Jari Holopainen

Aalto University · Department of Electronics and Nanoengineering

Various applications, including reconfigurable intelligent surfaces, radio frequency identification, and ambient backscatter devices, are based on scattering. Predicting the scattering properties of these systems accurately and universally in a computationally efficient manner is crucial. In this paper, we propose a model for predicting the scatter...

This paper investigates a thin low-pass filtering antenna array based on dual-polarized Vivaldi elements. The low-pass filtering in the antenna elements reduces the requirement for the front-end filtering between the antenna and the microwave electronics, resulting in improved overall out-of-band suppression, size reduction, and lower cost. The arr...

This paper presents a band-pass filtering antenna array based on corrugated Vivaldi antenna elements and finline waveguides. The low-pass section of the filtering antenna element is realized by periodically corrugating the inner edges of the Vivaldi elements. The structure can be considered as a periodic transmission line that inherently acts as a...

Orthogonality of the characteristic modes with respect to the weight operator of the generalized eigenvalue equation (GEE), and in the far-field, is investigated in the case of lossy conducting and dielectric objects. Linking the weight operator to radiated power is shown to provide orthogonal far fields in the lossless case. In the lossy case, bot...

This article presents a wideband, dual-polarized antenna array with inverted BoR elements. The antenna structure is based on the conventional body-of-revolution (BoR) element, but the structure is inverted; i.e., instead of metallic cones, the elements are metalized cavities inside a dielectric block. This structure allows a more lightweight and lo...

This article investigates a dielectric-loaded Vivaldi-type antenna array that is formed inside a plastic block. It utilizes the inverted body-of-revolution (BoR) structure, where cone-shaped cavities are formed in a dielectric material and metalized from the inside. The metalized cavities form an array of inverted BoR elements that are fed by a sin...

This letter presents a novel concept of beam-steerable transponder based on antenna array and phased modulators. The steerability of the beam is achieved by optimally delaying the modulated reflected signal at each antenna element (i.e., changing the phase in frequency domain) with load modulation technique. In this manner, the reflected backscatte...

This Letter presents a Bluetooth antenna for metal‐cased smart jewellery. The designed antenna is competent enough to operate in free space; moreover, antenna performance is investigated with cubical shape model which has the electrical properties similar to human body tissue. The measured prototype achieves 68% total efficiency in the free space a...

This letter presents a new concept of broadband transponder based on frequency-reconfigurable cluster antenna and phase-variable modulators. The transponder in this concept has multiport antenna, whose elements have strong mutual coupling between them. The technique presented in this concept takes advantage of the coupling between the antenna eleme...

This letter presents an ambient backscattering transponder with independently beam-switchable receive and transmit antennas. The independently switchable antennas make it possible to collect ambient waves from the direction where they are the strongest and further modulate and redirect the waves towards the receiver possible in another direction th...

Realising capacity demands of future wireless communications require improved spectral efficiency in the sub‐6 GHz frequency bands. This study proposes a novel eight‐element multiple‐input–multiple‐output (MIMO) antenna that can be tuned from 1.7 to 6 GHz. The design is based on the antenna cluster concept, where weighted feeding of multiple antenn...

Realizing capacity demands of future wireless communications requires improved spectral efficiency in the sub-6-GHz frequency bands. This paper proposes a novel eight-element multiple-input multiple-output (MIMO) antenna that can be tuned from 1.7 to 6 GHz. The design is based on the antenna cluster concept, where weighted feeding of multiple anten...

The upcoming standards of wireless communications result in additional and more stringent requirements for antennas in mobile phones. In this paper, we present a frequencyreconfigurable antenna that could potentially be suited for future mobile devices. Frequency reconfigurability is achieved through a cluster of mutually coupled antenna elements t...

We describe a teaching experiment conducted in a hands-on antenna course in Aalto University. The course was specifically designed to fulfill the higher level (senior master's and post-graduate) educational objectives and it was implemented by applying the principles of the “progressive inquiry” model. The model was introduced and applied in two pr...

Locating items rapidly and accurately has become a crucial part of our modern society and industry. Accurate locating not only saves time and money but also reduces waste, as products do not get lost along supply chains. One promising indoor tracking method is provided by radio-frequency identification (RFID) technology. The main benefit of RFID te...

In this paper, a simulated and measured results of a broadband monopole antenna is presented. The proposed design will be used in the RF power scavenger application of the 2016 IEEE AP-S Student Design Contest. The antenna has a −6-dB impedance bandwidth from 930 MHz up to 2420 MHz and omnidirectional radiation pattern in the horizontal plane. The...

This paper introduces an S-parameter-based method for characterizing and improving the electromagnetic (EM) isolation between antennas in handsets. Eight different antenna placements are investigated across a frequency range of 400– 6000MHz covering all possible LTE-A bands. Simulations of realistic antenna elements validate the theoretical results...

This letter presents a new concept for frequency-reconfigurable antennas. The concept involves a multiport antenna, whose elements are mutually coupled. By properly weighting the excitation signals in each port, the total reflected power can be minimized, and radiation efficiency maximized. Different frequency components of the transmitter can be w...

