Modern radar and electronic warfare systems are increasingly reliant on multi-antenna architectures. Today’s electronic warfare (EW) military applications utilize signals in the electromagnetic spectrum or directed energy for air, sea, and land sensing and targeting operations. For the validation, debugging, and characterization of these systems, all test equipment must exhibit phase-coherent multichannel capabilities to address the corresponding measurement needs.
Wireless communication systems have evolved from simple to complex modulation schemes up to the multiple-input, multiple-output (MIMO) with two or more transmitters and receivers for achieving greater data thoroughput. Common configurations of MIMO systems include 2x2, 4x4, and 8x8. They can be utilized in a wide range of wireless standards, such as HSPA+, 802.11g/n/ac, LTE, etc., and are touted to provide enhanced bandwidth for the emerging 5G standard.
A key advantage of MIMO that contributes to a higher thoroughput is the use of spatial domain for simultaneous power and data transfer (spatial multiplexing). MIMO also has beam steering capabilities; radio frequency (RF) signals can be directed precisely by controlling the signal propagation phase over several antennas. MIMO ensures higher reliability without the need for additional power or higher bandwidth.
MIMO signals are described as coherent if they exhibit a constant relative phase at every instance in time. In real-life applications, however, no two signals are perfectly coherent due to several reasons. First, there is always some level of phase noise in the system due to synthesizers being time uncorrelated. Other factors include phase drift between the signal generators, signal generation chains, and temperature effects (thermal phase drift) in synthesizer components.
Radar and electronic warfare systems utilized in military and aerospace applications leverage MIMO beam steering capabilities for search and rescue (SAR), weather monitoring, and target tracking, to name a few. Military radar systems have imaging capabilities that propagate RF waves in the direction of a target and analyze the reflected signals. More than several decades of development have resulted in high-sensitivity radar capable of detecting fine details to a high degree of accuracy. In defense applications where precision is critical, phase-coherent signal analysis is non-negotiable.
MIMO system testing requires test systems capable of generating multiple signals with phase coherence, usually with minimal deviations or constant amplitude and phase difference values (ideally < 1° phase drift). Some challenges involved in designing such set-ups include precise phase control capabilities, simplicity, and compactness. Phase-coherent measurements can be carried out using a test system including signal generators that utilize a common synthesizer signal. The ideal multi-channel phase-coherent test set-up should be flexible and scalable to meet different user requirements while delivering the same quality of results.
Rohde & Schwarz is a leading manufacturer of electronic test equipment for precise measurements. R&S® signal generators provide an easy-to-use, low-profile solution for generating phase-coherent signals with a uniform synthesizer signal for all instruments. Join Ezer Bennour and Luke Cirillo, leading engineers at Rohde & Schwarz, for a webinar covering the importance of phase-coherent measurements in a variety of real-world use cases. This webinar will also showcase relevant Rohde & Schwarz test and measurement solutions to meet these requirements.