The advantage of the dog bone slot is that, it is compact as compared to rectangular slot. But for dual polarized antenna still rectangular shape slot is a preferred option as it yields better cross-polar performance. The left most corner
of Fig 1 depicts the rectangular slot while the right most corner depicts dog-bone slot. The performance of the slot has been optimized in the presence of the Cband patch using Ansoft Ensemble.

3. SIMULATED RESULTS OF SINGLE ELEMENT

Figure 2 shows the simulated return loss performance of single patch at C band and single slot at X-band. Return loss bandwidth of 120 MHz is observed from the graph at 5.35 GHz while the return loss is 900 MHz at center frequency 9.6 GHz for VSWR ratio of 2:1. Simulated gain of single patch at C-band is 7.1 dBi at 5.35 GHz. At 9.6 GHz simulated gain of single slot is 4.5 dBi. Figure 3 shows the
simulated return loss of the patch at C-band and dogbone slot at X-band. In this case the return loss bandwidth for patch and slot are 100MHz and 800MHz respectively. After designing single radiating element at X-band its sensitivity analysis is carried out for various dimensional tolerances. The ‘a’ and ‘b’ dimensions of the dog-bone slot as shown in Fig 1 are increased in steps of 0.2 mm which results in lower side frequency shift in the return loss performance.

Similarly linear decrease in ‘a’ and ‘b’ dimensions of dog-bone slot results in upper side frequency shift in return loss performance. These results are shown in Figs 4 and 5. Similarly length ‘l’ and width ‘w’ of the rectangular slot is also varied and its effect on return loss performance is shown in the Figs 6 and 7. It is
observed that simple rectangular slot is less sensitive in comparison to dog-bone slot. Inter-element spacing‘c’ between patch and slot is also varied and its effect on the return loss performance of slot and patch is observed. The changes are more prominent at X-band slot than C-band patch. Return loss performance of patch is not dependent on the position of slot, this can be observed from Fig 8. Return loss performance of slot shown in Fig 9 becomes poor and shifts towards lower side with decreasing the spacing ‘c’. Based on this study minimum lateral distance ‘c’ between patch and slot is 3.0 mm which is ~λ/10 at 9.65 GHz.

4. DESIGN OF 2X2 PLANAR ARRAY

Single element is duplicated in both X and Y directions to form planar array. 2×2 patch elements are combined using microstrip lines. 2×2 slots are fed by an asymmetric stripline feed network. Spacing between patch elements is 0.8 λ, in both X and Y directions. Inter element spacing between patches is optimized for maximum gain of array.