Amir Borji

Low-cost, high-efficiency quasi-planar array of waveguide-fed circularly polarized microstrip antennas

A low-cost quasiplanar Ku-band array of circularly polarized microstrip antennas benefiting from a low-loss waveguide feed network is demonstrated (patent pending). The 32 elements of the array which are arranged in a 2-by-16 configuration are subdivided into four two-by-four subarrays. To maintain feed losses and thus the overall noise temperature at a minimum, the subarrays are excited using a one-by-four corporate feed network of hollow metallic waveguides. This network is composed of E-plane components such as Tee-junctions and bends and is manufactured out of only two metallic pieces that accommodate the feed network in the form of milled grooves. Because of insensitivity of the exploited E-plane components to air gaps or slight misalignments, the pieces are secured together with only four screws without welding, braising, or conducting adhesives. Owing to a low-loss foam substrate, the array elements show high circular polarization gain of 9 dBic and wide relative bandwidth of 4%. To achieve circular polarization, use is made of circular patches with two nearly perpendicular perturbations. Using sequential rotation of the elements along with quadrature phase shifting, the axial ratio of the array is reduced to 1 dB over 4% of bandwidth. The measured circular polarization gain of the array amounts to 23 dBic with an aperture efficiency of 63% in the Ku-band of frequencies. The achieved efficiency, which is higher than the reported efficiency for comparable planar arrays with microstrip feed networks, can be credited to the low losses of only 0.2 dB in its waveguide corporate feed. The paper also presents measurement results for an arrangement of two inclined single arrays mounted in parallel. This configuration which has a measured circular polarization gain of 25.7 dBic with an axial ratio of 1 dB is desirable for mobile low-profile antenna systems.

Novel Two-Layer Millimeter-Wave Slot Array Antennas Based on Substrate Integrated Waveguides

A novel slot array antenna with two layers of substrate integrated waveguides (SIW) is presented for millimeter-wave wireless applications. Unlike conventional SIW-based slot arrays, in this structure a feed waveguide is placed underneath the main substrate layer containing the slot array and is coupled to the branches of the array via slanted slots. The proposed feeding structure results in a considerable reduction in size and eliminates unwanted radiations from the feed network. Experimental results for two slot arrays with 4 £ 4 and 6 £ 6 elements operating at 60GHz are presented showing 14.8dB and 18.5dB gain, respectively. Furthermore, a novel doubly tapered transition between SIW and microstrip line is presented which is particularly useful in mm-wave applications.

Efficient, Low-Cost Integrated Waveguide-Fed Planar Antenna Array for Ku-Band Applications

Low-cost printed circuit board waveguide (PCB-WG) technology is employed to develop new waveguide-fed microstrip antenna arrays with low profile and light weight while maintaining high efficiency and gain at 12.5 GHz. The proposed corporate feed network has two parts: on the antenna layer, microstrip lines are used to form a 2

Rapid calculation of the Green's function in a rectangular enclosure with application to conductor loaded cavity resonators

\times

Fast convergent Green's function in a rectangular enclosure

4 sequentially rotated subarray of circularly polarized microstrip patches and on the feed layer SIW is utilized to combine any number of these subarrays to form a larger array. Since SIWs transmit the power over a large portion of the feed network, losses are substantially reduced and spurious radiations from feed circuit are eliminated. Several microstrip arrays with PCB-WG feed were designed and fabricated using standard PCB process. Comparing the results with those of a hybrid array with conventional waveguide feed shows that there is only a negligible degradation in gain and efficiency when bulky and expensive aluminum waveguides are replaced by PCB-WGs.

TEM properties of shielded homogeneous multiconductor transmission lines with PEC and PMC walls

A new technique for rapid calculation of the Greens functions in a rectangular cavity is presented. The method is based on a best polynomial approximation in three dimensions, which is implemented through a fast cosine transform. Generating the required samples for polynomial modeling is greatly accelerated through Ewald summation technique. To validate the efficiency of the resulting Chebyshev series for the potential Greens functions, a surface integral-equation (SIE) formulation is used to compute the resonant frequency of conductor loaded cavity resonators. The new scheme is proved to be considerably faster than Ewald transform in filling the method of moments (MoM) matrix. A SIE with the MoM can now be efficiently used for electromagnetic analysis and optimization of conductor or dielectric loaded resonators and filters with rectangular enclosures.

Compact two-layer slot array antenna with SIW for 60GHz wireless applications

Ewald summation technique has been proven to be a highly efficient method for rapid calculation of the potential Greens functions in rectangular cavities. It is known that in addition to potential Greens functions, curl of the vector potential Greens function is also needed when applying the mixed potential integral equation method to dielectric objects. In this paper the Ewald sum technique is applied for rapid calculation of these components of the dyadic Greens functions. Several numerical implementation issues including the extraction of singularity when using the Ewald summation method ate also addressed for the first time, leading to further enhancement in computational speed accuracy, and numerical stability.

High efficiency antenna array with optimized corporate hybrid feed

This paper describes a very fast computational technique for the solution of two-dimensional static boundary value problems within a homogeneous rectangular enclosure with any combination of perfect magnetic and electric conducting walls. A fast convergent series representation of the pertinent Greens function combined with a least-square MoM and point-matching technique leads to a fast and reliable numerical solution. Characteristic impedances of single and coupled shielded metallic rods are computed as an example application of the present method. The results are compared with those of the finite-element method with excellent agreement and much less CPU time.

Relation Between Reflection Phase and Surface-Wave Bandgap in Artificial Magnetic Conductors

In a variety of microwave and millimeter-wave applications where high performance antennas are required, waveguide slot arrays have received considerable attention due to their high aperture efficiency, low side lobe levels, and low cross polarization. Resonant slot arrays usually suffer from narrow bandwidth and high cost due to high precision required in manufacturing. Furthermore, because of using standard rectangular waveguides, the antenna array is thick and heavy and is not suitable for monolithic integration with high frequency printed circuits.

Diagnosis and tuning of multiple coupled resonator filters

A low-cost Ku-band array of circularly polarized microstrip antennas benefiting from a low-loss waveguide feed network is demonstrated (patent pending). The 128 elements of the array which are arranged in a 4-by-32 configuration are subdivided into four 4-by-8 subarrays. To maintain feed losses and thus the overall noise temperature at a minimum, the subarrays are excited using a 1-by-4 corporate feed network of hollow metallic waveguides. Due to a low-loss foam substrate, the array elements show high circular polarization gain of 7.5 dBic and wide relative bandwidth of 4%. The measured circular polarization gain of the array amounts to 25.6 dBic with an aperture efficiency of 51% in the Ku-band of frequencies