摘要:

The measurement of incoherent radar-echo powers much smaller than receiver noise can be achieved by using long-period postdetector integration.Suitable very stable integrators usually operate by integrating over successive discrete periods, ‘dumping’ the total and restarting at the end of each period. This behaviour is different from that of the continuous integrator of the ‘sliding rectangular window’ type, which may be considered as a passive low-pass filter. In the discrete-interval integrator the ‘dumping’ phase is independent of the signal and the filtering analogue is not clear.It is shown that the signal/noise improvement produced by the discrete-interval integrator may be calculated by sampling theory, taking into account the continuously varying nature of the signal. Integration over periodstais found to produce the same improvement as a low-pass filter of equivalent noise cutoff frequency 1/2ta.The relationship between the sampling and filtering approaches is studied, and methods are derived for calculating the reduction of detectable receiver input echo power for c.w. radars and for pulse radars having range gates narrower and wider than the pulse width.The effect of the i.f. filter response on the improvement produced by an integrator is illustrated by examples.

DOI:10.1049/piee.1965.0148

出版商:IEE    

年代:1965

数据来源: IET

摘要:

Measurements of the amplitude probability distributions of atmospheric radio noise in a power bandwidth of approximately 400c/s, made at the Radio Research Station, Singapore, from September 1958 to July 1960, are presented for frequencies of 24 kc/s, 145 kc/s, 11 Mc/s and 20 Mc/s. Results are normalised to the r.m.s. amplitude to show the diurnal and seasonal variations of noise structure.The temporal variations in parameters derived from the distributions are also illustrated and the results explained by reference to the prevailing meteorological and ionospheric conditions. Parameters relating to noise amplitude are the mean power and the average value of the noise-envelope voltage; those relating to noise structure are the ratio of the r.m.s. to the average value and the dynamic range.The programme of measurements was similar to that made at the Radio Research Station in England during the International Geophysical Year. Wherever possible, the Singapore data are compared with the corresponding results for England.

DOI:10.1049/piee.1965.0149

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The considerations leading to the development of secondary surveillance radar (s.s.r.) for air-traffic control are listed. The evolution of s.s.r. is described from a simple responder capable of operation with primary radar to a complex system employing special frequencies and coding facilities on the ground-to-air and air-to-ground channels. The evaluation at London Airport of a relatively simple independent s.s.r. system in 1954 and 1956 and subsequent international discussions on the subject led to standardisation of system characteristics in 1957 by the International Civil Aviation Organisation (ICAO). Development of a British system designed to satisfy all the ICAO requirements was finished at the end of 1960 and was evaluated at London Airport during 1961. It was concluded that this system could reliably form the basis of an air-traffic-control radar recognition system. An experimental height-transmission equipment employing the air-to-ground coding system is described, and requirements for future system development are outlined.

DOI:10.1049/piee.1965.0150

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The characteristics of a new travelling-wave aerial (consisting of a conventional zigzag aerial to which a conducting mast is connected at alternate crossover points) are described. Electrical performance is improved, with regard to operating bandwidth, for two versions of this aerial, and, in one case, v.s.w.r. also is improved. Both aerials are mechanically stronger than the simple zigzag aerial.

DOI:10.1049/piee.1965.0151

出版商:IEE    

年代:1965

数据来源: IET

摘要:

A perfectly conducting, infinitely long cylindrical wire of radiusasurrounded by an insulating layer of a cylindrical sheath of free space of radiusbis immersed in a homogeneous, warm plasma of infinite extent. Using the linearised plasma theory and approximate boundary conditions, the dispersion equation for the propagation coefficient along the wire is derived. The numerical solution of the dispersion equation for a wide range of values for the radius of the cylindrical wire and the width of the insulating sheath shows that the propagation coefficient along the cylindrical wire is close to that of the plasma mode in an unbounded plasma, in the frequency range for which the electromagnetic and the plasma space waves are excited, that is for frequencies above the plasma frequency. It is therefore concluded that, for a finite antenna immersed in a warm plasma without or with an insulating sheath, it is appropriate to include in the approximation for the current distribution along the antenna a part which has the propagation coefficient of the order of magnitude of the plasma wave.