This paper presents a dual-resonant PIFA (Planar Inverted F-Antenna) for a wireless on-body breathing monitoring system utilizing Bluetooth. Gap-coupled, dual resonance structure is used to achieve a large band and robust operation in different environments. According to simulations, the antenna has a-10 dB impedance bandwidth of 210 MHz, and rough...

In today's wireless communication systems, the need for more frequency bands and higher data rates provides challenges for designing compact, efficient, and environment-insensitive handset antennas. One way of obtaining this is by using frequency-reconfigurable Multiple-Input Multiple-Output (MIMO) antennas to both minimise the antenna volume and t...

A novel frequency reconfigurable 4G Multiple-Input Multiple-Output (MIMO) handset antenna is presented and verified with experimental results. Frequency tuning is used to minimize the antenna volume and to compensate for the losses related to user-originated impedance detuning. Both antenna elements are independently frequency reconfigurable and ca...

A novel design strategy for multi-standard mobile handset antennas is presented and verified with experimental results. The results show that the presented antenna operates with better than -3 dB (50%) efficiency across the frequencies of 698-2900 MHz and 3250-3600 MHz, thus having state-of-the-art performance. The antenna is shown to have a robust...

A new, extended model to evaluate the performance of Global Positioning System (GPS) antennas in mobile terminals is introduced. The new model is demonstrated using three different antennas with two orientations, and it is shown to give a more reliable prediction of the GPS antenna performance compared to the earlier model. Also, a new parameter fo...

The performance of mobile terminal antennas in the case of a non-planar ground plane is studied. The effects of bending are analysed using computer simulations and a resonator-based equivalent circuit model for improving the understanding of the phenomenon. Results show that bending the ground plane can have a considerable effect on the operation a...

This letter introduces a novel 2.6-GHz multiple-input-multiple-output (MIMO) antenna system for mobile terminals. The antenna structures consist of a broadband main antenna covering most of the LTE-A bands and a narrowband second antenna operating at the 2.6-GHz band. The main antenna is a traditional monopole-type capacitive coupling element (CCE)...

The incorporation of new services in handheld devices, such as the Digital Video Broadcast—Handheld (DVB-H) operating at the lower ultrahigh-frequency (UHF) band poses a challenge for antenna designers. Wideband small antennas or electrically tunable narrowband small antennas are needed to fulfil the performance requirement. It is well known that b...

Reducing the effect of the hand and the head of a user on the operation of mobile terminal antennas is investigated with simulations and measurements. The study is made at 900 and 2000 MHz. The shielded antenna structure consists of two antenna elements. Non-self-resonant antenna elements are required to obtain an improved antenna performance. Depe...

This paper studies the influence of the user's hand on the mutual coupling of dual-antenna structures on a mobile terminal. The terminal consists of two planar inverted-F antennas (PIFA) on a typical 100 x 40 mm 2 mobile terminal chassis operating at 900 MHz, 2000 MHz, 3500 MHz and 5300 MHz bands. The hand was placed at different positions while th...

The implementation of internal broadband antennas for lower UHF-band cellular systems (including low-band LTE) in mobile terminals is studied. Especially, the limits for the minimum size of capacitive coupling element-based antenna structures inside different-sized handsets are evaluated and compared. The paper also increases general understanding...

This letter reports a systematic simulation study of the performance of mobile terminal antennas in the vicinity of the user's hand. The effects of antenna dimensioning and antenna location on the ground plane of the device are demonstrated. The studied performance parameters are quality factor, radiation efficiency, and frequency detuning. Based o...

This paper presents a comprehensive simulation study on the performance of coupling element-based dual-antenna structures on a mobile terminal at the 2,000 MHz Universal Mobile Telecommunications System (UMTS) frequency band with varying two significant hand effects; vertical position of hand along terminal chassis, and distance between hand palm a...

This paper deals with the effect of the user's hands on the performance of lower UHF-band antennas in handheld terminals. It is studied that how the input impedance, efficiency, and far-field directional pattern of the internal broadband digital television antenna are affected by the presence of the user's hands. The main part of the study has been...

Interaction between a mobile terminal antenna and a hand of a user is investigated with an experimental study using capacitive coupling element antennas and homogeneous anthropomorphically shaped hand phantoms. The frequency bands used in the study are 880-960 MHz and 1710-1880 MHz. The significance of the shape, size and position of the antenna el...

A novel method to improve the isolation between antenna elements on a mobile terminal at the 900-MHz frequency band is introduced. The characteristics of dual-antenna systems have been studied by simulations. The purpose is to use a combination of balanced and unbalanced antenna structures. In addition, the diversity performance in three different...

Capacitive sensors have been designed for use as user proximity sensors in mobile-phone antennas. Sensor-induced losses were measured in 900- and 1800-MHz capacitive coupling element antennas and a 1900-MHz planar inverted-F antenna (PIFA) and compared to the RF losses caused by an impedance-matching sensor. The lengths of the capacitance sensors v...

The user body effect on the operation of mobile terminal antennas is investigated based on equivalent circuit modelling. The purpose is to increase the understanding of the phenomenon, which is important, for example, when designing mobile terminal antennas with minimised user effect.

