Glossary of terms

90 Degree (90º) Hybrid: A 4-port component that splits an input signal into two output signals of the same amplitude and a 90 degree difference between them. The forth port is an isolation port.


Amplitude Balance: The amplitude balance is the difference in the power levels at any given frequency for the same input level when measured at the output ports. Please see the individual product application note for more information.


Characteristic Impedance: For a RF/microwave signal traveling in a transmission line, the characteristic impedance is the ratio of the amplitudes of the voltage and the current in Ohms. Characteristic impedance is determined by the geometry and materials of the transmission line structure. For a uniform line it is not dependent on its length. The characteristic impedance can be calculated based on the physical dimensions and dielectric properties of the transmission line structure. Most RF and microwave systems are designed to operate with a characteristic impedance of 50 or 75 ohms.


Coherent Signals: Multiple RF or microwave signals exhibiting attributes such that when input to a power combiner their wave forms add constructively. For RF and microwave signals, the attributes of frequency, amplitude, phase must be identical at the same moments in time for signal coherence to exist.


Combining Loss: The Loss of output signal power due to the vector summing of semi-coherent input signals that differ slightly in phase and/or amplitude. The combining loss of semi-coherent signals is proportional to the phase and amplitude unbalance of the signals. Identical coherent signals summed through a power combiner exhibit no combining loss beyond the normal insertion loss specified for the combiner.


Directivity: Directivity is a measure of the quality of the directional coupler. Directivity = Coupling-Isolation


Frequency Range: The span of frequency over which the component maintains all specified performance values.


Group delay (GD): This specification relates to the phase linearity of a filter versus frequency. Since a phase delay occurs at the output of a filter it is important to know if this phase shift is linear with frequency. If the phase shift is nonlinear with frequency, the output waveform will be distorted. Linear phase shift will result in constant group delay since the derivative of a linear function is a constant.


Impedance: This value, specified in ohms, is the filter’s source (input) and the terminating (output) impedances. Input and output impedance should match the impedance of the transmission path in which the filter is placed. An impedance of 50 ohms is almost universal throughout RF and microwave system designs, although an impedance of 75-ohms is used in cable television systems.

Insertion Loss (IL): This is the ratio of signal amplitude before a filter to the amplitude at its output. At any frequency it is defined as: IL=10Log(Pl/Pin), where Pl is the load power and Pin is the power from the input source. Insertion loss should be as low as possible regardless of the power-handling ability of the filter. For example, heat dissipation increases at higher power levels, and lower insertion loss can help reduce it. When signal levels are low, high insertion loss can reduce the output after the filter to an unacceptable level.

Isolation: This relates to the ability of a diplexer or duplexer to reject the transmit (Tx) frequency without affecting the receive (Rx) frequency, and the ability to reject the receive (Rx) frequency without affecting the transmit (Tx) frequency. This is called Rx/Tx isolation and the greater the isolation the more effectively the filter can isolate the Rx from the Tx and vice versa. Higher values of isolation translate into cleaner transmit and receive signals.


Input VSWR: Voltage standing wave ratio measured at the components input port with all output ports terminated with 50 ohms.

Microstrip Circuit: Microstrip is a planar transmission line circuit constructed of thin strip-like lines separated from a ground plane by a dielectric substrate. Commonly used for constructing RF and microwave devices utilizing discrete components attached to the top of the circuit board.


Mismatch Loss: A measure of power loss due to reflections within a device. Signal Reflections occur when there is a mismatch between the source and load impedances.


Passband: The spectral region in which a filter has the least attenuation and thus allows the most signal to pass. Passband is usually defined at the 0.5 dB, 1 dB, or the 3 dB (half-power) points or others depending on the requirements of the host system design.

Power handling: This is the RF input power beyond which the performance of the filter may degrade or fail, expressed in watts (W). It is typically specified as a continuous wave (CW) value, as an average value that is usually 10 times its CW rating, or both.


Phase Balance: The phase balance is the difference in phase angle between the signal at one output port and any other output port.


PIM (Passive Intermodulation): The production of unwanted signals from the nonlinear mixing of two or more signals in a passive component. PIM problems may be minimized by careful contact and current path junction design (including connector mating interfaces), use of linear materials such as silver and avoidance of or shielding from non-linear ferromagnetic materials, such as nickel and cleanliness in the manufacturing process.

Power Combiner: A device that combines or sums “N” number of input signals to a common output. Power combiners and dividers are often one in the same component.


Power Divider: A device that divides or splits an input signal into “N” number of output signals. Power combiners and dividers are often one in the same component.


Power Rating: The maximum amount of continuous input power (in watts) a component can safely handle without permanent performance degradation.


Power Split: The theoretical power ratio from input to output of a power divider (in dB) expressed by the formula: Power Split = 10 log (1/N), where: N = number of outputs of an equal power divider. Often referred to as theoretical loss.


Stripline Circuit: Stripline is a strip conductor sandwiched by dielectric between a pair of ground planes. In practice, “classic” stripline is usually made by etching circuitry on a substrate that has a ground plane on the opposite face, then adhesively attaching a second substrate (which is metalized on only one surface) on top to achieve the second ground plane. Stripline is most often a “soft-board” technology.


VSWR: The Voltage Standing Wave Ratio is a measure of how well a load is impedance-matched to a source. The value of VSWR is always expressed as a ratio with 1 in the denominator (2:1, 3:1, 10:1, etc.) It is a scalar measurement only (no angle). A perfect impedance match corresponds to a VSWR 1:1 meaning you will get all the power from source to load. VSWR()= Vmax/Vmin


Wilkinson Power Divider: A device capable of splitting an input signal into equal phase, equal amplitude output signals or combining like signals to a common port. A unique feature of the Wilkinson divider is output port isolation. Constructed of one or more quarter-wave length transformer sections matching input and output impedances with a resistor placed between the ends of each transformer section. First demonstrated by Ernest Wilkinson with the 1960 publication of his paper, “An N-Way Hybrid Power Divider.”


Zero Degree (0º) Power Divider: A power divider whose output signals are in-phase (having no phase difference, subject to specified design and manufacturing limitations).

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