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A novel broadband circularly polarized (CP) antenna with wide axial ratio (AR) beamwidth is proposed. It is composed of two curved arms shaped like an inverted “S.” The mechanisms of wideband CP operation and wide AR beamwidth are explained. To validate the concept, a prototype at C-band is manufactured and measured. Experimental results confirm that the antenna achieves an impedance bandwidth of 63% and a CP bandwidth of 42%. Furthermore, maximum AR beamwidth of 140° is achieved and wide AR beamwidth can be maintained in a frequency bandwidth of 35% in nearly all elevation planes. In addition, the antenna has the advantage of being easily extended to arrays. A four-element array using the proposed antenna is investigated through both simulations and experiments, and achieves 60% CP bandwidth and wide AR beamwidth. The proposed inverted-S antenna can realize wide CP bandwidth and wide AR beamwidth, and can easily form wideband CP arrays.

As a broadband antenna, we are now researching and developing a new-type antenna not only for using electromagnetic interference (EMI) measurements but also radiofrequency (RF) immunity tests including a radiator for transient immunity tests. In our previous studies, the complex antenna factors (CAF) and actual gains of the prototype antennas were measured by the 3-antenna method. However, there were periodic fluctuations of these characteristics due to the mismatch between the balun and the antenna feed point. In this paper, these characteristics of an improved folded-rhombic antenna without balun are reported.

High-performance SiGe HBTs and advancements in packaging processes have enabled system-in-package (SiP) designs for millimeter-wave applications. This paper presents a 122-GHz bistatic frequency modulated continuous wave (FMCW) radar SiP. The intended applications for the SiP are short-range distance and angular position measurements as well as communication links between cooperative radar stations. The chip is realized in a 130-nm SiGe BiCMOS technology and is based on a fully differential frequency-multiplier chain with in phase quadrature phase receiver and a binary phase shift keying modulator in the transmit chain. On-wafer measurement results show a maximum transmit output power of 2.7 dBm and a receiver gain of 11 dB. The chip consumes a DC power of 570 mW at a supply voltage of 3.3 V. The fabricated chip is integrated in an embedded wafer level ball grid array (eWLB) package. Transmit/receive rhombic antenna arrays with eight elements are designed in two eWLB packages with and without backside metal, with a measured peak gain of 11 dBi. The transceiver chip size is 1.8 mm × 2 mm, while the package size is 12 mm × 6 mm, respectively. FMCW measurements have been conducted with a sweep bandwidth of up to 17 GHz and a measured range resolution of 1.5 cm has been demonstrated. 2D positions of multiple targets have been computed using two coherently linked radar stations.

A folded rhombic antenna as a broadband antenna for using a radiator instead of vertical coupling plane (VCP) specified in IEC 61000-4-2 was designed so that its dimensions were reduced as 1/2 smaller than the original antenna. Three antennas were built, and the complex antenna factors of their antennas were measured by the 3-antenna method. As a result, it was found that a usable frequency range of the prototype antennas is from 400 MHz to 4.5 GHz. Since the complex antenna factors of the antennas were within ±2 degrees in phase values in frequency range from 150 MHz to 4.6 GHz, the proposed antennas are applicable for the transient electromagnetic-field radiator.

A folded rhombic antenna as a broadband antenna for measuring a transient electromagnetic field was designed so that its dimensions were reduced as 1/2 smaller than the original antenna. Antenna gains of their antennas were measured by the 3-antenna method. As a result, a usable frequency range of the antennas is from 400 MHz to 4.8 GHz.

An ultra-wideband planar rhombic antenna with Gaussian tapered profile is proposed for short pulse applications. Compared to a conventional linear rhombic antenna, the proposed antenna has a smooth Gaussian tapered edge, which can diminish the reflected pulse signal and thus can enlarge the bandwidth significantly. The proposed planar Gaussian tapered rhombic antenna was fabricated and its performance both in frequency domain and in time domain was investigated. Good agreements between the simulated and the measured results have been observed. Both of the simulated and the measured results show that the proposed antenna is featured by broad bandwidth, low cross polarization levels, and suitability for short pulse applications.

