Efficient laser-diode-single-mode-fibre coupling using two confocal lenses

A new method for coupling a laser diode to a single-mode fibre is described. It uses a spherical ruby lens and a g.r.i.n. rod lens, which are positioned nearly under confocal conditions. A high coupling efficiency of more than ?3 dB has been realised, and stringent alignment tolerances required for conventional coupling circuits have been overcome.     

Some results for an r.f.- and p.l.-modulated incoherent carrier

Possibilities of using incoherent carriers, amplitude-modulated by the message-modulated p.f.m., r.f.m. and p.l.m. have been investigated. It has been shown that, for noise bandwidths much smaller than the transmission bandwidth, efficient communication is possible, and s.n.r.s of 50?60dB are obtained for practical p.f.m.-a.m. and r.f.m.-a.m. systems. Some comparisons are also given.     

Quantitative analysis of 2-f.s.k. traffic detection

Two different methods of detecting signal flow in a noncoherent 2-f.s.k. channel are analysed with respect to the necessary signal/noise ratio for a certain error probability. It is found that separate detection of each frequency requires s.n.r. ?18 dB compared to about 19.5 dB for sum detection when the error probability is 10?7.     

Wideband coplanar waveguide-to-rectangular waveguide transition using fin-line taper

This letter introduces a new wideband coplanar waveguide-to-rectangular waveguide transition. The transition uses a uniplanar circuit in line with the waveguide, which eases the design and fabrication. The design does not require airbridges. Simulations and measurements of X-band (8.2-12.4 GHz) transitions based on both a low- and high-permittivity material (/spl epsiv//sub r/= 2.33 and 10.8) show that the transition works fine over the full frequency band. For /spl epsiv//sub r/= 2.33 the measured return and insertion loss of a back-to-back transition are more than 16 dB and less than 0.4dB, respectively. The corresponding values for /spl epsiv//sub r/= 10.8 are more than 10 dB and less than 1.0 dB, respectively, over 90% of the frequency band. The measured insertion loss values indicate losses of less than 0.14 dB and 0.36 dB at the center frequency for a single transition on a substrate with /spl epsiv//sub r/= 2.33 and 10.8, respectively.     

Two-loop ternary adaptive delta modulation

A 2-loop ternary adaptive delta-modulation system is described which produces a peak s.n.r. of 20.5 dB, and for an s.n.r. of 15 dB, its dyamic range is 22dB when the input signal is RC shaped noise band limited to 2.5 kHz and the sampling rate is 8 kHz.     

Coaxial directional couplers with exceptional directivity and v.s.w.r. over wide frequency bands

A design of coaxial directional coupler is described for use in laboratory calibration work in which directivity better than 40 dB and v.s.w.r. better than 1.02 are necessary over wide frequency ranges. The coupling factor varies with frequency in a regular manner, but this is not a serious disadvantage.     

Tunable X band GaAs f.e.t. amplifier

The design of a frequency-tunable X band amplifier using GaAs Schottky field-effect transistors is described. By using a broadband input matching circuit and a frequency-tunable output matching circuit, the gain of 7±0.5 dB obtained from a single-stage amplifier may be varied from 8 to 10 GHz, with corresponding terminal v.s.w.r.s, over any 600 MHz band width, better than 2:1. A single-stage amplifier gives a noise figure of 4.7 dB with a gain of 5.8 dB, and a 2-stage amplifier a 6.0 dB noise figure with 12.5 dB power gain.     

宽带折线栅圆极化器的分析与优化设计

介绍了折线栅圆极器的分析理论和优化设计方法,给出了折线栅等效导纳计算公式的几个待定常系数的确定方法以及在设计频带内的最优常系数值,重新推导了多层折线栅级联网络的传输矩阵的计算公式,修正了文献上公式的错误.基于折线栅圆极化器的分析理论采用遗传算法优化设计了25～35 GHz频带范围内的折线栅圆极化器,并给出了HFSS仿真结果,表明轴比仿真值小于1dB的带宽大于40％,并且插入损耗低,验证了采用的分析和设计方法的有效性.     

A 4?8 GHz dual gate m.e.s.f.e.t. amplifier

A two-stage dual-gate f.e.t. amplifier with small signal gain of 20 ± 0.75 dB, covering an octave bandwidth (4?8 GHz) and having a dynamic gain control range in excess of 60 dB is reported. The gain frequency response, input and output v.s.w.r. are described as a function of second-gate voltage. The performance of the dual-gate f.e.t. amplifier as a fast r.f. switch is also presented.     

Partial correction of transmission errors in d.p.c.m. without recourse to error correction coding

A method for partially correcting transmission errors in a 1st-order d.p.c.m. system, without recourse to channel coding, is described. A simple detection algorithm based on the statistical properties of a sequence of differences between adjacent samples of a modified decoded sequence is used to identify the erroneous samples. Three different correcting algorithms are described. Substantial improvements in the decoded waveform are achieved, and, for a Markov input process, an error rate of 0.04% in the first and second most significant digits, an improvement in s.n.r. of 7dB is achieved.     

