Knowles directional couplers from DLI for turnkey or custom designs
Microwave module trends are clear; there is a race to produce smaller, lighter weight and lower cost products with higher performance output. Engineers are working to build more complex designs including multi-band systems, wider bandwidths and at higher frequency. Not forgetting everything has to be surface mount assembly as well! These trends are placing enormous pressure on designers, as well as the component size, weight, performance and precision of the components integrated into the systems, to offer competitive system solutions. Knowles brand, DLI is focusing on miniature passive devices to provide COTS solutions that address these concerns to 18+ GHz
A
great example is the recently released directional couplers. These provide an example of how high permittivity,
temperature stable materials can reduce size/weight and provide excellent performance repeatability. These small size directional couplers are manufactured using DLI’s precision thin film technology and offer a great option for microwave systems in commercial, military and space applications.
custom solutions are also available to suit individual size and performance parameters. Figure 2 shows typical measured performance of the 8 to 12 GHz model coupler mounted to a test board. The “Thru” path insertion loss is less than 0.5dB with a very flat coupling response, and isolation greater than 25dB. Designed for a 50 characteristic impedance, they offer a turnkey surface mount solution for high frequency power monitoring. The four port couplers are excellent for high frequency signal monitoring applications where board space is a premium and quality power detection or injection is required. COTS devices covering C, X and Ku bands offer quick turn solutions in a solder surface mount package with flexible PCB feed line configuration. Both 10dB and 20dB coupling values are available within each frequency band both with a common footprint for maximum flexibility. Typical applications of these four port
directional couplers are: • Built-in Test (BIT)
Figure 1: Miniature Octave-band SMT Couplers 4 to 18 GHz
The devices are designed to provide high
directivity, excellent repeatability and stable frequency over the temperature range -55 to +125ºC. Chip and wire mount devices with the same performance are also available -
• Power monitoring, incident/reflected amplifiers, antennas system protection
• Fault/Failure sensing • Calibration loops • Signal injection Directional Coupler Electrical Schematic - while the Schematic is simple, the design is not. The high precision of DLI’s thin film
Figure 3: Directional couplers shown on evaluation board
technology enables repeatable performance in a miniature size (only 0.120 x 0.080 inches for the 8 to 12 GHz model). These designs achieve low VSWR and high directivity thru advanced EM modelling techniques to compensate for surface mount transitions and even and odd mode phase velocity dispersion. Coupled with precision fabrication they provide repeatable high performance solutions for coupling needs. The high isolation and directivity of the couplers enables separation of reflected power from incident power, enabling detection of system faults such as failed amplifiers, antenna connections for protection against damage, or to switch in redundant amplifiers for example. They can also be utilised in AGC loops, or injection of calibration signals. The temperature stability of the proprietary ceramics enables extreme phase stability better than 10ppm/°C. This combination of high dielectric constant, outstanding temperature stability and Q enables smaller components with low insertion loss and repeatable stable RF performance across DLI’s product offerings. Two couplers can be cascaded to implement a dual directional coupler for simultaneous measurement of incident and reflected power. DLI’s understanding of the challenges of
SMT, chip & wire assembly and millimetre wave electronics have developed a broad array of passive components needed to realise systems in SMT technology without compromising performance. Accomplished with precision thin film manufacturing; exacting process control and extensive ceramic dielectric development, size reductions by factors of three or more are possible by the use of an outstanding temperature stable High Q dielectric. As microwave modules evolve, operation over wider temperatures is becoming more common and requires additional design time and effort to mitigate. However, many of the DLI brand products eliminate this concern by utilising this High Q dielectric that is designed to be frequency stable over temperature - microwave devices such as COTS SMT filters (bandpass, lowpass and highpass to 20+ GHz), COTS SMT power dividers, two and four way in phase (bandwidths up to 2-18GHz, COTS SMT), gain equalisers up to 40 GHz, SMT broadband DC blocking capacitors (including Milli-CapTM, 100 MHz to 60 GHz bandwidth), microwave Hi-Q capacitors and custom solutions to 60 GHz.
Figure 2: Typical measured performance graph
14 CIE Aerospace/Military/Defence Supplement July/August 2016
www.knowlescapacitors.com
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