Measuring Communication and Radar Signals
With today’s complex modulation schemes, increased popularity of wireless transmission and pulsed communication modes, the need to accurately and efficiently measure RF power has become crucial to obtaining optimum performance from communication systems and components. There are also various complex types of Radar signals used in different Radar applications. In almost all applications, it is necessary to perform basic RF pulse measurements. There are many challenges for Radar pulse measurements at system level testing due to pulse timing for many scenarios and capturing a large number of pulses. Although there are various instruments to measure pulse signals, peak power meters or USB peak power sensors are typically the most accurate one for time-domain RF power measurements for both Radar and communication signals. Peak power solution provides both time-domain graphical and tabular format that display numerical list of parameters detailing pulse characteristics including rise time, fall time, pulse width, overshoot and droop. The 55 Series USB power sensor provides the best method for meeting these challenges accurately and reliably with complex pulse signals such as RADAR and modern digitally modulates communication signals (i.e. LTE and Wi-Fi).

Analysis of a Simple Pulse Measurement
IEEE Std 181-2003 Standard Transition Pulses and Relative Waveforms Terms and Definitions provides fundamental definitions for general use in time domain pulse technology. Several key terms that are defined in this standard appear in the numerical display of the automatic pulse measurements using a peak power meter.


Fig.1: Analysis of a simple pulse measurement

The key terms defined by the IEEE standard are abstracted and summarized below. These terms are referenced to the standard pulse illustrated in Fig 1.
 

Term	Definition
Base Line	The two portions of a pulse waveform which represent the first nominal state from which a pulse departs and to which it ultimately returns.
Top Line	The portion of a pulse waveform which represents the second nominal state of a pulse.
First Transition	The major transition of a pulse waveform between the base line and the top line (commonly called the rising edge).
Last Transition	The major transition of a pulse waveform between the top of the pulse and the base line. (commonly called the falling edge).
Proximal Line	A magnitude reference line located near the base of a pulse at a specified percentage (normally 10%) of pulse magnitude.
Distal Line	A magnitude reference line located near the top of a pulse at a specified percentage (normally 90%) of pulse magnitude.
Mesial Line	A magnitude reference line located in the middle of a pulse at a specified percentage (normally 50%) of pulse magnitude.

Table 1: IEEE Standard Pulse Terms and Definitions

Automatic Marker and Pulse Measurement - Graphical and Numerical Display
The 55 series USB Peak Power sensor captures, displays and analyzes RF pulse power in time domains. Boonton Peak Power Analyzer software for 55 series USB power sensor is to displays the signal on a time domain graphical format called trace window as well as display measured pulse parameters numerically in a tabular format called automated measurements. The sensor reconstructs the waveform from points that fall within the display’s time window. This window is defined by the timebase and trigger delay. Numerical mode or tabular format displays text parameters of 16 time and power measurements for up to 8 channels simultaneously as well as xx automated marker measurements. Automatic pulse measurements are made on repetitive signals that meet the amplitude and timing conditions according to IEEE definitions.

The 55 Series USB Power sensor automatically analyzes the waveform data by using Real-Time Power ProcessingTM techniques and calculates key waveform parameters 100 times faster than conventional power meter. By selecting the "Trace" button a graph view displays the same pulse in time domain measurement. With the advantage of docking capabilities of the software, each measurement window allows convenient display for both graph and tabular windows with the numerical information. (Fig. 2)


Fig. 2: "Auto Meas" and "Trace" buttons allow to see both graphical and numerical display of the same pulse measurement

The calculated values are displayed in text mode in a tabular format by selecting the "Auto Meas" menu button from the software. Automated measurements are displayed on two tables, pulse and marker measurements. Automated marker measurements return power reading at specific time offsets from the trigger point where the markers are placed. For a pair of markers, the measurement includes average power, minimum and peak power over the interval between markers, and power ratio between markers. All automatic measurements are limited to the USB Sensor’s time window. Two vertical markers allow power level measurements at specific times relative to the trigger event. Automatic marker measurements table shows all related parameters as set in between two vertical marker positions.


Fig. 3: Boonton 55 Series graphical display showing rise time of a pulse using Boonton Peak Power Analyzer software
 

Pulse Measurements displayed on the automated measurements window are computed based on the IEEE Std 181-2003 definitions and can be set by clicking on the "Pulse Def" button. Distal, mesial, proximal and pulse units as well as pulse gate parameters can be adjusted to the user’s preference. Measurements such as rise time, fall time, and pulse width are affected by these adjustments. The list of displayed measurement parameters are: peak power, pulse power, average power, pulse width, rise time, fall time, overshoot, pulse period, pulse repetition rate, duty cycle, top amplitude, bottom amplitude, off time, edge delay and the delay between two RF pulses (skew). Fig. 4 shows an example of numerical parameters display for pulse measurements with the details on measurement parameters including rise time, fall time, PRF etc.

