Conventional distributed baluns employ /spl lambda//2 transmission lines or /spl lambda//4 coupled lines. By adding only one or two lumped capacitors, the required coupled-line lengths of a new balun structure can be made as short as /spl lambda//24. Design curves for these miniaturized impedance-transforming baluns are derived using a systematic even- and odd-mode analysis technique. This approach also provides valuable insight into the tradeoffs between coupled-line lengths, number of capacitors, bandwidth, and impedance-transforming ratios. Experimental results of a single-capacitor balun with /spl lambda//9 coupled lines and a two-capacitor balun with /spl lambda//24 coupled lines will be presented. Both baluns achieved 0.5-dB amplitude balance and 5/spl deg/ phase balance, with over 10-dB return loss from 1.1 to 1.6 GHz.

Analysis and design of miniaturized lumped-distributed impedance-transforming baluns

A modification of the Wilkinson power divider is presented that eases planar implementation while maintaining performance. By adding transmission lines between the resistor and the quarter-wave transformers of the traditional design, a range of valid solutions exists that meet the conditions of being reciprocal, isolated between the output ports, and matched at all ports. The proposed design is particularly useful at millimeter-wave frequencies where reduced physical dimensions make a circuit configuration suitable for low-cost package-level implementation difficult using traditional methods. Two frequency bands are demonstrated. At V-band, the circuit gives 0.3-dB excess insertion loss, 19-dB isolation, and 50% bandwidth. At the W-band, the circuit gives 0.75-dB excess insertion loss, 24-dB isolation, and 39% bandwidth.

/pdf/modified-wilkinson-power-dividers-for-millimeter-wave-4nzn1u38si.pdf

Modified Wilkinson Power Dividers for Millimeter-Wave Integrated Circuits

Because of the inherent structural flexibility in coupling design and topological arrangement, substrate integrated waveguide (SIW) filter topologies enjoy better out-of-band frequency selectivity and/or in-band phase response with the allocation of finite transmission zeros (FTZs). In the first article in this series, basic design rules and fundamental electrical characteristics have been presented that indicate the superior performances of SIW structures and their filter applications. Advanced design techniques and innovative structure features have recently been reported in a large number of publications. They include cross couplings realized by physical and nonphysical paths and SIW filters with dual-mode or multimode techniques. Miniaturization-enabled techniques including low-temperature cofired ceramic (LTCC) technology have been developed and applied to the development of SIW filters to reduce the size for low-gigahertz applications using nontransverse electromagnetic (non-TEM) modes. Wideband SIW filters, multiband SIW filters, and reconfigurable SIW filters have also been reported by various research groups. This article reviews these advanced and innovative SIW filter technologies, and related examples are presented and discussed.

Substrate Integrated Waveguide Filters: Design Techniques and Structure Innovations

Gap waveguide technology represents an interesting alternative as low-loss, cost-effective, and high-performance transmission line and package of microwave and millimeter-wave systems. A Ka-band coupled-resonator filter for a radio link diplexer, which requires high selectivity to isolate transmit and receiving channels, is proposed and realized using gap waveguide technology. The band-pass filter, which has a central frequency of 37.37 GHz and a pass bandwidth of 560 MHz, is fabricated between two parallel metal plates, leaving an air gap between them. After milling one of the plates, silver-plating is applied on them. Measurements show a minimum in-band insertion loss of 1 dB and agree quite well with simulations.

/pdf/ka-band-gap-waveguide-coupled-resonator-filter-for-radio-5cljx85cou.pdf

Ka-Band Gap Waveguide Coupled-Resonator Filter for Radio Link Diplexer Application

In this paper, the fundamental characteristics of a novel third-order RF balanced-to-unbalanced filter, namely, a balun filter, for integrated RF module applications are presented. This center-tapped transformer-based new device works concurrently as a balun, an extracted-pole bandpass filter, and a matching network. As coupled resonant tanks are employed to perform the balun type of operation, traditional coupled-resonator filter theory can thus be used to design and analyze such a new device. Moreover, an extracted-pole technique is used not only for creating a transmission zero, but also provides a capability to match the filter with a complex load. In addition to providing a simple design procedure for the device, its working mechanism is also revealed mathematically. Specifically, return-loss sensitivity with respect to each resonator admittance and complex load matching capability are discussed in details. This balun filter has been implemented in a multilayered low-temperature co-fired ceramic substrate, demonstrating its promising potentials in miniaturized RF front-end modules. Experimental measurements are also presented to validate the theory and computer simulations.

/pdf/an-ltcc-balanced-to-unbalanced-extracted-pole-bandpass-3bfdtlte0o.pdf

An LTCC balanced-to-unbalanced extracted-pole bandpass filter with complex load

This paper presents the design method and performance characteristics of a chip-type balun using a multilayer structure. The design method for a chip-type balun is based on the lumped-element equivalent circuit of quarter-wave transformer. The proposed design method and equivalent circuit can make it easy to design the ceramic multilayer chip-type balun. The size 2012 and 3216 chip-type baluns were designed and fabricated using the proposed design method and the equivalent-circuit model of a quarter-wave transformer. Fabrications and measurements of designed chip-type baluns show smaller size than conventional chip-type baluns and good agreement with simulated results.

