GENERAL M2 GLOBAL�S standard and 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 satisfy the following parameters for many popular applications: bandwidth, VSWR, isolation, insertion loss, temperature, and size. These along with 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 a given port when 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 is possible for some device configurations.
ISOLATION This parameter is used to specify the reverse loss sign of an isolator, between your output and input ports. All isolators described in 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 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 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 includes a measured VSWR of 1.2 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 will be the return loss equivalent to the circulator VSWR, in this instance 20.8 dB. If an evaluation termination having 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 can be used to specify the forward loss characteristics of an 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 possible. 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 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 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 all have sufficient magnetic shielding for general handling and mounting, and could be mounted within 1/2 inch of one another (or from other magnetic materials) without degrading electrical performance. For more stringent applications (mounting in direct contact with a magnetic plate), additional shielding may be required, 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 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 should be specified to exceed power levels that may 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 needed for pulsed signals with high peak power.
POWER RATING The input power to an isolator or circulator could be supplied from a 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 ought to 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 special 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 capacity for a particular model. Peak power levels up to 5 kW are possible on certain models. Contingent around the peak power level and other parameters, units could be provided that will operate to altitudes well over 100,000 feet.
High peak powers may cause an increase in the insertion loss 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 required for breakdown or arcing. The increased insertion loss would cause more power to be dissipated in the ferrite region of the device, which could result in overheating. Special ferrite materials are used to avoid this case. 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 also the type of cooling available. The insertion loss of an isolator or circulator causes a small fraction of the input power to be absorbed and dissipated within the ferrite region and 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 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 large amount of power. The temperature of the ferrite region as well as the internal voltage will increase, 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 also the cooling that might 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, some 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 will depend on the particular model and size the lot to become matched. Phase matched pairs usually can 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 line of insertion phase versus frequency.