RF transceivers used for aerospace and defense fields

What are RF transceivers?

The term "transceiver" refers to a device that combines a transmitter and a receiver into a single module. An RF transceiver is a device that sends and receives radio frequency (RF) signals. In any wireless communication system, the position of the RF transceiver is typically between the baseband MODEM and the PA/LNA. LNA stands for low noise amplifier, and PA for power amplifier. ADC/DAC chips and chipsets of various analog/digital modulation schemes are found in baseband modems.

How do RF transceivers work?

A tuner and an antenna makeup RF transceivers. The tuner separates the broadcast signals, while the antenna receives them. An RF amplifier is used to send signals by increasing the signal power coming from the antenna for a longer range. This signal is subsequently transformed into electromagnetic waves by the antenna. The antenna of the receiver is where these EM waves pass.

The incoming signals are subsequently modified back into the current by the receiver's antenna. When transmitting information back to its source, this process is reversed. Information that was encoded prior to transmission can be extracted by detectors or demodulators. Additionally, localized interference and noise are limited using radio methods. Oscillators are also helpful when sending a fresh signal. They produce sine waves that are encoded and sent through radio.

In communication networks, RF transceivers serve as the bridge between two devices. Wireless communications would be practically impossible without them.

Working principle of RF and circuit analysis

Radiofrequency acronym The term "RF radio frequency" refers to radio frequency current, which is a high-frequency alternating current change in electromagnetic waves. This frequency can be broadcast into space and has a range of 300 KHz to 300 GHz. Low-frequency current is defined as alternating current with changes per second less than 1000; high-frequency current is defined as alternating current with changes per second larger than 10,000; and radio frequency is one type of high-frequency current. High frequency (more than 10K); radio frequency (300K–300G); microwave band (300M–300G); high frequency (greater than 10K); radio frequency (300K–300G); microwave band (300M–300G); high frequency (greater than 10K). Cable television systems utilize radio frequency transmission, which is a widely used technique in the field of wireless communications.

An electrical component, such as power amplifiers, low noise amplifiers, and antenna switches, is sent out through the antenna resonance in a radio signal called an RF chip. The receiving channel and the transmitting channel are the two main components of the RF chip architecture.

RF transceiver modulation techniques

• Digital information is transmitted using the phase of a carrier wave with a fixed frequency using the phase shift key (PSK) digital modulation technology. RFID, Bluetooth, and wireless LANs are examples of common applications.
• A digital modulation method called frequency shift key (FSK) combines two or more frequencies to encode digital data. Applications like garage door openers that require low data rates and low-frequency transmissions are employed for it.
• To communicate digital data, the amplitude shift key (ASK) modifies the transmitted signal's amplitude. It is utilized in many different applications, including tire pressure monitoring, wireless base stations, and home automation.
• Angle modulation, which includes FM and PM, in which the carrier wave's frequency or phase is changed, respectively, is frequently used to transmit analog signals.
• The simplest format, on-off key (OOK), merely involves turning the signal on and off to communicate data like Morse code.
• Amplitude modulation (AM), which transmits the necessary information typically in an analog form, such as audio signals, involves changing the amplitude or height of the carrier wave.

RF transceivers vs. RF transmitters

We can understand that a transmitter can only be used to transmit signals, whereas a transceiver can do both. Transceivers are often perceived as a tradeoff in terms of performance, functionality, portability, and flexibility, and if there were any applications where they would actually be useful, they would be mobile and portable. To achieve a lower size/weight/cost, transceivers have to give up some features and performance.

A transceiver is portable since it only requires the space of one module while performing the duties of two distinct modules. In some situations, a separate transmitter is less practical because it probably weighs more and takes up more space. They are beneficial, however, because each might profit from its own design, without compromising in areas like I-F frequency selection, conversion frequencies, and audio stages, and they are simpler to construct and operate on.

A separate transmitter typically uses more power, which increases the cost. Additionally, the cost of a single transceiver is substantially less than the cost of a transmitter and receiver combined. A transceiver is less expensive to produce than a separate transmitter and receiver since it uses a single frequency generation/tuning system, power supply, and other components. The answer to how to select from them depends on your application.

Transceivers vs. Transponders

The National Aeronautics and Space Administration (NASA) says that transceivers and transponders are frequently found in satellite communications systems. In a transponder, the received signal is used to derive the transmit carrier frequency, and the frequency linkage in a transponder enables ground stations to recover Doppler shift information and ascertain the speed and range of the sending.

Multiple sending sources can share a single channel thanks to the multiplexed transponders used by communications satellites. Relay stations with dozens or hundreds of transponders and a bandwidth of tens of MHz are essentially what communications satellites are. Traditionally, satellite transponders worked on the 'bent pipe' principle and simply amplified the signal and switched the frequency from uplink to downlink before transmitting it back. 'Regenerative' satellite transponders are more recent satellite receivers that have some onboard processing. Before being transmitted back to Earth, the signal is demodulated, decoded, and reencoded in these schemes. Regenerative transponders can greatly increase the signal-to-noise ratio despite being more complicated and energy-intensive.  They can implement selective processing, such as compression or multiplexing, of the data in the digital domain before retransmission.

