RF Mixer Testing | RF Mixer Test and Measurement
This article on RF Mixer testing covers various test and measurement parameters used to evaluate RF mixer. It mentions test setup used for RF Mixer testing.
About RF Mixer: It is a three port device marked as RF, IF and LO ports. It takes two inputs and produces single output. The output usually will have sum, difference, leakage of inputs and harmonics of inputs.
The RF mixer has many uses. The most popular among them is as frequency converter. This is due to the fact that mixer does not change amplitude and phase of input signals while performing frequency translation. In the RF down conversion, difference of input frequencies will be passed using appropriate band pass filter. Here input ports are designated as RF and LO while output port is designated as IF port.
In the RF up conversion, sum of input frequencies will be passed using appropriate band pass filter. Here input ports are designated as IF and LO ports and output port is designated as RF port.
Test Setup for RF Mixer Testing
Following table mentions generic specifications of RF mixer. These specifications are verified during RF mixer testing.
| RF Mixer Specifications | Description |
|---|---|
| Frequency of operation | The manufacturer provides frequency range at RF, LO and IF ports for which mixer has been designed. |
| Conversion Loss | It is measured between input and output ports. It is the ratio of output power to the input power. In terms of dB, conversion loss is the difference between output power(dB) and input power(dB). It is very useful parameter in RF mixer testing. |
| Noise figure | It is a measure of noise added by the RF mixer itself during frequency
conversion operation. For passive mixer type, noise figure is equal to insertion loss as
this mixer do not have any gain associated with it. Noise Factor = (Si/Ni)/(So/No) Noise Figure = 10 Log10(Noise Factor) |
| Isolation | It is measured between LO-RF ports or LO-IF ports. It the measure of leakage of local oscillator power at IF port or RF port. It means how much of LO signal is attenuated while traveling from its port to either one of the other two ports. Manufacturer specifies LO/RF isolation and LO/IF isolation in the datasheet. It is one of the critical parameter to be considering in RF mixer selection and RF mixer testing. |
| Dynamic range | It is the range over which RF mixer works satisfactorily. Linear dynamic range is the difference of input P1dB (maximum signal level at which device operates in linear region ) and MDS (Minimum Detectable signal). The two tone spurious free dynamic range is defined by 2/3 * (Input_IP3 - MDS) /td> |
| 1dB Power and Third Order Intercept (TOI) points | The point when output power does not follow increase in input power linearly is 1dB compression point. At this point input and output power are referred as 1dB input/output powers respectively. TOI is usually 10 to 15 dB higher than P1dB compression point. |
| Harmonic suppression | As mixer produces sum and difference as well as harmonics of input frequencies, it is desired to check the level of harmonics. It is recommended to have harmonic suppression to certain amount such that it will not affect in the normal functioning of the RF mixer. |
| Input and output VSWR or return loss | It is the measure of how well mixer ports are performing in order to reflect or pass the signal fed at their respective ports. For example, to measure VSWR at RF port, signal power is applied to LO port and unused IF port is terminated with 50 ohm impedance. |
All these parameters are mentioned by the RF mixer manufacturers in the data sheets or manuals. RF mixer is selected as per design requirement.
In order to test RF mixer separately test jigs are used or separate test PCB with appropriate dielectric material has been designed. The figure-3 mentions typical RF mixer conversion loss measurement using VNA (Vector Network Analyzer). The other equipments which can also be required for RF mixer testing are spectrum analyzer for harmonics and spurious measurement, power meter for P1dB and power measurement etc. The directional coupler is used for VSWR measurement.
What is difference between or comparison between
Following links mention difference or comparison between various equipments:
comparison between VSG and VSA
DIfference between SNA ans VNA
Oscilloscope Bandwidth versus Rise time
Oscilloscope vs Logic Analyzer
Difference between Oscillscope types
Comparison between spectrum and network analyzer