Nuts and Volts - September/October 2018

September/October 2018 85

OPEN COMMUNICATION ; BY LOU FRENZEL W5LEF

Antennas come in a wide range of forms depending on the application, service, and frequency of operation. Some antennas you can’t even see -- like the four or five units in your smartphone. These antennas are single element devices, a metal structure, or printed circuit board (PCB) pattern that are connected to a receiver or transmitter by a transmission line.

Now, another type of antenna is emerging to address the forthcoming exotic 5G cellular systems and other advanced wireless products like Wi-Fi routers. This antenna is the phased array: a group of antennas that work together to provide some significant benefits and capabilities not available with the simple antennas we know.

Phased arrays have been used for years in military radars for long range detection of missiles. They’re also widely used in military and commercial aircraft radars and some satellites. These phased arrays are expensive, but today thanks to new technology and higher frequencies, phased arrays are smaller and more affordable making them practical for new wireless devices. This article is an introductory tutorial on this special antenna type you need to know about.

Antenna Types

Different types of antenna elements are used to make up an array. Those commonly used in phased arrays are the dipole and patch; refer to Figure 1. The dipole is a basic half wavelength conductor fed at the center. A patch is usually a half wavelength copper square on a PCB. Other antenna types have been used. The spacing between the antenna elements varies with the design but is generally a little more or less than a half wavelength.

Remember the relationship between frequency (f) and wavelength (λ): Here, λ is in meters and f is in MHz.

For example, a frequency of 1,296 MHz has a wavelength of:

λ = 300/1296 = 0.23 meters or 23 cm A half wavelength is:

λ/2 = 11. 5 cm or about 4. 5 inches

(NOTE: There are 2. 54 cm per inch.)

Also keep in mind that the length of an antenna depends on the frequency of operation. A half wavelength is generally computed with the expression: L = 492/f where f is the frequency in MHz and the length L is in feet. This formula can also be used where L is in meters:

λ = 150/f The higher the frequency, the smaller the antenna. At

One of these exotic antennas is in your future.

hat do you think of when you hear the term antenna? Do you picture a cell phone tower, an old TV antenna, a vertical whip antenna used for CB radio, or a wire antenna used by hams? Or, something else completely?