Beam scan using the quasi-optical antenna mixer array

The quasi-optical antenna mixer system transforms an RF signal into an intermediate frequency signal just after it spatially receives the RF signal and the local oscillator's (LO) signal. In this paper, we present a novel beam scanning system using the quasi-optical antenna mixer array and describe its principle of operation and the experimental results in the microwave band. The arrival direction of RF signals can be controlled by adjusting the LO incident angle and/or the LO frequency without implementing RF circuits such as phase shifters. Therefore, the novel beam-scanning system has no loss due to RF circuits and can be easily designed because of its simple composition     

Adaptive hybrid free space optical/radio frequency communication system

Wireless communication has achieved lot of attention and the demand is continually increasing day by day. Radio frequency (RF) is highly attracted by various wireless communication applications. The RF spectrum is already very crowded and the rapid increase in the use of wireless services has led the problems of RF spectrum exhaustion and eventually RF spectrum deficit. Free space optical (FSO) communication is a viable technology with a plenty of bandwidth, license-free spectrum and interference free link. On the other hand, FSO channel is severely corrupted by atmospheric turbulence and non-predictive weather scenarios. We suggest a hybrid FSO/RF communication system in our previous research, which can mitigate the issues of the individual links. In this research, we investigate the performance of the proposed adaptive system for reliable data transmission. We develop modulation and power adaptive schemes for maximizing the mutual information. The proposed adaptive system is compared with non-adaptive system, which gives 2.75 dB gain for the joint power and 0.75 dB gain for the separate power constraint.     

Bandwidth-reduced Brillouin optical time-domain analysis based on a quarter of the frequency of modulation

Aiming at the problem of high requirement for the signal generator in the Brillouin optical time-domain analysis(BOTDA) system, a quarter of the Brillouin frequency shift(BFS) of modulation is proposed to reduce the required bandwidth of the sensing system. A functional model for solving the intensity of each-order sideband of the output light of electro-optic modulator(EOM) is proposed and applied, so the spectrum with suppressed the carrier and the first-order sidebands while maximizing the se...     

超宽带射频接收机的研制

超宽带(UWB)短距离无线通信技术是当前国内外研究的热点,直接序列超宽带(DS-UWB)方案和多带－正交频分复用(MB-OFDM UWB)方案是两个主要候选方案,其中多带-正交频分复用方案是较受重视的方案.本文针对MB-OFDM UWB系统,提出了一种双载波-正交频分复用(DC-OFDM UWB)的射频解决方案.该方案采用了两个相邻的子载波实现宽带通信,两个子载波是在中频部分采用合路/分路的方式,以降低硬件实现难度和系统的复杂度.设计了UWB射频接收机中的低噪声放大器(LNA)、频率合成器和解调器等关键部件,并建立了DC-OFDM UWB接收机实验演示平台.测试结果表明,研制的射频接收机满足FCC规定的射频指标要求,该方案也适用于其它的宽带通信系统中.     

A Quadrature Modulation Transmitter Using Two Frequency Synthesizers

This brief analyzes a novel quadrature modulation transmitter architecture. The proposed architecture consists of only two frequency synthesizers, thereby reducing the RF and analog components such as RF mixer, analog filter, and digital-to-analog converter. Simulation results show that the bit-error rate and the spectral efficiency of the proposed method are close to those of conventional quadrature modulation scheme. The quadrature modulation transmitter can be implemented fully digitally through the proposed architecture if the all-digital frequency synthesizer is used. [All rights reserved Elsevier].     

Demonstration of photonically controlled GaAs digital/MMIC for RFoptical links

We report design, fabrication, and test of a monolithic GaAs optoelectronic integrated circuit (OEIC) implementing a broad-band optically driven digital/analog radio frequency (RF) interface. The integrated circuit (IC) was fabricated using a foundry-compatible enhancement/depletion metal-semiconductor field-effect transistor (MESFET) process with no added lithography steps. A single optical fiber carries externally amplitude modulated 0.85-μm light to the on-chip GaAs metal-semiconductor-metal interdigitated photodetector. RF as well as simultaneous digital information encoded at up to 10 Mb/s using a novel waveform set is transmitted over the fiber. The serial digital data is self-clocked into on-chip registers to control the RF signal chain, which includes a three-bit digital attenuator. The circuit operates in an asynchronous mode to detect digital and RF on the single optical-fiber input, control RF level, and transmit the 2-8-GHz RF to the IC's electrical output. Measurements characterizing the RF and digital performance of the IC as well as a demonstration of the full optoelectronic mixed-mode functioning of the IC are presented     

