GENERAL M2 GLOBAL�S standard and high power isolator and circulator products 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 satisfy 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 various parameters and available alternatives.
VSWR VSWR, or Voltage Standing Wave Ratio, is really a measure of the signal reflected from the given port whenever a signal is used 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 just one.10 can be achieved for some device configurations.
ISOLATION This parameter is used to specify overturn loss characteristic of an isolator, between your output and input ports. All isolators described within this catalog consist of a circulator by having an internal termination. The three parameters, isolation, VSWR, and insertion loss, are required to specify electrical performance of the 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 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 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 will be the return loss equivalent to the circulator VSWR, in this instance 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, depending on 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 could be minimized by using low loss ferrite and dielectric materials, by silver plating circuit elements. Insertion lack 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 typical, although some models are restricted to 0 to 50�C. Special temperature compensation could 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 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 available to improve RFI shielding. Leakage values up to 100 dB could 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 may occur under normal or anticipated fault conditions. Maximum reverse power depends upon 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, depending 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 case of a pulsed source, both peak and average power components of the pulse train ought to be specified in order to determine adequate safety margins.
CW (or average) power ratings depend on frequency and on device configuration. Low frequency waveguide devices generally have the highest power ratings.
Isolators and circulators for top peak power applications have particular design features to prevent 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 capability of a particular model. Peak power levels up to 5 kW are possible on certain models. Contingent around the peak electricity and other parameters, units can 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, due to non-linearity effects of the ferrite material. This increase can occur at peak power levels considerably lower than that required for breakdown or arcing. The increased insertion loss would cause more power to be dissipated within the ferrite region from the device, that 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 loss of an isolator or circulator causes a small fraction from the input capacity 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 does not reach an excessive temperature. Mounting the unit to a heat sink is enough in many cases if the average power is moderate.
In high power applications, a component with a high VSWR connected to the output port of an isolator will reflect a large amount of power. The temperature from the ferrite region along with the internal voltage will increase, 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 the cooling that might be required under worst case conditions.
CONNECTORS The connectors utilized on coaxial models are N-Type or SMA female. Other connectors can be provided according to 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 is determined by 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 is also specified. It is generally defined as a deviation from a best fit straight line of insertion phase versus frequency.