Coaxial Coupler and Directional Detector Sample 2 to 40 GHz

This article was originally published in a Microwaves & RF article, in May 1987.

Stripline techniques enable two components to give flat response from 2 to 40 GHz.

A coaxial systems reach higher fre­quencies, it then be­comes critical to sample and level signals over broad instantaneous bandwidths. Two coaxial components from KRYTAR serve these purposes pre­cisely: models 102040013 and 202040013 are a 13-dB directional coupler and directional detector, both operating from 2 to 40 GHz (Fig. 1).

Model 102040013 is a 13-dB strip­line directional coupler that uses a patented, nonuniform tapered line. The coupler is designed with offset coupled striplines used in a three- layer construction, with coupled lines etched on opposite sides of a thin center board that is in turn sandwiched between two dielectric boards of equal thickness. The de­sign was synthesized with Krytar’s proprietary CAD program and, as a result, features flat RF perfor­mance not found in similar products. The coupler’s frequency sensitivity or coupling flatness is quite smooth at ±0.5 dB from 2 to 20 GHz, falling to a still respectable ±0.8 dB at 40 GHz. The frequency response of the coupler was measured with an ATE system built around a Wiltron 560A scalar network analyzer.

The coupler offers low insertion loss of 2.0 dB, in spite of its high operating frequencies. Directivity is 12 dB up to 20 GHz and 10 dB up to 40 GHz. The coupler has maximum VSWR of 2.0:1. Specifications are summarized in the table below.

Model 202040013 is a directional detector consisting of a low-VSWR, zero-bias Schottky detector mount­ed directly on the housing of the model 102040013 coupler. Elimina­tion of the RF connector between the detector and the coupler saves space, minimizes frequency-re­sponse ripple normally caused by coupler/detector impedance mis­matches, and improves the overall ruggedness of the design.

The detector circuitry is housed inside a hermetic coaxial detector module. This module is easily re­placed in the field by unscrewing the detector output connector assembly (Fig. 3). The detector module is the same as used in the company’s se­ries of 100-MHz-to-40-GHz zero-bias Schottky detectors. It was specifi­cally designed to provide fast pulse response with an output capacitance of only 3 pF. This and a typical de­tector video impedance of 4 kohms give a typical unloaded output pulse rise time. of under 30 ns. The fre­quency response of the directional detector is ±0.8 dB from 2 to 20 GHz and ±1.5 dB from 2 to 40 GHz (Fig. 3). Frequency-response data were obtained by using a model 202040013 to externally level the output of a Wiltron model 6669A swept signal generator, and then monitoring the directional detector output with an ATE system incorpo­rating a Hewlett-Packard HP 436A power meter.

The 40-GHz directional coupler and detector are ideal for a wide va­riety of applications, including pow­er monitoring in broadband EW sys­tems and test setups and signal lev­eling in test systems. Both are available with either female 2.4-mm or female K connectors. The direc­tional detector employs a female SM A, female BNC or SMC jack. The coupler housing is 1.75 X 0.65 X 0.40 in. (4.45 X 1.65 X 1.02 cm); the detec­tor adds the 1.40-in. (3.56 cm) height of the detector module.