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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, within the frequency range 300 MHz to 40 GHz. All models have been optimized to satisfy the following parameters for many popular applications: bandwidth, VSWR, isolation, insertion loss, temperature, and size. These and other parameters could be selectively optimized for your specific application. The following is a brief description of the various parameters and available options.
VSWR VSWR, or Voltage Standing Wave Ratio, is a measure of the signal reflected from the given port whenever 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 is used to specify the reverse loss characteristic of an isolator, between your output and input ports. All isolators described within 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 does not have an intrinsic isolation value. With a termination around the third port, the isolation measured would depend on the VSWR of both the 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 has a measured VSWR of just one.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 equal to the circulator VSWR, in this instance 20.8 dB. If an evaluation 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, depending on the phase distinction 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 models have 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, and 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 range 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 utilize temperature compensation maaterials where possible. Operating temperatures from -20 to +65�C or from -40�C to 100�C are normal, although some models are restricted to 0 to 50�C. Special temperature compensation can be provided for most units to function from -55 to +125�C.
MAGNETIC SHIELDING Catalog units have the ability to sufficient magnetic shielding for general handling and mounting, and could be mounted within 1/2 inch of one another (or using their company 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 available to improve RFI shielding. Leakage values up to 100 dB can be provided in a nominal cost. RFI leakage is usually not specified for Puck configurations.
TERMINATION RATING The termination is designed to safely dissipate reverse power in to the isolator heat sink. The termination power rating ought to be specified to exceed power levels that might occur under normal or anticipated fault conditions. Maximum reverse power depends upon 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 required 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 case of a pulsed source, both peak and average power aspects of the pulse train ought to be specified in order to determine adequate safety margins.
CW (or average) power ratings rely on frequency and on device configuration. Low frequency waveguide devices generally have the highest power ratings.
Isolators and circulators for high peak power applications have particular design features to prevent breakdown or arcing, which may otherwise cause permanent degradation in performance. Proper connector selection, optimized internal geometry, and encapsulation are required to maximize the peak power capability of a particular model. Peak power levels as much as 5 kW are possible on certain models. Contingent on the peak power level and other parameters, units can be provided that will operate to altitudes of over 100,000 feet.
High peak powers can cause an increase in the insertion reduction in below-resonance designs, because of non-linearity effects of the ferrite material. This increase can happen at peak power levels considerably lower than that necessary for breakdown or arcing. The increased insertion loss would cause more power to be dissipated within the ferrite region of the device, that could result in overheating. Special ferrite materials are utilized to avoid this case. Such non-linearity effects don't occur in above resonance models.
The CW power rating of the isolator or circulator is determined by its insertion loss, the internal geometry of the ferrite region, and the type of cooling available. The insertion lack of an isolator or circulator causes a small fraction of the input capacity to be absorbed and dissipated in the ferrite region and the conductor surfaces as heat. Adequate cooling techniques should insure the ferrite material does not 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, an element with a high VSWR attached to the output port of the isolator will reflect a large amount of power. The temperature from the ferrite region as well as the internal voltage will increase, causing performance to deteriorate or arcing to happen below the rated power level.
Isolators and circulators that meet stringent peak and average power levels require design considerations 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 utilized on coaxial models are N-Type or SMA female. Other connectors can be provided based on operating frequency and package size; however, some types may cause some electrical degradation.
INSERTION PHASE Many applications require isolators and circulators to be supplied as phase matched sets. Although our catalog models are not phase matched, this selection can be provided on the specified basis. The tolerance in phase matching will depend on the particular model and size the lot to be matched. Phase matched pairs can usually be provided to within �5 degrees. Linearity from the insertion phase also can be specified. It is generally defined as a deviation from the best fit straight type of insertion phase versus frequency.