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New analytical expressions and numerical results for the mode coefficients, the directivity, and the quality factor and computationally convenient expressions for the input admittance of a symmetrical biconical antenna of arbitrary length <inline-formula> <tex-math notation="LaTeX">$L$ </tex-math></inline-formula> and cone angle <inline-formula> <tex-math notation="LaTeX">$\theta _{0}$ </tex-math></inline-formula> are presented. The quality factor for a wide-angle biconical antenna is evaluated using three alternative formulations: 1) the evanescent energy stored outside the circumscribing sphere; 2) the total evanescent energy stored in all space; and 3) by equivalent circuit model, and these are all compared with Chu&#x2019;s lower limit for an ideal antenna. Numerical calculations based on the analytical formula for antenna admittance confirm the conjecture that Foster&#x2019;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. Finally, the ratio of directivity to <inline-formula> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> of an electrically small biconical antenna is shown to approach 78&#x0025; of the value of an ideal omnidirectional antenna.

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