RF Transceivers Zero-IF Architecture

The zero-IF (ZIF) design is a substitute for the superheterodyne architecture, which has reemerged as a potential remedy in recent years. A ZIF receiver converts the received signal down to the baseband in-phase (I) and quadrature (Q) signals using a single frequency mixing stage with the local oscillator (LO) set directly to the frequency range of interest. Due to the fact that all analog filtering occurs at baseband, where filters are significantly easier to design and less expensive than specialized RF/IF filters, this architecture lessens the demanding filtering needs of the superheterodyne. As a result of the ADC and DAC now using baseband I/Q data, the sample rate in relation to the converted bandwidth can be decreased, resulting in significant power savings. ZIF transceivers offer significant SWaP reduction for various design features due to a simplified analog front end and fewer components.

However, there are issues with this system architecture that must be resolved. A carrier leakage and an image frequency component are introduced during this direct frequency conversion to the baseband. Due to their orthogonality, the imaginary parts of the I and Q signals cancel out mathematically. It is hard to maintain a perfect 90° phase offset between the I and Q signals due to real-world issues including process variation and temperature deltas in the signal chain, which leads to weakened image rejection. Furthermore, carrier leakage components are introduced in the mixing stage due to insufficient LO isolation. Image and carrier leakage can reduce a receiver's sensitivity and lead to unwanted transmit spectrum emissions if not fixed.

Pros and cons of the Zero IF Program

Pros of the Zero IF Program

• By doing away with the requirement to shift the signal to the IF first, the zero IF approach simplifies the architecture.
• Mirror image suppression in the superheterodyne solution can be resolved by zero IF solutions.
• Since no IF filter or additional circuits are required for the zero IF approach, single-chip integration is simple.

Cons of the Zero IF Program

• Without IF pre-processing, the baseband output level can vary greatly depending on the strength of the incoming signal.
• Due to the basic oscillator's frequency matching the RF frequency, signal leakage interference may result.
• When the signal is close to the 0 frequency after mixing, a DC shift may happen.
• To bring the RF frequency perfectly close to the 0 frequency, the local oscillator must be precisely phase-locked.

RF transceivers Superheterodyne Architecture

Superheterodyne architecture has been the foundation of radio design for aerospace and defense systems since its beginnings. The single or twin-mixing stage superheterodyne design is frequently used in army radios, data links for unmanned aerial vehicles (UAVs), and SIGINT receivers. The advantages of this design are obvious: good frequency planning can result in very low spurious emissions, the intermediate frequency (IF) filters can control the channel bandwidth and selectivity, and the gain distribution across the stages enables a trade-off between noise figure and linearity optimization.

The performance of the superheterodyne has improved significantly over the past century of use over the entire signal chain. Devices that use RF and microwave energy have greater performance while using less electricity. The sample rate, linearity, and effective number of bits (ENOB) have all grown thanks to ADCs and DACs. As processing power in FPGAs and DSPs has grown over time in accordance with Moore's Law, more effective algorithms, digital correction, and more integration have been made possible. Device pin density has decreased due to advancements in package technology, which has also improved thermal handling.

RF transceivers Applications

When wireless communication has begun, an RF transceiver is in use. Its primary use is to adapt audio, data, and video information so that it can be transferred through wireless mediums. RF transceivers are used to convert between IF and RF frequencies. It is utilized in Wimax/WLAN/ZigBee/LTE networks, radio transmission and reception, television signal transmission and reception, and satellite communication.

How to choose RF Transceivers?

Understanding your system's characteristics in-depth and becoming knowledgeable about pertinent RF concepts and terminology are the first steps. AAC's RF textbook is a wonderful place to start if you don't have any familiarity with wireless communication. A link budget calculator and a free space path loss calculator are also available. The key characteristics that must be taken into account when choosing a transceiver IC for your system are covered in detail in the sections that follow.

Data Rate

You may need to check that the device can transfer bits quickly enough to keep up with your data stream in some circumstances. In other situations, a low data rate IC is what you're searching for. When all you need to do is send one temperature reading every 10 minutes, a transceiver tuned for 2 Mbps is not what you want.

Frequency Band

Obviously, if your system must operate within the 915 MHz ISM band, you do not want a 2.4 GHz device. Find a transceiver that can operate on a wide range of frequencies if you're unsure which band is best for your purpose. The SPIRIT1 from STMicro—the most intriguing part number I've ever seen—can operate in the following frequency ranges 150–174 MHz, 300–348 MHz, 387–470 MHz, and 779–956 MHz.

Modulation Type

Studying the advantages and disadvantages of the various modulation schemes may reveal that, given the anticipated operating circumstances of your specific application, some are preferable to others. For instance, frequency shift keying (FSK) is a better option than amplitude shift keying (ASK) if your system will be subjected to high levels of RF noise since FSK is less sensitive to changes in the received signal's amplitude.

Choosing a transceiver that supports many modulation schemes is an alternative strategy. This enables you to test out various possibilities and perhaps even modify your modulation parameters in response to changes in the RF environment or the mode of operation of the device.