by Tore N. Anderson and Dr. Ronald S. Posner
Antennas for Communications
Reprint from Satellite Communications, January 1995

Table of Contents

Ultra Low Transmission Loss Tallguide TG87 and TG115 Components

Modern satellite earth station uplinks make EIRP demands which often require colossal transmitter powers. System engineers, exposed to transmitter power backoff linearity, to rain attenuation, to uplink power control, multi-carrier signals, feed combining loss, orbital arc obstructions and to various distances between control room and antenna site locations, are continually forced to boost power. Since antenna radiated power, EIRP, is equal to the antenna gain plus transmitter HPA power less the waveguide run loss, the system designer, until recently, was forced to use a larger antenna, beef up transmitter power or move the transmitter next to the antenna. Such expensive alternatives outrage any cost-conscious budget constraints. Boosting antenna size, along with upgrading site civil works or multiplying transmitter power two or three times, can be a financial manager's nightmare. To make matters even worse, the waveguide run length is frequently dictated by existing site conditions or is biased by customer preference. Under these circumstances, moving a control room nearer to the antenna may prove an impossible task. What often remains is a waveguide power loss accounting for more than half the antenna system EIRP gain.

A design engineer is faced with an infinite number of choices in any EIRP decision. Antenna size or transmitter power can be increased to offset waveguide loss. Waveguide loss can be reduced to keep antenna size, civil works and transmitter power manageable. To complicate matters even more, to achieve superior operational reliability, complex strategies can be employed, such as uplink power control, to pin EIRP demands against the local weather. It is the wealth of potential design freedoms and system needs that spearhead engineering technique.

Several kinds of curvatures have been exploited to map waveguide into TallGuide and to map TallGuide into TallGuide bends and twists. Unmistakably, the most promising curvature is the hyperbolic secant curvature. Because TallGuide often operates in high power applications, several kW average power, even the smallest power conversions constitute watts of power. It is for this reason that TallGuide uses optimum curvature components. Electroforming techniques are employed to manufacture the complex internal contours and to provide high strength components.

In all practical installations, the TallGuide run length is many times the wavelength. Therefore the trapped resonate frequencies form a series of very fine comb lines. Even though residual higher order TallGuide mode generation is very weak, trapped mode conversion affects linearity whenever the operating frequency coincides with one of the comb lines. It is for this purpose that the mode suppressor is introduced. With the mode suppressor, all higher order mode energy is absorbed, thereby removing the unwanted trapped energy from the TallGuide system. Further, since the TallGuide wavelength is longer than the wavelength in standard waveguide, TallGuide linearity is superior to standard waveguide. TallGuide has been tested on numerous communications and radar systems in both narrow and broad band signal modulation modes. No negative linearity effect is measured for data, video, multi-carrier video, FM, phase modulation and ultra short pulse radar signals.

The mode suppressor is a reciprocal device. Any input/output orientation is satisfactory. The mode suppressor may be placed anywhere in the TallGuide run. For high power applications, however, it is recommended that the mode suppressor be placed on the antenna side of the TallGuide system just before the TallGuide transition to standard waveguide.

TallGuide is a means to increase uplink EIRP. TallGuide EIRP power savings are 6 times compared to standard waveguide. Moreover, interfacility waveguide loss is significantly reduced without any signal quality degradation.

Ultra low loss TallGuide removes the power loss and length restrictions of standard waveguide. At the same time, it removes the huge antenna system escalation costs needed to remedy the power loss of ordinary waveguide.

AFC manufactures, markets and sells worldwide satellite dish antennas, conical horn antennas, radomes, antenna feeds, microwave and waveguide components, ultra low loss waveguide transmission line TallGuide, and shelters. Our customers serve the broadcast, communications, radar, weather and cable industry, defense, government, and government agencies worldwide.