Amir Mortazawi

Voltage-controlled RF filters employing thin-film barium-strontium-titanate tunable capacitors

Tunable lowpass and bandpass lumped-element filters employing barium-strontium-titanate (BST)-based capacitors are presented. A new metallization technique is used, which improves the quality factor of the tunable BST capacitors by a factor of two. The lowpass filter has an insertion loss of 2 dB and a tunability of 40% (120-170 MHz) with the application of 0-9 V DC bias. The bandpass filter (BPF) has an insertion loss of 3 dB and a tunability of 57% (176-276 MHz) with the application of 0-6 V DC. The third-order intercept point of the BPF was measured to be 19 dBm with the application of two tones around 170 MHz.

Tunable barium strontium titanate thin film capacitors for RF and microwave applications

The measurement results for thin film barium strontium titanate (BST) based voltage tunable capacitors intended for RF applications are reported. At 9 V DC, BST capacitors fabricated using MOCVD (metalorganic chemical vapor deposition) method achieved 71% (3.4:1) tunability. The measured device quality factor (Q) for BST varactors is comparable with the device Q for commercially available varactor diodes of similar capacitance. The typical dielectric loss tangent was in the range 0.003-0.009 at VHF. Large signal measurement and modeling results for BST thin film capacitors are also presented.

Quasi-optical transmit/receive front ends

Quasi-optical (QO) active circuits have originally received interest for power generation by large-scale power combining of solid-state devices at microwave and millimeter-wave frequencies. Here, we present an overview of QO components developed with functionality in mind, with an emphasis on bidirectional amplifier arrays for transmit/receive (T/R) front ends. We discuss possible advantages of the QO architecture for communications and radar. The following three QO bidirectional arrays are presented: 1) a nine-element X-band patch antenna array with different polarizations in T/R modes; 2) a 24-element X-band slot lens array with switches for the T/R paths; and 3) a 22-element K/spl alpha/-band patch lens array using monolithic microwave integrated circuits (MMICs).

Analysis and measurement of hard horn feeds for the excitation of quasi-optical amplifiers

Measurement and analysis of hard horn feeds for excitation of quasi-optical amplifiers has been performed. A computer program based on the mode matching technique has been developed in order to determine the aperture field distribution for pyramidal hard horns. This program can be used to optimize a hard horns field distribution and bandwidth. Simulation and measurement results for a 31 GHz hard horn feed are presented.

A Ka-band power amplifier based on the traveling-wave power-dividing/combining slotted-waveguide circuit

An eight-device Ka-band solid-state power amplifier has been designed and fabricated using a traveling-wave power-dividing/combining technique. The low-profile slotted-waveguide structure employed in this design provides not only a high power-combining efficiency over a wide bandwidth, but also efficient heat sinking for the active devices. The measured maximum small-signal gain of the eight-device power amplifier is 19.4 dB at 34 GHz with a 3-dB bandwidth of 3.2 GHz (f/sub L/=31.8 GHz, f/sub H/=35 GHz). The measured maximum output power at 1-dB compression (P/sub out/ at 1 dB) from the power amplifier is 33 dBm (/spl sim/2 W) at 32.2 GHz, with a power-combining efficiency of 80%. Furthermore, performance degradation of this power amplifier due to device failures has also been simulated and measured.

A DC Voltage Dependant Switchable Thin Film Bulk Wave Acoustic Resonator Using Ferroelectric Thin Film

In this paper, a new application of ferroelectric thin film based on electrostrictive and piezoelectric effects is reported. Electrostrictive resonances in the thin film can be controlled with the application of the DC electrical field. A switchable thin film bulk wave acoustic resonator (FBAR) is proposed using barium strontium titanate (BST) thin film. The measured resonator has a parallel resonance at 2.035 GHz and a series resonance at 1.975 GHz with 25 V DC bias applied. The electromechanical coupling coefficient was calculated to be approximately 7.07% which is comparable to AIN FBARs. Acoustic parameters of BST thin film were extracted by optimizing the resonators transmission line model to fit the measurement results. Simulation results for a switchable BST FBAR filter operating at 2 GHz are also presented.

Improving Power Amplifier Efficiency and Linearity Using a Dynamically Controlled Tunable Matching Network

This paper presents a tunable matching network that enhances both efficiency and linearity of power amplifiers (PAs). A medium-power amplifier with a varactor-based matching network is designed, fabricated, and tested. It is demonstrated that not only the power efficiency at reduced drive levels can be improved but also the AM-AM and AM-PM distortions of the PA are reduced when the tunable matching network is biased according to the input drive level. Moreover, under 3GPP WCDMA modulated input, the PA with a dynamically controlled tunable matching network achieves up to 5% improvement in drain efficiency when compared with a PA employing a fixed matching network.

A high-power Ka-band quasi-optical amplifier array

Results for a high-power Ka-band quasi-optical amplifier array are presented in this paper. The amplifier consists of a 45-element double-sided active array with a hard-horn feed. Excess heat is removed via a metal carrier integrated into the array with liquid cooling at the periphery. Each unit cell of the array consists of transmitting and receiving patch antennas, driver and power amplifier monolithic microwave integrated circuits on input and output layers, and a through-plate coaxial transition, which connects the input and output layers. An estimated 25 W is radiated when the amplifier is used as an antenna feed, otherwise 13 W is collected into waveguide. Experimental results and construction details are discussed.

A compact dual-polarized multibeam phased-array architecture for millimeter-wave radar

A broad-band dual-polarized phased array is presented, which allows for independent beam control of the vertical and horizontal polarization with multibeam scanning in azimuth and elevation. The system is based upon a compact tray architecture with element spacing of 0.6/spl lambda/. Using stereolithography, a miniature dual-polarized waveguide front end was fabricated, which provides a low-loss transition to the microstrip phase-shifting circuitry. A p-i-n diode switch followed by a low-noise amplifier is implemented for each tray to allow for the electronically controlled beam scanning with a 49/spl deg/ field of view. The phased array demonstrates broad-band characteristics from 34 to 40 GHz with better than 20-dB cross-polarization signal discrimination.

Adaptive Input-Power Distribution in Doherty Power Amplifiers for Linearity and Efficiency Enhancement

A new technique based on an adaptive input-power distribution is introduced to overcome the limitations of practical Doherty power amplifiers. The proposed Doherty amplifier employs an extended-resonance power-divider at its input. By taking advantage of the auxiliary cells nonlinear input impedance, the extended-resonance divider is designed such that it provides a proper power-dependent power-division between the main and auxiliary cells. Therefore, the two cells are efficiently driven and can generate output current and voltage characteristics similar to the ideal Doherty amplifier, resulting in both linearity and efficiency improvements. The performance of the new Doherty amplifier is compared with a conventional design through simulations and measurements. The proposed Doherty amplifier achieves a measured ACLR improvement of 5-7 dB over a wide range of output power levels, as well as an increased power-added-efficiency of up to 5% for WCDMA signals. The proposed Doherty design does not require complex circuitry and yields a compact circuit.