Farhan A. Ghaffar

Theory and Design of a Tunable Antenna on a Partially Magnetized Ferrite LTCC Substrate

For the first time, a theoretical model is presented to predict the frequency tuning of a patch antenna on a partially magnetized ferrite substrate. Both extraordinary (E) and ordinary (O) modes of the antenna are studied. The permeability tensor of the partially magnetized ferrite is calculated through the proposed theoretical model and is subsequently used to analyze the antennas performance in a microwave simulator. Prototype antennas were built, using two different bias windings, embedded in a multilayer ferrite LTCC substrate, to demonstrate E and O mode tuning. The use of embedded windings negates the requirement of bulky electromagnets, thus providing miniaturization. The concept also eliminates the demagnetization effect, thus reducing the typically required bias fields by 95%. The prototype measurements at 13 GHz demonstrate an E-mode tuning range of 10%. The proposed theoretical model has been validated by simulations and measurements. The design is highly suitable for compact, light-weight, tunable and reconfigurable microwave systems.

Tunable Bandpass Filter Based on Partially Magnetized Ferrite LTCC With Embedded Windings for SoP Applications

Tunable filters that are based on ferrite materials often require large and bulky electromagnets. In this work, we present a tunable filter in the Ku-band, which is realized in multilayer ferrite LTCC substrate with embedded bias windings, thus negating the need of a large electromagnet. Also, because of the embedded windings, the bias fields are not lost at the air-substrate interface and therefore the field and current requirements are reduced by an order of magnitude as compared to the previously reported filters. A simulation strategy that uses full permeability tensor with arbitrarily directed magnetic fields has been used to model the filter on a partially magnetized ferrite substrate. Special attention has also been paid to approximate the non-uniform magneto-static fields produced by the embedded windings. The complete design is implemented in 10 layers of ferrite LTCC, making it the first magnetically tunable filter with embedded windings and extremely small size [(5 × 5 × 1.1) mm3]. The filter demonstrates a measured tunability of 4% and an insertion loss of 2.3 dB. With the small form factor, embedded windings, and low bias requirements, the design is highly suitable for compact and tunable SoP applications.

24-GHz LTCC Fractal Antenna Array SoP With Integrated Fresnel Lens

A novel 24-GHz mixed low-temperature co-fired ceramic (LTCC) tape based system-on-package (SoP) is presented, which incorporates a fractal antenna array with an integrated grooved Fresnel lens. The four-element fractal array employs a relatively low dielectric constant substrate (CT707, εr = 6.4), whereas the lens has been realized on a high-dielectric-constant superstrate (CT765, εr = 68.7 ). The two (substrate and superstrate) are integrated through four corner posts to realize the required air gap (focal distance). The fractal array alone provides a measured gain of 8.9 dBi. Simulations predict that integration of this array with the lens increases the gain by 6 dB. Measurements reveal that the design is susceptible to LTCC fabrication tolerances. In addition to high gain, the SoP provides a bandwidth of 8%. The high performance and compact size (24 × 24 × 4.8 mm3 ) of the design makes it highly suitable for emerging wireless applications such as automotive radar front end.

A Partially Magnetized Ferrite LTCC-Based SIW Phase Shifter for Phased Array Applications

The theory and design of a half-mode substrate-integrated waveguide ferrite low-temperature cofired ceramic-based phase shifter are presented in this paper. Unlike typical ferrite-based designs, the biasing is done through embedded windings in a multi-layer substrate that not only obviates the requirement of bulky electromagnets, but also prevents loss of bias fields at the air-to-ferrite interface. The phase shifter is operated in the partially magnetized state of ferrite substrate. Through the combined effect of embedded windings, half-mode waveguide operation, and partially magnetized state, the required bias fields have been reduced by 90% as compared with conventional ferrite-based designs employing electromagnets. A complete analytical model, backed up by electromagnetic simulations and measured results from a prototype, is presented in this paper. The fabricated prototype demonstrates a phase shift of 83.2° at a center frequency of 13.1 GHz and a figure of merit of 83.2°/dB. As a proof-of-concept, the proposed phase shifter design is monolithically integrated with a two-element antenna array to demonstrate a measured beam steering of 30°. The phase shifter design is highly efficient in terms of required bias fields, and it has a small form factor and can be easily integrated with other electronic components and systems.

A Ferrite LTCC Based Dual Purpose Helical Antenna Providing Bias for Tunability

Typically, magnetically tunable antennas utilize large external magnets or coils to provide the magneto-static bias. In this work, we present a novel concept of combining the antenna and the bias coil in one structure. A helical antenna has been optimized to act as the bias coil in a ten layer ferrite LTCC package, thus performing two functions. This not only reduces the overall size of the system by getting rid of the external bias source but also eliminates demagnetization effect (fields lost at air-to-substrate interface), which reduces the required magneto-static field strength and makes the design efficient. RF choking inductor and DC blocking capacitor have been monolithically integrated as package elements to allow the magnetostatic and microwave excitation at the same time. The design has been optimized for its low frequency and high frequency performance in two different simulators. A measured tuning range of 10% is achieved at a center frequency of 13 GHz. The design is highly suitable for low cost, compact, light-weight and tunable microwave systems.

