Improved frequency selection of echoloss bridge direction
A return loss, directivity technology, applied in waveguide-type devices, transmission monitoring, instruments, etc., can solve problems such as directivity limitations
Inactive Publication Date: 2007-01-10
TEKTRONIX INC
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Therefore, the directionality of the bridge is still limited by the inherent directionality
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[0023] Figure 4 shows an imperfect return loss bridge. Energy reflections occur between port P1 and the balun along the ground traverse between board layers (eg, front-to-back transitions through vias), represented by open circuit segment OST and inductance L. Similarly, at port P2 and with a coupling resistor R 0 Similar reflections can occur between junctions of / K, which introduce significant parasitic effects. In the example, the coupling of such layer crossings is shown by the associated open section OST and the inductance L, which is coupled via the corresponding transmission line section TL. Figure 5 shows significant parasitic effects in response to intrinsic directionality. figure 2 The minimal parasitic effect pattern in weakens the return loss of port P2 and acts like the inherent directivity to produce the apparent directivity. For the frequency range from 25MHz to 2.5GHz, 20dB or more is required for a bridge, and in this example, the apparent directivity is ...
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A frequency selective improved directivity of a return loss bridge is achieved by generating a counteractive reflected energy vector to cancel a reflected energy vector caused by imperfections, such as parasitic effects and an unbalanced balun, in the return loss bridge. The counteractive reflected energy vector of equal magnitude, but opposite in phase, to the undesired reflected energy vector may be induced into a transmission path between a test port and a coupled port. In one embodiment an open circuit stub in the transmission path between the test port and a coupling resistor coupled to the coupled port may be inserted to generate the counteractive reflected energy vector of the desired magnitude with a transmission line between the open circuit stub and the coupling resistor providing the desired phase. Alternatively the counteractive reflected energy vector may be coupled from the return loss path between the coupling resistor and the test port to the coupling port, the magnitude of the counteractive reflected energy vector being determined by a coupling coefficient and the phase being determined by a length of transmission line. To provide tunability PIN diodes may be used with the transmission line to control both the magnitude and phase of the energy at the coupled port, the coupling coefficient being greater than that needed for counteracting the magnitude of the reflected energy vector.
Description
technical field [0001] The present invention relates to frequency domain instrumentation, and more particularly to frequency selective improvement of return loss bridge directivity. Background technique [0002] A return loss bridge is a three-port device in which one coupling port directionally couples a fixed amount of radio frequency (RF) energy from the transmission path between the transmission port and the test port, that is, the bridge couples some Propagates the energy of the energy wave to the coupled port while blocking the energy of the energy wave propagating in the forward direction. The return loss bridge can therefore be used to measure the return loss (reflected power relative to the incident power) of the load terminating the forward energy wave at the test port. Since it is impossible to completely stop the forward energy wave, there is a certain difference between the coupled energy and the blocked energy at the coupled port. It is already known that "di...
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IPC IPC(8): H01P5/12H04B17/00G01R27/04G01R27/32G01R27/06H01P5/16H03H7/38
CPCH03H7/38H01P5/16
Inventor D·J·达勒布罗克斯
Owner TEKTRONIX INC