Beyond the Beam: The Impact of Coaxial Cables on Phased Array Technology

Phased array radar technology has been gaining popularity since its initial introduction in the 1960s and is now being used in a variety of applications, from military and defense to civilian sectors and even space exploration. This cutting-edge technology has revolutionized radar systems by offering unparalleled flexibility, precision, and speed.

At the heart of phased array radar lies a sophisticated antenna system composed of numerous individual elements, each capable of independently emitting and receiving radio waves. Unlike traditional radar systems that rely on mechanically rotating antennas, phased array radars electronically steer their beams, enabling rapid and precise target acquisition. This breakthrough is made possible by meticulously controlling the phase of radio waves emitted from each antenna element.

The success of phased array radar systems depends heavily on the seamless integration of their components, particularly the coaxial cables that connect the transmitter, receiver, and antenna elements. These cables are not just conduits for transmitting signals; they play a crucial role in maintaining the integrity of the radar system’s operation. The accuracy and stability of these coaxial cables are vital in preserving the precise phase relationships required for effective beamforming. Even the slightest variation in the phase of signals can lead to errors in beam direction and target accuracy, underscoring the importance of using high-quality, well-maintained coaxial cables in phased array radar systems.

Phased Array Radar Technology

Phased array radars have become a common element of other radar systems. They are employed in space to track spacecraft and research distant planets, in the air for missile defense systems, and in many ground systems by the military for the tracking of ships, aircrafts, and other objects.

Phased array radars consist of a flat antenna containing hundreds to thousands of individual elements, as opposed to past antennas that used one large transmitter. The use of multiple antenna elements helps improve reliability and lessen system failures. The multiple radiating elements electronically steer an antenna beam of radio waves with precision, eliminating the need for cumbersome mechanical adjustments. Electronic beam steering is accomplished by precisely controlling the phase of radio waves of each individual antenna element. These antenna elements are fed by high-frequency transmission lines. The precision of the signal phase delivered to each element is contingent upon the phase accuracy and stability of the employed cable assemblies.

Electronic steering is highly beneficial for phased array radars, as they can quickly shift in pattern or direction by manipulating the phase relationship between multiple antenna elements. These changes can be made much quicker than a conventional rotating radar dish, which takes significantly longer to complete a rotation. With an electronically steered antenna, Quick, adaptable scanning patterns can be employed, allowing control over the time a radar can focus on a target. More time spent on a target means more precise data.

Typically, broadcasting signals from multiple antennas risks an interference pattern that can reduce signal strength and distort data. However, for phased array radars, careful control and adjustment of the phase of individual antenna elements can result in a directable beam. This technique is called beamforming. As the accuracy of this beam is highly dependent on phase, the interconnects must be designed to maintain those precise phase relationships. Any deviation hinders the antenna’s ability to track or direct signals effectively.

Coaxial Cables: The Critical Connection

Coaxial cables serve as the vital link between the transmitter, receiver, and individual radiating elements of phased array antennas. This role in phased array radar systems is especially critical and significantly impacts overall system performance. Phased array radars offer many advantages over traditional radars, including:

Increased Scanning Speed: Enables quick scanning of large areas
Improved Accuracy: Enhances the precision of target detection and measurement
Multiple Beams: Supports tracking multiple targets at the same time
Adaptability: Allows the radar to quickly adjust to changing conditions
Electronic Beam Steering: Provides precise control over the direction of the radar beam without mechanical movement

Two types of coaxial cables are typically used in phased array radar systems: phase-stable coaxial cables and phase-matched coaxial cables.

Phase Stable Coaxial Cables

In today’s increasingly sophisticated electronic systems, phase-stable cables are designed for phase consistency despite environmental factors such as extreme temperatures. Any inconsistencies in coaxial cable performance can directly impact the system’s functionality. Applications requiring extreme phase stability utilize specialized cables designed to minimize phase variations. These cables employ materials with consistent electrical properties and construction that resists phase shifts caused by bending.

Factors that impact phase-stable coaxial cables include:

Cable Length: The physical length of the cable directly impacts its electrical length and phase shift of the signal. Shorter cables are less likely to introduce a large phase shift.
Bending: The bend of a cable can potentially create inconsistencies in phase. Tight bends or kinks can distort signal transmission.
Temperature: The dielectric material can be sensitive to temperature changes, and due to these changes, the electrical properties of the dielectric can shift, causing phase changes in the signal.
Dielectric Material: Electrical properties vary between dielectric materials. For instance, PTFE exhibits a significant phase shift around room temperature, which leads to instability. Other materials like foam fluoropolymer provide exceptional phase stability with minimal fluctuations across a broader temperature spectrum.
Connectors: Loose or low-quality connectors or a poorly designed interface can result in unwanted reflections and phase changes.
Frequency: Higher frequencies are generally more susceptible to phase fluctuations compared to lower frequencies.

