Matthew A. Morgan

We report on the development of transmission-line reflectionless filters operating with passbands at 100 and 230 GHz, and stopband absorption up to 500 GHz, the highest operating frequencies yet recorded for such filters. The designs are based on a previously reported mathematical solution to the reflectionless condition, now successfully implemented for the first time, using an advanced thin-film fabrication process on Alumina substrates. Submillimeter wave wafer probe measurements show good agreement with theory.

We report on the development of transmission-line reflectionless filters operating with passbands at 100 GHz and 230 GHz, and stopband absorption up to 500 GHz, the highest operating frequencies yet recorded for such filters. The designs are based on a previously reported mathematical solution to the reflectionless condition, now successfully implemented for the first time, using an advanced thin-film fabrication process on Alumina substrates. Sub-millimeter wave wafer probe measurements show good agreement with theory.

Provides society information that may include news, reviews or technical notes that should be of interest to practitioners and researchers.

We report on the development of millimeter-wave, lumped-element reflectionless filters using an advanced thin-film fabrication process. Based on previously demonstrated circuit topologies capable of achieving 50Ω impedance match at all frequencies, these circuits have been implemented at higher frequencies than ever before by leveraging a thin-film process with better than 2 μm feature size and integrated elements such as SiN Metal-Insulator-Metal (MIM) capacitors, bridges, and TaN Thin-Film Resistors (TFRs).

Single-ended circuit topologies, and a theorem for the development thereof, are presented with which one may realize constant-resistance (or reflectionless) filters, having ideally zero reflection coefficient at all frequencies and from all ports, suitable for elliptic and pseudo-elliptic filter responses. The proposed theorem produces topologies of a type known as the coupled-ladder, which has been previously studied for only polynomial responses (e.g. Butterworth, Chebyshev, etc.). A comparison between these topologies and another classical approach known as the economy bridge reveals that those proposed here have a number of theoretical and practical advantages. The theory is tested by the construction of a sixth-order, low-pass reflectionless filter exhibiting a pseudo-elliptic frequency response. Measured results are in excellent agreement with theory, and show return loss better than 20 dB throughout the pass-band, the transition-band, and up to two octaves into the stop-band.

Single-ended circuit topologies, and a theorem for the development thereof, are presented with which one may realize constant-resistance (or reflectionless) filters, having ideally zero reflection coefficient at all frequencies and from all ports, suitable for elliptic and pseudo-elliptic filter responses. The proposed theorem produces topologies of a type known as the coupled-ladder, which has been previously studied for only polynomial responses (e.g. Butterworth, Chebyshev, etc.). A comparison between these topologies and another classical approach known as the economy bridge reveals that those proposed here have a number of theoretical and practical advantages. The theory is tested by the construction of a sixth-order, low-pass reflectionless filter exhibiting a pseudo-elliptic frequency response. Measured results are in excellent agreement with theory, and show return loss better than 20 dB throughout the pass-band, the transition-band, and up to two octaves into the stop-band.

Modifications of the authors' previously published, generalized, lumped-element, reflectionless filter topologies are presented, which remove the original constraints on the relative values of its prototype parameters. Thus, any transfer function which can be realized as the transmission or reflection coefficient of a conventional ladder prototype may now be implemented in reflectionless form, i.e., having the same transfer function in transmission but with identically zero reflection coefficient at both ports and at all frequencies from dc to infinity, given ideal elements. The theoretical basis of these modifications is explained and then tested via the construction of passive, reflectionless low-pass filter prototypes that, in the prior topology, would have required negative reactive elements. The results show excellent agreement with theory.

A teaching assistant once told me that, as microwave engineers, impedance matching is "what we do." We do much more than that, of course. But I think it is true that this is what most of our more complex tasks ultimately boil down to. To design an amplifier, you have to match the impedance of the transistor. To design an antenna, you have to match its radiation impedance. We do it by rote, without thinking, like a writer punctuating sentences. It is no wonder that the Smith chart-the classic graphical tool for analyzing and displaying an impedance match-has become our field's own personal totem.

We report on the development and characterization of a compact, full-waveguide bandwidth (WR-10) signal source for general-purpose testing of mm-wave components. The monolithic microwave integrated circuit (MMIC) based multichip module is designed for compactness and ease-of-use, especially in size-constrained test sets such as a wafer probe station. It takes as input a cm-wave continuous-wave (CW) reference and provides a factor of three frequency multiplication as well as amplification, output power adjustment, and in situ output power monitoring. It utilizes a number of custom MMIC chips such as a Schottky-diode limiter and a broadband mm-wave detector, both designed explicitly for this module, as well as custom millimeter-wave multipliers and amplifiers reported in previous papers.

We report on the development of a prototype integrated receiver front-end that combines all conversions from RF to baseband, from analog to digital, and from copper to fiber into one compact assembly, with the necessary gain and stability suitable for radio astronomy applications. The emphasis in this article is on a novel digital data link over optical fiber which requires no formatting in the front-end, greatly reducing the complexity, bulk, and power consumption of digital electronics inside the antenna, facilitating its integration with the analog components, and minimizing the self-generated radio-frequency interference (RFI) which could leak into the signal path. Management of the serial data link is performed entirely in the back-end based on the statistical properties of signals with a strong random noise component. In this way, the full benefits of precision and stability afforded by conventional digital data transmission are realized with far less overhead at the focal plane of a radio telescope.