Compact Ka-Band One-Port Vector Reflectometer Using a Wideband Electronically Controlled Phase Shifter

Abstract

In this paper, the design and implementation of a compact one-port Ka-band (26.5-40 GHz) vector reflectometer or network analyzer (VNA), operating in full Ka-band frequency range, are presented. The design follows that of a recently developed VNA but with the goal of producing a wideband version. The most critical component of this design is a wideband electronically controlled phase shifter, designed using nonuniformly spaced p-i-n diode-loaded slots incorporated in the broad wall of a rectangular waveguide. Nonuniform placement of the slots is shown to significantly reduce unwanted resonances within the operating bandwidth. Also, the new design provides the possibility of using a more accurate three-port S-parameter characterization instead of the previously used two-port approach. The design foundation and measurement results are presented.Index Terms-Microwave measurements, millimeter-wave imaging, millimeter-wave measurements, phase shifters, reflectometry.

Sensitivity analysis of a single-port vector reflectometer with a wideband phase-shifter

“…Non-coherent VNAs use the standing-wave voltage measurements, usually made with diode detectors, to estimate Γ [5]- [14]. These VNAs do not provide as good of the dynamic range, bandwidth and accuracy [9] as those VNAs designed based on tuned-receiver coherent detection schemes [4]. Yet, factors such as simple design, small size (hand-held VNAs), ease of use and the fact that they cost a fraction of a coherent VNAs make them quite attractive for a number of applications such as nondestructive testing (NDT), materials characterization and imaging [2].…”

“…One-port VNAs have been realized using a number of schemes such as: multi-probe [5], [6], [10]- [12], single movable detector [13] and single fixed standing-wave detector with electronic phase-shifters [7]- [9]. The phase-shifter-based design operates on the principle of electronically "moving" the standing-wave along a transmission line and over a fixed detector diode.…”

“…Using the latter, the standing-wave voltage at different, but known phase shifts, is measured using a single fixed detector. Thus, using at least 3 such measurements, it is possible to estimate a unique value for Γ [5], [7], [9].…”

“…At higher frequencies, such off-the-shelf phase-shifters are difficult to find or do not exist all together [8]. So, a novel electronically-controlled phase-shifter at Ka-band (26.5 -40 GHz) was developed in [8] and improved in [9] by making it wideband. The design of this phase-shifter is based on placing a number of minimally-perturbing PIN diode-loaded slots on a waveguide wall.…”

“…These phase-shifters suffered from drawback that can potentially degrade measurement uncertainty. The X-band phase-shifter had insertion loss as high as 8dB and the Ka-band phase-shifters did not provide sufficient phase shifts [8], [9]. This paper presents a sensitivity analysis of a general oneport electronic phase-shifter based wideband reflectometer system.…”