Thick-film 3-stage m.i.c. IMPATT diode-amplifier on ferrite

A 3-stage hybrid m.i.c. gallium-arsenide IMPATT-diode amplifier is described with an output of 1.05 W at 9.2 GHz, a large-signal gain of 21 dB and a bandwidth to ?3 dB greater than 1 GHz; the amplifier is stable at all input levels. The concept of an effective radius, first proposed to explain the properties of disc capacitors, has been used successfully in the circulator design. Close attention has been paid to screening the unencapsulated diodes to prevent r.f. radiation and to incorporating resistive-loading circuits to suppress spurious out-of-band oscillations.     

High-power pulsed and c.w. silicon double-drift IMPATT amplifiers at X-band

The letter presents some reflection-amplifier results for Si double-drift pulsed and c.w. IMPATTs. Peak r.f. powers of up to 11.6 and 16.5 W with instantaneous (?1 dB) bandwidths ~20% at gains >6 dB have been obtained at 10 GHz with 1- and 2-diode combinations when bias modulated with a pulsewidth of 4 ?s and p.r.f. of 1 kHz. A 2-diode c.w. combination has given a power of 7 W (c.w.) at 10.7 GHz with a gain of 6.5 dB and instantaneous (?1 dB) bandwidth of 400 MHz.     

GaAs m.e.s.f.e.t. linear power-amplifier stage giving 1 W

A balanced GaAs m.e.s.f.e.t. power stage has been developed for the 7?8 GHz satellite communication frequency band. At 7.5 GHz, the output power at 1 dB comparession 1 W with a power added efficiency of 37%. The small-signal gain was 6.65 ± 0.45 dB across the frequency band. The small-signal gain, phase, group delay and input and output v.s.w.r. as function of frequency are described. Large-signal gain saturation and 3rd-order intermodulation distrotion measurements are also presented.     

A new circuit topology for continuous group delay synthesis

A new circuit topology is realized in order to synthesize group delay continuously. The circuit is based upon a new variable coupling coefficient coupled line section and a microstrip feedback loop. The new variable coupler is designed by periodically loading an edge coupled microstrip coupler. With this new design, coupling variation of more than 10 dB may be achieved. To the best of the authors knowledge, this is the first report of this type of microstrip coupler. The complete circuit consumes no do power and exhibits more than 500 ps of continuous variable true time delay. Insertion loss is better than 3 dB and return loss is better than 15 dB     

Effect of laser noise on analogue fibre optic systems

A simple theory taking into account both source noise and receiver noise contribution to the s.n.r. performance of analogue fibre optic systems is derived and experimentally verified. Experiments indicate that high quality a.m.-v.s.b. video transmission (s.n.r. > 60 dB) is not feasible with state-of-the-art gain-guided laser diodes.     

Zener-diode noise generators

Zener diodes operated in the breakdown region have been investigated as transfer noise standards in the r.f. region. A close correlation has been found between the variation in excess noise ratio (e.n.r., dB) and the temperature coefficient of Zener diodes. In particular, diodes having zero temperature coefficient of voltage also have zero temperature coefficient of e.n.r.     

Large-core high n.a. fibres for data-link applications

High-n.a. fibres are required for optical-fibre data links. A germania-silica-core/silica-clad fibre has been produced by an alteration to the m.c.v.d. process, by the use of helium as a lining agent and the addition of P2 O5 to the core, with a measured n.a. of 0.38 and an attenuation of less than 5 dB/km at 0.89 ?m wavelength.     

2~4 GHz宽带高效率功放的设计

针对宽带高效率功放的设计要求,基于宽带匹配网络设计了一款GaN宽带高效率功率放大器,其工作频率覆盖整个S波段。仿真结果显示,该功放在整个S频段内漏极效率(DE)大于62%,功率附加效率(PAE)大于57%,增益大于10.6 dB。实测结果表明,该功放在整个频段内DE大于54%,PAE大于48%,增益大于9 dB,增益平坦度在1 dB以内,实现了S波段高效率宽带功率放大器的设计。     

A broadband Ka-band microstrip circulator for integrated millimeter wave systems

A Ka-band microstrip circulator, using ferrite with 4π M=5000 G, have been developed. By optimizing the circulator configuration, broadband n=2 Chebyshev response performance are obtained over 7 GHz bandwidth. The circulator have isolation of greater than 15 dB, and insertion loss of less than 1.0 dB.     

Iterative demodulation, demapping, and decoding of coded non-square QAM

It is shown that a non-square (NS) 2/sup 2n+1/-ary quadrature amplitude modulation (QAM) can be decomposed into a single parity-check (SPC) block encoder and a memoryless modulator in such a way that the inherent block encoder has a recursive nature. When concatenated with a forward-error-correcting (FEC) code, iterative demodulation, demapping, and decoding of the FEC code and the inherent SPC code of NS-2/sup 2n+1/-QAM is then possible. Simulation results show that coded NS-8QAM performs nearly 2 dB better than standard 8QAM and star-8QAM, and nearly 1 dB better than 8-ary phase-shift keying when the FEC code is a rate-1/2, 16-state convolutional code, while coded NS-32QAM performs 0.75 dB better than standard 32QAM.