Siegfried Martius

Dielectric data of ceramic substrates at high frequencies

The dielectric constants of standard ceramic substrates like alumina and LTCC have been determined in the frequency range from 1 to 50 GHz. For the measurements cylindrical disk resonators and printed microstrip line resonators on substrates have been prepared. The RF-data have been measured with network analyzers and suitable wafer probe stations, the calculations of the dielectric data have been done on basis of two different simulation programs. The preparation of the samples and the test conditions of both resonator methods have proven to yield reliable results over a wide frequency range.

Novel tunable hexaferrite bandpass filter based on open-ended finlines

In this paper a novel tunable bandpass filter based on open ended finlines is presented. Hexagonal ferrite spheres are used as resonators to cover a tuning frequency range from 39GHz to 68GHz. The measured insertion loss of the filter varies from 5.3dB to 7dB with a typical 3dB-Bandwidth between 300MHz and 400MHz. An off-resonance isolation of about 60dB is achieved although only two spheres are used.

Design of artificial dielectrics for anti-reflection-coatings

With the increasing interest in new artificial materials ranging from meta-materials to photonic bandgap materials there is a growing need for accurate models of artificial materials. We examine the design of a three-layer structure with an artificial dielectric as an anti-reflection-coating on both sides of a dielectric slab. We present a field-equivalent circuit theory to calculate the effective dielectric constant of the structured dielectric. The materials discussed in this paper have a lateral periodicity smaller than ¿/10 and can easily be manufactured from high density polyethylene (HDPE) for frequencies up to 20 GHz. The field-analog circuit theory can also be used to calculate the polarization dependence of the artificial dielectric. Theoretical results of three geometrically different structures were compared with waveguide measurements at X-band and showed excellent agreement. Applications such as the design of new components at millimeter and submillimeter wave frequencies are discussed, considering the X-Band measurements as a scaled model.

Novel coupled microstrip wideband filters with spurious response suppression

Wideband coupled line filters with spurious response suppression (2/0) in the millimeter wave range are reported. The first filter exhibits a relative bandwidth of 62% with a return loss better than 20 dB and a suppression of the second spurious passband of more than 40 dB. The very high necessary couplings to achieve that large bandwidth in combination with the spurious suppression are realized by removing partially the ground metallization beneath the proposed coupling sections. The filters are directly compatible to microstrip circuits without the need for complicated transitions. They do not require techniques like substrate suspension or dielectric overlay to match the even- and odd-mode phase velocities, but are realizable on a classical substrate with ground. Further, simulation and measurement results of a second, high selective filter (11th order) with an even higher bandwidth of 78% are shown. Measurement and simulation results are fitting very well.

A hybrid broadband millimeter-wave diode ring mixer with advanced IF extraction technique

We report on a hybrid octave-bandwidth millimeter-wave diode mixer with advanced IF extraction. The design uses a reproducible, low cost hybrid technology including thin- film circuit and flip-chip mounted diode chips. Side coupled Marchand baluns with IF tap provide balanced RF and LO signals as well as serve for extracting the IF signal. Measurement results for fixed, low IF frequency show a conversion loss around 10 dB from 35 to 67 GHz. Furthermore the mixer is suitable for IF frequencies up to 23 GHz. These features allow very flexible applications of the presented mixer in broadband test and measurement systems.

A quasi-lumped ultra-broadband contiguous SSL-diplexer from DC to 80 GHz

A contiguous planar diplexer in suspended stripline technology with ultrawideband channels from DC to 40 GHz and 40 GHz to 80 GHz is presented. The design of the diplexer is based on quasi-complementary LC lowpass and highpass prototypes which are directly transformed into transmission line elements by using a quasi-lumped approach. This very straightforward design procedure requires no susceptance annulling networks and no introduction of unit elements which could limit the diplexers operation bandwidth. For achieving an optimal compatibility with external circuits, an ultra-broadband SSL-MSL (suspended stripline - microstrip line) transition with a return loss of more than 18 dB from DC to 83 GHz was designed. The realized diplexer is extremely compact (6×4.5mm) and features a return loss of more than 12 dB from DC to 81 GHz with very low channel insertion losses of typically less than 1 dB after proper optimization.

Novel tunable hexaferrite bandpass filter based on rectangular waveguide coupled shielded coplanar transmission lines

In this paper a novel tunable high isolation bandpass filter is presented. The filter consists of two shielded coplanar transmission lines coupled by a rectangular waveguide. Hexagonal ferrite spheres are used to cover a tuning frequency range from 50 to 80GHz. Measurement results up to 69GHz are shown. The measured insertion loss of the filter lies between 7.1 and 9.3dB. An off-resonance isolation better than 60dB is achieved what is extraordinarily high for a two spheres filter. The typical 3dB-bandwidth is about 250MHz. As planar transmission lines are used, the filter can be integrated into a coplanar or microstrip environment easily what is advantageous for the construction of highly integrated modules. The operating frequency range can be expanded up to 80GHz by replacing the 1.85mm-connectors by 1mm-connectors or using other suitable waveguide transitions, thus covering considerably more bandwidth than rectangular waveguide based coupling structures.

A novel DGS-Marchand balun from 40 to 80 GHz with IF-tap for mixer design

Novel wideband planar Marchand baluns in the millimeter wave range from 40 to 80 GHz are presented. The circuits can be fabricated in a regular thin-film process due to less stringent specifications by using defected ground structure (DGS) technology. The return loss of the balun is better than 10 dB from 40 -80 GHz and better than 15 dB from 43-73 GHz. The amplitude balance is better than 2 dB from 40-80 GHz and better than 0.5 dB from 43-73 GHz. The phase balance error is smaller than 8deg over the entire frequency range. Simulation and measurement results are fitting very well. Several additional versions of the proposed balun are presented providing IF-paths to build a complete double-balanced mixer circuit. To show the applicability of the baluns, a low cost hybrid ring mixer for an IF of 500 MHz has been fabricated. Measurement results show a flat conversion loss of about 9 dB from 33 -69 GHz. Further measurement results for a second mixer for IF frequencies up to 23 GHz are presented.

An Octave-Bandwidth Double-Balanced Millimeter-Wave Mixer

The paper reports on an octave-bandwidth double-balanced mixer which operates in the millimeter-wave range from 35 to 70 GHz. The design uses a low cost hybrid technology: A thin-film circuit is fabricated on an alumina substrate, and the diodes are flip-chip mounted. Balanced signals are provided by side coupled Marchand baluns. As a result the conversion loss averages out at 13 dB