一种宽频压控振荡器及高速双模预分频器的设计与实现

针对射频无线收发机的需求,利用开关电容阵列和多个VOD核的结构设计了一个分段线性超宽频压控振荡器(VCO).采用全电流模逻辑(CML)结构的双模预分频器能满足振荡器最高频率输出的要求.基于IBM 0.35SiGe BiCMOS工艺的流片测试结果表明,电源电压为2.8V时,该压控振荡器的频率能够覆盖2.75～5.73GHz的频段,调频灵敏度约为100MHz/V,在偏离中心频率1MHz处,单边带相位噪声最佳值达到了-120.32 dBc/Hz,预分频器后仿最高工作频率达9.6GHz,两部分核心总工作电流为10mA.     

Equal-gain loci and stability of a microwave GaAs MESFET gate mixer

The performance of a microwave GaAs MESFET gate mixer is theoretically investigated to clarify the existence of a conditionally stable RF frequency range as well as an unconditionally stable frequency range in which maximum available conversion gain (MACG) can be defined. For the unconditionally stable range, the MACG and load and source impedances are calculated as functions of RF frequency. For the conditionally stable range, the stability circle and equal gain loci are shown for source RF and load IF impedances. The conditionally stable region of the GaAs MESFET mixer appears around F_T of the MESFET. Higher conversion gain is easily obtained by choosing a MESFET for which the F_T is close to the RF frequency     

A 20 GHz microwave sampler

A microwave sampler circuit which operates over the frequency band of 1-20 GHz and has a number of novel features is described. These features include a wideband microstrip-to-slot balun and a wideband active isolator the function of which is to reduce the local oscillator to RF leakage from the input port of the sampler. The signal-to-noise ratio over the input bandwidth is greater than 20 dB at an input power level of -32 dBm. This signal-to-noise ratio was measured in an IF bandwidth of 175 MHz and includes the contribution from the IF amplifier. The sampler, which is made on alumina using MIC techniques, has an integrated impulse generator driven with a sinusoidal local oscillator of only 20 dBm over the frequency band of 250-350 MHz. The IF signal is in the 10-175-MHz band. The RF input VSWR is better than 2:1 up to 20 GHz, and the oscillator to RF breakthrough is better than -58 dBm (-78 dBc) when driven with a local oscillator of 20 dBm. This unusually low leakage was achieved by using the active isolator prior to the sampling circuit     

Direct downconversion of multiband RF signals using bandpass sampling

Abstract-Bandpass sampling can be used by radio receivers to directly digitize the radio frequency (RF) signals. Although the bandpass sampling theory for single-band RF signals is well established, its counterpart for multiband RF signals is relatively immature. In this paper, we propose a novel and efficient method to find the ranges of valid bandpass sampling frequency for direct downconverting multiband RF signals. Simple formulas for the ranges of valid bandpass sampling frequency in terms of the frequency locations of the multiple RF bands are derived. The result can be used to design a multiband receiver for software defined radios.     

Photonic generation of BFSK RF signals based on optical pulse shaping

A novel method to generate binary frequency shift-keying(BFSK) radio frequency(RF) signals in optical domain is proposed.In the proposed system,an optical short pulse train is converted into super-Gaussian RF pulses with high frequency based on optical pulse shaping by two Mach-Zehnder fiber interferometers(MZIs).And the generated RF signals are coded using a fast electro-optic switch.By properly designing the MZIs,BFSK RF signals with desired code pattern and modulation index can be generated.A theoretical model for describing the system is developed,and the generation of BFSK RF signals in millimeter-wave regime is demonstrated via simulations.     

