Signal Chain Discussion Series: Transmit/Receive Module

Though transmit/receive modules (TRMs) have been used for some time in active electronically scanned array (AESA) radar technology, the benefits of phased array antenna and multi-input-multi-output (MIMO) for 5G applications have brought this technology to the mainstream. Given that phase array antennas for millimeter-wave 5G may employ up to, and possibly beyond, 64 antennas elements in a single antenna system, demands for compact and high performance TRMs is on the rise.

TRMs consist of both a transmit chain and a receive chain connected to the same antenna, along with phase and amplitude shifting electronics. In some architectures, the phase and amplitude shifting elements are included in both the transmit and receive chains, but newer common leg, or shared, architectures may use one chain of phase and amplitude shifting elements with a method of isolating the transit and receive chain, such as with a switch or circulator. Given that circulators are generally rather large discrete modules and high frequency RF switches are often more compact and lower cost, switches may be the more commonly used solution for shared architecture TRMs.

Circulators and switches may also be used to isolate the transmit and receive chains at the antenna connection port, depending if frequency domain multiplexing (FDM) or time-domain multiplexing (TDM) is used. Transmit chains in TRMs include high power amplifiers (HPAs), driver amplifiers, pre-amplifiers, and occasionally filters depending on the spectrum requirements of possibility of transmitter-induced interference. Receive chains in TRMs consist of limiters, low-noise amplifiers (LNAs), gain stages, band pass filters, and potentially other filtering elements.
A TRM typically has to fit within the footprint of a single element of the antenna system, along with mechanical fixturing, interconnect, environmental protection, and thermal management systems. This means that the TRM is often made in a highly compact assembly that likely also includes its own environmental protection and interfacing with thermal management components. Therefore, the individual components and devices of a TRM are likely to be semiconductor-based or extremely compact to enable the smallest footprint TRM possible.

The performance requirements for 5G TRMs differ from radar TRM requirements in that 5G applications require the lightest and most compact solution possible while radar TRMs have looser footprint requirements and can rely more on larger discrete components to meet performance goals. Hence, the transmit and receive performance of a 5G TRM must meet next generation communication requirements in even more compact geometries.

TRM Transit Chain Performance Parameters

• Peak Power Output
• Phase Noise
• Harmonic and Non-harmonic Spurious
• Power Efficiency

TRM Receive Chain Performance Parameters

• Noise Figure
• Channel Gain
• Cross-channel Consistency
• STC Amplitude/Phase Consistency
• Image Frequency Rejection Ratio
• Isolation

Learn more about Pasternack’s RF Components for 5G Applications: https://www.pasternack.com/pages/RF-Microwave-and-Millimeter-Wave-Products/5g-rf-solutions.html