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 meet 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 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 (with an impedance plot recorded in a specified reference plane), can 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 can be used to specify overturn loss characteristic of an isolator, between the output and input ports. All isolators described within 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 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 depends on the VSWR of both 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 includes 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 an evaluation 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 an isolator or circulator. Most in our catalog designs include 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 lack 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 function from -55 to +125�C.
MAGNETIC SHIELDING Catalog units all have 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 tighter applications (mounting in direct contact 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 could 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 in to 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 needed for pulsed signals with high peak power.
POWER RATING The input capacity to an isolator or circulator can be supplied from the continuous wave (CW) or a pulsed source. In the situation of a pulsed source, both peak and average power aspects of the pulse train ought to be specified in to determine adequate safety margins.
CW (or average) power ratings rely on frequency as well as 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 avoid breakdown or arcing, which may otherwise cause permanent degradation in performance. Proper connector selection, optimized internal geometry, and encapsulation have to maximize the peak power capability of 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 could be provided that will operate to altitudes well over 100,000 feet.
High peak powers can 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 lower 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 the 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 causes 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 are necessary to insure the ferrite material does not reach an excessive temperature. Mounting the device to a heat sink is enough 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 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 considerations 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 could 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 the specified basis. The tolerance in phase matching is determined by 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 generally defined as a deviation from the best fit straight line of insertion phase versus frequency.