N8480S Series Balance Thermocouple Power Sensors

Introduction

The Keysight N8480S Series Balance Thermocouple Power Sensors are intended to be used as measurement standards for RF power. They are suitable for use in a microcalorimeter-based primary measurement standard and as a secondary or reference measurement standard. The new balance thermocouple power sensors offer a broad frequency range DC up to 18/50 GHz, high maximum input power of +20dBm, fast measurement speed/settling time as well as ease of maintenance.

The new series of balance thermocouple power sensors introduce a new measurement method that is suitable for the highest echelon of RF power traceability. These power sensors are intended to be used within microcalorimeters as a primary measurement standard and individually as a transfer or reference measurement standard for RF power in coaxial sensors available in Type-N and 2.4mm connector styles. It is based on the calorimetric style power measurement where the measurement approach is direct DC to RF power substitution. The unknown RF power is substituted by traceable DC power.  

The Keysight N8480S Series balance thermocouple power sensors are designed with dual thermopile power detectors constructed on a single chip. There are two sets of thermopiles in the detectors that are constructed to be closely matched for power cancelation and thermal stability. One set of thermopiles detects the heat generated by RF power in the load resistor and the second set of thermopiles detects heat generated by a DC-fed load resistor. When the DC power applied to the DC load resistor is equivalent to the RF power, the two thermopiles will be equivalent, and the sensor is at balance.

The new series balance thermoelectric power standard mainly consists of a thermocouple IC that is built on a thin-film circuit in a cartridge assembly that serves as a transition from coaxial to co-planar waveguide (CPW) in a bulkhead assembly. In the direct RF-DC substitution RF power measurement setup, load resistor R1 acts as a heater to the thermopile that dissipates RF power, PRF, that generates voltage difference across the RF side of thermopiles VTH1. DC power or Low Frequency (LF) Power, PDC, can be dissipated in R2 to generate VTH2 across the DC side thermopiles. The RF and DC thermopiles are arranged in reverse polarity so that the voltages across the thermopiles are canceled out at the equilibrium or when at balance.

Performance Specifications

Specification definitions

There are two types of product specifications:

• Warranted specifications are specifications which are covered by the product warranty and apply over a range of 0 to 55 °C unless otherwise noted. Warranted specifications include measurement uncertainty calculated with a 95% confidence.

• Characteristic specifications are specifications that are not warranted. They describe product performance that is useful in the application of the product. These characteristics are shown in italics. 

Characteristic information is representative of the product. In many cases, it may also be supplemental to a warranted specification. Characteristics specifications are not verified on all units. These are several types of characteristic specifications. They can be divided into two groups: 

One group of characteristic types describes ‘attributes’ common to all products of a given model or option. Examples of characteristics that describe ‘attributes’ are the product weight and ‘50-ohm input Type-N connector’. In these examples, product weight is an ‘approximate’ value, and a 50-ohm input is ‘nominal’. These two terms are most widely used when describing a product’s ‘attribute’. 

The second group describes ‘statistically’ the aggregate performance of the population of products. These characteristics describe the expected behavior of the population of products. They do not guarantee the performance of any individual product. No measurement uncertainty value is accounted for in the specification. These specifications are referred to as ‘typical’. 

The power sensors will meet its specifications when: 

• Stored for a minimum of two hours at a stable temperature within the operating temperature range, and turned on for at least 30 minutes 

• The power sensors are within its recommended calibration period

• Used in accordance with the information provided in the User’s Guide