Experiments involving the generation and detection of artificial periodic inhomogeneities have been performed at the High Frequency Active Auroral Research Program (HAARP) facility. Irregularities were created using powerful X-mode HF emissions and then probed using short (10 μs) X- and O-mode pulses. Reception was performed using a portable software-defined receiver together with the crossed rhombic antenna from the local ionosonde. Echoes were observed reliably between about 85 and 140 km altitude with signal-to-noise ratios as high as about 30 dB. The Doppler shift of the echoes can be associated with the vertical neutral wind in this altitude range. Small but persistent Doppler shifts were observed. The decay time constant of the echoes is meanwhile indicative of the ambipolar diffusion coefficient which depends on the plasma temperature, composition, and neutral gas density. The measured time constants appear to be consistent with theoretical expectations and imply a methodology for measuring neutral density profiles. The significance of thermospheric vertical neutral wind and density measurements which are difficult to obtain using ground-based instruments by other means is discussed.

This paper presented a rhombic ring monopole antenna with stripline and ring resonator for multiband operation. The antenna is created by adding a stripline in a rhombic ring radiator and placing a ring resonator on the bottom layer of the radiator. It can support the multiple resonant frequencies for wireless communication systems. The antenna dimension is about 36 × 48 mm2. The results confirm the good agreement between simulation and measurement. The antenna operates with |S11| level < −10 dB on impedance bandwidths of 16.11%, 9.8%, and 37.43% at the resonant frequencies of 1.8 GHz, 2.45 GHz, and 3.5 GHz, respectively covering the application bands of LTE 1800, WLAN IEEE802.11b/g, WiMAX and IMT Advance Systems. The radiation patterns are omni-directional at all of operating frequencies and the average gain of the antenna is about 2.4 dBi.

A novel excitation source model, which is more accurate for practical situation approximation, is presented in the paper. Based on the model, the input impedance, gain and directivity of a rhombic antenna are analysed by using moment method and microwave network theory. And the results obtained can be instructional on the design of rhombic antenna and over-the-horizon (OTH) communication system.

A rhombic grid array antenna (RGAA) is proposed and its frequency-scanning performance is discussed. The RGAA has numerous bent radiation elements, forming rhombic cells and loops. As the frequency is increased, the radiation beam from the RGAA becomes a forward-fire beam. It is found that, as the bend angle of the radiation elements is decreased, the useful antenna characteristics shift to a lower frequency region. It is also found that the RGAA provides a more stable gain within a frequency band bounded by the 3- and 4-guided-wavelength resonances of the loops, compared with a conventional grid array antenna having non-bent radiation elements. Further investigation reveals that the VSWR is small within a frequency band bounded by the 3- and 4-guided wavelength resonances, as desired, and the bend radiation elements of the RGAA contribute to increasing the radiation efficiency.

This letter develops a printed two-element parallel array consisted of dual rhombic loops and a reflecting plate for broadband, high-gain, and circular polarization (CP) operation. An improved mixed feedline network of bud-shape junction is suggested for the parallel antenna array design. The bud-shape junction not only converts the coplanar stripline to the microstrip line, but also expands the impedance-match bandwidth. The dual parasitic rhombic loops are applied to broaden the CP operation bandwidth. The antenna array is simulated and fabricated with good agreement obtained between the simulation and experimental results. The fabricated prototype shows that the bandwidth of AR 12 dB is 18.1%, 18.8%, and 12.1%, respectively. A 2 × 4-array structure is also presented using this bud-shape junction, and it is easy to be expanded to large arrays for high-gain applications.

A conventional grid array antenna (GAA) composes of wire radiation elements and wire feed elements, both backed by a conducting plate. This chapter presents a novel GAA from the perspective of realizing a beam‐scanning antenna. The radiation elements for this GAA are bent with angle 2α forming a structure with numerous rhombic cells. This GAA is referred to as a rhombic grid array antenna (R‐GAA). The chapter shows that the gain for the R‐GAA has less variation with frequency than the gain for the conventional GAA over the band of interest. It considers the analysis that is performed using the method of moments, where the ground plane (GP) is assumed to be of infinite extent. The chapter shows the frequency response of the gain in the beam direction. Across a frequency range, the gain for the R‐GAA with bent radiation elements has less variation than that for a conventional GAA with straight radiation elements.

We present an analysis of mutual coupling effects on radiation pattern and individual coupling in a conformal array of cross rhombic antennas. Analysis is made using both full-wave simulation and numerical approaches implemented in Matlab. The array consists of a truncated hexagonal pyramid, with a cross rhombic antenna in each pyramidal face, including the one on the top, having a 7-antennas-array. Results of radiation pattern and S11 parameters are presented, showing mutual coupling effects among the elements.

