Analytical Model of the Split-Coaxial Balun and Its Application to a Linearly-Polarized Dipole or a.pdf
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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 55, NO. 7, JULY 2007 1909
Analytical Model of the Split-Coaxial Balun and Its
Application to a Linearly-Polarized Dipole or a
CP Turnstile
Sergey N. Makarov, Senior Member, IEEE, and Reinhold Ludwig, Senior Member, IEEE
Abstract—A simple analytical transmission line model of a
split-coaxial balun is proposed and tested. It is based on the cou-
pled symmetric transmission line approach. The model leads to a
closed-form analytical expression for the termination impedance/
transfer function of the complete antenna system that includes
antenna, balun, and a non-splitted coaxial line of certain length.
It accepts the impedance of a center-fed symmetric antenna
as input parameter. The model is in excellent agreement with
full wave simulations and is confirmed by a series of prototype
measurements. It can be applied to a linearly-polarized radiator
or to a broadband circularly-polarized turnstile, where the phase
quadrature is created by two complex-conjugate impedances. The
present model only describes the impedance matching properties
of the balun but is not capable of predicting the balance quality of
baluns.
Index Terms—Antenna feeds, antenna theory, baluns, dipole an-
tennas, turnstiles.
I. INTRODUCTION
AN initial motivation for this work was a necessity to designa low cost mast-conformal linear 20%-wideband UHF
wire dipole (400–500 MHz) with the controllable complex
antenna factor (CAF) and the controllable phase characteris-
tics. Some commercially available dipole antennas are either
narrowband (cover the desired band in steps of 20–25 MHz) or
have a sufficient bandwidth (300–1000 MHz—TV dipoles or
EMI dipoles) but an unknown phase transfer function. The most
involved part of the design becomes a balun that simultaneously
plays the role of a lossless impedance matching network and an
antenna support (a mast).
Conventional baluns for symmetric wire dipole antennas are
briefly reviewed in several scholarly sources -
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