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Planar power dividers with a good match over a wideband of frequencies are designed using Klopfenstein impedance taper. To validate the proposed design procedure a 2-way stripline and a 2-way microstrip power divider are designed based on simulation, fabrication, and measurement. The measured return loss reveals better than –24 dB (from 4.3 GHz to 19.5 GHz) for a stripline configuration and –27 dB (from 2.2 GHz to 12 GHz) for a microstrip line configuration. Guidelines for accurate simulation and experimental verification are also presented.
A probe station based antenna measurement setup is presented. The setup allows for measurement of complex impedance and radiation patterns of an on-wafer planar antenna, henceforth referred to as the device under test (DUT), radiating at broadside and fed by a coplanar waveguide (CPW). The setup eliminates the need for wafer dicing and custom-built test fixtures with coaxial connectors or waveguide flanges by contacting the DUT with a coplanar RF probe. In addition, the DUT is probed exactly where it will be connected to a transceiver IC later on, such that no de-embedding of the measured data is required. The primary sources of measurement errors are related to calibration, insufficient dynamic range (DR), misalignment, scattering from nearby objects and vibrations. The performance of the setup will be demonstrated through measurement of an on-wafer electrically short slot antenna (.0/35 × .0/35, 5 mm2) radiating at 2.45 GHz.
Double-ridged waveguide horns can provide better than 10:1 relative frequency bandwidth over which they exhibit excellent impedance match and power transfer characteristics. However, the radiation pattern of such an antenna generally becomes more complex at the high end of its operating frequency range. That is, the pattern degenerates from being predominantly single-lobed at lower frequencies to a more complicated pattern exhibiting four gain maxima around the principal axis, all of which are greater than the gain on the principal axis. Here, we present some numerical simulations that appear to indicate that this behavior might not be directly related to higher order modes in the feed region and is not due to manufacturing imperfections, but rather is simply due to the overall taper of the horn itself.
The groundwave correction method of measuring the gain of a vertical antenna over a lossy ground plane is an accepted means of performing a gain measurement without the need for a standard reference antenna. However, on antenna ranges where the ground plane is not uniform, this approach may not yield accurate results over certain portions of the test band due to discontinuities in the ground. This paper shall present a method for using surface impedance methods to predict the performance of an outdoor antenna test range that has a non-uniform ground. Comparison with measured data shall also be presented over the commercial HF and VHF bands.
A method is presented to measure the antenna pattern of an AUT where the antenna port is inaccessible. That means that it is not possible to connect a test cable, nor can the termination be changed physically. In some cases there is no test port at all. The only variation possible is to change the input impedance of the first receiver or LNA by switching it on and off. An RCS-technique can be used to retrieve the radiation pattern. By experimental comparison between the conventional pattern measurement technique and the RCS-technique it is shown that pattern determination via RCS-measurements is feasible. In addition, the measurement method offers the advantage of directly reducing the influence of systematic measurement errors. On the other hand, the penalty is put on power efficiency and a subsequent limited dynamic range.
This paper presents a method for measuring signal backscattering from an RFID tag and calculating tag radar cross-section (RCS), which depends on the chip input impedance. We present a derivation of a theoretical formula for RFID tag radar cross-section and an experimental RCS measurement method using a network analyzer connected to an antenna in an anechoic chamber where the tag is also located. The return loss of the antenna measured with and without the tag present in the chamber allows one to calculate the power backscattered from the tag and find tag RCS. Measurements were performed in anechoic chamber using RFID tag operating the base station (called “RFID reader”). RFID tag antenna is loaded with the chip whose impedance switches between two impedance states, usually high and low. At each impedance state, RFID tag presents a certain radar cross section (RCS). The tag sends the information back by varying its input impedance and thus modulating the back-scattered signal.
In making accurate measurements of antenna gain one must correct for the impedance mismatches between (1) the signal generator and transmitting antenna, (2) between the receiving power sensor and the receiving antenna and (3) between the signal generator and receiving power sensor. This is true for both far-field gain measurements and near-field gain measurements. It has recently come to our attention that there is a lack of clarity as to the form the mismatch factor should take when correcting near-field measured data. We show that a different form of impedance mismatch factor is to be used with the voltage domain equations of near-field than has been used with the power domain Friis transmission equation.
In this paper is presented an experimental investigation of conventional array calibration in the presence of various kinds of joint discontinuities between array panels. Two rigid array panels were positioned such that the element lattice was continuous across a narrow joint. Three kinds of discontinuities were applied to the joint: (1) an angle, (2) a gap (including an edge), and (3) a step between panels. Each type was investigated for joints oriented in the E-plane and the H-plane. Each discontinuity was also varied in magnitude so as to observe parametric effects. Planar near-field-range (NFR) measurements were made in a conventional array calibration mode and a near-field pattern mode. Processing included separating the pattern component due to element transmission (impedance) change from that due to pattern shape change. Results show that conventional calibration methods quickly become inadequate to calibrate these discontinuities because they change element pattern shapes.