By using a pair of shorting pins, the dual-frequency operation of a single-feed rhombic microstrip antenna with a pair of slits is presented. This shorted dual-frequency microstrip antenna can result in a much reduced antenna size, and provide a tunable frequency ratio of ∼1.26–2.33 for the two operating frequencies by varying the inset slit length. Simulated results with the use of the software also have been conducted to study the characteristics of these antennas. Details of the proposed designs are described and discussed. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 183–186, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10411

We present design and construction results of a 2.4 Ghz cross rhombic antenna to be used in a cubesat. Computational design agrees with experimental results after its construction. cross rhombic antenna is a novel planar structure of our own design, presenting circular polarization and medium gain; it is built over a RF60A substrate withεr=6.15, decreasing its size to fit the required dimensions of satellite. A special characteristic of this design is the enhancing of operational bandwidth using a technique we have been studying, related to softening the structures with sharp edges. Results show applicability and success of our technique.

The radiating properties of diamond shaped short circuited slot line in metal plane on dielectric substrate studied theoretically. The analysis of surface current performed by method of induced electromotive forces. The analysis presented here is verified experimentally. The effect of transversal radiation is described. Slot rhombic antenna can be used in vehicle wireless communication systems.

A Kraus grid array antenna (K-GAA) and a rhombic grid array antenna (RGAA) are investigated as frequency beam-scanning antennas. The fundamental radiation characteristics, including the beam direction and gain, are discussed. The resonance for the RGAA is reduced by adding perturbation elements to the hexagonal loops, thereby enhancing the gain bandwidth.

At present, almost all of the ionospheric sounders for the HF-band around the world are fixed. As a result the areas of sounding are restricted and the equipment cannot be fully exploited. After studying the design of the ionospheric vertical sounding antenna and the standard of parameter setting, a portable vertical sounding antenna based on portable single station ionospheric sounding system is designed that can be spanned easily. Compared to the traditional delta antenna and rhombic antenna, this one has the advantage of lower antenna height, smaller occupied area, smaller VSWR and better radiation performance, which achieves the broadband impedance and antenna pattern. The result suggests that this one is better than a conventional portable ionospheric VI sounding antenna.

A NASA research program has been instituted which seeks to replace the present hydraulic and pneumatic control systems on commercial aircraft with electro-optical and electro-mechanical devices. This new technology should be lighter, cheaper, and easier to maintain, but may be susceptible to high-amplitude externally-generated electromagnetic fields. To determine the expected level of interference, a rhombic antenna utilized by the Voice of America for international short-wave broadcasting was modeled using NEC-4D. The predicted gain and take-off angle were calculated, along with the electric-field intensity at several data points located near the ground.

Проведено компьютерное моделирование ромбических антенн станции вертикального зондирования ионосферы “Базис” поддиапазонов 1 – 6 МГц и 5 – 20 МГц. Проанализированы полученные технические характеристики. Определена оптимальная частота переключения станции между антеннами двух поддиапазонов A computer simulation of the rhombic antennas of ionosonde “Basis” for operation in the subbands 1-6 MHz and 5–20 MHz was performed. The obtained antenna specifications were analyzed. The optimal frequency of switching between antennas for two subbands was evaluated

A 77-GHz rhombic antenna as well as a rhombic antenna array designed for automotive radar applications are presented in 6×6mm2 and 12×8mm2 embedded wafer level ball grid array (eWLB) packages respectively. For the sake of antenna characterization, a 2×2mm2 monolithic microwave integrated circuit (MMIC) including a 77-GHz transceiver and a frequency multiplier is integrated in the package. The frequency multiplier generates the eighteenth harmonic of its input signal and scales a 4.25-GHz input signal to a 76.5-GHz output signal. This enables the antenna beam pattern characterization using a commercial signal source. As the dimensions of a single-element antenna in package (AiP) hardly exceeds the dimension of the MMIC, an AiP typically suffers from an asymmetric beam pattern and limited gain. This paper proposes a highly directional rhombic antenna array solution with more than 10 dBi gain and a symmetric beam pattern.