Continuously tunable photonic radio-frequency notch filter

We present a continuously tunable nonrecursive radio-frequency (RF) photonic filter. The filter provides fine tuning through the use of a novel RF phase shifter and coarse tuning using an an optical variable time delay. This architecture permits wide-band continuous tuning of the filter null frequency and is useful in applications such as moving target indication (MTI) in an airborne radar.     

Low-Cost Specification Based Testing of RF Amplifier Circuits using Oscillation Principles

In this paper, we propose a low-cost approach for testing GHz RF amplifiers. It is demonstrated for the first time that GHz RF amplifiers can be tested for their specifications using oscillation principles. In the test mode, the RF test signal is “self generated” by the amplifier with the help of additional external circuitry which forces the amplifier to oscillate (Barkhausen criterion) around its characteristic frequency. The RF sinusoidal output from the oscillating RF amplifier is down-converted to a lower frequency enabling low frequency test response analysis as well as increased sensitivity to parametric deviations. In addition to the detection of catastrophic failures, it is shown that multiple RF specifications (Gain, P1dB, and Noise Figure) can be predicted via analysis of the frequency of the down-converted response. To account for RF parasitics on the production floor, a calibration technique is proposed in the test-setup. Thus, the proposed method reduces test cost significantly by reducing the cost of test setup (by as much as 80%) and significantly reducing test time. The viability of the proposed test method is demonstrated both by simulation experiments and measurement.     

2kW射频板条CO2激光器射频频率漂移特性研究

为了研究射频板条CO2激光器射频频率波动对输出光束的影响,采用等效电路分析和实验测量的方法研究了射频频率对激光器输入输出特性的影响。计算得到射频频率变化2MHz时引起的阻抗实部变化率为0.01%,说明射频频率漂移对放电部分等效电路参量影响很小。射频频率采用79.4MHz,80.0MHz,80.7MHz,81.4MHz,82.0MHz和82.7MHz,以设计频率81.4MHz对应的输出功率为基准,占空比设置为80%时,频率漂移1MHz则激光功率下降约150W。激光功率随频率变化趋势与理论结果一致。结果表明,射频频率变化引起的阻抗匹配问题是导致输出功率波动的主要原因,可以通过改进匹配网络来克服射频频率的波动对激光器性能的影响。     

Some properties of radio frequency gas discharges in air at atmospheric pressure

Measurements were made on steady-state gas discharges maintained by RF power in air at atmospheric pressure. The frequency range 1-30 MHz was covered. It was found that these discharges operate as either RF glow or RF arc discharges. The characteristics of each are very similar to those of the corresponding dc discharge types. These RF discharges are quenched after each half-cycle and must be reignited in the following half-cycle. The minimum voltage for reignition is about 350 V. After reignition the discharge voltage is high (≥275 V) for glows and low (≥30 V) for arcs. The discharge type can alternate with polarity. The resulting asymmetric voltage-current characteristic can cause rectification. By their non-linear behavior discharges can produce high-order harmonics of the frequency at which they are maintained. These discharge properties account for various interference problems caused by parasitic RF discharges in the vicinity of high-power RF transmitters.     

Analysis of high speed p-i-n photodiode S-parameters by a novel small-signal equivalent circuit model

A novel small-signal radio frequency (RF) equivalent-circuit of the side-illuminated input tapered waveguide-integrated p-i-n photodiodes (WG PIN PD) is proposed. The proposed RF equivalent-circuit involves both the carrier-transit effect and the external resistance-capacitance (RC) time constant limitation on the frequency response of the p-i-n PD. The carrier-transit effect is realized by adding an RC circuit to an ideal voltage-controlled current source as the input opto-RF equivalent circuit. The carrier transit-time effect is equivalently represented by the time-constant of this input RC circuit. This new equivalent circuit model fits well with both the measured reflection and optoelectronic conversion parameters of the WG PIN PD in a broad frequency range from 45 MHz to 50 GHz.     

