Factors to Consider When Selecting the Right RF Power Amplifier

Power amplifiers are a crucial component of an RF communication system. Like other amps, RF power units amplify the signals that are supplied to its inputs. Due to the complicated modulation schemes of these signals, they’re quite complex, and engineers often find it difficult to choose the right amplifier. Here, we’ll look at some important specifications to consider when choosing an RF amplifier.

Gain

Amplifiers have numerous specifications, but gain is one of the most important. Gain is a measure of the unit’s ability to boost a signal provided to an input terminal, and it is shown in decibels or dB. An amplifier’s gain will vary across frequencies. At a higher frequency, an amp’s losses will typically increase.

Bandwidth/Flatness

Bandwidth is another vital specification to consider when purchasing an RF amplifier. It’s described as the range between the lowest and highest frequencies in the response curve where the amp provides the most efficient gain. An amplifier’s flatness is its gain response across its total operating bandwidth.

Impedance

If a system application requires networking and transmitting antennas, impedance is a crucial consideration. In most cases, amplifiers are optimized and designed for 50 ohm impedance. If there’s a mismatch, reflection, losses, and component damage may occur.

Harmonics

Here, harmonics are undesirable signals that duplicate operating frequencies. These unwanted signals often mix with others in a system, creating additional intermodulation distortion. Though they cannot be completely isolated, they can be suppressed with various design techniques.

The Third Order Intercept Point

The TOI or third order intercept point is a theoretical value in a linearity diagram. A signal’s third order components are generated during each amplification process. An amplifier’s gain will begin to diminish as it reaches a saturation point. From there, if input power continues to increase, the third order and fundamental signal powers will converge at the TOI. The calculation is used during the design phase to determine an amplifier’s non-linearity behavior.

Adjacent Channel Rejection Ratio or ACLR

In most scenarios, a small portion of the power that’s transmitted through the proper channel will spill over into adjacent channels because of intermodulation distortion. ACLR is the ratio between the power as transmitted and that measured at adjacent channels. It plays a key role in today’s wireless communications systems such as LTE, where signals are sent via several channels within allocated bandwidth. In some instances, amplifiers must also accommodate modulated signals.

Noise Figure

This measurement is the difference between a power amplifier’s input signal to noise ratio and output signal to noise ratio numbers. The lower an amplifier’s noise figure value is, the better it will perform. Noise figures are always higher than one because the output signal to noise ratio exceeds input SNR.8.

One dB Compression

Once an amplifier reaches a compression region, no further amplification will occur, and the gain response will flatten. One dB compression is a point on the linear diagram’s response curve. It’s one decibel below the line where amplifier gain saturation starts becoming non-linear.

Peak-to-Average Power Ratio

In simple terms, this measurement is the ratio between an amplifier’s peak and average signal power levels.

Maximum Output and Input Power

An RF amplifier’s maximum output and input power handling should be considered during the selection process. Exceeding an amp’s input power level may damage it, especially when multiple amps are used in cascading fashion. The amplifier’s output power must be able to support the application’s requirements after losses and flatness across operating bandwidth are considered.

Power Consumption and Size

When selecting an RF amplifier, its physical size should be considered. Amplifiers range in size from a few millimeters to several meters tall and wide, and your choice will depend on the usage environment and application.

RF amplifiers generate significant heat during operation, and proper air circulation is a must-have. The amplifier’s power consumption is another crucial factor to consider. Some models, especially those used at high power, have high external cooling and AC power requirements.

In Closing

 RF power amplifier selection depends on several factors, most of which are explained above. An amplifier’s specifications may be found on the manufacturer’s data sheet, and its S-parameters are typically required for design and evaluation purposes. Proper matching is crucial to the efficient transmission and reception of signals. By considering the factors above, users can find RF amplifiers that suit any application’s requirements. For more information on power amplifiers and how Elite RF can help you click here.  To learn more take a look at some of our other articles: The Difference Between Gass and Gan RF power amplifiers OR What is Amplifier linearity and how do you measure it?