In this paper, we show how a rhombic antenna can be operated in a degenerate fashion in order to produce a switched beam. The antenna demonstrator designed to operate at 1 GHz is shown to beam scan in elevation by about 10°, controlled only by the use of a switched 500 Ω resistor. Under these conditions, the antenna exhibits a sending end impedance variation of 1.6:1. This type of antenna could find application for use in low-cost vehicular and asset-tracking applications. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 84–86, 2001.

A grid array antenna composed of V-shaped and rhombic elements is proposed. It is found that the beam direction of the proposed antenna with 2α = 60° scans the range of θ = 3° to 31° as a function of frequency. The gain for this scanned beam is almost constant, at approximately 21 dBi.

In this paper, the CPW-fed monopole antenna with various parameters were constructed and studied to demonstrate the proposed bandwidth-enhancement technique and band-reject function. The broadband characteristic was obtained by adjusting the length and width of the notch on ground plane. The broadband antenna operates -10 dB return loss bandwidth over 118% from 3.11 to 11.88 GHz. Furthermore, embedded a straight slit close to quarter wavelength on one of the ground plane. It plays a role as a filter to eliminate the useless band 5.1 to 5.81 GHz. This antenna has advantages of ease manufacture, good radiation characteristic, small size and omni-directional patterns.

This paper demonstrates a novel multiband rhombic microstrip antenna (MSA) with multiple slots printed on a single-layer PTFE substrate. The antenna is fed by a coplanar gap coupled with a V-shaped patch. Three inverted V-shaped slots are assumed on the rhombic patch and hence four resonant frequencies are obtained. Broadside radiation patterns and gain of over 5.0 dBi are also obtained. Experiments were carried out to verify the results estimated by IE3D simulator. Good agreements between simulated and measured results are confirmed. To further evaluate the performance, rhombic MSA with six inverted V-shaped slots is also investigated. Again, this antenna model accomplishes excellent multiband performances over the seven observed frequencies. Thus, the rhombic MSA with multiple slots is well suited as an alternative design for a multiband planar antenna.

By an optimum design method, the sloping vee traveling wave antenna spectrum response ratio is extended over a range between four and six to one while preserving a high magnitude of directivity. A modification of an optimum design method for horizontal vee traveling wave and horizontal rhombic antennas is used for the sloping vee traveling wave and sloping rhombic antennas. A comparison between examples of the design procedure and gain response over a broad frequency spectrum and several elevation angles for both a horizontal vee and sloping vee antenna at the same average height is made. A forward gain contour plot with frequency and elevation angle of each antenna design demonstrates the increase in spectral performance possible with the sloping vee antenna.

A computer method for determining the antenna design parameters which maximize system response under the propagation conditions encountered on the specific propagation path is described. The method described is applied to design of rhombic antenna systems specifically but is applicable to other types of antennas whose response can be expressed mathematically.

This paper presents the rhombic slot antenna that has a broadband characteristic by using a low cost foam-substrate. The feed line is embedded in the middle of the triplate to prevent unwanted and spurious radiation. The proposed rhombic slot antenna has a rectangular patch with supplementary section to improve the impedance bandwidth performance. Experiments using a 2/spl times/1 array antenna are performed to validate the simulation. A bandwidth of 40% can be achieved. The electrical characteristics of the proposed antenna make it attractive for use in satellite communications.

A method is proposed for calibrating field strength in anechoic chambers for points less than 0.8 m high. A method using a two-wire rhombic antenna is proposed for immunity testing at frequencies less than 30 MHZ. A method using a GTEM cell for testing small equipment provides the economy of standard TEM cell testing without having to use an anechoic chamber. An advanced conductive immunity test circuit is proposed which allows voltages of up to 100 V to be applied. >

The high frequency performance characteristics of a two-wire rhombic illuminator under common-mode excitation are studied using the Numerical Electromagnetics Code (NEC-2). The electrical length of the overwall wire structure ranges from approximately 700 wavelengths at 500 MHz to approximately 1400 wavelengths at 1 GHz. Efficient segmentation schemes are required to extend the analysis up to 1 GHz. The rhombic illuminator radiates more effectively as the frequency of operation is increased from 500 MHz to 1 GHz. Based on the resulting damping characteristic of the rhombic illuminator wire current at these frequencies, only a portion of the wire structure must be modeled. This technique allows one to analyze such a structure efficiently at very high frequencies. The general characteristics of the antenna impedance, wire currents, and radiated fields are discussed. >

Two types of circularly polarized linear antenna having a rhombic loop configuration are investigated. One type of circularly polarized antenna is a single feed dual rhombic loop antenna (DRLA). The DRLA consists of two rhombic loops of the same size and is located above an infinite ground plane. The other is a hula hoop antenna (HHA). The HHA is fed from a coaxial cable, of which the inner conductor is connected to the antenna itself and the outer conductor is connected to the ground plane. Two types of feed are introduced for each of the DRLA and the HHA. The antenna characteristics for each feed model are calculated by the method of moments. The results are in good agreement with the measured data.

