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This paper presents a gap waveguide based compact monopulse array antenna, which is formed with four unconnected layers, for millimeter-wave tracking applications at W-band (85-105 GHz). Recently developed gap waveguide technology removes the need for galvanic contact among metallic layers of waveguide structures, and thereby, makes the proposed antenna suitable for easy and low-cost manufacturing. In this context, a low-loss planar Magic-Tee is designed to be used in a monopulse comparator network consisting of two vertically stacked layers. The gap waveguide planar monopulse comparator network is integrated with a high-efficiency 16×16 corporate-fed slot array antenna. The measured results of the comparator network show the amplitude and phase imbalance values to be less than 0.5 dB and 2 • , respectively, over the frequency band of interest. The fabricated monopulse array antenna shows relative impedance bandwidths of 21% with input reflection coefficients better than −10 dB for the sum and difference ports. The null in the difference radiation pattern is measured to be 38 dB below the peak of the sum radiation pattern at 94 GHz. The measured gain is about 30 dBi for the same frequency. The low-loss performance of the comparator network and the feed-network of the proposed array, together with the simple and easy manufacturing and mechanical assembly, makes it an excellent candidate for W-band compact direction-finding systems.

A bandwidth-enhanced 8 × 8 cavity-backed slot array antenna for fixed beam applications is presented. The antenna consists of four 2 × 2 subarrays fed by ridge gap waveguide and a modified bow-tie coupling slot in the cavity layer. The proposed bow-tie coupling slot provides additional 10 % impedance bandwidth as compared to the traditional rectangular coupling slot. The fabricated prototype demonstrates an |S11| ≤ −10 dB fractional impedance bandwidth and a 3 dB gain-drop bandwidth of approximately 28 % and 25 %, respectively, with peak gain of 26.4 dBi, aperture efficiency > 60 % and cross-polar discrimination > 40 dB. Measurements show good agreement with simulations. Moreover, we show the impact of the dimensions and shape of the cavity coupling slot on the bandwidth enhancement. The bandwidth enhancement is explained by the double-ridge slot behavior of the bow-tie coupling slot, which shows a more wideband behavior than the traditional rectangular coupling slot behaving like a cross-section of a waveguide.

Surface distortions change the radiation characteristics of reflector antennas. Using functional calculus, radiation integral is analyzed, and the first variational derivative of the radiation field with respect to surface profile is extracted. The variational derivative can show the radiation pattern sensitivity to surface distortion. All formulations are based on the Physical Optics approximation. The final formula for variational derivative depends only on the original undistorted antenna parameters, so it can be used for all types of distortions. It has been shown that the formulations are more general than those in previous works. Different polarization states for feed antenna are studied, and variational derivative amplitudes are plotted to depict the regions that have greater effects on the main-lobe and the first few side-lobes levels. Some periodic, aperiodic and local distortion profiles are considered, and the exact and approximated distorted patterns are compared to check the accuracy of the presented procedure.