its reflector and uses a pulsed radar system to eliminate the clutter interference such that a dynamic range of more than 80 dB can be obtained. The measured far field patterns of two 8-ft reflector antennas, a prime focus fed antenna and a Cassegrain antenna, at 11 GHz were compared with those calculated by Ohio State University's Reflector Antenna Code. The computer code simulation's approach is also briefly described     

VHF/UHF radar Part 2: Operational aspects and applications

For Part 1 see ibid., vol.14, no.2, p.61-72 (April 2002). Low-frequency radars have the potential to counter stealth efforts and detect low-flying targets beyond the horizon. Part 2 of this paper discusses approaches to target classification and the problems of vulnerability to jamming and operation in a densely populated frequency band. The anti-jamming capabilities of VHF radars are analysed based on measurements conducted with the FHR experimental radar LARISSA and it is demonstrated that electromagnetic compatibility (EMC) with other users of the band can be achieved using a spectral signal-shaping technique. The paper is completed by an overview of possible and existing VHF/UHF radar applications     

Study of the output spectra of ruby laser

The frequency separation between transverse modes of a ruby laser is measured using a Fabry-Perot interferometer and a high-speed camera. The results are compared with the theoretical predictions based on the curved-reflector theory. Satisfactory agreement is obtained. The measurements are verified by studying the output of the laser after application of transverse mode selection. The mode selection technique is based on the control of the reflector size, and results in single-transverse-mode operation at high pumping levels. Time dependence of the longitudinal mode spectrum of a single-transverse mode laser is studied. Particularly orderly mode-hopping sequences from shorter to longer wavelengths are observed. The spectrum of a relatively high-output laser which shows regular pulsations is similarly examined. The spectrum shows some interesting features, which include a near continuum during regular pulsations and repetitive shifts of the high intensity portion of the spectrum from short to long wavelengths.     

Curved edge modification of compact range reflector

For many years, the compact range has successfully been used to design and evaluate many electromagnetic radiation and scattering systems. However, it has had limited use for large structures because of the large discrepancy between the reflector and target zone sizes. The limitation results from the large edge diffracted signal which emanates from the termination of the reflector. Previous attempts to solve this problem have involved using serrated edges to diffuse the diffracted field. While this reduces the edge diffracted field in the target zone, it is not eliminated. In addition, one has introduced many new corners which also diffract into the target zone. A curved edge modification is presented which reduces the edge diffraction by an order of magnitude or more and in the process does not create new mechanisms which perturb the plane wave in the target zone. Using this curved modification, one is able to design a compact range reflector whose target zone cross section approaches the size of the reflector parabolic surface. This makes the compact range ideal for scale model measurements since larger targets (antennas) can be measured. It also makes it more practical to consider systems which can measure full scale vehicles.     

Propagation of Wide-Band Signals at VHF/UHF

The experimental jam-resistant secure voice communications (JRSVC) system developed by M.I.T. Lincoln Laboratory was used to conduct a series of VHF/UHF (225-400 MHz) propagation measurements, representative of a veriety of tactical communications situations, both ground to ground and ground to low-flying aircraft. Results are unusual in two regards: they were made with the receiver in motion, covering many contiguous propagation paths, and the JRSVC system, by frequency-hopping over almost an octave and averaging the results, largely eliminated the effects of frequency-selective (multipath) fading that generally dominate VHF/UHF propagation measurements.     

An all-band TV tuner IC with 10-GHz 100-V mixed analog/digital Sibipolar technology

An all-band TV tuner IC with an on-chip PLL and a high-voltage output stage is developed. The use of a self-aligned bipolar technology called high-voltage compatible sidewall base contact structure (HV-SICOS) allows the integration of 1-GHz analog circuits, 1-GHz low-power ECL-I²L PLL circuits, and a 0.5- to 30-V tuning diode bias current on the same chip. The analog block has a VCO and mixer pair for the VHF/CATV and another pair for the UHF bands, a UHF input amplifier, an IF amplifier, and a VCO signal switching circuit. To suppress the digital noise level for mixed analog/digital mode operation, the PLL is constructed with high-speed ECL circuits for divide-by-four and dual modulus prescalers, and low-power I²L circuits. An isolation area is placed between the analog and digital blocks. Conversion gain of 24 dB for VHF/CATV and 33 dB for UHF, a noise figure of 10 dB, and 1% cross modulation of 95 dB-μV are obtained. This IC operates with a total power dissipation of 200 mW on a 3-mm×4-mm chip     

A 65 nm CMOS Multistandard, Multiband TV Tuner for Mobile and Multimedia Applications

This paper presents a direct conversion, multistandard TV tuner implemented on a 65 nm digital CMOS process occupying less than 7 . The tuner is compliant with several digital terrestrial, fixed and mobile TV standards, including DVB-T, DVB-H, T-DMB, and ISDB-T. It achieves a 3/3.2/3.5 dB noise figure at VHF, UHF, and L-band, respectively, while the measured sensitivity at UHF for the QPSK-frac12 DVB-T mode is at the PCB connector. The implemented RF front-ends support both single-ended and differential inputs. An integrated - fractional-N synthesizer operating from 1.2 to 1.8 GHz achieves less than 1 integrated phase error, thus enabling a maximum SNR in excess of 37 dB for VHF and UHF. Multistandard capability is also enabled by programmable channel-select filters. Power consumption is less than 140 mW in DVB-T mode for all three bands.     

