Horizontally Polarized Log Periodic Antennas (HLPA) have found wide application in HF communications circuits because they provide good electrical characteristics (radiation pattern coverage, power gain and low VSWR) over the complete HF spectrum. In addition, it is possible to control and optimize the elevation plane coverage obtained from HLPAs by proper placement of the antennas relative to the ground.
Choosing the right type of antenna for use on a HF link is very important if the best link performance is to be achieved. The choice of antenna types is large and, at times, baffling. A number of antennas that will more or less satisfy the requirements in question are available, finding the optimal solution is far from simple for the systems planner. It requires a knowledge of iononspheric behavior as well as antenna engineering, operating conditions and siting considerations. Because of this, the systems planner usually enlists the help of the antenna specialist to analyze the propagation conditions and find (or design, if necessary) an antenna to fit the requirement. In essence, the antenna specialist, to carry out this function effectively, needs to be a physicist, applications engineer, structural engineer and applied mathematician. This bulletin sets out to dispel that myth, explain how antenna types vary in performance and how these differences can be most effectively exploited.
The radiation pattern; i.e., the power radiated in any direction of maximum radiation, in the elevation (vertical) plane, is strongly influenced by the presences of ground beneath the antenna. This is because the radiated signal is equal to the sum of the signal radiated directly from the antenna and that reflected from the ground. The relative phase of these components changes with the antenna’s height above ground, electrical characteristics of the ground and polarization, either adding to or cancelling the field due to the direct ray. For Rotatable Log Periodic Antennas (RLPA) such as ASC Models 2004 and 2731 mounted on a single, central support structure; such a asymmetric configuration would cause undue physical stress to the rotator. To alleviate this problem, the apex of the antenna is elevated to a point where the whole antenna is at a constant physical height above ground. This results in a variable take-off angle as a function of frequency.
CPI ASC Signal Division is a global manufacturer of satellite earth station antenna products for broadcast, government, military, and enterprise satellite communication applications. The Next Generation Controller (NGC) provides antenna pointing and tracking operation for transportable and large, fixed antennas (including Ka-band) operating on stationary and inclined-orbit satellites, as well as additional functions such as environmental system control, built-in spectrum analyzer, uplink power control, and redundancy control. The in-depth NGC online training program covers all topics needed for all levels of system personnel, whether they monitor, use, administer, configure or install NGC systems. The self-paced courses and tested certifications are delivered as integral parts of the SatProf Training and GVF Certification Program.