Fig. 4: Boonton 55 Series numerical (Text) display of a pulse measurement showing details like rise time, fall time, PRF etc

 

Text	Term	Definition and Related Remote Programming Functions
Width	Pulse Width	The interval between the first and second signal crossings of the mesial line.  IVI Function: Btn55xxx_FetchWidth ( ViSession Vi, ViConstString                     Channel, ViInt32* IsValid,ViReal32* Val );
Rise	Risetime	The interval between the first signal crossing of the proximal line to the first signal crossing of the distal line IVI Function: Btn55xxx_FetchRiseTime ( ViSession Vi,                      ViConstString Channel, ViInt32* IsValid, ViReal32* Val);
Fall	Falltime	The interval between the last signal crossing of the distal line to the last signal crossing of the proximal line. IVI Function: Btn55xxx_FetchFallTime ( ViSession Vi,                      ViConstString Channel, ViInt32* IsValid, ViReal32* Val );
Period	Pulse Period	The interval between two successive pulses (reciprocal of the Pulse Repetition Frequency). IVI Function: Btn55xxx_FetchPeriod ( ViSession Vi,                        ViConstString Channel, ViInt32* IsValid, ViReal32* Val );
PRF	Pulse Repetition Frequency	The number of cycles of a repetitive signal that take place in one second. IVI Function: Btn55xxx_FetchPRF( ViSession Vi,                     ViConstString Channel, ViInt32* IsValid, ViReal32* Val);
Duty	Duty Cycle	The ratio of the pulse on-time to off-time. IVI Function: Btn55xxx_FetchDutyCycle( ViSession Vi,                        ViConstString Channel, ViInt32* IsValid, ViReal32* Val );
Offtime	Off-time	The time a repetitive pulse is off (equal to the pulse period minus the pulse width). IVI Function: Btn55xxx_FetchOfftime ( ViSession Vi,                     ViConstString Channel, ViInt32* IsValid, ViReal32* Val );
PulsPk	Pulse Peak	The maximum power level of the captured waveform. The peak amplitude during the pulse. IVI Function: Btn55xxx_FetchPulsePeak( ViSession Vi,                        ViConstString Channel, ViInt32* IsValid, ViReal32* Val );
Pulse	Pulse Power	The average power level across the pulse width, defined by the intersection of the pulse rising and falling edges with the mesial line. IVI Function: Btn55xxx_FetchPulseOnAverage( ViSession Vi,                     ViConstString Channel, ViInt32* IsValid, ViReal32* Val);
Overshoot	Overshoot	The difference between the distortion following a major transition and the IEEE top line in dB or percent, depending on the channel units. IVI Function: Btn55xxx_FetchOvershoot( ViSession Vi,                        ViConstString Channel, ViInt32* IsValid, ViReal32* Val );
Droop	Droop	Power droop of the pulse. IVI Function: Droop is a parameter of FetchPowerArray () method. It will display a droop value if it exists with a pulse.
PulsAvg	Average Power	Average power of a pulse period. IVI Function: Btn55xxx_FetchPulseCycleAvg( ViSession Vi,                        ViConstString Channel, ViInt32* IsValid, ViReal32* Val );
Top	Top Amplitude	The IEEE-defined top line, i.e. the portion of a pulse waveform, which represents the second nominal state of a pulse. IVI Function: Btn55xxx_FetchIEEETop( ViSession Vi,                     ViConstString Channel, ViInt32* IsValid, ViReal32* Val);
Bottom	Bottom Amplitude	The IEEE-define base line, i.e. The two portions of a pulse waveform which represent the first nominal state from which a pulse departs and to which it ultimately returns. IVI Function: Btn55xxx_FetchIEEEBottom( ViSession Vi,                        ViConstString Channel, ViInt32* IsValid, ViReal32* Val);
Skew	Skew	Time difference between the mesial level of two different pulses on two channels using two sensors. IVI Function: Several Skew functions exist depending on internal or external trigger output.                     Btn55xxx_GetInternalSkew( ViSession Vi, ViConstString Channel,                     ViReal32* InternalSkew);                     Btn55xxx_GetExternalSkew( ViSession Vi, ViConstString Channel,                     ViReal32* External);
EdgDly	Edge Delay	The time between the left edge of the display and the first mesial transition level of either slope on the waveform. IVI Function: Btn55xxx_FetchEdgeDelay ( ViSession Vi,                     ViConstString Channel,ViInt32* IsValid, ViReal32* Val );

Table 2: List of numerical parameters for pulse measurement

List of Automatic Pulse Parameters and Recommended APIs
Table 2 is a list of 15 parameters which are displayed in a tabular format using 55 Series USB power sensor and Boonton Peak Power Analyzer software. All these parameters can be accessed remotely by using Boonton provided IVI functions in any programming language. The FetchPowerArray () function is one of the recommended method which will return you an array of the current automatic amplitude measurements performed on a periodic pulse waveform. Also below is a list of recommended IVI functions which can be used in any remote program for a pulse measurement.