arXiv subjects

Ramakrishna Janaswamy

Publications and source records attributed to Ramakrishna Janaswamy.

3 recordsLinked to original sources

arXiv2023

Exact Transient Analysis of a Biconical Antenna of Arbitrary Length and Cone Angle

Starting from a new factorization of the frequencydomain modal expansion coefficients, we generate analytical expressions in time-domain for the various quantities of interest of a biconical antenna of arbitrary length and cone angle. In particular, expressions are generated for the impulse response of feed current and the radiated fields as well as the transient effective length. Comparison with measured results available in the literature is carried out for the antenna effective length. The response due to any other feed voltage pulse can be obtained in terms of the impulse response via convolution. Results are presented for a Gaussian and a fast-rising feed voltage pulse. For the fast rising feed voltage pulse, the transient radiated energy density is shown to decay less rapidly than as inverse square distance over significant distances from the antenna. The expressions presented in the paper are all general and exact and not subject to any analytical approximations.

physics.class-ph↗

arXiv2022

Input Admittance, Directivity and Quality Factor of Biconical Antenna of Arbitrary Cone Angle

New analytical expressions and numerical results for the mode coefficients, the directivity and the quality factor as well as computationally convenient expressions for the input admittance of a symmetrical biconical antenna of arbitrary length $L$ and cone angle $θ_0$ are presented. The quality factor for a wide-angle biconical antenna is evaluated using three alternative formulations: (i) the evanescent energy stored outside the circumscribing sphere, (ii) the total evanescent energy stored in all space and (iii) by equivalent circuit model, and these are all compared with Chu's lower limit for an ideal antenna. Numerical calculations based on the analytical formula for antenna admittance confirm the conjecture that Foster's reactance theorem remains invalid even for perfectly conducting antennas. Furthermore, the variation of directivity of a wide-angle biconical antenna is a slowly varying function of its electrical length and is shown to depart significantly from that of a thin cylindrical dipole. Lastly, the ratio of directivity to $Q$ of an electrically small biconical antenna is shown to approach 78\% of the value of an ideal omnidirectional antenna.

physics.app-ph↗

arXiv2018

A State Space Technique for Wildlife Position Estimation Using Non-Simultaneous Signal Strength Measurements

A novel state-space technique is presented to estimate the location and airborne movements of VHF tagged wildlife individuals with fixed VHF arrays. The approach combines a movement model (Ornstein- Uhlenbeck random process in the transverse (horizontal) plane and a Cox- Ingersoll-Ross process in the vertical direction) to ensure biologically-consistent trajectories in three-dimensions, and an observation model to account for the effect of range, altitude and bearing angle on the received signal strength. The observation model of received signals accounts for low-end saturation from receiver noise, high-end saturation from receiver non-linearities as well as a wireless multipath phenomena, which modulates the received signal according to range, the altitude and radiation characteristics of the Yagi array. A pattern function for the Yagi array is synthesized that facilitates linearization of the received signals and subsequent application of Kalman filtering. We first validate the model using a simulated trajectory and then estimate the space-time trajectory of a migrating VHF-tagged shorebird, which was tracked with a regional automated radio telemetry network. The algorithm accurately predicted the average movement trajectory given the system parameters and the initial conditions (average error $<$ 1 km). The modeled shorebird track represents a first estimate in three-dimensional (3D) of a radio tagged bird using a fixed telemetry array, and was qualitatively reasonable, but exhibited some sensitivity in the vertical plane and to initial conditions.

eess.SP↗