P.W. van der Walt

Design of a Ten-Way Conical Transmission Line Power Combiner

Axially symmetric power combiners, such as radial line and conical line combiners, are very effective in combining the output signals from a large number of power amplifiers over a wide band with low losses. The main problem with radial lines is the behavior of the characteristic impedance against radial distance, which makes design of radial combiners difficult and normally optimization based. In this paper, a step-by-step design procedure is presented for the design of a conical line combiner. The design strategy relies on the transverse electromagnetic properties of the conical line to eliminate the need for complex full-wave optimization in the design process. Circuit models are instead employed and optimized to achieve a wide matched bandwidth. A ten-way prototype was developed at X-band, which displayed more than an octave matched bandwidth with low insertion loss

A Wien-bridge oscillator with high-amplitude stability

A FET-stabilized Wien-bridge oscillator, capable of maintaining an output voltage of 5 V to an accuracy of 0.02 percent with total harmonic distortion 0.01 percent, is described. A linear model is presented for the amplitude-stabilizing control loop from which useful design relationships are developed.

A novel matched conical line to coaxial line transition

A novel smooth constant impedance transition between a coaxial and conical transmission line is described. The transition is of special relevance to high power radial combiners, as the maximum field strength in the transition can be limited to about 15% above that in the coaxial line.A novel smooth constant impedance transition between a coaxial and conical transmission line is described. The transition is of special relevance to high power radial combiners, as the maximum field strength in the transition can be limited to about 15% above that in the coaxial line.

Short-Step-Stub Chebyshev Transformers Impedance

A transfer function for short-step impedance transforming filters consisting of short cascaded TEM transmission-line sections and at least one commensurate length open-circuit stub is described. Element values are given for a particular family of octave-bandwidth short-step transformers that are much more compact than existing short-step transformers.

Low phase noise cylindrical cavity oscillator

A low phase noise oscillator operating at 9.2 GHz is presented. A cylindrical metal cavity with air as dielectric is used as the resonator. To minimize the phase noise of the oscillator, the resonator must be designed to have a high quality factor (Q-factor). A high Q-factor is obtained by designing the resonator to operate in the TE011 mode. A tuning screw is used to tune the resonant frequency without significantly affecting the Q-factor, while also separating the resonant frequencies of the degenerate TE011 and TM111 modes. The signal is coupled to the resonator by means of rectangular apertures. The coupling is designed to minimize the phase noise of the oscillator. A dual mode waveguide filter was developed and inserted into the oscillator loop in order to prevent oscillation at unwanted frequencies. The output signal of the oscillator was measured at different locations in the loop and clearly showed that the resonator can be used as a filter to minimize the phase noise. Phase noise levels of -115 dBc/Hz and -146 dBc/Hz were obtained at offset frequencies of 10 and 100 kHz.

Design constraints in conical line power combiners

A study is presented on the constraints on the size of conical line power combiners. The constraints are imposed by the occurrence of higher order modes which cause unpredictable behavior in electrically large structures. A simple method is presented to estimate the maximum size of the combining structure to ensure predictable transverse electromagnetic mode behavior.

Dynamic RFI measurement systems on a ROACH-2 platform ICEAA-IEEE APWC-EMS

We describe developments in a radio frequency interference (RFI) detection instrument dubbed RATTY 2. With uncertain RFI environments in mind, the system is hardware and software reconfigurable, functioning either as a spectrometer or a transient-signal analyser. RATTY 2 is equipped with a 900 MHz bandwidth, 10-bit, non-interleaved analogue-digital converter (ADC) and the data is processed on a Reconfigurable Open Architecture Computer Hardware 2 (ROACH) platform. A computer is used for post-processing dynamically-stored data. Two different strategies were followed in designing the RF front-end systems for signal conditioning prior to digitisation: 1) a single mixer, down-converting topology, and 2) a multiple Nyquist-zone sampling configuration. The two systems are evaluated and compared in this paper.

An in situ Tunable Diode Mounting Topology for High-Power

An in situ tunable diode mounting topology for waveguide switches is presented and utilized to design and fabricate two evanescent-mode X-band switching modules of approximately 15% and 25% fractional bandwidth. The ability of the mounting topology to operate in a high-power environment is verified in an evanescent-mode X-band switch using six packaged p-i-n diodes, successfully reflecting 4 kW of pulsed power

X

Two inexpensive waveguide absorbing loads are constructed and measured, each using a single thin resistive sheet absorber supported by styrofoam walls, and 50 mm in length. It is found that a V-cut wedge displays less reflection than a tapered wedge, with -30 dB reflection across a band 8.5 - 12.4 GHz.

-Band Waveguide Switches

An S-band combline filter with improved passband separation is presented. The filter utilizes a perturbed housing to increase the capacitive end-loading of the resonators, thereby reducing the length and increasing the stop-band width. Different perturbations of the housing are investigated. A narrowband filter is constructed and measured.