Drayton L. Hanna

Design of a broadband dipole in close proximity to an EBG ground plane

One of the known advantages of an electromagnetic bandgap (EBG) ground plane is the fact that a straight-wire dipole can be located parallel and in very close proximity to the ground plane. For such a structure and geometry, a reasonable impedance match to 50 n) can be achieved with more bandwidth than when the dipole is located in close proximity to a PEC ground plane. However, in addition to impedance, radiation-pattern properties must be considered when evaluating the antennas overall performance and usable bandwidth. Here, we consider the performance properties of a folded bowtie dipole element in close proximity to an EBG ground plane, with emphasis on examining the bandwidth and pattern characteristics. We demonstrate that a dipole element can be designed to exhibit a matched input impedance over approximately a 1.4:1 bandwidth with respect to a 50 n characteristic impedance, when located in close proximity to the EBG ground plane. While the shape of the radiation pattern of the antenna remains relatively unchanged over much of this operating bandwidth, we show that the usable bandwidth of the antenna-EBG combination is limited to approximately 1.5:1, due to pattern degradation at both the lower and upper frequencies. Details of the design approach and feed structure used to match the impedance of the dipole to 50 fl are discussed. Finally, we show that with this element design, the reflection phase bandwidth of the EBG ground plan-e does not limit the matched impedance bandwidth of the antenna. A -portion of ,t ,he work detailed here was presented at the 2005 Antenna Applications Symposium.

A Performance Comparison of Fundamental Small-Antenna Designs

In this paper, the performance properties of several fundamental small-antenna designs are compared as a function of overall length and size (ka), where the antennas operate at or very near the same frequency. The objective of this work is to determine which basic design approach or configuration, if any, offers the best performance in terms of: achieving an impedance match; the radiation-pattern shape; the radiation efficiency; the half-power bandwidth; and the 2:1 VSWR bandwidth. The fundamental antenna designs studied here include the spherical folded helix, the cylindrical folded helix, the matched disk-loaded dipole, the matched spherical-cap dipole, and the multi-arm spherical resonator. In addition to discussing the different antenna designs, the fundamental approaches used in impedance matching and optimizing the bandwidth of these small antennas are described. Both numerical simulations and measured results are presented.

Multiple-beam low-profile low-cost antenna

A novel planar multiple-beam antenna is described. Each RF input radiates a directional beam in a different azimuth direction to achieve 360° coverage in azimuth. Elevation scan was not required; the beams are at a fixed elevation angle. Gain was maximized over 50° to 35° elevation for each beam, with beam maximum at 24° elevation. Measured gain was about 15 dBi and very wideband. Compared with phased arrays, this new antenna is lower cost, wider bandwidth, and uses a low-height planar aperture which provides numerous simultaneous low-elevation beams. A prototype was tested over 8.2-12.2 GHz with vertical linear polarization. The antenna diameter including ground plane and radome was 6.156” (156.4 mm), which is 5.2 wavelengths at 10 GHz, no other ground plane was used. The antenna height including radome is 0.961” (24.4 mm) which is 0.8 wavelengths at 10 GHz.

Validation of Negative Refraction in a Metamaterial Wedge using QPSK Modulated Signals

The phenomenon of negative refraction in a Metamaterial wedge is known to be relatively narrowband. Here, we first experimentally estimate the negative refraction bandwidth of a Metamaterial wedge using a slab and a series of CW measurements. We subsequently measure the RF bandwidth of the Metamaterial wedge using a series of simple QPSK modulated signals. The measured RF bandwidth correlates well with the bandwidth estimate made using the slab and CW measurements.

Horizon nulling helix antennas for GPS timing

Global Positioning System (GPS) antennas installed at fixed site infrastructure are susceptible to interference incident along the direction of the horizon. In this paper, a series of quadrifilar helical antennas are presented for the application of GPS timing. The first antenna employs a novel method of reactive loading along the length of the multi-turn helix. The phase distribution along the helix creates a deep null in the gain pattern at the horizon while maintaining sufficient beam width in the zenith direction. The horizon null minimizes ground based interference. The second antenna achieves similar performance by varying the pitch of the helix arms along the length of the antenna. The third antenna operates over L1 and L2 frequencies using concentric helices. A novel method is presented to decouple the concentric helices based on distributed trap circuits along the length of the helix arms, which preserves the horizon nulling patterns at both frequencies. The proposed antennas offer improved performance over previous horizon-nulling designs. Additionally, the proposed antennas can be manufactured at a lower cost compared to other interference mitigating antennas based on the simple architecture.

A HORIZON RING NULLING SHORTED ANNULAR PATCH ANTENNA WITH SHUNTED STUBS

A dual-band shorted annular ring patch antenna with interference rejection at the horizon is presented for GPS timing applications. It is shown that the dimensions of the annular ring can be optimized to make a null in the RHCP pattern at low elevation near the horizon for all azimuth angles. This null attenuates interfering signals originating from ground based sources. The antenna achieves circular polarization utilizing radial shunted stubs. The effect of the stubs on the resonance is analytically derived and verified through simulations. A novel feed configuration that incorporates a coplanar waveguide transition improves the impedance match for both L1 and L2 GPS frequency bands compared to previous designs that present compromises between the feed impedance of the two bands. Additionally, since the shunted stubs reduce the number of required electronic components compared to other antennas with similar horizon nulling capability, the cost is reduced. A prototype antenna operating at GPS L1 and L2 bands has been fabricated and validated through measurements.

Horizon ring nulling shorted annular patch GNSS antenna with shunted stubs

A low cost dual-band shorted annular ring patch antenna is presented for the application of GNSS reception with interference rejection at the horizon. It is shown that the antenna can achieve circular polarization with a single feed pin using two shunted stubs along the inner wall of the ring. The effect of the shunted stubs on the antenna resonance is analytically derived and verified through simulations. The dimensions of the annular ring were designed to create a deep null in the RHCP gain pattern at the horizon and around all azimuth. Additionally, a novel feed configuration is presented using a coplanar waveguide transition to improve impedance matching for the LI and L2 GPS frequencies.

Experimental verification that a metamaterial wedge supports the propagation of a bandlimted modulated signal

We have performed CW measurements on the metamaterial wedge providing detailed insight into its behavior and operating bandwidth limitations. Measurements with a narrowband modulated signal have demonstrated that negative refraction exists with a practical QPSK signal modulation scheme. The CW measurements indicated that the metamaterial wedge would not allow the successful transmission of a QPSK modulated signal having bandwidths in excess of 4% to 5%. This bandwidth limitation was demonstrated experimentally where successful transmission of a modulated signal having 406.4 MHz was performed. A modulated signal having a bandwidth of 838 MHz could not be successfully transmitted through the wedge.