AD9858在超短波无线电通信领域中的一种应用

介绍了AD9858在超短波无线电通信领域中的一种应用.基于AD9858设计一种频率合成器,该频率合成器采用"DDS 倍频"的方案,具有相噪低、跳速快等优点,可用于超短波无线电通信系统.     

基于业务的VHF UHF通信可达预测模型

甚高频( VHF),超高频(UHF)通信广泛应用于广播、航空移动和导航等业务中,如何根据不同的业务种类确定其可达距离是实际应用中重要环节.目前,人们对VHF,UHF场强预测有了很深入的研究,但是对完整的VHF,UHF收发系统及噪声影响下的可达距离分析较少,这使得人们在需要预测可达距离时,往往根据经验进行判断,误差较大且不具备实时性.提供了完整系统,根据国际电联(ITU)建议书,预测场强和信噪比,对比相应业务种类,进而得到相应距离上是否可达的预测结果.     

VHF/UHF硅外延电调变容管

本文简述了器件原理,并给出VHF/UHF硅电调变容管的设计结果.WB30系列VHF/UHF硅电调谐变容二极管,其管芯为双外延台式钝化结构,采用金属陶瓷微带管壳封装.制得的器件,其变容比 C_3/C_(25)≥4.5,串联电阻 r≤1.5Ω,截止频率f_c≥12GHz(VHF波段);及r_s≤0.8Ω,f_c≥22GHz(UHF).结果表明WB30型VHF/UHF硅电调变容管已与日本NEC公司的VHF/UHF硅外延平面电调变容管1S2209/1S2208的性能相当.电调变容管的统调特性及其串联电阻直接与电视高频头的增益相关.用WB30型电调变容管制作的UHF频段电视机用高频头——一级高放及一级二极管混频,已获得5～6dB的增益.     

Hologram-based compact range for submillimeter-wave antenna testing

A hologram-based compact antenna test range (CATR) is being developed to overcome challenges met in antenna testing at submillimeter wavelengths. For the first time, this type of CATR has been built for testing of a large reflector antenna at submillimeter wavelengths. The CATR is based on a 3-m computer-generated hologram as the focusing element. This paper discusses the design and the construction of the CATR, and the verification of the CATR operation with quiet-zone tests done for the CATR prior to the antenna testing. Assembly of the CATR, testing of the 1.5-m reflector antenna at 322 GHz, and the disassembly were all done within two months in 2003. The quiet-zone field measurement results are analyzed in this paper. The CATR was concluded to be qualified for antenna testing. The antenna testing is described in a separate paper.     

DSTBC在高速超短波跳频电台中的应用

在简单介绍了差分空时分组码(DSTBC)技术的基础上,结合未来高速超短波跳频电台的发展情况和特点,对DSTBC在未来高速超短波跳频电台中应用的可行性进行了研究和探讨。理论及仿真结果表明,工作为300MHz频率,天线间距0·3m的双天线跳频电台采用差分空时分组码后,其性能增益为12dB,在复杂度增加不多的情况下,大大提高了抗衰落性能。     

Octave-Bandwidth UHF/L-Band Circulator

Test data are presented on two aluminum-substituted yttrium-iron-garnet (YIG) materials that have low-saturation magnetizations that permit the extension of ferrite devices well into the UHF/VHF region. In particular, one composition has a saturation magnetization of 300 gauss and a line width of 50 oersteds. Measurements are presented that compare the new materials with previously available higher-saturation magnetization materials. A broad-band UHF/L-band four-port circulator that operates over a 2-to-1 frequency band has been developed, using this 300 gauss material. Insertion loss is 1 db or less from 665 to 1320 Mc (with constant magnetic field) and 0.5 db or less from 800 to 1150 Mc. A compact and favorable circulator package design was obtained by using coaxial hybrids and dielectric-loaded strip transmission line. Data on the broad-band magic-tee used in the circulator are included. Isolator measurements down to 200 Mc are reported. Reverse-to-forward magnetic-loss ratios of 36 at 600 Mc and 12 at 300 Mc were obtained.