The Wide and Diverse World of RF Antennas
900 MHz Patch Antenna
Electromagnetic (EM) Antennas are an essential component for virtually all transmission and reception systems that operate in the RF, microwave, millimeter-wave (mmW), and terahertz (THz) frequency ranges. Another way to look at EM Antennas, is that these antennas can be designed to convert conducted EM signals to radiated EM signals, and vice versa, from kilohertz frequencies to terahertz frequencies, to enable communication and sensing at a distance. Without EM antennas constructed using conductors and dielectrics, there are very few other methods of performing this function, and these other methods generally can’t be fabricated, installed, operated, or maintained with the same level of cost and ease. Hence, modern conductor/dielectric-based EM antennas are ubiquitous in communication and sensing systems.
These antennas can be divided into two categories based on the antenna pattern of the element. It is important to note that the reception and transmission of an EM antenna is intrinsically symmetrical. If the antenna pattern allows for relatively efficient reception/transmission from signals in a 360 degree pattern in the horizontal , it is an omnidirectional antenna. If the antenna pattern is limited to less than 360 degrees in the horizontal it is a directional antenna.
Omnidirectional antennas are generally useful for receiving/transmitting signals in all directions simultaneously. This can be desirable if reception/transmission of signals in all directions is needed, such as with some legacy radio stations. However, there are often occasions where the signal direction is known or limited in direction. For instance, for radio telescopes it is known that the signals will be received in a given direction (from space), and an omnidirectional antenna would be less efficient at receiving faint signals from the stars. In cases like this, a directional antenna with much higher antenna gain can be used to receive more of the signal energy in a given direction.
An example of a highly directional antenna is a Yagi antenna. These types of antennas are frequencies used for transmitting/receiving communication signals over long distances when the direction of the incoming signal or target is known. Another example of a highly directional antenna is a waveguide gain horn antenna. These antennas are commonly used in test and measurement applications, such as when measuring the performance of another antenna, or when receiving/transmitting signals at higher waveguide bands. Directional antennas can also be fabricated in relatively low-weight and flat panel designs for ease of manufacturing on common RF substrates, such as PCBs. These panel and patch antennas are often used in consumer and industrial telecommunications due to their relatively low-cost manufacturing, small format, and low-weight.
Other than these examples, there are omnidirectional and directional antennas designed for every environment that EM antennas are used. For instance, there are dome antennas for use on mobile platforms or exterior surfaces where it is ideal to have a low-profile antenna design as opposed to a more traditional dipole-type or whip antenna.
Courtesy of Pasternack