Aus Bildungsstreik 2009
GENERAL M2 GLOBAL�S standard and 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 designs include been optimized to meet the following parameters for many popular applications: bandwidth, VSWR, isolation, insertion loss, temperature, and size. These and other parameters can be selectively optimized for your specific application. The following is really a brief description of the several parameters and available alternatives.
VSWR VSWR, or Voltage Standing Wave Ratio, is really a measure of the signal reflected from a given port whenever a signal is used to that port. For critical applications, a Smith Chart (with 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 just one.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 the isolator, whereas a circulator is totally 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 the termination and the circulator port. Most isolators are specified at 20 dB, but values of 26 dB can be obtained for narrow band applications.
Example: A circulator has a measured VSWR of 1.2 for those three ports. If an ideal test termination having 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 put 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 distinction between the two VSWRs.
INSERTION LOSS This parameter is used to specify the forward loss characteristics of the isolator or circulator. Most of 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 can 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 restricted 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 typical, although some models are limited to 0 to 50�C. Special temperature compensation could 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 can 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 Designs include an RFI leakage specification at close proximity of -40 dB. Special packaging and sealing methods are available to improve RFI shielding. Leakage values as much as 100 dB can be provided at a nominal cost. RFI leakage is usually not specified for Puck configurations.
TERMINATION RATING The termination is designed to safely dissipate reverse power into 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 on the customer application, but might 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 rich in peak power.
POWER RATING The input capacity to an isolator or circulator could be supplied from a continuous wave (CW) or a pulsed source. In the case of a pulsed source, both the peak and average power components 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 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 have to maximize the peak power capacity for a particular model. Peak power levels up to 5 kW are possible on certain models. Contingent around the peak electricity and other parameters, units could be provided that will operate to altitudes of over 100,000 feet.
Drop in Isolator
High peak powers may cause an increase in the insertion reduction in below-resonance designs, due to non-linearity effects of the ferrite material. This increase can happen at peak power levels considerably less than that required for breakdown or arcing. The increased insertion loss would cause more capacity to be dissipated in the ferrite region from the device, that could result in overheating. Special ferrite materials are used to avoid this situation. Such non-linearity effects do not occur in above resonance models.
The CW power rating of an isolator or circulator is dependent upon its insertion loss, the internal geometry of the ferrite region, and the type of cooling available. The insertion loss of an isolator or circulator leads to a small fraction of the input power to be absorbed and dissipated in the ferrite region and the conductor surfaces as heat. Adequate cooling techniques are necessary to insure the ferrite material doesn't reach an excessive temperature. Mounting the unit 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 attached to the output port of the isolator will reflect a substantial amount of power. The temperature from the ferrite region along with the internal voltage increases, 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 case conditions.
CONNECTORS The connectors used on coaxial models are N-Type or SMA female. Other connectors can 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 the specified basis. The tolerance in phase matching is determined by the particular model and size of the lot to become matched. Phase matched pairs can usually be provided to within �5 degrees. Linearity of the insertion phase also can be specified. It is generally defined as a deviation from a best fit straight type of insertion phase versus frequency.