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 models have been optimized to satisfy the following parameters for most popular applications: bandwidth, VSWR, isolation, insertion loss, temperature, and size. These along with other parameters can 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 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 at a specified reference plane), can 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 overturn loss sign of an isolator, between your output and input ports. All isolators described within 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 created 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 depends 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 has a measured VSWR of just one.2 for those three ports. If an ideal 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 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 difference 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 you possibly can. For these applications, the insertion loss could be minimized by using low loss ferrite and dielectric materials, by silver plating circuit elements. Insertion loss of .10 dB is routinely achieved being produced 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 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 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 can be mounted within 1/2 inch of 1 another (or from other magnetic materials) without degrading electrical performance. For tighter applications (mounting in direct connection 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 generally 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 should 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, depending 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 a continuous wave (CW) or perhaps a pulsed source. In the situation of a pulsed source, both peak and average power components of the pulse train should be specified in 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 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 electricity and other parameters, units could be provided that will operate to altitudes of over 100,000 feet.
High peak powers may cause an increase in the insertion reduction in below-resonance designs, because of non-linearity effects of the ferrite material. This increase can occur 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 of the device, that could result in overheating. Special ferrite materials are utilized 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 determined by 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 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 device to a heat sink is sufficient in many cases if 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 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 things to consider for many parameters. These include normal and worst-case load VSWR conditions and the cooling that might be required under worst of all conditions.
CONNECTORS The connectors used on coaxial models are N-Type or SMA female. Other connectors can be provided based on operating frequency and package size; however, certain 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 feature can be provided on the specified basis. The tolerance in phase matching is determined by 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 usually defined as a deviation from a best fit straight line of insertion phase versus frequency.