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Radiation efficiency of electrically small antennas largely depends on antenna geometry. However, the actual mechanism that governs the antenna radiation efficiency remains unclear, although various models have been developed since the 1940s. Extant circuit models are either intuition-based or mathematic representations of input impedance/far-field spherical mode functions for structurally simple antennas with limited uses and physical insight. In this article, a recently developed physical micromodeling circuit (MMC) model is utilized to explain the nature of radiation of an electrically small antenna of arbitrary configuration. It is theoretically discovered and experimentally validated for the first time that the radiation efficiency decisively depends on mutual radiated power associated with partial segments of the antenna. A circuital figure of merit for describing the total mutual radiated power is introduced to quantify the measure. The graphical representation of the figure of merit called the holographic radiation diagram is also proposed for illustrating the correspondence of the positive and negative radiated power and the antenna structure. The applications of the proposed theory to antenna design is demonstrated by designing a highly efficient loop antenna. The physical circuit model paves a new way of understanding electromagnetic (EM) radiation problems. [ABSTRACT FROM AUTHOR]

A photoconductive antenna (PCA) is modeled using a higher order solution derived from the Boltzmann's equation to accurately predict anomalous behaviors in this system. In the case concerning the application of high bias fields, photoexcited carriers gain sufficient energies, so that they become hot carriers. Moreover, screening fields in PCAs are numerically investigated in the first picoseconds subsequent to the excitation using hot-carriers effects. To explore another exotic phenomenon in a PCA, its driving photocurrent is decomposed into DC and THz components. Then, the saturation behavior of the THz component peak and the sublinear dependence of the DC component with respect to an externally applied bias are numerically investigated. Furthermore, depending on the accumulation of photoexcited carriers, velocity overshoot phenomenon may occur in the driving photocurrent against the applied bias. These phenomena cannot be predicted by the conventional drift-diffusion model. To simplify the analysis of PCAs, a time-dependent equivalent circuit model is proposed for describing the associated operational principles. Finally, using a coherent detection scheme and the circuit model, it will be shown that owing to the screening fields, the THz power saturates with respect to the applied laser power. [ABSTRACT FROM AUTHOR]

This Part I of two papers introduces a design flow for micromechanical RF channel-select filters with tiny fractional bandwidths capable of eliminating strong adjacent channel blockers directly after the antenna, hence reducing the dynamic range requirement of subsequent stages in an RF front-end. Much like VLSI transistor circuit design, the mechanical circuit design flow described herein is hierarchical with a design stack built upon vibrating micromechanical disk building blocks capable of ${Q}$ ’s exceeding 10 000 that enable low-filter passband loss for tiny fractional bandwidths. Array composites of half-wavelength coupled identical vibrating disks constitute a second level of hierarchy that reduces the filter termination impedance. A next level of hierarchy couples array composites with full-wavelength beams to affect fully balanced differential operation. Finally, identical differential blocks coupled with quarter-wavelength beams generate the desired passband. Part II of this study corroborates the efficacy of this design hierarchy via experimental results that introduce a 39-nm-gap capacitive transducer, voltage-controlled frequency tuning, and differential operation toward demonstration of a 0.1% bandwidth, 223.4-MHz channel-select filter with only 2.7 dB of in-band insertion loss and 50 dB of stopband rejection. [ABSTRACT FROM AUTHOR]

Abstract: A single layer single probe‐fed wideband microstrip antenna is presented and investigated. By cutting a U‐slot in the rectangular patch, and by incorporating two identical U‐shaped parasitic patches around both the radiating edges and the nonradiating edges of the rectangular patch, three resonant frequencies are excited to form the wideband performance. Details of the antenna design is presented. The measured and simulated results are in good agreement, the measured impedance bandwidth is 1.44 GHz ( 4.82 ‐ 6.26 GHz), or 26.2 % centered at 5.5 GHz, which covers WLAN 5.2 GHz ( 5.15 ‐ 5.35 GHz), WLAN 5.8 GHz ( 5.725 ‐ 5.825 GHz), and WIMAX 5.5 GHz ( 5.25 ‐ 5.85 GHz) bands. The measured peak gains at the three resonant frequencies are 7 . 73 dB, 7 . 01 dB, and 4 . 55 dB, respectively. An equivalent circuit model which is based on the transmission line theory, the asymmetric coupled microstrip lines theory, and the π‐network theory is established. This equivalent circuit model is used to give an insight into the wideband mechanism of the proposed antenna, and is also used to explain why the three resonant frequencies shift at the variations of different parameters from a physical point of view. The error analysis is given to demonstrate the validity of the equivalent circuit model. [ABSTRACT FROM AUTHOR]

