Uniform Gain Power-Spectrum Antenna-Pattern Theorem and Its Possible Applications

Abstract

Abstract-For certain applications in radio astronomy, viz. radio spectrographs, spectrum monitoring etc., only the amplitude power spectrum coverage within an angle of observation could be of interest. Ideally, the antenna structures of such instruments should illuminate this covering angle with a fixed uniform gain. This might be achieved using a combination of dipole antennas, a single vertical dipole, a loop antenna etc., but are subjected to limited bandwidth. This limitation could be overcome if many electrically-identical wideband antennas are positioned across the perimeter of a circle lying in the horizontal plane such that the antennas' adjacent half power beam angles touch each other. It has been theoretically observed that if two identical antennas are positioned at an angle with respect to one-another in such a way that their adjacent half power beam angles coincide, then if the amplitude power spectrums of the two are added, the result is effectively an amplitude power spectrum obtained from a single antenna having an uniform gain and uniform signal to noise ratio within the angle subtended by them. This angle also happens to be equal to the half power beamwidth of the individual antennas. A proper design using frequency independent antennas might possibly result to an user specified uniform amplitude power spectrum gain coverage across any required angle, with a theoretically unlimited bandwidth. More number of identical antennas might be positioned in similar fashion for extending the angular coverage. Joardar and BhattacharyaThe power spectrums from these antennas could be directly added which effectively represent the power spectrum from a single antenna possessing uniform gain coverage within an angle equal to the product of individual half power beamwidth angle with one less the number of antennas, thus achieving user defined gain, wide bandwidth, and uniform signal to noise ratio across the angle. It is also possible to recover the time domain signal by applying Fourier Transform on the outputs of the antennas followed by an addition of their amplitudes while keeping the phase information identical to that of one antenna (taken as reference), and taking its inverse Fourier Transform.

Method for Broadening the Beamwidths of Crossed Dipole for Wideband Marine GPS Applications

“…But the formations of the radiation patterns in the vertical plane have obvious discrepancies over the wide operating frequency band, i.e., the radiation patterns are non-uniform versus frequency (the patterns at the lower frequencies are usually narrower than those at the higher frequencies) [9]. It is reasonable to assume that the non-uniform radiation patterns are not desirable for the GPS applications in the whole frequency bands [14,20]. In this paper, a method to broaden the beamwidths of a crossed dipole antenna is proposed.…”