The Phillips Laboratory has designed and constructed a continuous wave illuminator for studying the responses of large-scale systems subject to vertically or horizontally polarized electromagnetic stresses incident from the horizontal. The illuminator is developed by a nonuniform two-wire transmission line oriented over the system under test. When the wires are driven from a common mode voltage with respect to the ground a vertically polarized electric field is generated and when the wires are driven from equal but opposite voltages a horizontally polarized electric field is developed. The structure is called the rhombic illuminator since the wire configuration is very similar to the rhombic antenna. In order to illustrate the use of the illuminator, data are presented for the illumination field and for the response of an illuminated aircraft recorded at the Phillips Laboratory.

It is reported that a rhombic loop antenna the perimeter of which is about 1.3 lambda /sub 0/( lambda /sub 0/: centre wavelength) can radiate circular polarisation (Morishita and Hirashawa, 1994). This antenna can have a traveling wave type current distribution, which has approximately a constant amplitude and a linearly changing phase. This current distribution is realized by making one point open or loading an infinitely large impedance on the proper position of the loop. In the present paper, two types of single feed dual rhombic loop antennas for circular polarization are proposed. Each antenna consists of two rhombic loops of the same size and is located above an infinite ground plane. The antenna characteristics including axial ratio, current distribution, radiation pattern and input impedance are calculated by the method of moments with respect to the gap position, the rhombus vertex angle and the feed type. The calculated results are in good agreement with the measured data.

In the early days, the rhombic antenna gained favour because of its wide band frequency characteristics. This type of antennas was first introduced in the early 1930's [1], They were used primarily in the HF band. Until recently, travelling wave rhombic antennas have never been seriously considered for the use in the UHF band where they may have many advantages over the standing wave antennas [2]. A previous study [3,4] of the travelling wave V-antennas revealed that these antennas do not lend themselves to increase in the directional gain by increasing the length of the antenna arms indefinitely. This was attributed to the radiation of most of the power from the input end of the antenna leaving relatively low power to be radiated from the far ends. A similar study showed clearly that the end sections of the arms of tubical travelling wave rhombic antennas do not radiate appreciably and the directional gain of the antenna cannot be increased by increasing the arms of the antenna beyond a certain limit.

A four rhombic loop antenna for circular polarisation is proposed. This antenna has a high gain of about 9.7 dBi and a broad beam of more than 130° half power beam width. Four parasitic loops are added inside the original four loops to increase the axis ratio bandwidth. A broadband balun is incorporated into the antenna for impedance matching. Details of the antenna design and experimental results are presented.

The paper discusses a technique for fitting quasiparabolic layers to measured vertical electron density profiles. The method adopted is to represent individual ionospheres by the appropriate combination of E, E-F valley, F1 and F2 layers connected by joining layers. The method produces quite accurate representations of measured ionospheric profiles. The advantage of using quasiparabolic layers is that analytical solutions of various ray parameters can be obtained, including the effect on signal strength of ray tube divergence. Furthermore, tilted ionospheres can also be considered. The methods are illustrated by application to two vertical electron density profiles obtained from the same ionogram. The primary difference in the profiles is that one contains an E-F valley. Results are presented showing not only the effects of the profile differences, but also the effects of tilts, antenna patterns and ionospheric absorption.

A complete analysis has been carried out of the twoconductor rhombic antenna as an EMP simulator. The distribution of current along the conductors and the electric field in the working space bounded by rhombic wires have been determined at low, middle, and high frequencies. The analysis indicates that, at low frequencies, when the termination is the characteristic impedance, a traveling-wave current with very low standing-wave ratio propagates along the wires of the rhombic structure; but it is very sensitive to the load. As the frequency is increased, the standing-wave ratio also increases somewhat and it becomes less sensitive to the load. The electric field in the working space exhibits a reasonably constant amplitude with a standing-wave ratio of 1.5 or lower at all three frequencies.

