Design of a 74-MHz antenna for radio astronomy

Describes the design and construction of an 8000 m² 74-MHz phased array dedicated to measurement of the solar-wind velocity using the interplanetary scintillation (IPS) technique, and a simple and novel autocalibration system that measures and connects phase and amplitude errors to a level of 1° and 0.2 dB rms. In the IPS technique, intensity fluctuations of compact radio sources caused by plasma turbulence in the solar wind are observed with multiple antennas. The time lag between the antennas is estimated using a cross-correlation analysis. The primary requirement of such a system is sensitivity so that one may observe a large number of compact sources. A secondary requirement is high beam efficiency so that one may observe near the Sun. The scan angle was limited to allow the largest possible array element and thus the simplest feed system. The feed was designed to have independent phase and amplitude control of each element. Although this is not strictly necessary it permits the use of the feed as a phase switched interferometer with which any element can be correlated against any other group of elements. This provides a simple and accurate calibration of the entire array. The antenna was completely prefabricated, the site preparation was minimal, and the installation was quick and accurate. The system is remotely operated. The control information, system diagnostics, and data are transmitted over a leased telephone line. The entire system is powered by storage batteries charged by solar cells. In addition to IFS it has been used extensively for pulsar observations which have similar requirements     

A system plan for a 900-MHz portable radio telephone

The system concepts for a high capacity personal radio telephone system are described. Previous systems for mobile radio telephone service have been based on a rigid assignment of frequencies to specific small geographic areas within the total coverage area. This approach has led to conservative geographic frequency reuse constraints and the requirement for accurate location techniques in the system. Through the utilization of the power imbalance that exists in the proposed portable radio telephone system between base and portable unit transmitters these constraints are eliminated. It will be shown how this power imbalance allows the selection of the optimum signal for the portable unit and relaxed requirements on location and reuse of frequencies. The required signal-to-interference ratios must be obtained within a design reliability level over the coverage area. Computer simulation of the frequency reuse plan and the propagation variability over the area indicates the nominal repeat intervals necessary as a function of this reliability level. A reuse plan that obtains the required repeat intervals with a high degree of spectral efficiency, through the combined use of geographic and frequency separation, will be presented. This system called tertiary offset, achieves a significant increase in interference protection by splitting each channel into a group of three channels and utilizing each subgroup in a different pattern of reuse over the area. The improvement due to this plan will be shown.     

Superconductor digital RF development for software radio

We review a new “direct digitization” approach for “digital RF” architectures for software radio. Although direct digitization usually implies the simultaneous digitization of all channels in a particular band at a downconverted IF, we use this term to refer exclusively to the direct digitization of all bands, from near DC to RF. Furthermore, we present results on band selection and digitization of RF signals directly at the carrier frequency with high resolution. These novel approaches are enabled by a superconductor analog-to-digital converter technology using an ultra-fast IC logic known as Rapid Single Flux Quantum (RSFQ) logic, with performance capable of enabling envisioned software radios     

Compact bandpass filters for 800-MHz band land mobile radio equipments

Compact bandpass filters for 800-MHz land mobile radio equipment has been developed using coaxial resonators with a high dielectric constant material of εr= 35. The use of dielectric material of high Q and a dielectric substrate for coupling capacitors made possible the construction of compact low-insertion-loss filters. The performance characteristics of these filters are described.     

A 200-MHz sub-mA RF front end for wireless hearing aid applications

A hearing-aid system with RF connection between both ear-pieces is described and its transceiver is introduced. A suitable 200-MHz RF front end has been implemented in a 0.8-μm BiCMOS technology. Low power consumption and area constraint were key requirements. The chip comprises a low noise amplifier (LNA), a single balanced mixer, a varactor tuned LC local oscillator with buffer and a 16/17 dual-modulus prescaler. The LNA has a measured gain of 17.5 dB at 200 MHz. The conversion g_m of the mixer is 1.88 mS. The overall voltage gain and noise figure are 26 dB and 5.2 dB, respectively. The voltage-controlled oscillator's (VCO's) phase noise is -104.7 dBc/Hz at an offset of 24 kHz     

软件无线电跳频电台接收机射频前端设计

基于软件无线电的基本要求和发展趋势,提出了一种应用在软件无线电跳频电台中接收机射频前端电路结构,分析了接收机射频前端的总体设计方案,包括前端各部分增益的分配、动态范围的分配、噪声系数及灵敏度的计算,讨论了对器件选择的考虑.实际测试结果表明,该射频前端性能指标满足设计要求.     

