In this article we will look at some basic principles of radio communication antennas. It is important to have knowledge of the basic principles of antennas. In a radio communications environment, it is most important for any station to pay great attention to the installation of the antenna. While each radio station’s hardware, including the transmitter and receiver, is important, ultimately the quality of the antenna plays the most important role in overall performance. As the saying goes: “A radio station is only as good as its antenna.” Therefore, we will place special emphasis on the basic principles of antennas, and I will try to keep our discussion intuitive and simple without getting into too much mathematics.

The performance of any antenna, especially a high-frequency HF ground station, is generally affected by several factors, including its basic design, the structural materials used to build the antenna, the placement of the antenna relative to its surroundings, terrain relief, height from the ground, Ground quality (including soil dielectric constant and conductivity), antenna direction relative to the ground (vertical, horizontal, inclined, etc.), etc. Many of these factors also apply to terrestrial VHF/UHF communications antennas.
Antenna gain and directional antenna gain are not absolute quantities. This is a characteristic measured compared to another reference antenna. It represents the relative improvement in an antenna’s performance during transmission (TX) and reception (RX) compared to a standard reference antenna. The gain of the transmitting antenna is characterized by power gain, and the gain of the receiving antenna is called directional gain. However, the power gain of a TX antenna does not mean that the total power delivered by the transmitter to the antenna during transmission is somehow increased or doubled. Transmitter power is not increased by antenna gain.
From the past to the present, the free space resonant half-wavelength dipole (referred to as the standard dipole) has been used as a reference. The gain characteristics of all other antennas are measured relative to this standard dipole, with the gain in dBd, the last letter (d) indicating the dipole reference. The disadvantage of the standard reference dipole is that, although its properties can be reproduced in free space, its radiation pattern is circular and non-uniform in all directions in three-dimensional (3D) space. Therefore, another reference antenna was designed for this purpose. This is an isotropic omnidirectional antenna. An omnidirectional antenna is a hypothetical antenna that does not exist in the real world. However, the advantage of this antenna is that it has a perfectly spherical radiation pattern and therefore a uniform radiated power density in all directions in 3D space.
Omnidirectional antennas can be easily used as reliable references for mathematical modeling and are widely used in modern antenna designs. Antenna gain measured for an omnidirectional antenna is specified in dBi. Here (i) represents omnidirectional. Omnidirectional antennas are now more or less the de facto reference antennas in the industry and antenna design community. In order to achieve portability and compatibility of the old standard dipole antenna and the reference omnidirectional antenna, the gain relationship between them was mapped.
Summarizing the concept of antenna power gain, we find that by concentrating the transmitted power in a narrow beam in one or more directions and preventing the energy from being distributed in unnecessary directions, the antenna successfully manages a spatially controlled radiated power. , thereby effectively increasing the power density in the desired direction without requiring additional power from the transmitter. Likewise, upon reception, the intercepted electromagnetic waves are summed to produce higher induced voltages and currents at the antenna. The TX and RX behavior of the antenna are basically inverse of each other. In another article we will discuss gain in the receive direction of the antenna in more detail.