The sonobuoy transmitting antenna system has been used for anti-submarine warfare. This system is composed of the transmitting antenna, the RF transmitting circuit, the converting circuit sound source into VHF radio frequency and the hydrophone sensor system for receiving of a sound source generated by a submarine. In this thesis a λ/4 vertical ground plane one as a sonobuoy transmitting antenna is considered and measured at anechoic chamber. A purpose of the λ/4 vertical ground plane transmitting antenna system is to transmit from the location information of a sound source generated by the submarine to the receiving antenna system mounted on the ship or the airplane. A received ultrasonic wave is converted to RF signal. The frequency range assigned for this system is 136 MHz to 173.5 MHz. In addition, the measured spurious radiation of sonobuoy transmitting antenna system is compared with a military specification(MIL Spec.) results.
In this thesis, the measured results of sonobuoy antenna with impedance matching circuit is described at VHF band. This antenna is used as sonobuoy transmitting antenna for the naval air systems. Since radiation pattern and power density depend on impedance matching between transmitting RF part and antenna with termination resistance, design of matching circuit is very important. Matching circuit is designed by smith chart using the optimum values of L and C. In SWR measured by network analyzer, SWR of antenna with matching circuit observed 1.5 below at the assigned VHF band. It shows very excellent performance comparison with conversional product that is used for the same object. The measured azimuth/elevation radiation patterns and the spurious radiation characteristics are also shown the satisfaction of military specification.