一种电流复用共栅低噪声放大器的低功耗433/915-MHz射频前端的设计

This paper presents a wideband RF front-end with novel current-reuse wide band low noise amplifier(LNA),current-reuse V –I converter,active double balanced mixer and transimpedance amplifier for short range device(SRD) applications.With the proposed current-reuse LNA,the DC consumption of the front-end reduces considerably while maintaining sufficient performance needed by SRD devices.The RF front-end was fabricated in 0.18 μm RFCMOS process and occupies a silicon area of just 0.11 mm2.Operating in 433 MHz band,the measurement results show the RF front-end achieves a conversion gain of 29.7 dB,a double side band noise figure of 9.7 dB,an input referenced third intercept point of –24.9 dBm with only 1.44 mA power consumption from 1.8 V supply.Compared to other reported front-ends,it has an advantage in power consumption.     

基于软件无线电跳频电台射频前端的研究

基于软件无线电的基本要求和发展趋势,提出了一种应用在软件无线电跳频电台中宽频段接收机的前端电路设计方案,分析了接收机射频前端二次混频方案结构的可行性,在对方案中各功能模块研究分析的基础上,完成了射频前端的滤波嚣、混频器、放大器等各模块的设计工作,并对整个系统进行了建模设计和仿真验证.仿真结果表明,接收机前端电路噪声系数...     

Broadband RF stage architecture for software-defined radio inhandheld terminal applications

Broadband RF is a general-purpose common RF stage for every standard within a set of RF bands. The RF stage architecture presented in this article is suitable for software-defined radios. This article first defines the conceptual scheme of a handheld software defined radio (SDR) terminal, and then describes how the direct conversion principle is applied to the SDR. The discussion focuses on receiver hardware implementation and systematic control     

A low EVM zero-IF RF transmitter for cognitive radio application

A zero-IF transmitter for Cognitive Radio (CR) application is presented. To effectively reduce the interference between Power Amplifier (PA) and Voltage Controlled Oscillator (VCO), two VCOs are adopted, one is 450 MHz and the other is from 1148 MHz to 1252 MHz with an 8 MHz step, so the frequency of them are different from the operational frequency of PA. The Local Oscillator (LO) of the modulator generated by mixing the signals of the two VCOs has a low phase noise of −82 dBc/Hz with an offset of 1 kHz. The measurement result of the transmitter shows that the Adjacent Channel Power Ratio (ACPR) is less than −47.5 dBc at 27 dBm output, and the Error Vector Magnitude (EVM) is less than 1.7%.     

基于软件无线电跳频电台射频前端的研究

基于软件无线电的基本要求和发展趋势,提出了一种应用在软件无线电跳频电台中宽频段接收机的前端电路设计方案,分析了接收机射频前端二次混频方案结构的可行性,在对方案中各功能模块研究分析的基础上,完成了射频前端的滤波器、混频器、放大器等各模块的设计工作,并对整个系统进行了建模设计和仿真验证。仿真结果表明,接收机前端电路噪声系数低,镜像抑制良好,增益合理,选择性合适,均满足设计要求。     

RF direct orthogonal phase under-sampling technique for software defined radio

A novel under-sampling technique that has the same effect as using RF direct sampling is proposed. Simulation and an experiment to prove its validity have been carried out.     

Multipath delay spread and path loss correlation for 910-MHz urban mobile radio propagation

Performance of some mobile radio systems is limited both by multipath delay spread and average path loss. This paper presents data indicating a low correlation between delay spread and path loss at 910 MHz for 100 small areas within a 2 × 2 ½-km region. Some small areas with low path loss have large delay spread. The region extends from 1.5 to 3.5 km from a base station on a 120-m high building in New York City. The region is representative of heavily built-up downtown districts of many large U.S. cities.     

A 6 × 320-MHz 1024-channel FFT cross-spectrum analyzer for radio astronomy

A wide-band FFT spectrum analyzer, which we call FX, has been in operation since 1983 at the Nobeyama Radio Observatory for spectroscopy of radio waves from interstellar molecules. It processes an input of six 320-MHz-bandwidth data streams to produce the output of fifteen cross-power spectra of 1024 frequency channels each. Its highly parallel pipeline architecture made it possible to achieve the above speed, 10¹⁰butterfly operations per second, which is 10⁵times that of usual mainframe computers. The FX incorporates about 4500 newly developed CMOS LSI chips. They are designed using CAD (computer-aided design) and have 3900 or 2000 gates/chip, operate at a clock rate of 10 MHz, and consume 100 mW/chip or less. For 80-MHz bandwidth signal at an optimum input level, the SNR (signal-power to noise-power ratio) of the FX is better than 10 dB, which is adequate for astronomical use.     

