GENERAL M2 GLOBAL�S standard and 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 could be selectively optimized for the 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 applied 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 is possible for some device configurations.
ISOLATION This parameter can be used to specify overturn loss characteristic of an isolator, between your output and input ports. All isolators described in this catalog contain a circulator with 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 created 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 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 1.2 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 equal to the circulator VSWR, in this case 20.8 dB. If an evaluation 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 difference between the two VSWRs.
INSERTION LOSS This parameter can be used to specify the forward loss characteristics of an isolator or circulator. Most of 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 possible. For these applications, the insertion loss can be minimized by utilizing 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 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 limited to 0 to 50�C. Special temperature compensation could 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 more stringent 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 close proximity of -40 dB. Special packaging and sealing methods are available to improve RFI shielding. Leakage values as much as 100 dB can 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 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 on the customer application, but might be as high as the power 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 rich in peak power.
POWER RATING The input power to an isolator or circulator could be supplied from the continuous wave (CW) or perhaps a pulsed source. In the situation of a pulsed source, both the peak and average power aspects 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 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 electricity 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, due to 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 in the ferrite region of the device, that could result in overheating. Special ferrite materials are utilized 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 leads to a small fraction of the input capacity to be absorbed and dissipated within 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, an element with a high VSWR attached to the output port of an isolator will reflect a substantial amount of power. The temperature of 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 also the cooling that would be required under worst of all 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 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 the lot to become matched. Phase matched pairs usually can be provided to within �5 degrees. Linearity of the insertion phase also can be specified. It is generally defined as a deviation from a best fit straight line of insertion phase versus frequency.