As we explore phase shifting, let’s first refresh our memory on how AC power works. In single phase power, voltages oscillate between -120 and +120 volts in a sinusoidal pattern. Three-phase power smooths out these peaks and troughs by adding another two cycles oscillating at the same frequency. Each of the three phases applies —or shifts— at 120 degrees to each other, which means the positive and negative sums never equal zero.
We can apply this multi-phase arrangement in several different areas. Here are two examples:
- An electric utility well can apply phase shifting upstream of consumer usage to help balance line loads.
- In audio phase shifting, a sound engineer can produce a strange guitar or another instrumental effect by overlaying a second phase-shifted signal on the original. When these signals are 180 degrees out of phase— one wave starts at half the time period of the first wave from the same source, causing a positive wave to meet the second negative wave— the sound waves will actually cancel each other out. Theoretically, this will produce silence, and it explains the principle behind active noise-reducing headphones.
RF Phase Shifting: How Does a Phase Shifter Work?
While audio and electrical supply applications are forms of phase shifting, we usually use the term to refer to a “phase shift module,” or the manipulation of radio waves. Just like sound and electricity, or waves on water for that matter, radio waves of the same frequency can combine with each other to amplify or cancel signals when their phases align correctly.
We can illustrate this principle with an array of dipole antennas, which normally send out a signal in all directions, to direct signals based on how each signal’s phase angle is aligned. Microwave frequencies, which operate between 300 MHz and 300 GHz frequencies, are the normal target of this kind of phase shifting. Antenna arrangements that allow for this type of directional RF transmission are known as phased arrays.
RF Phase Shifter Design & Types of Phase Shifters
There are several types of devices we can use to accomplish RF phase shifting, and we can divide them into four different categories:
Active – A powered device that electronically amplifies the signal while performing a phase shift operation
Passive – No power is added, but the device attenuates a signal as a part of the operation
Analog – Phase shifting is continuously variable
Digital – A discreet set of phase shifts
We can also categorize RF phase shifters by the type of technology they use. Semiconductor solutions play an active role in transistors or a passive role in diode usage. Non-semiconductor-based solutions are available in the form of ferrite and ferroelectric-based designs, as well as microelectromechanical systems (MEMS).