Log-periodic Array Research Articles

Bandwidth limitations of log-periodic microstrip patch antenna arrays

Results are presented for the frequency dependence of the propagation constant of uniform microstrip patch arrays that allow the bandwidth limitations of log-periodic patch arrays to be deduced. It is found that direct coupling of the patch to the feed line limits the log-periodic bandwidth to about a 2:1 frequency range. However, the introduction of series reactance into the equivalent circuit such as by the use of overlaid patches indicate that log-periodic action over a very wide bandwidth is possible which will then be limited by the uniform substrate and production tolerances.

Decameter storm radiation, I

A log-periodic array, 3 km long in the E-W direction is in operation at the Clark Lake Radio Observatory. The solar brightness distribution is swept once per second in the 65-20 MHz frequency range. The analysis of the interferometer records allows the determination of one dimensional solar burst positions, to an accuracy of 0.1 R⊙ at 60 MHz and 0.3 R⊙ at 30 MHz, approximately.

Meter and decameter wavelength positions of solar bursts of July 31?August 7, 1972

The positional analysis of solar bursts at meter and decameter wavelengths during the period July 31-August 7, 1972 is presented. The observations were taken with two arrays — a log periodic array of 16 elements situated on an E-W base line of 3.3 km and portions of the new Clark Lake array in the form of a Tee (an E-W arm of 32 log spiral antennas and a N-S arm of 16 similar antennas). The new array operates over the frequency range 10–120 MHz and has angular resolutions of approximately 3.′5 at 100 MHz and 8.′5 at 40 MHz in the E-W direction. In the N-S direction the instrument has a resolution of 6′ at 100 MHz and 15′ at 40 MHz. During this period the activity was often so complex that we represent it only by ‘snapshots’ taken at representative times at three representative frequency ranges 90–110 MHz, 60–80 MHz and 30–50 MHz. Most of the activity during this period was associated with the active regions McMath 11976 and 11970. The radio-emissive regions were also closely associated with the Fe xv (284 A) coronal maps produced by NASA-GSFC from OSO-7 observations (Figures 1, 2 and 3). Except near the CMP of the region 11976, two regions of continuum emission were often observed — one a relatively smooth continuum and the other a continuum superimposed with many type Ill’s and other fine structure. It seems possible to interpret these continua in terms of plasma waves originating from two sources located at different heights or with different electron density gradients. The angular size of type III sources seems to increase with decreasing frequency. This implies that the open field lines along which the type III electrons travel have larger angular extent at greater height.

50 Ω Log-periodic monopole array with modulated-impedance microstrip feeder

It is demonstrated theoretically and experimentally that a log-periodic monopole array with a meander-line feeder may be expected to exhibit high values of voltage standing-wave ratio. Improved match can be obtained by allowing the impedance of the feeder to go to a higher value near each monopole. A good match to 50 \Omega is achieved in this way.

Meter and Decameter Wavelength Positions of Solar Radio Bursts of July 31–August 7, 1972

(Solar Phys.). The positional analysis of solar bursts at meter and decameter wavelengths during the period July 31–August 7, 1972 is presented. The observations were taken with two arrays – a log periodic array of 16 elements situated on an E–W base line of 3.3 km and portions of the new Clark Lake array in the form of a Tee (an E–W arm of 32 log spiral antennas and a N–S arm of 16 similar antennas). The new array operates over the frequency range 10–120 MHz and has angular resolutions of approximately 3.′5 at 100 MHz and 8.′5 at 40 MHz in the E–W direction.

Coronal Density Structures in Regions of Type III Activity

(Solar Phys.). We identify from daily K-corona observations the coronal regions located above type III burst sources. The radio observations were made with the east–west log-periodic array at Clark Lake Observatory. East–west positions of 260 isolated type III bursts during March and April 1971 have been measured between 20 and 65 MHz (disregarding storms of type III bursts). The K-corona observations are made with the HAO K-coronameter at Mauna Loa, Hawaii. During 1971, the heights of observation were 3.6′, 5′, 9′ and 13′ above the limb.

Mutual coupling effects on a dipole log periodic when used as an array element

A measurement program conducted to observe the effects of mutual coupling on element VSWR in a three element linear log periodic dipole antenna array is described. The data collected are presented as a function of frequency, interelement spacing, and scan angle.

The effects of transverse-feed displacements on log-periodic dipole arrays

The impedance and radiation characteristics of a center-fed dipole with transverse feed-point displacement are derived. The effects of the feeder displacement upon the characteristics of a log-periodic array with such a dipole as its basic element are then reviewed.

Loop coupling to a periodic dipole array

Conditions are found experimentally for optimising the coupling between a looped feeder (transposed transmission line) and a log-periodic array of radiating dipoles. Under optimum conditions, the coupling is sufficient to be useful in practical antennas.

Log-periodic antennas with modulated impedance feeders

The proper phasing of the active region of a log-periodic array can be obtained by means of a feeder without the conventional transposition of the wires. This is of practical importance for arrays of monopoles and slots where the transposition is not possible. However, the input impedance of such structures, when fed from a line with constant impedance, varies greatly with frequency. The impedance variation has been traced to reflections from a stop region between the antenna feedpoint and the active region. By introducing a step modulation of the characteristic impedance of the feedline, the reflections can be reduced and a stable impedance obtained.

A log-periodic antenna with vertically polarized omnidirectional radiation

This communication reports the results of an experimental investigation of a new log-periodic (LP) antenna. The antenna consists of an LP array of radial waveguides excited by a two-wire transmission line. The antenna exhibits a vertically polarized omnidirectional radiation pattern which is essentially constant over the designed bandwidth.

Helical log-periodic array

A helical log-periodic array is designed considering the same parameters as those used in an existing log-periodic dipole array. The impedance and radiation characteristics are measured for both arrays. It is observed that the arrays have similar characteristics. Moreover, the advantage of the helical array is that its transverse dimension becomes much smaller.

Log periodic Yagi-Uda array

The log periodic Yagi-Uda array is introduced in this paper. The concept used for extending the frequency bandwidth of the basic Yagi-Uda antenna by employing log periodic principles is presented; and its connection with the log periodic array with parasitic elements is established on the basis of the measured performance. The results of experiments on a log periodic Yagi-Uda dipole array show that the antenna characteristics of the basic antenna are preserved with frequency. Because of the mirror symmetry of the structure, it is shown that a log periodic monopole is realizable.