Ku-band Frequency Research Articles

A fully integrated Ku-band Doherty amplifier MMIC

The design and performance of a fully integrated Ku-band Doherty amplifier monolithic microwave integrated circuit (MMIC) is presented. The circuit is implemented in 0.25-μm pHEMT MMIC technology and demonstrates the feasibility of the Doherty approach at Ku-band frequencies. The fabricated devices achieved a two-tone power-added efficiency of 40% with a corresponding third-order C/I ratio of 24 dBc at 17 GHz. To the author's knowledge this is the first fully integrated pHEMT Doherty amplifier MMIC as well as the first experimental results for a Doherty amplifier at Ku-band reported to date.

CAD and optimization of compact ortho-mode transducers

We describe a hybrid computer-aided-design technique, which employs the standard generalized scattering matrix description and a new method, based on the three-dimensional generalized admittance matrix representation, for the efficient and reliable analysis of compact ortho-mode transducers (OMT). A rigorous investigation of the numerical convergence properties of the electromagnetic simulators is carried out by using as a benchmark the measurements of a specifically built structure. The electromagnetic simulators are used for the efficient computer-aided optimization of the OMT and a procedure for the dynamical optimization of such components is introduced and tested by designing several OMT's operating at L, S, and Ku frequency bands. The component design, entirely carried out at computer level, has demonstrated significant advantages in terms of development times and no need of post-manufacturing adjustments. The very satisfactory agreement between experimental and theoretical results further confirms the validity of the proposed technique.

A new self-aligned and T-shaped gate technology for GaAs power MESFETs

A new self-aligned and T-shaped gate technology suitable for the fabrication of GaAs power MESFET was demonstrated using optical lithography. The process employed methods to solve the problems of high gate resistance and low breakdown voltage inherent in power MESFET. The devices with 0.5 μm T-shaped gate, fabricated on a high–low doped epitaxial layer, showed an uniform transconductance of 150 mS/mm at gate biases ranged from −0.8 to +0.8 V and a high gate-to-drain breakdown voltage of 35 V. The cut-off frequency and the maximum frequency of oscillation were measured to be 25 and 90 GHz, respectively. The power performance, measured at a drain bias of 8 V and an operation frequency of 12 GHz, displayed an associated gain of 10.0 dB and a power-added efficiency (PAE) of 56%. These are the highest PAE and gain in MESFET structure ever reported at Ku-band frequencies. The mean time to failure of the MESFET at 125°C was evaluated to be 2×10 8 h. These good electrical performances were due to the new MESFET design incorporating an undoped GaAs cap and a thick lightly doped active layers. The MESFETs developed in the present work are expected to be very useful as a power amplifying device for satellite applications.

Frequency detector with power combiner dividers

The author describes a microwave frequency detector made in microstrip technique. The system consists of two power dividers and three transmission lines. Ratio of amplitudes of output signals determines frequency of input signal. Despite simple structure, the frequency detector has very attractive parameters. Practically made the detectors worked in S in Ku frequency band.

Influence of the biasing scheme on the performance of Au/SrTiO3/LaAlO3 thin film conductor/ferroelectric tunable ring resonators

The performance of gold/SrTiO3/LaAlO3 conductor/ferroelectric/dielectric sidecoupled, tunable ring resonators at Ku-band frequencies is presented. The tunability of these rings arises from the sensitivity of the relative dielectric constant (εr) of SrTiO3 to changes in temperature and dc electric fields (E). We observed that the change in εr which takes place by biasing the ring up to 450 V alters the effective dielectric constant (εeff) of the circuit resulting in a 3λ resonant frequency shift of nearly 12% at 77 K. By applying a separate dc bias between the microstrip line and the ring, one can optimize their coupling to obtain high Q bandstop resonators with δfn −1 = f0/Δf3dB as high as 12,000. The 3λ resonance was tuned from 15.75 to 17.41 GHz while keeping δfn −1 above 768 over this range. The relevance of these results for practical microwave components will be discussed.

Ku- and C-band SAR for discriminating agricultural crop and soil conditions

A method is proposed to estimate both green leaf area index (GLAI) and soil moisture (h/sub v/), based on radar measurements at the Ku-band (14.85 GHz) and C-band (5.35 GHz) frequencies. The Ku-band backscatter at large incidence angles was found to be independent of soil moisture conditions and could be used alone to estimate GLAI. Then, the Ku-band estimate of GLAI could be used with a measurement of C-band backscatter in a canopy radiative transfer model to isolate the value of h/sub v/. This concept was demonstrated with a set of Kuand C-band synthetic aperture radar (SAR) backscatter data acquired over agricultural fields in Arizona. The demonstration showed promise for operational application of the method, though several limitations were identified. Since both Ku- and C-band /spl sigma//sub /spl deg// are sensitive to soil roughness, this approach must be applied only to fields of similar soil roughness or row direction. This limitation may be less serious for farm management applications since crop type and cultivation practices are generally well known and can be taken into consideration. Another limitation of the use of Ku- and C-band /spl sigma//spl deg/ is the apparent saturation of the Ku-band signal with increasing GLAI. Operational implementation of this approach will require dual-frequency sensors aboard an aircraft or orbiting satellite.