Phase-Matched Coaxial Cables

Phase-matched cables are pairs or groupings of cables with matched electrical lengths. Engineered to reduce phase variations over temperature, phase-matched cables exhibit predictable phase tracking behavior, or the cable assembly’s ability to preserve a reliable phase relationship between transmitted and received signals. These phase variations are affected by electrical length, operating temperature, and initial phase matching tolerances. The challenge to maintain electrical lengths is mainly caused by temperature fluctuations; even with precise initial calibration, coaxial cables are vulnerable to phase shifts caused by varying thermal expansion and contraction rates. These shifts can result in phase mismatches and lead to system performance degradation.

For applications requiring phase stability in varied temperature environments, accurate phase tracking becomes imperative. Since higher frequencies are used for improved resolution and accuracy, minimal phase change and consistent phase tracking are crucial.

Factors Impacting Phase for Coaxial Cables

Phase is an essential parameter for many RF systems, ensuring optimal operation for coaxial cables and connectors. Since phased array radars are highly sensitive to variations in phase, the coaxial cables used in these systems need to be phase stable to enable the precise control of phase that make these radars desirable.

Electrical Length

Electrical length is the measurement of the physical length of a cable divided by its wavelength. It varies based on a number of factors and is influenced by frequency, signal delay, and the cable’s physical properties, including dielectric material and dimensions. Dielectrics typically provide stable performance but environmental factors like temperature fluctuations and physical stress can impact electrical characteristics.

Low Insertion Loss

Insertion loss quantifies the reduction in signal power as it travels through a coaxial cable. Maintaining low insertion loss is critical for maximizing signal transmission distance. Lower insertion loss allows the signal to travel farther before its strength becomes insufficient for reliable reception.

Dielectric Material and Temperature

Phase performance over temperature is a particularly critical parameter. RF coaxial cables often utilize PTFE dielectrics due to their wide operating temperature range and low dielectric loss; however, PTFE exhibits a phase transition near room temperature, leading to non-linear phase length variations and significant hysteresis with temperature fluctuations. This characteristic poses challenges for phase sensitive systems in varying thermal environments. Most high quality, high performance coaxial cables are made using dielectric materials whose dielectric constant is very stable across a relatively wide range of temperatures. As the environmental temperature changes around the cable, the metal conductors of the coaxial structure undergo a well-understood thermal expansion and contraction. To address these issues, Times Microwave Systems has developed specialized cable assemblies using materials like silicon dioxide and proprietary dielectrics to minimize temperature-induced phase changes.

PhaseTrack Coaxial Cables from Times Microwave Systems

PhaseTrack cable assemblies from Times Microwave Systems are engineered for applications where precise phase control is essential and phase change over temperature must be minimized. Featuring the proprietary TF4® dielectric, a foam fluoropolymer, these cables deliver exceptional phase stability by eliminating the significant phase shifts typically seen with PTFE dielectrics between 15°C and 25°C. With diameters ranging from 0.047” to 0.318”, PhaseTrack cables support a broad frequency range and operate reliably across diverse temperature conditions. Their versatility is further enhanced by a comprehensive selection of connectors, including standard and high-frequency options, as well as four different jacket materials, making them ideal for demanding environments. Additionally, these cables are double shielded for excellent shielding effectiveness, minimizing signal interference. A vapor seal interlayer is included to prevent moisture and contaminants from compromising electrical performance under any conditions.

Takeaways

Precise phase control is paramount for the successful operation of numerous RF and microwave systems, demanding consistent phase relationships between components. As a critical interconnect, coaxial cables significantly impact overall system performance, especially in complex phased array radar systems, where meticulous phase control and minimal signal loss are essential for achieving optimal accuracy, speed, and reliability. The increasing complexity and performance requirements of modern systems necessitate highly stable phase components, driving continuous innovation in coaxial cable technology.

The integration of phased array radar systems across various sectors underscores their transformative impact, making them indispensable tools in both military and civilian applications. As these systems become increasingly sophisticated, the importance of understanding and addressing the challenges posed by coaxial cable performance becomes paramount. Industry leaders like Times Microwave Systems are at the forefront, developing cutting-edge solutions that ensure the stability and accuracy of phase relationships, enabling effective beamforming and target acquisition. The future of radar technology hinges on the continued innovation and precision engineering of these critical components, ensuring reliable operation even in the most challenging environments and empowering next-generation systems to operate with greater accuracy and efficiency.