Variable-phase-shift-based RF-baseband codesign for MIMO antenna selection

We introduce a novel soft antenna selection approach for multiple antenna systems through a joint design of both RF (radio frequency) and baseband signal processing. When only a limited number of frequency converters are available, conventional antenna selection schemes show severe performance degradation in most fading channels. To alleviate those degradations, we propose to adopt a transformation of the signals in the RF domain that requires only simple, variable phase shifters and combiners to reduce the number of RF chains. The constrained optimum design of these shifters, adapting to the channel state, is given in analytical form, which requires no search or iterations. The resulting system shows a significant performance advantage for both correlated and uncorrelated channels. The technique works for both transmitter and receiver design, which leads to the joint transceiver antenna selection. When only a single information stream is transmitted through the channel, the new design can achieve the same SNR gain as the full-complexity system while requiring, at most, two RF chains. With multiple information streams transmitted, it is demonstrated by computer experiments that the capacity performance is close to optimum.     

Balanced RF Duplexer with Low Interference Using Hybrid BAW Resonators for LTE Application

A balanced RF duplexer with low interference in an extremely narrow bandgap is proposed. The Long‐Term Evolution band‐7 duplexer should be designed to prevent the co‐existence problem with the WiFi band, whose fractional bandgap corresponds to only 0.7%. By implementing a hybrid bulk acoustic wave (BAW) structure, the temperature coefficient of frequency (TCF) value of the duplexer is successfully reduced and the suppressed interference for the narrow bandgap is performed. To achieve an RF duplexer with balanced Rx output topology, we also propose a novel balanced BAW Rx topology and RF circuit block. The novel balanced Rx filter is designed with both lattice‐ and ladder‐type configurations to ensure excellent attenuation. The RF circuit block, which is located between the antenna and the Rx filter, is developed to simultaneously function as a balance‐to‐unbalance transformer and a phase shift network. The size of the fabricated duplexer is as small as 2.0 mm × 1.6 mm. The maximum insertion loss of the duplexer is as low as 2.4 dB in the Tx band, and the minimum attenuation in the WiFi band is as high as 36.8 dB. The TCF value is considerably lowered to ?16.9 ppm/°C.     

An Ultra-Broadband Doubly Balanced Monolithic Ring Mixer for Ku- to Ka-band Applications

A novel 12-40 GHz ultra-broadband doubly balanced monolithic ring mixer with a small chip size covering the Ku- to Ka-band applications implemented by a 0.15-mum pseudo- morphic high electron-mobility transistor process is presented. The proposed mixer consists of two spiral transformer baluns and a band-reject filter. The use of the spiral baluns leads to the achievement of a chip size less than 0.8 times 0.8 mm². The radio frequency (RF) spiral balun with a band-reject filter served by an L-C resonator is used to improve the bandwidth of the mixer and to provide an output port for the intermediate frequency (IF) extraction as well. The mixer exhibits a 6-12 dB conversion loss, high isolation over 12-40 GHz RF/local oscillation bandwidth, a DC-8 GHz IF bandwidth, and a 1-dB compression power of 14 dBm for both down- and up-converter applications.     

Noise in SiGe HBT RF Technology: Physics, Modeling, and Circuit Implications

This paper presents an overview of the physics, modeling, and circuit implications of RF broad-band noise, low-frequency noise, and oscillator phase noise in SiGe heterojunction bipolar transistor (HBT) RF technology. The ability to simultaneously achieve high cutoff frequency (f/sub T/), low base resistance (r/sub b/), and high current gain (/spl beta/) using Si processing underlies the low levels of low-frequency 1/f noise, RF noise, and phase noise of SiGe HBTs. We first examine the RF noise sources in SiGe HBTs and the RF noise parameters as a function of SiGe profile design, transistor biasing, sizing, and operating frequency, and then show a low-noise amplifier design example to bridge the gap between device and circuit level understandings. We then examine the low-frequency noise in SiGe HBTs and develop a methodology to determine the highest tolerable low-frequency 1/f noise for a given RF application. The upconversion of 1/f noise, base resistance thermal noise, and shot noises to phase noise is examined using circuit simulations, which show that the phase noise corner frequency in SiGe HBT oscillators is typically much smaller than the 1/f corner frequency measured under dc biasing. The implications of SiGe profile design, transistor sizing, biasing, and technology scaling are examined for all three types of noises.