Boonton 4540 RF Power Meter Application in a Transponder Type
Contents
1. 5 Observing power profile of pulse burst and single sub pulse In this specific radar application several parameters are required due to the complexity of the signal Total average power is always desirable and was easily obtained in modulated mode using the 51075A Power Sensor and is shown in Fig 3 a This mode dis plays the average power of 48 858 dBm as measured over the entire PRT 1 sec This signal in particular is comprised of a 112 us train of 112 sub pulses Each sub pulse has a pulse width of 0 5 us and is positioned in either the first half or second half of each mi crosecond interval using PPM Because of these signal parameters it is desirable to obtain the characteristics of the pulse train as well as the individual sub pulses These measurements are made using the 57318 Peak Power Sensor Fig 3 b shows an entire pulse train in pulse mode Notice the width of the pulse at the top left corner of the screen 112 us Also given are the peak and average powers over the course of the pulse train Fig 3 c illustrates the time resolution of the 4540 series In this figure the pulse train is expanded so that several Sub pulses are visible Notice that some are approximately 0 5 while others appear to be double that length This is due to the PPM method used The chosen parameters pulse width rise time fall time peak power pulse average power and marker power ratio are displayed at the top of the screen The final2. Signal using the Boonton 4540 series This section introduces a practical example of using the 4540 series power meter to measure a combined transponder radar system The signal waveforms of this system are organized in a compli cated fashion The RF section provides 1090 MHz transmit and re ceive signals at standard transponder operating frequency which is a pulsed waveform encoded as Pulse Position Modulation PPM with 0 5 us pulse widths The pulses are transmitted in bursts ev ery second with each burst lasting 112 us The profile of the radar transceiver system is shown in the Fig 2 a Boonton 4540 RF Power Meter Application in a Transponder Type Pulsed Radar System 2 c Measuring transponder bursts d Measuring sub pulses within a signal burst Fig 2 Using the 4540 RF Power Meter to measure baseband pulses Application Note Boonton 4540 RF Power Meter Application in a Transponder Type Pulsed Radar System 3 The Boonton 4540 RF power meter is used in the testing and de bugging of the baseband and RF signal levels from the transceiver outputs before transmit to high power amplifiers The following detailed steps are followed during the measurements 1 Calibration Two types of power sensors are used 57318 Peak Power Sensor peak power and 51075A Power Sensor CW average power Both sensors fit the transponder frequency requirement L band and the transceiver power level requirements The special aspe
3. ZB Boonton amen Boonton 4540 RF Power Meter Application in a Transponder Type Pulsed Radar System Michael Mallo Rockee Zhang and Andrew Huston Radar Innovations Laboratory the University of Oklahoma Abstract The Boonton model 4540 Series is the instrument of choice for capturing display ing and analyzing RF power in both the time and statistical domains Applications include pulsed RF signals such as radar TDMA and GSM and pseudorandom or noise like signals such as CDMA WLAN and WiMAX The 4540 Series is a single or dual channel RF Power Meter that can measure modulated or CW signals using peak and average Boonton power sensors This application paper focuses on discussing the usage of the 4540 Series RF power meter in advanced radar system test and development especially in developing and testing a transponder type radar system for aviation scenarios Boonton 4540 RF Power Meter Application in a Transponder Type Pulsed Radar System Generally radars use both continuous wave CW and pulsed wave forms to detect and track targets Similar to wireless communica tions complicated modulations may be applied to the signal wave forms to improve range resolution and detection performance The power sensors within the 4540 Series can cover the frequency band from 500 Hz to Ku band 18 GHz which is the operating fre quency band for most tracking radars and ground based weather radars The high dynamic range 70 to 4
4. 4 dBm CW power or 55 to 20 dBm pulsed power is useful for debugging the power level at all ranges of the RF sections in a radar system Compared to similar products on the market the 4540 Series has the advantage of time resolution 0 2ns which can be useful to observe the de tailed and transient power structures of the radar signal Using the Boonton 4540 series at different stages of the radar transceiver The block diagram of a generic pulsed Doppler radar transceiver is shown in Fig 1 where the baseband waveform generator produces the required waveforms and modulation schemes the intermedi ate IF stage modulates the baseband waveforms up to the trans mit frequency band and demodulate the received RF waveforms back to baseband Ba teband Baseband Waveform Transmit Baseband DAFP Receive Fig 1 A generic diagram of pulsed Doppler radar transceiver Even though the power meter is a relatively simple instrument compared to an oscilloscope it can be used at the baseband to check 1 the required waveform power level for the IF and con version stages 2 the power profile of the baseband signal as sociated with the waveform envelope with respect to time and 3 the power level before the ADC and DSP stages This stage has a lower frequency coverage lt 200 MHz but requires a relatively large dynamic range due to the IF amplification generally 70 100 Application Note dB which fits within the dy
