GENERAL M2 GLOBAL�S standard and high power isolator and circulator products are available in Coax, Waveguide, Drop-in, Puck, and Dual Junction configurations, over the frequency range 300 MHz to 40 GHz. All models have 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 the specific application. The following is really a brief description of the several parameters and available alternatives.
VSWR VSWR, or Voltage Standing Wave Ratio, is a measure of the signal reflected from a given port whenever a signal is applied to that port. For critical applications, a Smith Chart (with an impedance plot recorded at a specified reference plane), can 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 sign of an isolator, between the 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 totally defined by its VSWR and insertion loss. Although a circulator can be created into an isolator by terminating one port, it doesn't have an intrinsic isolation value. With a termination on the third port, the isolation measured would depend on the VSWR of both the termination and also 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 includes a measured VSWR of just one.2 for those three ports. If a perfect test termination with a VSWR equal to 1.00 were put on Port 3, the resulting isolation from Port 2 to Port 1 would be the return loss equal to the circulator VSWR, in this case 20.8 dB. If a test termination having 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 difference between the two VSWRs.
INSERTION LOSS This parameter can be used to specify the forward loss characteristics of the 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 you possibly can. 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 range 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 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 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 all have sufficient magnetic shielding for general handling and mounting, and could be mounted within 1/2 inch of 1 another (or using their company magnetic materials) without degrading electrical performance. For more stringent 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 for sale 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 made 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 on the customer application, but may be as high as the power applied to the input port.
Isolators are rated for reverse power levels between 1 and 500 Watts, depending 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 can be supplied from the continuous wave (CW) or perhaps a pulsed source. In the case of a pulsed source, both the peak and average power aspects of the pulse train should 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 have the highest power ratings.
Isolators and circulators for top peak power applications have special design features to avoid 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 up to 5 kW are possible on certain models. Contingent on the peak electricity and other parameters, units could be provided that will operate to altitudes well 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 less than that necessary for breakdown or arcing. The increased insertion loss would cause more power to be dissipated within the ferrite region from 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 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 from the input capacity to be absorbed and dissipated within the ferrite region and also the conductor surfaces as heat. Adequate cooling techniques should insure the ferrite material doesn't reach an excessive temperature. Mounting the unit to a heat sink is sufficient in many cases when the average power is moderate.
In high power applications, an element with a high VSWR connected to the output port of the isolator will reflect a large 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 electricity.
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 utilized on coaxial models are N-Type or SMA female. Other connectors could 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 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 usually can 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 line of insertion phase versus frequency.