A circuit model for the shielding effectiveness (SE) estimation of a metallic enclosure is proposed, whose off-center aperture is irradiated by the obliquely incident and arbitrary polarized plane wave. This new model has advantages in the following aspects. First, it can deal with the arbitrary angular and polarized incident wave other than the normal incident wave. The incident wave angle and polarization direction are considered in the proposed analytical formulas. Second, higher-order modes such as TEmn and TMmn are included to enable the model to be applicable in higher frequencies. Third, the impedance of the enclosure wall is considered rather than the perfect conductor assumption used in the published literatures, which removes the deficiency that the aperture impedance is zero when the length of the aperture is equal to an integral number of the wavelengths. The influences on the SE from different parameters such as the incident wave angle, the polarization direction as well as the enclosure wall thickness are investigated. Finally, the accuracy of the proposed model is validated by measurements, simulations and comparisons with other literatures. The proposed method is particularly useful for the shielding enclosure design in the electronic manufacturing industry. [ABSTRACT FROM AUTHOR]

The conventional techniques to measure the input impedance of an antenna are based on comparing the reflected signal to the incident signal at the antenna port at a given frequency. A network analyzer connected to the antenna under test through a feeding cable is the most common impedance measurement setup. The induced current on the outer surface of the feeding cable in the electrically small antenna (ESA) case, however, significantly interferes with this process. Therefore, the traditional methods to measure the input impedance such as using a network analyzer may not be suitable for an ESA. A remote impedance measurement technique based on the impulse responses of an ESA terminated to three standard loads, short/open/matched load, is introduced. Two different types of antennas are designed and simulated using a full-wave simulator and then the impulse responses are computed using a transient simulator software. Thereafter, two different circuit models are introduced and the parameters of these models are computed using three impulse responses. The input impedance of both antennas are computed directly from the full-wave simulations as well as the remote measurement technique and the results are compared. Finally, both antennas are prototyped, measured, and the input impedances of the antennas are compared for the direct measurement using a network analyzer and the proposed technique. The presented results confirm the accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

Magnetoelectric (ME) antennas utilize the direct or converse ME effects at acoustic resonance to receive or transmit electromagnetic (EM) signals, making ultra-compact antennas feasible. This work presents a miniaturized ME antenna working at very low frequency (VLF) band. A piezoelectric wafer and magnetostrictive foils are bonded together to form the 12 × 2.1 × 0.08 cm3 ME antenna. The near-field coupling between the ME antenna and magnetic rod coil has been measured to verify the reciprocity. The proposed entire circuit simulation models agree well with the experimental results, explaining the maximum power gap and frequency offset phenomenon. In addition, both practical and simulation results confirm that near-field coupling depends on mutual inductance rather than EM radiation. Based on the emulation of circuits, L -section impedance matching networks are introduced to improve the original power transmission coefficient by 21 dB. The ME antenna is lightweight, wide-band, and easy to match compared with a conventional coil. • A mutual inductance coupling circuit model between a VLF ME antenna and a magnetic rod coil is established. • Impedance matching networks are introduced to improve the original power transmission coefficient by 21 dB. • The reciprocity of the ME antenna in the near-field region is verified. • ME antenna is lightweight, wide-band, and easy to match compared with a conventional coil. [ABSTRACT FROM AUTHOR]

An approach for modeling antenna impedances and radiation fields in terms of fundamental eigenmodes is presented. Our method utilizes the simple frequency behavior of the characteristic modes to develop fundamental building blocks that superimpose to create the total response. In this paper, we study the modes of a dipole, but the method may be applied to more complicated structures as the modes retain many of their characteristics. We show that the eigenmode-based approach results in a more accurate model for the same complexity compared to a typical series RLC resonator model. Higher order modes can be more accurately modeled with added circuit complexity, but we show that this may not always be necessary. Because this method is based on the physical behavior of the fundamental modes, it also accurately connects circuit models to radiation patterns and other field behavior. To demonstrate this, we show that far field patterns, gain, and beam width of a dipole can be accurately extrapolated over a decade of bandwidth using data at two frequency points. [ABSTRACT FROM PUBLISHER]

This paper discusses how symbolic computation combined with a circuit model can be used for analyzing planar multilayer structures, in a manner suitable for educational approach. Working in the Fourier domain, expressions for the transversal spectral Green's functions are evaluated in compact, closed form using the symbolic computation capability of the Mathematica package. Printed antennas were analyzed through the method of moments. Further validation was achieved with the IE3D and HFSS packages. [ABSTRACT FROM AUTHOR]

We propose a modified Wheeler cap method to accurately measure the radiation efficiency of patch antennas with multiple resonances by modeling their impedance as a high-order circuit model. The radiation efficiency is obtained from the power consumption ratio between the radiation and loss conductances using a circuit model we developed. Our technique is validated by measuring the efficiencies of a circularly polarized microstrip patch antenna and a triple-band microstrip patch antenna. The measurement results are in close agreement with those produced by simulations, whereas the Wheeler cap method with a series-(or parallel-) resonant circuit model is shown to be unreliable. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to provide a self-consistent analytical model for the approximate current distribution induced on an arbitrarily loaded wire antenna of moderate length operating in its receiving mode. The results of our analysis shed light on a debated issue regarding the circuit model of a receiving antenna and show that currently available simplified analytical models for receiving dipoles fail to satisfy basic power conservation requirements. These general findings are applied to the proper homogenization of composite materials and surfaces, and to minimum-scattering receivers and absorbers. [ABSTRACT FROM AUTHOR]

