Novi rezultati u projektiranju i mjerenju antena za osobne pokretne komunikacije

Mobile communications are taking more and more importance in everyday life, creating the need for smaller and lighter mobile terminals. Unlike the electronic circuits, the size of an antenna is not technology related, but imposed by the wavelength of a given application. This makes antenna miniaturization to an art of compromise between size and radiation performances. In this presentations we will first state the limitations of antenna miniaturization, by reminding of the well known laws linking gain, bandwidth and antenna size. Then some well known ways to reduce antennas sizes will be reviewed and illustrated on a practical example designed and realized in our laboratory. Finally, we will deal with the non trivial problem of small antenna measurement: the problems encountered when measuring small antenna will be presented and some clues on how to proceed correctly will be given.Pokretne komunikacije postaju sve važnije u svakodnevnom životu, a time se povećava potreba za što manjim i lakšim pokretnim komunikacijskim uređajima. Za razliku od elektroničkih sklopova, veličina antene nije određena stupnjem tehnološkog razvoja već je zadana frekvencijskim područjem koje se koristi za određenu primjenu. Zato je minijaturizacija antena umjetnost kompromisa između malih izmjera i dobrih osobina zračenja. U ovom su radu ograničenja minijaturizacije antena prikazana kroz povezanost dobitaka, širine pojasa i izmjera antene. Zatim su opisani neki uobičajeni postupci za smanjivanje izmjera antena. Njihova je primjena prikazana na praktičnoj izvedbi koja je projektirana i izrađena u našem laboratoriju. Konačno se razmatraju problemi pri mjerenjima malih antena: izneseni su problemi koji su uočeni pri mjerenju malih antena kao i naputci za njihovo prevladavanje

Classic Electrically Small Antennas Versus in/On-Body Antennas: Similarities and Differences

Electrically small antennas (ESAs) have been discussed since the early radio days, when all antennas were small compared to the wavelength. The boom of mobile phones triggered a second wave of intense research activity on these devices, which continues today where virtually everything has a wireless connection. This intense research activity has produced interesting and usefully results on the physical limitations of such antennas, design rules and optimal designs. Since the beginning of the century, the number of medical, sports, or security applications (to name just some of them) requiring implantable or wearable communication devices has grown at a high speed, launching the interest for wearable or implantable ESAs. Many interesting designs have been published to this date, but we only start understanding the fundamentals of such antennas. Neither physical bounds on their radiation characteristics nor optimal designs or design rules are yet available. In this contribution, I will highlight the main similarities and differences between classic ESAs and antennas for wearables and implants, illustrated by practical example

Patch Antenna System for CubeSats in L band

An L-band patch-antenna system for CubeSat applications is presented in this paper. The high-permittivity dielectric loading reduces the size of individual antennas to make them suitable for a CubeSat platform. Two circularly polarized patch antennas were designed for the downlink and uplink frequencies of 1.53 and 1.63 GHz, respectively, and the antenna prototypes were characterized. A two-element, sequentially rotated antenna array was designed using the uplink patch element at 1.63 GHz, with a beam tilt of 20° from broadside. The array is to be employed in a system of four arrays that provide two tilted beams with dual-band coverage in each beam, for an increased system capacity. The arrays are located on the backside of the 3U-CubeSat solar panels, facing Earth. While the panels are stowed, the antennas of two arrays are interleaved, reducing the required stowage volume

Wideband Cavity-Backed CubeSat Antenna in S band

The Telemetry, Tracking and Command (TT&C) antennas are a crucial component of small satellites, as their in-orbit attitude is not always well-defined. The TT&C antenna design for a CubeSat is an even more challenging task, considering the volume restrictions imposed by the standard, and the bandwidth requirements for a duplex communication. A detailed design process of a low profile S-band antenna, suitable for CubeSat applications, is presented in this paper. The fabricated prototype exhibits a 10-dB impedance bandwidth of 40%, and a 3-dB AR-bandwidth of 32%

Design of atomic clock cavity based on a loop-gap geometry and modified boundary conditions

In this study, we investigate a concept that can be used to improve the magnetic field homogeneity in a microwave cavity applied in a novel, high-performance atomic frequency standard. We show that by modifying the boundary conditions in the case of a loop-gap geometry, a good improvement of the field homogeneity can be obtained. Such a design demonstrates high potential to improve the frequency stability; it is compact and hence suitable for a future generation of compact, high-precision frequency standards based on vapor cells and a pulsed optical pumping (POP) regime (POP atomic clocks)

Stacked patch antenna and hybrid beamforming network for 5G picocell applications

This paper addresses the design of an antenna array for a portable picocell station with omnidirectional coverage. The proposed solution includes a stacked patch antenna as a single radiating element of the antenna array and a hybrid beamforming network. The antenna element works at 26 GHz with a bandwidth of 20% and a gain of approximately 8.5 dB along the operational bandwidth. The antenna is fed by a suspended stripline transitioned from a waveguide. This antenna element is used to compute a 5x12-element antenna array fed by the hybrid beamforming network. Results are analytically obtained for a fixed analog beamforming network that generates a csc squared pattern shape in elevation. Additionally, a digital beamforming network is computed to perform beamsteering for a desired set of constraints in the azimuth plane. Simulated results of the complete system yield promising insights on the capacity of the proposed design to provide omnidirectional coverage

2G/3G Serpentine Shape Inverted-F Antenna for Near Body Application

In this contribution, we present a miniature antenna placed in a leg bracelet for body worn applications. It operates in both the 820-960 MHz and the 1.7-2.1 GHz bands. The radiating element, based on an inverted-F antenna, occupies a 37 mm × 37 mm area and is printed on a flexible substrate that extends a multilayer circuit board. The serpentine shape helps to widen the bandwidths as well as minimize the size. The antenna is characterized for different situations: standalone, inside the plastic casing and worn close to the body inside the same casing. Both simulations and measured results are presented, and they agree well. The design steps are reviewed with the aid of current distribution simulation plots

Study of Field Misalignment in a Cavity Used for Atomic Clock Applications

In vapor cell atomic clocks the atom-field interaction is typically obtained inside a microwave cavity resonator in which the microwave driving field together with a static magnetic field and an optical field are applied to excite the atoms. These fields are generally well-controlled, mutually aligned to a common quantization axis. Since the exploited atomic transition is sensitive to any potential axis misalignment, the performance of the clock can also be affected. We study the effect of such misalignment for the case of a cylindrical cavity used in vapor-cell atomic clocks, taking into account the misalignments of the optical detection field and the static magnetic field required for the atomic transition. Both the geometry of the cavity and the factors contributing to losses can play role in the degradation of the signal and are taken into account in the misalignment problem discussed

Ultra-Wide Band Diversity Antenna for Omnidirectional Coverage

In this paper, a 41 x 42.2 mm2 ultra-wide band (UWB) diversity antenna is designed to operate in the frequency band 5.45- 7.45 GHz with the isolation better than 15dB. To achieve omnidirectional coverage pattern diversity is applied. The proposed design is suitable for UWB applications requiring reliable radio link and coverage