Armin Talai

A finite 3D field simulation method for permittivity gradient implementation of a novel porosification process in LTCC

High frequency substrates show a manifold variety of complex permittivities for different applications. Recent research results demonstrated the possibility of local decrease of the permittivity on LTCC by chemical etching processes, which enables the design of high quality antennas on LTCC. This paper shows a novel approach on the determination of the quantitative reduction of the effective permittivity by scanning electron microscope analyses in combination with finite 3D field simulations of the resulting inhomogeneous material. By the characterization of two different porosified LTCCs it could be shown that this process is suitable for direct antenna integration on glass-ceramic substrates with enhanced values of relative permittivities.

Electromagnetic analysis of conductor track surface roughnesses from 1 GHz to 110 GHz

Conductor tracks comprise a frequency dependent attenuation of electromagnetic waves, since with increasing frequency the current flow is displaced to the near surface region due to the skin effect. Therefore, the effective length of the conductor is increased by the surface roughness, while its effective cross-section is decreased by current displacement, both leading to higher metallization loss. In this paper, surface topographies of typical conductor materials were recorded by confocal microscopy and rebuilt as 3D CAD models. Subsequent electromagnetic simulations reveal the influence due to roughness on high frequency characteristics for physical vapor deposited, thick film and photochemically etched microstrips.

The influence by trapezoidal conductor shapes on ring-resonator based material characterization up to 110 GHz

Material characterization by ring-resonator based measurements is well established since the early 20th century. Since then, the demand on spectral complex permittivity characterizations of RF materials and dielectric covers at higher microwave frequencies rises. Nowadays, both free space applications, e.g. 77 GHz automotive radar systems, and dielectrics for microchip packages require accurate knowledge of the relative permittivity in order to optimize RF circuit designs. With increasing frequencies, the conductor shape of photochemically etched ring-resonators gets more influence on the effective ring radius, and therefore the measured resonance frequencies, which results in an error for the relative permittivity determination. This paper provides correction factors for the ring radii up to 110 GHz, compensating the altered field distribution due to trapezoidal edges.

Electromagnetic analysis of fringed microstrip lines on porosified LTCC

Recent investigations demonstrated that porosification of LTCC enables a local modification of material properties, in particular of the effective permittivity. These studies revealed that the electric field strength is highest at the lower conductor track edges on the porosified substrate. The local field strength peaks cause substantial influence on the effectiveness of permittivity reduction due near-surface material abrasions. In this paper, the influences of these randomly fringed boundaries on electromagnetic properties are investigated for different degrees of fraying. The gained results are compared to measured screen print edges by scanning electron microscope image analysis of co-fired and post-fired gold conductors, and will contribute for reliable circuit design on porous LTCC in the future.

Embedded cavity based dielectric loss measurements for LTCC substrates up to 110 GHz

In literature there exists manifold techniques for measuring the permittivity of substrates. Printed circuit board (PCB) based methods like dielectric resonators are in general limited to determine the absolute value of the complex permittivity since e.g., a half wave resonator only provides information on the electrical length, which is inversely proportional to the square root of the absolute value of the permittivity. Additionally, dielectric loss measurements are more difficult, expensive and often limited to discrete frequency points due to resonance based measurement principles. In this paper, a PCB based dielectric loss measurement system is presented, operating from a few GHz up to 110 GHz, which is based on a differential measurement of a microstrip line on dense low temperature cofired ceramics (LTCC) and a microstrip on a LTCC layer with an embedded cavity. The cavity reduces the dielectric loss of the transmission line by replacing a certain amount of substrate with air. Subsequent electromagnetic time domain field simulations allow the dielectric loss assignment over the measured transmission frequency range.

A semi double-ridged quasi TE-waveguide based microwave bulk material characterization system

Accurate microwave material characterization is essential for reliable high frequency circuit design. Therefore, various characterization techniques have been developed, comprising advantages and drawbacks for the respective conditions. In this paper, a material characterization system is presented, which enables a broadband measurement for both dielectric loss and relative permittivity of bulk substrates with variant geometrical dimensions. Strips of different dielectric bulk materials under test (MUTs) are mounted on top of an open semi double-ridged waveguide. Differential phase and amplitude broadband measurements with the MUTs are performed by a vector network analyzer, providing information on the introduced change in electrical length and dampening. The combined evaluation by measurement and electromagnetic simulations allow broadband assignments of the complex permittivity to the MUTs.

A Coplanar Waveguide Resonator Based In-Line Material Characterization Sensor for Bulk and Metallized Dielectrics

Abstract Microwave Materials such as Rogers RO3003 are subject to process-related fluctuations in terms of the relative permittivity and dielectric loss. The behavior of high frequency circuits like patch-antenna arrays and their distribution networks is dependent on the effective wavelength. Therefore, fluctuations of the complex permittivity will influence the resonance frequency and beam direction of the antennas. This paper presents a grounded coplanar waveguide based sensor, which can measure the complex permittivity at 77 GHz, as well as at other resonance frequencies, by applying it on top of the manufactured depaneling. The relative permittivity of the material under test (MUT) is a function of the resonance frequency shift and the dielectric loss of the MUT can be determined by transmission amplitude variations at the resonances. In addition, the sensor is robust against floating ground metallizations on inner printed circuit board layers, which are typically distributed over the entire surface below antennas. Furthermore, the impact from conductor surface roughness on the measured permittivity values is determined using the Gradient Model.

A grounded coplanar waveguide resonator based in-line material characterization sensor

Microwave Materials such as Rogers RO3003 are subject to process-related fluctuations in terms of the relative permittivity. The behavior of high frequency circuits like patch-antenna arrays and their distribution networks is dependent on the effective wavelength. Therefore, fluctuations of the relative permittivity will influence the resonance frequency and antenna beam direction. This paper presents a grounded coplanar wave-guide based sensor, which can measure the relative permittivity at 77 GHz, as well as at other resonance frequencies, by applying it on top of the manufactured depaneling. In addition, the sensor is robust against floating ground metallizations on inner printed circuit board layers, which are typically distributed over the entire surface below antennas.

A simplified equivalent model for microwave characteristics of porosified LTCC

High frequency materials show a manifold variety of complex permittivities for different applications. Recent research results demonstrated that porosification of Low Temperature Cofired Ceramics (LTCC) represents a new manufacturing technology, which enables local selective reduction of the relative permittivity. The permittivity gradients were measured and subsequently modeled to perform electromagnetic field simulations. The results of the generated complex CAD model can be used, to create a simplified equivalent model, which is suitable for rapid RF circuit design on porosified LTCC. Since material properties vary between circuit components on dense and porous LTCC, the permittivity-dependency on the lumped elements of the transmission line model is considered. It is shown that the introduced porosification gradient can be transferred to an equivalent circuit diagram according to the transmission line model.

A new approach for a dual-polarized low cost patch antenna with low cross- polarization, high bandwidth and high isolation

In this paper a new approach for a dual-polarized broadband patch antenna is presented. A novel feeding approach enables a high -10dB bandwidth up to 21 % as well as an isolation more than -29 dB. The realized antenna gain is > 6 dBi in the frequency range of 1320 MHz to 1680 MHz. Additional, due to the reflector shaping, a low back radiation is achieved. Since standard components and FR4 material are used, the antenna concept enables an effective low cost antenna production.