DOI:10.1049/piee.1965.0152

出版商:IEE    

年代:1965

数据来源: IET

摘要:

A transverse-network representation for hybrid modes in inhomogeneously filled waveguides is derived using a method employed previously in the representation of slotted waveguides. It is shown that hybrid modes may be represented by a pair of coupled radial-line modes of pure H and E type. General expressions for the input impedances and admittances of the H- and E-type radial lines are developed at the rod boundary, and particular expressions for the unbounded rod and Goubau line are also presented. The influence of the above impedances and admittances upon the propagation characteristics of dielectric-loaded waveguides is considered for circularly symmetric and asymmetric modes. In particular, it is shown that the appearance of a backward-wave region can be interpreted as a frequency-pulling effect of one radial-line resonator upon the other. The extension of the representation to inhomogeneous waveguides with azimuthally nonuniform terminations is also briefly mentioned.

DOI:10.1049/piee.1965.0153

出版商:IEE    

年代:1965

数据来源: IET

摘要:

A lumped linear nonseries-parallel 3-terminalRCnetwork containing three internal nodes is analysed by taking specific numerical examples. Although in every case a series-parallel equivalent is obtainable, there are considerable differences between the various cases. Three examples are considered in detail in the paper. In two of these, one extra factor is required, and in all three cases excess elements are required, to obtain a series-parallel equivalent. A brief note is included on the results of an automatic analysis of a number of examples of this network using a digital computer.

DOI:10.1049/piee.1965.0154

出版商:IEE    

年代:1965

数据来源: IET

摘要:

A new synthesis technique, involving a voltage amplifier with shunt feedback or a current amplifier with series feedback, is developed forRCactive filters. Illustrative examples together with some experimental results are included; close agreement with theory is demonstrated.Tables have been prepared giving Horowitz's optimum polynomial decomposition for various Butterworth and Cheby̅shev low-pass filtering characteristics.

DOI:10.1049/piee.1965.0155

出版商:IEE    

年代:1965

数据来源: IET

摘要:

A critical study of the methods available for the measurement of radio interference from high-voltage insulators has been made by comparing the results obtained with the various methods for a range of insulators. It was found that the method which measured the noise current through a resistor coupled to the high-voltage system by a capacitor gave consistent results for all insulators. The second method, which measures the noise currents in the earth lead of the insulator, gave results which depended upon the size of the insulators. This method was subsequently modified by using an artificial earth plane connected to the measuring set. The results then approached those of the first method. A third method assumes that the onset voltage of visual corona is the criterion for the onset of radio interference. It was found that some radio interference was generated before visual corona commenced and that the levels at the critical visual corona voltages depended upon the types of insulators used.

DOI:10.1049/piee.1965.0161

出版商:IEE    

年代:1965

数据来源: IET

摘要:

Investigations were made into the origins and causes of radio interference from high-voltage insulators, and factors which affect the interference level were studied. Pin-type, multicone post-type and pedestal-type insulators were used. In pin-type insulators, over their working voltage range practically all interference was generated in the region of contact between the high-voltage conductor and the porcelain. The interference was reduced to a very low level by applying a conducting paint or a semiconducting glaze to the insulator head. In multicone post-type and pedestal-type insulators most of the interference originated in the metal-cap/first-shed region, and the cement joint between the metal cap and first shed was the predominant source of interference. Control of the voltage stresses by using stress distributor and guard ring, and application of conducting paints to the cement joint, caused a large reduction in the interference and increased the voltage at which interference was first observed. Radio interference from pin-type insulators was also studied in air of different humidities. Increasing humidity caused a decrease in radio interference. The effect was relatively small in the drier conditions, but large reduction in interference was observed in humidity conditions near the saturation value.

DOI:10.1049/piee.1965.0162

出版商:IEE    

年代:1965

数据来源: IET