5. ct of the waveform modulation in this case PPM short pulse PM makes both sensors useful for power measurements Boonton pro vides a sensor calibration measurement table along with the quick Start guide However following the standard sensor calibration procedure in the manual first is recommended to guarantee accu racy Ensure the system is warmed up at least 3 minutes before the calibration The AutoCal option accessible via the Calibration menu performs the sensor calibration automatically 2 Pre checking power levels The signal power level from the transmitter output should not ex ceed 0 dBm Be aware that the sensor itself cannot handle more than 20 dBm peak power Maintaining transmitter output power below 10 dBm is preferable Also signals below 40 dBm peak power or 70 dB CW power cannot be sensed only the instrument noise floor will be visible 3 Selecting the pulsed CW power or statistical mode The greatest challenge with this measurement is the need to check the burst of pulses 1 sec period and 100 us length rather than a single sub pulse within the burst Pulsed mode is the best option for measuring this particular type of radar waveform The reason is the power sensor limits the rise time in this case approximately 100 ns while a single pulse has a rise time of about 10 ns anda pulse width of 500 ns Using modulated mode is better for looking at continuously modulated periodic signals The 4540 s statistica
6. l mode is an appropriate option for noise radar which is continuous with a randomly fluctuating signal power 4 Adjusting time and power scales Adjusting the time and power scales of the display area is a simple yet crucial task A proper choice of axes is integral to effectively illustrate data The available options depend upon the mode in use While in modulated mode or pulse mode the Time option is available from the Main menu Within the Time menu are options to adjust the Time Base 10 ns Div to 1 min Div Position either Middle Right or Left or 30 div Trig Delay 0 ns to 100 us and Position Control Preset or Vernier To adjust the power scale while in modulated mode or pulse mode the user must navigate to the Main Channel menu and then select the desired input channel Channel 1 or Channel 2 This brings up the options to adjust the Vert Scale 0 1 to 50 dB Div and the Vert Center 100 dBm to Application Note 100 dBm Furthermore the Units dBm Watts Volts dBV dBmV and dBuV can be selected from the Main Channel Extensions menu While in statistical mode the Time option on the Main menu is replaced with the Stat option This new menu allows the user to adjust the horizontal axis which is actually the power axis in sta tistical mode via the Horiz Scale 0 1 1 2 or 5 dB Div and Horiz Offset 50 00 to 50 00 dB options The vertical axis in statistical mode displays the range from 0 0001 to 100 0
7. measurement was performed in statistical mode using the 57318 Peak Power Sensor This mode gives the probability as a percentage in the vertical log arithmic scale that the signal contains certain relative power levels Boonton 4540 RF Power Meter Application in a Transponder Type Pulsed Radar System 4 a Average power measurement of pulse b Power measurements of one burst of train in modulated mode pulse train in pulse mode Zz E 2 E E xi i lz z max m as m x A ig CS i 7 deta ea ree WA AAR OA T c Pulse train sub pulse power measurements in pulse mode d Power measurements of pulse train in statistical mode Fig 3 Using the 4540 RF Power Meter in a modulated mode b and c pulse mode and d statistical mode Application Note Boonton 4540 RF Power Meter Application in a Transponder Type Pulsed Radar System 5 Summary Power meter is an important tool for radar engineering Boon ton model 4540 Series Peak Power meter is a powerful yet low cost tool for advanced radar system development and trouble shooting Using this power meter for measuring a transponder type radar signal with complicated pulse modulation scheme is demonstrated in this application note Performing appropriate calibration selecting correct measurement mode power sensor and correctly controlling the user interfaces are the key steps to ensure accurate power measurements Comparing to similar product we have been used thi
8. namic range performance of the 4540 Series It is recommended that modulated mode is used when com plicated baseband modulations such as phase modulations are involved and pulse mode is used when the baseband waveforms are pulsed with a relatively wide bandwidth At the IF stages signal powers before and after the mixers which are primary concerns are measured to ensure that the conversion loss falls within the required system budget To address this problem the power me ter and sensor need to be well calibrated before the measurement Checking with the linearity data on the reference level test docu ment along with the user s manual is a good approach Finally at the RF stage the frequency is the highest and the signal power level can vary It is necessary to check the projected power level at the desired measurement point to make sure there will be no damage to the power sensor Another important application of the power meter at the RF front end is the transceiver self calibration test functions widely used in today s weather radars For this case a portion of the transmit power is sampled and looped back into the receiver channels comparing the received power with expec tation gives a good indication of the transceiver RF chain A well calibrated power meter is a good tool to give a fast diagnosis of the RF system budget and is useful for field inspection at all stages of the transceiver chain Measuring the Transponder Radar
9. s power meter has nice graphic in terface comprehensive functionality and easy to learn features which are very appropriate for university laboratories and engi neer training programs m Wireless Telecom Group Boonton Microlab Noisecom Wireless Telecom Group Inc 25 Eastmans Rd Parsippany NJ United States Tel 1 973 386 9696 Fax 1 973 386 9191 www boonton com Copyright 2010 All rights reserved Note Specifications terms and conditions are subject to change without prior notice
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