# Characterization of a COTS-Based RF Receiver for Cubesat Applications +
## 4 Test Method
### Component-Level Test Description  
The component-level tests have allowed to verify that, for each component, the schematic and layout implementation have been correctly designed and no issues have occurred during the prototype's fabrication and components' mounting. The main purpose of this type of test is to measure the main functional parameters of the RF components, such as the power gain, the input and output return loss, the 1-dB compression point, and the noise figure. The execution of such a test has been made possible thanks to the adoption of the RF test points. They are typically used to monitor the power level along the signal path to control and improve the design of a system. The RF test points selected for the receiver are surface-mount connectors that have 2.3 mm \(\times\) 2.3 mm \(\times\) 1.35 mm size and can operate from Direct Current (DC) to 11 GHz [24]. Figure 3 shows their basic operating principle. When the plug is \"not-mated\" to the connector, the \"1\" and \"2\" pins are short-circuited. From the signal point of view, that short-circuit is a piece of metal (2.3 mm long and 0.35 mm width) that exhibits a small inductance, negligible at the receiver operative frequencies. The voltage standing wave ratio is about 1 at 2 GHz and the attenuation is smaller than 0.1 dB [24]. When the plug is \"mated\" to the connector, the \"1\" pin disconnects from the \"2\" pin and it connects to the \"3\" pin that is the positive of the plug. If the \"1\" pin is connected to the input or output of an RF component of the receiver, the \"1\" pin would allow access to the input or output of that component as if it were an evaluation board. The plug breaks the RF signal path on the board and routes it toward the plug itself, which can be a coaxial connector linked to a measurement instrument. The basic operation of the RF test point has been exploited to form the input and output ports for each component of the receiver. Each port (regardless if it is an input or output) has been made by connecting the \"1\" pin of the test point to the input/output pin of the RF component. In this way, the component can be isolated from the rest of the circuit and can be tested individually. For the component-level tests of the active elements, some mechanical switches have been foreseen for debug purposes. The switches allow to power on the active components individually to avoid the influence of the other components under test. Moreover, the switches provide the possibility to shut down the whole board when passive elements are under test. Figure 3: Operating scheme of the RF test point selected for the RF receiver prototype: (**a**) not-mated to plug; (**b**) mated to plug. The RF test points are very effective to measure the S-parameters of the passive components (as the filters) and, as it is known, the S-parameter measurement requires an appropriate calibration kit that must be compatible with the mate-connector used to connect the network analyzer to the RF test points. To perform a more accurate network analyzer calibration, the calibration kit has been custom-designed on the same receiver board, rather than purchasing a commercial one. Such a choice has also been cost-effective because, as the calibration frequencies were smaller than 3 GHz, the custom calibration kit could have been designed using lumped components, especially for the 50 \(\Omega\) load. Figure 4 shows the calibration kit schematic and a photograph of its implementation on the prototype board. The calibration system of the \"load\" was made using a 50 \(\Omega\) resistor with very high accuracy, i.e., \(\pm\)0.1%. The calibration system of the \"short\" was made using a 0 \(\Omega\) resistor. The calibration system of the \"open\" was made foreseeing a simple footprint without any component mounted on the board. Finally, the calibration system of the \"through\" was made by designing a coplanar microstrip with a 50 \(\Omega\) characteristic impedance.