Mohammad Nikfalazar

Beam Steering Transmitarray Using Tunable Frequency Selective Surface With Integrated Ferroelectric Varactors

A tunable frequency selective surface (FSS) with beam steering capability is presented. The FSS is used as a transmitarray with a bandpass characteristic in Ku-band. The periodic sub-wavelength (λ0/25) unit-cells are composed of capacitive and inductive structures creating a bandpass for an incident wave. By patterning the capacitive elements on a screen-printed barium-strontium-titanate (BST) thick-film ceramic, the resonant frequency of the FSS can be tuned. This technology offers a simple and cost effective way for integrating varactors into the FSS and is particularly attractive for microwave circuits with a high varactor density. A prototype is fabricated including two capacitive layers with an overall size of 40 mm × 40 mm. Each layer includes a total of 1600 integrated BST varactors that are fabricated by using a patterning and metallization process. A transmitted wave passing through the FSS will experience a phase shift, which can be tuned by tuning the passband. This allows steering the transmitted wave to a certain direction by applying a phase gradient along the FSS interface. A phase shift range of 360° can be covered by cascading several FSS panels. The prototyped tunable FSS demonstrates the feasibility of the proposed technology and its potential for beam steering.

Beam Steering Phased Array Antenna With Fully Printed Phase Shifters Based on Low-Temperature Sintered BST-Composite Thick Films

This letter presents a novel approach to fully-printed phase shifters for electronically steering the beam of a phased array antenna at S-Band. The phased array consists of four microstrip patch antenna elements and phase shifters, as well as a four-to-one feeding network. As key components in the circuit, the phase shifters are provided with a microstrip loaded-line topology, equipping fully-printed metal-insulator-metal (MIM) varactors with low-temperature sintered BST composite thick films between the top and bottom silver electrodes. Furthermore, a simple biasing concept is implemented for controlling the phase shifter. The fully-printed, low-cost phase shifters achieved a phase shift of 274° and a FoM of 37.3°/dB at 3 GHz. The length of the phase shifters was 0.2λ, where their phase shift versus length resulted in a 14.4°/mm measurement, outperforming all previously reported phase shifters based on fully-printed low-temperature sintered BST thick film. The beam-scanning range of the four-antenna element array was ±30°.

Steerable Dielectric Resonator Phased-Array Antenna Based on Inkjet-Printed Tunable Phase Shifter With BST Metal-Insulator-Metal Varactors

This letter presents a steerable phased-array antenna at C/X-band. The phase shifters used in the design, are implementing inkjet-printed barium strontium titanate (BST) thick-films. This method enables low-voltage tuning and low fabrication cost. The phase shifter is tuned by integrated metal-insulator-metal varactors, whose electrodes are fabricated by photolithography and inkjet-printed dielectric layer. A tunability of 46% at 8 GHz is achieved by applying 50 V across a 1.2- μm-thick BST film. The 11-unit-cells loaded-line tunable phase shifter achieves a figure of merit above 40°/dB from 7 to 8.5 GHz. Dielectric resonator antenna, fabricated from bulk-glass ceramic, has been implemented as radiating element with a stacked architecture for wide bandwidth and high gain. A beam steering of ±30° has been measured with a 1 ×4-element phased array in the anechoic chamber.

Fully printed tunable phase shifter for L/S-band phased array application

In this paper, a novel fully printed method is presented for fabrication of phase shifter devices, aiming for phased array applications. This technology offers a simple and low cost way compared to other available technologies. The proposed phase shifter contains tunable ferroelectric varactors in metal-insulator-metal (MIM) configuration, which are fully printed on top of a carrier substrate. The printed phase shifter exhibits a figure of merit (FoM) of 70°/dB at 1.72GHz and shows a high potential for an implementation in fully printed phased array antennas.