The Implementation of internal broadband antennas for digital television receiver (DTV) in mobile terminals operating at the lower UHF band is studied comprehensively. Certain challenges such as inherently narrow impedance bandwidth of electrically small antennas and limited volume available for the antennas inside mobile terminals are identified a...

This paper presents a comprehensive simulation study on the performance of broadband coupling-element-based multiantenna structures on a mobile terminal at the 2000 MHz Universal Mobile Telecommunications System (UMTS) frequency band with varying two significant hand effects; vertical position of hand along terminal chassis, and distance between ha...

In this paper, compensation of the effect of the user's finger on the operation of a mobile terminal antenna is studied, using antenna selection as the compensation method. A dual-element antenna is compared with a single-element antenna occupying the same total antenna volume. The results show that antenna selection can provide an improvement of a...

In this paper a frequency-reconfigurable mobile terminal antenna with a tuning range of one octave is presented. The antenna is based on a capacitive coupling element (CCE) and switching between two separate matching circuits controlled with RF MEMS switches. The tuning concept using MEMS is compared with similar tuning cases using HEMT switches. T...

In this paper the feasibility of balanced antenna structures in the mobile terminal environment has been investigated concerning bandwidth and radiation properties. It has also been studied if the effect of the user's hand on frequency de-tuning and decrease in radiation efficiency could be reduced with the balanced antenna structures compared to t...

In this letter, it is shown how the behavior of a capacitive coupling element (CCE)-based mobile terminal antenna can be modeled at the UHF band as a combination of the separate wavemodes of the structure. The proposed equivalent circuit model improves the general understanding of the operation of the antenna structure. It can be used for analyzing...

A five-element inverted-F antenna array on mobile terminal for both multiple input multiple output (MIMO) communications and radio direction finding (RDF) applications is presented. The multi-element antenna (MEA) system has been designed to be used in the frequency band of the future Long Term Evolution (LTE) system at 3400-3600 MHz and integrated...

This paper discusses the effects of conductive objects such as the display or the battery of the mobile terminal on the performance of mobile terminal antennas based on direct coupling, i.e. antennas fed across a slot in the mobile terminal chassis without any antenna elements. In addition, a method using inductive loading to partly compensate thes...

This paper discusses the issues in antenna design for future mobile communications terminals caused by the addition of more and more antennas into the devices. There can be more than 10 different radios in the terminal and some of them will utilise adaptive antenna systems with more than 5 antennas. Thus it is possible that a future terminal device...

A novel antenna structure based on optimized direct feed is presented in this paper. The antenna structure consists of the chassis of a mobile terminal, a feed structure and a matching circuitry. The chassis is cut in two pieces, which are connected with an inductor. The value of the inductor is tuned so that the lowest resonant frequency of the ch...

This paper reviews different recent approaches taken towards the realisation of space-efficient antenna structures for mobile terminals without the use of traditional self-resonant antenna structures, but instead by coupling the RF power directly to the wavemodes of a regular-sized terminal chassis. Several realisations of possible coupling structu...

In this letter, it is shown that inverted-top wavetraps, which are quarter-wavelength-long resonators, can be used to control the near-fields of a mobile terminal antenna. The local reduction of the near-fields is especially important for the operation of the hearing aid of the user. The reshaping of the near-fields may also enable reduced specific...

2008. Minimization of power loss and distortion in a tuning circuit for a mobile terminal antenna. Abstract Broadband tuning circuits of small antennas may have high power losses and/or high distortion if the designer does not pay attention to the placement of the lossy and nonlinear components in the circuit. In this paper, experimental results of...

In this paper, broadband frequency tuning of mobile handset antennas using switches and passive reactances is studied. The idea is applied to a compact coupling element antenna, for which a dual-band (E-GSM900 and GSM1800) tuning circuit is designed and prototyped. The objective was to have a sufficient impedance bandwidth and good efficiency. The...

The user effect study for handheld DVB antennas was performed by simulating the radiation and total efficiencies of the antennas as a function of frequency. Because of the losses caused by the user, a 4-dB margin to the realized gain specification in the antenna prototypes located in free space is needed to fulfil the DVB-H specification also when...

This paper gives a brief overview on some typical development trends of the small antennas used in multi-system mobile communications terminals. The main challenge in this development has been and will be to fit all the antennas needed for up to over 10 radio systems into a small, thin handheld terminal, whose total volume should in many cases stay...

The current trend in mobile terminals is an increasing number of systems. The volume occupied by the antennas of the radio systems is becoming more and more problematic and new low-volume antenna solutions are needed. Since the EMC shielding and the ground plane operate as the main radiating structure especially below 1 GHz, a very small antenna st...

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In this overview paper we have studied different options for implementing antennas in multi-system mobile terminals that are becoming more and more common. The presented recent results included broadband antenna elements with multi-frequency matching circuits and the use of tunable or selectable centre frequency. All the solutions are based on the...

In this licentiate thesis the implementation of small internal DVB-H antennas for handheld multisystem radios is studied, and several prototypes and simulated designs are presented and evaluated. Since the volume that can be reserved for antennas is very restricted, the limits for the size of capacitive coupling element based antenna structures ins...