A design of the ceramic chip balun using the multilayer configuration

This letter presents a W -band micromachined air-cavity bandpass filter (BPF) using a novel integration method of a micromachined silicon air-cavity resonator with silicon pillars. With silicon pillars, which were fabricated simultaneously with a deep reactive ion etching process for forming a cavity structure, a micromachined silicon air-cavity can be easily integrated on a package substrate with a flip-chip interconnection. In this work, a thin-film substrate with a flip-chip interconnection was employed as a package substrate, in which the silicon pillars were used as the current probe between the air-cavity resonator and TFMS input/output feeding lines. With the novel integration of the air-cavity resonator, a W-band four-pole BPF has been successfully demonstrated on a thin-film substrate with a flip-chip interconnection, which exhibits a minimum insertion loss of 1.3 dB and return loss better than 16 dB with a 4.9% 3-dB fractional bandwidth at a center frequency of 93.7 GHz.

$W$ -Band Bandpass Filter Using Micromachined Air-Cavity Resonator With Current Probes

This paper presents substrate integrated waveguide (SIW) cavity resonator and SIW quasi-elliptic filter with low insertion loss and high selectivity based on LTCC for 60-GHz application. The SIW cavity resonators with high Q factor are suggested and applied for the filter having low insertion loss and high selectivity, the resulting Q value and the resonance frequency are 224.5 and 60.371 GHz, respectively. In the filter design, the quasi-elliptic filter using positive and negative couplings is applied to get high selectivity, the positive and negative couplings are evaluated by the holes between resonators and the slots on ground planes, respectively. The proposed SIW quasi-elliptic filter exhibits an insertion loss 1.77 dB at 60.8 GHz and the return loss is better than 10.2 dB with a 3-dB fractional bandwidth of 11 % (6.92 GHz). The measured insertion loss is lower and the selectivity is higher than those in previous works due to the effects of the high Q resonators and quasi-elliptic structure adapting the negative coupling. The overall size of the fabricated filter is 4.6 mm ×2.8 mm× 0.2 mm.

SIW (substrate integrated waveguide) quasi-elliptic filter based on LTCC for 60-GHz application

The surface of AlGaN/GaN high-electron-mobility transistors (HEMTs) tends to be easily damaged during device fabrication, especially during high-temperature annealing. In order to resolve this problem, a prepassivation process was developed using remote-mode plasma-enhanced chemical vapor deposition (RPECVD) systems. It is important in the prepassivation process to protect the region under the gate during high-temperature ohmic annealing and utilize a low-damage SiNx etching process to minimize any surface damage. It was observed that the DC characteristics were significantly improved and the current collapse phenomenon was markedly suppressed for AlGaN/GaN HEMTs by employing the prepassivation process proposed in this work in comparison with a conventional process. According to the experimental results, the prepassivation process coupled with a gate field plate successfully suppressed the current collapse phenomenon in AlGaN/GaN HEMTs. RF output power densities of 6.9 W/mm at 2.3 GHz and >8.9 W/mm at 4 GHz were achieved for AlGaN/GaN HEMTs on Si and SiC substrates, respectively.

https://iopscience.iop.org/article/10.1143/JJAP.49.041002/pdf

SiNx Prepassivation of AlGaN/GaN High-Electron-Mobility Transistors Using Remote-Mode Plasma-Enhanced Chemical Vapor Deposition

This paper presents embedded substrate integrated waveguide (SIW) BPF and microstrip line-to-embedded microstrip line transition based on LTCC for 60-GHz application. The embedded SIW BPF is placed in LTCC substrate for compact system and integrated passive and active device on the other layer. But embedded SIW BPF performance is changed by interconnection via and transition. In order to low-loss interconnection with embedded passive device, microstrip line-to-embedded microstrip line transition with compensation circuit using series and shut line is proposed and implemented. The insertion loss of fabricated transition with compensation circuit is approximately 1 dB and return loss is below 10 dB from 56 GHz to 69 GHz. The proposed embedded SIW BPF including transition with compensation circuit exhibits a total insertion loss 2 dB at 61.8 GHz and the return loss is better than 16.2 dB with a 3-dB fractional bandwidth of 11.7 % (7.23 GHz). The measured insertion loss is lower than those in previous works. The overall size of the fabricated filter is 8 mm × 2.7 mm× 0.3 mm.

Chan-Sei Yoo

Papers

A design of the ceramic chip balun using the multilayer configuration

$W$ -Band Bandpass Filter Using Micromachined Air-Cavity Resonator With Current Probes

SIW (substrate integrated waveguide) quasi-elliptic filter based on LTCC for 60-GHz application

SiNx Prepassivation of AlGaN/GaN High-Electron-Mobility Transistors Using Remote-Mode Plasma-Enhanced Chemical Vapor Deposition

A 60 GHz embedded SIW (substrate integrated waveguide) BPF Considering the Transition Effect