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GENERAL M2 GLOBAL�S standard and high power isolator and circulator goods are available in Coax, Waveguide, Drop-in, Puck, and Dual Junction configurations, over the frequency range 300 MHz to 40 GHz. All designs include been optimized to satisfy the following parameters for many popular applications: bandwidth, VSWR, isolation, insertion loss, temperature, and size. These along with other parameters could be selectively optimized for the specific application. The following is a brief description of the various parameters and available options.
VSWR VSWR, or Voltage Standing Wave Ratio, is really a measure of the signal reflected from a given port when a signal is applied to that port. For critical applications, a Smith Chart (by having an impedance plot recorded in a specified reference plane), could be provided with each device. A typical specification for VSWR is 1.25; however, values of 1.10 can be achieved for some device configurations.
ISOLATION This parameter can be used to specify overturn loss characteristic of an isolator, between your output and input ports. All isolators described in this catalog contain a circulator with an internal termination. The three parameters, isolation, VSWR, and insertion loss, have to specify electrical performance of an isolator, whereas a circulator is completely defined by its VSWR and insertion loss. Although a circulator can be made into an isolator by terminating one port, it doesn't have an intrinsic isolation value. With a termination around the third port, the isolation measured depends on the VSWR of both termination and the circulator port. Most isolators are specified at 20 dB, but values of 26 dB can be acquired for narrow band applications.
Example: A circulator includes a measured VSWR of 1.2 for all three ports. If an ideal test termination with a VSWR equal to 1.00 were placed on Port 3, the resulting isolation from Port 2 to Port 1 would be the return loss equivalent to the circulator VSWR, in this case 20.8 dB. If a test termination with a VSWR of 1.05 were placed on Port 3, the isolation from Port 2 to Port 1 would vary between 18.2 and 22.5 dB, with respect to the phase difference between the two VSWRs.
INSERTION LOSS This parameter can be used to specify the forward loss characteristics of an isolator or circulator. Most in our catalog designs include an insertion loss specification between 0.2 to 0.4 dB. Many low noise systems require an isolator with as low an insertion loss as possible. For these applications, the insertion loss could be minimized by utilizing low loss ferrite and dielectric materials, by silver plating circuit elements. Insertion loss of .10 dB is routinely achieved in production for certain device configurations.
OPERATING TEMPERATURE RANGE The operating temperature selection of an isolator or circulator is limited by the properties of magnets and ferrite materials. Generally, as the operating frequencies decrease, isolator temperature sensitivity increases. Catalog units make use of temperature compensation maaterials where possible. Operating temperatures from -20 to +65�C or from -40�C to 100�C are typical, although some models are restricted to 0 to 50�C. Special temperature compensation can be provided for most units to operate from -55 to +125�C.
MAGNETIC SHIELDING Catalog units have the ability to sufficient magnetic shielding for general handling and mounting, and can be mounted within 1/2 inch of one another (or from other magnetic materials) without degrading electrical performance. For tighter applications (mounting in direct contact with a magnetic plate), additional shielding are usually necesary, usually increasing package size.
RFI SHIELDING Standard Models have an RFI leakage specification at closeness of -40 dB. Special packaging and sealing methods are for sale to improve RFI shielding. Leakage values as much as 100 dB could be provided at a nominal cost. RFI leakage is generally not specified for Puck configurations.
TERMINATION RATING The termination is made to safely dissipate reverse power into the isolator heat sink. The termination power rating ought to be specified to exceed power levels that may occur under normal or anticipated fault conditions. Maximum reverse power depends on the customer application, but may be as high as the ability applied to the input port.
Isolators are rated for reverse power levels between 1 and 500 Watts, based on device configuration and termination capabilities. Special design considerations are needed for pulsed signals with high peak power.
POWER RATING The input power to an isolator or circulator can be supplied from the continuous wave (CW) or a pulsed source. In the situation of a pulsed source, both the peak and average power aspects of the pulse train should be specified in to determine adequate safety margins.
CW (or average) power ratings depend on frequency as well as on device configuration. Low frequency waveguide devices generally have the highest power ratings.
Isolators and circulators for high peak power applications have special design features to avoid breakdown or arcing, which would otherwise cause permanent degradation in performance. Proper connector selection, optimized internal geometry, and encapsulation are required to maximize the peak power capacity for a particular model. Peak power levels as much as 5 kW are possible on certain models. Contingent on the peak electricity and other parameters, units could be provided that will operate to altitudes of over 100,000 feet.
High peak powers may cause an increase in the insertion loss in below-resonance designs, because of non-linearity effects of the ferrite material. This increase can happen at peak power levels considerably less than that necessary for breakdown or arcing. The increased insertion loss would cause more capacity to be dissipated within the ferrite region of the device, which could result in overheating. Special ferrite materials are utilized to avoid this situation. Such non-linearity effects don't occur in above resonance models.
The CW power rating of the isolator or circulator is dependent upon its insertion loss, the interior geometry of the ferrite region, and the type of cooling available. The insertion lack of an isolator or circulator leads to a small fraction of the input power to be absorbed and dissipated in the ferrite region and also the conductor surfaces as heat. Adequate cooling techniques are necessary to insure the ferrite material doesn't reach an excessive temperature. Mounting the device to a heat sink is enough in many cases when the average power is moderate.
In high power applications, a component with a high VSWR connected to the output port of the isolator will reflect a substantial amount of power. The temperature from the ferrite region as well as the internal voltage increases, causing performance to deteriorate or arcing to occur below the rated electricity.
Isolators and circulators that meet stringent peak and average power levels require design things to consider for many parameters. These include normal and worst-case load VSWR conditions and also the cooling that would be required under worst of all conditions.
CONNECTORS The connectors used on coaxial models are N-Type or SMA female. Other connectors could be provided according to operating frequency and package size; however, certain types may cause some electrical degradation.
INSERTION PHASE Many applications require isolators and circulators to become supplied as phase matched sets. Although our catalog models are not phase matched, this feature can be provided on a specified basis. The tolerance in phase matching will depend on the particular model and size of the lot to become matched. Phase matched pairs can usually be provided to within �5 degrees. Linearity from the insertion phase also can be specified. It is usually defined as a deviation from the best fit straight type of insertion phase versus frequency.