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 designs include been optimized to meet the following parameters for most 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 really a brief description of the several parameters and available options.
VSWR VSWR, or Voltage Standing Wave Ratio, is a measure of the signal reflected from the given port when a signal is applied 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 1.10 is possible for some device configurations.
ISOLATION This parameter is used to specify the reverse loss characteristic of an isolator, between the output and input ports. All isolators described in this catalog consist of 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 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 acquired for narrow band applications.
Example: A circulator has a measured VSWR of just one.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, depending on 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 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, 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 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 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 1 another (or using their company magnetic materials) without degrading electrical performance. For more stringent applications (mounting in direct connection 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 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 upon 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, based on device configuration and termination capabilities. Special design considerations are required for pulsed signals with high peak power.
POWER RATING The input capacity to an isolator or circulator could be supplied from the continuous wave (CW) or perhaps a pulsed source. In the case of a pulsed source, both 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 generally have the highest power ratings.
Isolators and circulators for high peak power applications have particular 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 capacity for a particular model. Peak power levels as much as 5 kW are possible on certain models. Contingent around the peak power level and other parameters, units can be provided that will operate to altitudes well over 100,000 feet.
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 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 case. 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 interior geometry of the ferrite region, and also the type of cooling available. The insertion lack of an isolator or circulator causes 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 does not 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 attached to the output port of an 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 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 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 aren't phase matched, this feature can be provided on a specified basis. The tolerance in phase matching is determined by the particular model and size of the lot to be matched. Phase matched pairs can usually be provided to within �5 degrees. Linearity from the insertion phase is also specified. It is usually defined as a deviation from a best fit straight type of insertion phase versus frequency.