The rhombic simulator excited by a pulse generator is investigated experimentally. The voltage pulse at the driving point of the simulator and the associated current pulses that travel along the conducting tubes that form the rhombus have been measured with different loads. The complex sequence of electromagnetic pulses (including the incident pulse, the reflected pulses from the load, and other reflection points) have been measured on the metal ground plane. The origin (localization) of each pulse has been carried out. From the Fourier transformation of the waveforms in the time domain, the spectrum of the electromagnetic pulse in the frequency domain is obtained. It is shown that the characteristics of the simulator with the two types of excitation (continuous wave and pulse) are consistent.

A nonuniformly spaced array of 25 side-terminated vertical half rhombics is synthesized for the entire high-frequency band. The array is to be used for both transmitting and receiving, as a sky-wave Doppler radar for sea scatter measurements. The array has the capability for providing a maximum transmitting-receiving product gain in the order of 60 dB at low take-off angles, a product azimuth pattern with a nominal beamwidth of 2\deg , a 40\deg sectoral coverage, a final product sidelobe level of -38 dB, and a grating-lobe level of -30 dB.

A linearized hydrodynamic theory is used to deduce expressions for the electromagnetic and electroacoustic components of the far fields of a horizontal rhombic antenna immersed in on isotropic warm plasma, assuming a general value for the propagation constant of the current distribution. The far-field patterns of the EM mode and the P mode are computed and shown in tabular and graphical forms for β = β and for different ratios of source to the plasma frequency. The optimum design formulae of the antenna in the plasma are also derived and compared with the corresponding formulae in free space.

The paper describes three antenna arrays used in conjunction with receiving and recording apparatus for some of the solar radio astronomy and ionospheric research problems at the Physical Research Laboratory, Ahmedabad.Three pairs of cross-polarized rhombic antennas have been constructed to record the dynamic spectra of solar radio bursts covering the frequency range of 40–240 MHz. These are equatorially mounted and driven by a common synchronous motor to follow the sun continuously for about ±4 hours around the local noon.A steerable broadside collinear array of 16 half wave dipoles backed by a reflector has been constructed for radio star scintillation studies at 110 MHz. This array is also equatorially mounted and can be used to follow a radio source continuously.A simple radio interferometer, operating at 110 MHz, consisting of two Yagi antennae spaced 10 wavelengths apart has been constructed. This will be used for both the solar as well as radio star scintillation work.The effective areas, matching ...

An experimental program at approximately 50 mc has been carried out over a 1295-km east-west ionospheric-scatter path to determine the comminucation capacity of the propagation medium using ordinary modulation techniques. Binary error-rate studies using dual-narrow-band frequency-shift-keyed terminal equipment were made to observe the dependence of error rate in scatter propagation on signal-to-noise ratio, multipath factors, and Doppler shifts. With respect to multipath limitation, using antennas of 6° beamwidth, error rate is found to be independent of transmission speed to 500 binary digits per second. Tests were made using dual-diversity narrow-beam rhombic antennas, and dual- and quadruple-diversity broad-beam Yagi antennas. The use of four Yagi antennas gave very promising results as compared to use of two narrow-beam antennas. Frequency shifts of 2, 4, and 6 kc were used to determine the effect of meteor Doppler components in the received signal, leading to recommendations for minimum frequency shift. Though actual modulation tests have so far been made at a frequency of 49.6 mc only, systematic observations of longdelay signals of the order of 10 to 80 msec were made at 30 and 40 mc, using pulse techniques. These delayed signals arrived at the receiver via the F 2 backscatter mode, and were occasionally of sufficient strength to cause binary errors for circuits operating in these frequency ranges. Studies of intelligibility for voice transmission were made using narrow-band frequency modulation and single-sideband modulation. Using 20-kw power, the frequencymodulation tests with dual-diversity receivers and narrow-beam rhombic antennas gave good results at levels of signal-to-noise ratio exceeded for 90 per cent of the year at 50 mc.