Distributions of multipath delay spread and average excess delay for 910-MHz urban mobile radio paths

Distributions of average excess delay and delay spread for Gaussian wide-sense stationary uncorrelated scattering channels associated with 100 small scale areas at different locations within a2 times 2.5-km region of New York City are presented. For delay spread the mean is1.3 mus, the standard deviation is0.6 mus, the maximum value observed is3frac{1}{2}mus, and 10 percent of the areas exceeded2frac{1}{2} mus; for average excess delay the mean is1.1 mus, the standard deviation is0.9 mus, the maximum is4 mus, and 10 percent of the areas exceeded2 mus. The region is representative of the heavily built-up areas of many large cities in the United States.     

Optimization of energy efficiency for cognitive radio with partial RF energy harvesting

The cognitive radio (CR) with energy harvesting is a potential technology to improve both the spectrum efficiency (SE) and the energy efficiency (EE). In this letter, we consider that the secondary users can harvest radio frequency (RF) energy from primary signal and its own signal. The goal is to maximize the energy efficiency of the CR system subject to sufficient protection to the primary user and the power constraint. An efficient algorithm is proposed to optimize the sensing time and the power of the secondary transmitter. Simulation results show that the EE is further improved by using the proposed mechanism.     

The performance of a new 915-MHz direct contact applicator with reduced leakage

The technical feasibility of commercially developing a safe and effective direct contact diathermy applicator operating at the industrial, scientific, medical (ISM) frequency of 915 MHz is demonstrated. The basic design consists of a circular waveguide which is internally loaded with two orthogonal pairs of forward ridges to obtain circular polarization and two rear ridges with a probe to excite the guide. Two prototype designs are considered: the small applicator (15 cm diameter) has one annular choke covered with a 2.5-cm thick microwave absorber, and the large applicator (25 cm diameter) has two additional concentric chokes to limit leakage radiation. The performance of the applicators was evaluated in terms of the requirements of a ORH microwave diathermy test protocol to control stray radiation and deliver a thermally effective absorbed dose rate to simulated muscle tissue of a phantom with a 1-cm or 2-cm fat layer. The net power required to deliver a thermally effective 235-W/kg specific absorption rate (SAR) to such a planar phantom was determined. For this net power, leakage levels considerably less than 5 mW/cm2 (at 5 cm from applicator-phantom boundary) were obtained for the applicators in direct contact with the phantom. If a small spacing (1 cm) between these applicators and planar phantoms is introduced, the net power required to deliver an effective SAR to a phantom and the associated leakage can become excessive. For the small applicator, the required net power for inducing an SAR of 235 W/kg in muscle tissue of a 1-cm fat layer phantom is about 330 W and the leakage is about 120 mW/cm2. For a 2-cm fat layer phantom, these values are somewhat higher. For the large applicator, using a 1-cm fat layer phantom, the values are about 200 W and about 17 mW/cm2. Again, for a 2-cm fat layer phantom, these values are somewhat higher.     

RF performance of diamond MISFETs

A cutoff frequency (f_T) of 11 GHz is realized in the hydrogen-terminated surface channel diamond metal-insulator-semiconductor field-effect transistor (MISFET) with 0.7 μm gate length. This value is five times higher than that of 2 μm gate metal-semiconductor (MES) FETs and the maximum value in diamond FETs at present. Utilizing CaF₂ as an insulator in the MIS structure, the gate-source capacitance is reduced to half that of the diamond MESFET because of the gate insulator capacitance being in series to the surface-channel capacitance. This FET also exhibits the highest f _max of 18 GHz and 15 dB of power gain at 2 GHz. The high-frequency equivalent circuits of diamond MISFET are deduced from the S-parameters obtained from RF measurement     

Amorphous SiC as a structural layer in microbridge-based RF MEMS switches for use in software-defined radio

This paper reports an effort to develop amorphous silicon carbide (a-SiC) films for use in shunt capacitor RF MEMS microbridge-based switches. The films were deposited using methane and silane as the precursor gases. Switches were fabricated using 500 nm and 300 nm-thick a-SiC films to form the microbridges. Switches made from metallized 500 nm-thick SiC films exhibited favorable mechanical performance but poor RF performance. In contrast, switches made from metallized 300 nm-thick SiC films exhibited excellent RF performance but poor mechanical performance. Load-deflection testing of unmetallized and metallized bulk micromachined SiC membranes indicates that the metal layers have a small effect on the Young’s modulus of the 500 nm and 300 nm-thick SiC MEMS. As for residual stress, the metal layers have a modest effect on the 500 nm-thick structures, but a significant affect on the residual stress in the 300 nm-thick structures.