Nonlinearity of p-i-n photodetectors

At higher operating frequencies, the field dependence of the carrier velocity in p-i-n photodetectors generates harmonics and intermodulation products that can degrade the dynamic range of RF fiber-optic links. The authors present both a perturbational theory and measured harmonic data for a p-i-n photodiode operated at very high power densities which show that this and other detector nonlinear effects need not seriously compromise link performance. In particular, neither transit-time nor static nonlinearities in p-i-n photodiodes need limit the dynamic range of fiber-optic links operating below 5 GHz. The fact that the theoretical bandwidth of the photodiode, with all parasitic capacitance and inductance ideally removed, is 17 GHz, suggests that comparable spur-free performance should be achievable at X and Ku-band frequencies, once packaging parasitics are reduced.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Very Small Aperture Terminal (VSAT) Systems for Digital Satellite Communication: An Overview

This paper presents an overview of digital satellite communication systems based on low-cost, very small aperture terminals (VSATs) located directly at subscribers' premises. Over the last few years, such VSAT systems have become feasible because of a combination of recent advances in satellite and earth station technology. These include the deployment of higher power satellites, the use of Ku-band (14/12 GHz) frequencies, the availability of lowcast earth station antennas and microwave electronics, along with the development of cost-effective implementations for modulation, spectrum spreading, forward error control (FEC) and protocol processing. Digital communication services which potentially achieve reasonable combinations of VSAT cost and satellite usage are identified for consideration. Specific applications considered are: one-way data distribution, point-to-point data, two-way interactive-data packet networking, digital voice (including telephony and packet voice messaging), and satellite ISDN. App...

Microwave photoconductors

AbstractAn optically controlled microwave attenuator is described. The bulk semiconductor properties of cadmium selenide are demonstrated effectively at Ku band frequencies. The device is configured monolithically with a low capacitance resistive channel. Electrical resonance is achieved with symmetric inductance loops which bridge the channel ends.

Orbiter environment at S- and Ku-band frequencies

Detailed measurements of the electric field strength associated with the Ku-band radar and S-band communication link were made by the Plasma Diagnostics Package (PDP) on STS 51F. These measurements were made while the PDP was attached to the Remote Manipulation System arm and again while the PDP was released as a subsatellite. The results indicate that cargo elements that remain inside of the scan limits of the radar should experience fields less than 2 V/m and that elements that may encounter the main beam can use 300 V/m as a design guideline with adequate safety margin. S-band fields tended to be several dB lower than worst-case predictions. Safe design practice indicates that an electric field E = 100/r (r in meters) should be used as a guideline for deployable systems. S-band electric fields within the cargo bay envelope should be less than 2 V/m even with edge diffraction effects and reflections from other payloads taken into account. The absolute accuracy of these measurements is about 2 dB.

Mixed planning approach at Geneva

This article reports on the proceedings of WARC-ORB-85, held in Geneva in August and September this year. Agreements reached included a priori allotment planning for new frequencies, improved coordination, with the possibility of burden sharing in accommodating new entrants for currently used C band and Ku band frequencies, and first come, first served for other frequencies — a mixed planning approach. The article also considers the issues remaining after the conference that will dominate the intersessional period to WARC-ORB-88.

Direct modulation and active mode locking of ultrahigh speed GaAlAs lasers at frequencies up to 18 GHz

It is demonstrated that an ultrahigh speed window buried heterostructure GaAlAs laser fabricated on a semi-insulating substrate can be used as a narrowband signal transmitter in the Ku band frequency range (12–20 GHz). The modulation efficiency can be increased over a limited bandwidth by a weak optical feedback. A stronger optical feedback enables one to actively mode lock the laser diode at a very high repetition rate up to 17.5 GHz, producing pulses ∼12 ps long.

High-Frequency Doubler Operation of GaAs Field-Effect Transistors

A comprehensive study of single-gate GaAs FET frequency doublers is presented. Special emphasis is placed on exploring high-frequency limitations, while yielding explanations for previously observed lower frequency phenomena as well. Extensive Iarge-signal simulations demonstrate the underlying relationships between circuit performance characteristics and principal design parameter. Verifying experiments include straight frequency doubler and a self-oscillating doubler, both with output signal frequencies in Ku-band. The self-oscillating doubler appears especially attractive, yielding an overall dc-to-RF efficiency of 10 percent. The type of transistor employed in the numerical and experimental examples possesses a gate length of 0.5 µm and a gate width of 250 µm.