Antenna systems are increasing in complexity at a rapid pace as advances are made in electronics, signal processing, communication, and navigation technologies. In the past, antenna design requirements have focused on parameters such as gain, efficiency, input impedance, and radiation pattern (e.g., beamwidth and sidelobe level). For some new systems, the group delay characteristics of the antenna are important, where the group delay is proportional to the derivative of the insertion phase as a function of frequency. The group delay is required to stay within certain bounds as a function of frequency and pattern angle. Unfortunately, there are not well established methods or standards for calibrating antenna group delay like the standard methods used for gain and input impedance. This paper presents a method for calibrating the group delay of three antennas based on an extension of the widely used three-antenna gain and polarization calibration methods. No prior knowledge of the gain or group delay of the three antennas is required. The method is demonstrated by a measurement example where it is shown that multipath errors and time gating can be critical for calibrating the group delay.
Measurements of the insertion loss and impedance in antenna characterization are very important and should be traced back to national attenuation and impedance standards. Vector network analyzers commonly used to measure the impedance are not suitable for millimeter-wave antenna measurements because movement of DUT (Device Under Test) during measurement is required and long cable of high loss for connection between the network analyzer and the DUT mounted high above the floor increases measurement uncertainty. In this paper, a conventional microwave subsystem based on external mixer configuration is modified to measure the impedance of DUT without using the vector network analyzer in millimeter-wave frequency range.
There is a great interest in the automotive and military sectors for small and broadband antennas that meet modern communication needs. These needs require ultra-wide bandwidth (>10:1) UWB antennas, such as the spiral antenna. However, the physical size at the low-frequency end typically becomes too large for practical applications. To reduce the size of the antenna, miniaturization techniques must be employed such as the use of high-contrast dielectric materials. Size reduction using high-contrast materials has been demonstrated for narrowband antennas, such as patch antennas, but not for broadband antennas to our knowledge. Therefore, the concept of miniaturizing a broadband spiral antenna using dielectric materials will be investigated experimentally and numerically. Issues that arise from dielectric loading such as impedance reduction will also be addressed. It will be shown using the results from these studies that there are practical limitations to the amount of miniaturization which can be achieved.
A novel antenna miniaturization approach utilizing artificial transmission-line (ATL) structures whose impedance and phase velocity are mainly controlled by distributed reactive elements is explored. First, the slow- wave phenomena and impedance control in ATL will be demonstrated. Then, miniaturization of a resonating structure will be presented. Finally the application of ATL on antenna structure will be demonstrated. The proposed miniaturization approach is inherently suitable for broadband miniature antenna designs, such as spiral antennas, and provides additional design degree of freedom.
The purpose of this paper is to present antenna measurement techniques of antenna modules for Satellite Digital Audio Radio System (SDARS). SDARS employs dual-transmitter broadcasting formats which include simultaneous transmission of signals from both satellites and terrestrial transmitters. An SDARS antenna efficiently receives both satellite and terrestrial signals: it has relatively good circularly polarized gain at high elevation angles and acceptable linearly-polarized gain at the horizon. Popular SDARS antennas are small ground- depended patch antennas etched on ceramics and ground- independent mast antennas such as quadrifilars. Ceramic patch antennas have a relatively narrow bandwidth of operation. Thus, tuning such antennas to the right frequency is critical. The measurement techniques presented help engineers and technicians evaluate SDARS antennas and determine whether they are correctly designed. We shall describe hardware platforms for evaluating impedance, radiation characteristics, and real-world performance. Parameters such as VSWR, antenna gain, axial ratio, as well as receiver satellite C/N and terrestrial BER will be discussed.
The Air Force Research Laboratory (AFRL) Materials Measurement Laboratory (MML) is a state of the art facility for the characterization of the electromagnetic properties of materials at radio frequencies. The two-fold mission of the MML is to provide material characterization services to AFRL and to conduct R&D to develop or improve RF material characterization technology. The goal of the MML is to perform—or develop the ability to perform—material property measurements to the highest degree of accuracy possible with state of the art test equipment. Characterization measurements range from determination of RF reflection or transmission loss to the extraction of the dielectric permittivity and magnetic permeability of material samples. The MML has the ability to characterize material samples from below 100 MHz to above 18 GHz over material test sample temperatures ranging from – 150oC to greater than 1000oC. While maintaining capabilities using ‘standard’ material measurement techniques (circular coax and rectangular waveguide), the MML’s most highly utilized system is based on the GTRI focused arch apparatus. The MML also employs resonant cavity fixtures, open-ended coax probes and impedance meters to provide a capability to evaluate material samples of a wide variety of shapes and sizes.
