Cincinnati Electronics Corporation

John E Brunner

A short monopole RF antenna tuned over a predetermined RF frequency band in response to binary control signals includes a conductive tubular radiating element extending generally at right angles to a ground plane on which the antenna is mounted. A conductive top load inductively coupled to the element extends approximately parallel to the ground plane so that stray capacitance subsists between the ground plane and top load. The antenna is tuned in response to the control signals to a frequency in the band by selectively short-circuiting different plural series-connected inductors in proximity with the top load. Plural leads extend through the interior of the tubular element between a source of the control signals and switches for selectively short circuiting the inductors. The inductors are electrical conductors in a tube-like structure. The leads extend through the interior of the tube-like structure. Electrical conductors in the tube-like structure are in a return path to the control signal source. The switch for each inductor includes a pair of diodes positioned outside of the tube-like structure. The lead for each inductor extends through the tube-like structure and is electrically insulated from the electrical conductors. A feed for the antenna is connected to the tube at a location in proximity to the ground plane. An inductor is connected between the location where the feed is connected to the tube and the ground plane for approximately matching the feed to the tuned element for low frequencies in the RF range.

Tunable short monopole top-loaded antenna

A high-Q load circuit is matched to a drive circuit with an L-type filter network including series and shunt reactances which are both either inductive or capacitive. While a first of the reactances is effectively removed from the network, the value of the second of the reactances is varied until the impedance magnitude of the load and network, as seen from the drive circuit, reaches a predetermined magnitude, and a predetermined relationship exists for the polarity of the phase of the voltage and current supplied by the drive circuit to the network. When the impedance magnitude seen by looking from the drive circuit into the network reaches the predetermined magnitude and the correct phase polarity exists, the first reactance is reconnected into the network and then varied until a predetermined relationship exists between the phase angle between the voltage and current applied by the drive circuit to the network.

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Hamilton, OH, United States of America

John E Brunner