BD112: Bidirectional Detector for WR-340 Waveguide

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Frank Houston
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BD112: Bidirectional Detector for WR-340 Waveguide General Description BD112 is a bidirectional detector intended for simultaneous sampling of incident and reflected waves in high-power 2450 MHz

1 left) combines the following components: 4-port directional coupler (70-dB coupling) Attenuators Zero-bias Schottky diode detectors The detector delivers well-scaled DC voltages proportional to

1 BD112: Bidirectional Detector for WR-340 Waveguide General Description BD112 is a bidirectional detector intended for simultaneous sampling of incident and reflected waves in high-power 2450 MHz industrial applications using WR-340 (R-26) rectangular waveguide. The bidirectional detector (Fig. 1 left) combines the following components: 4-port directional coupler (70-dB coupling) Attenuators Zero-bias Schottky diode detectors The detector delivers well-scaled DC voltages proportional to power of the waves propagating in forward and reverse directions in the main waveguide. The detector module is fastened to a parent waveguide by means of six M3 or similar-diameter screws after machining of appropriate holes in the waveguide wall. As an option, an assembly consisting of the module fixed to a precisely machined parent waveguide with standard or customized length can be provided (Fig. 1 right). The standard length is 174 mm. Fig. 1. Bidirectional detector BD112 (left); an assembly with a parent waveguide (right). Specifications Waveguide of destination Waveguide wall thickness Waveguide surface flatness at BD interface Frequency range Maximum input power Directivity Output voltage polarity Internal time constant Statistical spread of output voltage Output voltage temperature variation (+5 C to +65 C ) Dimensions Mass Operating temperature Storage temperature WR-340, R-26 (86.36 mm x mm) 2 mm 0.04 mm MHz 10 kw or user-defined 25 db min Positive 0.15 ms 1 db (3- deviation) < 3 db 73 mm 73 mm 29.5 mm 220 g -10 C to +65 C -40 C to +125 C Office: S-TEAM Lab, Budova FEI STU B212, Ilkovicova 3, SK Bratislava, Slovak Republic Tel./fax: support@s-team.sk

and FWD outputs are referred to GND. The forward wave is supposed to propagate in the direction of the arrow on the nameplate.

2 BD112 Pin Assignment Pin Signal Description 1 RFL Reflected (reverse) power output 2 (not connected) 3 (not connected) 4 (not connected) 5 (not connected) 6 FWD Forward (incident) power output 7 (not connected) 8 GND Signal ground 9 (not connected) Notes: RFL and FWD outputs are referred to GND. The forward wave is supposed to propagate in the direction of the arrow on the nameplate. Dimensional Drawing Fig. 2. BD112 connector pin numbering. Fig. 3. Basic BD112 dimensions. All dimensions are in millimeters. Rev. C0 2/5 31-Oct-2017

3 P IN (kw) BD112 Typical Transfer Characteristic A typical detector transfer curve for the maximum input power 10 kw, ambient temperature TA = 25 C, frequency 2450 MHz and load resistance RL = 33 k is shown in Fig. 4, where PIN is the power of a wave propagating in the waveguide in a given direction and VOUT is the output voltage of the corresponding channel V OUT (mv) Fig. 4. Typical BD112 transfer characteristics in both directions. The transfer curve can be approximated by a polynomial P d V d2v d3v d4v d5v d6v where P = PIN in kilowatts, V = VOUT in volts, and di are temperature-dependent coefficients, listed in the table below. The curve above has been computed for TA = 25 o C (boldface in the table) 1. TA ( o C) d1 d2 d3 d4 d5 d E E E E E E-11 Please be aware that the function is a statistical average based on evaluation of a number of detectors. Behavior of individual detectors may differ. For more critical applications, requiring accurate, temperature-independent power measurement, use bidirectional power meter BPM112 instead. Notes: 1 Currently, only data for this temperature are available. Rev. C0 3/5 31-Oct-2017

4 D (db) BD112 Typical Directivity (Both Directions) f (MHz) Fig. 5. Typical BD112 directivity (both directions). Waveguide Machining Template Fig. 6. Waveguide machining template. All dimensions are in millimeters. The pattern is centered about the waveguide axis. The waveguide wall thickness must be 2 mm. Suggested are M3 x 25 screws (stainless or galvanized steel). Complying with the specified waveguide wall thickness and flatness of its surface interfacing with the BD112 is essential for the specified measurement accuracy. The slope of the coupling factor as a function of the wall thickness is about -0.6 db/mm (increasing the wall thickness decreases the output power readings). To avoid problems with manufacturing precision waveguide components, a calibrated assembly consisting of a BD112 module fixed to a parent waveguide can be ordered. Standard waveguide length is 174 mm; customizing the length is possible. Rev. C0 4/5 31-Oct-2017

5 BD112 Wiring Example Fig. 7. Example of BD PLC connection. Time Constant Internal time constant of BD112 is set to approximately 0.15 ms (cutoff frequency about 10 khz). To improve interference immunity in CW applications, time constant can be increased by an optional external RC filter as indicated in the wiring diagram (R1, C1 and R2, C2). The filter, if applied, should be placed as close to PLC inputs as possible. Rev. C0 5/5 31-Oct-2017

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