Microwave measurement of intrinsic material properties can be performed with transmission-line fixtures such as waveguides or free-space focused beams. However, analyses of measured data usually assume idealized sample geometries. In this paper, Finite Difference Time Domain (FDTD) calculations are used to study the systematic error from non-ideal geometries, in free-space and waveguide measurements of impedance sheets. Analytical models of these errors are developed. FDTD analysis can be used to numerically invert intrinsic material properties from measured freespace transmission coefficients. The focused beam is simulated in FDTD with a sum of weighted plane waves with a Gaussian spectral distribution. The transmission coefficient is predicted by propagating the focused beam through a material slab or sheet; and the dielectric or impedance properties are derived from the transmission coefficient. The focused beam diameter is preferably several wavelengths, which requires large sample size (>1 square meter) at low frequencies. A modified focused beam technique is described that incorporates a finite aperture in a metal groundplane to measure samples with reduced dimensions, even at low frequencies. Calculations are compared to laboratory measurements. FDTD calculations are also applied to study the effect of gaps in waveguide fixtures, since gap and edge effects in both waveguide or free-space aperture fixtures contribute to measurement error.
MW HF phased antenna array, capable of very wideband frequency and scan coverage, is constructed as part of the High Frequency Active Auroral Research Program (HAARP). Operation of the HAARP Developmental Prototype (DP), consisting of 96 dipoles, demonstrated importance controlling even mode excitation originated by electrical asymmetry of the phased active array. For this purpose antenna matching units (AMU) are using hybrids with resistive termination on its even mode ports. Accurate predictions of the array ERP and safe operation of the extended to full 360 dipoles array require a trusted model. This paper presents an application of the measurement and analytic array characterization used for the active array performance prediction and optimization. Mixed mode sparameters of sampled dipoles were measured before multiport mixed-mode S-matrices were constructed using learned array symmetry properties. Created mixed-mode Smatrix model allows for estimation of the ERP, prediction of dipoles power distributions, the AMU and even mode termination impedance optimization for better efficiency.
The installation and operation of large horizontal UHF phased array antennas in arctic regions is challenged by severe environmental conditions. It can be shown that large and moderate snowfall can impact the operation of exposed dipole array elements and reduce aperture efficiency. Reflection coefficients measured at the antenna terminal of an embedded array element can vary drastically as a function of snow depth. In this paper we will describe several measurements that show embedded array element impedance variations versus snow height. Measured results will be presented for an array operating from 400 MHz to 470 MHz.
Recently, remarkable efforts have been spent to develop GPR (Ground Penetrating Radar) systems able to detect shallow anti-personnel mines. In order to achieve high resolutions, large bandwidths are necessary; furthermore antennas must operate detached from ground. The paper describes how an existing surface based antenna, developed for high resolution inspection of man-made structures, has been optimized following a combined measurementssimulation approach. The novel antenna is the basic element of a polarimetric array, composed of 35 elements, that will be part of a multi-sensors demining system under development in the frame of a European Union funded project (DEMAND). Measurements have been carried out in the frequency domain, by the means of an S-parameters modal decomposition. Results concerning bandwidth, leakage, impulse response of array channels and input impedance of the basic element are reported in the paper. Comparison between measurements results and simulations are presented.
Generally, microstrip patch antennas excited to radiate circular polarized waves have serious weakness for narrow bandwidth of axial ratio and impedance in comparison with others (lens, horns, and etc)[1-3]. For this reason, it has been difficult to use microstrip patch antenna for satellite communications in spite of several advantages which are low profile, light weight, ease to fabricate, low cost, and so on [4-5]. In this paper, novel microstrip patch antenna is presented for satellite communications at Ka band. The proposed antenna provides wide axial ratio and impedance bandwidth compared with conventional circular polarized (CP) microstrip patch antenna. These operating characteristics are analyzed.
Determination of Scan Element Pattern (SEP) and of Scan Impedance (SI) of wideband arrays is desirable, in addition to patterns and gain. Scan Element Pattern gives array gain versus scan angles and frequency, while Scan Impedance is the impedance versus scan angle and frequency that must be matched. Some organizations have been measuring SEP in transmit mode, with all elements terminated and the center element driven. This procedure gives erroneous results, as the mutual couplings are all passive. The way of properly measuring SEP is to place the array in a gain measurement setup as a receive antenna, so that all elements are terminated and properly excited. The nominal center element is connected to the receiver; the Scan Impedance mismatch is included in SEP. Knowledge of Scan Impedance is important, as it controls the impedance matching possibilities. It is however difficult to measure. Network analyzers (HP8510) measure impedance both (S11 and S22) by transmitting a signal and measuring the reflected signal, thus do not allow operation in a mode with all elements excited. A full feed network can be employed, with the network modified to allow measurement of the current and voltage at the center element. This method is seldom used. Because of the importance of SI, use is often made of waveguide simulators, and simulation codes. The infinite array Floquet unit cell codes must be used with caution as these codes omit edge effects; these may be very important in some types of coupled arrays. A planar array code is used to simulate both transmit (single element excited) SEP, and receive SEP. Data on SEP and SI are presented.