A Ferrite LTCC-Based Monolithic SIW Phased Antenna Array

In this paper, we present a novel configuration for realizing monolithic substrate integrated waveguide (SIW)-based phased antenna arrays using Ferrite low-temperature cofired ceramic (LTCC) technology. Unlike the current common schemes for realizing SIW phased arrays that rely on surface-mount component (p-i-n diodes, etc.) for controlling the phase of the individual antenna elements, here the phase is tuned by biasing of the ferrite filling of the SIW. This approach eliminates the need for mounting of any additional RF components and enables seamless monolithic integration of phase shifters and antennas in SIW technology. As a proof of concept, a two-element slotted SIW-based phased array is designed, fabricated, and measured. The prototype exhibits a gain of 4.9 dBi at 13.2 GHz and a maximum E-plane beam-scanning of ±28° using external windings for biasing the phase shifters. Moreover, the array can achieve a maximum beam-scanning of ±19° when biased with small windings that are embedded in the package. This demonstration marks the first time a fully monolithic SIW-based phased array is realized in Ferrite LTCC technology and paves the way for future larger size implementations.

Gain-enhanced LTCC system-on-package for automotive UMRR applications

A novel Low Temperature Co-fired Ceramic (LTCC) based SoP for automotive radar applications is presented. For the first time a combination of a relatively low dielectric constant LTCC substrate and a high dielectric constant LTCC superstrate has been incorporated to enhance the overall gain of the module. The superstrate can provide additional protection to the integrated circuits (IC) in the harsh automotive environment. A custom cavity in the LTCC substrate can accommodate the IC, which feeds an aperture coupled patch antenna array. The cavity is embedded below the ground plane that acts as a shield for the IC from antenna radiation. It is estimated that with mere 10 dBm of transmitted RF power the miniature SoP module (sized 2.0 cm × 2.0 cm × 0.22 cm) can communicate up to 67 m. The designs compactness, robustness, transmission power and resultant communication range are highly suitable for Universal Medium Range Radar (UMRR) applications.

Ferrite LTCC based phased array antennas

Two phased array antennas realized in multilayer ferrite LTCC technology are presented in this paper. The use of embedded bias windings in these designs allows the negation of external magnets which are conventionally employed with bulk ferrite medium. This reduces the required magnetostatic field strength by 90% as compared to the traditional designs. The phase shifters are implemented using the SIW technology. One of the designs is operated in the half mode waveguide topology while the other design is based on standard full mode waveguide operation. The two phase shifter designs are integrated with two element patch antenna array and slotted SIW array respectively. The array designs demonstrate a beam steering of 30° and ±19° respectively for a current excitation of 200 mA. The designs, due to their small factor can be easily integrated in modern communication systems which is not possible in the case of bulk ferrite based designs.

A ferrite nano-particles based fully printed process for tunable microwave components

With the advent of nano-particles based metallic inks, inkjet printing emerged as an attractive medium for fast prototyping as well as for low cost and flexible electronics. However, at present, it is limited to printing of metallic inks on conventional microwave substrates. For fully printed designs, ideally, the substrate must also be printed. In this work, we demonstrate a fully printed process utilizing a custom Fe2O3 based magnetic ink for functional substrate printing and a custom silver-organo-complex (SOC) ink for metal traces printing. Due to the magnetic nature of the ink, this process is highly suitable for tunable microwave components. The printed magnetic substrate is characterized for the magnetostatic as well as microwave properties. The measured B(H) curve shows a saturation magnetization and remanence of 1560 and 350 Gauss respectively. As a proof of concept, a patch antenna is implemented in the proposed stack up which shows a tuning range of 4 % around the center frequency.

Theory and design of a half-mode SIW Ferrite LTCC phase shifter

A half mode SIW based Ferrite LTCC phase shifter is presented in this work. A theoretical model to predict the phase shift in the partially magnetized state has been derived. Contrary to the bulky external magnets employed by conventional ferrite phase shifters for biasing, this design uses bias windings embedded within the ferrite substrate. This not only enables miniaturization but also reduces the required bias fields considerably by avoiding the demagnetization effect (fields lost at air-dielectric interface for external biasing schemes). The design is optimized with the aid of magnetostatic and microwave simulations which are later verified through measurements of a prototype. The fabricated phase shifter provides a differential phase shift of 110°/cm and an FoM of 55°/dB for an applied DC current of 240 mA.