Large-Signal Characterization of an 870MHz Inverse Class-F CrossCoupled Push-Pull PA using Active Mixed-Mode Load-Pull

An inverse class-F cross-coupled push-pull PA in a 0.5um SiGe technology is presented. It is shown that inverse class-F in combination with CBC compensation is preferred over class-F operation in terms of gain roll-off and efficiency as function of collector supply voltage. The active mixed-mode load-pull system is used to set up the proper output differential and common-mode impedances at the fundamental (870MHz) and harmonics to experimentally verify inverse class F operation with a measured PAE of 67% at 20dBm output powe

Simulations of a FIR oscillator with large slippage parameter at jefferson lab for FIR/UV pump-probe experiments

We previously proposed a dual FEL configuration on the UV Demo FEL at Jefferson Lab that would allow simultaneous lasing at FIR and UV wavelengths [1]. The FIR source would be an FEL oscillator with a short wiggler providing diffraction-limited pulses with pulse energy exceeding 50 microJoules, using the exhaust beam from a UVFEL as the input electron beam. Since the UV FEL requires very short pulses, the input to the FIR FEL is extremely short compared to a slippage length and the usual Slowly Varying Envelope Approximation (SVEA) does not apply. We use a non-SVEA code [2] to simulate this system both with a small energy spread (UV laser off) and with large energy spread (UV laser on)

Modeling paraxial wave propagation in free-electron laser oscillators

Modeling free-electron laser (FEL) oscillators requires calculation of both the light-beam interaction within the undulator and the light propagation outside the undulator. We have developed a paraxial optical propagation code that can be combined with various existing models of gain media, for example, Genesis 1.3 for FELs, to model oscillators with full paraxial wave propagation within the resonator. A flexible scripting interface is used both to describe the optical resonator and to control the codes for propagation and amplification. To illustrate its capabilities, we numerically investigate two significantly different FEL oscillators: the free-electron laser for infrared experiments (FELIX) system and the vacuum-ultraviolet (VUV)-FEL oscillator of the proposed high-gain fourth generation light source. For the FELIX system, we find that diffraction losses are a considerable part of the single-pass cavity loss (at a wavelength of 40 µm). We also demonstrate that a resonator with hole coupling may be a viable alternative to a standard resonator with transmissive optics for the high gain VUV-FEL oscillator

11.9 W output power at 4 GHz from 1 mm AlGaN/GaN HEMT

A high electrical breakdown field combined with a high electron saturation velocity make GaN very attractive for high power high frequency electronics. The maximum drain current densities of AlGaN/GaN HFETs range from 1.0 A/mm to 1.5 A/mm [1-3]. Hence, it is obvious that breakdown voltages over 160 V are required to achieve record output power densities larger than 30 W/mm [3] for class A operation. Maximum RF output power of GaN based HEMTs is significantly less than what can be estimated from its DC characteristics, the so-called DC to RF dispersion [4]. This gate lag effect and a good passivation of the AlGaN surface under the gate contact are key elements in achieving high power HEMTs

11.9 W Output Power at S-band from 1 mm AlGaN/GaN HEMTs

We present radio-frequency (RF) power results of GaN-based high electron mobility transistors (HEMTs) with total gate widths (Wg) up to 1 mm. The AlGaN/GaN epi-structures are MOVPE-grown on 2-inches semi-insulating (s.i.) 4H-silicon carbide substrates. The HEMTs have been fabricated using an optimized process flow comprising a low-power Ar-based plasma after ohmic contact metallization, cleaning of the AlGaN surface prior to the Schottky gate metallization using a diluted ammonia (NH4OH) solution, and passivation of the AlGaN surface using a silicon nitride layer deposited by plasma enhanced chemical vapor deposition. We will show that the best RF power performance has been achieved by HEMTs with iron-doped GaN buffer layers (GaN:Fe). Devices with a total gate width of 1 mm yielded a maximum output power of 11.9 W at S-band (2 - 4 GHz) under class AB bias conditions (VDS = 40 - 60 V, and VGS = -4.65 – - 4.0 V)

11.9 W output power at S-band from 1 mm AiGaN/GaN HEMTS

In this paper we present an optimized process for fabrication of dispersion-free small (Wg = 80 µm) and large (Wg = 0.25 mm, 0.5 mm, and 1.0 mm) gate periphery n.i.d. AlGaN/GaN HFETs grown by MOVPE on s.i. 4H-SiC substrates. First small periphery devices were fabricated on three epistructures all having 30nm undoped Al0.3Ga0.7N barrier layer: two using a very thin (1-2 nm) undoped AlN with undoped GaN buffer layer (1.2 µm) and one using a Fedoped semi-insulating (s.i.) GaN layer

11.9 W output power at S-band from 1 mm AiGaN/GaN HEMTS

In this paper we present an optimized process for fabrication of dispersion-free small (Wg = 80 µm) and large (Wg = 0.25 mm, 0.5 mm, and 1.0 mm) gate periphery n.i.d. AlGaN/GaN HFETs grown by MOVPE on s.i. 4H-SiC substrates. First small periphery devices were fabricated on three epistructures all having 30nm undoped Al0.3Ga0.7N barrier layer: two using a very thin (1-2 nm) undoped AlN with undoped GaN buffer layer (1.2 µm) and one using a Fedoped semi-insulating (s.i.) GaN layer