Highly conducting SrMoO3 thin films for microwave applications

We have measured the microwave resistance of highly conducting perovskite oxide SrMoO3 thin film coplanar waveguides. The epitaxial SrMoO3 thin films were grown by pulsed laser deposition and showed low mosaicity and smooth surfaces with a root mean square roughness below 0.3 nm. Layer-by-layer growth could be achieved for film thicknesses up to 400 nm as monitored by reflection high-energy electron diffraction and confirmed by X-ray diffraction. We obtained a constant microwave resistivity of 29 μΩ·cm between 0.1 and 20 GHz by refining the frequency dependence of the transmission coefficients. Our result shows that SrMoO3 is a viable candidate as a highly conducting electrode material for all-oxide microwave electronic devices.

Inkjet printed BST thick-films for x-band phase shifter and phased array applications

This paper presents a novel method of inkjet printed Barium-Strontium-Titanate (BST) material for low-cost RF application. To demonstrate its capability in phased array antenna application, a compact continuously tunable load line phase shifter in the frequency range from 8 GHz to 10 GHz is realized. The BST thick-film is printed at the areas which interdigital capacitors are later patterned. A phase shift of 175° and the figure of merit (FoM) of 20° /dB at 10GHz are achieved. The size of the planer circuit is 8mm × 6mm.

Load modulation for high power applications based on printed ceramics

This paper addresses the design and measurement of a low cost tunable impedance matching network (TMN) employing Barium-Strontium-Titanate (BST) for high frequency and high power applications. Based on requirements of a class AB mode high power amplifier, a pi-topology circuit was designed, photo-lithographically processed and measured. The work demonstrates a tunable matching network, transforming low impedance Zi=(4..13)-(3.5..13)j Ohm to a fixed 50 Ohm load, exhibiting insertion losses of not more than 0.9dB at 2.0 GHz. For initial testing, a tunable PA was designed by implementing the TMN at its output. First system measurements show an output power of 40.5dBm with a drain efficiency of 58% at 2.0 GHz.

Wideband tunable GaN HEMT module utilizing thin-film BST varactors for efficiency optimization

This work covers the design and measurement of a low cost tunable impedance matching network (TMN) for highly linear and high power RF applications at telecommunication frequencies. A single transistor cell, was wire-bonded to a TMN and the performance of the tunable amplifier module was evaluated from 1 GHz to 2.5 GHz. The TMN transforms the GaN HEMT output impedance to fixed 50 Ohm load. Tuning allows efficient operation of the transistor over the targeted frequency range. Peak drain efficiency of 66% and a peak output power of 37.5 dBm were measured. Two-tone measurements reveal an OIP3 around 47 dBm which is comparable to a bare GaN HEMT.

Tunable microwave component technologies for SatCom-platforms

Modern communication platforms require a huge amount of switched RF component banks especially made of different filters and antennas to cover all operating frequencies and bandwidth for the targeted services and application scenarios. In contrast, reconfigurable devices made of tunable components lead to a considerable reduction in complexity, size, weight, power consumption, and cost. This paper gives an overview of suitable technologies for tunable microwave components. Special attention is given to tunable components based on functional materials such as barium strontium titanate (BST) and liquid crystal (LC).

Temperature dependence of a tunable phase shifter based on inkjet printing technology

This work adresses the temperature dependence of tunable components based on inkjet printed low temperature sintered Barium-Strontium-Titanate (BST) thick-film layers. To evaluate the temperature dependence, metal-insulator-metal (MIM) parallel-plate capacitors were fabricated and characterized over a temperature range between -60°C and 100°C. A relative capacitance shift below 8.3% was measured in the unbiased state and 1.4% in the biased state. To evaluate the impact of this shift, a phase shifter was fabricated and characterized within the same temperature range. Around 4.5 GHz a maximum figure of merit of 46.7°/dB was measured, having a 92.7° phase shift by applying 50V tuning voltage. The relative phase shift due to temperature is below 4.7%, which shows promising results for a wide temperature operation range.