In the operation of short-wave radiotelephone circuits selective fading is observed which is a result of the combination at the receiving antenna of waves which have arrived from the transmitter over paths of different lengths. The poor quality resulting from this fading may be mitigated by increasing the directivity of the receiving antenna in the vertical plane so as to favor the waves arriving at one angle to the exclusion of others. Friis and Feldman have described an experimental system designed to accomplish this end which they call a "musa" receiving system. This system was found under certain transmission conditions to give an improvement in the grade of circuit which could be obtained. A commercial installation of this type has now been constructed for use on the single-sideband circuits of the American Telephone and Telegraph Company from England. Two receivers have been provided for the operation of four radiotelephone circuits. The antenna system consists of a row of 16 rhombic antennas two miles long, each antenna connected by a separate transmission line to receivers located near the center of the row of antennas. In each receiver the signals from the antennas are combined in the proper phase to permit simultaneous reception from three adjustable vertical angles. The three signals are then added through delay-equalizing circuits or discretely selected on the basis of amplitude to obtain diversity reception.

The article of record may be found at http://dx.doi.org/10.1063/1.1721325 The expression for the driving point impedance of a generalized electric circuit as vizualized by the author is partially integrated, and the physical significance of certain terms is discussed in connection with their application to antenna problems. Upon postulating an unattenuated traveling wave as a first approximation to the current along either a terminated rhombic or Vee antenna, a formula is derived for the free space radiation impedance of each. The expression radiation impedance is used for that portion of the driving point impedance which may be determined from the complex power into the external fields. The resistive component of the impedance for the rhombic antenna checks with the radiation resistance as listed by Leonard Lewin in a discussion of a paper by Donald Foster, with Lewin apparently obtaining his formula by the solid angle Poynting vector method.

Rhombic antennas were the first type employed in the study of propagation via ionospheric scatter. By the use of electrically long leg-lengths gains of the order of 20 decibels were obtained. Experimental measurements using model techniques indicated that assumptions usual in the design of rhombic antennas remained valid even for leg-lengths of 25 to 40 wavelengths. In order to obtain a more compact antenna, while retaining the gain, experimental investigation was carried out on corner-reflector and Yagi-types of antennas. By the use of 60 degree corner-reflector and a collinear array, a corner reflector antenna having gain of 19.9 db. was constructed. By exercising care in adjusting the lengths of parasitic elements, a Yagi antenna, 4.2 wavelength, having a gain of 14.2 decibels, was designed. An array of four such Yagis, having a horizontal spacing of 1.8 wavelengths and a vertical separation of 1.6 wavelengths was measured to have a gain of 19.0 decibels. Full scale corner-reflector antennas and Yagi antennas have been erected and have proved to be operationally satisfactory.

This paper discusses the theoretical methods employed by the authors in dimensioning horizontal rhombic receiving antennas. Experimental proof is given of the engineering accuracy of the directivity calculations on which this work is based. There are included brief descriptions of the antenna-to-transmission-line coupling circuits and the resistance terminations for rhombic antennas.

In this paper, the use of an inclined rhombic antenna as a means for reducing the effect offading is discussed. Equations are given for determining the angle at which a rhombic antenna should be inclined to obtain a desired response pattern at various elevation angles in the vertical plane containing the major axis.

With the increased use of the ionospheric scatter mode of propagation in the VHF range, the horizontal rhombic antenna is employed in many instances because of its simplicity, high performance, and low maintenance costs. Designers of these long rhombics have no doubt realized that the "maximum output" and "maximized" designs described by Harper and others do not take into account current attenuation due to radiation and cannot generally be employed when l/\lambda>8 because of the requirement that the first ground factor maximum should agree closely with the free space vertical pattern maximum. This leads to the conclusion that power gain is the logical basis for design. In order to formulate an expression for power gain, a relation must be established between the radiation resistance with uniform current distribution and radiation resistance with exponential current distribution. The expression derived by Lewin is compared to that derived by Zuhrt. Gain curves are drawn using the formulas, and the "maximum output" and lobe alignment design are compared on the basis of gain with the design based on maximizing the vertical pattern function at the desired angle of radiation. It is found that only under certain conditions does the "maximum output" design have greater gain for the same leg length. The maximum gain condition is discussed together with optimum termination loss, attenuation rates, and surge impedance formulas for multiple wire rhombics. In general, the analysis does not invalidate the design conditions previously derived, but rather increases the emphasis on the general alignment condition and gain and decreases the importance of the "maximum output" and "maximum alignment condition" which were derived on the basis of a constant input current and uniform current distribution.