A low profile planar antenna, comprising a driven element coupled with one or more parasitic elements is proposed. The design is suitable to be used into a handheld device due to the antenna reduced dimensions (33 × 15 × 1 mm3). To facilitate the integration of other components, such as cameras or speakers, a ground plane area at the right side of the antenna is provided. The study carried out reveals the relevance of the arms location over the performance of the antenna. The theoretic analysis is reinforced using a network model and a parametric study. The coupling between elements controls the behavior of the antenna. In this sense, a weak coupling between the driven element and at least one parasitic element enhances the bandwidth, whereas a multiband behavior is achieved by a tight coupling. Finally, the PCB (Printed Circuit Board) influence has also been analyzed. ©2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 359–364, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24893 [ABSTRACT FROM AUTHOR]

A cascade of resistively loaded etched rings in waveguide is proposed to act as the load in a balanced FMCW reflected power canceller topology using a slotted waveguide array antenna. A synthesis technique using derived equivalent circuit models is presented and tested. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 977–981, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23262 [ABSTRACT FROM AUTHOR]

This paper proposes the integration of an antenna with a photodetector for high capacity wireless communications. A waveguide photodetector (WGPD), illuminated on the side, is used to convert the RF-modulated optical power into a microwave signal. That microwave signal is used to feed an antenna built on the same plane as the photodetector. The WGPD is a standard p-i-n device grown on a semi-insulating InP. The performance of this RF/photonic antenna in the frequency range 17–20 GHz is studied theoretically and experimentally. An equivalent circuit model for the WGPD is developed to predict the photodetector impedance as a function of frequency. The photodetector is matched to the input impedance of the antenna. The agreement between measurement and the circuit model results for the WGPD impedance is very good. It is envisioned that a large number of such RF/Photonic antenna elements could be networked together into a star configuration, feeding in and out of a radio hub. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 179–184, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10550 [ABSTRACT FROM AUTHOR]

A network model is presented for the inverse capacitively fed microstrip antenna, consisting of a ground plane, a radiating patch, and a small patch on top, fed by a probe that penetrates the radiating patch. This structure has the advantage that the capacitor can be easily designed and mounted on an existing structure a posteriori. Based on the characteristics of the original antenna, capacitive coupling between the patches allows matching of this antenna. The network model gives full physical insight, is easily implemented, and allows a much faster design than full-wave models. All formulas necessary to use the model in practice are provided. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 16–19, 2002; DOI 10.1002/mop.10217 [ABSTRACT FROM AUTHOR]

Multiple-input multiple-output (MIMO) scheme refers to the technology where more than one antenna is used for transmitting and receiving the information packets. It enhances the channel capacity without more power. The available space in the modern compact devices is limited and MIMO antenna elements need to be placed closely. The closely spaced antennas undergo an undesirable coupling, which deteriorates the antenna parameters. In this paper, an ultra wide-band (UWB) MIMO antenna system with an improved isolation is presented. The system has a wide bandwidth range from 2–13.7 GHz. The antenna elements are closely placed with an edge to edge distance of 3 mm. In addition to the UWB attribute of the system, the mutual coupling between the antennas is reduced by using slotted stub. The isolation is improved and is below − 20 dB within the whole operating range. By introducing the decoupling network, the key performance parameters of the antenna are not affected. The system is designed on an inexpensive and easily available FR-4 substrate. To better understand the working of the proposed system, the equivalent circuit model is also presented. To model the proposed system accurately, different radiating modes and inter-mode coupling is considered and modeled. The EM model, circuit model, and the measured results are in good agreement. Different key performance parameters of the system and the antenna element such as envelope correlation coefficient (ECC), diversity gain, channel capcity loss (CCL) gain, radiation patterns, surface currents, and scattering parameters are presented. State-of-the-art comparison with the recent literature shows that the proposed antenna has minimal dimensions, a large bandwidth, an adequate gain value and a high isolation. It is worth noticeable that the proposed antenna has high isolation even the patches has low edge-to-edge gap (3 mm). Based on its good performance and compact dimensions, the proposed antenna is a suitable choice for high throughput compact UWB transceivers. [ABSTRACT FROM AUTHOR]

This paper presents an isolation enhancement of two closely packed multiple-input multiple-output (MIMO) antenna system using a modified U-shaped resonator. The modified U-shaped resonator is placed between two closely packed radiating elements resonating at 5.4 GHz with an edge to edge separation distance of 5.82 mm ( λ ∘ /10). Through careful adjustment of parametric modelling, the isolation level of −23 dB among the densely packed elements is achieved. The coupling behaviour of the MIMO elements is analysed by accurately designing the equivalent circuit model in each step. The antenna performance is realized in the presence and absence of decoupling structure, and the results shows negligible effects on the antenna performance apart from mutual coupling. The simple assembly of the proposed modified U-shaped isolating structure makes it useful for several linked applications. The proposed decoupling structure is compact in nature, suppress the undesirable coupling generated by surface wave and nearby fields, and is easy to fabricate. [ABSTRACT FROM AUTHOR]